Hydrolysis kinetics in anaerobic digestion of waste activated sludge enhanced by α-amylase

The thermodynamics of waste activated sludge (WAS) hydrolysis process enhanced by additional α-amylase were evaluated in this paper. The effects of enzyme dosage and temperature on WAS hydrolysis were further discussed based on the analysis of variance (ANOVA). The results showed that the rate constant of α-amylase hydrolysis process (α-amylase = 0.06 g/g dry sludge (DS)) increased from 0.106 to 0.215 h−1 with the temperature increasing from 40 to 70 °C, and the reaction activation energy for VSS hydrolysis reduced from 62.72 kJ/mol (control test) to 20.19 kJ/mol (α-amylase treatment). Kinetics analysis indicated that the enzymatic hydrolysis process well fitted the first-order kinetics model at 50 °C, and the conversion coefficients (α) of VSS to soluble chemical oxygen demand (SCOD), carbohydrates and NH4+–N was found to be 0.266, 0.043 and 0.038, respectively. The model could certainly provide a dynamical description of mechanism and would be benefit to analysis, design, optimization and control of enzymatic hydrolysis process of WAS.

► The thermodynamics of WAS hydrolysis enhanced by α-amylase was investigated.
► The reaction activation energy was obtained.
► The substances conversion during WAS hydrolysis at the temperature of 50 °C was analyzed.
► The conversion coefficients of VSS to SCOD, carbohydrates and NH4+–N were obtained.
► ANOVA was used to analyze the effect of enzyme dosage and temperature on WAS hydrolysis.