Improved Yields of Soluble Substrates from Primary Sludge Fermentation under Alkaline Condition

A series of batch experiments on improving production of soluble substrates such as soluble chemical oxygen demand (SCOD), Short-chain fatty acids (SCFAs), soluble protein as well as soluble carbohydrate from primary sludge fermentation were conducted controlling pH at 4, 7, 10 and uncontrolled (the blank test). Results presented that pH 10 had great advantages over improvements of soluble organic materials especially for SCFAs than pH 7, 4 and blank test in any fermentation time. Sludge hydrolysis and acidification at pH 10 were more efficient than those at other pH values and the blank test. The maximal yields of SCOD (5755 mg/L) and total SCFAs (3510.86 mgCOD/L) were attained simultaneously at pH 10 on the 5th day. Meanwhile, soluble protein and carbohydrate were up to 1746.55 mgCOD/L and 226.41 mgCOD/L respectively, with increasing amounts in excess of 4 and 8 times of their initiative yields. Better hydrolysis and acidification produced more SCFAs, nevertheless, less SCFAs were consumed to be converted to methane, which resulted in large improvement of SCFAs production.