Nov 10, 2010 ... Project Proposal and Feasibility Study ... Currently, the wastewater treatment
system for the hospital and other ...... For example, the city of Shell.
Project Proposal and Feasibility Study Team: Pure Pastaza (8) Team Members: James Dykstra Rachel Koopman Ben Vander Plas Sungmin Youn Date: December 6, 2010 Institution: Calvin College Class: ENGR 339/340 Senior Design Project
© 2010, Calvin College and James Dykstra, Rachel Koopman, Benjamin Vander Plas, Sungmin Youn
Executive Summary Shell Mera is a town located in the Eastern foothills of the Ecuadorian Andes approximately 94 miles Southeast of Quito. Hospital Vozandes del Oriente (HVO) is a hospital located in Shell that is maintained by Hoy Cristo Jesús Bendice (HCJB) Global. HCJB is a non-profit mission organization committed to Biblical values and community development principles. Pure Pastaza, a senior design team from Calvin College, in conjunction with HCJB is developing a design for a wastewater treatment system for HVO. Currently, the wastewater treatment system for the hospital and other buildings on the property includes a pipe network and collection system leading to an overloaded septic tank with no leaching field. Therefore, effluent from the septic tank passes directly into the Motolo River south of the hospital without receiving further treatment. The condition of the tank is currently unknown and it may not be sealed properly and therefore leaking contaminants into the ground. There is also no appropriate method or suitable location established for septage disposal, which has consequently been discharged directly into the river. The hospital is in need of an alternative method for treating its wastewater and disposal of the sludge produced. Various treatment alternatives have been analyzed and compared from a standpoint of stewardship and cultural appropriateness. Pure Pastaza is recommending a design that utilizes a bar screen for preliminary treatment followed by a series of facultative ponds. This design has been chosen due to its simplicity, cost effectiveness and relatively low maintenance, effectively solving the issue of sludge disposal. The total project cost has been estimated to be $113,833. This includes engineering design, construction and a 15% contingency.
Table of Contents List of Figures .............................................................................................................................................. iii List of Tables ............................................................................................................................................... iv 1.
Introduction ...................................................................................................................................... 1 1.1
The Team ............................................................................................................................ 1
1.2
Team Bios ........................................................................................................................... 1
1.3
Project Context ................................................................................................................... 2
1.4
HCJB Background .............................................................................................................. 2
1.5
Problem Statement .............................................................................................................. 3
1.6
Project Background............................................................................................................. 4
1.7
Design Norms ..................................................................................................................... 5
1.8 2.
1.7.1
Stewardship............................................................................................................ 5
1.7.2
Cultural Appropriateness ....................................................................................... 5
1.7.3
Transparency.......................................................................................................... 6
Objectives ........................................................................................................................... 6
Design Alternatives.......................................................................................................................... 7 2.1
2.2
Preliminary Treatment Alternatives.................................................................................... 7 2.1.1
Bar Screen .............................................................................................................. 7
2.1.2
Grit Chamber ......................................................................................................... 8
Primary Treatment Alternatives .......................................................................................... 9 2.2.1
2.3
2.4
2.5
Secondary Treatment Alternatives .................................................................................... 10 2.3.1
Maturation Ponds ................................................................................................. 10
2.3.2
Constructed Wetlands .......................................................................................... 11
Sludge Handling Alternatives ........................................................................................... 11 2.4.1
Background .......................................................................................................... 11
2.4.2
Sludge in Current Septic Tank ............................................................................. 11
2.4.3
Sludge Produced by Treatment System ............................................................... 12
Alternative Selection......................................................................................................... 12 2.5.1
3.
Waste Stabilization Ponds ..................................................................................... 9
Design of Facultative Ponds ................................................................................ 12
Additional Considerations ............................................................................................................. 14 3.1
Biogas Feasibility Study ................................................................................................... 14
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3.2 4.
5.
High Chlorine Concentrations .......................................................................................... 14
Budget ............................................................................................................................................ 15 4.1
Project Cost ....................................................................................................................... 15
4.2
Prototype Budget .............................................................................................................. 16
Conclusion ..................................................................................................................................... 16
Acknowledgements ..................................................................................................................................... 18 Bibliography ............................................................................................................................................... 19 Appendix A: Gantt Chart ............................................................................................................... 21 Appendix B: Wastewater System Loads........................................................................................ 24 Appendix C: Facultative Pond and Wetland Area Calculations .................................................... 28 Appendix D: Bar Screen Calculations ........................................................................................... 33 Appendix E: Soil Percolation Calculations.................................................................................... 34
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List of Figures Figure 1: Map of Ecuador ............................................................................................................................. 4 Figure 2: Bar Screen ..................................................................................................................................... 8 Figure 3: Grit Chamber Design..................................................................................................................... 8 Figure 4: Anaerobic Pond Cross Section ...................................................................................................... 9 Figure 5: Facultative Pond Process Components ........................................................................................ 10 Figure 6: Facultative Pond Biological Process ........................................................................................... 10 Figure 7: Constructed Wetland Cross Section ............................................................................................ 11 Figure 8: Biogas Collection Diagram ......................................................................................................... 14 Figure 9: Process Schematic ....................................................................................................................... 16 Figure 10: Preliminary Pond Location on Site............................................................................................ 17
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List of Tables Table 1: Construction Cost of Facultative Ponds........................................................................................ 15 Table 2: Design and Engineering Costs ...................................................................................................... 15 Table 3: Total Project Cost ......................................................................................................................... 15 Table 4: Prototype Budget .......................................................................................................................... 16 Table 5: Equivalent Persons Calculations for Non-patients ....................................................................... 25 Table 6: Equivalent Persons Calculations for Hospital Patients ................................................................. 26 Table 7: Calculation of Daily Hospital Waste Stream and BOD Flow Rates ............................................. 27 Table 8: Average and Peak Daily Flow Calculations ................................................................................. 27
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1. Introduction 1.1 The Team Pure Pastaza is comprised of four senior students at Calvin College, each of whom will graduate in the spring of 2011 with a Bachelor of Science Degree in Civil and Environmental Engineering. The team is committed to utilizing engineering within a Biblical framework to promote social justice and environmental sustainability both locally and abroad. This commitment is manifested in a project to design a wastewater treatment system for a hospital in Shell Mera, Ecuador.
Ben Vander Plas
Rachel Koopman
Sungmin Youn
James Dykstra
1.2 Team Bios Ben Vander Plas Ben’s hometown is in Richland, Michigan and he currently resides in Grand Rapids, Michigan. He has gained valuable home construction experience working with Habitat for Humanity in Battle Creek, MI for the past two summers. Using engineering to provide for the needs of others is the purpose of his education. Plans following graduation include engineering employment or mission work, depending on God’s leading in the future.
Rachel Koopman Rachel is most recently from Rochester, MI but spent most of her life in Shanghai, China. Last summer Rachel worked for NTH Consultants in their Environmental Compliance group where she learned that environmental consulting is her true passion. After graduation she is getting married and hopes to pursue a career in environmental engineering.
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Sungmin Youn Sungmin grew up in Seoul, South Korea and currently resides in Grand Rapids, Michigan. He enjoys working on this project because he sees the possibility of significant improvements to the quality of human life and the surrounding environment in the future. Through this design project, he became more certain about pursuing in-depth studies of biological and physical treatment processes at the graduate level. He would like to pursue a graduate degree in environmental engineering to become better prepared for a lifetime of engineering service that addresses interesting, dynamic, and life-changing problems.
James Dykstra James is originally from Kalamazoo, Michigan and currently resides in Grand Rapids, Michigan. He has three summers of experience working in the environmental engineering field with Kieser & Associates in Kalamazoo, Michigan. There he was involved with stormwater treatment, watershed management, and low impact development projects. He also performed groundwater and surface water quality monitoring. After graduation, he is open to pursuing further career opportunities at Kieser and eventually working in Spanish-speaking countries doing development work. He is passionate about environmental issues, social justice and third-world development.
1.3 Project Context Pure Pastaza has partnered with Hoy Cristo Jesús Bendice (HCJB), a non-profit mission organization committed to Biblical values and community development principles, to design a wastewater treatment system for a hospital in Shell, Ecuador. This project is part of Engineering Senior Design (ENGR 339/340) at Calvin College. Engineering 339 is the first course in the senior design project sequence. Emphasis is placed on design team formation, project identification, and production of a feasibility study. Students focus on the development of task specifications in light of the norms for design and preliminary validation of the design by means of basic analysis and appropriate prototyping. Lectures focus on integration of the design process with a Christian worldview, team building, and state-of-the-art technical aspects of design. Engineering 340 is the second course in the senior design project sequence. Emphasis is placed on the completion of the design project initiated in Engineering 339. A final presentation is given at the May senior design project program.
1.4 HCJB Background HCJB's water engineers and health professionals are dedicated to improving the health of rural communities through clean water and preventive health care. In each project, they depend on voluntary support to carry out their work and the benefiting communities bear significant responsibility for the resources to obtain clean water. The mission of HCJB is, “…to enable communities to help themselves through the facilitation of Christ centered sustainable community development. Through the provision of water, sanitation and hygiene education projects we seek to realize permanent health improvements in the communities with whom we work at both a physical and spiritual level.” They work with communities, international, national and local organizations to set up projects that are sustainable, low cost, use appropriate technology and are easily operated and maintained by the community without outside dependency.
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1.5 Problem Statement Hospital Vozandes del Oriente (HVO) is a hospital located in Shell, Ecuador built and maintained by HCJB Global. Currently, the wastewater treatment system for the hospital and other buildings on the property includes a pipe network and collection system leading to a septic tank. The existing septic tank is overloaded and therefore does not have an acceptable residence time. Furthermore, there is no leaching field, which means that effluent from the septic tank passes directly into the Motolo River south of the hospital without receiving further treatment. The condition of the tank is currently unknown and it may not be sealed properly and therefore leaking contaminants into the ground. HCJB has researched expanding the septic tank capacity and concluded that in order to handle the current flow, the tank should be four times its current size. This option has been deemed infeasible due to cost and site requirements. There is also no appropriate method or suitable location established for the disposal of produced sludge. The hospital has experienced issues with the local municipality regarding sludge disposal which led to the sludge being deposited directly into the river. The hospital is therefore in need of an alternative method for treating the wastewater and disposing of the sludge produced.
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1.6 Project Background 1 Shell Mera is a town located in the Eastern foothills of the Ecuadorian Andes approximately 94 miles Southeast of Quito (Figure 1). Today, Shell is a large town of 5,000 people, with a church, hospital, schools, hotels, and a missionary guest house making it a worthwhile destination. The economy is mostly composed of small businesses and agriculture, but the town’s beauty is in its large variety of plants, insects, and landforms. The town is located at an elevation of 3,500 feet (1000 m) and has a moderate climate of rainy and 60°F, averaging around 48 inches of rainfall per year. HCJB global built the 28 bed mission hospital in May of 1958 and has since Figure 1: Map of Ecuador1 upgraded the facility. Most of the physicians at HVO are board-certified Americans, but host a family medicine residency for Ecuadorian nationals. A full range of family medicine services including obstetrics, general surgery, and orthopedics are offered to the people of Shell and the surrounding area at HVO. Classical “tropical diseases” are frequently diagnosed and treated including tuberculosis, malaria, dengue, intestinal parasites, and bacterial dysentery. The hospital also promotes a health program that teaches the surrounding villages in the jungle how to care for their villages. More specifically the health program teaches these communities how to find, prevent and treat falciparum malaria.
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1.7 Design Norms 1.7.1
Stewardship
With God’s gift of creation to humanity comes the responsibility of caring for the earth and its resources. This responsibility involves a respect for the health and well being of others today as well as of future generations. The HVO wastewater treatment system is designed to protect the surrounding environment and health of residents while conserving the available natural and economic resources. HVO is devoted to protecting the health of residents in Shell through medical care. Developing a solution to the problem of environmental contamination in the area is a step toward improving the health of the patients along with the rest of the population. The design assists the mission of the hospital by promoting preventative healthcare, a healthy environment and setting an example for others to follow. It is essential to understand the needs of the hospital to avoid overdesign of the system and the resulting unnecessary costs. HVO must carefully allocate appropriate funds to each area of its ministry, and a wastewater treatment system is no exception. By selecting the most cost effective solution to the problem, the economic resources of the hospital are conserved. Natural resources available to the hospital must also be used wisely. The design is meant to efficiently use the property owned by HVO without damaging the quality of the land. The selection of alternatives involves consideration of the smallest footprint possible. The location of system components seeks to keep the most useful land unaltered. Water conservation is also an important aspect being considered. By eliminating wasteful practices of water usage, the hospital and surrounding residences promote better stewardship of resources.
1.7.2
Cultural Appropriateness
When considering a design it is very important to have knowledge of the culture in which it is being implemented. It is easy for engineers to think in terms of what is acceptable and functional in their particular location or cultural background. However practices need to be modified to develop an effective and successful design for use in a different cultural setting. This idea heavily influences the design of the HVO wastewater treatment system. In general wastewater treatment in Ecuador is not a high priority. For example, the city of Shell discharges raw sewage into open water. This is an important consideration since public perception of the design has a great impact on its sustainability. Part of the goal of the design is to educate and promote awareness of the importance of wastewater treatment. Municipal officials have been considering developing a treatment process for the city’s wastewater. If residents of the city see that this can be done simply, effectively, and with clear benefits at HVO, there may be an increase in the priority level of treating sewage. Although the city of Shell is relatively urban and developed, much of the water treatment technology used in developed countries is inappropriate in this setting. The technical background and skilled labor necessary to operate certain types of advanced water treatment processes is not available locally. The hospital also does not have the economic means to construct and operate large scale and sophisticated 5
machinery. There have been many cases in which systems requiring complex maintenance have been implemented in developing countries only to be neglected and put out of commission (Mara 2004). In order for the design to have adequate sustainability, the problem of difficult maintenance must be avoided. Although more advanced technologies may have higher treatment capabilities, the system for HVO will require simple construction and very little maintenance therefore ensuring continued successful operation for the life of the design.
1.7.3
Transparency
A comprehensive understanding of a design is important for the designers as well as the users and other affected parties. The ability of users to maintain and operate the design depends on their knowledge of the technology involved. Pertinent information must be communicated to those affected by using a transparent design. An effort must be made to educate users and local residents about the process to ensure the HVO treatment system is sustainable. As wastewater treatment is very uncommon in Ecuador there is likely limited knowledge regarding its purpose and available methods. The goal of the system must be clear to those using the hospital and surrounding residences. It is also important for operators at HVO to understand the treatment process well enough to know essential maintenance practices and how to monitor the system performance regularly. This will avoid problems of overloading or discontinued use of the treatment system. Educating hospital patients about the design will help spread knowledge of wastewater treatment in the surrounding area. This can be done with public displays within the hospital describing the purpose and technology of the process. The result is an aid in the transformation of the cultural attitude toward wastewater treatment.
1.8 Objectives The main objective of this design project is to present a preliminary design for a wastewater treatment system for the hospital and surrounding area. In addition, a suitable method for sludge handling is studied and recommended. The following criteria have been established as the constraints for the design: •
Low capital, operation, and maintenance costs
•
Minimum use of mechanical and electrical parts to ensure ease of operation and maintenance
•
All parts and materials should be available locally
•
Due to the lack of a reliable power source, design must be capable of operating without electricity
•
Design must not require the use of any chemicals or materials that might damage the downstream environment
•
As there is limited space available on the hospital property, design footprint should be minimized 6
•
The effluent of the system must satisfy reasonable water quality standards
•
Sludge production should be minimized
•
Design must be culturally acceptable to the local population
•
Design should not pose any risk of harm to the system operators or users
The quality of the effluent stream is constrained to a BOD concentration of 2 mg/L when mixed in the receiving water. Assuming an effluent dilution of eight volumes of river water, the maximum allowable effluent BOD concentration of the treatment system is 20 mg/L (UK Royal Commission Standards). Stabilization ponds are assumed to have a suspended solids removal similar to that of BOD removal (8090%). As the Motolo River is likely to have a high natural concentration of suspended solids, it is unnecessary to set TSS standards for the effluent in this case. Along with a wastewater treatment system, an appropriate sludge handling method must be developed that meets the same design constraints listed above. In addition, the expected sludge accumulation in a new wastewater treatment system also needs to be handled appropriately to meet the design constraints. The feasibility of sludge reuse is studied in this design project. The possibility of using the existing sludge as microbial seeds in the waste stabilization ponds is also considered. In the near future, HVO will expand the size of the hospital, which in turn to increase the number of patients. Therefore, the designed wastewater treatment system and sludge handling method must be able to treat the projected flows and loads. From data of the increased number of patients for the last twenty years, the growth rate for is predicted to be about one percent per year. To be conservative, all calculations are based on 20 percent growth rate over a 20 year project life.
2. Design Alternatives 2.1 Preliminary Treatment Alternatives 2.1.1
Bar Screen
Preliminary treatment of the wastewater begins with removal of coarse solids with bar screens. A basic schematic of a bar screen is shown in Figure 2. The purpose of screening is to prevent blockages and damage to downstream components. Although mechanically raked bar screens are available, the design for the HVO system uses a manually raked system. This adheres to the design criteria of little to no power usage. However there is required maintenance involving the cleaning of the bar screen and disposal of the resulting solid waste (Mara 2004). In addition to the flow path through the bar screen a bypass allows wastewater to continue flowing in the event of blockages or rises in upstream water levels. Regular cleaning of the bar screen helps prevent overflow problems in this component of the system. Based on calculations shown in Appendix D most commercial bar screen designs will be acceptable for the design due to the relatively low flow rates in the system. The HVO treatment system will use a manually raked bar screen in a position upstream of the primary treatment of the waste stream. 7
Fine screening is also commonly used in the preliminary treatment of wastewater. This requires complex mechanical screens and is not a necessary component of treatment. Therefore fine screening has been determined to be infeasible for the HVO treatment system.
Figure 2: Bar Screen 2
2.1.2
Grit Chamber
The second component of preliminary treatment is grit removal. The objective is to prevent grit and other inorganic solids from entering downstream processes and causing abrasion damage. A grit chamber is used to slow the flow and allow larger particles to settle out (Mara 2004).. A basic design of this apparatus is shown in Figure 3. There is a centrifugal push toward the wall (A) followed by gravity pull (B) and sweep toward the center (C). Heavy particles fall to the bottom (D) while light material stays in suspension (E). The removed grit particles can be buried without the risk of contamination due to the lack of organic material. The HVO system would likely use a gravity fed vortex design. However if more information is obtained characterizing the actual content of grit material in the HVO waste stream, this component may be eliminated to reduce unnecessary system costs
Figure 3: Grit Chamber Design 3
2 3
Mara 2004 www.aerresearch.com/html/GritSystemDesignGuide.pdf
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2.2
Primary Treatment Alternatives
2.2.1
Waste Stabilization Ponds
2.2.1.1
Background
Following the removal of coarse solids and inorganic material in the preliminary treatment, the wastewater stream enters the waste stabilization ponds. These are large shallow basins which treat wastewater by natural processes involving bacteria and algae. There are three main types of stabilization ponds which use different processes for treatment. These types can be used in series or separately (Mara 2004). 2.2.1.2
Anaerobic Ponds
An anaerobic pond is generally the first of a series of ponds and is relatively deep (2-5m). The primary purpose of anaerobic ponds is BOD (biochemical oxygen demand) removal. Due to the high organic loading there is no dissolved oxygen or algae in the pond. Retention times are generally short (~1 day) depending on the initial BOD loading of the influent wastewater and the surrounding temperature (Mara 2004). Issues of odor are understood to be a significant problem, especially if careful maintenance is not observed. Safety is also a concern with the inherent drowning hazard of a deep body of water. Figure 4 shows a cross section of a typical anaerobic pond.
Figure 4: Anaerobic Pond Cross Section 4
2.2.1.3
Facultative Ponds
Facultative ponds can be used as primary or secondary treatment. Like anaerobic ponds they are designed for BOD removal. Unlike anaerobic ponds they are relatively shallow (1.0-1.8m) to allow for the growth of algae near the surface (top ~300 mm). The algal photosynthetic activities generate oxygen for the BOD removal. This process is dependent on temperature, mixing, and pond inlet design. Wind provides a portion of necessary mixing to allow algae to move into the zone of effective light penetration. Any fence surrounding the pond must allow air to move through freely (Mara 2004). The process components of a facultative pond are shown in Figure 5. The biological process involved is shown in Figure 6. This design alternative was selected for the HVO treatment system due to economic advantages as well as a lack of maintenance required.
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Figure 5: Facultative Pond Process Components 5
Figure 6: Facultative Pond Biological Process
2.3
Secondary Treatment Alternatives
2.3.1
Maturation Ponds
The objective of maturation ponds is to remove fecal bacteria and viruses. The process is mostly aerobic although some algal growth takes place. This can provide a level of quality suitable for water re-use in agriculture or aquaculture (Mara 2004). Since HVO has no plans of reusing water, effluent wastewater will be discharged into the Motolo River. Therefore a maturation pond provides an unnecessary level of treatment and is not included in the system design.
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2.3.2
Constructed Wetlands
The processes of natural wetlands are applied to constructed wetlands for the treatment of wastewater. Rooted aquatic plants called ‘macrophytes’ are grown in gravel beds and usually receive wastewater after some form of primary treatment. A cross section of a constructed wetland design can be seen in Figure 7. The advantage of this secondary treatment is the removal of suspended solids and nutrients. Wetlands are also occasionally preferred based on aesthetic reasons. This alternative is not implemented on the basis of unnecessary treatment for this specific case as well as the high cost and land use.
Figure 7: Constructed Wetland Cross Section 6
2.4 Sludge Handling Alternatives 2.4.1
Background
There are two situations where sludge handling must be addressed, one includes the sludge build up in the current septic tank, and the other includes the future sludge build up in the facultative pond. The current septic tank contains approximately 6 m3 of sludge (20% of the septic tanks volume) which has an environmental quality that is unknown. In the past HVO has experienced some resistance from the local municipality when attempting to landfill the sludge, this resistance led to the dumping of the sludge directly into the Motolo River which defeated the purpose of the septic tank.
2.4.2 2.4.2.1
Sludge in Current Septic Tank Land Application
One potential use of the sludge currently in the septic tank includes land application. Due to the lack of knowledge regarding the quality of the waste and the fact that HVO does not have agricultural land there is not much need or use for land application other than potentially selling the sludge for land application elsewhere.
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2.4.2.2
Microbial Seed
Another potential usage of the sludge currently in the septic tank includes using it to seed the facultative pond. These ponds need to be seeded with old waste in order to develop the necessary microbial population to begin the decomposition of the waste. This option is the most feasible given the lack of agricultural land and resistance from the local municipality to landfill.
2.4.3 2.4.3.1
Sludge Produced by Treatment System Background
During the first few years the facultative pond is in use, sludge will accumulate linearly in the pond but once the pond reaches equilibrium, the sludge will decompose at approximately the same rate as it enters the system. This equilibrium depends of maintenance of the surface water and pond embankments. Removal of floating scum and macrophytes from the surface water maximizes the photosynthesis necessary for treatment and prevents fly and mosquito breeding. The vegetation on the embankments must be cut and pruned as needed to prevent the generation of mosquito breeding habitats. The use of slow growing grass or vegetation will minimize the frequency of this task. The sludge depth should be measured once a year to ensure that it is no more than one third the design depth of the pond, if it is greater than one third of the depth it may interfere with the natural decomposition and treatment processes of the pond. In this case the pond should be partially dredged. 2.4.3.2
Alternatives
Typical facultative ponds need to be cleaned out every 8-20 years. In order to clean out a facultative pond the first cell must be closed off by closing two gates and allowing the sewage to drain directly into the next cell. All the water in the first cell is then drained completely and the sludge is dried by the heat of the sun. The length of time for drying varies depending on the weather and climate, for Shell, Ecuador it would depend on the time of year and amount of rainfall at the time. After the sludge is dried it must be removed by a vac truck or shovels and either land applied or land filled. In this case the sludge will be stabilized and no longer harmful to the residence in the surrounding area or the environment and therefore there should be no issues with the local municipalities in terms of land filling. If resistance is met then selling the sludge for land application elsewhere is the next best option. This process of drying out the cells must then be repeated for the rest of the cells in the pond until the entire pond has been dredged.
2.5 Alternative Selection 2.5.1
Design of Facultative Ponds
The design for the HVO treatment system uses a series of facultative ponds as the primary treatment. Facultative ponds have the advantage of simplicity of construction and maintenance. Mostly unskilled labor can be used for the pond maintenance. This includes removal of scum and vegetation from the pond surface and banks, keeping inlets and outlets clear, and repairing any damage to the embankments. There are minimal problems with mosquito breeding and odor as long as the system is properly maintained. Maintenance includes alternating flow paths to avoid stagnant regions, restoring embankments, and drying and excavating of accumulated sludge after a given time period. The minimum land area required
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depends on the BOD of the wastewater entering initially (BOD i ), the peak flow rate (Q), and the surface BOD loading (λ s ). 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 =
𝐵𝐵𝐵𝐵𝐵𝐵𝑖𝑖 𝑄𝑄 λ𝑠𝑠
The surface loading is designed as a maximum mass rate per area that can be applied before the pond becomes anaerobic, which constitutes failure. A design value including a factor of safety is determined using the mean air temperature (T) of the coldest month in Shell, Ecuador. λ𝑣𝑣 = 350(1.107 − 0.002𝑇𝑇)𝑇𝑇−25
The retention time is determined from the resulting area, depth of the pond (~1.5m), and the mean flow (Q m ) adjusted for rate of evaporation. 𝜃𝜃 =
𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 ∗ 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷ℎ 𝑄𝑄𝑚𝑚
The depth of the pond liquid must lie in the range of 1-1.8m. The lower depth limit prevents the emergence of vegetation leading to ideal conditions for mosquito breeding. The upper limit keeps the pond from becoming predominantly anaerobic, which would nullify the design safety factor for a fluctuating load. The influent BOD concentration is estimated at 151 mg/L. The quality of the effluent is constrained to a BOD concentration of 20mg/L (UK Royal Commission Standards). Stabilization ponds are assumed to have a suspended solids removal similar to that of BOD removal (80-90%). As the Motolo River is likely to have a high natural concentration of suspended solids, it is unnecessary to set TSS standards for the effluent in this case. An area of 291m2 is required for the first receiving pond at a depth of 1.5m. More detailed calculations in Mathcad are shown in Appendix A. A compartmentalized structure of multiple ponds in series is used to successively treat the waste stream. Pipe networking and valves between each pond allow for control of different flow paths. Individual ponds can be taken out of service to be desludged while continuing flow through the remaining ponds. The piping system will allow water to drain from one pond while it is bypassed to allow drying. After being emptied of liquid and allowed to dry, the sludge produced is removed by manually excavating and transporting the material by wheelbarrow or other available hauling equipment. Soil percolation tests conducted by a previous engineering group at the hospital site give an estimated coefficient of permeability for the planned location of the pond. The soil is permeable enough to necessitate a liner for the pond bottom to prevent groundwater contamination. A 1-2ft liner of compacted clay contains the wastewater while preventing growth of reeds and other plants in the pond which would encourage mosquito breeding. The location of the pond is the furthest distance possible from residences to avoid potential odor or aesthetic problems. The perimeter is surrounded by a protective fence for safety of residents in the surrounding area. There is also space for vehicular access for regular maintenance and monitoring. 13
3. Additional Considerations 3.1 Biogas Feasibility Study Biogas is produced in every system where organic matter is decomposed. Many anaerobic wastewater treatment systems contain or are capable of containing a biogas collection system which is linked to a generator for energy production. In a facultative pond it is desirable to have an anaerobic pit over which the biogas collection system is placed. The system would consist of a floating composite cover made of a self-draining geomembrane material, inlet and outlet pipes and a combustion engine used as a generator to convert the gas into energy. An example of this system is found below in Figure 8.
Figure 8: Biogas Collection Diagram 7
The total amount of BOD 5 removed from the current loadings on the system is 4207 g/day under the assumption of 86.8% removal efficiency. Given that 0.0378 liters of biogas is produced per gram of BOD 5 removed it is found that for this system, approximately 159 L of biogas is produced per day. It is known that 0.006 kWh are produced per liter of biogas, using this conversion factor, approximately 0.04kW are produced per day under the current loading from HVO on the system. The small amount of energy produced by the system is not enough to justify the added construction and maintenance costs.
3.2 High Chlorine Concentrations HVO is currently using chlorine in large quantities for disinfection in the current septic tank. Members of the HCJB staff have expressed concerns about the effects of high levels of chlorine on the wastewater treatment process with respect to the oxidation of organic matter, as well as impacts on concrete material. Chlorine is commonly used as an inexpensive form of disinfection in wastewater treatment systems and will have no adverse effects on the oxidation of the organic matter. The presence of chlorine in the wastewater before treatment by the facultative ponds will allow for disinfection before the oxidation process occurs. The impact of chlorine on concrete should not be an issue; most pools throughout the 7
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world are made of concrete and contain high levels of chlorinated water. There is no known research to support that there are any adverse effects on concrete due to high levels of chlorine.
4. Budget Outlined below is the production cost in country and the team prototype budget.
4.1 Project Cost The final construction cost for this system of facultative ponds in Ecuador is approximately $14,985. The values used in this estimate are from different suppliers in the United States, the individual pricing for each part would need to be checked in country to approximate a more accurate number. Table 1 shows the cost of construction and materials for the facultative pond and Table 2 shows the design and engineering costs. The total cost of the project including contingency is $113,833 shown in Table 3. Table 1: Construction Cost of Facultative Ponds
Item PVC Piping
Quantity 100
Unit m
Unit Cost $20
Total Cost $2,000
Bentonite Clay
500
m2
$20
$10,000
Chain Link Fence Control Valves Labor
92 8 30
m days
$5 $50 $65
$460 $400 $1,950
Excavation
500
m3
$0.35
$175
-
-
$0
$0
Variable Costs
TOTAL
$14,985
Table 2: Design and Engineering Costs
Personnel Engineer Engineer Engineer Engineer
Quantity 210 210 210
Unit hr hr hr
Unit Cost $100 $100 $100
Total Cost $21,000 $21,000 $21,000
210
hr
$100
$21,000
TOTAL Table 3: Total Project Cost
Budget Component Construction Design and Engineering Contingency of 15% TOTAL
Cost $14,985 $84,000 $14,848 $113,833
15
$84,000
4.2 Prototype Budget The final prototype budget includes all necessary materials to make a 1:50 scaled model of the proposed design. The breakdown of the prototype budget is shown in Table 3 below. Table 4: Prototype Budget
Item Tarp [5-m x 7-m] PVC Piping Valves
Quantity 1 2 8
Unit m -
Unit Cost $3.60 $3 $20
Item Cost $3.60 $6 $160
Framing
10
m3
$7
$70
Gravel [20-lb bag]
1
-
$20
$20
TOTAL
$260
5. Conclusion In summary Pure Pastaza is designing and modeling a wastewater treatment system for the Hospital Vozandes del Oriente, a hospital sponsored and built by HCJB global. The current capacity of the septic tank is inadequate and results in essentially untreated wastewater discharging into the Motolo River. Pure Pastaza is proposing a facultative pond system connected directly to the current sewer line as the most feasible treatment option. Due to the lack of agricultural land in the area there is little need for fertilizer applied to surrounding land. This makes the facultative pond system advantageous since there is little to no sludge removal necessary. The system process including waste characteristics and estimated removal is described in Figure 9 below. The preliminary site plan is shown in Figure 10.
BOD = 151 mg/L
BOD = 20 mg/L Facultative Pond
Flow = 32 m3/day
TSS 80-90% Removal
Sludge: Land Application Figure 9: Process Schematic
16
Figure 10: Preliminary Pond Location on Site
One of the greatest advantages of the design is the minimal cost and labor for maintenance necessary to ensure the system operates properly. The total project cost has been estimated to be $113,833. This includes engineering design, construction and a 15% contingency. Establishing an effective wastewater treatment system will reduce the risk of water born diseases and provide a cleaner environment in years to come. It is the hope of Pure Pastaza that this wastewater treatment system will improve the quality of life and contribute to a healthier livelihood for the residents of Shell, Ecuador.
17
Acknowledgements We would like to thank the following people for their invaluable assistance during the preliminary design process: Professor David Wunder, Senior Design Advisor Professor Wunder has guided and mentored us throughout the semester, drawing upon his expertise in the environmental engineering field. Stephanie Smithers, HCJB Global Stephanie has been our contact in Ecuador and has provided us with data, information and helped to answer many of our questions about the site. Tom Newhof, Prein & Newhof Tom is our team’s industrial consultant and has provided us with valuable information from his first-hand experience with waste stabilization ponds in professional practice. He has also directed us to valuable contacts.
18
Bibliography Cotruvo, Joseph A., Gunther F. Craun, and Nancy Hearne. Providing Safe Drinking Water in Small Systems: Technology, Operations, and Economics. Boca Raton: Lewis, 1999. Print. Mara, Duncan D. Sewage Treatment in Hot Climates. London: Wiley, 1976. Print. Mara, Duncan D. Domestic Wastewater Treatment in Developing Countries. London: Earthscan, 2004. Print. Mehtar, Shaheen. Hospital Infection Control: Setting up with Minimal Resources. Oxford: Oxford UP, 1992. Print. Niewoehner, John, Ron Larson, Elfadil Azrag, Tsegaye Hailu, and Jim Horner, Peter VanArsdale. "Opportunities for renewable energy technologies in water supply in Developing country villages." NREL Technical Monitor (1997). Print. Shilton, Andy. Pond Treatment Technology. London: IWA Pub., 2005. Print. "Sludge Treatment Reuse and Disposal." United Nations Environmental Program. Web. 10 Nov. 2010. .
19
Appendices
20
Appendix A: Gantt Chart
21
ID
Task Name
Duration
Start
Finish 26
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
First Semester PPFS Outline--Table of Contents (email to team Advisor) Work Breakdown Structure (WBS) (email to team Advisor) Innotec Grant Proposal Scheduled WBS (email to team Advisor) Research - High Concentration Chlorine Estimating waste load Elevator Presentation Research low cost low energy wastewater treatment options Project Brief to Industrial Consultant (with cc to team Advisor) Project web-site (posted) Preliminary Cost Estimate (email to team Advisor) Draft PPFS to Team Advisor Revised/updated project web-site (and new poster if major changes) PPFS submit to Team Advisor and post on Web Page as PDF Preliminary Design Memo submit to Team Advisor (as required) Interim Second Semester Pond Layout Design Hydraulic Analysis of Pipe and Pond System Hydraulic Design Based on the Analysis Bar Screen Calculations and Design Website Update Oral Presentations Model Build Updated Posters and Demos Meet with Industrial Consultant Individual Notebook Check Team Description for Banquet Program Website Update Draft Design Report for CEAC Review Scheduling Reviews (Individual Team) Draft Design Report for Faculty Review Project Night Poster Oral Presentations Senior Banquet and Projects Night Website Upgraded to Final, Notebooks Turned In, Course Evaluation Final Design Report Due
Project: Gantt Chart.mpp Date: Sat 12/4/10
Oct '10 3
50 days Mon 10/4/10 Fri 12/10/10 2 days Mon 10/4/10 Tue 10/5/10 5 days Mon 10/4/10 Fri 10/8/10 10 days Mon 10/4/10 Fri 10/15/10 0 days Mon 10/18/10 Mon 10/18/10 14 days Mon 10/18/10 Thu 11/4/10 14 days Mon 10/18/10 Thu 11/4/10 3 days Mon 10/18/10 Wed 10/20/10 26 days Mon 11/1/10 Mon 12/6/10 3 days Mon 10/18/10 Wed 10/20/10 4 days Wed 10/20/10 Mon 10/25/10 5 days Mon 11/8/10 Fri 11/12/10 11 days Mon 11/1/10 Mon 11/15/10 6 days Wed 11/17/10 Wed 11/24/10 6 days Mon 11/22/10 Mon 11/29/10 5 days Mon 12/6/10 Fri 12/10/10 15 days Wed 1/5/11 Tue 1/25/11 74 days Mon 1/31/11 Wed 5/11/11 6 days Mon 1/31/11 Mon 2/7/11 5 days Mon 2/7/11 Fri 2/11/11 5 days Mon 2/14/11 Fri 2/18/11 5 days Mon 2/14/11 Fri 2/18/11 5 days Mon 2/14/11 Fri 2/18/11 8 days Wed 2/23/11 Fri 3/4/11 35 days Mon 3/7/11 Fri 4/22/11 6 days Wed 3/2/11 Wed 3/9/11 10 days Mon 3/7/11 Fri 3/18/11 3 days Mon 3/14/11 Wed 3/16/11 3 days Wed 3/16/11 Fri 3/18/11 5 days Mon 4/4/11 Fri 4/8/11 6 days Mon 4/4/11 Mon 4/11/11 5 days Mon 4/18/11 Fri 4/22/11 6 days Wed 4/20/11 Wed 4/27/11 5 days Mon 4/25/11 Fri 4/29/11 10 days Mon 4/25/11 Fri 5/6/11 1 day Sat 5/7/11 Sat 5/7/11 1 day Mon 5/9/11 Mon 5/9/11 1 day Wed 5/11/11 Wed 5/11/11
Task
Milestone
External Tasks
Split
Summary
External Milestone
Progress
Project Summary
Deadline
Page 1
10
17
10/18
24
Nov '10 31 7
14
21
Dec '10 28 5
12
Project: Gantt Chart.mpp Date: Sat 12/4/10
19
26
Jan '11 2
9
16
23
Feb '11 30 6
13
20
Mar '11 27 6
13
20
27
Apr '11 3
Task
Milestone
External Tasks
Split
Summary
External Milestone
Progress
Project Summary
Deadline
Page 2
10
17
24
May '11 1
8
15
Appendix B: Wastewater System Loads
24
Table 5: Equivalent Persons Calculations for Non-patients Non-patients
Missionary / Visitor Residences
Duplexes
1
Live & Work 2 2 2 2 2 1 2 2 2 2 2
Adults Work2
3
Live
Visit
4
Children School Age Below School Age6 5
2 2 2 2 3 3
1
1 1
2 2 2 2
Person·days 2.0 3.0 3.0 3.0 3.0 3.7 4.0 3.3 3.3 3.3 3.3
Visiting Staff Quarters
6
6.0
Casitas
4
4.0
Non-resident Missionaries
5
1.7
Staff
63
21.0
Inpatients friends/family Outpatients friends/family Emergency friends/family Laundry Restaurant - hospital Restaurant - the bar
10 40 23
1.3 5.0 2.9
Notes / assumptions
European/other western North American North American Current family homes are occupied by the Wolffs, Benedicks, North American Kappens, Tachneys, Umbles, Bartons, Martins. North American North American North American North American There are 4 duplexes and it has been assumed that they are North American all half-full as sometimes they could all be occupied with 8 North American people and sometimes with none. North American These are the accomodations for the visiting interns and Ecuadorian - Mestizo residents. There are 6 quarters and they are always full. There are 8 casitas. Assume 2 are occupied with 2 people in Ecuadorian - Indigenous each. There are 5 missionaries who work in the hospital but live North American outside of the hospital water system. There are 63 staff who work a variety of hours. Over a month all work 160 hours except 5 nurses who each work Ecuadorian - Mestizo 120 hours/month. All staff get two weeks holiday a year as a national entitlement. Ecuadorian - Mestizo Assume that each patient has one visitor who stays for 3 Ecuadorian - Mestizo hours. Ecuadorian - Mestizo / Indigenous No info Ecuadorian - Mestizo No info Ecuadorian - Mestizo No info Ecuadorian - Mestizo
KEY 1 2 3 4 5 6
Those who both live on the hospital property and work at the hospital, 24-hr contribution to hospital sewer system Those who work in the hospital but live away from the hospital, 8-hr contribution to hospital sewer system Those who live on the hospital property but don't work at the hospital, 16-hr contribution to hospital sewer system Visitors to the hospital, 3-hr contribution to hospital sewer system School age children will be in school for 8 hours and may return home for lunch, 16-hr contribution with a 0.75 scaling factor Assumed to be on hospital property all day, 24-hr contribution with a 0.5 scaling factor Water used comes from the hospital system but discharges into the town sewer system
Summary Total equivalent population = Water Usage (m3 / person·day) = Water Usage (m3 / day) =
72.8 0.045 3.3
Nationality
Table 6: Equivalent Persons Calculations for Hospital Patients Patients Visitors / day Person·days Notes 1 40 5 Assume 3 hours per patient. Outpatients 2 23 23 Assume 24 hours per patient. Emergency 10 20 Assume 48 hours per patient. Inpatients3 1 2 3
1200 outpatients per month (40/day) 700 emergency patients per month (23/day) Based on an average value for the number of inpatients per day Summary Total equivalent population = 48.3 Water Usage (m3/person·day) = 0.5 Water Usage (m3/day) = 24.2
Nationality Ecuadorian - Mestizo / Indigenous Ecuadorian - Mestizo / Indigenous Ecuadorian - Mestizo
Table 7: Calculation of Daily Hospital Waste Stream and BOD Flow Rates Water Usage
Type of Person
3
[m /person·day]
Hospital Patients Non-patients
0.5 0.045
BOD Production [g/person·day] 40 40 TOTAL
Table 8: Average and Peak Daily Flow Calculations Average Flow Growth rate per Project life with expansion year [years] 3 [m /day] 20 32.1 0.9%
1
Hospital Waste Stream1
Equivalent Population
Water Usage [m /day]
[m /day]
BOD [g/day]
48.3 72.8 121.2
24.2 3.3 27.4
23.9 3.2 27.2
1933 2913 4847
Peak Factor 6.29
Based on 99% of water used entering waste stream
3
Peak Daily Flow 3
[m /day] 202
3
Appendix C: Facultative Pond and Wetland Area Calculations Pond and Constructed Wetland Preliminary Calculations Design Parameters Estimated average wastewater flow rate with expansion of 20% 3
m
Qavg := 32.1 day
Equivalent population served (population estimates spreadsheet) P := 121.2
Peak factor (Mara 2004, eqn. 7.5) −1
PF := 14⋅ P
6
= 6.293
Maximum wastewater flow rate 3
m
Qmax := Qavg ⋅ PF = 202.015⋅ day
Mass of BOD per person per day kg BODmass := .040 day
Mass of BOD from population per year kg BODmass_tot := BODmass⋅ P = 4.848⋅ day
Influent BOD concentration (average) BODi :=
BODmass_tot Qavg
= 151.028⋅
mg L
Temperature (average of coldest month, °C) Ts := 14.4
28
Primary Alternative 1: Anaerobic Pond Volumetric loading (Mara 2004, Table 10.1) 1
(
)
λ v := 10⋅ Ts + 100 ⋅
1000
⋅ kg = 0.244⋅
3
m ⋅ day
kg 3
m ⋅ day
Designed pond depth (2 to 5m) Da := 2m
BOD removal of anaerobic pond (Mara 2004, Table 10.1) BODra :=
(2⋅ Ts + 20) 100
= 0.488
Area of pond (if retention time is greater than one day) BODi⋅ Qavg
A a :=
λ v ⋅ Da
2
= 9.934 m
Retention time (Mara 2004, eqn. 10.2) θa :=
A a⋅ Da
Qavg θa = 0.619⋅ day
Minimum retention time θa1 := 1day
Area of pond (if retention time is less than one day) A a1 :=
(Qavg⋅ θa1) Da
2
= 16.05 m
29
Primary Alternative 2: Facultative Ponds First Facultative Pond in Series BOD surface loading with safety factor (Mara 2004, eqn. 11.3)
(
λ sf := 350⋅ 1.107 − 0.002⋅ Ts
λ sf = 0.016⋅
)
T s − 25
kg
⋅
2
10000m ⋅ day
kg 2
m ⋅ day
Minimum required area of facultative pond 1 A f1 :=
BODi⋅ Qavg λ sf
2
= 307.686 m
Designed depth of facultative pond (must be 1.0 to 1.8m) Df := 1.5m
Net evaporation rate erate := 5
mm day
Effluent flow from facultative pond 1 Qe1 := Qavg − 0.001⋅ erate⋅ A f1
Mean flow (avg of influent and effluent)
(
)
Qm1 := 0.5⋅ Qavg + Qe1
Retention time of pond 1 θf1 :=
(Af1⋅ Df ) Qm1
= 14.378⋅ day
First-order rate constant for BOD removal (for 14.4°C) kfp := 0.3day
−1
T s − 20
⋅ 1.05
= 0.228⋅ day
−1
Effluent BOD concentration of pond 1 BODi mg BODefp1 := = 35.269⋅ 1 + kfp ⋅ θf1 L
30
BOD removal of pond 1 BODrf1 := 1 −
BODefp1 BODi
= 0.766
Second facultative pond in series Minimum required area of facultative pond 2 A f2 :=
BODefp1⋅ Qm1
2
= 71.851 m
λ sf
Effluent flow from facultative pond 2 Qe2 := Qe1 − 0.001⋅ erate⋅ A f2
Mean flow (avg of influent and effluent)
(
)
Qm2 := 0.5⋅ Qe1 + Qe2
Retention time of pond 2 θf2 :=
(Af2⋅ Df ) Qm2
= 3.358⋅ day
Effluent BOD concentration of pond 2 BODefp1 mg BODefp2 := = 19.966⋅ 1 + kfp ⋅ θf2 L
BOD removal of pond 2 BODefp2 BODrf2 := 1 − = 0.434 BODefp1
Total BOD removal of two ponds in series BODrftot := 1 −
BODefp2 BODi
= 0.868
31
Secondary Alternative: Constructed Wetland Porosity of gravel bed (estimate) ε gravel := 0.4
Depth of constructed wetland (commonly used value) Dcw := 0.6m
First-order rate constant kcw := 68.6⋅ ε gravel
4.172
T s − 20
⋅ 1.06
⋅ day
−1
= 1.082⋅ day
−1
Retention time (arbitrarily chosen) θcw := 0.5day
Area of constructed wetland A cw :=
(θcw⋅ Qavg) ε gravel ⋅ Dcw
2
= 66.875 m
Effluent BOD concentration BODecw := BODefp2⋅ e
− kcw⋅ θ cw
= 11.621⋅
mg L
BOD removal of constructed wetland BODecw BODrcw := 1 − = 0.418 BODefp2
Total BOD removal with facultative ponds and constructed wetland BODrtot2 := 1 −
BODecw BODi
= 0.923
32
Appendix D: Bar Screen Calculations Bar Screen Calculations Projected peak daily wastewater flow 3
m
Qpeak := 202 day
Assumed velocity m Vopt := 0.610 s
Net area required A req :=
Qpeak Vopt
−3 2
= 3.833 × 10
m
Net area ratio selected Ra := 0.667
Total wetted area required for channel A tot :=
A req Ra
−3 2
= 5.746 × 10
m
33
Appendix E: Soil Percolation Calculations Soil Percolation Tests Test 1 D1 := 4.75cm t1 := 60min
Coefficient of permeability for test 1 D1 −5m k1 := = 1.319 × 10 t1 s
Test 2 D2 := 13.5cm t2 := 101min
Coefficient of permeability for test 2 D2 −5m k2 := = 2.228 × 10 t2 s
Both tests result in a k coefficient greater than 10-6 m/s. Therefore the soil is permeable enough to need a pond lining to prevent groundwater contamination
34
