ceac presentation friday, april 23, 2010 aaron raakaaron lammersbrent longchris crock
TRANSCRIPT
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CEAC Presentation Friday, April 23, 2010
Aaron Raak
Aaron Lammers
Brent Long
Chris Crock
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IntroductionCarabuela, Ecuador
has a Flawed Wastewater Treatment SystemOverloaded
Septic TankFailed Leaching
Field
Worked with HCJB to Remedy the Problem
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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
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Project ManagementMethod of Approach
Decision ProcessTask Division
Individual Partner Team
Group Meeting
Divide Tasks
Individual Research
Group Meeting
Individual Design
Divide Tasks
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Design Norms/CriteriaEffective TreatmentCulturally
AppropriateSustainabilitySite AppropriateLow CostUser FriendlinessLife of Design
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RequirementsPerformance 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)
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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
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General System DescriptionBar 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 removalSludge Drying Beds
• Treat sludge from Imhoff Tank and Grit Chamber• Four sludge drying beds for treatment cycling
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Bar Racks Grit
Chamber Imhoff Tank
Sludge Treatment
Stabilization Ponds
Q = 196 m3/dayBOD = 32 kg/dayTSS = 40 kg/day
Q = 196 m3/dayBOD = 19.6 kg/dayTSS = ?
Q = 196 m3/dayBOD = 32 kg/dayTSS = ?
Q = 196 m3/dayBOD = 32 kg/dayTSS = ?
Solids = ?
Irrigation
Q = 196 m3/dayBOD = 0.51 kg/dayTSS = ?
Solids = ?
General System Description
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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
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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 0.3—0.6 m/s• Openings between 20—50 mm• Rack for dewatering screenings• Redundancy accounted for
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Structural Design - Bar RackStructural Design•Bar Rack
• Ultimate moment design• Uses minimum steel and cover• Two open channels and racks for redundancy• Two depressed steel plates for dewatering
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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
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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
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Structural Design• Grit Chamber
• Ultimate moment design• Uses minimum steel and cover• Two open channels and sutro weirs for
redundancy
Structural Design – Grit Chamber
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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
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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
(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 ft3 per
resident (3,370 ft3) Up to 6 months of sludge storage
Environmental Design – Imhoff Tank
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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
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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
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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
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Structural Design – Lagoons
Pond System1 Facultative Ponds2 Maturation Ponds
Dimensions21 meters x 21 metersDepths of 1.5 meters and 0.5 meters
Redundancy
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Open sand drying bedsCovered sand drying bedsDrying lagoon
Decision: Open bedsLower costEffective treatment
Design Decisions/Alternatives – Sludge Treatment
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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
Environmental Design – Sludge Treatment
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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
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HydraulicsTownspeople connect roof
drains to sewersA large rainfall event could flush
the systemModel showed 15x increase in flow
during 10-year eventWill require an overflow weir to
prevent flushing
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HydraulicsStorm inflow: 3100 m3/dayDesign inflow: 196 m3/day
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Grant ProposalEstimated cost of construction = $25,000Probably too much for residentsWe are applying to HCJB for a grant to cover
the cost of constructionMaintenance costs to be covered by
CarabuelaEstimated $14,000/year
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Questions??