Homoacetogenic bioaugmentation with Clostridium magnum WY-4 enhances upflow anaerobic sludge blanket reactor resilience under progressive organic loading and short-term complex shock.

Upflow anaerobic sludge blanket (UASB) reactors are widely used for treating high-strength organic wastewater but are vulnerable to short-term complex shocks caused by increased organic loading, hydraulic retention time regulation, and partial sludge loss. At the same time, the role of homoacetogenic bioaugmentation in improving UASB recovery after such disturbances remains poorly understood. This study evaluated the potential of a novel homoacetogenic strain, Clostridium magnum WY-4 (WY-4), to enhance UASB resilience. Two laboratory-scale UASB reactors were operated for 184 days, and reactor performance, volatile fatty acids (VFA), extracellular polymeric substances (EPS), N-acyl-homoserine lactones (AHL), and microbial community dynamics were analyzed. Under stable conditions, WY-4 had only a limited effect on reactor performance. During and after the shock, however, bioaugmentation markedly accelerated recovery. The maximum effluent VFA concentration in the WY-4 reactor during the shock reached 190 mg/L, 53% lower than in the control. Propionate degradation was enhanced, with only trace amounts remaining in the bottom zone of the WY-4 reactor, whereas acetate and propionate continued to accumulate in the control. During the first nine days of recovery, methane yield was approximately 20% higher in the WY-4 reactor. Principal component analysis showed a faster recovery of AHL profiles, accompanied by altered AHL-EPS relationships. Although dominant microbial populations changed little, the WY-4 reactor maintained greater microbial richness and diversity. The homoacetogenic bioaugmentation with WY-4 enhanced UASB resilience by reducing VFA accumulation, accelerating methane recovery, and promoting restoration of AHL-mediated quorum sensing following short-term complex shock.