Study of Biodigester Design for Fuel and Fertilizer

Abstract

Design of a biogas plant supplying energy for the students' cafeteria while utilizing the abundant human waste has been done with an aim of significantly reducing wood consumption. Major fuels used in the cafeteria to prepare three meals per day for 3500 student's electricity, Naphtha, and fuel wood. Three years data have been examined to study the pattern of the energy demand, amounts, and price of the energy sources with emphasis on wood. Feed stock potentials, its compositions, nearness to the cafeteria, and various other criteria have been considered in the site selection. It has been found that technically possible to produce as much as 30 cu/m/day biogas in the selected site contributing to 44.5% reduction in wood consumption. Performance of digesters in the climate and weather condition of the region for similar feedstock has been assessed to determine the appropriate digester model. Chinese fixed dome and Deenbandhu models are common and have shown good performance. Detail design and dimensioning of the digester have been done. Financial feasibility has been evaluated using NPV (net present value), internal rate of return (IRR) and simple payback method. Positive NPV, 18.5% IRR and a payback period of 6.27 years have been calculated indicating the financial feasibility.