Influence Of Ozonation Disintegration On Sludge Characteristics And Study On A Concept Of In-situ Sludge Reduction Process

To achieve sustainable use of water resources, the treating rate of sewage water must be increased to protect the natural water environment. The activated sludge treatment process is one of the most common methods used to remove organic contaminants in a sewage wastewater treatment plant. As a result, a considerable amount of activated sludge was produced using activated sludge method. The conventional management and disposal methods of sewage sludge were under stronger public opposition and stricter regulatory pressure. Therefore, the management and disposal of excess biomass have become a difficult problem in a wastewater treatment plant.In order to implement both domestic wastewater treatment and sludge reduction, the technical study of sludge reduction of combining the chemical method with biological method was developed, integrating the merits of MBR and in-situ sludge ozonation. Effects of ozonation on sludge characteristics and operation of MBR were also studied.Total study period was divided into three stages. At first stage, a series of batch studies were carried out to investigate the effect of ozonation on sludge properties (MLSS,MLVSS,SCOD,TN,NH₃-N,TP,pH,SOUR et al.) at different ozone concentrations and action times. The reaction mechanisms of sludge ozonation were also developed based on the variation laws of sludge properties. At the second stage, 36 series of batch experiments were carried out to study the effect of ozone concentration and action time onΔSCOD which was used to indicate the efficiency of sludge ozonation reaction. Statistics of the experimental results by the dual linear regression were analyzed to build up mathematical model of sludge ozonation reaction. At the last stage, two laboratory scale membrane bioreactors (MBR_S) were operated in parallel for a long period of 60 days to evaluate the influence of sludge ozonation on sludge yield and permeate quality. The test reactor is with 0.025gO₃/gSS ozone dosage exposed to sludge, and the control reactor is without any ozone exposed to sludge. Based on above studies, the main results can be conducted as foliowings:(1) It was found that ozone could disrupt the cell walls and cause the release of plasm from the cells, which was reused by microbe under cryptic conditions result in the excess sludge reduction. The content of soluble organics (SCOD) in the solution increased from 7mg·L^-1 to 306.7mg·L^-1 by 43 times with 40.25 mg·L^-1 ozone concentration exposed to sludge. Sludge ozonation also resulted in the contents of TN and TP increased in the solution.(2) There are some changes in pH and SOUR of sludge mixed liquor, but the microbial activity just decreased by 35% from 9.92mgO₂/gVSS·h to 6.45 mgO₂/gVSS·h at the 0.03 gO₃/gSS ozone concentration.(3) With the independent variable of ozone concentration (C) and action time (t), the mathematical model with dependent variable ofΔSCOD isΔSCOD = k₀×C^4.106×t^1.276 . After analyzing, we found the influence sequence was as following: C > t.(4) Two systems both did not discharge sludge except sampling during a long period of 60 days of experiment operation, the sludge concentration of control reactor increased by 5126mg·L^-1 from 6284mg·L^-1 to 11410mg·L^-1. But the sludge concentration of test reactor just increased by 513mg·L^-1 from 6223mg·L^-1 to 6736mg·L^-1. The results show that sludge yield coefficient of control reactor is 0.1147 and the test reactor is 0.0096, both of which are smaller than sludge yield coefficient in conventional activated-sludge process. Furthermore, it was found that the yield of sludge of test reactor is close to zero excess sludge production.(5) The membrane effluent COD,NH₃-N,TP concentration of test reactor all were higher than control reactor. The TP of test reactor is twice as high as control reactor, and both of them are below 3.5 mg·L^-1. Ozonation influenced the removal efficiency of COD and NH₃-N slightly, and average removal rates of test reactor were respectively 92.43% (COD) and 95.7% (NH₃-N).The new process concept of in-situ ozonation for sludge reduction is different from the conventional sludge recycle. The ozone could be added to MBR directly in this site treatment process. Therefore, the ozone oxidation tank could be saved, and the footprint and construction cost could also be saved. This paper analyzed the possibility of in-situ ozonation for sludge reduction in membrane bioreactor, which was of practical significance for industrial promotion.