Senior Design Friday, April 23, 2010

1. Senior Design Friday, April 23, 2010 Chris Crock Aaron Lammers Brent Long Aaron Raak

2. Introduction • Carabuela, Ecuador has a flawed wastewater treatment system • Overloaded septic tank • Failed leaching field • Worked with HCJB to remedy the problem

3. Design Norms/Criteria • Effective Treatment • Culturally Appropriate • Sustainability • Site Appropriate • Low Cost • User Friendliness • Life of Design

4. Performance Requirements • Water Effluent • E. Coli count < 1000/100 mL • Biochemical Oxygen Demand (BOD) under 2.0 mg/L • Helminth eggs < 1 egg/100mL • (WHO standards set E. coli limit for leafy crops at 1,000/100mL; at this level of treatment other pathogens are assumed to be treated as well) • Sludge Effluent • 1000 E. Coli/gram solids • < 1 Helminth egg/ g solids • (With alfalfa, requirements need to only meet Class B sludge treatment. The US EPA determined that sludge which goes through one of six processes of significant reduction of pathogens may be applied to crops)

5. Functional Requirements • Handle the waste of the entire connected population for 20 yrs (1800 residents) • No electricity • The system must fit in 0.5 hectares • No chemical additives • Shall not need experts outside of the village for construction

6. General System Description General System Description • Bar Racks • Racks for large solids and objects • Two open channels with inclined bars • Dewatering plate for screenings • Grit Chamber • Settle out large particles (sand, grit, etc.) • Two open channels acting as grit chambers • Velocity control weir • Imhoff Tank • Settle out discrete organic materials and small particles • Store organics for later treatment • Anaerobic digestion of organic solids • Two tanks and settling chambers • Stabilization Lagoons • One facultative pond for Biochemical Oxygen Demand (BOD) reduction • Two maturation ponds for further BOD reduction and pathogen removal • Sludge Drying Beds • Treat sludge from Imhoff Tank and Grit Chamber • Four sludge drying beds for treatment cycling

7. Q = 192 m3/day BOD = 32 kg/day TSS = 48 kg/day FC = 2x107 /100 mL General System Description Q = 192 m3/day BOD = 32 kg/day TSS = 48 kg/day FC = 2x107 /100 mL Q = 192 m3/day BOD = 32 kg/day TSS = 48 kg/day FC = 2x107 /100 mL Q = 192 m3/day BOD = 16 kg/day TSS = 32.6 kg/day FC 2x107 /100 mL Bar Racks Grit Chamber Imhoff Tank Solids = 16 m3/month Q = 192 m3/day BOD = 0.51 kg/day TSS = 3.2 kg/day FC = 915 /100 mL Sludge Drying Bed Irrigation Stabilization Ponds

8. Environmental Design - Bar Rack • Important to remove larger solids • Bar Racks • Design depends mostly on clear space between bars • Velocity should be within 0.3—0.6 m/s • Openings between 20—50 mm • Rack for dewatering screenings • Redundant system

9. Structural Design - Bar Rack • Bar Racks Structural Design • Analysis of moments in the chamber • Designed steel and concrete for worst case loads • ACI 318M-05 Metric Building Code and Commentary • Steel reinforcing requirements • Concrete requirements

10. Environmental Design – Grit Chamber • Important to remove particulate • Grit Chamber • Design largely depends on the velocity the water (0.3 m/s) • Velocity controlled by Sutro weir • Grit removed is treated in sludge drying beds • Redundant system

11. Structural Design – Grit Chamber • Structural Design • Ultimate moment design • ACI 318M-05 Metric Building Code and Commentary • Two open channels and sutro weirs for redundancy

12. How an Imhoff tank works Sedimentation Outflow Inflow Anaerobic Digestion V V0 Stokes Settling Velocity Stokes Rearranged for Particle Removal Sedimentation Anaerobic Digestion

13. Environmental Design – Imhoff Tank • Environmental Design • Two tanks in one structure for redundancy • Sedimentation • Based off design guides and rules of thumb • Overflow rate of 600 gal/ft2 day • Retention Time of 2 hours • Digestion • Based on case study of Imhoff tank in Honduras • Sludge storage for 0.053 m3 per resident (95.4 m3) • Up to 6 months of sludge storage

14. Structural Design – Imhoff Tank • Structural Design • Analysis of forces and moments in tank • Finite Element Analysis (FEA) • Structural analysis • Designed steel and concrete to hold for highest loads • ACI 318M-05 Metric Building Code and Commentary • Similar to case study tank in Honduras • Final Design: 9.25m long x 8.6m wide x 7.5 m tall

15. Concrete Structures Walkthrough

16. Environmental Design – Lagoons • Loading Rates • BOD: 100mg/L • Helminth Eggs: 1000 Eggs/L • E-Coli: 2x107Coliforms/100mL • Reduced Rates • BOD: 2.7mg/L • Helminth Eggs: 0.10 Eggs/L • E-Coli: 915 Coliforms/100mL

17. Structural Design – Lagoons • Pond System • 1 Facultative Ponds • 2 Maturation Ponds • Dimensions • 48meters x 24 meters • Depths of 1.5 meters and 0.5 meters • Redundancy

18. Environmental Design – Sludge Treatment • Must hold sludge for several weeks to dewater • Must hold sludge for longer to make it safe for fertilizer • Designed to hold 1 year’s worth of sludge for Imhoff tank • Area: 960 m2

19. Structural Design – Sludge Treatment • Beds have layers of sand and gravel • Shear gates to control sludge flow • Low walls of earth or concrete • Under drain system of PVC pipe

20. Storm Water • Townspeople connect roof drains to sewers • A large rainfall event could flush the system • Model showed 15x increase in flow during 10-year event • Will require an overflow weir to prevent flushing

21. Storm Water • Storm inflow: 3100 m3/day • Design inflow: 192 m3/day

22. Project Funding • Estimated cost of construction = $31,000 • Probably too much for residents • We wrote a grant to cover the cost of construction • Maintenance costs to be covered by Carabuela • Estimated $14,000/year

23. Conclusion • Designed a complete system to treat Carabuela’s wastewater for irrigation reuse • Removal of BOD, TSS, and Pathogens • BOD (98.7%) • TSS (93.4%) • Pathogen Removal • E. Coli (99.995%) • Helminth Eggs (99.99%) • Created construction drawing for the system • Wrote an operations and maintenance manual

24. Questions??