Mathematical models have been developed for the design of anaerobic continuous digesters for the production of biogas from municipal solid waste (MSW) in Port Harcourt metropolis, Nigeria. Field and laboratory investigations were conducted and used to determine the physical, chemical and bio-kinetic properties of the MSW relevant to the digester design. The design models were simulated for total solids (TS) concentration of 4-10% and fractional conversion of 0.2-0.8 using Microsoft Visual Basic Version 6.0 program. The simulation results were analyzed with Microsoft Chart Editor; and mathematical relationships established between TS concentration and volume of digester; residence time; volume of biogas produced; net heat required; and cost of digester. It was found that, at maximum fractional conversion of 0.8, whereas the TS concentration varied directly as the volume of digester, it was inversely proportional to the time of digestion for the same levels of percentage stabilization. This is indicative of an accelerated growth rate of microbes with increasing TS concentration.
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