Study On The Efficiency Of MBR Treatment Of Salinity Domestic Sewage And The Change And Control Of Membrane Fouling Based On Microbial Quorum Sensing

At present,the world’s freshwater resources are increasingly scarce,and the use of seawater has been paid more and more attention.However,the use of seawater,especially the salty sewage produced by large-scale domestic seawater,is discharged to urban sewage plants,and the pollution caused by it has not yet been treated systematically.This study used a membrane bioreactor(MBR)to treat municipal wastewater with different salinities,and mainly studied the effects of different influent salinity on the system’s processing capacity,membrane pollution and quorum sensing signal molecules;and used molecular biological technology to analyze the change of microbial community structure in the reactor under different influent salinity.Firstly,the influence of salinity on the treatment effect of the membrane bioreactor was investigated,and the pollutant removal efficiency and membrane pollution changes in the MBR startup phase,MBR stable operation phase and salinity change phase were studied respectively.During the MBR start-up phase,the organic matter,nitrogen nutrients and phosphorus nutrients of the initial effluent fluctuated,and the system gradually stabilized after 12 days.During the stable operation of MBR,the influent salinity of reactor-a was 0 g/L,and it always maintained a stable operation state,and the influent salinity of reactor-b was 10 g/L(all calculated as Na Cl),after the influent salinity was changed,the treatment effects of organic matter,nitrogen nutrients and phosphorus nutrients showed a phenomenon of first declined and then rised,indicating that microorganisms had a certain ability to self-regulate to adapt to changes in salinity in the environment,making MBR had a better salt resistance on the impact of the degree of impact.During the salinity change stage,the reactor inlet water salinity increased with a gradient of 5 g/L,from 0 g/L to 20 g/L(all in Na Cl).As the inlet water salinity increased,the removal rate of pollutants gradually decreases.when the salinity of the influent water did not exceed 10 g/L.The effect of salinity on MBR was reversible.When the salinity of the influent water exceed 10 g/L,the removal efficiency of each pollutant further decreased,at that situation MBR has been unable to withstand the impact of salinity.Secondly,the changes of membrane fouling during the treatment of salty domestic sewage in the MBR reactor were investigated,and the changes of the characteristics of the mixed liquor suspended solids(MLSS),the changes of the membrane surface characteristics and the changes of the concentration of microbial signal molecules were studied,respectively.By investigating indicators such as trans-membrane pressure(TMP)&MLSS,extracellular polymeric substances(EPS),sludge particle size,zeta potential and electrical conductivity,it is found that with the increase of salinity,TMP continued to rise,and MLSS had a downward trend.When the influent salinity was 10 g/L,the largest contribution to the growth of TMP is that the polysaccharides and proteins of EPS increased significantly.By investigating the concentration changes of 6 AHL-type signal molecules(C6-HSL,C8-HSL,C10-HSL,C12-HSL,3oxo C8-HSL,3oxo C12-HSL)at different stages,it is found that the signal molecule C8 in the system was stable during MBR operation.-The content of C8-HSL was the highest,and the addition of salinity promoted the content of the six signal molecules to increase in different degrees,and then the content gradually returned to the previous state as time goes by.In the salinity change stage,the content of short-chain signal molecules C6-HSL and C8-HSL in the system was the highest.When the influent salinity was 5 g/L,the secretion of 6 types of signal molecules was stimulated the most,and when the influent salinity was 20 g/L,the microorganisms can no longer adapt to the normal secretion of signal molecules.Finally,the application effect of signal molecule quenching(QQ)in MBR reactor and the changes of the microbial community structure in each stage of the system were investigated.The changes of TMP,the change of signal molecule concentration and the start-up stage,stable operation stage,and different salinity stages were respectively investigated.Through the changes of TMP and the concentration of signal molecules,it was found that the QQ bacteria added by external sources effectively reduced the growth rate of TMP,delayed membrane fouling,and had different effects on different signal molecules.Among them,the quenching effect of C6-HSL,3-oxo-C8-HSL,3-oxo-C12-HSL is weak;the quenching effect of C10-HSL and C12-HSL is more obvious;the quenching effect of C8-HSL was obvious extinguish effect.High-throughput sequencing was performed by inspecting the MBR activated sludge mixture sampling in the start-up phase,stable operation phase,different salinity phase,and quenching phase to analyze the changes in the microbial community structure at different stages,in order to analyze the salinity effect from the perspective of microorganisms.Through high-throughput sequencing analysis,it is found that during the stable operation of MBR,Bacteroidetes and Alphaproteobacteria have the largest impact on membrane fouling and AHL signal molecules;during the salinity change phase,Gammaproteobacteria was effective for treating influent salinity less than 10g/L,and Alphaproteobacteria contributeed the most to the treatment of membrane fouling with influent salinity greater than 10 g/L;in the quenching stage,Bacteroidetes contributes the most to the quenching of MBR signal molecules in salty domestic sewage.This paper studied the influence of salinity on membrane fouling and quorum sensing in the reactor,in order to deepen the understanding of MBR treatment of salty domestic sewage and system membrane fouling changes,and improve the effect of salinity on MBR microbial quorum sensing and quorum sensing.The understanding of the effect of quenching provides more theoretical references for membrane fouling control.