Senior Design Night
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Transcript Senior Design Night
Senior Design
Friday, April 23, 2010
Chris Crock
Aaron Lammers
Brent Long
Aaron Raak
Carabuela, Ecuador has a
flawed wastewater
treatment system
Overloaded septic tank
Failed leaching field
Worked with HCJB to
remedy the problem
Effective Treatment
Culturally Appropriate
Sustainability
Site Appropriate
Low Cost
User Friendliness
Life of Design
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)
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
Bar Racks
Grit Chamber
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
Settle out large particles (sand, grit, etc.)
Two open channels acting as grit chambers
Velocity control weir
Imhoff Tank
Racks for large solids and objects
Two open channels with inclined bars
Dewatering plate for screenings
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
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
Bar Racks
Q = 192 m3/day
BOD = 32 kg/day
TSS = 48 kg/day
FC = 2x107 /100 mL
Grit Chamber
Imhoff Tank
Q = 192 m3/day
BOD = 16 kg/day
TSS = 32.6 kg/day
FC 2x107 /100 mL
Solids = 16 m3/month
Sludge Drying Bed
Q = 192 m3/day
BOD = 0.51 kg/day
TSS = 3.2 kg/day
FC = 915 /100 mL
Irrigation
Stabilization Ponds
Important to remove larger solids
Bar Racks
▪ Design depends mostly on clear space between bars
▪
▪
▪
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Velocity should be within 0.3—0.6 m/s
Openings between 20—50 mm
Rack for dewatering screenings
Redundant system
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
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
Ultimate moment design
ACI 318M-05 Metric Building Code
and Commentary
Two open channels and sutro weirs
for redundancy
Outflow
Inflow
V
V0
Stokes Settling Velocity
Stokes Rearranged for Particle Removal
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
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
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
Pond System
1 Facultative Ponds
2 Maturation Ponds
Dimensions
48 meters x 24 meters
Depths of 1.5 meters and 0.5
meters
Redundancy
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
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
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 inflow: 3100 m3/day
Design inflow: 192 m3/day
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
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