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CEAC Presentation Friday, April 23, 2010 Aaron RaakAaron LammersBrent LongChris Crock.

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Presentation on theme: "CEAC Presentation Friday, April 23, 2010 Aaron RaakAaron LammersBrent LongChris Crock."— Presentation transcript:

1 CEAC Presentation Friday, April 23, 2010 Aaron RaakAaron LammersBrent LongChris Crock

2 Introduction Carabuela, Ecuador has a Flawed Wastewater Treatment System Overloaded Septic Tank Failed Leaching Field Worked with HCJB to Remedy the Problem

3 Project Management Team Member: Christopher Crock Team Member: Aaron Lammers Team Member: Brent Long Team Member: Aaron Raak Consultant: Tom Newhof Client: Bruce Rydbeck Advisor: Leonard DeRooy

4 Project Management Method of Approach Decision Process Task Division Individual Partner Team Group Meeting Divide Tasks Individual Research Group Meeting Individual Design Divide Tasks

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

6 Requirements Performance Requirements Water Effluent Coliform count < 1000/100 mL 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)

7 Functional Requirements Handle the waste of the entire population for 20 yrs (2700 ppl. for projected population) No electricity The system must fit in 0.5 hectares No chemical additives Shall not need experts outside of the village for construction Requirements

8 General System Description Bar Racks Screen 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 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

9 Bar Racks Grit Chamber Imhoff Tank Sludge Treatment Stabilization Ponds Q = 196 m 3 /day BOD = 32 kg/day TSS = 40 kg/day Q = 196 m 3 /day BOD = 19.6 kg/day TSS = ? Q = 196 m 3 /day BOD = 32 kg/day TSS = ? Q = 196 m 3 /day BOD = 32 kg/day TSS = ? Solids = ? Irrigation Q = 196 m 3 /day BOD = 0.51 kg/day TSS = ? Solids = ? General System Description

10 Design Decisions/Alternatives – Bar Rack Bar Racks Mesh screen fitted to the inlet of grit chamber Difficult to maintain Clogs easily Damages easily Mesh cage sitting on bottom of channel to catch large objects Complicated to make Costly to build Inclined bars that are manually raked Easy to maintain Simple to construct Fairly cost efficient

11 Environmental Design - Bar Rack Environmental Design Important to remove larger solids and particulate Bar Rack Design depends mostly on clear space between bars Velocity should be within m/s Openings between 2050 mm Rack for dewatering screenings Redundancy accounted for

12 Structural Design - Bar Rack Structural Design Bar Rack Ultimate moment design Uses minimum steel and cover Two open channels and racks for redundancy Two depressed steel plates for dewatering

13 Design Decisions/Alternatives – Grit Chamber Grit Chamber Vortex Grit Chamber Requires electricity Costly to buy Modified Vortex Grit Chamber Not proven technology Does not require electricity Cheap to make Old Septic Tank Cheap to modify Too large to settle only girt Difficult to maintain Rectangular Open Channel Does not require electricity Easy to maintain Requires manual labor Fairly cheap to construct

14 Environmental Design Important to remove larger solids and 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 Redundancy accounted for Environmental Design – Grit Chamber

15 Structural Design Grit Chamber Ultimate moment design Uses minimum steel and cover Two open channels and sutro weirs for redundancy Structural Design – Grit Chamber

16 Septic Tank Pros - Simple, Durable, Little Space Cons – Low efficiency, odors, already failed system Lagoon System Pros - Simple, Flexible, Little Maintenance Cons – Large open land, odors, mosquitoes Imhoff Tank Pros – Durability, little space, odorless effluent Cons – Less simple, regular desludging Design Decisions/Alternatives – Imhoff Tank

17 Environmental Design Two tanks in one structure for redundancy Sedimentation Based off Design guides and rules of thumb Overflow Rate of 600 gal/ft 2 day (Tchobanoglous) Retention Time of 2 hours (DEWATS) Clearance, overlap, other recommended dimensions Digestion Based on case study of Imhoff tank in Honduras Sludge storage for 1.87 ft 3 per resident (3,370 ft 3 ) Up to 6 months of sludge storage Environmental Design – Imhoff Tank

18 Structural Design Analysis of forces and moments in tank Finite Element Analysis for Sedimentation walls Structural analysis for primary load bearing walls and beams Designed steel and concrete to hold for highest loads ACI 318M-05 –Metric Building Code and Commentary Minimum reinforcing Minimum/maximum spacing Minimum cover Vertical and horizontal reinforcing based on analysis Similar to case study tank in Honduras Structural Design – Imhoff Tank

19 Aerated Lagoon Mechanical aerators to enrich wastewater with oxygen Better Removal Rates Less Land Expensive Facultative Lagoon Simpler Setup Less Maintenance More Land Less Expensive Design Decisions/Alternatives - Lagoons

20 Used Kinetics, Temperature Factors, and Hydraulic Residence Times to Size Lagoons Loading Rates BOD: 100mg/L Helminth Eggs: 1000 Eggs/L E-Coli: 2e7 Coliforms/100mL Reduced Rates BOD: 2.7mg/L Helminth Eggs: 0.10 Eggs/L E-Coli: 915 Coliforms/100mL Environmental Design – Lagoons

21 Structural Design – Lagoons Pond System 1 Facultative Ponds 2 Maturation Ponds Dimensions 21 meters x 21 meters Depths of 1.5 meters and 0.5 meters Redundancy

22 Open sand drying beds Covered sand drying beds Drying lagoon Decision: Open beds Lower cost Effective treatment Design Decisions/Alternatives – Sludge Treatment

23 Must hold sludge for several weeks to dewater Must hold sludge for longer to make it safe for fertilizer Designed to hold 1 years worth of sludge for Imhoff tank Area: 960 m 2 Environmental Design – Sludge Treatment

24 Beds have a layers of sand and gravel Shear gates to control sludge flow Low walls of earth or concrete Underdrain system of PVC pipe Structural Design – Sludge Treatment

25 Hydraulics 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

26 Hydraulics Storm inflow: 3100 m 3 /day Design inflow: 196 m 3 /day

27 Grant Proposal Estimated cost of construction = $25,000 Probably too much for residents We are applying to HCJB for a grant to cover the cost of construction Maintenance costs to be covered by Carabuela Estimated $14,000/year

28 Questions??

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