EVALUATION OF SLUDGE REDUCTION IN AN ACTIVATED SLUDGE PROCESS USING LYSOZYMES

A sludge collection tank was set up for the sludge return process of a conventional activated sludge (CAS) process. Lysozymes were then added into the sludge collection tank. The present study investigated the sludge reduction effect and the capacity for treating pollutants and analysed the possible causes behind the sludge reduction. The results show that when the sludge load was 0.5 kg (chemical oxygen demand)/kg (mixed liquor suspended solids). d, the amount of the excess sludge in the system with added lysozymes reduced by 37.33% compared with the amount of the excess sludge in the CAS system; in addition, the efficiency of the system with added lysozymes to treat organic compounds did not decrease due to the addition of lysozymes. An analysis of the causes for the sludge reduction shows that the energy uncoupling that occurred due to the alternation of the aerobic and anaerobic conditions of the sludge in the system with added lysozymes had almost no impact on reducing the amount of sludge in the system; the increase in the activity of the sludge in the system as well as the enhancement in the endogenous metabolic capacity caused the sludge reduction. Denaturing gradient gel electrophoresis analysis shows that there was no significant difference in the microbial diversity between the system with added lysozymes and the CAS system, which indicates that the lysozymes did not promote the reduction in the sludge yield by altering the microbial community structure in the activated sludge system. Compared with the oxic-settlinganaerobic sludge reduction system, strict anaerobic operating conditions for the sludge collection tank were not required for the system with added lysozymes, and the residence time of the sludge in the sludge collection tank was nevertheless significantly reduced, which is an advantage for the practical application of sludge reduction.