Effect of sulphidogenesis on acid-phase digestion of waste activated sludge

 This paper reports the influence of sulfate-reducing bacterial activity on acidogenic digestion of waste activated sludge (WAS). A series of experiments was conducted by feeding WAS to a 10-l, completely mixed, mesophilic reactor maintained at pH 5.0 under sulfidogenic and non-sulfidogenic conditions. Analyses of volatile fatty acids indicated that the productions of acetic and propionic acids were slightly increased by sulfidogenic activity at 218 mg/l level of sulfate when COD sulfate ratio was 55:1. Higher amounts of methanol, ethanol and hydrogen were observed in the non-sulfidogenic condition, but ammonia was lower than in the moderate sulfidogenic runs. At 0.63 kg VS/m3 d loading rate the hydrolysis was above 90% in both moderate sulfidogenic and non- sulfidogenic runs. The results of these experiments showed the possible influence of moderate sulfidogenesis in the protein degradation of WAS anaerobic digestion. However, the acid-phase digestion was adversely affected by increasing the sulfate concentration to 400 mg/l.