Enhanced efficiency of biological excess sludge hydrolysis under anaerobic digestion by additional enzymes

In this investigation, the effects of commercial enzyme preparation containing alpha amylase and neutral protease on hydrolysis of excess sludge and the kinetic analysis of hydrolysis process were evaluated. The results indicated that amylase treatment displayed higher hydrolysis efficiency than that of protease. VSS reduction greatly increased to 39.70% for protease and 54.24% for amylase at the enzyme dosage of 6% (w/w), respectively. The hydrolysis rate of sludge improved with temperature increasing from 40 to 50 °C, which could be well described by the amended Arrhenius equation. Mixed-enzyme had great impact on sludge solubilisation than single enzyme. The mixture of two enzymes (protease:amylase = 1:3) resulted in optimum hydrolysis efficiency, the efficiency of solids hydrolysis increased from 10% (control test) to 68.43% at the temperature of 50 °C. Correspondingly, the concentration of reducing sugar and NH 4 + -N improved about 377% and 201%, respectively. According to the kinetic analysis of enzymatic hydrolysis process, VSS solubilisation process within prior 4 h followed first-order kinetics. Compared with control test, the hydrolysis rate improved significantly at 50 °C when either single enzyme or mixed-enzyme was added.