1. Design of Scalable Biogas Digester for the Developing World By: Tiffany Cheng, Thomas Davis Dawn Schmidt, Kyle Schroeder, Andrew Wu BME 272 3/16/10 Advisors: Dr. Dave Owens – Owen Graduate School of Management Dr. Paul King – Vanderbilt University School of Engineering

2. Meet the Rezas 6 members – Two parents, four children 1 cow (60-65% of families own at least 1 cow in rural Bangladesh) Make $45 per month Spend $10 on petroleum fuel per month Spend 2 weeks per year collecting additional fuel Interested in neighbor’s biogas digester To improve their standard of living

3. What is a BioGas Digester?

4. Biological Processes

5. Biogas Production Technology: An Indian Perspective (Nagamani, B. and K. Ramasamy, 1999) On average, a cow in India produces 3.6m 3 or 3600 L of biogas per day. This yields approximately 76,280 BTU/animal/day.

6. Neighbor’s Digester Cost $200 Expensive materials Hard to install Requires specialist

7. Overall Design Specifications Retail price $89 or less (present value) -Financed through Grameen Bank -8% housing loans leading to $96 paid in equal installments over a 12 month period ($8 monthly payments) Produces 2800 liters of biogas/day – 15,000 Kcal (59,500 BTU) – Cooks for 6 people Lasts at least 5 years Easy to install

8. Biogas Digesters Worldwide http://www.snisd.org.cn/images/05126b.JPG http://www.water-technology.net/projects/reading_sewage/images/Island-Road-2.jpg Floating DrumEgg Shaped http://www.saintsfarm.org/photos/biogas_digester_2_large.jpghttp://www.inforse.dk/asia/images/M_III_biogas3.jpg Plastic Bag Fixed Dome

9. Brainstorming Portable Small Digester Mixing in Digester Heating by Compost Materials Improve C:N ratio

10. Specific Design Criteria Cost Material availability Efficiency of gas production Longevity Ingenuity Maintenance Ease of Use Modular Production

11. Pairwise Comparison Matrix CostMaterial Efficiency of gasLongevityIngenuityMaintenance Ease of useModularProductionTotal Cost -111111118 Material Availability 0 -11110015 Efficiency of gas product 00 -1100114 Longevity 000 -100113 Ingenuity 0000 -00000 Maintenance 00111 -0115 Ease of Use 011111 -117 Modular 0100100 -13 Production 00001000 -1

12. 3 Proposed Designs 1.39m 2.4m 0.15m Brick and Mortar PVC Hooks Brick Plastic Hybrid

13. Full-Scale Brick Design Masonry and cement Readily available materials Requires sealant http://www.journeytoforever.org/biofuel_library/methane_nepal.html

14. Full-Scale Plastic Design Plastic Easier to install Mass producible

15. Full-Scale Hybrid Design Top ViewSide View Plastic Cover Brick Digester Tank

16. Decision for Choosing Design Criteria CriteriaBrickPlasticHybrid QualityWeightValueTotalValueTotalValueTotal Cost 8324432324 Ease of Use 73213 3 Material Availability 5525315420 Maintenance 5210420525 Efficiency of Gas Product 43123 3 Modular 31351539 Longevity 351541226 Production 1442233 Ingenuity 0103030 Total 114129120

17. Cost Analysis of 3 Proposed Designs BrickPlasticHybrid Materials$40.44$3.95$81.66 Manufacturing$0TBD$0 Transportation~$0variable~$0 Installation$6.72$0.96$3.84 Sealantvariable$0 Total$47.16 + sealant $4.91 + manufacturing and transportation cost$85.50

18. Properties of Various Plastics High Density Polyethylene Polyvinyl Chloride Polypropylene UV Stabilized Polyethylene Terephthalate HDPEPVCPP-UVPET Durability Fresh waterVery Good Weak alkalisVery Good Good UV radiationGoodVery GoodGood Thermal properties Max service temperature (°C)1105056.255 Mechanical Properties Yield Strength (MPa)19.341.423.650 Relative Permeability to PVDC (Saran) CO 2 12134.53175.28 CH 4 [Estimated]148.2342.26388.336.47 Price (USD/kg)2.161.522.141.61

19. Polyethylene Terephthalate (PET) Lowest permeability Highest yield strength – Tests showed that a 2L PET bottle can withstand at least 6 atm pressure Inexpensive material

20. Next Step: Prototype Testing Test biogas production in large (5 gallon) PET bottles Analyze biogas – Composition Dr. Debelak’s gas chromatography – Quantity of production Dr. Speece’s Wet Tip Gas Meter

21. Further Designs and Experiments PET 2L Bottles Testing – Determine maximum pressure – Determine fatigue limit – Quantify gas flow generated at given pressures Accessory Design and Testing – Sealants – Water traps – PVC pipes Estimation of per unit cost of manufacturing at various production levels