Enhanced Medium-Chain Fatty Acids Production by Iron–Carbon Microelectrolysis: Performance and Mechanisms

The low biodegradability and slack electron transfer of waste-activated sludge (WAS) posed significant challenges to medium-chain fatty acids (MCFAs) production. Herein, a viable iron–carbon microelectrolysis (ICME) technique was proposed to improve the synthesis of MCFAs from WAS through accelerating WAS disintegration and substrate transformation and increasing the electron transport efficiency, simultaneously. Results showed that the maximum MCFAs production in the ICME-mediated chain elongation (CE) process was up to 4.4 times that of the control. Mechanistic exploration revealed that the formation of microscopic galvanic cells drove boosted electron transfer within the ICME, which greatly enhanced the effect of direct interspecies electron transfer (DIET), and thus promoted hydrolysis, acidogenesis, and CE processes. Additionally, Fe²⁺ formed by ICME facilitated orthophosphate removal through precipitation. Microbial community analysis revealed an increase in the number of anaerobic populations associated with hydrolysis and acidogenesis. Overall, this study demonstrated the viability of ICME for promoting MCFAs production from WAS, offering a novel avenue for microelectrolysis-aided resource recovery.