[Enhanced hydrolysis of excess sludge by external enzymes]

The effects of external enzymes to enhance excess sludge hydrolysis were investigated. Protease and alpha-amylase were added singly and in combination, and it was found that external enzymes can enhance sludge hydrolysis. When treated with single enzyme, alpha-amylase had higher efficiency than protease, SCOD/TCOD rose from 16.3% to 22.3% and VSS reduction improved from 39.8% to 54.24% at the optimal dosage of 60 mg/g (calculated by addition of enzyme in TS). Furthermore, mixture enzymes showed better hydrolysis efficiency than single enzyme. The highest VSS reduction was observed at an enzyme mixture ratio of 1:3 with protease and amylase when the hydrolysis temperature was 50 degrees C, and the VSS reduction achieved 68.43%. Correspondingly, the concentration of reducing sugar and NH4+ -N rose from 37.29, 47.60 mg/L to 177.8, 143.43 mg/L, respectively. According to the kinetic and enzymatic analysis of hydrolysis process, sludge hydrolysis within prior 4 h was consistent with first-order reaction dynamic. During the hydrolysis, both protease and amylase activity rose gradually, the highest activity observed were 2.57 U/mL and 4.64 U/mL at 4h after hydrolysis. Thereafter, the enzyme activity decreased.