Cellular and compositional insight into the sludge dewatering process using enzyme treatment

Removal of intracellular water in microbial cells remains a key issue for sludge disposal, and here, a novel method of enzymatic treatment with two enzymes, lysozyme and protease, was employed. Total internal reflection fluorescence microscope (TIRF) was applied to image the bacteria in sludge and quantify the evolution of sludge bacteria for the first time. The ratio of dead/live bacterial cells was always higher in the presence of lysozyme than in the presence of protease, indicating that lysozyme has higher activity in inducing bacterial cell degradation and releasing intracellular water. The compositions of extracellular polymeric substances (EPS) were further measured, and the results show that the dewatering performance of sludge is correlated both to the release of cell contents and the variations in EPS composition during cell degradation. Moreover, kinetic analysis demonstrated that the enzyme-catalyzed reaction was substantially completed within 1 h, i.e., the reaction was quite rapid during the first 1 h, and thereafter, it gradually reduced to stability. The mechanism of enzymatic treatment of sludge explored in this study thus not only enhanced the understanding of sludge deep dewatering but also provided significant methodological clues for the disposal of sludge.