Enhanced VFAs production through anaerobic co-fermentation of dewatered sludge and food waste: Insights into performance, microbial dynamics and metabolic pathways

Anaerobic fermentation is a promising process for the recovery of high-value volatile fatty acids from food waste (FW). One of the main challenges, however, is that the fermentation environment tends to acidify and the system collapses. Dewatered sludge (DS), which is waste activated sludge being generated in large quantities in wastewater plants, is rich in organic matter. Therefore, this study investigated the feasibility and mechanism of co-fermentation of DS and FW. Results indicated that the production of VFAs (especially acetic acid and butyric acid) was significantly promoted when the FW:DS was 4:1 (VS ratio) with a concentration of 37,421 mg COD/L, which was nearly 9 times higher than that of single FW. The addition of DS improved the fermentation environment (suitable pH and ORP), increased microbial diversity and enriched functional microorganisms (Prevotella, Olsenella, and Pseudomonas). PICRUSt2 analysis indicated that the addition of DS balanced carbohydrate metabolism and upregulated the expression of key genes involved in the metabolic pathways from pyruvate to propionate and butyrate, such as MUT, MCEE and pct. Overall, this study provides a promising approach to produce VFAs from FW with DS and improves the resourceful use of dewatered sludge.