Preliminary Conversion Mechanisms in Anaerobic Digestion of Biological Sludges

Abstract

The purpose of this study is to evaluate digester performance and examine the preliminary conversion steps in the anaerobic digestion of biological sludges that contain intact viable cells. Activated sludge of totally biological origin is fed to laboratory‐scale anaerobic digesters. Particulate protein accounts for more than 80% of the degradable COD in the digester effluents. Carbohydrate concentrations are substantial, and lipids, soluble COD, and volatile acids concentrations are very low. Experiments with lysed (i.e., autoclaved) biological sludge indicate that hydrolysis of particulate protein is the major, rate‐limiting step in the digestion of biological solids. Results also suggest that percent COD destruction is independent of influent concentration, supporting the use of a first‐order rate to describe hydrolysis. A previously presented kinetic model, which considers cell death/lysis and hydrolysis of particulate biomass, is applied to the data presented herein.