Metabolic regulation of waste activated sludge fermentation: Dictating product spectrum through strategic manipulation of incompletely oxidizing sulfate-reducing bacteria

Incomplete oxidative sulfate-reducing bacteria (io-SRB) enhance short-chain fatty acids (SCFAs) production from waste activated sludge (WAS) fermentation by consuming hydrogen to lower its partial pressure, which alleviates the thermodynamic constraints of the acetogenesis process. However, limited information available for the functional structure of io-SRB that regulate acetogenic metabolism, even for the whole WAS fermentation process, persists as a critical knowledge gap. This work elucidated the effects of io-SRB strategic manipulation on SCFAs production. The group inoculated with propionate-, butyrate-, and valerate-metabolizing io-SRB at a ratio of 1:4:1 (v/v) achieved the highest SCFAs production (2083.9 ± 156.3 mg COD/L), which was 1.1–1.2 times higher than the other groups. Carbohydrates could serve as substrates for SCFAs production. This group gained the highest utilization of soluble carbohydrates (105.0 ± 9.2 mg COD/L). Mantel test identified a synergistic interaction between carbohydrate-utilizing, butyrate-producing anaerobic fermentative bacteria (AFB) and io-SRB. These AFB were enriched in this group. Carbohydrate utilization was activated through microbial activity. Additionally, the life cycle assessment demonstrated the environmental benefits of the distinct strategic manipulation of io-SRB. This work provides an applicable strategy for advancing value-added chemicals recovery from WAS fermentation.