Continuous Alkaline Fermentation with Peroxydisulfate Pretreatment of Dewatered Sludge: Microbial Mechanisms for Doubling the Production of Volatile Fatty Acids

Peroxydisulfate (PDS) pretreatment promotes sludge reduction and utilization, and it acidifies the anaerobic fermentation (AF) system, yet the continuous alkaline conditions demonstrated superior volatile fatty acids (VFAs) production from the sludge AF. For evaluating the feasibility of integrating PDS with continuous alkaline AF of sludge to enhance VFA production, six different dosages (0, 0.02, 0.04, 0.08, 0.1, and 0.2 g PDS/g VS) were evaluated under continuous alkaline conditions (pH = 10). The findings indicated that adding 0.08 g of PDS/g of VS increased the abundance of VFA-producing bacteria, such as Actinobacteriota, Chloroflexi, and Patescibacteria. Meanwhile, this condition also reduced the abundance of amino acid metabolism and increased the abundance of carbohydrate metabolism. Additionally, the abundances of β-glucosidase [EC: 3.2.1.21], α-glucosidase [EC: 3.2.1.20], and other key VFA production enzymes increased. At this dosage, the highest VFA yield was achieved, which was 5278.86 mg COD/L (3 times higher than alkaline AF alone). Economic analysis revealed that the potential net benefit at a dosage of 0.08 g PDS/g VS was approximately triple that of alkaline AF alone. This research aims to establish a robust theoretical foundation for the utilization of PDS in sludge alkaline fermentation.