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 experimen ts was conducted by feeding WAS to a 10-l, completely mixed, mesophilic rea ctor maintained at pH 5.0 under sulfidogenic and non-sulfidogenic condition s. Analyses of volatile fatty acids indicated that the productions of aceti c and propionic acids were slightly increased by sulfidogenic activity at 2 18 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 condi tion, but ammonia was lower than in the moderate sulfidogenic runs. At 0.63 kg VS/m(3) d loading rate the hydrolysis was above 90% in both moderate su lfidogenic and non-sulfidogenic runs. The results of these experiments show ed the possible influence of moderate sulfidogenesis in the protein degrada tion of WAS anaerobic digestion. However, the acid-phase digestion was adve rsely affected by increasing the sulfate concentration to 400 mg/l.