Investigation of a new anaerobic side-stream reactor (ASSR) process for sludge reduction in biological wastewater treatment

摘要

Preliminary research on the anaerobic side-stream reactor (ASSR) process and examination ofliterature led us to develop the hypothesis that deflocculation and subsequent sludge hydrolysisoccur more effectively under the short period of anaerobic digestion and that recirculation of thissludge back to the aeration basin could lead to more effective excess sludge reduction. To verifythis hypothesis, an anaerobic batch study was conducted and three activated sludge (AS) systemswith different schemes of ASSR were operated side-by-side in the laboratory. The anaerobicbatch test showed that maximum solubilization of key floc cations, extracellular polymericsubstances, and enzyme activity occurred within 2 days of anaerobic digestion. For the operationresults for three laboratory systems, the observed sludge yield from system #1, AS with 2.5-day-SRT ASSR, was the lowest (0.252 mg TSS/mg COD) among the three systems. These resultsindicate that AS with a short-SRT ASSR brought the greatest solids reduction. In addition, thissludge reduction did not cause negative effects on sludge settling and effluent quality, indicatingthat sludge recirculation between a short-SRT ASSR and the aeration basin provides the mostfavorable condition for sludge reduction in the AS in spite of extremely long solid retention time(SRT). The study also found that the amount of released organic matter and actual volatile solidsreduction occurring in a short-SRT ASSR were much smaller than those from long-SRT ASSR,although the ASSR system led to much lower sludge yield. These results indicate that the successof the ASSR process is not solely dependent on the extent of hydrolysis or anaerobic sludgedegradation in ASSR but on the interaction between AS and ASSR.