Mathematical model for meso- and thermophilic anaerobic sewage sludge digestion.

A mathematical model is developed to describe the dynamic behavior of mesophilic (35 +/- 5 degrees C) and thermophilic digestion (55 +/- 5 degrees C). Special emphasis is given to acetotrophic methanogenesis and propionate degradation, as the steps that determine the stability of anaerobic digestion, as well as to hydrolysis rate, which determines the degradation efficiency of particulate degradable organic carbon. Within the range of 6-20 (mesophilic) and 2-8 d (thermophilic) hydraulic retention time (HRT), the observed maximum growth rates for acetotrophic methanogens are 0.