A simple mathematical model for anaerobic digestion process

Six different conversion processes have been identified in the anaerobic digestion of particulate organic material to methane. Hydrolysis followed by intermediate acids formation and fermentation to produce methane by five different groups of microorganisms. These may be largely grouped into two major groups, namely the acid producing microorganisms and methane producing microorganisms. Monod kinetic rate equation applies to a strain of bacteria growing on a single rate-limiting substrate. By identifying the kinetic coefficients of the Monod kinetic rate equation for every single component of the solids in wastewater an improved prediction of the anaerobic digestion process can be made using Monod kinetic rate equation. Separate kinetic coefficients for acid formation and methane formation must be identified from the literature or determined through laboratory analysis. Municipal wastewater may be considered as a mixture of carbohydrates, proteins, lipids and a very small proportion of other materials. By an extensive literature review, many Monod kinetic coefficients for the above said components were selected and a very few assumed. Several loading conditions for different proportions of influent wastewater characteristics simulating actual operations were tested using this model. The model can be used to set operating parameters such as BOD loadings, retention times and temperatures that will produce desired efficiency in the systems within practical limits.