Enhanced economic benefit of recycling Fe3O4 for promotion of volatile fatty acids production in anaerobic fermentation of food waste

Fe3O4 addition in anaerobic fermentation of food waste (FW) is promising for enhancing volatile fatty acids (VFAs) production. However, the large amount of Fe3O4 in the digestate fertilizer leads to the waste of resources and possible toxicity to organisms. Thus, this study investigated the feasibility of Fe3O4 recycling for VFAs enhancement in anaerobic fermentation of FW and performed the cost-benefit evaluation of this process. Results revealed that Fe3O4 could be successfully recycled twice with recovery rates of 71.5% and 65.5%, respectively. X-ray diffraction analysis revealed a slight change to the Fe2O3-like structure after 2-time recycling. The VFAs yields were enhanced by 17.2% and 17.0% in Cycles 1 and 2 owing to the enhanced activities of hydrolytic and acid-forming enzymes. The net income of the Fe3O4 recycling process was about 13-fold higher than that of the conventional treatment process, suggesting a promising and economically feasible strategy for enhancing VFAs production.