Oct 16, 2015 - idea behind this is that monopolists or market leaders have little .... The third, or upper, quartile shows the value up to which 75% of the sample's .... Emergence of labour markets, intermediate goods and service providers, ...... online at www.airvac.com/pdf/Vacuum Sewers 101.pdf, updated on 2008. Naret ...
In partial fulfillment of the requirements for the degree of Master of Environmental Sciences at the Albert-Ludwigs-University of Freiburg Faculty of Environment and Natural Resources
Characterization of vacuum sewer systems in Germany and the potential as leapfrogging technology in the Global South
Submitted by
Marc Beckett Student ID 3527339
First examiner
Second examiner
Prof. Dr. Rüdiger Glaser
Prof. Dr. Günter Tovar
University of Freiburg
University of Stuttgart
Director of Institute for Physical Geography
Director of Institute for Interfacial Process Engineering and Plasma Technology
‘The history of men is reflected in the history of sewers’ Victor Hugo
Abstract Challenges with the current way of wastewater service provision require new approaches to address challenges resulting from environmental, economic and demographic changes. Vacuum sewers pose a form of alternative sanitary sewerage and have gained increased attention due to their potential cost and environmental advantages over conventional sewerage systems. Multiple research projects have included vacuum sewers in efforts to separate wastewater streams beyond the separation of storm and wastewater. Increased rates in the recovery of nutrients and biogas from wastewater compounds have been demonstrated. Despite their development more than 100 years ago, knowledge and application of vacuum sewers remains underexploited. In order to investigate the driving and hampering factors governing the distribution of vacuum sewers, expert opinions were collected together with data from 64 vacuum sewer projects in Germany. Crucial barriers to a wider distribution appear to derive from the operational complexity and sensitivity of technology. Too few reference projects combined with the weighted influence of few badly running systems hinder a wider application. The benefits are predominantly perceived within the environmental domain, such as exfiltration prevention and material flow separation for subsequent utilization but until now rarely realized. Evaluation of operational data revealed remaining uncertainty reflected in high variability in operational parameters. The degree of uncertainty is discussed around the question whether vacuum sewers pose a leapfrog alternative to expand sewerage cover in industrializing countries in order to avoid lock in effects on the path of development. While, the theoretical conditions for leapfrogging appear to be met to the greater extent, mixed experiences from Botswana, Namibia and South Africa underline that the local socio-technical environment is the governing factor for technology transfer to industrializing countries.
Table of Contents Abstract ............................................................................................................................................... 4 Table of Contents ............................................................................................................................... 5 1.
Introduction .................................................................................................................................... 9
2.
Background Information .............................................................................................................. 11 2.1.
Status quo –current wastewater collection systems ........................................................ 11
2.2.
Current trends in the wastewater sector ........................................................................... 14
2.3.
Vacuum sewers .................................................................................................................... 15
2.4
Overview of vacuum systems in place worldwide ........................................................... 21
2.5.
Wastewater service provision in the Global South........................................................... 26
2.6.
Environmental and technological leapfrogging theory ................................................... 28
2.6.1.
Theory explained ......................................................................................................... 28
2.6.2.
Leapfrogging examples .............................................................................................. 29
2.7.
Scope of the study .............................................................................................................. 31
3. Methodology .................................................................................................................................... 32
4.
3.1.
Expert interviews ................................................................................................................ 32
3.2.
Operator survey .................................................................................................................. 33
3.3.
Statistical analysis ............................................................................................................... 34
Results............................................................................................................................................ 35 4.1.
Literature review on environmental leapfrogging ........................................................... 35
4.2.
Expert interviews on vacuum sewers ................................................................................ 39
4.2.1.
Sample characteristics and rating .............................................................................. 39
4.2.2.
Positive and negative aspects of vacuum sewers .................................................... 41
4.2.3.
Critical factors during planning, construction and operation of vacuum sewers .. 43
4.2.4.
Risk factors affecting the success of vacuum sewers ............................................... 44
4.2.5.
Barriers preventing a wider distribution of vacuum sewers .................................. 44
4.2.6.
Measures to overcome barriers ................................................................................. 46
4.2.7.
Demand for circular economy concepts .................................................................... 46
4.2.8.
Future of vacuum sewers ........................................................................................... 47
4.2.9.
Potential for vacuum sewers in the Global South ................................................... 48
4.3.
Results from the operator survey ....................................................................................... 49
4.3.1.
Sample characteristics.................................................................................................. 49
4.3.2.
Structural characteristics of vacuum sewers in Germany ........................................ 50
4.3.3.
Operational data ......................................................................................................... 55
4.3.4.
Cost composition in vacuum sewers ......................................................................... 59
4.3.5.
Reasons for vacuum sewer selection ........................................................................ 61
4.3.6.
Frequency and causes of failures ............................................................................... 62
5.
6.
4.3.7.
Complaints from the connected people .................................................................... 66
4.3.8.
Opinions of participants ............................................................................................. 67
Discussion ...................................................................................................................................... 70 5.1.
System characteristics of vacuum sewers in Germany ..................................................... 70
5.2.
Operational comparison of vacuum sewers in Germany ................................................. 72
5.3.
The cost situation for vacuum sewer systems ................................................................... 77
5.4.
Operator satisfaction ........................................................................................................... 80
5.5.
Good perception of vacuum sewers within boundaries .................................................. 88
5.6.
Leapfrogging and technology transfer .............................................................................. 91
5.7.
Limitations of the study ...................................................................................................... 97
Synthesis and Outlook ................................................................................................................. 98
Publication bibliography ................................................................................................................... 100 Acknowledgement ............................................................................................................................. 106 Annex .................................................................................................................................................. 107 Sewerage connection rates in African countries ......................................................................... 107 Expert Interview Questionnaire .................................................................................................... 108 Pros and cons of vacuum sewers .................................................................................................. 110 Statement of Affirmation .................................................................................................................. 114
List of Figures Figure 1: Layout of a conventional sewer system (Miszta-Kruk 2016)) Figure 2: Layout of a septic tank (King County 2016) Figure 3: Composition of water treated at treatment facilities (Statistisches Bundesamt 2013b) Figure 4: Age structure of sewer networks in Germany according to population sizes (E) (Berger et al. 2016) Figure 5: Overview of a vacuum sewer system involving the vacuum valve unit at the valve pits, vacuum mains and the central vacuum station (Sustainable Sanitation and Water Management 2012) Figure 6: Left: Schematic layout of a collection pit; Right: prefabricated collection pit (Naret 2007) Figure 7: Left: Vacuum valve unit (Günthert, Cvaci 2005); right: individual valves can be remotely monitored (FLOVAC 2017) Figure 8: Saw-tooth profile of a vacuum sewer line (Naret 2007) Figure 9: Layout of a vacuum station with the collection tank in the ground and the sewage pumps outside of the tank. (Naret 2007) Figure 10: Parallel vacuum pump arrangement at the vacuum station in Böblingen-Dagersheim (Mohr 2016). Figure 11: Biofiler used for odour control from a vacuum tank. Right: woodchips are a common filling material (Günthert, Cvaci 2005) Figure 12: Number of vacuum sewer projects implemented by ROEDIGER (blue) and AIRVAC (red) between 1973 and 2008 (Terryn, Lazar 2016) Figure 13: Vacuum sewer system in Palm Jumeirah, Dubai (Bilfinger Water Technologies GmbH) Figure 14:Deterioration of vacuum sewer based sanitation in Kosovo, Cape Town (Taing et al. 2011) Figure 15: Layout of the sanitation and reuse concept in Outapi (Zimmermann et al. 2015).
10 10 12 13 16 17 17 18 19 19 20 21 22 23 24
Figure 16: Schematic overview on how water management was designed in DEUS 21 with vacuum sewers being the selected technology for wastewater conveyance (www.deus21.de) 25 Figure 17: Vacuum pipe installed in existing channels; the PE pipe is attached to the wall of the channel (Bayer, Kopfhammer 2012). 25 Figure 18: Progress on sanitation coverage (%) by region (WHO, UNICEF 2015) 27 Figure 19: Percentage of population served by different sanitation technologies (Strande et al. 2014) 27 Figure 20: Disparity in access to improved sanitation between rural and urban areas Left: global (WHO, UNICEF 2015); right: 35 African countries (red= urban; blue=rural) (Mitullah et al. 2016) 28 Figure 21: Visualization of an Environmental Kutznets Curve (Sauter, Watson 2008) 29 Figure 22: Changes in the installation capacity of Chinese wind energy (Dai, Xue 2013) 30 Figure 23: M-PESA banking menu on a feature phone (https://businesstoday.co.ke/) 31 Figure 24: Left: Example of Box-Whisker-Plot (Sullivan, LaMorte 2016); Right: Example of histogram 35 Figure 25: Number of referrals to aspects within the interviews 42 Figure 26: Number of different aspects referred to in the interviews 43 Figure 27: Number of mentioned barriers affecting the distribution of vacuum sewers 45 Figure 28: Measures to overcome barriers 46 Figure 29: Development of vacuum sewer projects over time 50 Figure 30: Distribution of surveyed systems by federal state 51 Figure 31: Distribution network lengths 51 Figure 32: Distribution of system size measured by number of collection chambers 52 Figure 33: Density of collection chambers 52 Figure 34: Number of connected people 53 Figure 35: Additional information provided by the operators 54 Figure 36: Type of service area 54 Figure 37: Histogram on annual electricity demand per person 55 Figure 38: Distribution of values for total work hours 55 Figure 39: Histogram on the work input related to the collection chambers 56 Figure 40: Histogram on the work input at the vacuum station 57 Figure 41: Distribution of work input related to the vacuum lines 58 Figure 42: Average work input composition for various activities in vacuum sewers; VS: vacuum station; VL: vacuum lines; CC: collection chambers (n=40) 59 Figure 43: Total operational cost per connected person 60 Figure 44: Proportional contribution of material, personnel and electricity costs by category 60 Figure 45: Average cost composition of vacuum sewers in Germany; O&M and emergency activities include material and personnel costs (n=22) 61 Figure 46: Responses to reasons for vacuum sewer installation 62 Figure 47: Failure frequencies at the vacuum station 63 Figure 48: Failure sources at the vacuum station 63 Figure 49: Failure frequency at the vacuum lines 64 Figure 50: Common failure reasons in vacuum lines 64 Figure 51: Frequency of failures at the collection pits 65 Figure 52: Failure causes at the collection chambers 66 Figure 53: Frequency of complaints from the people served by vacuum sewers 66 Figure 54: Operator opinions on selected statements (1/2) 68 Figure 55: Operator opinions on selected statements (2/2) 69 Figure 56: Development of network length (A) and collection chamber (B) over time 71 Figure 57: Development of number of people connected to vacuum sewers over time 72 Figure 58: Relationship between the presence of a monitoring system at the collection chambers and A: electricity demand and B: total work hours 75 Figure 59: Reconditioning time in different sewerage systems (Miszta-Kruk 2016) 76 Figure 60: Sewer tariffs in municipalities with vacuum sewers 79
Figure 61: Tariffs for stormwater drainage in municipalities with vacuum sewers 79 Figure 62: Relationship between satisfaction of the operator and total annual operational costs (the figure inside the box indicates the number of answers in each group) 81 Figure 63: Relationship between total annual work hours and satisfaction 81 Figure 64: Relationship between operator satisfaction and A: network length and B: number of collection chambers 82 Figure 65: Relationship between operator satisfaction and system age 82 Figure 66: Relationship between operator satisfaction and A: network/chamber ratio and B: electricity demand 83 Figure 67: Relationship between operator satisfaction an failure rate at the vacuum lines; A: clogging; B: cracks/ leaks 84 Figure 68: Relationship between satisfaction and failures at the vacuum station; A: vacuum pump, B: sewage pump, C: electric system; D: biofilter 85 Figure 69: Relationship between operator satisfaction and failure rates at the collection chambers; A: vacuum valves; B: valve controller; C: filling level sensor; D: monitoring system 86 Figure 70: Relationship between operator satisfaction and operator experience in years 87 Figure 71: Sewerage connection rates in 35 African countries (Mitullah et al. 2016) 107
List of Tables Table 1: Life span of various vacuum sewer components (Schluff 1996; IWR - Ingenieurbüro für Wasserwirtschaft und Ressourcenmanagement 2016; Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft 2004; Günthert, Cvaci 2005) 21 Table 2: Functional groups and indicators of an TIS (in Binz et al. 2012 based on Bergek et al. 2008) 37 Table 3: Overview of sample for expert interviews and quantifiable responses on experience with vacuum sewers, expertise as well as personal and estimated industry rating of the vacuum sewer technology 39 Table 4: Results from the correlation analysis for different variables of the expert interviews 41 Table 5: Possible risk factors affecting vacuum sewers 44 Table 6: Satisfaction of participants with the operation of their system 49 Table 7: Satisfaction of the participants with the collaboration with the system provider 50 Table 8: Comparison of reported operational data 73 Table 9: Estimation on fulfillment of conditions for leapfrogging (conditions according to Perkins 2003) 92 Table 10: Performance of the international TIS on vacuum sewers (based on Binz et al. 2012) 93 Table 11: Positive and negative aspects of vacuum sewers mentioned din the interviews 110
1. Introduction The benefits of sanitary engineering are widely acknowledged and an essential service of general interest. The implications of sanitation, wastewater collection and treatment for public health, the environment and prosperity are undisputable. Elements of the wastewater infrastructure not only contribute to good hygienic conditions in the human environment, but also play an important role in flood protection and the protection of water bodies (Bock et al. 2016). Sewer systems have been an integral part of human settlements since the early stages of civilization. Early reports of sanitary systems reach back to the Mesopotamian Empire (3500-2500 BC) (Lofrano, Brown 2010). High civilizations, such as the Indus community (2500 BC), the Egyptians (2100 BC), the Greeks (300 BC – 500 AD), the Romans (600 BC – 476 AD) addressed sanitary matters across the centuries. However, for the longest time wastewater handling became insufficient for growing settlements since practices focused on conveyance and rather than treatment. With the collapse of the Roman Empire the so called ‘sanitary dark ages’ (Lofrano, Brown 2010) began (467 - 1800 AD). It was not until the Industrial Age of the 19th century when the relationship between public health and sanitation was addressed. Growing cities in Europe and the US started to take action to improve environmental conditions and construct sewer and treatment facilities (Lofrano, Brown 2010). The most widely distributed centralized sewer system is the gravity sewer. Gravity systems that collect wastewater, as well as stormwater are called combined sewer. Although pollution is usually minor, the surface runoff needs to be treated, since rainwater comes into contact with particles on the surfaces of built environments. The driving force in conventional sewers is gravity and sufficient flow volumes are required in order to wash the mixed sewage along the gradient to the treatment plant. The wastewater is collected at the individual premises and introduced to the network. Stormwater usually drains from the surfaces, such as roads or roofs.
Introduction
p. 9 / 114
Figure 1: Layout of a conventional sewer system (Miszta-Kruk 2016))
In contrast to centralized sewers, onsite sewer technologies are more common in rural areas where no sewer infrastructure exists. A septic tank (Figure 2) is a watertight chamber buried underground which collects the wastewater and allows for sedimentation of solids and moderate anaerobic treatment (Tilley et al. 2008). The effluent needs to be dispersed or infiltrated into the ground. Although septic tanks provide some form of treatment and the users are not exposed to wastewater the reduction of pollutants is fairly low with remaining environmental and health risks. Septic tanks require emptying on a regular basis, which is often the responsibility of the owner (Tilley et al. 2008).
Figure 2: Layout of a septic tank (King County 2016)
Introduction
p. 10 / 114
Besides septic tanks, rural communities often use unconventional or alternative sewerage systems in order to convey wastewater. One type of alternative sewerage system is vacuum sewerage. Vacuum systems use differential air pressure instead of water to convey wastewater. The technology was invented in the late 1800s but neglected until around 1970. Vacuum systems are commonly applied in flat topography, flooding areas or water protection areas since leakage is very rare. Investment costs are much lower than in gravity systems since the pipes are much smaller and can be laid at lower depths (Islam 2016; Terryn, Lazar 2016). These characteristics have lead to the consideration, that vacuum sewers might pose a good alternative for implementation in developing countries ( (Elawwad et al. 2014a). However, despite their potential environmental and economic advantages distribution of vacuum sewers remains limited. The scientific community paid little attention to evaluate structural data, as well as operational performance and costs. There seems to be a knowledge gap on the governing factors driving and more interestingly hampering the distribution of the vacuum sewer technology. The aim of this thesis is to further close this gap and examine the technology against the theory of technological leapfrogging in developing countries. Chapter 2 will provide the background and underlying knowledge relevant to this thesis. The current state as well as emerging trends in the wastewater sector are presented, followed by the introduction to the concepts of vacuum sewerage and technology leapfrogging. The interview and survey methods used to create and assess data and information on vacuum sewers are described in Chapter 3. Chapter 4 will provide the outcomes of the surveys in a mix of quantitative and qualitative data while Chapter 5 will discuss the results from this study in the context of existing knowledge.
2. Background Information 2.1.
Status quo –current wastewater collection systems
Although gravity sewers have been very effective in providing sanitary and drainage services there are a couple of challenges associated with the concept. First, the construction of a gravity sewer network is very expensive. Deep excavations are required to install large pipes with a slope of at least 3 to 5% reaching down to 8m (Miszta-Kruk 2016; Little 2004). Construction becomes even more complex when groundwater needs to be removed. When slope is insufficient to convey the sewage to the treatment plant or the distance to the treatment plant becomes too large, additional lift stations are required Background Information
p. 11 / 114
between different sections of the pipe network (Tilley et al. 2008). At a lift station, a submersible sewage pump elevates the wastewater to a new pipe section, which lays at lower depths. In combined sewers, a minimum pipe diameter is required to accommodate flow in heavy rainfall events. However, in absence of large amounts of stormwater the volume of wastewater can be too low to wash objects accumulating in the system. This is a common problem in older sewer networks, which have been designed for larger water quantities before water efficiency increased in the past decades. Consequently, network operators have to flush the pipes with pressurized water. This highlights the inability of large infrastructure to adapt to changes. The contrary problem occurs in heavy rainfall events. In 2013, wastewater treatment plants received around 9.8 billion m³ of wastewater (Statistisches Bundesamt 2013a). Only around 51% (5 billion m³) result from residential or industrial sources (Statistisches Bundesamt 2013a). The remaining volumes derive from stormwater and groundwater infiltrating into the sewerage system (Figure 3). The additional water can overload the capacity of the wastewater treatment facility. The treatment processes are most efficient at high pollutant concentrations in the wastewater (Kjerstadius et al. 2015). The rainwater dilutes the wastewater, which affects the treatment efficiency and can result in overflowing treatment plants in which case untreated, or partially untreated, wastewater is introduced into the environment.
Figure 3: Composition of water treated at treatment facilities (Statistisches Bundesamt 2013b)
Further, environmental problems arise from the difficulty to detect cracks and leakages in the network. Exfiltration can occur posing a potential hazard to groundwater resources (Dohmann 1999). Studies show that up to 167 L/d*cm² of pipe surface can exfiltrate from Background Information
p. 12 / 114
damaged sewers. Pollutants have been detected in groundwater bodies in up to 60m depth (Rutsch et al. 2008). In areas with high groundwater tables or water protection areas gravity sewers have to be equipped with additional measures to minimize the risk of pollution. This is a problem especially in aging sewer networks and Figure 4 shows that that the share of older sewer networks increases with population size leading to increasing costs for repairs.
Figure 4: Age structure of sewer networks in Germany according to population sizes (E) (Berger et al. 2016)
Damages and cracks to the pipe material can have many origins. While material degradation or physical damages from interventions (e.g. roots or illegal connections) can cause damages, another reason can be corrosion resulting from the formation of Sulphuric acid (Austermann-Haun 2010). Furthermore, hydrogen sulphide poses a health risk to technical staff during the inspection of pipes from the interior (Weismann, Lohse 2007). Finally, until today it is common practice in conventional sewer systems to rely on drinking water as transport medium for feces, urine and other ‘wastes’ (DWA 2008). It raises the question whether it is environmentally and economically reasonable to use potable water for toilet flushing. This especially applies to regions with limited available water resources. A growing world population and the uncertainties of changing rainfall patterns induced by climate change already put tremendous pressure on our fresh water resources, urgently needed for agricultural production, hygiene and industrial activities. Less water intensive
Background Information
p. 13 / 114
modes of sewage transportation would be particular welcomed in regions experiencing water scarcity.
2.2.
Current trends in the wastewater sector
The previous section described common challenges of widely distributed sewer systems. While centralized combined sewers are expensive and bulky, decentralized septic tanks have their limitations regarding treatment capacity. Both systems include environmental risks predominantly from pollutants potentially leaking into the environment possibly contributing to eutrophication, soil and groundwater contamination. The challenges mentioned above highlight the importance to rethink the current sewer and sanitary concepts. Large-scale societal transformations such as urbanization, induced by global changes in climate and demographics pose new pressures on societies and their supporting infrastructure. The mere size and longevity of wastewater infrastructure allow little flexibility to these changes and the costs of sewer construction, operation and maintenance form a large cost factor in public budgets and account for around 70% of the sewerage tariffs paid by the connected people with a smaller proportion dedicated to treatment (Müller 1997; Hentrich et al. 2000). New ways of water management can pose a financial relief to municipalities, which can then allocate budgets to other important sectors. This applies especially to rural communities where per capita costs for sewerage infrastructure can be ten times higher than in urban areas (Schluff 1996). Around 20% of Germany’s sewer network has medium or severe deficiencies, with another 45% showing minor damages (Berger et al. 2016). Under the aspect of aging infrastructure and expected renewal or refurbishment, financially viable alternatives become eminently important. This importance is increasingly acknowledged by politics. Many publicly funded research schemes explore concepts and technologies for more sustainable water management. Between 2013 and 2016 the German Ministry for Education and Research allocated 33 Mio € to 13 R&D projects addressing the development of adaptations of urban water management to new challenges (Deutsches Institut für Urbanistik 2013). Further, the German government made changes to the Federal Water Act in order to address environmental and sewerage related challenges. Stormwater is to be infiltrated locally wherever it’s possible (Besonderes Verwaltungsrecht, Wasserrecht 2017). Background Information
p. 14 / 114
Especially, newly developed residential areas are to implement separate collection systems for wastewater and storm water. This results in a load reduction for sewer systems and treatment facilities during storm events, a common problem where untreated or partially untreated sewage emits to the environment due to insufficient capacity of treatment facilities to accommodate water quantities that are much larger than their design capacity. Additionally, increased infiltration of stormwater allows for more natural water cycle. In addition, the recovery of energy in form of biogas has been subject to recent efforts (Kjerstadius et al. 2015) and wastewater treatment plants are more frequently equipped with measures for energy recovery (Kollmann et al. 2016). While relevant agricultural nutrients predominantly occur in urine, carbon compounds relevant for biogas production occur in higher concentration in feces (DWA 2008).In January 2017, the German federal government revised the Sewage Sludge Ordinance in order to promote nutrient and especially phosphorous recovery from sewage sludge and wastewater at treatment facilities (Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit 2017). The prerequisite for tapping the potential of the approaches mentioned above is the separation of different streams containing the relevant compounds for the targeted treatment processes. Processes targeting the generation of biogas or the recovery of nutrients are more efficient when the carbon and nutrient loads are concentrated and the highest recovery potential for biogas and nutrients is achieved by a high degree of source separation (Kjerstadius et al. 2015). In fact, the highest potentials were achieved with vacuum-based systems (vacuum toilets and vacuum sewers). In summary, the above mentioned aspects highlight the needs, as well as the potentials for new concepts in urban water management, which allow more flexibility to changes, are more environmental friendly and enable the promotion of circular economy principles by recovering nutrients and recycling energy.
2.3.
Vacuum sewers
A vacuum sewer system is an alternative sewerage system and works in a similar way as water distribution systems. The only difference is the direction of flow (Islam 2016). While water supply uses positive pressure to ‘push’ the water from the treatment plant to the point of consumption, vacuum sewers use negative pressure to ‘draw’ the wastewater from the point of generation to the wastewater treatment plant (Islam 2016). Background Information
p. 15 / 114
Figure 5: Overview of a vacuum sewer system involving the vacuum valve unit at the valve pits, vacuum mains and the central vacuum station (Sustainable Sanitation and Water Management 2012)
Figure 5 illustrates the layout of a vacuum sewer system. The wastewater that accumulates
at the building level flows into the closely located collection chamber via a gravity line. The pit consists of two chambers, with one housing the interface valve, control unit and monitoring equipment while the lower compartment contains the sump that receives the sewage from the house (see Figure 6). The evacuation cycle is triggered when a certain amount of wastewater has accumulated in the sump. The differential pressure propels the sewage along the vacuum network towards the vacuum tank located at the vacuum station along with vacuum generating pumps. At the vacuum station, sewage pumps forward the wastewater to the treatment plant or intercepting main lines (e.g. gravity sewers).
Background Information
p. 16 / 114
Figure 6: Left: Schematic layout of a collection pit; Right: prefabricated collection pit (Naret 2007)
The vacuum valve (Figure 7, left) forms the interface between the negative pressure in the network and the atmospheric pressure. In most designs, the valve opens and closes pneumatically. Air gets trapped in the sensor pipe and the pressure increases. Then the water level sensor in conjunction with the control unit signal the valve to open. The differential pressure between the system and the atmosphere then propels the collected sewage into the vacuum line towards the vacuum tank at finally to the vacuum station.
Figure 7: Left: Vacuum valve unit (Günthert, Cvaci 2005); right: individual valves can be remotely
monitored (FLOVAC 2017)
Vacuum valves can be equipped with a monitoring system (Figure 7, right) to facilitate the localization of malfunctioning valves and surveille operations. The profile of the vacuum sewer line is a significant feature of the system. The most common profile is the saw-tooth profile (Figure 8). The saw-tooth profile enables to overcome heights up to 6m in flat terrains (U.S. Environmental Protection Agency 1991). This small positive slope towards the vacuum station is maintained by lifts, which cause
Background Information
p. 17 / 114
static losses and together with the friction losses they limit the maximum length of the vacuum network (Naret 2007).
Figure 8: Saw-tooth profile of a vacuum sewer line (Naret 2007)
One great advantage of the vacuum network is the high transport velocity of 4.5 – 6 m/sec (Naret 2007) and thus much higher than the required velocity for self-cleaning which is estimated at 0.6-0.9 m/sec (U.S. Environmental Protection Agency 1991; Tilley et al. 2008). It ensures that the pipes are cleaned regularly and aerated sufficiently, which prevents the formation of odorous or corrosive compounds. Further, clogging and blockages are very unlikely and since the network is tight no wastewater can exfiltrate to the environment. Any leaks are detected very quickly since this would result in decreased vacuum, increased pump activity and thus higher electricity costs (Günthert, Cvaci 2005). Vacuum mains are usually made from PVC or PE. PVC pipes are usually cheaper, widely available but break down easier. On the other hand, PE pipes have thicker walls and thus are more resistant but come at higher cost (Naret 2008). The network can be laid in much lower depths than in conventional gravity sewers. Usually frost conditions determine the depth. Typically the pipes are laid at around 90cm (U.S. Environmental Protection Agency 1991) in narrow open trenches and due to flexibility can be installed around obstacles, for example other infrastructure mains. Division or isolation valves allow for the separation of individual sections of the pipe network. They can facilitate the localization of leakages in the network and are used to divide the service area in sub-areas, adding operational flexibility and reducing costs (Schluff 2013). The heart of the system is the vacuum station. The layout in Figure 9 shows, It accommodates the technological components such as the vacuum and sewage pumps, electronic components for monitoring and communication. Additionally, the control and monitoring systems are equipped with an alarm system, which notifies the operator via a
Background Information
p. 18 / 114
text message in the event of a fault. Usually it is the only point of the system where electricity is needed.
Figure 9: Layout of a vacuum station with the collection tank in the ground and the sewage pumps outside of the tank. (Naret 2007)
The vacuum pumps, shown in Figure 10 generate the differential pressure for the sewage transport mechanism (Figure 10). Operating pressure varies between - 0.5 – - 0.7 bar. Vacuum pumps do not run continuously but rather in cycles for short periods of around 3-5 h/ day in order to maintain sufficient vacuum pressure in the system. The opening of the valves at the collection chambers results in periodic pressure loss. When the system pressure drops below a certain threshold (e.g. -0.5 bar) the vacuum pumps start running and restore operating pressure (e.g. -0.6 bar). The number of pumps is selected so that the remaining pumps can deliver normal operation while another pump is serviced or broken.
Figure 10: Parallel vacuum pump arrangement at the vacuum station in Böblingen-Dagersheim (Mohr 2016). Background Information
p. 19 / 114
The vacuum pumps are connected to the vacuum tank. The tank forms the collection point of the domestic sewage. Further, the tank functions as a buffer for the negative pressure created by the vacuum pumps in order to maintain the system pressure over a longer period of time. In many layouts the tank is installed under ground but can also be placed inside the vacuum station. Most systems have submersible wastewater pumps located inside the tank. Duplicate pumps, each of them capable of delivering the design capacity at the specified head conditions are installed (Naret 2007). Odorous air from the vacuum tank is directed to an exhaust air treatment, commonly a biofilter. The microorganisms living in the filling material decompose organic pollutants and odorous compounds. Filling material can compose of woodchips, root wood, bark mulch, turf, coconut fibre or activated carbon (Günthert, Cvaci 2005).
Figure 11: Biofiler used for odour control from a vacuum tank. Right: woodchips are a common filling material (Günthert, Cvaci 2005)
The individual components of vacuum sewer systems have different life spans after which they have to be replaced. The construction elements, such as the vacuum station, lines and collection chambers, have higher life spans then the mechanical and electrical components, which are more exposed to wear. The life spans of the major components of vacuum sewers are presented in Table 1.
Background Information
p. 20 / 114
Table 1: Life span of various vacuum sewer components (Schluff 1996; IWR - Ingenieurbüro für Wasserwirtschaft und Ressourcenmanagement 2016; Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft 2004; Günthert, Cvaci 2005) Component
Life span
Varying factors
(years) Damage from other excavations; Design faults; selected material Vandalism; selected materials
Vacuum main / line
50 – 80
Vacuum station (building)
50
Vacuum pumps
12.5 - 20
Sewage pumps
12.5 - 15
Vacuum tank
25 - 40
Inadequate maintenance; continuous run; type and brand, cavitation Inadequate maintenance; continuous run; type and brand; dry running; cavitation; clogging Material; maintenance; corrosion
Division valves
20
Material; brand; mechanical wear
Collection chambers
30-55
Vandalism, storm water, upwelling
Valve unit
(30) 6.25
Maintenance; user education on flushable objects; brand; size; opening frequency; mechanical wear
12.5 25
Maintenance; power supply; vandalism
-
Membrane Controller
Monitoring system
2.4
Overview of vacuum systems in place worldwide
Since the first installation of modern vacuum in the 1970s the number of projects has constantly increased. Figure 12 displays the number of projects in several countries realised by the two biggest system providers, AIRVAC and ROEDIGER, until the year 2008.
Figure 12: Number of vacuum sewer projects implemented by ROEDIGER (blue) and AIRVAC (red) between 1973 and 2008 (Terryn, Lazar 2016)
Background Information
p. 21 / 114
Due to the large number of vacuum projects, only few can be presented here. The most famous vacuum sewer project was realized on the man-made island Palm Jumeirah. The system was commissioned in 2007 and serves around 23,000 people via 40 km of network and 16 vacuum pumps (Bilfinger Water Technologies GmbH).
Figure 13: Vacuum sewer system in Palm Jumeirah, Dubai (Bilfinger Water Technologies GmbH)
Although most projects involving the vacuum sewer technology appear to run well some cases exist that highlight the need for careful planning, operational and maintenance procedures as well as organisational structures. The community of Ernsgarden, Germany implemented a vacuum sewer system in 1978 for around 1,700 people and has experienced ongoing problems with its 17 km long network. During strong rainfall events and when groundwater tables rise the risk of introduced water is very high. Further, the community realized a high susceptibility to failures especially due to false user behaviour. This resulted in increased personnel deployment for repair and maintenance and thus higher operational costs(Gemeinde Magazin Ernsgaden 2016). Its potential cost advantages, flexible design character and environmental benefits make the vacuum technology a considerable alternative in low-income areas. So far, a small number of projects have been realised in developing countries. In Kosovo, an informal settlement in South Africa’s Cape Town, a vacuum sewerage system was completed in 2009. In an area with flat, sandy terrain and high groundwater the vacuum technology seemed appropriate (Taing et al. 2011). Unfortunately, the system has continuously been hampered by poor management from both the residents and the service providers (Beauclair 2010). Introduced objects resulted in valve failures and the valve pits over-filled with sewage (Figure 14). The acquisition of spare parts from Germany proofed to be expensive and time-consuming. In hindsight, the municipality lacked the Background Information
p. 22 / 114
technical capacity to operate and maintain the system. Trainings for the technical staff were not carried out and insufficient attention was given to the social context of an informal settlement. Education and awareness programmes targeted at the end users were neglected. Additionally, the high staff turnover and lack of ownership made it difficult to hold anybody accountable for the failures and responsible for resolving the problems. Mixed experiences were made with several vacuum sewer systems in Namibia. The local authorities of Ondangwa, Gobabis, Henties Bay, Kalkrand and Stampriet each implemented a vacuum sewer in the period between 2001 and 2010 (Mäkinen 2015). Vacuum sewers were selected due to the potential cost savings in flat terrain and sandy soils. However, the local operators faced a series of operational and organisational challenges similar to the system in Cape Town. The vacuum sewer in Gibeon was not operating anymore after only 4 years.
Figure 14:Deterioration of vacuum based sanitation in Kosovo, Cape Town (Taing et al. 2011)
The Cuve Waters Project aims at demonstrating the potential of integrated water management in rapidly growing informal settlements in Outapi, Namibia. The sanitation and water reuse component of the project implemented a new sanitation concept for around 1,500 residents in 2012. Communal washhouses, cluster units and individual houses were connected to the vacuum sewer system. At the small treatment plant, the wastewater is at first treated in an anaerobic treatment process where biogas is harvested. Finally, the water is disinfected by UV radiation. The sludge is used for subsequent soil conditioning. The treated water is collected in a pond and used as irrigation water (see Figure 15). The project increased the access of the local population to sanitary services. Diarrheal diseases dropped by 46% and open defecation decreased by 20%. The implementation also resulted in increased agricultural activity and higher yields through Background Information
p. 23 / 114
the use of reclaimed water. Further benefits included the biogas yield which was sufficient to run the treatment infrastructure and the creation of additional employment opportunities (Zimmermann et al. 2015).
Figure 15: Layout of the sanitation and reuse concept in Outapi (Zimmermann et al. 2015).
In 2005, the Fraunhofer IGB led DEUS 21 project was designed to demonstrate an innovative approach to semi-decentralised integrated urban water management for 100 households in Knittlingen, Germany. Some of the houses, which were connected to the vacuum sewer, installed vacuum toilets and kitchen grinders in order to reduce water consumption but increase organic load in the wastewater through disposal of kitchen wastes. The vacuum station further served as a compact treatment plant. Here the wastewater was treated using a modern membrane bioreactor, which enabled the generation of biogas (Zech et al. 2008). Other references in which vacuum sewers have played a central part of an integrated water management concept are Jenfelder Au, Hamburg (Freie und Hansestadt Hamburg
Background Information
p. 24 / 114
2014), Flintenbreite, Lübeck (Oldenburg 2008) and Vauban, Freiburg (Otterpohl et al. 2004) .
Figure 16: Schematic overview on how water management was designed in DEUS 21 with vacuum sewers being the selected technology for wastewater conveyance (www.deus21.de)
Vacuum sewers are not limited to new development areas but can be installed in existing sewer networks. When an old gravity sewer would require extensive and expensive refurbishment or the municipality decides to switch from a combined sewer to a system where wastewater and storm water are drained separately vacuum sewers installed in the existing sewer network can be a good solution to save costs (Figure 17). This has been successfully implemented in 2011 the German municipality Schwalmtal – Rainrod with 140 connections (Bayer, Kopfhammer 2012).
Figure 17: Vacuum pipe installed in existing channels; the PE pipe is attached to the wall of the channel (Bayer, Kopfhammer 2012). Background Information
p. 25 / 114
2.5.
Wastewater service provision in the Global South
While in Germany the connection rate to centralized sewer infrastructure is around 96% (Statistisches Bundesamt 2013c) the situation is very different in other regions of the world. WHO, UNICEF (2015) estimate that around 2.4 Billion people around the world lack access to improved sanitation facilities causing millions of hygiene related deaths, especially affecting children under five years. The vast majority lives in countries of the Global South in Southern Asia (953 Mio), Sub-Sahara Africa (695 Mio) and Eastern Asia (337 Mio). According to the definition by the WHO ‘an improved sanitation facility is one that hygienically separates human excreta from human contact’ (WHO, UNICEF 2017). Improved sanitation is assumed when users are connected to a sewer system or septic tank, or use sophisticated pit latrines with slabs or composting (WHO, UNICEF 2017). Due to the implications of insufficient sanitation on hygiene and health, affecting educational and economic activities improving access to sanitation has been subject to numerous efforts of national and international development programs. A WHO study in 2012 calculated that for every $1 invested in sanitation, there was a return of $5.50 in lower health costs, more productivity and fewer premature deaths (WHO 2012). The matter of sanitation has been included in the Millennium Development Goals (MDGs) and their successor the Sustainable Development Goals (SDGs). It is estimated that 2.1 billion people gained access to improved sanitation facilities since 1990 (WHO, UNICEF 2015). Despite these successes in the past two decades, strong regional differences exist across world regions. As shown in Figure 18 large advances have been made in many regions in Asia and the Americas increasing sanitation coverage by 14-27%. In the same time, sanitation coverage in Sub-Sahara Africa increased by only 6%. Increased access to improved sanitation does not include information on the connection to a centralized treatment facility. Only little information is available on this subject. A study conducted by the World Bank (2015) focused on the sanitation in Indonesia and Vietnam concluded that less than 10% of generated wastewater is collected and conveyed to centralized treatment plants. The majority of urban citizens in both countries rely on septic tanks.
Background Information
p. 26 / 114
Figure 18: Progress on sanitation coverage (%) by region (WHO, UNICEF 2015)
This is supported by Figure 19, showing that sewer connection rate is low in Sub-Saharan Africa, South and South-East Asia.
Figure 19: World population served by different sanitation technologies (Strande et al. 2014)
Infrastructure investments are concentrated on large-scale municipal infrastructure ‘neglecting the connecting infrastructure and household support to connect’ (World Bank 2015). Based on a survey of 35 African countries, the average level of access to sewerage is 30% (Mitullah et al. 2016). The average is heavily influenced by high connection rates in Northern Africa (up to 95% in Algeria). In 20 countries connection rates are below Background Information
p. 27 / 114
20%. Generally), and especially in African countries, a strong disparity exists between rural and urban areas with much lower connection rates in rural areas (Figure 20). The mentioned trends and figures indicate that the increase in sanitation provision is not necessarily related to an increase in sewerage cover. Other forms of improved sanitation, such as septic tanks and improved latrines, probably play a more dominant role in the provision of sanitary services.
Figure 20: Disparity in access to improved sanitation between rural and urban areas Left: global (WHO, UNICEF 2015); right: 35 African countries (red= urban; blue=rural) (Mitullah et al. 2016)
However, due to strong population growth, land-urban migration, in conjunction with increasing industrial activity in many emerging economies, rapid development of wastewater collection and treatment is crucial. Smart solutions need to be implemented in order to avoid exacerbating costs and the challenges mentioned earlier.
2.6. Environmental and technological leapfrogging theory 2.6.1.
Theory explained
The concept of leapfrogging originates from the field of industrial organization. The main idea behind this is that monopolists or market leaders have little incentive to make innovations because they are earning from their established products. According to the leapfrogging theory it is possible for other competitors to not only catch up with the leading organizations but leapfrog ahead of them through innovation (Rosenkranz 1997). This means that they can avoid stages of a development process that the leaders have previously gone through. Instead, the innovation allows to jump ahead. The concept of leapfrogging has also been discussed in the environmental debate and development theory. Instead of introducing old and ‘dirty technologies of the past’ (Perkins 2003) and repeating the development path of other countries, developing Background Information
p. 28 / 114
countries might be able to ‘leapfrog’ stages of development by investing in ‘modern, clean technologies as an integral part of capacity addition’ (Shalizi 2003). Further, developing societies could avoid getting ‘locked’ in large, costly and fossil fuel based technologies and infrastructures lie industrialized countries (Rip, Kemp 1998; Unruh 2000; Binz et al. 2012). According to Tukker, leapfrogging is defined as a situation where a developing country learns from the mistakes of the industrialized countries by directly building more sustainable modes of consumption and production using innovative, environmental friendlier concepts (Tukker 2005). The environmental Kutznets Curve Figure 21 visualizes the relationship between economic growth and environmental pollution during the transitional stages of development (Sauter, Watson 2008). The examples of industrialized economies or more recently, of China, with its large increase in carbon emissions and environmental pollution over the past two decades underline the relationship.
Figure 21: Visualization of an Environmental Kutznets Curve (Sauter, Watson 2008)
Environmental leapfrogging could pose an approach to accelerate economic development in the industrializing world, while simultaneously improving the environmental impact of economic activities and public services, such as wastewater service provision. 2.6.2.
Leapfrogging examples
Technological leapfrogging is not only a theoretical concept. In the 1960s, South Korea was a latecomer country in the steel industry (Sauter, Watson 2008). Through world market access to state of the art technology, large plant sizes and enabling policy environments strengthening national education, training and innovation South Korea’s steel industry leapfrogged the European and American steel industries, in economic as well as environmental terms (Sauter, Watson 2008).
Background Information
p. 29 / 114
Renewable energy systems are often considered as potential leapfrogging technologies in order to avoid carbon-based energy generation in large power plants. The case of China’s wind industry underlines how a latecomer country can become a promoter of cleaner technologies. Earlier donors required the import of wind turbines and exempts from customs in order to promote export from the leading producers in Denmark, Spain and Germany (Sauter, Watson 2008). These regulations hindered the development of a domestic production capacity. The formulation of a coherent policy framework (e.g. Renewable Energy Law in 2006) and publicly funded R&D led to a significant increase in installed wind turbines (Dai, Xue 2013). Between 2002 and 2012 the accumulated installation increased from 447 MW to 78,264 MW (see Figure 22) while transitioning from import dependency to a major producer of wind energy and innovator in wind turbine capacity (Dai, Xue 2013). The case of China’s wind energy industry highlights the importance of building domestic technological capacity in the adaption of new technologies and leapfrogging.
Figure 22: Changes in the installation capacity of Chinese wind energy (Dai, Xue 2013)
A prominent example of leapfrogging is the distribution of mobile phones across the developing world (Howard, Mazaheri 2009). As shown in Figure 20, 89% of people living in rural Africa have access to cell phone services, in urban areas the figure rises to 99%. Instead of building the communications network required for landlines, mobile phones enabled people in the Global South to surpass the linear stage of development and leap directly to decentralised, mobile communication. Considering the relative current development of mobile communications, technology adoption occurred extremely fast Mobile services found applications beyond telephone communication such as health care Background Information
p. 30 / 114
purposes and enabling farmers to access information, among others (Karippacheril et al. 2013, Mothobi, Grzybowski 2017). The most famous example is the case of mobile banking in East-Africa. Launched in 2007 by Kenyan company Safaricom in collaboration with Vodafone, mobile money, MPESA, allows users to pay bills, shop or send money to other registered users via the mobile network (Mothobi, Grzybowski 2017). Many people in rural areas use the mobile currency, which can be withdrawn or deposited to the phone number at widely distributed vendors. In the absence of banking offices, MPESA enables the rural community to participate in modern banking and other important aspects of public life (e.g. access to information). The concept has been so successful that it was quickly introduced in other East-African countries, Senegal, Cote d’Ivore, Madagascar, Mali, Niger, Botswana, Cameroon, South Africa as well as Afghanistan, Jordan and other countries. (Mothobi, Grzybowski 2017).
Figure 23: M-PESA banking menu on a feature phone (https://businesstoday.co.ke/facebooksets-eyes-m-pesa)
2.7.
Scope of the study
The previous chapters described the theoretical background for the study. As mentioned above vacuum sewers can have advantages over conventional sewage systems. One of the research questions targeted in this study is to find out why vacuum sewers have not been more successful and more distributed despite their potential advantages over conventional sewer systems. There seems to be a demand to explore the barriers that are inhibiting a wider application of the vacuum system in order to develop solutions to further exploit the potential in the future. Further, it is the aim of this study is to evaluate data from existing vacuum sewer projects in order to assess operational parameters, such as costs and labor, among others. The results will provide an overview over experiences with vacuum sewers.
Background Information
p. 31 / 114
Finally, this research will critically assess whether vacuum sewer can pose a sustainable solution to increase wastewater service cover in countries of the Global South. The comparative cost advantage and the environmental benefits that vacuum sewers can have over conventional sewer systems can be attractive for regions where the current sanitary service provision is inadequate. A comparison will be driven to the settings for leapfrogging technologies, such as renewable energy (e.g. wind turbines) and mobile phones.
3. Methodology Since vacuum sewers have so far enjoyed limited attention by the scientific community the used literature in this study is complemented by information provided by public, private and non-governmental organizations. The literature is critically assessed for its suitability for scientific contribution. More peer-reviewed literature exists on the concept of technological and environmental leapfrogging. The present study discusses the main arguments derived from advocates and opponents of the theory and projects the pros and cons of the theory to the case of vacuum sewers. Potential applications and required conditions will be analyzed in order to give an estimate on whether vacuum sewers can contribute to the extension of sewerage cover in countries of the Global South.
3.1.
Expert interviews
In order to find answers to inhibiting factors for technology distribution, potential application of vacuum sewers in countries of the Global South, the knowledge of experts is required. Experiences from actors involved in the planning, construction and operation of vacuum sewers are evaluated in form of semi-structured interviews. Semi-structured method is chosen in order to provide some guiding questions but allow for more in-depth answers from the interviewees. Targeted interviewees are representatives from technology providers (system manufacturers), planners, scientists, decision makers and operators who are identified from previous collaborations with the Fraunhofer IGB as well as from individual research. The interviews are conducted over the phone since some interviewees are based outside of Germany and face-to-face interviews are impractical. Therefore, interviews are held in either English or German. The interviews are recorded, summarized and analyzed for patterns, relationships and controversies. For data 3. Methodology
p. 32 / 114
protection reasons the interviews are anonymised. The quantitative data from the interviews is analysed for correlation. Where possible, answers from the qualitative questions are grouped into categories in order to identify important aspects guiding the perception on vacuum sewers and current trends in water management. The questionnaire for the expert interviews can be found in the Annex. The recorded interviews and documentation are stored on a separate data carrier.
3.2.
Operator survey
In addition to the expert interviews a stronger emphasis is given on the experiences and opinions of the technical personnel working with vacuum sewers on a regular basis. Therefore, an operator survey is carried out in order to capture relevant operational parameters, system characteristics and personal knowledge from current vacuum sewer operators in Germany. The survey is carried out online since personal interviews either face-to-face or via the phone are unfeasible given the large number of systems in Germany.
Thus,
an
online
survey
is
created
using
the
platform
https://www.soscisurvey.de. SoSci Survey is a platform designed for social research projects and free for research and other non -profit projects. It enables a simple and fast development of survey and data processing. The answers from participants can be downloaded for further processing in Excel, R or SPSS. Operators are identified from provided
information
by
three
large
system
manufacturers
QUA-VAC,
Vakuumanlagenbau GmbH and AQSEPTENCE Group) with whom data protection agreements have been arranged. Operators receive an email invitation to participate in the online survey which is estimated to take around 10-15 minutes. The survey which is conducted via the internet is accessible from the 12th of April, 2017. Results up to the 15th of June, 2017 are considered within this thesis. The survey can be accessed via https://www.soscisurvey.de/vakuum/. The survey consists of four modules. The first module surveys system characteristics of the respective vacuum sewer system. Questions target location, age, length, connected households and more. The second module targets operational data regarding working hours, costs and failure rates, among others. Questions in the third module aim at catching the personal opinion from the operators regarding contentment, suggestions for improvement, ratings and views on given statements. The final fourth module surveys personal information such as occupation, work experience, age and sex. 3. Methodology
p. 33 / 114
The system characteristics are evaluated and compared across the variety of settings using basic statistical measures. Where possible, answers from both the expert and the operator survey are tested against quantified data.
3.3.
Statistical analysis
The quantified data from the expert interviews and the operator survey enables the statistical evaluation of the participants’ responses. This facilitates the identification of patterns, trends and relationships of different variables in the sample. While the arithmetic mean is often used in order to describe the distribution of observations, outliers or extreme values can heavily influence it. The median is more robust against this influence. When median and mean are close to each other, the distribution is symmetric (Moore et al. 2009). In skewed distributions, the values for mean and median differ. Thus, both measures are included in the evaluation of the data used in this study. In addition to the median, the variability is calculated for the investigated variables by determining the lower and upper quartiles. Quartiles are further measures in descriptive statistics. The first quartile shows that 25% of the sample’s values are equal or lower than this value. The third, or upper, quartile shows the value up to which 75% of the sample’s values are included. The visualization of distribution can be achieved using a boxplot Figure 24. The box includes 50% of a sample’s values. The boundaries of the box are formed by the lower and upper quartile and the black line indicates the median. The minimum and maximum values within the observations are shown by the whiskers. Visualization of variability is supported by histograms (Figure 24). Histograms are bar plots, which divide the sample in equally large categories and display the frequency of observations within the interval in order to show the probability distribution of the investigated variables.
3. Methodology
p. 34 / 114
Figure 24: Left: Example of Box-Whisker-Plot (Sullivan, LaMorte 2016); Right: Example of histogram
According to Moore et al. (2009) correlation ‘measures the direction and strength of a linear relationship between two quantitative variables’. The values for correlation range from -1 to +1. The closer the correlation value is to 1 the stronger the interrelation is between the variables. On the other hand, a negative correlation towards -1 indicates a negative relationship among the variables while a correlation value around 0 indicates independence between the variables. Correlation does not provide information regarding which variable is dependent and which is independent. Correlation is usually written as ‘r’.
𝑟=
1 𝑛−1
∑(
𝑥𝑖− 𝑥̅ 𝑠𝑥
)∗(
𝑦𝑖− 𝑦̅ 𝑠𝑦
)
Where 𝑥̅ = arithmetic mean s = standard deviation
4. Results 4.1.
Literature review on environmental leapfrogging
In contrast to the concept of vacuum sewerage, more scientific literature is available on the concept of leapfrogging. However, the discussion remains vague on how to achieve leapfrogging. Perkins (2003) states that conventional approaches to leapfrogging require five conditions to be met. Firstly, a shift from end-of-pipe measure towards ‘clean’ production strategies is required. Preventive and pollution mitigating concepts rather than ‘clean-up’ technologies are needed in order to ‘simultaneously advance the goals of economic development and environmental protection’ (Perkins 2003). Secondly, efforts need to start at the early stages of industrialization in order to avoid the lock-in with carbon intensive technologies and long-term investments. This way damages and financial implications from continuous environmental degradation can be prevented. The third Results
p. 35 / 114
condition refers to the technology transfer from industrialized countries where most companies are based that develop and own potential technologies. It is believed that transnational corporations transfer their know how and technologies to subsidiaries in developing countries since local firms often lack the financial resources to adopt technologies, TNCs are viewed as the most likely accelerator of technology transfer. An increase in external pressure on local companies is another condition for leapfrogging. For example, through stronger environmental legislation and enforcement, or subsidy cuts, which are common for electricity and water, companies would be encouraged to improve their environmental performance. Warhurst, Bridge (1997) describe this as policy leapfrogging to facilitate environmental and technological leapfrogging. Additional policies would have to address the provision of a favorable environment for technologies including education and training facilities, infrastructure and stable economic and legal conditions (e.g. property rights) (Ilori et al. 2002). The final condition refers to international assistance in investment concessions and to ‘overcome lack of information on availability, cost and performance of competing technologies’ (Perkins 2003). While Perkins defines a set of success criteria, Binz et al. (2012) provide a more conceptual framework to assessing leapfrogging potential. The technological innovation systems (TIS) approach is based on the assumption that innovation uptake is the result of the interaction of complementary actors within complex networks (Carlsson et al. 2002). Different leapfrogging trajectories exist, which can be distinguished by the degree of coupling of national and international TIS as opposed to competence development by national isolation. Further, the direction of competence formation can characterize leapfrogging trajectories. Export oriented competence formation describes the path, where a developing country builds the capacities with the intention to export technologies back to industrialized countries. In contrast, foreign direct investment describes the classic case of most scientific literature, in which a developing country provides incentives to international actors for the introduction of technological innovation (Binz et al. 2012). The examples of mobile technology or the Chinese wind turbine industry are examples of leapfrogging via the direct investment trajectory. According to Bergek et al. (2008) the TIS, and thus leapfrogging potential, of a country for a specific technology can be assessed by eight functional groups. The functional groups and their indicators are shown in Table 2.
Results
p. 36 / 114
Table 2: Functional groups and indicators of TIS (in Binz et al. 2012 based on Bergek et al. 2008) Functional group Indicator Knowledge R&D projects, no. of involved actors, no. of conferences and workshops development Activities of industry associations, websites, conferences, linkages among Diffusion of innovation knowledge stakeholders Influence on the Government targets, press articles, visions, perception on growth potential direction of search Entrepreneurial No. of experiments, no. of new entrants, diversification activities experimentation No. of niche markets, tax and regulation regimes, environmental standards Market formation Growth of interest groups and lobbying activities Creation of legitimacy Availability of human and financial capital, complementary assets for key Resource mobilization actors Emergence of labour markets, intermediate goods and service providers, Development of information flows and spill overs positive externalities
Despite the success of some leapfrogging cases, the theory is criticized for being overoptimistic (Perkins 2003). Critics argue that the advocates of the leapfrogging approach often simplify the possibilities for technology transfer and that the discussion often lacks a complete understanding of the requirements (Binz et al. 2012). ‘Clean’ technologies currently available often produce residuals or other pollutants and lack competitiveness with established alternatives. More innovation is required to highlight the benefits and facilitate leapfrogging. Further, it cannot be assumed that technologies are suitable in all environments and Huber (2008) states that it cannot be expected that innovations and best environmental practices diffuse from advanced lead markets throughout the world. Current trends indicate that many developing countries follow the path of environment-intensive development (Perkins 2003). Further, Sauter and Watson (2008) point out that examples for successful leapfrogging, such as the distribution of mobile phones is based on the successful commercialization by industrialized countries followed by direct investment. As latecomers, developing countries would benefit from a competitive international market and scale effects, which lead to a relatively low price. In addition, reliance or even dependence on foreign firms and technologies could lead to the opposite effects, hampering growth and industrial development (Rip, Kemp 1998; Juma et al. 2001). Another critical aspect expressed by Howard, Mazaheri (2009) refers to the process of acquiring new knowledge and skills related to the technology. The bypassing of a technology might be accompanied with the bypassing of learning relevant skills from experience, which could affect the effective adoption of the new technology. Building
Results
p. 37 / 114
technological capacities is essential for successful leapfrogging (Dai, Xue 2013; Sauter, Watson 2008). Leapfrogging is a complex concept requiring multiple enabling conditions and strong public support. Current discussions and approaches might underestimate the challenges and difficulties to achieve a decoupling of pollution and economic growth. Nevertheless, examples as mentioned above emphasize the possibility of successful technology transfer, leapfrogging
of
development
stages
and
independent,
domestic
technology
advancements in the Global South.
Results
p. 38 / 114
4.2.
Expert interviews on vacuum sewers
4.2.1. Sample characteristics and rating A total of 16 expert interviews were conducted of which 14 were recorded using a smartphone application. During one interview, the recording did not work and notes were taken. One questionnaire was filled in by the expert and sent back via email. Table 3 gives an overview of the sample. For data protection reasons the interviewed persons are anonymized. The majority of experts work in Germany and therefore referred to the situation of vacuum sewers in Germany. One participant works in the Netherlands, one in Sweden and one in Thailand. Table 3: Overview of sample for expert interviews and quantifiable responses on experience with vacuum sewers,
Expert
Role
# 1 8 12 4 13 5 11 6 7 9 10 14 3 15 16 2
1
² ³ 4 5
Results
Consultant Consultant Decision Maker
Experience with VS
Expertise
Personal rating
In years
none (0) expert (10)
Very bad (0) – very good (10)
26 15 4
9 6 9
10 7 6
Estimated rating in industry Very bad (0) – very good (10) 2 4 7
System 20 10 10 10 manufacturer System 20 9 manufacturer Planner 20 7 7 5.3³ Planner 5 8 54 54 Scientist 2 8 (theory) 10 4 Scientist 5 2 7 3 Scientist 9 5 10 Scientist 3 3 5 Scientist 15 6 Operator 10 8 7 7 Operator 5 6 6 Operator 3 9 8 7 Env. 2 1 10² Technology Provider1 10.25 6.66 7.9 5.44 Average 7 8 7 5.15 Median other technologies than vacuum sewers ‘in very hot or very cold climates’ average from three site estimates (site A:3; site B: 6; site C:7) ‘at par with other sewer systems; very different depending on skill of operator’ calculated only for groups with 2 or more members
Rating per role5
Pers.
Ind.
8.5
3
6
5.2
8.5
7.3
7
6.7
p. 39 / 114
The sample is composed of five scientists, three, operators, two planners, two system manufacturers, two consultants, one decision maker and one environmental technology provider. All interviewed experts were male and between 20 and 70 years old (average: 46.75; median 45.5 years). When asked about the individual experience with vacuum sewers (in years) the answers show a large spread across the sample between 2 and 26 years with an average of 10.25 years and median of 7 years. Small negative correlation was detected between the role (occupation) and the years of experience (r=-0.23). The participants were asked to rate their own expertise regarding the vacuum sewer technology on a scale from 0 (none) – 10 (expert). The answers spread from 1 to 10 with 53% (8/15; one person did not give a rating) of the interviewed people considered themselves an 8 or higher. The average expertise among the group is 6.66 (median 8). There seems to be no correlation between the answers for expertise and role (r= 0.07) but a moderate correlation (r=0.44) between the years of experience and expertise. The participants were asked to rate the vacuum sewer technology on a scale from 0 (very bad) to 10 (very good). All responses were in the positive half (5 or higher) with the average at 7.9 and the median at 7. However, some participants added remarks to their rating which bound their answer to certain conditions (see experts #2 & 11). Two experts (#13 & 14) refused to answer the question because they felt the question was not specific enough. Almost no correlation (r=-0.04) can be attributed between the personal rating of vacuum sewers and the respective role (occupation). Little negative correlation (r=0.17) can be found between the personal rating and the degree of expertise and some positive correlation (r=0.28) seems to exist between the personal rating and the years of experience with vacuum sewers. Further, the experts were asked how they think other members of their industry would rate the technology on the same scale (0-10). The answers ranged from 2 to 10 but in contrast to the personal ratings the ratings assumed for the industry were lower with an average at 5.44 (median= 5.15. Experts 2,9,13 and 14 did not state a rating. Almost no correlation (r=-0.02) was found between the personal and the industry ratings. A strong correlation (r=0.85) between the estimated rating of the industry and the role was detected. A moderate correlation (r=0.47) was detected for the industry rating and the expert’s level of expertise. The investigated correlations are displayed in Table 4.
Results
p. 40 / 114
Table 4: Results from the correlation analysis for different variables of the expert interviews
Role
Work experience
Expertise
Personal rating
Role
1
Work experience
-0.23
1
Expertise
0.07
0.44
1
Personal rating
-0.04
0.28
-0.17
1
-0.05
0.47
-0.02
Estimated industry 0.85 rating 4.2.2.
Estimated industry rating
1
Positive and negative aspects of vacuum sewers
The answers from the interviews were screened for positive/ advantageous and negative/ disadvantageous aspects of vacuum sewers. The identified aspects were collected and assigned to a respective category. The formed categories refer to aspects regarding ‘Flexibility’, ‘Planning and Construction’, ‘Financials’, ‘Environment’ and ‘Operations’. Similar responses which referred to the same aspect but in different wording were collected under the same aspect and separated by ‘/’. The counts represent the number of referrals to a certain aspect (Figure 25). The number of different aspects for each category was also counted (Figure 26). In total, the interviewees referred to positive aspects in 76 cases. In 57 cases, negative aspects were mentioned or referred to. This results in a positive balance of +19 in favor of the positive aspects of vacuum sewers. In the ‘Flexibility’ category slightly more positive than negative aspects were mentioned (balance +3). The most frequently mentioned positive aspects of vacuum sewers refer to the application in rural areas as well as the potential for fast growing cities. In contrast, the majority of negative aspects see a restriction to rural areas, with limited application in urban areas with high population densities and wastewater quantities.
Results
p. 41 / 114
Total
76
57 17
Operations Environment
Positive
28
18
0
Negative
10 13
Financials Planning & Construction
21
9
Flexibility
7
0
10
20
40
60
80
Number of referrals Figure 25: Number of referrals to aspects within the interviews
In the category ‘Planning and Construction’, the experts mentioned more positive than negative aspects (balance +11). The most often mentioned positive aspects are the small pipe diameters of the vacuum sewer network and the beneficial application in flat terrains. In contrast, the high quality demand of construction due to the sensitivity towards errors, was the predominant negative aspect among the participants. In the ‘Financials’ category, more negative than positive aspects were named (balance 2). Most participants referred to higher operational costs and costly components. In contrast the positive aspects mentioned referred to the specific cases of construction in flat terrain and flood protection areas. The interviews did not reveal any negative aspects of vacuum sewers, which could be attributed to the category ‘Environment’ (balance +18). The most frequently mentioned positive aspect referred to the potential separation of waste streams and the simultaneous collection of food wastes through kitchen grinders. Additionally, the water saving potential through vacuum toilets and the prevention of wastewater leakages (exfiltration) into the environment were among the more frequently mentioned aspects. The balance for aspects attributed to the category ‘Operations’ is negative (balance -10). Main limiting aspects are the sensitivity of the system and technical complexity of vacuum sewers. In contrast, the easy error identification was mentioned as the dominant positive operational aspect of vacuum sewers.
Results
p. 42 / 114
Figure 26: Number of different aspects referred to in the interviews
Figure 26 shows the number of different aspects in each category. All categories show a larger variation of aspects in the positive domain than in the negative domain. For the majority of categories the difference is fairly small. The largest difference occurs in the category ‘Environment’, where six different positive aspects were referred to while no negative aspects were mentioned. In total, 33 different positive aspects and 19 negative aspects of vacuum sewers were mentioned. 4.2.3.
Critical factors during planning, construction and operation of vacuum sewers
The experts were asked which aspects around the planning, construction and operation of vacuum sewer systems they consider as critical. The requirement of experienced and skilled personnel was a common critical factor across all three project stages. For the planning stage the surrounding conditions, such as an existing sewer network, the possibility to connect only individual houses and the habits of the population were mentioned as critical. During construction, very accurate supervision, installation in saw tooth profile and the use of PE pipes connected via welded fittings were highlighted as critical aspects by the experts. Critical factors affecting the operations were training, the availability of skilled personnel and the management of spare parts, as well as the simultaneous extraction of air and wastewater.
Results
p. 43 / 114
4.2.4. Risk factors affecting the success of vacuum sewers In addition to the previous question the expert were asked on possible factors which can pose a risk to the success of vacuum sewer projects. The answers are shown in Table 5 Table 5: Possible risk factors affecting vacuum sewers
Planning Phase
Construction Phase
Qualification of the planner Construction not always given
Operational Phase services Noise levels can be a problem
sometimes a problem
Planner often not qualified Too
many
lifts
pose
a Right model and manufacturer
and don’t accept help from problem for the stabilization needed the system provider
of the vacuum
Slope of house connections
Sometimes use of siphons or installation against gradient
Vacuum sewers have to be welding of fittings designed over a period of 20 years which is a limitation Systems
are
complicated;
often
too Objects
enter
or
are
inspection forgotten in the pipes
pipes and check valves are obsolete
due
to
remote
monitoring Smallest
mistakes
during
construction can cause large problems Material failure Treatment of pipes
(e.g.
sawing) can lead to leaks and sand infiltration
4.2.5. Barriers preventing a wider distribution of vacuum sewers The experts were asked about possible factors preventing a wider distribution of vacuum sewers. The mentioned barriers are shown in Figure 27. The responses are grouped in the categories ‘Technical’, ‘Demand’, ‘Reputational’, ‘Financial’ and ‘Other’ barriers. Overall, 64 reference were made to barriers.
Results
p. 44 / 114
Only few technical barriers were mentioned. Similar to the answers on negative aspects the interviewees referred to a higher sensitivity and complexity of the vacuum technology. Reputational barriers were referred to in 16 cases. The most dominant factors in this category are the stronger influence of systems that are not functioning well on the general reputation, as well as the lack of experience with vacuum sewers and resulting skepticism. The sector barriers refer to the structure of the wastewater sector and the way the selection for a sewer network is made. Fourteen references were made to sector barriers. The experts described the wastewater industry as conservative, requiring a lot of time to accept innovations. Further, it was mentioned, that the decision-makers (e.g. clients, municipalities) often have a preference which and that alternative sewer systems, such as the vacuum technology are not always considered when a new sewer network is planned. Total
64
Reputation
16
Sector
14
Financial
14
Demand
12
Technical
5
Other
3 0
10
20
30
40
50
60
70
Figure 27: Number of mentioned barriers affecting the distribution of vacuum sewers
In the fourteen references to financial barriers the experts referred to the lost cost advantage when the construction of vacuum sewers is associated along with other utilities, such as stormwater pipes, gas and electricity lines. Further, the experts mentioned that the choice of a sewer alternative is dependent on the cost and that gravity sewers are the cheapest way of sewage transport. Barriers related to the demand for sewer technology were mentioned twelve times. The majority of barriers referred to the already well developed sewer infrastructure and little demand for new constructions. Further, it was mentioned that vacuum sewers have high
Results
p. 45 / 114
potential when exploitation (e.g. treatment and resource recovery) is also attached, which is not very common yet. 4.2.6. Measures to overcome barriers Complementing the previous question on barriers for a wider application of vacuum sewers the experts were asked about possible solutions to overcome the obstacles. Not all participants answered the question in depth and referred to the solution of the mentioned barriers. The experts’ answers are grouped and shown in Figure 28. Experts referred to aspects of public relations activities emphasizing education and awareness raising. Further, additional positive references are required, ideally on large scale. Financial incentives and institutional changes, promoting source separation , would also help to overcome the barriers. 9
8
8
Frequency
7 6 5
4
4
3
3
2
2 1 0
Public relations Positive references Institutional activities changes Measure
Financial incentives
Figure 28: Measures to overcome barriers
4.2.7.
Demand for circular economy concepts
The experts were asked on their opinion on the demand for circular economy concepts. The background of this is that vacuum sewers have been used in projects which aimed at demonstrating material flow separation and the subsequent exploitation of wastewater streams (e.g. blackwater, greywater, urine) for the recovery of biogas and nutrients as well as the reuse of wastewater. The answers were grouped according to whether or not they indicate a demand for circular economy concepts. The answers were screened for statements which indicate whether or nor a demand for circular economy exists. Among the 15 experts who answered the question, eleven gave Results
p. 46 / 114
statements which indicate a demand. Eleven of the fifteen responses included both, statements, which indicate demand, and statements which indicate no demand. Four of the fifteen responses either indicated demand or no demand for circular economy concepts. The majority of experts was confident regarding the potential of circular economy approaches and predicts increasing application in the future, while only few already recognize a growing demand today. Mentioned drivers include the prevention of water pollution, reduction of wastewater amounts sent to treatment facilities, nutrient recovery with emphasis on phosphorous and dissatisfaction with the current situation. The limiting factors referred to in the interviews include little interest from the population regarding wastewater, the current economics of circular economy approaches, the necessity for further demonstration and unclear legislation, as well as a well-developed infrastructure. 4.2.8. Future of vacuum sewers The experts were asked on their opinion on how the future of vacuum sewers will look like. The answers are grouped according to whether they indicate a wider application in the future or now. Many experts expressed statements in both directions. Of the 14 answers where an indication could be identified, six answers included indications for both, increased application and no increased application of vacuum sewers in the future. Six experts referred to a wider application while two answers indicate no wider application in the future. The majority of answers indicating a wider application in the future refer to potential settings in the future, such as higher water price, demographic changes, increasing importance of source separation and the necessity to refurbish old sewers in rural as well as in urban areas. Two responses refer to great potential in areas where no infrastructure is in place at the moment, as well as areas experiencing water stress in hot climates. Two experts already observe increasing demand, for example through an increase in sold vacuum valves. In contrast, potential factors limiting a wider distribution include the little demand for new sewer networks, due to the longevity, limited development of new residential areas, high costs and limited application in built environments, as well as the difficulty to connect to houses with a deep sewer connection and the challenge to handle stormwater. One
Results
p. 47 / 114
expert stated that other sewer technologies are more suitable for source separation and circular economy approaches than vacuum sewers. 4.2.9. Potential for vacuum sewers in the Global South Finally, the interviewed experts were asked to give their opinion on whether vacuum sewers are a viable technology for expanding wastewater services in the Global South. The answers to this question were much differentiated. Most of the answers included parts suggesting a suitability for the application in the Global South as well as sections, which lead to a contrary interpretation. Some experts referred to existing vacuum sewer projects in Namibia and Botswana. According to three experts, the experiences with the vacuum systems in Botswana are positive, while in Namibia only the project in Outapi seems to run well and experiences with other vacuum projects in the country are less positive. The majority of interviewees agrees that the technology addresses the challenges associated with sanitation and wastewater service provision in developing countries. Challenges referred to include the unavailability of water for flush systems, sanitation related security issues, especially for women and budget constraints for the sewer construction. Further, two experts stated that vacuum sewers make sense where energy generation play an important role and flow separation could contribute to the generation of biogas, as well as the reuse of water. In addition, three experts mentioned the suitability of vacuum sewers for fast growing cities and densely populated urban areas due to the flexibility of the system and decentralised approaches to wastewater. One experts also stated, that the technology makes the most sense where no or hardly any infrastructure exists. Many of the statements, which indicate optimism towards the application of vacuum sewers in the Global South, included specific conditions. The statement would indicate a recommendation if one or multiple conditions are met. Common conditions include the availability of funding, technical knowledge, the involvement of the right actors and the assurance that someone takes care of the system. The answers of almost all experts included statements, which indicate the challenges for vacuum sewers to be successful in developing countries. Similar to the answers on the negative aspects of vacuum sewers the statements refer to the operational complexity and the running costs. While the construction of infrastructure is often funded with the support of donors, such as the World Bank, the operation and maintenance needs to be Results
p. 48 / 114
financed by the local authority and eventually by the users. The cost of operation as well as the installation (e.g. vacuum pumps) are mentioned as challenges for regions where ‘the cost situation is a different one’ (expert #14).Some experts expressed the concern that trained technicians and engineers are not always available in order to ensure continuous operation. In addition, three experts referred to the experiences with vacuum projects in rural Namibia. Besides operational challenges, vandalism, theft and waste disposal were reported as negatively affecting the functionality of vacuum sewers. Two experts mentioned that a lot of training and consulting is invested for the systems to run.
4.3.
Results from the operator survey
According to expert #11 around 400 vacuum operators exist in Germany. In addition, Terryn, Lazar (2016) state that around 325 vacuum projects have been realized by AIRVAC and ROEDIGER in Germany with no indication on the realized systems by other providers such as QUAVAC, VAB, Schluff and FLOVAC. Generally, the amount of information varied significantly among the 64 operators ranging from basic structural data to operational costs and work hour estimates. Despite the low response rate, the survey represents a around 16% of vacuum systems in Germany and a quantification of critical parameters of vacuum sewer systems in Germany. 4.3.1.
Sample characteristics
The participants were asked about personal information in order to characterize the sample. All but one participant were male. The relevant work experience ranges from 3 to 45 years with an average of 23.5 years (median=25 years). The participants were given the opportunity to rate the operation of their vacuum system on a scale from 0 (totally dissatisfied) to 10 (totally satisfied). The results are displayed in Table 6. Table 6: Satisfaction of participants with the operation of their system
Dissatisfied
Neutral
Satisfied
Rating
0
1
2
3
4
5
6
7
8
9
10
Answer
0
1
2
3
5
4
6
6
13
7
2
s Total
11
4
34
%
22.5%
8%
69.5%
Results
p. 49 / 114
The table reveals that the majority of operators are content with the operation of their system. On the other hand, every 4th to 5th operator is not satisfied. Further, the operators were asked about their satisfaction on the collaboration with the system manufacturer. Table 7 shows the vast majority of participants perceives the collaboration as good to excellent. Only three operators were not content with the partnership. Table 7: Satisfaction of the participants with the collaboration with the system provider
Rating
Terrible
Very bad Bad
Neutral Good
Very
Excellent
good Answers Total %
1
0
2
4
19
15
6
3
4
40
6.5%
8.5 %
85 %
4.3.2. Structural characteristics of vacuum sewers in Germany Tis section summarizes the structural data of 64 investigated vacuum sewer systems in Germany, which have been commissioned since 1970. Figure 29 shows the number of vacuum sewer projects for each time period since 1970. The number of commissioned vacuum projects increases. A strong increase is observed between 1990 and 1994. The number of projects and has been stable since then.
Figure 29: Development of vacuum sewer projects over time
The majority of systems (45; n=62) has been constructed in the “old” federal states which refer to the Federal Republic of Germany until the reunification in 1991. Thus, 17 systems have been constructed in the “new” federal states, which made up the German
Results
p. 50 / 114
Democratic Republic (DDR). The most systems represented in this study are locate in Bavaria (Figure 30; ‘Bay’).
Figure 30: Distribution of surveyed systems by federal state
In total, 15,484 collection chambers and 550 km of vacuum lines serve around 41,788 people. One response represents 123 km or around 22 % of the total network length but is distributed over eight smaller systems taken care of by the same operator. The shortest network is only 450 m long. The majority of networks are smaller than 6 km (median=4.5 km; mean=10.5 km).
Figure 31: Distribution network lengths
The number of collection chambers is a good measure for the size of the vacuum system. Most vacuum systems are have up to 200 collection chambers (Figure 32) which is also reflected in the median of 134 (mean=276.5).Further, the largest system consists of 2,500
Results
p. 51 / 114
collection
chambers,
while
the
smallest
system
has
9
house
connections.
Figure 32: Distribution of system size measured by number of collection chambers
The ratio between network length and collection chambers gives an indication on the population density of the area. The values, for which the distribution is shown in Figure 33, range between 11.43 m/chamber, indicating a more densely populated area, and 480 m/chamber for service areas with very low population densities. More than half of the systems have densities within the range 21 to 50 m/cc (median=45m/cc; mean=62 m/cc).
Figure 33: Density of collection chambers
The operators provided the number of people served by vacuum sewers. As Figure 34 shows, the values vary over a wide range (35-6,500 people). However, the majority of systems seem to be designed for smaller communities up to 500 people (median= 367; Results
p. 52 / 114
mean= 835). In few cases, very large values were reported by the operators. Some operators, who reported large values referred to multiple systems in their responsibility.
Figure 34: Number of connected people
Additional information was provided by the operators and displayed in Figure 35.Seven (n=60) systems were reported to serve areas with seasonal differences in population (e.g. holiday sites). In 16 systems (n=60) the collection chambers are equipped with monitoring systems. For 38 systems, operators have a maintenance agreement with the system manufacturer. More than half of the operators (35 of 64) reported that their system has been expanded since their first commissioning, meaning that collection chambers and vacuum lines have been added. For 13 systems, it was reported that additional
Results
p. 53 / 114
connections are planned. The degree of extension ranges from 10 to 500 collection. resulting in a total of 1055 collection chambers to be added in the future.
Figure 35: Additional information provided by the operators
As shown in Figure 36 the majority of operators (42 out of 59 answers) characterized their service area as residential area, while 13 described the service area as a mixed with residential, commercial and other functions. Only three systems were reported to service recreational areas and one system was installed in a commercial area.
Figure 36: Type of service area
Results
p. 54 / 114
4.3.3. Operational data Operational data covers information on the electricity demand for vacuum sewers in Germany, as well as the work hours related to operation and maintenance (O&M) and emergencies at the vacuum station, vacuum lines and collection chambers. The electricity consumption per connected person lies in the range of 4.56 to 171.43 kWh/p*a with the average at 69.71 kWh/p*a (median= 61.33 kWh/p*a). The distribution of values is shown in Figure 37.
Figure 37: Histogram on annual electricity demand per person
Total work input is measured by the total working hours divided by the number of collection chambers. The work input ranges from 0.1 to 24 h/cc*a. The average is around 4.7 h/cc*a (median=2.97 h/cc*a). Figure 38 illustrates the large variation among the systems.
Figure 38: Distribution of values for total work hours
Results
p. 55 / 114
O&M and emergency work at the collection chambers is displayed in Figure 39. Due to variation in system size the work hours are calculated in relation to the number of collection chambers. For O&M work the majority of operators invest less than 1h/cc*a (median= 0.57 h/cc*a; mean= 0.72 h/cc*a). Few system require 2-3 h/cc*a and very few even more than 4 h/cc*a.Emergency related work at the collection chambers is slightly lower (median=0.57 h/cc*a; mean=1.38 h/cc*a) but also shows a large variation.
Figure 39: Histogram on the work input related to the collection chambers
At the vacuum station O&M activities (Figure 40; A) require around 60 h/a (median; mean=266.4 h/a). Emergency related work at the vacuum station (Figure 39; B) is lower (median=15 h/a; mean=104. h/a).
Results
p. 56 / 114
A
B
Figure 40: Histogram on the work input at the vacuum station
The work at the vacuum lines is shown in Figure 41 (A; B) and calculated in relation to the network length. While the median for O&M work is 1.49 h/km*a (mean=5.22 h/km*a) emergency activities are less frequent (median= 0.61 h/km*a; mean= 3.76 h/km*a).
Results
p. 57 / 114
B
Figure 41: Distribution of work input related to the vacuum lines
The Figures show that for all work categories majority of systems is in the lower part of the spectrum, further underlined by the median values. However, strong variation exists with some very strong deviations showing that some systems require a lot of work input. This is underlined by large difference between the median and the mean.
In addition to the results above, Figure 42 illustrates the share of specific activities related to the total work input for vacuum sewers. The values are calculated based on the average of 40 vacuum systems for which sufficient information was available. Average was chosen over median because median values are not proportional to the number of observations and thus don’t sum up to 100%. O&M activities at the vacuum station, vacuum lines and collection chambers make up for 65% of the total work hours while the remaining 35 % are related to emergency activities. With 37 %, O&M activities at the vacuum station take up the biggest proportion followed by O&M work at the collection chambers (22%). The emergency activities at the collection chambers account for 19 % of the total work hours Results
p. 58 / 114
while 11% are attributed to emergencies at the vacuum station. The vacuum lines require the least hours with 6% of O&M and 5 % for emergencies.
Figure 42: Average work input composition for various activities in vacuum sewers; VS: vacuum station; VL: vacuum lines; CC: collection chambers (n=40)
4.3.4. Cost composition in vacuum sewers In order to estimate the total operational costs of the investigated systems the costs for electricity, material and personnel were added. Thus, only systems, which provided the respective information for all three categories, were considered. The operational costs are a critical parameter for the evaluation of vacuum sewer performance. Given that the size of the investigated systems varies heavily, the individual sections of operational costs were calculated in relation to the number of collection chambers and connected people. The cost for material varies between around 6 and 151 €/cc*a (median=25 €/cc*a; mean=38.42 €/cc*a). Per capita the costs range from 13.11 to 218.28 €/p*a with an average at 58.88 €/p*a (median: 42.41 €/p*a). The distribution of total operational cost per connected person is shown in Figure 43. For electricity costs a general rate of 0.2 €/kWh was assumed for all systems. The cost for electricity ranges from around 3 to 263 €/cc*a with an average of 52 €/cc*a (median 37.04 €/cc*a).
Results
p. 59 / 114
Figure 43: Total operational cost per connected person
In order to calculate personnel costs for the individual systems, an hourly rate of 35€/h was assumed for the operators, who did not provide an hourly rate. This value is based on the median of 21 reported rates. Like for the other cost segments a big range of personnel costs can be observed. The reported values range from 5 to 504 €/cc*a with an average of 124.46 €/cc*a (median 54 €/cc*a). Figure 44
illustrates that the highest cost factor is personnel cost. The smaller pie charts
shows which work category contributes to the total operational costs. Personnel costs at the vacuum station and the collection chambers each account for around 21% of the total costs while work at the vacuum lines account for only 5%.
Figure 44: Proportional contribution of material, personnel and electricity costs by category
Results
p. 60 / 114
The three cost segments result in total annual operational costs ranging from 46.38 to 736.4 €/cc*a with an average at 214.94 €/cc*a (median: 145.67 €/cc*a). Figure 45 illustrates the relative cost composition. Electricity costs remain at 31 % (range 6.3-76%). Material and personnel for O&M activities account for around 41% (range 10.5-93,5%). Emergency related activities contribute to 28% of the annual costs (range 0-67%).
Figure 45: Average cost composition of vacuum sewers in Germany; O&M and emergency activities include material and personnel costs (n=22)
4.3.5.
Reasons for vacuum sewer selection
The survey included a question, which asked for the reasons for the selection of vacuum sewers in the respective drainage area. Figure 46 shows the responses by the operators. The majority of reasons relate to environmental conditions, such as high ground, flat terrain, water protection and flooding areas and unfavorable soil. These are all circumstances under which conventional sewerage is difficult and expensive. Lower investment costs for vacuum sewers and the main reason for nine vacuum sewer systems. Material flow separation and the possibility to finance the sewer network with additional public funding was a minor motivation for the installation of vacuum sewers.
Results
p. 61 / 114
Figure 46: Responses to reasons for vacuum sewer installation
4.3.6.
Frequency and causes of failures
The operator survey included an assessment on the frequency and causes of failures at the vacuum station, the vacuum lines and the collection pits. The results are displayed in Figure 47 to Figure 52.
Failure frequencies for critical elements of the vacuum station are shown in Figure 47. Few systems experience very frequent failures on a daily or weekly basis affecting vacuum and sewage pumps as well as the electrical system of the vacuum station. Up to ten systems are concerned with failures once a month with the sewage pumps being the most susceptible component. Nevertheless, 35 out of 48 systems experience problems with the sewage pump once a year or less frequently. A similar pattern applies to the vacuum pumps. In 41 systems, failures occur once a year or never while five systems report to have issues once a month. One operator reports weekly failures for vacuum pumps. The electrical system, which includes the controls and monitoring of the vacuum station, fails once a week in three cases, once a month in six systems and once a year in 26 cases. Eleven operators report not experience any problems with the electrical systems. Failures affecting the exhaust air treatment, which in most cases composes of a biofilter, was reported in ten cases of which two refer to failures on a monthly and eight on yearly basis. Operators of 33 systems reported to have no problems with the component.
Results
p. 62 / 114
Figure 47: Failure frequencies at the vacuum station
The most frequently mentioned cause for failures is the clogging of the sewage pump. Other causes include power cuts, electric control errors and defects related to construction and technology (Figure 48).
Causes of failures at the vacuum station 14
12
Number of systems
12 10
8 8
6 6
4 4
2 2 0
Clogging of sewage pump
Power cuts
Electric control errors
Technical Construction defeciencies deficiencies
Figure 48: Failure sources at the vacuum station
The failure frequencies for cracks and clogging in vacuum lines is shown in Figure 49. The vast majority of operators report not to have any problems with either failures. Cracks and Results
p. 63 / 114
leakages seem to affect the network slightly more often than clogging. However, three systems experience cracks or leakages on a weekly basis and in twelve systems the error occurs once a year. Clogging is reported to happen once a week in three systems, once a month in three systems and once a year in seven cases. Common sources of errors include other construction activities, the introduction of foreign objects as well as errors during the construction of the vacuum network ( Figure 50).
Failure frequency at the vacuum lines 32 33
Number of systems
35 30 25 20 12
15
7
10 5 0
0
3
0
Daily
3
Weekly
3
0
Monthly
Crack/ leakage (n=47)
Yearly
Never
Clogging (n=46)
Figure 49: Failure frequency at the vacuum lines
Reasons for failures at the vacuum lines Number of systems
6 5
5
5 4
4 3 2 1 0 Other construction activities Foreign objects
Construction errors
Figure 50: Common failure reasons in vacuum lines
Figure 51 displays the frequency of failures affecting the components of the collection pits. The interface valve and the valve controller are affected in higher frequencies than the filling sensor or the monitoring system. One operator reports to have issues with the vacuum valve as well as with the valve controller on a daily basis while another operator Results
p. 64 / 114
says that problems with the monitoring system occur every day.While monthly problems with the monitoring systems occur in four systems and once a year in additional three systems the majority of 25 operators reports to not experience failures of the monitoring system. It is noteworthy, that only 16 operators initially reported to have a monitoring system in place. Thus the actual number of systems which are equipped with a monitoring provisions and don’t experience any failures is eight. Regarding the vacuum valve failures occur on a weekly basis in eleven cases, once a month in 17 systems and 15 operators reported decreased functionality affects their system once a year. In two cases operators reported not experience any failures at the vcauum valve. In eight systems the valve controller is affected once a week, whille 22 operators report a monthly failure rate. In twelve systems the valve controllers are affected once a year while four operators say that the failure does not occur in their system. The filling sensor, in most systems a pipe or floating device, is less often affected. Failure of this component occurs once a week in two systems, once a month in eight systems and once a year in 10 systems. Operators of 19 systems report not have any problems with the filling sensor.
Failure frequency at the collection pits
Number of systems
30
25
25
22
20 15
0
15 12
11 8
10 5
19
17
2
1 1 0 1 Daily
8
10
4
3
0
Weekly
Monthly
Yearly
Valve (n=46)
Valve controller (n=47)
Filling sensor (n=39)
Monitoring system (n=33)
2
4
Never
Figure 51: Frequency of failures at the collection pits
The dominant source of error is clogging of the valve and the pipes inside the collection pit. Flooding, as well as technical and material deficiencies also lead to failures at the collection pits. Frost was reported to lead to failures in three systems Figure 52.
Results
p. 65 / 114
16
14
14
Reasons for failures at the collection chambers (n=31)
12
9
10
8
8 6
4
4
3
2 0
Clogging of Flooding with vacuum valve stormwater
Technical deficiencies
Membrance defect
Frost
Figure 52: Failure causes at the collection chambers
4.3.7. Complaints from the connected people The operator survey included a question for the frequency of specific complaints from the people connected to vacuum sewers. Information is provided for the three most frequent complaints odor, noise and decreased functionality of the system (Figure 53). Complaints related to unpleasant odors seem to a minor issue in the investigated systems. One operator reported complaints from the residents on a daily basis, while three operators reported complaints on a monthly basis and eight stated that complaints occur only once a year. Regarding noise complaints one system experiences weekly complaints, five on a monthly basis and once a year in 18 cases. The connected people are reporting constrained functionality of the vacuum system more frequently. Six operators reported that the serviced people complain about the functionality of the system on a weekly basis, while eleven communities experience disturbances once a month. In 13 systems the residents are disturbed once a year. In the majority of systems complaints related to noise (n=22) and odor (n=31) do not occur and 13 operators reported never to experience complaints
related
to
the
functionality.
Figure 53: Frequency of complaints from the people served by vacuum sewers
Results
p. 66 / 114
4.3.8. Opinions of participants The operators were asked for their opinion regarding a number of given statements. The participants could state the point of view on a 5-step scale indicating whether they agree to the statement. The results are shown in Figure 54 and Figure 55. As shown in A not all operators think that the vacuum system is the best option in their service area. Only 21 of 48 operators believe this is the case while 13 disagree with this statement. Around half of the operators agree to the increased complexity of vacuum sewers compared to other sewer options (B). Only seven participants believe that vacuum sewers are not necessarily more complex. A similar pattern can be seen regarding increased costs in vacuum sewers (D). Operators of 29 systems (n=47) agree or strongly agree to this statement while only nine participants disagree. Thus, it is not surprising that only 11 out of 46 operators believe that the advantages of vacuum sewers outweigh the disadvantages (G) while 19 disagree and 15 remain neutral. Interestingly the number of operators who would recommend the use of vacuum sewer technology is equal to the number who would not recommend its application (9, C). Since almost all vacuum sewers have been installed in rural areas the question occurred whether the operators believe that vacuum sewers could be used in urban settings (E). Only nine were confident that this would be the case while 18 did not believe in a potential urban application. Further, the survey asked the participants whether they believe vacuum sewers could be a suitable technology to expand sewerage cover in the Global South (F). Only two operators believed so. Around half of the operators did not believe that vacuum sewers are a good technology for developing countries. Finally, the participants gave their opinion on the separation of different wastewater streams such as grey-and blackwater (H). Only around half of the operators had an opinion on this matter (24 out of 48). In 13 cases participants believe that a further separation is useful while 11 disagreed to this statement. Generally, a large number of neutral participants characterized the survey. In 5 out of 8 statements, the neutral group was the largest.
Results
p. 67 / 114
A
C
B
D
Figure 54: Operator opinions on selected statements (1/2)
Results
p. 68 / 114
E
F
G
H
Figure 55: Operator opinions on selected statements (2/2)
Results
p. 69 / 114
5. Discussion 5.1.
System characteristics of vacuum sewers in Germany
The present survey is the first study on vacuum sewers of this kind for vacuum projects in Germany. Günthert, Cvaci (2005) conducted a similar analysis in order to compare vacuum and pressure sewer systems. However, the survey included only 16 systems in Bavaria. The present operator survey gives an overview over structural parameters of more than 60 vacuum sewer systems in Germany. Figure 29 shows how many of the surveyed systems have been commissioned between 1970 and 2017. From 1990, the number of commissioned vacuum systems increases significantly. One contribution to this increase might have been the reunification of East- and West-Germany. In 1989 only 73% of EastGermany’s population was connected to a waste water treatment plant (Hentrich et al. 2000). In comparison, West-Germany had a connection rate of 93%. Therefore, the new federal states of the reunified Germany had to expand the cover of their wastewater infrastructure. The East German states are characterized by low population densities which increases the per capita cost for sewerage lines and treatment facilities. This might have led to an increased interest in vacuum sewers. More than half (11 of 21) of the systems which were installed between 1990 and 2000 were commissioned in the new federal states. In the same time 10 systems have been installed in the old states. This is almost the same number (9) as in the period between 1980 and 1990. On the other hand, between 2000 and 2010 only 4 of 21 systems were commissioned in the new federal states. These figures indicate that the reunification contributed to an increased demand for vacuum sewers since 1990 and that vacuum sewers are very beneficial in areas where wastewater infrastructure is underdeveloped. Today 87 % of people living in the new states are connected to a centralized wastewater treatment facility (old states 97.7 %) with further 10.2 % connected to septic tanks (Statistisches Bundesamt 2013b). Further, the findings show that demand for vacuum sewers has been stable in the old federal states most likely a consequence of the well-developed gravity sewer networks. However, these results should be interpreted with care. As Figure 30 shows, the vast majority of surveyed systems is in Bavaria. The systems in East-Germany are well distributed across the different federal states. In contrast, old states, other than Bavaria, are less represented in the survey. This could either reflect the reality showing that vacuum systems are less common in the old federal states except for Bavaria. Or the sample is biased by the source of information. Operators were identified via the system Seite 70 von 114
manufacturers. The respective employees of the company could be responsible for a certain region which would explain why so many systems are located in so few states. The study showed that the networks of 62% of the surveyed systems are up to 5 km. Regarding the number of collection chambers around 73% of the systems are smaller than 200 chambers. In 68% of cases vacuum sewers drain the sewage of up to 500 people. These figures are expected to be higher since the histograms in section 3.3.1 include outliers. The responses indicate that some operators reported data for multiple systems, as highlighted by one response for 120 km of vacuum lines representing around 22% of the total surveyed network length. Due to the small sample size and their relevance for operational data they were not dismissed. However, the figures highlight that good experiences exists with small systems. The development of the project size of vacuum sewers is displayed in Figure 56. From the trend line it can be seen that the newer systems are constructed with shorter networks (A) and fewer collection chambers (B). The same can be seen for the number of connected people (Figure 57). The most likely reason is the high connection rate due to the well-developed gravity network.These findings support the comment by expert #1 from the interviews, who states that vacuum sewer projects in Germany become smaller making it difficult to establish additional positive large-scale demonstrations which was mentioned as a possibility to overcome A
B
current barriers.
Figure 56: Development of
network length (A) and collection chamber (B) over time
Discussion
p. 71 / 114
Figure 57: Development of number of people connected to vacuum sewers over time
5.2.
Operational comparison of vacuum sewers in Germany
The operator survey revealed information on the critical operational parameters work input by activity and electricity demand. Both surveys indicated that a major drawback of the vacuum sewer technology are the high work input and failure frequencies, due to the operational complexity and sensitivity of the technology. Analysis of operational performance indicators, electricity demand, failure rates and work hours revealed that strong variations exists among the systems. However, it could be demonstrated that the majority of systems show operational parameters in lower ranges, which is also reflected by low median values compared to mean values, which are more susceptible to outliers. In 50% of the systems work input is within the range of 1.3 to 6.7 h/cc*a (1st and 3rd quartile). This confirms the impression from the interviews that the few badly running systems affect the reputation and distribution of the technology more than the majority of positive references and that more positive references could help to overcome this barrier. Until now, few studies have investigated operational parameters in vacuum sewers. Table 8
presents a comparison with two studies from Bavaria, Germany, and the USA.
Discussion
p. 72 / 114
Table 8: Comparison of reported operational data
Source
Günthert, Cvaci
Naret 2009
Present study
2005
(data from 2003)
2017
Region
Bavaria, GER
USA
Germany
Systems
16
49
64
Category
Guideline /Survey
Survey
Survey
100 – 190
100- 690
12-3,840
𝑥̅ =300
𝑥̅ =266 median: 60 0-1,800
Vacuum station
Vacuum lines
O&M [h /a]
0-85
Emerg. [h /a] O&M [h /a] Emerg. [h /a] O&M
𝑥̅ =30 -
𝑥̅ =50 -
h/valve*a
h/valve*a
0.16-0.25
0.2-1.9
0-10.9
𝑥̅ =0.9
𝑥̅ =1.38 Median 0.57 0-2.57
0.16-0.25
Total
𝑥̅ =53 Median 12 0-720 𝑥̅ =50 Median= 6 h/cc*a
Emerg.
Power
0-110 𝑥̅ =10
Collection Chambers
0-200
𝑥̅ =100 Median: 15 0-720
73-146
[kWh/cc*a]
0.1-1.35 𝑥̅ =0.6
𝑥̅ =0.71 Median: 0.48
200-570
14.5-1,314
𝑥̅ =400
𝑥̅ =246 Median 200
The three studies followed different approaches and comparison is not possible in all categories. The survey conducted by Günthert, Cvaci (2005) had characteristics of a guideline focusing on economically operating systems, with less information on the actual observations. The operator survey mentioned in Naret (2009) gives information on the range and averages for different categories but does not include median values, which as demonstrated above is more representative. Further, the data on work at the vacuum line does not include information on network length. The present study did not include information on the number of vacuum stations, which leads to the wide range in work input at the vacuum station. Finally, any comparison needs to consider that the surveys have been conducted at different times and that Discussion
p. 73 / 114
differences could have many origins, such as technical and operational improvements but also decreased reliability from aging components. When comparing the work input at the vacuum station the present study reveals much lower O&M requirements than the two other studies. The median for the systems in surveyed in this study is lower than the lower end of the range reported by the other surveys. The range and average for emergency related work hours on the other hand are much higher which is most likely a consequence of the missing information on the number of vacuum stations per system although it can be expected that the majority of systems consist of one vacuum station. The median however is low, which leads to the assumption that further improvements have facilitated the work related to the vacuum station. The work input related to the vacuum lines is hard to compare since information on the network length is missing in Naret (2009) and larger networks will have higher work requirements. Nevertheless, the arithmetic means for O&M work are similar indicating no significant changes. Larger differences exist regarding emergency related work. The average work input in Naret (2009) is 5 times lower than in this study, once again highlighting the need to relate work input to units (e.g. length) for comparison. However, the comparison underlines that the vacuum lines require lower attention than other components. When comparing the work hours related to the collection chambers it is important to consider that estimates in Günthert, Cvaci (2005) refer to recommendations from the system manufacturers and refer to inspection only. Comparison with the experiences from the two operator surveys indicate that they are too optimistic. Even if the same time is added for maintenance the range of 0.32 to 0.5 h/valve*a the minority of systems in both surveys would lay in this range. A possible explanation could be that transportation time is not included in the estimates but included in the surveys. Since collection chambers are distributed over the service area, a lot of time is dedicated to transportation. Mean values for O&M in both systems differ by around 29 min/valve*a which could also originate in the higher house to chamber ratio in American systems in addition to the influence of extreme outliers. The difference is much lower for emergency related activities (6.6 min/valve*a) The energy demand of systems is a good measure for system performance since it’s mainly affected by the vacuum pump and failures (e.g. open valves, cracks in the network) result Discussion
p. 74 / 114
in increased pump activity in order to restore vacuum. Günthert, Cvaci (2005) state that economical vacuum systems have an electricity demand of 73 to 146 kWh/cc*a. Both surveys indicate that this might be overoptimistic since not even the lowest values reported in Naret (2009) fall in this range and only eight of 31 surveyed systems in this study (median=200 kWh/cc*a). Literature on electricity demand seems overoptimistic. Some reports refer to an annual electricity demand of 10-50 kWh/ person (Münch, Winker 2009; DIN EN 1091, 1997). The median in this survey is 58 kWh/p*a (𝑥̅ =68.3 kWh/p*a) but 15 systems qualified for this range. On the other hand, this could lead to the conclusion that only few systems run well and the majority of systems are not operated in the most economical way for different reasons. Figure 58 shows the impact of a monitoring system at the collection chambers on the electricity demand (A) and the total work hours (B). Vacuum sewers which have a monitoring system have a lower electricity demand per collection chamber. This underlines the effectiveness of the monitoring system to detect and communicate failures at the collection chambers. On the other hand, systems with a monitoring system show higher work input. The median for O&M work at the collection chambers is four to five times (2 h/cc*a) higher than for systems without surveillance (0.44 h/cc*a).This might be a result of the more frequent identification of failures or maintenance requirements. If this is the case, then it is surprising, that a monitoring system, which is designed to facilitate the operation leads to more working hours and possibly higher costs. Increased sensitivity of
A
B
Figure 58: Relationship between the presence of a monitoring system at the collection chambers and A: electricity demand and B: total work hours Discussion
p. 75 / 114
the technology was mentioned in the expert interviews. The monitoring system seems to add to this. The investigation of failure rates revealed that the most frequent faults at the station affect the sewage pumps and electrical system. Failures at the vacuum lines are rare occurring less than once a year In the vast majority of systems underlying the environmental benefit of the technology. As expected the highest failure rates affect the vacuum unit (valve and controller) at the collection pits. The major cause of failures at all sections of the system is clogging resulting from false user behavior and the disposal of objects. These findings confirm the statements from the interviews on increased sensitivity, despite technology related failures are minor. Günthert, Cvaci (2005) found that 70% of the failures are caused by the residents and only 2.5% relate to system failures. Climate conditions resulting in frost and flooding account for around 12% and highlighting the necessity of correct planning by qualified planners. In a comparative study on failure rates in vacuum, pressure and gravity sewers in Poland Miszta-Kruk (2016) made very similar findings on failure frequencies and causes in vacuum sewers. In addition, the author estimated that around 99% of failures in gravity sewers occur at the network and reconditioning time is higher in the majority of cases. In vacuum sewers reconditioning time was less than 1h in 60% of events and less than 2h in 86% of failures (Figure 58). These findings show that despite higher failure rates vacuum sewers have shorter repair times since the affected components are accessible from the surface and do not require staff to enter the sewer network.
Figure 59: Reconditioning time in different sewerage systems (Miszta-Kruk 2016)
Discussion
p. 76 / 114
Efforts facilitating the operation should address the major contributors to the work input O&M at the vacuum station and collection chambers as well as the emergency activities at the collection chambers account for around 78% of the total work input. The promotion of remote maintenance, which was highlighted in the interviews, could contribute to this. Further, increased attention should be given to the user behavior, which is the cause for the vast majority of failures. Measurers, whether technical or educational, preventing the introduction of foreign objects need to be developed. Nevertheless, a comparison with the few references available indicate that overall system performance has improved over time.
5.3.
The cost situation for vacuum sewer systems
The operational cost situation of vacuum sewers is a critical aspect for the distribution of the technology. This was highlighted in both surveys. As seen in Chapter 3 the operational costs of the investigated vacuum system show high variability (13.11 to 218.28 €/p*a). The share of each cost factor varies heavily between the systems material (5-75%) electricity (6-76%) and personnel costs (10-84%). These variations indicate that a high degree of uncertainty remains with the technology and that operational cost is very dependent on the local conditions. Literature on operational costs in vacuum sewers is rare making it difficult to evaluate the results. Günthert, Cvaci (2005) state that in economically operated systems the electricity costs account for around 15 % based on a rate of 0.13 €/kWh. In this study, only eight systems fall in the range of 10 to 20 %, assuming a higher rate of 0.2 €/kWh. Günthert, Cvaci (2005) also stated that population or chamber density influences the electricity consumption of vacuum sewers and that the most economical range is within 30 to 50 m/chamber. According to this measure, only 18 of 51 investigated systems in this study are within the range indicating that not all systems are designed in a financially advantageous way for different reasons. Local conditions might not always allow for system layouts as recommended. Further, Günthert, Cvaci (2005) state that personnel cost should account for around 70% of operational costs. The present survey revealed that only three systems fall in this range (65-74%) indicating that either the systems investigated in 2005 operate much better or that literature is over optimistic regarding operational costs in vacuum sewers since personnel cost have a higher impact on the total
Discussion
p. 77 / 114
operational costs. These conclusions are intensified by the low rate of 45 €/cc*a in compared to 140 €/cc*a (median; mean=212 €/cc*a) in this study. The comparison with gravity sewers has shortcomings. Nevertheless, it is assumed that operational costs are 2 to 4 times higher in vacuum sewers are compared to conventional sewerage (Günthert, Cvaci 2005). Despite the high variability across the investigated systems in this survey, the median of 42.42 €/p*a is within the range of 45 €/p*a reported for 50% of municipalities surveyed in Sander (2003). Since the majority of sewers in Germany are gravity sewers this figure is expected to be mainly represent the operational cost of conventional sewers. Further, the impression of high operational costs needs to be put into perspective of the overall project costs, which includes the investment costs. Few studies addressed the comparison of project costs between vacuum sewers and gravity sewers. However, all concluded that overall project costs are lower in vacuum sewers (Terryn et al. 2014; Islam 2016; Elawwad et al. 2014a) Since service providers recover their costs via sewer tariffs, the comparison of tariffs between areas with vacuum sewers and others can put the cost into perspective. Since the vast majority of sewers in Germany consist of gravity sewers the tariff average for Germany was used. In fact, a comparison of sewerage tariffs in 44 municipalities with vacuum sewers with the average for Germany (2,13 €/m³, Leptien et al. 2014) revealed that 27 out of 44 surveyed municipalities have tariffs above German average ( Figure 60). On the other hand, 17 systems have lower tariffs indicating that vacuum sewers are not more expensive despite the fact that sewerage costs are normally higher in rural areas (Schluff 1996). This comparison should be drawn carefully since vacuum systems usually make a lower share of the sewerage system and thus the impact on the tariff could be varying. On the other hand, the comparison for stormwater tariffs showed that all municipalities with vacuum sewers have tariffs below the German average of 0.85 €/m² (Figure 61). Vacuum sewers are predominantly located in rural communities where less sealed surface area and more infiltration result in less surface runoff needs to be treated.
Discussion
p. 78 / 114
Sewerage charges in municipalities with vacuum sewers (n=44)
€/m³
Sewerage charge €/m³
Average for Germany (2013)
4,16 4,5 3,88 3,61 4 3,35 3,22 3,1 3,09 3,5 2,91 3,27 2,96 3 2,89 2,95 2,81 2,8 2,7 2,63 3 2,55 2,48 2,43 2,38 2,26 2,22 2,21 2,2 2,16 2,15 2,5 2 1,96 1,88 1,91 1,95 1,9 1,87 1,88 1,78 1,68 1,65 1,6 2 1,56 1,42 1,33 1,33 1,5 1,05 1 0,5 0 52 67 74 77 89 110 124 128 140 146 152 154 160 174 179 187 193 202 205 210 225 234
Municipality
Figure 60: Sewer tariffs in municipalities with vacuum sewers
Stormwater charges for municpalities with vacuum sewers (n=14) Cost for stormwater (€/m²)
Average in Germany (2013)
€/m² sealed surface area
0,9 0,8 0,7 0,6
0,66 0,59
0,53
0,5
0,46
0,5
0,41
0,38
0,4
0,34
0,3
0,46 0,35
0,39 0,3
0,24
0,2
0,2 0,1 0 87
110
124
127
128
141
146
151
152
153
174
187
225
240
Municipality
Figure 61: Tariffs for stormwater drainage in municipalities with vacuum sewers
In addition to that, Islam (2016) points out that ‘environmental and social cost and benefit resulting from construction process by making influence in traffic interruption, noise creation, air pollution, employment generation and some other aspects are not considered in cost estimates, although they are quite important parameters’. This is supported by expert #11, who states that many necessary repairs to the sewerage system are often postponed due to the impact on traffic and business in the affected area. Vacuum lines can be repaired with much lesser impact since they consist of plastic pipes that are buried at lower depths and the affected line section can be identified quickly. Discussion
p. 79 / 114
The sensitivity of the systems was mentioned a major barrier of the vacuum technology. And the fact that around 28% of operational costs account for emergency activities (personnel and material) lead to the conclusion that technology distribution is still hampered by a high degree of uncertainty. The case of the municipality Pützkau, Germany, is an example for this. In an evaluation of 14 sewerage options using the comparative cost method showed that vacuum sewerage was the most economical and environmental friendly alternative. But the community chose to install decentral treatment facilities instead due to concerns around the operational complexity and failure rates of vacuums ewers (Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft 2004). The present study is the first time that operational costs have been assessed to this extent. The high degree of uncertainty was confirmed but despite the high variability the majority of systems seem to have operational costs within the range of conventional sewerage systems. The data can provide further support to municipalities and planning agencies, which conduct the comparative cost method in order to evaluate the most economical sewerage system.
5.4.
Operator satisfaction
The interviews, as well as the operator survey, indicate a good perception of vacuum sewers and that the majority of investigated systems work well (Table 6). However, the experts also referred to the bad reputation resulted from few bad working systems. The operational satisfaction was analyzed against a number of possible factors. Due to the small sample size of dissatisfied operators (n=10) operators from the neutral group (rating 5 out of 10) were included. Since the operator rating not only indicates the attitude toward the vacuum sewer technology but also towards the own job performance. Figure 62 shows the relationship between the satisfaction and the annual operational costs. Unsurprisingly, those systems for which operators reported to be dissatisfied (rating 0-5 of 10) with the operations have higher annual operational costs. In contrast, systems with more satisfied operators (rating 6-10 of 10) have lower costs. The median for annual costs is around 50 €/cc*a higher for the group of unsatisfied operators compared with the satisfied operators. Since cost is an important parameter for system performance it is understandable that higher costs result in lower satisfaction. Surprisingly, the highest
Discussion
p. 80 / 114
reported costs are outliers in the satisfied group (indicated by black dots), which questions the clear relationship between costs and satisfaction.
Figure 62: Relationship between satisfaction of the operator and total annual operational costs (the figure inside the box indicates the number of answers in each group)
A more balanced pattern can be observed for the total annual work hours per collection chamber. The median for the unsatisfied operator group is slightly lower (2,9 h/cc*a) than for the satisfied operators (3 h/cc*a). However, the upper side of the box shows the 3 rd quartile of the group, which indicates that 75 % of the sample are represented below the line. The larger size of the box for the satisfied group shows that the work input has a higher variation among the represented systems. In addition, the two systems with the highest work input are taken care by satisfied operators. According to Figure 63 there seems to be no clear relationship between satisfaction and work input.
Figure 63: Relationship between total annual work hours and satisfaction
Discussion
p. 81 / 114
Additionally, the operator satisfaction was compared with structural data of the systems (Figure 64). When comparing network length (A) and number of collection chambers (B) of the satisfied and unsatisfied groups the impression arises that operators of larger vacuum sewers tend to be less satisfied than operators of smaller systems are. Regarding the network length (A) the medians of the two groups are very similar but the unsatisfied group has a larger variation. Looking at the number of collection chambers (B) the median, as well as the variation are higher for the unsatisfied operators. On the other hand, the group of satisfied operators also contains larger systems indicated by the outliers. A
B
Figure 64: Relationship between operator satisfaction and A: network length and B: number of collection chambers
Figure 65 illustrates the relationship between system age and operator satisfaction. Operators of older systems seem to be less satisfied than those of systems that are more recent. A possible explanation might be that system components need to be replaced
Figure 65: Relationship between operator satisfaction and system age Discussion
p. 82 / 114
after a certain time. The individual components of vacuum sewer systems have different life spans after which they have to be replaced. The construction elements, such as the vacuum station, lines and collection chambers, have higher life spans then the mechanical and electrical components, which are more exposed to wear. (see Table 1) Thus, older system could have a higher maintenance requirements which affects the operator satisfaction. The life span of many components is similar to the age range of systems of dissatisfied operators. It is likely that the replacement and the decreased reliability of key elements of the system contributes to the dissatisfaction of operators. However, it is difficult to assess this relationship in this study, since the information on when components have been renewed is not sufficiently available and the fact that the oldest system is run by a satisfied operator as indicated by the outlier (black dot) and the similar work hour ranges contradict this theory. A similar pattern can be observed in Figure 66. The systems of the satisfied operators seem to have a lower electricity demand per collection chamber than the systems of the unsatisfied operator group (B). Especially under the consideration, that a higher electricity consumption is an indicator for more frequent failures associated with higher work, material and financial input. The higher chamber density of systems of dissatisfied operators (A) underlines this theory, since electricity consumption increases with decreasing population density. Thus, it can be concluded that dissatisfied operators experience failures more frequently contributing to dissatisfaction and higher electricity demand. A
B
Figure 66: Relationship between operator satisfaction and A: network/chamber ratio and B: electricity demand Discussion
p. 83 / 114
Further, the participants of the survey were asked about the frequency of failures in their systems. The question targeted specific failures of certain components. The operators were given the options daily (365x/a), weekly (52x/a), monthly (12x/a), annually (1x/a) and never (0x/a). Then the failure rates were compared with the satisfaction of the operators. Figure 67 shows the case for clogging (A) and cracks or leaks (B) at the vacuum lines. Generally clogging of vacuum lines occurs more often that cracks or leaks, which happen only once a year if at all. Both failures seem to occur only a few times a year. It can be seen that neither clogging nor cracking of vacuum lines occur in systems of satisfied operators. Repairing of failures at the lines requires much effort, especially when related to cracks or leaks. Thus, a relationship between failure rate and satisfaction seems logical.
A
B
Figure 67: Relationship between operator satisfaction an failure rate at the vacuum lines; A: clogging; B: cracks/ leaks
Figure 68 displays the failure rates for various common failures at the vacuum station. Failures at the vacuum pumps (A) are quite rare and do not seem to affect the degree of satisfaction. In contrast, failures at the sewage pumps (B) can occur more often. Unsatisfied operators experience this far more often, than operators from the neutral or satisfied group and sewage pump failure seems to contribute to the discontent of operators. The failure rates for the electric system (C) as well as the biofilter (D) are again much lower. Although no clear relationship between the operator satisfaction and the failure rates for the two components can be seen, they seem to occur more frequently in systems of unsatisfied operators.
Discussion
p. 84 / 114
A
C
B
D
Figure 68: Relationship between satisfaction and failures at the vacuum station; A: vacuum pump, B: sewage pump, C: electric system; D: biofilter
Figure 69 illustrates the failure rates of different components within the collection chambers. Obviously larger systems have a higher chance of experiencing failures. In order to ensure comparability the failure rates were calculated by dividing the number of failures with the number of collection chambers in the system. The failure rates are expressed in %/a. Thus, a system with 100 collection chambers and a monthly (12x/a) valve failure frequency has a failure rate of 12%/a. The median is more than times (13.8%/a) the median value for satisfied operators (4,2%/a). As expected, the failure rate for vacuum valves (A) is much higher in systems of unsatisfied operators. However, the group of satisfied operators also includes system with higher failure rates but are considered as Discussion
p. 85 / 114
outliers in the statistical analysis. A similar pattern can be observed for the valve controller (B). The valve and the controller are the two components, which are the most susceptible to failures. Failure rate for the filling level sensor (C) is also higher for systems of unsatisfied operators but the low median indicates that generally failures at these components do not occur very frequently. Regarding the monitoring system, the failure rates for systems of dissatisfied operators are very high but the sample size (n=2) is very small. The majority of operators who use a monitoring system in their collection chambers is satisfied and does not experience frequent failures.
A
C
B
D
Figure 69: Relationship between operator satisfaction and failure rates at the collection chambers; A: vacuum valves; B: valve controller; C: filling level sensor; D: monitoring system
Discussion
p. 86 / 114
Finally, the operator satisfaction was compared against the experience of the operators measured in years Figure 70. Vacuum operators in both groups have many years of work experience. The higher values (median, 1st and 3rd quartile) are within the group of satisfied operators. These results indicate that more experienced operators are also more satisfied with their system, which could be related to the individual skill level and technical expertise.
Figure 70: Relationship between operator satisfaction and operator experience in years
The analysis of structural, operational and personal information revealed factors governing operator satisfaction. Vacuum sewers operated by satisfied personnel are characterized through lower operational costs, younger system age, lower population densities, experienced operators and lower failure rates especially for sewage pumps as well as the vacuum valves and controllers. On the other hand, system size and annual work input seem to have a lesser impact on the satisfaction of the operators. While these findings might not seem very surprising since higher failure rates, costs and work hours result in less contentment of the responsible operator, they do underline that operator satisfaction can be considered as an indicator for system performance. By itself, operator contentment is not an objective measure to estimate whether a vacuum system is running well or not. However, backed with quantified operational performance indicators, like in this chapter, the picture becomes clearer and reveals further areas for improvement.
Discussion
p. 87 / 114
5.5.
Good perception of vacuum sewers within boundaries
The interviews revealed a positive rating of the vacuum sewer technology among the experts (average 7.9; median: 7). This is supported by the fact that the majority of operators is content with the operation of their system (average 6.5; median: 7). Lower values for the industry ratings (average: 5.44; median 5.15) confirm the initial hypothesis of this study that the reputation of vacuum sewers is not solely positive and that the interviewees are aware of the criticism towards the technology. Every 4th to 5th operator is not satisfied with the operation highlighting that issues around all stages of vacuum projects still exist. However, the good degree of operator satisfaction contradicts the opinions on the statements (Figure 54, Figure 55). Only 23% of operators believe that the benefits of vacuum sewers outweigh the drawbacks while 40% disagree with the statement. Further, only 44% of the operators believe that vacuum sewerage is the best option for their service area and 34% would recommend the technology. A possible explanation might be that the operators, who work with the system on a more frequent basis, are more concerned about the aspects ‘Financials’ and ‘Operations’ which had negative balances during the expert interviews. In contrast, the more positive ratings among the other actors seem to be influenced by the categories ‘Environment’, ‘Planning & Construction’ and ‘Flexibility’. The mentioned benefits for ‘Planning & Construction’ (e.g. less excavation, good at high groundwater and flat terrain) were reasons for many surveyed systems (Figure 46) and unfold in lower investment costs. Apart from the prevention of exfiltration the mentioned environmental aspects, which seem to have the largest impact on the positive rating, are not commonly realized (e.g. water savings with vacuum toilets, resource recovery from flow separation). Further, the expert ratings were often bound to conditions which indicate that vacuum sewers are perceived beneficial only in very specific conditions. Further, the lower variety of negative aspects (Figure 26) indicates that the drawbacks of the vacuum sewer technology revolve around few but very important aspects. The good agreement from both surveys on increased costs and operational complexity seem to be the major barriers preventing wider application.
Discussion
p. 88 / 114
The subjective answers to the two questions give the indication that the majority of vacuum sewers work well and due to the limited number of references as a result of well developed gravity sewerage system, the few not well running systems strongly affect the reputation of the technology. Perception of the technology seems to be dependent on individual weighting of the different aspects and whether beneficial potentials are exploited. It is noteworthy that the impression of a good perception of vacuum sewers is based on the ratings given by the experts which in some cases bound their answers to very specific conditions such as ‘in extreme climates’ or ‘where it fits’. The analysis for barriers of vacuum sewer distribution indicate the absence of drivers for the technology in Germany. Firstly, demand for new sewers is currently limited due to the longevity of infrastructure and because conventional sewerage is already widely distributed in central Europe. Construction activities mainly take place in already developed areas and rarely in new development areas where no sewer is present. Secondly, there seems to be uncertainty about the economics of vacuum sewers. While there seems to be consensus that vacuum sewers are in theory cheaper to construct than conventional sewers some experts say that the cost advantage in practice often diminishes since more excavation is required when stormwater pipes have to be laid and other infrastructure networks (gas, electricity etc.) affect the economics of the sewer project. Vacuum sewer projects are also less attractive because less money can be earned with them. In Germany, engineering offices in the construction industry can be contracted for the planning, design, project management and/or project realisation of construction projects. The engineering offices have an interest in larger projects as they can earnmore. Another economical barrier arises during the planning phase of vacuum sewers. Dynamic comparative cost assessments (‘Kostenvergleichsrechnung’) are not always conducted and thus vacuum sewers are not always considered as a sewer option for a new project. One expert even states that during the assessment vacuum sewers are calculated more expensive than they actually are. This can have multiple reasons, such as the lobby activities of the duct industry or limited experience with the real costs of vacuum sewers. This reputational barrier is extended through the stronger impact bad references have over positive examples of vacuum sewer projects. The lack of experience in planning, constructing and operating vacuum system also leads to systems which do not function Discussion
p. 89 / 114
well. The lack of experience combined with the impact of negative references create skepticism and prejudice towards the technology and reputational barriers seem to reinforce the existing sector barriers which exists due to the institutional, organizational and regulatory structure of the wastewater sector and wastewater projects. The wastewater sector is described as very conservative by some experts implying a certain difficulty for changes and innovations while holding onto established procedures and structures. One expert underlines this with the long time it took until plastic pipes were used in sewer systems. The good coverage of conventional gravity sewers indicates that engineering offices, planners and construction companies have long experience with gravity sewers and the sector is tailored to this option, which is further emphasized by the preference of municipalities, who are the clients for sewer projects. Further, there appears to be a missing regulatory part addressing vacuum sewers. Technical standards and norms, as well as a solid legal basis are perceived to be underdeveloped or absent. This again underlines the perception of a new technology and limited awareness on vacuum sewers since standards for vacuum sewers do exist (DIN EN 1091, 1997) Interestingly only few technical barriers were mentioned. However, all identified barriers seem to be entangled with each other and affect one another. A sector which is cautious about innovations, limited demand for a product and a bad reputation resulting from the lack of experience hinder a wider distribution of vacuum sewers, especially when the theoretical advantages of vacuum sewers, like less excavation or environmental benefits, such as material flow separation can not unfold. One major positive aspect of vacuum sewers is the potential to separate waste water streams and subsequently exploit wastewater as resource for e.g. biogas or nutrient recovery. There seems to be a growing but yet little demand for the concepts although operators are skeptical about a further separation of wastewater streams. Little water stress (for Central and Northern Europe), well developed sewer networks and thus little demand as well as few political or societal drivers for the exploitation of wastewater seem to be the relevant barriers for vacuum sewers. While the interviewed experts estimate an increasing demand for circular economy concepts the operators do not believe that a further separation of wastewater, for instance into grey and blackwater, makes sense (Figure 55). Nevertheless, increasing public efforts in the recovery of Discussion
p. 90 / 114
phosphorous and biogas suggest a growing interest in the exploitation of wastewater. The promotion of the separation of sanitary and stormwater drainage via the new Federal Water Act (Besonderes Verwaltungsrecht, Wasserrecht 2017; Berger et al. 2016) is a step to future activities regarding the exploitation of wastewater as a resource. Further positive vacuum references in conjunction with improvements of O&M lowering labour and costs, could contribute to a wider acceptance of vacuum sewers.
5.6.
Leapfrogging and technology transfer
In the discussion around technological, environmental and economic leapfrogging an important prerequisite is that the technological innovation in question, poses an environmental advantage over conventional approaches. In the scientific discourse, emphasis is given on energy sphere and carbon pollution, which is why carbon lock-in is an often-mentioned concern for the technological economic development of industrializing countries. In contrast, vacuum sewers address the water and soil pollution coming from settlements and economic activities. By applying the global pollution index (IPG) Panfil et al. (2013) estimate that vacuum sewers (IPG=1.14) have a much lower impact on the environment (soil, flora, fauna, humans) than gravity sewers (IPG=3.22). The environmental advantages of vacuum sewers over conventional sewerage systems were highlighted interviews as well as in parts of the operator survey. These findings support the opinion of Terryn, Lazar (2016) who state that ‘The vacuum sewer system is an ecoinnovative solution in wastewater management due to reduction of the environmental impact, considering the high security of the system in what concerns the spillage and odors, energy savings, therefore internalizing the externalities’. In terms of cost, literature, expert interviews and operator survey agree that investment costs are lower for vacuum projects compared to gravity sewers (Islam 2016; Elawwad et al. 2014b; Panfil et al. 2013; Terryn et al. 2014). Thus, the vacuum technology fulfils the environmental and economic requirements to qualify as leapfrogging technology. However, the actual financial performance also depends on the operational costs, which showed a large variation among the investigated systems. Variations in operational parameters (work, electricity, cost) indicate that a degree of uncertainty remains with the technology. Estimates on the suitability for implementing vacuum sewerage in the countries of the Global South were mixed during the surveys. While the experts agreed that the Discussion
p. 91 / 114
technology addresses current challenges in sewerage services in developing countries, the interviewees expressed concerns on the availability of sufficient technically qualified personnel (experts #1,4,6,7,9. The majority of surveyed operators did not believe that the vacuum technology is suitable. However, the largest number of ‘Don’t know’ answers was observed for the statement on the suitability for developing countries. This might indicate that many operators did not feel comfortable to answer this question since it might be too generic and provocative or they felt they did not know enough about the wastewater situation in the Global South. In theory, vacuum sewers seem meet the conditions for leapfrogging technologies. Global trends show that the conditions for successful leapfrogging described by Perkins (2003) are met to the greater extent (Table 9). Increasing awareness of environmental concerns lead to the acknowledgement of the necessity to shift from end-of-pipe-measures to cleaner production. A good potential for vacuum sewers exists since the sewerage coverage is low in many regions which are industrializing. On the other hand, sewerage has little priority on the political agenda but with increasing urbanization, industrial activity and income, societies will increase pressure on politics. The condition on technology transfer from industrialized countries is met in the sense that large vacuum sewer companies exist, which are engaged in projects in many countries around the world. However, the number of providers is low and have few subsidiaries in countries of the Global South. Financial and technical assistance does exist beyond development cooperation but the involved actors focus on either very large sewer schemes (e.g. World Bank) or very local sanitation projects (e.g. NGOs). Table 9: Estimation on fulfillment of conditions for leapfrogging (conditions according to Perkins 2003) Condition Estimation + Increased acknowledgement of environmental aspects Shift from end-of-pipe to - strong focus on energy domain cleaner production Start at early stages of industrialization
Technology transfer from industrialized countries Increase in external pressure
International assistance
Discussion
+ Good potential since sewer coverage often remains underdeveloped - low priority since public focus is on income generating services e.g. electrification and transportation - Only few system providers exist - challenge to build and provide service without subsidiary + engaged in projects in many countries of the world + increasing urban population, industrial activity and income put pressure on public institutions to act; + water shortages +
Financing organizations promote larger infrastructure other actors focus on local small-scale sanitation technical and educational exchange is well developed p. 92 / 114
Analysis of the international TIS for vacuum sewers shows currently low to medium performance in many functional groups but bigger potential in the future (Table 10). ‘Knowledge development’ and ‘Diffusion of innovation’ show low performance because modern vacuum sewers have been developed more than 40 years ago but have not received much attention from the scientific community reflected in few scientific publications and few research projects. More attention is given to integrated urban water management, which occasionally includes vacuum sewers. The functional groups involving the private sector (‘Entrepreneurial experimentation’, ‘Market formation’, ‘Resource mobilization’ and ‘Development of positive externalities’) currently show low performance but good future potential. Less than ten technology providers currently exist with strong focus on Germany and the USA. Most companies have own patents on the vacuum valves, monitoring and control systems, leaving only few intermediate markets for durable components, such as pumps and pipes. ‘Influence on the direction of search’ shows good performance since the matter of sanitation is on the international agenda (e.g. SDGs). The potentially higher TIS performance in the future is based on current trends in the wastewater sector promoting the development of new business fields, such as energy, nutrient and potentially water reclamation from wastewater. These trends were confirmed in the interviews. Table 10: Performance of the international TIS on vacuum sewers (based on Binz et al. 2012)
Functional group
Indicator
Knowledge development
R&D projects, no. of involved actors, no. of conferences and workshops
Diffusion of innovation knowledge
Activities of industry associations, websites, conferences, linkages among stakeholders
Influence on the direction of search
Government targets, press articles, visions, perception on growth potential
Medium to high
Entrepreneurial experimentation
No. of experiments, no. of new entrants, diversification activities
Low
Market formation
Discussion
No. of niche markets, tax and regulation regimes, environmental standards
Performance of the int. TIS Few on integrated urban water management; weak presence at Low to conferences, workshops and Medium international networks; few publications Vacuum sewers have not only recently been developed; no real Low industrial association on vacuum sewers
Medium (but potentially High)
Int. organizations promote centralized infrastructure; reports on water scarcity; SDGs; increasing number of vacuum projects in different regions Little activity; few spatially concentrated providers Application only in rural areas; emerging circular economy; promotion of separated sewers; increasing environmental standards; fast growing regions without sewers p. 93 / 114
Creation of legitimacy
Resource mobilization
Development of positive externalities
Growth of interest groups and lobbying activities Availability of human and financial capital, complementary assets for key actors Emergence of labour markets, intermediate goods and service providers, information flows and spill overs
Low to Medium
Strongly institutionalized and active lobbying for decentralized concepts in the USA and Germany; no specific focus on vacuum sewers
Low to medium
Low interest for private sector in vacuum sewers; cheaper alternative for public sector
Low to medium (potentially high)
Few intermediate markets; potential for service providers; knowledge distribution increasing; potential for exploitation of wastewater as a resource
While the theoretical conditions for sanitary leapfrogging involving the vacuum sewer technology seem mostly fulfilled, the real application is far more dependent on the local socio-technical environment. The importance of local technical and institutional capacities has been highlighted many times in the discussion on leapfrogging (Sauter, Watson 2008; Perkins 2003; Binz et al. 2012). The mixed experiences from South Africa, Namibia and Botswana presented above and referred to in the interviews confirm that this is also the case for vacuum sewers (experts #1,4,6,10,11,13). Expert #13 mentioned that the German Development Cooperation (GIZ) made multiple inquiries on the vacuum technology but estimated that technical knowledge in the respective regions could not be assured. Further, expert #4 referred to the difficulty to provide adequate service in the target country when the technology provider is based in Germany. Building the relevant structures and relationships in the target country is difficult and takes time. Regional proximity to lead markets seem to play another important role in the adoption of eco-innovations. Terryn, Lazar (2016) postulate that the uptake of a technology depends more on the proximity to the lead market than the actual economic performance. The research targeted vacuum sewer distribution in Europe and showed that Austria, Czech Republic and Poland are early adopters of the vacuum technology, while countries with higher GDPs as well as higher numbers of potential beneficiaries had slow innovation uptake. The authors state that ‘decision makers are likely to be influenced by decisions that socially neighboring countries have already made’ (Terryn, Lazar 2016). The fact that most vacuum sewer projects and providers are located in Germany and the USA is another challenge for successful implementation in countries of the Global South.
Discussion
p. 94 / 114
However, the case of Outapi shows that integrated water resource management can work but requires the involvement of the right actors and the commitment for assistance from actors that already have experience with the technology. As expert #10 stated, individual technology lines have developed a life on their own, which gives the potential for intermediate markets. The predominantly positive experiences in neighboring Botswana further bare the potential for building such a regional hub for vacuum sewers and possibly integrated water management. The tendency to use established technologies with less uncertainty is understandable (Perkins 2003). Radical innovations have a high level of uncertainty (Terryn, Lazar 2016). Although the vacuum technology is not necessarily a radical innovation since it has been developed a long time ago, a degree of uncertainty remains. This could be demonstrated by the high variability in operational parameters. However, looking at the reasons for the high uncertainty in vacuum sewers the majority of technical problems are related to the user behavior and disposal habits in the operational phase. Many developing countries struggle to establish adequate solid waste management procedures (Guerrero et al. 2013). The example from Kosovo, Cape Town, underlined that this is a problem for the sustainable operation of vacuum sewers. The question is, whether this issue can be addressed via technical modifications, increased focus on end-user education or waste management programs implemented together with the vacuum technology. Further, the sensitivity of the technology also unfolds during the planning and construction phase, during which careful supervision by experienced personnel is required (experts #5,10,11). This was experienced during the construction of the Molepolole Sewerage Scheme in Botswana (Ridderstolpe, Stenbeck 2011). Another critical aspect when assessing the leapfrogging potential of vacuum sewers is the comparison with existing experiences. Famous examples of leapfrogging (e.g. wind turbines, mobile phones) built on well-developed international markets and a higher degree of standardization than currently exists in vacuum sewerage. Further, comparison is limited since vacuum sewerage is a semi-centralized infrastructure approach with small service areas while successful leapfrogging has involved decentral technologies more open to private sector involvement and thus a larger client base. Wastewater services rarely generate income and, apart from the small proportion of private sector involvement in wastewater collection and treatment, the number of clients is restricted to the public sector. Further, infrastructure investments in industrializing countries often require loans Discussion
p. 95 / 114
from international actors, such as the World Bank or KFW. These agencies are more involved in larger projects promoting centralized infrastructure (experts #3 &10; Binz et al. 2012). On the other hand, as shown in Chapter 2 advances in sanitation coverage have been predominantly achieved with onsite technologies. Trends towards more decentralized approaches are further confirmed by growing interest in decentral treatment options (Binz et al. 2012). Further demonstration of vacuum sewers in semicentralized sewerage schemes could increase the number of potential applications. Until now, few experiences have been made in urban environments. The city of Cologne is commissioning a vacuum system in Mühlheim in 2017 (IWR - Ingenieurbüro für Wasserwirtschaft und Ressourcenmanagement 2016). Further, the second phase of the project “Integrated Resource Management in Asian Cities: the Urban Nexus”, funded by the German Federal Ministry for Economic Cooperation and Development and carried out by GIZ, started in 2016. Currently, a demonstration of a vacuum sewer system is being prepared in the Vietnamese city of Da Nang (around 1 million inhabitants, high growth rate). Around 110 residential buildings and a food market will be connected to the system by the end of 2017, serving around 550 people in Da Nang. In case of successful demonstration of the system, the city of Da Nang wants to extend the vacuum sewer to other parts of the Son Tra Peninsula (currently 200,000 inhabitants) and to integrate it into the Da Nang Sustainable City Development Program. (Mohr 2014; GIZ 2014). The two projects will demonstrate the feasibility of vacuum sewers in urban contexts. If successful, the experiences could promote the shift towards decentral or semi central wastewater infrastructure concepts involving the vacuum sewer technology. In summary, theoretical considerations of vacuum sewers and global trends favor the qualification as leapfrogging technology. However, sensitivity and complexity of the operation cause a remaining uncertainty with the technology. Practical examples of leapfrogging are comparable only to some extent since the main actors in wastewater services are predominantly public agencies. The potential future benefits of vacuum sewers also depend on the development of new business field related to energy, nutrient and water reclamation. Finally, the suitability depends very much on the socio technical environment of the region in question as underlined by current experiences from Namibia, Botswana and South Africa.
Discussion
p. 96 / 114
5.7.
Limitations of the study
Before interpreting the results of this study, it is important to consider the limitations of the research methodology. First, any conclusions drawn from the survey or interpretation of the correlation between the variables must consider the small sample size. The vacuum technology is not widely distributed and thus it was difficult to identify a larger number of people working with vacuum sewers. In addition to that, the nature of a semi-structure survey allows for different lines of conversation. The interviews were not conducted in a strict manner but rather adapted to the line of conversation. This way each interview had its own dynamics and contributes to differences in the answers. Furthermore, some questions were formulated quite open and each person might understand the question in a different way and in some cases the experts found that the question was not differentiated enough to answer the question. This especially applied to the question for a rating of the technology. The cases for experts #2,11,13 and 14, who either bound their rating to conditions or refused to answer the question, show that a general rating does not capture the complexity of infrastructure projects and the rating is individual for each system since environmental, technical and socio-demographic settings can vary significantly. A major challenge during the interviews was the balancing of different levels of detail while ensuring comparability. The operator survey is the first of this kind and size in Germany. The collected data can contribute to better planning of future systems based on operational parameters. However, the design of the survey has some drawbacks. The number of collection chambers per systems was not included in the questions. Further, failures are not quantified but assigned to frequency categories and extrapolated making comparison difficult. A comparison with other sewerage systems would have put the finding in this study into perspective but unfortunately reports on operational data were limited. A similar survey targeting areas with different sewerage systems could provide a better comparison. Finally, sample bias cannot be excluded since the operators were identified via the system manufacturers and operators reported the parameters instead of the author collecting the data. Regarding the transferability of vacuum sewers to countries of the global South, the approach followed in this thesis is very generic and theoretical. Each country has different natural, policy and societal environments and historic as well as economic backgrounds.
Discussion
p. 97 / 114
The diversity of settings as well as the individuality of infrastructure projects would actually require sets of very specific case studies in order to estimate the potential for technological and environmental leapfrogging. Given the importance of wastewater services for the livelihoods of billions of people in the Global South the approach of reviewing scientific literature and projecting data from an industrialized country to the entire Global South is limited. Thus, it focusses on theoretical considerations and macro-level trends.
6. Synthesis and Outlook The present study investigated the governing aspects of the vacuum sewer technology from a qualitative, quantitative and theoretical perspective. The two surveys revealed that the application of vacuum sewers is currently restricted to rural areas but have good potential to extend with advances in circular economy principles such as the reclamation of wastewater resources. Further application is seen in the gradual replacement of aging sewer networks especially in urban areas. Further demonstration is still required for this application. The current technological level is good but sensitivity and complexity remain drawbacks. These are reflected in failure rates predominantly governed by disposal habits of the end-users. Further, the present study showed a detailed analysis of operational parameters in vacuum sewers. The analysis confirmed the remaining degree of uncertainty due to high variability in work input, electricity and total operational costs. Nevertheless, the majority of investigated systems appear to work well as the operational parameters are at the lower end of the spectrum, which is also reflected in the operator satisfaction. Transferability to countries of the Global South is limited and very dependent on the local socio-technical
environments.
Theoretical
considerations
confirm
the
potential
environmental and financial benefits but negative references raise concerns on the applicability. Nevertheless, the case of Outapi, Namibia, demonstrates that technology transfer can result in local developments of individual technology lines and the integrated water resource management can be a possible solution to leapfrog conventional sewerage approaches. The vacuum projects in Cologne and Da Nang will be observed with great interest. Other projects in urban areas, such as in Helsinborg, Sweden or Christchurch, New Zealand, are
Synthesis and Outlook
p. 98 / 114
also under development. Evaluation of these semi centralized sewerage approaches will reveal great insights for the future development of vacuum sewers. In the meantime, research should tackle the facilitation of work related to the collection chambers. Measures of remote maintenance as well as for preventing foreign objects to enter the systems should be the focus of technological research. Finally, the transition towards resource oriented wastewater management will depend on more elements than wastewater conveyance. Technologies and concepts for decentralized treatment schemes and for the subsequent exploitation are equally required. Global trends indicate emerging decentral approaches. However, all actors muss make a big leap in order to make integrated water management the conventional practice of the future.
Synthesis and Outlook
p. 99 / 114
Publication bibliography Austermann-Haun, Ute (2010): Korrosion in Kläranlagen. In Hochschule Ostwestfalen-Lippe (Ed.). 33. Erfahrungsaustausch der Lehrerinnen und Lehrer des DWA Landesverbandes Nord. Lüneburg. Bayer, Markus; Kopfhammer, Nils (2012): Kanalisierung mittels Vakuumentwässerung; Roediger Vacuum; BilfingerBerger Facility Services; presentation. Beauclair, R. (2010): Development and Disappointment: an Ethnographic Study of Kosovo Informal Settlement's Water and Sanitation System Upgrade; Department of Social Anthropology; M.A. dissertation, University of Cape Town. Bergek, Anna; Jacobsson, Staffan; Carlsson, Bo; Lindmark, Sven; Rickne, Annika (2008): Analyzing the functional dynamics of technological innovation systems. A scheme of analysis. In Research Policy 37 (3), pp. 407–429. DOI: 10.1016/j.respol.2007.12.003. Berger, Christian; Falk, Christian; Hetzel, Friedrich; Pinnekamp, Johannes; Roder, Silke; Ruppelt, Jan (2016): Zustand der Kanalisation in Deutschland. Ergebnisse der DWA-Umfrage 2015. In Korrespondenz Abwasser, Abfall 63 (6). Besonderes Verwaltungsrecht, Wasserrecht (2017): Gesetz zur Ordnung des Wasserhaushalts (Wasserhaushaltsgesetz). WHG, revised 3/29/2017. Available online at https://www.gesetze-iminternet.de/whg_2009, checked on 7.7 2017. Bilfinger Water Technologies GmbH: Vacuum Sewer System in Palm Jumeirah, Dubai. Project Report. Binz, Christian; Truffer, Bernhard; Li, Li; Shi, Yajuan; Lu, Yonglong (2012): Conceptualizing leapfrogging with spatially coupled innovation systems. The case of onsite wastewater treatment in China. In Technological Forecasting and Social Change 79 (1), pp. 155–171. DOI: 10.1016/j.techfore.2011.08.016. Bock, Stephanie; Nickel, Darla; Langer, Margarethe; Wilhelm, Christian (2016): Wasser, Abwasser, Energie – Übergreifende Lösungen und Modellvorhaben zur Integration der Infrastrukturen. Edited by Deutscher Städte- und Gemeindebund und Deutsches Institut für Urbanistik. Available online at https://www.dstgb.de/dstgb/Homepage/Publikationen/Dokumentationen/Nr. 139, checked on 7/3/2017. Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit (2017): Veordnung zur Neuordnung der Klärschlammverwertung. AbfKlärV, revised 5/12/2017. Available online at http://www.bmub.bund.de/themen/wasser-abfall-boden/abfallwirtschaft/wasser-abfallwirtschaftdownload/artikel/klaerschlammverordnung-abfklaerv/, checked on 7/7/2017. Carlsson, Bo; Jacobsson, Staffan; Holmén, Magnus; Rickne, Annika (2002): Innovation systems. Analytical and methodological issues. In Research Policy 31 (2), pp. 233–245. DOI: 10.1016/S0048-7333(01)00138X. Dai, Yixin; Xue, Lan (2013): China's policy initiatives for the development of wind energy technology. In Climate Policy 15 (1), pp. 30–57. DOI: 10.1080/14693062.2014.863549. Deutsches Institut für Urbanistik (2013): BMBF-Fördermaßnahme "Intelligente und multifunktionelle Infrastruktursysteme für eine zukunftsfähige Wasserversorgung und Abwasserentsorgung (INIS)". Bundesministerium für Bildung und Forschung. Available online at https://nawam-inis.de/de/inis, checked on 7/10/2017. Dohmann, Max (1999): Wassergefährdung durch undichte Kanäle. Berlin, Heidelberg: Springer Berlin Heidelberg. DWA (2008): Neuartige Sanitärsysteme. With assistance of J Clemens, H Daebel, H Herbst, T Hillenbrand, J Longodong, M Oldenburg et al. Hennef: Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V.
Synthesis and Outlook
p. 100 / 114
Elawwad, Abdelsalam; Ragab, Mostafa; Abdel-Halim, Hisham (2014a): Vacuum sewerage system in developing regions and the impact on environmental management; Proceedings of the 4th International Conference on Environmental Pollution and Remediation. Elawwad, Abdelsalam; Rageb, Mostafa; Abdel-Halim, Hisham (2014b): An Economical and Environmental Comparison between Vacuum and Gravity Sewers in Decentralized Sanitation Systems with Egypt as a case study. Edited by Proceedings of the 4th IWA Specialist Conference on Resource Oriented Sanitation. Muscat. Freie und Hansestadt Hamburg (2014): Jenfelder Au - Newsletter Juli 2014. Neugikeiten aus dem neuen Viertel; http://www.jenfelderau-info.de/index.php/Newsletter.html; accessed; 15. December 2016. Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft (2004): Abwasserinvestitionen im ländlichen Raum. Entscheidungsfindung am Beispiel des Ortsteils Putzkau der Gemeinde SchmöllnPutzkau. Edited by Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft. Freistaat Sachsen - Staatsministerium für Umwelt und Landwirtschaft. Gemeinde Ernsgarden: Kanalsystem soll weiter optimiert werden. Available online at http://www.ernsgaden.de/index.php?id=9760,604, checked on 11/16/2016. Gemeinde Magazin Ernsgaden (2016): Vakuumkanal oder Druckkanal? Kanalsystem soll weiter optimiert werden; http://www.ernsgaden.de/index.php?id=9760,604; accessed: 15. December 2016, 2016 (1). GIZ (2014): Report on research on vacuum sewer collection system for Pilot Project An Hai Bac Ward in Eastern Coastal Asia of Da Nang, Vietnam. Guerrero, Lilliana Abarca; Maas, Ger; Hogland, William (2013): Solid waste management challenges for cities in developing countries. In Waste management (New York, N.Y.) 33 (1), pp. 220–232. DOI: 10.1016/j.wasman.2012.09.008. Günthert, F. W.; Cvaci, D. (2005): Vergleich von verschiedenen Entwässerungssystemen ('Comparison of different drainage systems'). Edited by Universität der Bundeswehr München. Hentrich, Steffen; Komar, Walter; Weisheimer, Martin (2000): Umweltschutz in den neuen Bundesländern: Bilanz im zehnten Jahr deutscher Einheit. Edited by Institut für Wirtschaftsforschung Halle (IWH). Available online at https://www.econstor.eu/bitstream/10419/77024/1/128.pdf, checked on 7/2/2017. Howard, Philip N.; Mazaheri, Nimah (2009): Telecommunications Reform, Internet Use and Mobile Phone Adoption in the Developing World. In World Development 37 (7), pp. 1159–1169. DOI: 10.1016/j.worlddev.2008.12.005. Huber, J. (2008): Pioneer countries and the global diffusion of environmental innovations. Theses from the viewpoint of ecological modernisation theory. In Global Environmental Change 18 (3), pp. 360–367. DOI: 10.1016/j.gloenvcha.2008.03.004. Ilori, M.O; Adeniyi, A.A; Oyewale, A.A; Sanni, S.A; Irefin, I.A (2002): Developing a manufacturing-based economy in Nigeria through science and technology. In Technovation 22 (1), pp. 51–60. DOI: 10.1016/S0166-4972(00)00054-7. Islam, M. Shafiqul (2016): Comparative evaluation of vacuum sewer and gravity sewer systems. In Int J Syst Assur Eng Manag. DOI: 10.1007/s13198-016-0518-z. IWR - Ingenieurbüro für Wasserwirtschaft und Ressourcenmanagement (2016): Investment costs for vacuum sewers; personal communication, 2016. Juma, Calestous; Fang, Karen; Honca, Derya; Huete-Perez, Jorge; Konde, Victor; Lee, Sung H. et al. (2001): Global governance of technology: meeting the needs of developing countries. In International Journal of Technology Management 22 (7-8), pp. 629–655.
Synthesis and Outlook
p. 101 / 114
Karippacheril, Tina George; Nikayin, Fatemeh; Reuver, Mark de; Bouwman, Harry (2013): Serving the poor. Multisided mobile service platforms, openness, competition, collaboration and the struggle for leadership. In Telecommunications Policy 37 (1), pp. 24–34. DOI: 10.1016/j.telpol.2012.06.001. King County (2016): How the septic system works. Available online at http://www.kingcounty.gov/depts/health/environmental-health/piping/onsite-sewagesystems/maintenance/how-OSS-works.aspx, checked on 7/12/2017. Kjerstadius, H.; Haghighatafshar, S.; Davidsson, A. (2015): Potential for nutrient recovery and biogas production from blackwater, food waste and greywater in urban source control systems. In Environmental technology 36 (13-16), pp. 1707–1720. DOI: 10.1080/09593330.2015.1007089. Kollmann, René; Neugebauer, Georg; Kretschmer, Florian; Truger, Barbara; Kindermann, Helene; Stoeglehner, Gernot et al. (2016): Renewable energy from wastewater - Practical aspects of integrating a wastewater treatment plant into local energy supply concepts. In Journal of Cleaner Production. DOI: 10.1016/j.jclepro.2016.08.168. Leptien, Christoph; Bellefontaine, Klemens; Breitenbach, Harald; Graf, Peter; Roosen, Christian (2014): Wirtschaftsdaten der Abwasserbeseitigung 2014. Ergebnisse einer in 2013 durchgeführten gemeinsamen Umfrage der Deutschen Vereinigung für Wasserwirtschaft, Abwasser und Abfall e. V. (DWA) und des Deutschen Städtetages sowie des Deutschen Städte- und Gemeindebundes. Edited by Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V. Little, C J (2004): A comparison of sewer reticulation system design criteria standards gravity, vacuum and small bore sewers. In Water SA (30(5)). Available online at http://www.wrc.org.za. Lofrano, Giusy; Brown, Jeanette (2010): Wastewater management through the ages: a history of mankind. In The Science of the total environment 408 (22), pp. 5254–5264. DOI: 10.1016/j.scitotenv.2010.07.062. Mäkinen, Marika (2015): Operation of vacuum sewer system - case Ondangwa, Namibia. Master of Science Thesis; Tampere University of Technology; https://dspace.cc.tut.fi/dpub/handle/123456789/24063?show=full; Accessed: 15.December, 2016. Miszta-Kruk, Katarzyna (2016): Reliability and failure rate analysis of pressure, vacuum and gravity sewer systems based on operating data. In Engineering Failure Analysis 61, pp. 37–45. DOI: 10.1016/j.engfailanal.2015.07.034. Mitullah, Winnie; Samson, Romaric; Wambua, Pauline; Balongo, Samuel (2016): Building on progress: Infrastructure development still a major challenge in Africa. Afrobarometer. Available online at http://afrobarometer.org. Mohr, Marius (2014): Concept for wastewater treatment on Son Tra Peninsula (Da Nang, Vietnam). Fraunhofer Institute for interfacial Engineering and Biotechnology (IGB). Moore, David S.; McCabe, George P.; Craig, Bruce (2009): Introduction to the practice of statistics. 6. ed., 2. print. New York NY u.a.: Freeman. Mothobi, Onkokame; Grzybowski, Lukasz (2017): Infrastructure deficiencies and adoption of mobile money in Sub-Saharan Africa. In Information Economics and Policy. DOI: 10.1016/j.infoecopol.2017.05.003. Müller, N. (1997): Kosten der Abwasserbeseitigung – Kritische Gedanken zur allgemeinen Kostendiskussion. In Korrespondenz Abwasser, Abfall (2). Münch, Elisabeth von; Winker, Martina (2009): Technology review "Vacuum Technology". Edited by GIZ. Naret, R. (2007): Vacuum Sewers - Design and Installation Guidelines. Course No C-8015. PDHengineer.com. Available online at
Synthesis and Outlook
p. 102 / 114
http://www.airvac.com/pdf/Vacuum_Sewers_Design_Installation.pdf, updated on 2007, checked on 15. December, 2016. Naret, R. (2008): Vacuum sewers 101. Edited by PDHengineer.com Course Number C-4028. Available online at www.airvac.com/pdf/Vacuum Sewers 101.pdf, updated on 2008. Naret, R. (2009): Vacuum Sewers – Operation and Maintenance and System Management Guidelines. Course Number C-4029. Edited by PDHengineer.com. Available online at www.airvac.com/pdf/Vacuum O&M and System Management.pdf, updated on 2009, checked on 15.December, 2016. Oldenburg, Martin (2008): Die ökologische Wohnsiedlung Flintenbreite, Lübeck. Edited by Otter Wasser GmbH. Available online at http://www.woche-der-umwelt.de/media/, updated on 2008, checked on 15. December, 2016. Otterpohl, R.; Braun, U.; Oldenburg, M. (2004): Innovative technologies for decentralised water-, wastewater and biowaste management in urban and peri-urban areas. In Water science and technology 48 (11-12), pp. 23–32. Panfil, Corina; Mirel, Ion; Szigyarto, Izabella; Isacu, Monica (2013): Technical, Economical, Social and Ecological characteristics of vacuum sewage system. In Environmental Engineering and Management Journal (12), pp. 1017–1022. Available online at http://omicron.ch.tuiasi.ro/EEMJ/. Perkins, Richard (2003): Environmental leapfrogging in developing countries: A critical assessment and reconstruction. In Natural Resources Forum 27, pp. 177–188, checked on 7/11/2017. Ridderstolpe, Peter; Stenbeck, Sten (2011): Molepolole Sewerage Scheme - Actions for Sustainable Sanitation and Wastewater Management. Edited by Water Revival Systems, StenStenbeck. The Swedish Trade Council and the Swedish Foreign Ministry. Rip, A; Kemp, R (1998): Technological change. In S Rayner, E L Malone (Eds.): Human choice and climate change. Vol. II, Resources and Technology. Columbus, Ohio: Battelle press, pp. 327-399. Rosenkranz, Stephanie (1997): Quality improvements and the incentive to leapfrog. In International Journal of Industrial Organization 15 (2), pp. 243–261. DOI: 10.1016/0167-7187(95)00518-8. Rutsch, M.; Rieckermann, J.; Cullmann, J.; Ellis, J. B.; Vollertsen, J.; Krebs, P. (2008): Towards a better understanding of sewer exfiltration. In Water research 42 (10-11), pp. 2385–2394. DOI: 10.1016/j.watres.2008.01.019. Sander, Thomas (2003): Ökonomie der Abwasserbeseitigung. Wirtschaftlicher Betrieb von kommunalen Abwasseranlagen. Berlin, Heidelberg: Springer. Available online at http://dx.doi.org/10.1007/978-3-64255480-3. Sauter, Raphael; Watson, Jim (2008): Technology Leapfrogging: A Review of the Evidence A report for DFID. Schluff, R. (1996): Entwässerungstechnik im Umbruch. Bemessung und Konstruktion der Unterdruckentwässerung. Stuttgarter Berichte zur Siedlungswasserwirtschaft. Schluff, Reinhold (2013): Vacuum Sewerage System. PHD Thesis. Edited by University Politehnica of Bucharest. Doctroal School of Power Engineering. Available online at www.schluff.com/dissertation.htm, checked on 7/12/2017. Shalizi, Zmarak (2003): Sustainable development in a dynamic world. Transforming institutions, growth, and quality of life. Washington, D.C, New York: World Bank (World development report, 2003). Available online at http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=77999. Statistisches Bundesamt (2013a): Erhebung der öffentlichen Abwasserbehandlung. Länge des Kanalnetzes, Abwasserbehandlungsanlagen, Angeschlossene Einwohnerwerte, Jahresabwassermenge, Synthesis and Outlook
p. 103 / 114
Schmutzwasser: Bundesländer, Jahre. Available online at https://wwwgenesis.destatis.de/genesis/online/data;jsessionid=48E893FE85B996B99CE790D87C5B9CFD.tomcat_GO_ 1_3?operation=abruftabelleBearbeiten&levelindex=1&levelid=1494416827443&auswahloperation=abruft abelleAuspraegungAuswaehlen&auswahlverzeichnis=ordnungsstruktur&auswahlziel=werteabruf&selectio nname=32213-0001&auswahltext=&werteabruf=Werteabruf, checked on 10.Mai.2017. Statistisches Bundesamt (2013b): Öffentliche Abwasserentsorgung nach Ländern 2013. Edited by Gesamtwirtschaft & Umwelt - Wasserwirtschaft - Wasserwirtschaft - Statistisches Bundesamt (Destatis). Statistisches Bundesamt. Available online at https://www.destatis.de/DE/ZahlenFakten/GesamtwirtschaftUmwelt/Umwelt/UmweltstatistischeErhebunge n/Wasserwirtschaft/Tabellen/Abwasserentsorgung_2013.html;jsessionid=6F973E103276EA27389E2197D 11B1C3B.cae4, updated on 10/16/2015, checked on 7/5/2017. Strande, Linda; Ronteltap, Mariska; Brdjanovic, Damir (Eds.) (2014): Faecal sludge management. Systems approach for implementation and operation. London: IWA Publ. Sullivan, Lisa; LaMorte, Wayne W (2016): Box-Whisker Plots for Continuous Variables. School of Public Health - Boston University. Available online at http://sphweb.bumc.bu.edu/otlt/mphmodules/bs/bs704_summarizingdata/bs704_summarizingdata8.html, checked on 7/13/2017. Taing, L.; Armitage, N. P.; Spiegel, A. (2011): Cape Town's problematic vacuum sewer: A reflection on the technical, social and institutional blockages that constrain municipal management; 12th International Conference on Urban Drainage, Porto Alegre/ Brazil. Terryn, Iulia C.; Lazar, Gabriel (2016): Driving forces affecting the adoption of Eco-innovation: A survey on vacuum sewer systems. In Environmental Engineering and Management Journal 15 (3), pp. 589–598. Terryn, Iulia Carmen; Lazar, Iuliana; Nedeff, Valentin; Lazar, Gabriel (2014): Conventional vs Vacuum sewerage system in rural areas - an economic and environmental approach. In Environmental Engineering and Management Journal (13(8)), pp. 1847–1859. Tilley, E; Ulrich, L; Luethi, C; Reymond, P; Zurbruegg, C (2008): Compendium of Sanitation Systems and Technologies. Edited by Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and Water Supply and Sanitation Collaborative Council (WSSCC). Available online at http://www.eawag.ch/de/abteilung/sandec/, checked on 2/20/2017. Tukker, Arnold (2005): Leapfrogging into the future. Developing for sustainability. In IJISD 1 (1/2), p. 65. DOI: 10.1504/IJISD.2005.008087. U.S. Environmental Protection Agency (1991): Manual. Alternative Wastewater Collection Systems; https://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB93116259.xhtml; accessed: 15.December, 2016. Edited by U.S. Environmental Protection Agency. U.S. Environmental Protection Agency. Unruh, Gregory C. (2000): Understanding carbon lock-in. In Energy Policy 28 (12), pp. 817–830. DIN EN 1091, 1997, 1997: Unterdruckentwässerungssysteme außerhalb von Gebäuden; DIN EN 1091. Warhurst, Alyson; Bridge, Gavin (1997): Economic liberalisation, innovation, and technology transfer. Opportunities for cleaner production in the minerals industry. In Natural Resources Forum 21 (1), pp. 1– 12. DOI: 10.1111/j.1477-8947.1997.tb00668.x. Weismann, Dieter; Lohse, Manfred (2007): Sulfid-Praxishandbuch der Abwassertechnik. Biogene korrosion, Geruch, Gefahr verhindern und Kosten beherschen: Vulkan Verlag. WHO (2012): Global costs and benefits of drinking-water supply and sanitation interventions to reach the MDG target and universal coverage. WHO/HSE/WSH/12.01. WHO; UNICEF (2015): 25 years progress on sanitation and drinking water. 2015 update and MDG assessment. Geneva, New York: World Health Organization; UNICEF.
Synthesis and Outlook
p. 104 / 114
WHO; UNICEF (2017): Improved and unimproved water sources and sanitation facilities. Available online at https://www.wssinfo.org/definitions-methods/watsan-categories/, checked on 7/10/2017. World Bank (2015): Improving On-site Sanitation and Connections to Sewers in Southeast Asia. Improving On-site Sanitation and Connections to Sewers in Southeast Asia. Edited by World Bank Water Sanitation Programm. Available online at http://blogs.worldbank.org/water/building-urban-sewerage-infrastructurewhere-sewage. www.deus21.de: DEUS 21: DEcentralised Urban infrastructure Systems. Available online at www.deus21.de, checked on 11/16/2016. Zech, T.; Mohr, M.; Trösch, W. (2008): Dezentrales Urbanes Infrastruktursystem DEUS 21: Förderkennzeichen 02WD0457. In Förderkennzeichen 02WD0457. Hg. v. Fraunhofer-Institut für Grenzflächen-und Bioverfahrenstechnik (IGB). Stuttgart. Stadt. Zimmermann, Martin; Deffner, Jutta; Müller, Katharina; Kramm, Johanna; Papangelou, Anastasia; Cornel, Peter (2015): CUVE waters - Sanitation and Water Reuse Implementation Concept.
Synthesis and Outlook
p. 105 / 114
Acknowledgement I would like to thank Prof Glaser and Prof Tovar for supporting me in following my research interest despite the little overlap with their own fields of research. Further, I would like to express my thanks to Dr Mohr, who guided the development and conduction of the research and who gave me the opportunity to work on various interesting projects across the water sector in the meantime. Thank you to the whole team at the Fraunhofer IGB, especially Steffen Görner, Stephan Scherle and Alexander Laug, for providing a good work atmosphere, delicious cakes and stimulating conversations over coffees. My great appreciations go to my friends who supported me during the past years and offered me balance. Thanks for the advices, distractions and drinks. Further, I would like to thank my caring girlfriend Corinna for the support and belief in me. I also want to thank my former roommate Arnd van Rickelen who recently passed away. Your life is an inspiration to all of us. Finally, I want to thank my family, who made it possible for me to follow my interests and supported me in many ways during the past years of studying. No words can express my gratitude for having you.
Acknowledgement
p. 106 / 114
Annex Sewerage connection rates in African countries
Figure 71: Sewerage connection rates in 35 African countries (Mitullah et al. 2016)
Annex
p. 107 / 114
Expert Interview Questionnaire
Annex
p. 108 / 114
Annex
p. 109 / 114
Pros and cons of vacuum sewers Table 11: Positive and negative aspects of vacuum sewers mentioned din the interviews Positive / advantageous
Negative / disadvantageous
Category
Referrals
Category
Referrals
Balance
Flexibility +
10
Flexibility -
7
+3
Good in rural areas
3
not
applicable
at
higher
4
population densities / not applicable in urban areas / limited wastewater quantity / not applicable in cities / transformation
in
built
environments complicated / limited to rural areas Decentral application
1
Not dismountable
1
can be installed in existing pipes /
1
Limited application
1
1
Minimum house connections
1
transformation of infrastructure / refurbishment of old network sections Flexibility regarding demographic change
required
Good in fast growing cities
2
Requires less space
1
Planning & Construction +
21
Planning & Construction -
10
less excavation / fewer civil
4
More complex construction /
5
works / easy installation / easy
high quality demand during
laying of pipes
construction / more complex construction high
supervision
sensitivity
=+11
/ for
construction errors flexible line management
1
Pressure difference limited to
2
6 m / difficult in great depths good at high groundwater
3
tightness must be ensured
2
table
Annex
p. 110 / 114
Positive / advantageous
Negative / disadvantageous 6
small pipe diameter
awareness on existence of
1
vacuum sewers limited 6
good in flat terrain planning
easier
than
for
1
gravity sewer
Financials + collection
pits
cheaper
than
10
Financials -
1
expensive
pumps in pressure sewers
12 through
unnecessary inspection
extras
= -2
8
/
pipes obsolete/
operational costs higher/ too expensive/ vacuum station expensive/ if stormwater pipe is
refurbished
the
cost
advantage of vacuum sewers are
minimal
excavation anyway/
because
takes not
sufficient
place
sensible
slope
if
exists/
pressure sewer better for small
number
of
house
connections/ using existing infrastructure
is
often
cheaper and more sensible / installation of buffer tanks is costly potential cost savings especially in
6
energy demand higher
2
1
only sensible if subsequent
2
flat terrain and flood protection areas little additional costs for source separation
exploitation
(energy
generation etc.) lower excavation costs
Annex
1
p. 111 / 114
Positive / advantageous
Negative / disadvantageous
electricity costs lower than in
1
pressure sewers
Environment +
18
Water savings (via vacuum toilets)
4
Good in extreme climates
1
No leakages / tightness
4
Good in water protection areas
1
No odors
1
Possibility of source separation /
7
concentrated
wastewater
Environment -
0
= +18
29
= -10
/
possible application of kitchen grinders / collection of food wastes
Operations +
19
Operations -
Electricity use at only one point
1
Complicated
technology
7
/high-tech system / higher failure probability / knowhow required / technical knowledge
important
/
Education on functionality of the system required No excess water
2
High
technical
effort
/
8
complex operations / high maintenance requirements / too
much
complex
effort /
/
too
immature
technology Very robust
1
Encrustation
when
2
blackwater pipes run through warm
rooms
/
potential
calcification No failures of pipes / no camera
2
screening necessary High flow velocities / no cleaning required
Annex
Noise of the system / very
4
loud machines 1
Sensitive system / false alarms
5
through sensitivity / system
p. 112 / 114
Positive / advantageous
Negative / disadvantageous more sensitive / clogging / gravity sewer more tolerant
Easy error detection / easy error
7
identification / failures easy to
Valve exchange unpleasant
1
for technical staff
detect / remote monitoring / remote maintenance Separation
between
collection
1
Low over capacity
1
3
Electricity needed
1
sump and valve compartment Good in flood areas
Annex
p. 113 / 114
Statement of Affirmation I hereby declare that the submitted master thesis was in all parts exclusively prepared on my own, and that other resources or other means (including electronic media and online sources), than those explicitly referred to, have not been utilized. All implemented fragments of text, employed in a literal and/or analogous manner, have been marked as such.
Marc Beckett Simrockstraße 35 50823 Köln Student ID 3527339
Köln, July 21st, 2017
Seite 114 von 114
