Effect of protease and cellulase on the characteristic of activated sludge

Sludge dewatering is a key part of sludge disposal since it can greatly reduce the volume of sludge and thus improve the treatment effect for handling and disposing. This study investigated the potential benefits of enzymatic pretreatment on activated sludge dewatering with protease and cellulase as a protein and polysaccharide degrading enzyme, respectively. Capillary suction time (CST) and the solid content after centrifugation were used to evaluate sludge dewatering. The particle size distribution, extracellular polymeric substances (EPS) content, infra-red (IR) spectrometry and microscope image were determined in an attempt to explain the observed changes in sludge dewaterability. The results indicated that adding protease and cellulase separately leads to an increase in CST and the increased value is higher with protease. Protease and cellulase both promote the degradation of protein and polysaccharide in the solids of activated sludge, leading to a smaller particle diameter and poorer dewaterability. However, due to the limited effects on the protein and polysaccharide content, the difference in sludge dewaterability is not large. Compared to the control, enzymatic pretreatment had no obvious effect on sludge IR spectrometry, while there was a detectable structure difference at a colloidal scale.