Application of Oxic-Settling-Anaerobic (OSA) Process for Excess Sludge Reduction and Valorization: A Pilot Plant Experiment

Abstract

In this study, the effects of different operating conditions on excess sludge minimization in an oxic-settling-anaerobic (OSA) process were evaluated. The experiment involved two systems operating in parallel, one implementing the OSA process and a conventional activated sludge (CAS) system as control, both configured according to a pre-denitrification scheme. Five periods (P1–P5) were studied, during which the OSA was operated under different layouts, which differed from the returned sludge to the anoxic (A) or aerobic (B) mainstream reactors and the hydraulic retention time in the anaerobic reactor of the OSA system (8–12 h). The excess sludge production in the OSA plant was lower in all the investigated configurations, indicating that successful sludge minimization was achieved. Specifically, the sludge production was lowered by approximately 12% (P1), 29% (P2), 40% (P3), 26% (P4) and 41% (P5). Scheme A enabled the establishment of the uncoupling metabolism and the extracellular polymeric substance (EPS) destructuration. In contrast, scheme B enabled the establishment of the maintenance metabolism in addition to the uncoupling metabolisms, whereas cell lysis and EPS destruction were minimized. This allowed for obtaining higher sludge reduction yield (26–40%) without compromising the effluent quality.

Keywords

• activated sludge
• anaerobic side stream reactor
• nutrients removal
• oxic-settling-anaerobic (OSA)
• sludge minimization