Sludge Digestion by Anaerobic Fluidized Beds. II: Kinetic Model

Abstract

A model has been developed to describe the gas production and soluble‐COD variations from the digestion of waste‐activated sludge in the anaerobic fluidized‐bed reactor. It indicates that a substantial rate increase can be attained by prehydrolysis of the biological sludge, external to the reactor. The model indicates that the rate‐limiting step is in the sludge hydrolysis. The model is developed from an assumption of first‐order kinetics in a set of series and parallel, irreversible reactions. That is, the formation of soluble substrate is first order with respect to the particulate biomass present, and that the production of methane is first order with respect to the soluble substrate present. The amount of particulate biomass can be approximated by the sludge‐suspended solids and that the amount of soluble substrate can be approximated by the soluble COD present in the reactor. The model correlates well with the laboratory data observed in the study.