Exogenous N-hexanoyl-L-homoserine lactone assists in upflow anaerobic sludge blanket recovery from acetate accumulation via aceticlastic methanogens enrichment.

Volatile fatty acids (VFAs) accumulation caused by shock loading severely hampers the performance and stability of anaerobic digestion. An upflow anaerobic sludge blanket (UASB) was operated to examine its performance, sludge properties, and microbial community behavior during shock loading and recovery with exogenous N-hexanoyl-L-homoserine lactone (C-HSL). After shock loading, chemical oxygen demand (COD) removal was significantly reduced from 79.09% to 65.63%. The abundance of Methanosarcinales also significantly decreased, which resulted in acetate accumulation (1,163.55 mg/L). Sludge granules disintegrated along with the decrease in extracellular polymeric substances (EPS). After supplying 1 μg/L C-HSL, COD removal resumed to 75.10%. Furthermore, C-HSL enhanced the abundance and metabolic activity of aceticlastic methanogens, decreased acetate concentration to 146.87 mg/L, improved EPS secretion, and caused the re-assembly of disintegrated sludges to form large granules. These results advanced our understanding of microbial community behavior and provided an attractive strategy for restoration of UASB recovered from shock loading.