Long-term exogenous addition of synthetic acyl homoserine lactone enhanced the anaerobic granulation process.

Although adding long-term acyl homoserine lactone (AHL) over one month was highly instructive for the development of an AHL-based anaerobic granulation strategy, the role of long-term exogenous AHL at different concentrations in the granulation process was poorly understood due to commercial exogenous AHL's extremely high cost. In this study, organic synthesis of N-decanoyl-homoserine lactone (C10-HSL) was employed for the first time to drastically reduce the cost of the AHL addition. Daily dosages of exogenous C10-HSL at 50 nM, 500 nM and 5000 nM were separately added into anaerobic bioreactors to promote the granulation process for as long as 168 days. 50 nM C10-HSL showed a negligible effect on the granulation process while 5000 nM C10-HSL achieved the best performance with the highest chemical oxygen demand (COD) removal, largest granule size and best extracellular polymeric substance production. Bacterial analysis indicated that exogenous C10-HSL showed a concentration-related effect in bacterial community organization. Besides, addition of 5000 nM C10-HSL resulted in the greatest promotion of Methanosaeta which was extremely important to the formation of anaerobic granule. This study provides a foundation for the future application of long-term exogenous AHL manipulation to improve the granulation process in an engineered ecosystem.