Role of initial pH in modulating sulfur cycle dynamics in sludge anaerobic fermentation.

The initial pH plays a crucial role in sludge anaerobic fermentation (AF), which affects short-chain fatty acids production. However, its effect on toxic hydrogen sulfide (H2S) gas has been neglected. The results show that when the initial pH changes from 7 to 4 (9), the cumulative H2S production increases (decreases) by 142 % (45.4 %). The initial acidic pH and alkaline pH both promoted sludge disintegration, directly increased dissolved sulfide and organic sulfurs release. The acidic initial pH further decreased the ratio of α-helix/(β-fold + random coil) and destroyed the released organic sulfurs structure, which was conducive to H2S production. However, the initial acidic pH damaged cell membranes integrity and inhibited H2S producer activity. Moreover, the initial acidic pH changes the sulfide balance and promotes H2S gas release, while the initial alkaline pH promotes metal sulfide formation. These deepen the understanding of the link between pH and the anaerobic sulfur cycle.