Weak electric field promotes anaerobic granular sludge formation to enhance medium-chain fatty acids synthesis

Granular sludges can resist the toxicity inhibition of medium-chain fatty acids (MCFAs) and enhance the chain elongation (CE) process. However, the granulation process is time-consuming and requires a suitable facilitating granulation mean. This study proposed two continuous fed Expanded Granular Sludge Bed bioreactors, one with electric field (EF) and one without, to demonstrate the promotion of sludge granulation by EF and the enhancement of MCFAs production efficiency by the anaerobic granular sludge (AnGS). Through more than 50 days of operation, the EF was demonstrated to be able to promote the granulation, and the formed AnGS enhanced MCFAs yield by 36 %. Besides, mechanism analysis indicated that the EF promoted microbial aggregation and extracellular polymeric substances (EPS) synthesis, which enabled AnGS to form more easily. Besides, AnGS formed with EF improved extracellular electron transfer capacity and microbial function activity, which also contributed to the production of more MCFAs. Overall, this study provides a method to facilitate AnGS granulation and revealed the underlying mechanisms, and offers important support for the diverse applications of AnGS in other bioresources recovery bioprocesses.