Fe-N-Modified Sludge Biochar for Enhanced Acetic Acid Production from Sludge Anaerobic Fermentation

Sustainable recycling of carbon resources from waste-activated sludge (WAS) is essential for advancing the circular wastewater economy. Anaerobic fermentation provides an eco-efficient pathway for converting organic matter from waste-activated sludge into volatile fatty acids (VFAs). In this study, Fe-N modified biochar was innovatively prepared from WAS for acetic acid yield enhancement, and the system realized the closure of the material cycle. Results show that adding Fe-N-modified biochar (made under the conditions of 0.2M FeCl3 and 10 g/L urea) led to a 38.8% increase in acetic acid yield (1745 mg/L) and a 5.7% increase in its percentage (60.5%) compared to the control. It also improved sludge hydrolysis and hydrolase activity. In addition, Fe-N-modified biochar increased the relative abundance of Chloroflexi, Actinobacteria, and Bacteroidetes, among which Chloroflexi is an electro-active microorganism that promotes the transformation of propionic and butyric acids to acetic acid, while Bacteroidetes is the primary microorganism responsible for VFA production. In summary, Fe-N-modified biochar may serve as an effective material for promoting acetic acid production during the anaerobic fermentation of WAS.