Abstract
A mathematical model for anaerobic digestion of municipal primary sludge (PS) was developed to describe methane production under dynamic conditions. Fundamentally the model was focused on elaborating the step of particle disintegration/hydrolysis that was presumed to be rate limiting in overall biological degradation of PS. A series of batch tests with fresh PS resulted in curves of methane production rate characteristically marked with two well-defined temporal peaks. The first immediate peak was easily associated to the presence of relatively readily degradable substrate, while it was necessary to consider a more elaborate particle disintegration/hydrolysis model to describe the second delayed peak. Based on the anaerobic respirograms and using a substrate characterization approach similar to ASMs, the composition of PS was classified into three fractions having different kinetics. The substrate fraction leading to the second peak was considered to degrade via disintegration and hydrolysis reactions. An approach compatible to ASM was used to model different substrate fractions and appropriate kinetic expressions and kinetic coefficients were worked out.
