Chemical Oxygen Demand and the Mechanism of Excess Sludge Reduction in an Oxic-Settling-Anaerobic Activated Sludge Process

Abstract

A modified activated sludge process, called the oxic-settling-anaerobic (OSA) process, achieved effective reduction in excess sludge production. Its key feature is the insertion of a sludge holding tank in the sludge return circuit to provide an anaerobic sludge zone. Our previous studies suggested that such excess sludge reduction might be associated with an increased sludge decay rate and the effective consumption of organic substrates generated during the retention of the thickened sludge in the sludge holding tank under a low oxidation-reduction potential (ORP) at