Volatile fatty acid augmentation and microbial community responses in anaerobic co-fermentation process of waste-activated sludge mixed with corn stalk and livestock manure

This study investigated the acidogenic and microbiological perspectives in the anaerobic co-fermentation of waste-activated sludge (WAS) mixed with corn stalk (CS) and pig manure (PM). The volatile fatty acids (VFAs) increased dramatically to over 5000 mg COD/L accumulation just within 4–5 days with the feedstock carbon to nitrogen (C/N) ratio regulation of 20/1. The CS and PM addition enhanced the compressibility of fermentation residuals by increasing the particle distribution spread index (DSI). Moreover, the external carbon addition conduced to bacterial consortia diversity rising and uneven population distribution in the co-fermentation, which contributed to VFAs accumulation potentially. The organic loading rate (OLR) correlated with bacterial community closely at the early stage (days 1–5), while the oxidation-reduction potential (ORP) and pH played more important roles on bacterial consortia at the terminal stage (days 6–10). The C/N ratio adjustment by CS and PM and proper optimizations of OLR, pH, and ORP at various running stages facilitated VFA accumulation during the co-fermentation operation.