Performance of a Pilot-Scale High-Rate Anaerobic Side-stream Reactor (ASSR) Process: Minimized Sludge Production and Generation of Biogas

A pilot-scale anaerobic side-stream plant in which a high-rate (hydraulic retention time, HRT ∼2 days) anaerobic side-stream reactor (ASSR) is incorporated into an activated sludge system was operated at the Amherst wastewater treatment plant (WWTP) to determine its ability to reduce sludge generation from wastewater treatment. During a total of 2 operational periods, the pilot system produced good quality of effluent, having both soluble chemical demand (sCOD) and total suspended solids (TSS) less than 30 mg/L despite long solids retention time (SRT), greater than 50 days, due to minimal sludge wastage. In terms of sludge production, the pilot system generated about 50% less sludge than the full-scale Amherst WWTP. As a key component of the ASSR process, the ASSR degraded activated sludge contributing to its low sludge generation yield while generating methane in spite of extremely short HRT. The batch digestion of the activated sludges from pilot ASSR process and full-scale activated sludge system showed pronounced differences in biogas generation; ASSR sludge produced about 78% more biogas than the CAS system during a 2 week digestion period, which suggested the presence of a large population of methanogens in activated sludge growing in the pilot ASSR process.