Granulation and response of anaerobic granular sludge to allicin stress while treating allicin-containing wastewater

In order to treat allicin-containing wastewater with antimicrobial characteristic, anaerobic granular sludge (AnGS) under allicin stress was cultivated, which completely granulated on day 143 in the up-flow anaerobic sludge bed (UASB). The mature allicin-tolerant AnGS had a granule size of 0.356–2.000 mm with an excellent settleability, and the chemical oxygen demand (COD) removal efficiency reached 93.26 %. Moreover, the tightly-bound extracellular polymeric substances (TB-EPS) and extracellular protein (PN) enchanted the formation and tolerance of AnGS under the allicin environment. Meanwhile, the short-chain N-acylhomoserine lactones (AHLs) including C4-HSL, C6-HSL and C8-HSL were utilized by quorum sensing (QS) to regulate EPS production during AnGS formation process, while the long-chain AHLs including C10-HSL, C12-HSL and C14-HSL had a positive effect towards the allicin stress. In addition, Acinetobacter and Petrimonas were observed to be the dominant allicin resistant genera, which along with the EPS producers of Comamonas and Thauera enhanced the AnGS tolerance. These results confirmed that the AHL-mediated QS regulated EPS production and the growth of functional bacteria involved in allicin-tolerant AnGS formation. This provides useful information for AnGS application in treating allicin-containing wastewater.