Facilitating biosynthesis of short chain fatty acids mediated by sulfite during anaerobic fermentation from algae-bacteria consortia

Algae-bacteria consortia (ABC) are a promising biotechnology for low-carbon wastewater treatment, yet the sustainable management of waste ABC (WABC) remains a challenge. This study investigates the effects of in-situ sulfite treatment on short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF) of WABC. Batch tests with 0–500 mgS/L sulfite revealed that the maximum SFCAs production reached 347.8 mg COD/g VS (2.88-fold increase vs the control group). Sulfite simultaneously achieved 60.3% pathogen inactivation through hydroxyl radical generation and Gram-positive cell wall disruption. Microbial analysis showed enriched SCFAs-producers and suppressed methanogens. Ecological process further clarified that sulfite reshaped microbial structure through heterogeneous selection and dispersal limitation. Economic analysis showed good feasibility, showing that sulfite required much less chemical input than other conventional pretreatments and achieved 103–228% higher net value. This work provides a lower-carbon route for WABC management through in-situ sulfite treatment, aligning sludge valorization with circular economy principles.