Modelling Continuous Anaerobic Digestion of Municipal Solid Waste in Biogas Production

In this study, mathematical models were developed for the anaerobic biodegradation of municipal solid waste (MSW) in Port Harcourt metropolis, Nigeria, in a continuously stirred tank bioreactor. The MSW in Port Harcourt is presently not treated before final disposal. The need to incorporate a treatment element into the management scheme has elicited various treatment proposals, including the anaerobic digestion of the waste in a continuous processing system, in order to generate biogas in the process. Bench-scale experimentation was conducted to investigate the behavior of the waste when subjected to anaerobic decomposition in a continuous reactor, leading to the formulation of process models. The development of the models was based on a material balance analysis of the continuous anaerobic biodegradation processes. The models were simulated over a range of fractional conversion (α) of 0.2-0.8 and percentage Total Solids (TS) concentration of 4-10 using the Microsoft Visual Basic Version 6.0 computer programming language. The results of the simulation were further analyzed with the Microsoft Chart Editor, which was used to establish relationships between the various process parameters, including the fractional conversion, time of digestion, effluent substrates and microbial concentrations, volume of gas produced and effluent substrates stabilization. It was found that, whereas the effect of 'α' on the time of digestion is a logarithmic function of the 'α', it is linear for the effluent substrate and microbial concentrations and a power function for the total volume of biogas produced.