1. CEAC Presentation Friday, April 23, 2010
Chris Crock
Aaron Lammers
Brent Long
Aaron Raak

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 Thank you Brent
Team Member:
Christopher Crock
Aaron Lammers
Brent Long
Aaron Raak
Consultant:
Tom Newhof
Client:
Bruce Rydbeck
Advisor:
Leonard DeRooy
Thank you Brent
For this project our general team structure involved our client, our advisor, our industrial consultant and our team members
Our client contact was Bruce Rydbeck. Bruce is the Director of Clean Water Projects at HCJB. He brought us the project and has provided us information and insight about Carabuela.
Our advisor is Professor De Rooy. He has oversaw our project throughout the design process and has given valuable insight about our structural design.
Our industrial consultant is Thomas Newhof from Prein and Newhof. We have met with him twice and he has provided us advice about wastewater treatment design and construction.
Our team members include myself (Aaron Lammers), Christopher Crock, Aaron Raak and Brent Long.

4. Project Management Method of Approach Decision Process Task Division
Group Meeting
Method of Approach
Decision Process
Task Division
Individual
Partner
Team
Divide Tasks
Individual Research
Group Meeting
Our Method of Approach throughout the design process has utilized team, partner and individual work.
Our general method and process for making decisions and dividing up tasks can be seen here.
To start we would meet as a whole team and discuss our options whether it be options for projects or options for treatment.
At the end of our meeting we would divide up tasks to individuals or partners to complete before our next scheduled meeting.
We would then research our options individually or with a partner.
We would then meet and each option would be presented to the rest of the team. We would discuss and come to a decision
At the end of the meeting we would once again divide up tasks to individuals or partners
Finally we would complete our individual or partner design whether it be environmental, hydraulic or structural
This process allowed us to work efficiently by utilizing each team members time while also keeping the rest of the team informed of progress. This process also has a series of checks by the whole group to reduce errors.
Divide Tasks
Individual Design

5. Design Norms/Criteria
Effective Treatment
Culturally Appropriate
Sustainability
Site Appropriate
Low Cost
User Friendliness
Life of Design
Effective Treatment
Appropriate BOD levels
Reduction in TSS
Appropriate pathogen removal for irrigation reuse
Culturally Appropriate
Local materials used for construction
Local construction methods and practices
Proven - similar wastewater treatment cases
Sustainability
No electricity
Lower levels of sophistication
Site Appropriate
Plan view footprint
Required equipment for construction
Low Cost
Cost of construction
Cost of maintenance
User Friendliness
Transparency
Trustworthiness
Simplicity in operation
Life of Design
Long lasting 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)
Performance Requirements- found from Ecuadorian gov’t and WHO
Water Effluent- standards are met for irrigation of leafy crops (alfalfa for grazing will be irrigated)
Sludge Effluent- Class B sludge can be used for fertilizer

7. Requirements 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
Functional Requirements- Design Life will handle a 20 yr. population growth, no electricity, 0.5 hectares of land as a footprint, should not need chemicals for treatment, and should use locals for construction and Operations and Maintenance

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
Bar Screen- remove large solids and objects in waste stream
Grit Chamber- remove smaller particles like grit and sand
Imhoff tank- primary settling and anaerobic digestion (50% of BOD reduced)
Sludge stored for six months
Stabilization Ponds- 3 ponds for secondary treatment. Further reduction of BOD and removal/inactivation of pathogens
Sludge treatment- 6 beds to dewater the sludge from imhoff and grit chamber

9. General System Description
Bar Racks
Grit Chamber
Imhoff Tank
Sludge Treatment
Stabilization Ponds
Q = 196 m3/day
BOD = 32 kg/day
TSS = 40 kg/day
BOD = kg/day
TSS = ?
Solids = ?
Irrigation
BOD = 0.51 kg/day
Must satisfy the requirements for water and sludge quality

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
Three alternatives were researched
Of these three the manually cleaned incline bar racks were the best choice
They were simple to construct, easy to maintain and fairly cost efficient

11. Environmental Design - Bar Rack
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
Most important in design was to remove the rags and floatables or larger objects in the waste stream
The openings in the rack would be the main factor for design for certain size objects to be removed
20 mm was the choice
The velocity had to fall with in the min and max range of 0.3—0.6 m/s
Width of the channel was the main factor in this design to allow for this velocity

12. 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
The bar rack structure was designed for redundancy
2 channels were constructed, ea. Having a bar rack
Minimum reinforcing and cover was needed for the design because of the small size of the chamber

13. Design Decisions/Alternatives – 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
Easy to maintain
Requires manual labor
Fairly cheap to construct
4 alternatives for design that we researched
The vortex grit chamber and old septic tank for grit chamber use could be marked off our choices fairly quickly
Vortex required electricity to power the pumps
Old septic tank was to large to only allow grit to settle (organics would have also settled in the grit chamber)
The modified grit chamber was not proven technology; therefore, we were unable to design and use this mode of treatment
Rectangular open channel was the last choice and proved to be easy to maintain, require no electricity, and was fairly cheap to construct

14. Environmental Design – Grit Chamber
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
Velocity was most important in this design to effectively remove only grit particles.
The velocity had to be 0.3 m/s
This was achieved with a sutro weir

15. Structural Design – Grit Chamber
Ultimate moment design
Uses minimum steel and cover
Two open channels and sutro weirs for redundancy
As with the bar racks chamber, the grit chamber was designed with minimum reinforcing and cover because of its small size
Again, two chambers were designed to allow for redundancy, and two sutro weirs were also designed

16. Design Decisions/Alternatives – Imhoff Tank
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
Septic Tank
The septic tank is the most common, small scale and decentralized treatment plant, worldwide. It is compact, robust and in comparison to the cost of its construction, extremely efficient. It is basically a sedimentation tank in which settled sludge is stabilized by anaerobic digestion.
The main advantages of a septic tank are that they are simple, durable, and require little space because of being underground.
The main disadvantages of septic tanks are the low treatment efficiency and the effluent not being odorless.
We decided to not use a septic tank because the septic tank that is currently used in Carabuela has lost all treatment ability because of the difficulty to desludge the tank and variable flows. Because of this the confidence of local residents in septic tank effectiveness has most likely been reduced to a point in which septic tanks are no longer appropriate to the location.
Lagoon System
Lagoons are artificial lakes. What happens in lagoons closely represents treatment processes which take place in nature.
The main advantages of lagoon systems are that they are simple in construction, flexible with respect to degree of treatment, and require little maintenance.
The main disadvantages of lagoon systems are that the wastewater pond occupies open land, there is always some odor, can even be stinky, and that mosquitoes are difficult to control.
We decided to not use a lagoon because of the limited land that would be available for use as a primary lagoon. We are using a lagoon system for tertiary treatment which occupies all of the available land.
Imhoff Tank
The Imhoff tank was invented and patented by a German engineering named Karl Imhoff in The tank combines two wastewater treatment processes, sedimentation and biological digestion, into one physical system. The tank consists of a settling compartment above the digestion chamber. Funnel-like baffle walls prevent up-flowing foul sludge particles from getting mixed with the effluent and from causing turbulence. The effluent remains fresh and odorless because the suspended and dissolved solids do not have an opportunity to get in contact with the active sludge to become sour and foul.
The main advantages of an Imhoff tank are durability, require little space because of being underground, and have an odorless effluent.
The main disadvantages of an Imhoff tank are that it is less simple than a septic tank and that it requires a regular desludging interval
We decided on using an Imhoff tank because of its small space impact, its odorless effluent and the simpler desludging process as compared to a septic tank. Also our client, Bruce, encouraged us to consider using an Imhoff tank for the primary treatment.

17. Environmental Design – Imhoff Tank
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
The Environmental design of the Imhoff tank was based off of design guides, case studies and rules of thumb based on experience.
The Imhoff tank is designed as two separate tanks in one structure to allow for redundancy and for maintenance. The tank has also been designed to allow for reversal of flow to encourage equal depositing of settled materials
The design was broken into two main components: Sedimentation and Digestion
Sedimentation
The sedimentation chamber was designed from design guides and rules of thumb from experience.
The overflow rate for each tank was chosen to be 600 gal/ft^2 day to determine the required plan view area for sedimentation.
The retention time in each tank was chosen to be 2 hours based on experience from the Decentralized Wastewater Treatment Systems manual. This is to reduce the possibility of the clean water to foul from contact with water from the digestion zone.
Clearance, overlap, gas vent areas and freeboard were based on recommendations from various design guides.
Digestion
The digestion chamber was designed based on a case study of an Imhoff tank in Honduras. The digestion zone has storage for a sludge volume of 1.87 cubic feet per resident or about 3,370 cubic feet total. This storage was designed for a desludging interval of about 6 months.

18. Structural Design – Imhoff Tank
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
The structural design of the Imhoff tank was designed using both finite element analysis and structural analysis. These were completed to define the maximum forces and moments that could occur in the tank. Finite Element Analysis was done on the sedimentation chamber walls while a structural analysis was done on the primary load bearing walls and the supporting beams.
American Concrete Institute 318M-05 guide was used to determine minimum steel reinforcing, minimum/maximum steel spacing, and minimum concrete cover.
Structural Analysis was used to determine the vertical and horizontal reinforcing required to resist the flexural and shear forces on the tank.
The design was also generally based on the Imhoff tank in Honduras.
Now I’ll pass it off to Brent to talk about lagoons.

19. Design Decisions/Alternatives - Lagoons
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

20. Environmental Design – 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

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

23. 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

24. Structural 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

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 m3/day
Design inflow: 196 m3/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??