Waste activated sludge treatment in an anaerobic dynamic membrane bioreactor at varying hydraulic retention time: Performance monitoring and microbial community analysis

Summary In this study, the variations in system performance and microbial community composition when treating waste activated sludge without prior chemical or physical pretreatment in anaerobic systems is examined. Two lab‐scale digesters, namely anaerobic dynamic membrane bioreactor (AnDMBR) and continuously stirred tank reactor (CSTR), were operated and maintained under mesophilic conditions at varying hydraulic retention times (10‐25 days). Decreasing the hydraulic retention time (HRT) affected the methane yield (MY) and methane production rate (MPR) proportionally in both systems. The AnDMBR's maximum MY of 252 mL CH4/g‐VS and MPR of 0.73 L/L/d were 25% and 34% higher than those obtained using the CSTR, respectively. Moreover, a decrease in HRT was accompanied by accumulation of butyric acid in the CSTR, which caused further performance deterioration. In both systems, AnDMBR's dynamic membrane acted as an added layer preventing methanogen wash‐out and retaining the essential microorganisms for stable sludge treatment. Dominance in the microbial composition shifted from a strict acetoclastic to a mixed acetoclastic and hydrogenotrophic methanogenic community and that a decrease in the ration of Bacteroidetes to Firmicutes was associated with the increased MY. The suitability of anaerobic dynamic membrane bioreactor (AnDMBR) treatment of waste activated sludge without prior pretreatment was studied The AnDMBR system performed better than a pseudo‐conventional AD system Volatile fatty acids gradually increased with decreasing hydraulic retention time Interestingly, decreased abundance of Clostridiales led to a decreased methane yield in both systems Methanosaeta concilii was the dominant methanogen within the AnDMBR