CEAC Presentation Friday, April 23, 2010

Aaron Raak

Aaron Lammers

Brent Long

Chris Crock

IntroductionCarabuela, Ecuador

has a Flawed Wastewater Treatment SystemOverloaded

Septic TankFailed Leaching

Field

Worked with HCJB to Remedy the Problem

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

Project ManagementMethod of Approach

Decision ProcessTask Division

Individual Partner Team

Group Meeting

Divide Tasks

Individual Research

Group Meeting

Individual Design

Divide Tasks

Design Norms/CriteriaEffective TreatmentCulturally

AppropriateSustainabilitySite AppropriateLow CostUser FriendlinessLife of Design

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)

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

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

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

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

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

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

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

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

Structural Design• Grit Chamber

• Ultimate moment design• Uses minimum steel and cover• Two open channels and sutro weirs for

redundancy

Structural Design – Grit Chamber

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

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

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

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

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

Structural Design – Lagoons

Pond System1 Facultative Ponds2 Maturation Ponds

Dimensions21 meters x 21 metersDepths of 1.5 meters and 0.5 meters

Redundancy

Open sand drying bedsCovered sand drying bedsDrying lagoon

Decision: Open bedsLower costEffective treatment

Design Decisions/Alternatives – 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

Environmental Design – Sludge Treatment

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

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

HydraulicsStorm inflow: 3100 m3/dayDesign inflow: 196 m3/day

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

Questions??