Impact of Salinity on Butyric Acid Production During Anaerobic Fermentation of Food Wastewater: Organic Composition, Enzyme Activity and Microbial Community

Food wastewater (FW) is rich in biodegradable organics and holds potential for producing high-value volatile fatty acids (VFAs) via anaerobic fermentation (AF). Among influencing factors, salinity plays a key role in butyric acid production, yet the underlying mechanisms remain unclear. This study investigates salinity-driven changes in butyric acid production by analyzing organic composition, enzyme activity, and microbial community shifts. Results showed that total VFAs yield remained stable (~13 g/L) under 0-12 g/L salinity, while 10 g/L notably enhanced butyric acid accumulation (7061.4 mg/L, 86.9% of VFAs). Further analysis revealed that high salinity accelerated substrate degradation, particularly carbohydrates and proteins, while dynamically regulating enzyme activity involved in butyric acid synthesis. Salt stress promoted the dominance of salt-tolerant bacteria, such as Bifidobacterium, and inhibited acetic acid production pathways. These findings suggest salinity can be strategically leveraged to steer AF toward high butyric acid selectivity, offering new insights into efficient FW valorization.