Operation Efficiency Analysis Of NaClO Online Oxidation Cleaning For MBR Based On BAC System

With the increasingly serious water pollution,the membrane bioreactor（MBR）technology stands out from many other wastewater treatment technologies because of its small area,low cost and high water yield.It has become a very competitive choice in the field of wastewater treatment and reuse.However,during the operation of MBR,membrane pollution will occur on the membrane pore and surface,and the formation of pollution layer will lead to the decrease of membrane water yield of MBR,further leading to the increase of MBR operation cost.The NaClO chemical cleaning of membrane components can effectively remove the pollutants blocking the membrane holes and surface,and greatly restore the membrane flux,but it will also have a serious impact on the activated sludge system,making the activated sludge in an unstable state.Previous studies of our research group showed that the activated sludge floc after high salt impact would have flocculation behavior,and powdered activated carbon（PAC）was added during recovery to enhance the bioflocculation process.Biological activated carbon（BAC）is a unique activated sludge system in which microorganisms and bacteria in activated sludge live on PAC.It has the function of adsorption of PAC and degradation of microorganisms,which can strengthen the impact resistance load of activated sludge system.This topic focuses on the study of the operation efficiency of MBR（B-MBR）under BAC system,focusing on the membrane pollution behavior under the condition of MBR online chemical cleaning,and building a new method to effectively mitigate the membrane pollution in the process of online oxidation cleaning.The main research contents and results include:（1）B-MBR pollutant removal test results show that:Compared with the control reactor（C-MBR）,the removal rate of chemical oxygen demand（COD）of B-MBR was increased by5.1%,the removal rate of total phosphorus（TP）was increased by 7.1%.However,ammonium nitrogen,NH₄⁺-N removal rate was not significantly increased,only increased by 2.1%;The structure of extracellular polymeric substances（EPS）in B-MBR and C-MBR was not significantly different by infrared spectroscopy.In the detection experiment of each component content extracted from EPS,it can be found that B-MBR and C-MBR have similar PN/PS values（1.79 and 1.88）,indicating that they have similar spatial configuration.From the perspective of EPS content release after impact,the total EPS concentration of C-MBR is1.82 times that of B-MBR,which indicates that B-MBR significantly improves the impact resistance of EPS after NaClO impact and plays a positive role in the mitigation of membrane pollution.（2）The analysis of the characteristics of activated sludge mixture showed that compared with C-MBR,the particle size of B-MBR increased by 18.97%,and the average particle size of B-MBR and C-MBR decreased by 11.18%and 13.72%,respectively,after the impact.B-MBR produced more powerful floc.The Chao1 index of B-MBR was 1256.11,and that of C-MBR was 1051.42.The microbial community richness of B-MBR was better than that of ordinary activated sludge.After NaClO online cleaning,the content of trihalomethane generated by C-MBR is 3.09 times that of B-MBR.B-MBR can indeed adsorb a certain amount of trihalomethane precursor,thus inhibiting the generation of trihalomethane.The internal reaction of B-MBR altered the response correlation between cyclic diguanylic acid（3’,5’-cyclic Diguanylic acid,c-di-GMP）and EPS（p>0.05）,but the general trend was consistent with that of C-MBR,i.e.,the EPS concentration increased when the concentration of c-di-GMP decreased.（3）The thermodynamic analysis shows that the electron-supplying capacityγ^-of C-MBR decreases by 88.61%and B-MBR by 68.21%after the impact.The serious degree ofγ^-decline will lead to the formation of thin pollution layer during the operation of MBR,and the subsequent accumulation of film pollution will accelerate.At the same time,the hydrophobicity of sludge surface is determined by the value of?G_sws,and it is found that B-MBR decreases 14.27 times.The exposure of hydrophobic substances on the surface of sludge in C-MBR was higher than that in B-MBR,which decreased by 24.91 times.B-MBR has a lower potential for membrane contamination.In the analysis of the force between floc and membrane,it is found that C-MBR（291.01 k T）has a higher energy barrier（377.90 k T）after impact,which inhibits the adhesion of contaminated substances on the membrane surface.