Performance and mechanism of iron-carbon enhancing medium chain fatty acids production from waste sludge

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 (113.78 mmol/L) and selectivity of MCCs were significantly enhanced by 30.50 % and 144.48 % respectively, at 20 g/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 Fe 2 + , 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.