1. 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 Figure 5. Gas chromatography of biogas concluded that produced biogas contained approximately 66.5% methane. Experimental Goal: To develop methods for quantifying the first term of the right hand side of the above equation: 1.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 2.Gas Chromatography is used to calculate volumetric production of methane gas. Design of Scalable Biogas Digester for the Developing World Tiffany Cheng 1, Thomas Davis 2, Dawn Schmidt 3, Kyle Schroeder 4, Andrew Wu 2 Advisors: Paul King, PhD; Dave Owens, PhD Vanderbilt University, Mechanical Engineering 1, Biomedical Engineering 2, Chemical and Biomolecular Engineering 3 & Civil Engineering 4 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 Continue collecting biogas until rate of biogas production is insignificant in order to calculate r n 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 INTRODUCTION DESIGN APPROACH RESULTS FUTURE DIRECTION ACKNOWLEDGEMENTS PROTOTYPE EXPERIMENTAL SETUP Figure 2. Determined path of design approach (gold) to minimize digester cost. 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. Figure 3. Filled PET bottle connected to inverted graduated cylinder. THEORETICAL FRAMEWORK 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. r n = rate of biogas generation Vi = volume of slurry input/load τ = residence time Q v = biogas volumetric flow rate CL = connection leakage rate PL = permeability leakage rate SSE = slurry solution exit rate IL = inlet loss rate (diffusion) N = retention days Χ = solids fraction ρ b = biogas density V b = biogas volume OBJECTIVES 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 DESIGN CRITERIA The digester must: Sell at a retail price of ≤ $89 Produce 2800L of biogas/day Adequately function for ≥ 5 yrs Be easily installable Outflow Biogas Collection Removable Cover Seal Inlet Biogas Slurry Figure 1. Schematic of biogas digester. http://www.journeytoforever.org/biofuel_library/methane_nepal.html 68% Methane65% Methane 100% Methane Biogas Sample 2 Pure Methane Biogas Sample 1 Cost Drivers C/N RatioMaterialsHeatingMixing BrickHybridPlastic PPPETPEPVC Volume of Digester Experimental Design f = freq. of biogas use t = time MANUFACTURING COST Raw PET Plastic Materials Power and Utilities 5 $26.32 $12.52 Labor of Manufacturing 5 $7.77 Machine Payment 5 $6.94 Subtotal$53.55 Profit Margin (32%) 5 $17.14 Subtotal $70.69 Tooling at 100,000 unit production level 5 $1.30 Subtotal $71.99 ADDITIONAL COST Installation Transportation Accessories Varies* $25.00 Estimated Total$96.99 PER UNIT COST BREAKDOWN Rosanne Delapp Roy Denney at Biosolids Facility Michael Sykes at Plastic-Mart.com 5 * Dependent on the efficiency of the supply chain Figure 6. Current full-size design of PET plastic biogas digester with an estimated manufacturing cost of $71.99. 0.7m 1.4m 1.35m 0.1m Slurry Intake Gas Release Slurry Exit 0.5mm PVC Gas Holder Digester