Greece. Abstract Data from 147 small municipal wastewater treatment plants (MWTP), with a population equivalent (p.e.) less than 10,000, have been collected ...
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Small municipal wastewater treatment plants in Greece *School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK **National Foundation for Agricultural Research, Institute of Iraklio, P.O. Box 1841, 71110 Iraklio, Crete, Greece Abstract Data from 147 small municipal wastewater treatment plants (MWTP), with a population equivalent (p.e.) less than 10,000, have been collected and analysed. Extended aeration plants are the most common (75%), followed by natural systems – waste stabilisation ponds (9%) and hydroponic silviculture (6%). Only 71 MWTP (out of the 147) were operational in 1997; the performance of only 15 of these was good, for 36 was moderate and for 20 it was poor. It was found that the reasons for poor performance, for the plant failure and for delays in commissioning were managerial and institutional, rather than purely technical. Keywords Cost; institutional evaluation; municipal wastewater; small treatment plants; wastewater treatment
Introduction
In the USA, the projected need for small wastewater treatment plants is far greater than that for large treatment plants. In the future, construction costs for new and improved small decentralized systems will run into many millions of dollars (Crites and Tchobanoglous, 1998). Greece as a EU Mediterranean country, is not far from this situation. There is a large number of small communities and the need for a clean environment has raised concerns for effective wastewater treatment. The percentage of the population living in small communities is low but most of them are located in tourist and sensitive areas where a clean environment is essential both in terms of the environment and income generation. The purpose of this study is to enlighten the municipal wastewater treatment for small communities in Greece by providing statistical information, discussing problems and suggesting solutions, on an integrated basis. The output is believed to be useful not only for Greece but for other countries as well that are planning to implement wastewater management policies. All data analyzed and presented in this paper are a selective output of a national survey of all MWTP in the whole of Greece (Tsagarakis et al., 1998a); only small plants are considered, i.e. those with p.e. less than 10,000. The time the survey visits took place was between summer 1995 and summer 1997. The collected data stem from: (a) information given by the personnel and management of plants, (b) available design data, and (c) on-thespot investigations. Additional data were acquired by post or telephone contact, when required. It is the first study that was implemented in an integrated way. There where statistical information is given; this has been done for all plants. Where further analysis is carried out like land requirements, construction and operation and maintenance (O&M) cost, only plants that could give reliable data were considered.
Water Science and Technology Vol 41 No 1 pp 41–48 © IWA Publishing 2000
K.P. Tsagarakis,* D.D. Mara,* N.J. Horan,* and A.N. Angelakis**
Existing conditions
The number of small plants amounts to 147 out of the 241 located during the survey. Their total potential capacity is equivalent to 7.5% of the population of the country served by wastewater treatment. Current capacity, referred to as today’s population equivalent (t.p.e.), is 3.2%. This means that, of the total population of Greece served, only 3.2% is currently served by small plants. Analysis of the data collected per size is shown in Table 1.
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Table 1 Distribution of MWTP by size Size in p.e.
No. of plants
Total p.e.
Total t.p.e.
K.P. Tsagarakis et al.
500–2,000
56
66,100
25,490
2,001–4,000
25
72,660
27,500
4,001–6,000
29
154,222
46,100
6,001–8,000
16
117,386
27,600
8,001–10,000
21
203,400
49,600
147
613,768
176,290
Total
Process evaluation
The number of plants providing primary, secondary or advanced treatment is 2, 133 and 12, respectively. Of these, 117 are suspended growth, 24 natural systems, and 4 attached growth systems. Further classification of the systems is provided in Table 2. The two primary treatment plants consist of mechanical pretreatment, sedimentation, chlorination and air drying for sludge dewatering. From those plants that provide at least the secondary treatment it is obvious that extended aeration is dominant system, as it provides additional advantages for Mediterranean climatic conditions. A typical flow train for the extended aeration type plants is that the liquid line consists of mechanical pretreatment, aeration, sedimentation, and chlorination. Those with nutrient control also include anoxic and anaerobic tanks (Figure 1a). Sequencing batch reactors (SBR) are not widely practised in Greece. The trend is to convert SBR to extended aeration plants and most of them are already in the process of redesign and reconstruction. Attached growth systems are also not popular in Greece. Advanced wastewater treatment plants are mainly regarded those that include nutrient control in a separate unit stage. Natural treatment systems are unusual in the way most of them have been established. Both waste stabilization ponds (WSP) and hydroponic silviculture were applied at a regional level, initially by means of a prototype plant. However, instead of monitoring the protoTable 2 Details of wastewater treatment systems surveyed Process
Primary treatment
No. of plants
p.e.
t.p.e.
2
5,000
4,000
1
10,000
10,000
Suspended growth
Activated sludge conventional Activated sludge extended aeration
110
512,368
128,500
Sequencing batch reactor
5
32,700
9,100
Intermittent decanted extended aeration
1
1,000
1,000
Trickling filters
2
20,000
10,000
Biological aerated flooded filters
2
1,200
600
13
18,600
4,950
Reed beds
2
4,700
2,400
Hydroponic silviculture
9
8,200
5,740
147
613,768
176,290
Attached growth
Natural systems
Waste stabilization ponds
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Total
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K.P. Tsagarakis et al.
effluent
Figure 1 Dominant wastewater treatment systems in Greece
type to improve design and operation, subsequent plants were mostly a direct copy of the initial design. This resulted in poorer performances than with the prototype, so engendering the feeling that such systems are not appropriate for wastewater treatment. There is currently a shift towards reed beds and it is believed that it is the optimum solution for small communities; this is also verified by the first reed bed in operation (Avgitidis et al., 1996). WSP have been implemented only in the Prefectures of Serres and Kavala. Process design comprises one facultative and one to three maturation ponds, including in some cases a rock filter prior to the outlet (Figure 1b). Their capacity ranges from 500 to 3,000 p.e. Maintenance is very limited and rooted macrophytes (even trees) occur in almost all the ponds. Some have also reported mosquito nuisance. Clearly, the existing WSP need to be upgraded in order to avoid the impression of their inappropriate applicability. Such upgrading should include anaerobic ponds, as they are extremely efficient in removing BOD5, so reducing land area requirements considerably (Mara and Pearson, 1998). Hydroponic silviculture is a natural wastewater treatment process, applied in small communities on the island of Evia in Central Greece, this consists of a septic tank, a lined multi-layered basin planted with trees and a seepage well (Figure 1c). Their capacity varies from 600 to 1,500 p.e. When this system was established, the tree spacing was so small that their roots blocked the subsurface flow very fast, so reducing the original bed porosity; as a result the whole basin had to be replanted. When this problem was first noticed it was too late as many installations had been constructed and planted in the same way. Further research should be carried on optimal tree species and their spacing and feasibility of coppicing.
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Operational evaluation
K.P. Tsagarakis et al.
It is important to know the status of small MWTP in Greece in order to locate and to evaluate any construction and/or operation problems. Depending on the status of the plant five categories have been considered. The first is the category of failure. In this category have been classified plants which are in operation for less than 10% of their prescribed time or 8 years since their construction was completed and have not operated since (this time is the average guarantee of the electrical and mechanical equipment given by the construction). Failure means that almost all of the mechanical equipment needs replacement and some tanks may need reconstruction. The second category is that of the plants under construction. The third category is that of the plants that are under construction, but construction works had paused for more than one year. The construction level in this category is about 50%, which is more or less equivalent to the construction of the civil works required. The fourth category is that of the plants in which almost all construction works have finished but the installations are not in operation due to other reasons. This means that even the mechanical equipment has been completely installed. The construction level in this category is more than 90%. The last category refers to the plants in operation. The number of plants per category and their percentage of the total are summarized in Table 3. Table 3 Status of the small MWTP Category
No. of MWTP
Percentage
1. Failure
13
8.8%
2. Under construction
31
21.1%
3. Construction incomplete
7
4.8%
4. Completed but not in operation
25
17.0%
5. In operation
71
48.3%
Total
147
100.0%
It is pitiful that there are 45 “problematic” plants (i.e. plants which failed, construction incomplete or completed but not in operation) equivalent to 31% of the total. The main causes of this are: (a) incomplete sewerage systems, 22 plants; (b) inadequate funds for construction, operation and maintenance, 15 plants; (c) legal proceedings arising from financial problems and public reactions, 4 plants; (d) absence of discharge structure, 2 plants; and (e) other causes, 2 plants. The average period not in operation for the plants in categories 3 and 4 (Table 3) is estimated to be 2.5 years. To avoid such problems, a general policy is needed for improving the management of the allocated funds, in order to avoid complete mis-investment. Construction of the sewerage, wastewater treatment and disposal facilities should be planned together in order to optimise project management. Institutional evaluation
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Small villages and towns are subject to central Prefecture administration for technical projects, as they are not always able to support technical services. Thus, construction of a MWTP is supervised by Prefecture engineers. Projects are mainly subsidized from national or EU funds, but O&M is financed from the community’s budget. The weak point here is that one service is responsible for choosing the system and supervising construction and another for operating it. The only service that small municipalities and communities can support with their existing personnel is accounting. What happens most commonly is that a local technician or unskilled employee is trained for some months to operate the plant, and
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Table 4 Performance evaluation of small MWTP in relation to the service agency responsible MWTP
Performance
(no)
Municipality
17
6
6
5
Specialized enterprise
10
3
6
1
5
2
2
1
Community
39
9
22
8
Total
71
20
36
15
Technical service
Poor
Moderate
Good
K.P. Tsagarakis et al.
Responsible agency
experience has shown that this is not adequate if there is no engineering and scientific supervision. Additional contracts with consulting companies are required, but rarely entered into. The construction supervision of the 147 plants has been carried out as follows: for 136 by the technical services of the Prefecture, and for 11 by the technical service of the municipality. From these only 4 are specialized enterprises for water supply and sewage, while the other are general technical services. The 71 plants in operation are administrated and supervised by different enterprises and services. Municipalities are in charge of 17; communities, 39; technical services of municipalities, 5; and specialized enterprises, 10. The performance of these plants has been classified as poor, moderate, and good according to the responsible agency (Table 4). Poor performance refers to plants whose effluent is almost always below quality required; moderate performance, to plants that operate very close to requirements; and good performance, to plants that operate consistently above requirements. This classification has been made according to effluent data given plant personnel and our onthe-spot investigation. Inappropriate fund management is highly related to the public services that delegate control and supervise transactions for the projects. Their inefficiency can subsequently influence the wastewater sector. Construction control efficiency (i.e. delay of payments) may delay the project from its start. In addition, many services are responsible for the same project and thus mis-coordination exists. A weak point is that the water sector is mainly governed by the Ministry of Agriculture, the Ministry of Environment and Public Works, and the Ministry of Development. It is proposed that only one national authority is in charge of water sector to provide more effective control and promote wastewater treatment. Changes are needed in the water sector through which: (a) specialized agencies will be promoted, (b) centralization of administration occurs in cases where there is inadequate individual viability; and (c) geographical and hydrogeological based agencies are established, which staffed with specialized personnel. It is then a political issue whether these services will operate the plant or it will be subcontracted to private companies. Future perspectives. At present, a new local administration structure is being implemented, called Ioannis Kapodistrias. The main innovation is that small local authorities compulsory merge to form municipalities. Practically this is equivalent to improvement of economic viability, local administration, and thus the potential of developing specialized agencies for water supply and sewerage. It is too early to evaluate the output of this structure but is expected to give a positive contribution to the municipal wastewater sector. Legislation. Greek legislation regarding small systems has to comply with the EU Council Directive Concerning Urban Wastewater Treatment, (EU 91/271, 1991). However, small
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plants do not always operate properly. Most of the time, the causes are non-technical and the majority of them could have alleviated by better administration for construction and operation. Effluent standards not only have to be established, but plants have to comply with them. This will require adequate funding for personnel, equipment and consumables. Johnstone and Horan (1994) provide further advice on this. K.P. Tsagarakis et al.
Technology choice and decision making. A specific trend in wastewater treatment selection has become apparent, not surprisingly perhaps as engineers and other decision makers prefer what is already widely applied and tested: the large number of extended aeration systems (110 out of 147) is evidence for this. Another critical concept is chosen destination for the effluent. Although relatively high crop water requirement has been reported for Greece (Tchobanoglous and Angelakis, 1996), the dominant effluent destination is not for irrigation, but the sea (Tsagarakis et al., 1998b), influenced by northern EU countries. Lack of training. It has been widely reported that training of operators of small MWTP should be carried out in order to secure a proper operation of the plant. This is clearly important as their everyday responsibilities cover almost everything. In order to operate well, plants should be designed and constructed properly. Yet at the local administrative level, where government engineers check plant design, there is inadequate specialization. Training programmes on environmental projects and pre-feasibility studies should be provided. Training of engineers, and other technical personnel, is relatively straightforward, but the training of other decision-makers, including politicians, is less so (and currently does not exist). Comparison of different technologies
The different systems used in Greece are compared in terms of land requirements, and construction and O&M costs. In addition reference is made to the extended aeration (EA) plants in regard to the sludge treatment they employ and nutrient control. Plant area
The land required by a MWTP is a primary concern especially in places where the available land is scarce or high cost. The availability of the land is the first decision making parameter required to choose between different treatment processes. Land requirements per p.e. used in 53 MWTP are presented in Table 5. The values given refer to the whole area of the instalTable 5 Plant area per p.e. for different small systems Area (m2) per p.e.
46
System
Sludge treatmenta
Primary treatment
AD
Extended aeration
T
3
0.16
0.11
Extended aeration
T, AD
24
1.08
0.69
Extended aeration
T, C, MD
10
0.68
0.42
SBR
T, AD
3
0.89
0.53
WSP
N/A
7
5.95
0.84
Reed bed
N/A
2
7.27
1.41
Hydroponic silviculture
N/A
2
2.86
0.37
No of plants
2
Mean
Standard deviation
0.42
0.03
a T, thickening; AD, air drying; C, conditioning; MD, mechanical dewatering.
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Figure 2 Construction cost of different systems in relation to plant capacity
lation, including any access paths or roads and other such as buildings and laboratory. In areas where the land cost is high, land-demanding systems cannot be applied. Construction cost
Construction cost is a crucial parameter of prime importance when a MWTP is being planned. There are many parameters that can influence it. The construction cost data of 54 MWTP are analyzed after subtracting any tax and discounting by the inflation rate at the beginning of the year 1999 (Anon., 1998) (Figure 2). At the time of analysis the exchange rate was US$ 1=GDR 285 (Greek Drachma). Operation and maintenance
O&M costs include personnel salaries, energy costs, chemicals, maintenance, and other. Annual O&M costs from 23 plants operating at more than 70% of their capacity are given in Figure 3. Analysis of the costs shows that personnel salaries account for 30% of the total O&M costs, energy 50, chemicals 11, maintenance 8 and other 1. The personnel employed can be divided into three main categories: scientific (with a higher education degree), tech-
Figure 3 Annual operation and maintenance costs for different systems in relation to plant capacity
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nical and unskilled. The percentage of personnel per category is 15, 60 and 25%, respectively. The average ratio of personnel employed per p.e. is 1/5,500. Conclusions and recommendations
K.P. Tsagarakis et al.
The main conclusions and recommendations which can be drawn from this study are as follows. Of the 147 MWTP considered, 48.3% are in operation, 17.0% are completed but not in operation, 4.8% are incomplete, 21.1% are under construction, and 8.8% have failed. 117 plants were suspended growth systems, 4 were attached growth systems and 24 were natural systems. Existing natural systems need to be upgraded in order to improve the impression of their applicability. Incomplete sewerage system, cessation of the plants’ construction-operation and without disposal system, due to inappropriate fund management has resulted in failure of 39 plants (i.e. 27% of the total). Construction of the sewerage, wastewater treatment and disposal facilities should be planned together in order to optimise project management. In general, performance of small MWTP can be characterized as moderate. It is believed that services in charge of construction and O&M are not the optimum ones. Training of state engineers and operators and centralization of the administration would be beneficial. Acknowledgements
This work was financed from the EU-93 AVI 876 Project. References Anon. (1998). Economical Indicators. Athens, Greece: Bureau of Economical Indicators, National Statistical Service of Greece. Avgitidis, V., Iossifidis, V. and Katsonis, E. (1996). Constructed wetlands technology for wastewater treatment, implementation in Greece. Proc. of Protection and Restoration of the Environment III, pp. 272–277. Chania, Greece, 28–30 Aug. Crites, R. and Tchobanoglous, G. (1998). New York: Small and Decentralized Wastewater Management Systems. WCB and McGraw-Hill. EU (1991). Council Directive Concerning Urban Wastewater Treatment (91/271 EEC of May 21, 1991). Official Journal L135/40, May 30. Johnstone, D.W.M. and Horan, N.J. (1994). Standards, costs and benefits: an international perspective. Instn. Wat. & Envir. Mangt., 8, 450–458. Mara, D.D. and Pearson, H.W. (1998). Design Manual for Waste Stabilization Ponds in Mediterranean Countries. Leeds, England: Lagoon Technology International. Tchobanoglous, G. and Angelakis, A.N. (1996). Technologies for wastewater treatment appropriate for reuse: potential for applications in Greece. Wat. Sci. Tech., 33(10–11), 17–26. Tsagarakis, K.P., Mara, D.D. and Angelakis, A.N. (1998a). Evaluation of wastewater treatment plants in Greece. Technica Chronica I, 18(3) (in press). Tsagarakis, K.P., Mara, D.D., Horan, N.J. and Angelakis, A.N. (1998b). Evaluation of reuse and disposal sites of effluent from municipal wastewater treatment plants in Greece: a preliminary study. Preprint of the 2nd Internat. Conf. on Advanced Wastewater Treatment, Recycling and Reuse, 2, 867–870. Milan, 14–16 Sept.
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