1. Design of Scalable Biogas Digester for the Developing World
By: Tiffany Cheng, Thomas Davis
Dawn Schmidt, Kyle Schroeder, Andrew Wu
BME 272- Senior Design Project
12/1/09
Advisors:
Dr. Dave Owens – Owen Graduate School of Management
Dr. Paul King – Vanderbilt University School of Engineering

2. Current Issue In Bangladesh and other third-world countries:
Poor waste management
Human health
Environment destruction
Costly energy resources
Potential solution: Biogas
HOWEVER, currently not
affordable for these countries
Costly: money, labor
NGOS: Non-governmental Organizations

3. Objective
Design a scalable biogas digester that is an appropriate technology for Bangladesh in order to:
Improve human health
Protect environment
Provide affordable and accessible energy
Define Appropriate technology

4. Design Requirements Two primary foci Biogas instrument design
Target population

5. Biogas Instrument Materials Long life span Durability Gas permeability
At least 5 years
Durability
Pressure
Temperature
Gas permeability
Affordability and availability

6. Biogas Instrument Structure Size Simplistic design Location
Gas capacity
Simplistic design
Little or no training required
Simple repairs and installation

7. Target Population Considerations
Cultural perspectives
Human waste
Risk averse population (needs proof)
Socioeconomic status
Average income/family = ~$60/month
Size of average family
6 people (4 children)
Degree of education
Related to ability to build and maintain digester

8. Goals
Overall Goal is to provide cheap energy to the people of Bangladesh
Create a viable energy source
One meal
Provides economic incentive for waste management
Pathogen free high quality fertilizer

9. Factors
Economical Issues will be determining factors for the success of the product
Cost of labor, cost of materials, cost of energy produced
Environmental factors will affect the energy produced
Temperature, soil condition, location

10. Performance Metrics
The main goal is to create a viable working product
Therefore economics will be the governing theory in determining the success of the product
Cost vs. benefits

11. Past Work
Weekly meetings with Dr. David Owens and business students from Owen
Met with Dr. Musaazi to learn about appropriate design for developing world
Created survey to verify and refine current design specifications
Researched current biogas digester solutions
Appropriate technology- technology was adapted to the respective local conditions

12. Fixed-dome Plant Size: 5-200 m3 Pro: Con:
Potential underground construction
Low cost
No moving parts
Long life spans 
Compact
Con:
Challenging construction
Frequent gas leaks
Fluctuating gas pressure
Gas production not immediately visible 
Pro- 
Low Cost in design
No moving parts
Long life spans (No rusting steels parts)
Can be constructed underground (No day/night fluctuations)/ Insulated 
Design is Compact
Con- 
Labor-intensive for gas-tight construction ( Produce just as much as floating-drum plants if it is gas-tight)
Not easy to be build ( Need to be supervised by experienced biogas technician)  
Gas leaks occur quite frequently 
Gas pressure fluctuates substantially (Complicate gas utilization)
Amount of gas produced is not immediately visible
Excavation can be difficult and expensive in bedlock. 

13. Floating Drum Plant Size: 5-15m3 for small to mid size farms Pros:
Constant pressure
Visible gas volume
Generally gas-tight
Cons:
More expensive
High level of maintenance
Short expected lifetime
Pros: 
Easy to understand and operate
Provides gas at constant pressure which allows for optimization of burner setting
Stored gas volume is immediately recognizable by the position of the drum
Gas-tightness is not a problem as long as gas holder is derusted and painted regularly
Cons:
Relatively more expensive than other solutions
Requires high level of maintenance to paint and remove rust
Short expected lifetime

14. Digester Shapes Egg-shaped vessel
Expensive
Cylinders w/conical covers and bottom
Less favorable surface-volume ratio
Shape – to withstand internal and external force

15. Digester Material Steel Concrete Plastic Masonry
Pro: Gas-tight; Con: Corrosion
Concrete
Pro: Unlimited Useful Life, Cheap; Con: Gas-tight
Plastic
Pro: Gas-tight; Con: Mechanical Stress, UV radiation
Masonry
Pro: Easy to Build; Con: Gas-tight
Shape – to withstand internal and external force

16. Gas Piping
At least 60% of failure biogas digester is due to defect in gas piping
Galvanized Steel Pipe
Standardized
Plastic Tubing
Inexpensive
No ferrous metal
biogas is 100% saturated with water vapor and hydrogen-sulfide
- Freely accessible and straight so that a rod can be pushed through to eliminate obstructions

17. Current Work Continuing research of current biogas solutions
First ideation cycle of potential solutions specific to Bangladesh

18. Future Work
Analyze results of survey in Bangladesh to determine true price point and product specifications
Design sketch prototypes of digester (Dec. 10th – Jan. 14th)
Select design and begin construction of functional prototype (Jan. 14th – Feb. 15th)
Test and refine functional prototype (Feb. 15th – Mar. 15th)
Finalize prototype and collect data (Mar. 15th – Apr. 1st)

19. Reference Human Development Index, United Nations, 2009
Project Pyramid, Information gathered during 2009 trip to Bangladesh
Van Nes, Wim J. Asia hits the gas. Renewable Energy World. 1: (2006).