senior design friday, april 23, 2010 aaron raakaaron lammersbrent longchris crock
TRANSCRIPT
Senior Design Friday, April 23, 2010
Aaron Raak
Aaron Lammers
Brent Long
Chris Crock
Introduction
Carabuela, Ecuador has a flawed wastewater treatment system Overloaded septic
tank Failed leaching field
Worked with HCJB to remedy the problem
Design Norms/Criteria
Effective Treatment Culturally Appropriate Sustainability Site Appropriate Low Cost User Friendliness Life of Design
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)
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
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
General System Description
Bar Racks Grit
Chamber Imhoff Tank
Sludge Drying Bed
Stabilization Ponds
Q = 192 m3/dayBOD = 32 kg/dayTSS = 48 kg/dayFC = 2x107 /100 mL
Q = 192 m3/dayBOD = 16 kg/dayTSS = 32.6 kg/dayFC 2x107 /100 mL
Q = 192 m3/dayBOD = 32 kg/dayTSS = 48 kg/dayFC = 2x107 /100 mL
Q = 192 m3/dayBOD = 32 kg/dayTSS = 48 kg/dayFC = 2x107 /100 mL
Solids = 16 m3/month
Irrigation
Q = 192 m3/dayBOD = 0.51 kg/dayTSS = 3.2 kg/dayFC = 915 /100 mL
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
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
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
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
How an Imhoff tank works
Sedi
men
tatio
n
Anae
robi
c
Diges
tion
V
V0
Inflow Outflow
Stokes Settling Velocity
Stokes Rearranged for Particle Removal
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
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
Concrete Structures Walkthrough
Environmental Design – Lagoons
Loading Rates BOD: 100mg/L Helminth Eggs: 1000 Eggs/L E-Coli: 2x107 Coliforms/100mL
Reduced Rates BOD: 2.7mg/L Helminth Eggs: 0.10 Eggs/L E-Coli: 915 Coliforms/100mL
Structural Design – Lagoons
Pond System 1 Facultative Ponds 2 Maturation Ponds
Dimensions 48 meters x 24 meters Depths of 1.5 meters and
0.5 meters Redundancy
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
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
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
Storm Water
Storm inflow: 3100 m3/day Design inflow: 192 m3/day
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
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
Questions??