Effects of pH on the Waste Activated Sludge Hydrolysis and Acidification under Mesophilic and Thermophilic Conditions

The effects of pH on the hydrolysis and acidification from WAS in mesophilic and thermophilic anaerobic fermentation was investigated in this study. Both the mesophilic and thermophilic waste activated sludge (WAS) hydrolysis were improved significantly at alkaline pHs than at other pHs. Themophilic conditions improved the WAS hydrolysis compared to that mesophilic ones. The accumulation of short-chain fatty acids (SCFAs) at alkaline pHs was greater than at acidic or uncontrolled pHs in mesophilic fermentation. While the thermophilic acidification was inhibitedly severely at strong alkaline or strong acid conditions. The maximum SCFAs obtained in this study was 3798.2 mg COD/L at pH 10.0 in mesophilic fermentation and 4775.9 at pH 8.0 in thermophilic respectively. Acetic acid was the prevalent acids in the SCFAs at various pHs under both temperature conditions. The mean sum of acetic acid and propionic acid accumulation were 1979.4 mgCOD/L and 2454.6 under mesophilic (pH 10.0) and thermophilic (pH 8.0) conditions respectively.