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

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 http://water1st.org/waterlog/?tag=bangladesh Costly: money, labor NGOS: Non-governmental Organizations http://water1st.org/waterlog/wp-content/uploads/2009/05/hanging-latrine-480x480.jpg

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

Design Requirements Two primary foci Biogas instrument design Target population

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

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

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

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

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

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

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

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.  http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

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 http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

Digester Shapes Egg-shaped vessel Expensive Cylinders w/conical covers and bottom Less favorable surface-volume ratio Shape – to withstand internal and external force http://www.water-technology.net/projects/reading_sewage/images/Island-Road-2.jpg http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

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

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

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

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)

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. 1:102-111 (2006). http://www.gtz.de/de/dokumente/en-biogas-volume1.pdf http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf http://www.gtz.de/de/dokumente/en-biogas-volume3.pdf http://www.gtz.de/de/dokumente/en-biogas-volume4.pdf