Background: Bangladesh suffers from many poverty-related issues, such as affordable energy.

1. Gas Release Slurry Intake Slurry Exit 0.7m Gas Holder 0.1m 1.35m 0.5mm 1.4m PVC Digester Design of Scalable Biogas Digester for the Developing World Tiffany Cheng1, Thomas Davis2, Dawn Schmidt3, Kyle Schroeder4, Andrew Wu2 Advisors: Paul King, PhD; Dave Owens, PhD Vanderbilt University, Mechanical Engineering1, Biomedical Engineering2, Chemical and Biomolecular Engineering3 & Civil Engineering4 THEORETICAL FRAMEWORK INTRODUCTION RESULTS • Background: • Bangladesh suffers from many poverty-related issues, such as affordable energy. • Project Pyramid from the Owen Graduate School of Management has identified biogas digesters as a potential energy solution. • Bacteria digest organic material in anaerobic conditions to produce biogas, which is generally 65% methane, 25% carbon dioxide, and 10% other gases • However, biogas digesters are currently inaccessible and expensive (≥ $200) in Bangladesh. • We propose designing a cost-effective biogas digester to improve the standard of living in Bangladesh. • Average Bangladeshi Family (6 members): • Bangladeshi family makes $45 per month • $10 per month spent on cooking fuel • 60-65% of families own ≥ 1 cow • The theoretical mass balance equation describes the net biogas available within the digester over time. By performing experiments to determine values of the corresponding terms within the equation, the optimal retention time and consequently, the optimal size of the digester can be determined. Figure 4. The difference in rate of biogas production between the variable and control digesters was calculated to determine the volume of biogas produced due to the 1.5L additional input of fresh cow manure. f = freq. of biogas use t = time • CL = connection leakage rate • PL = permeability leakage rate • SSE = slurry solution exit rate • IL = inlet loss rate (diffusion) rn = rate of biogas generation Vi = volume of slurry input/load τ = residence time Qv = biogas volumetric flow rate N = retention days Χ = solids fraction ρb = biogas density Vb = biogas volume Figure 5. Gas chromatography of biogas concluded that produced biogas contained approximately 66.5% methane. 100% Methane DESIGN APPROACH 68% Methane 65% Methane Cost Drivers Biogas Sample 2 Pure Methane Biogas Sample 1 C/N Ratio Materials Heating Mixing Biogas Collection PER UNIT COST BREAKDOWN Seal Removable Cover Inlet Brick Hybrid Plastic Biogas PP PET PE PVC Slurry Outflow Volume of Digester Experimental Design Figure 1. Schematic of biogas digester. http://www.journeytoforever.org/biofuel_library/methane_nepal.html Figure 6. Current full-size design of PET plastic biogas digester with an estimated manufacturing cost of $71.99. Figure 2. Determined path of design approach (gold) to minimize digester cost. OBJECTIVES * Dependent on the efficiency of the supply chain FUTURE DIRECTION PROTOTYPE EXPERIMENTAL SETUP • Biogas digester will meet the energy needs of an average family household. • The ideal biogas digester will: • Improve waste management • Create quality fertilizer • Reduce energy costs • Improve human health • Experimental Goal:To develop methods for quantifying • the first term of the right hand side of the above equation: • Gas Volume Production • Control: One 5 gallon, polyethylene terephthalate (PET) • bottle is filled with 17 L of 100% digester seed. • Variable: A second 5 gallon, PET bottle is filled with 17L • of 100% digester seed and 1.5 L of cow manure. • (Gas Production)variable- (Gas Production)control= • (Gas Production)input manure • Gas Chromatography is used to calculate volumetric • production of methane gas. • Continue collecting biogas until rate of biogas production is insignificant in order to calculate rn • Determine minimum acceptable digester thickness for a sealed and filled container • Apply experimental procedure to Bangladeshi cow manure in order to determine the optimal size for full-scale biogas digester • Work with companies to develop commercialization plan DESIGN CRITERIA ACKNOWLEDGEMENTS • The digester must: • Sell at a retail price of ≤ $89 • Produce 2800L of biogas/day • Adequately function for ≥ 5 yrs • Be easily installable We would like to thank the following for their support in making our senior design project possible: Dr. Dick Speece, PhD Dr. Kenneth Debelak, PhD The Lee family of Triple L Ranch Rosanne Delapp Roy Denney at Biosolids Facility Michael Sykes at Plastic-Mart.com5 Figure 3. Filled PET bottle connected to inverted graduated cylinder.