Performance and Mechanism of Iron-carbon Enhancing Medium Chain Fatty Acids Production from Waste Sludge

Abstract

A novel iron-carbon technique to enhance the production of medium-chain carboxylates (MCCs) from waste activated sludge (WAS) during anaerobic fermentation was proposed in this study. Results revealed that the maximal MCCs production (113.78mmol/L) and selectivity of MCCs were significantly enhanced by 30.50% and 144.48% respectively, at 20g/L iron-carbon. The optimal fermentation time was also shortened from 18 to 8 days. Mechanistic investigations disclosed that MCCs formation was significantly promoted by Fe2+, which was released from iron-carbon and assimilated by microorganisms. Further analysis showed that the solubilization (36.35%), hydrolysis (3.87%), and acidogenesis (33.47%) processes of WAS were promoted by iron-carbon, supplying more substrates (short-chain carboxylates (SCCs)) for the synthesis of MCCs. Iron-carbon enhanced the abundances of key microorganisms participating in the aforementioned bioprocesses, according to microbial community investigation. Additionally, the conductivity of sludge was improved by 127.84% with the addition of iron-carbon particles, thus improved the conditions for anaerobic biological activities.