Membrane Biofouling Control In Membrane Bioreactor Based On Quorum Quenching Theory

The development of membrane bioreactor(MBR)process is an important milestone in the field of wastewater treatment.Because of its high effluent water quality,low plant footprint,and easy operation,this process has been widely studied and applied for non-destructive treatment of various sewage worldwide.Although a great achievement on how to cost-effectively operate aerobic membrane bioreactor(Ae MBR)or anaerobic membrane bioreactor(An MBR)has been obtained,MBR membrane biofouling is still the main challenge limiting the further development of such technology.Recently,the quorum quenching(QQ)theory has been proposed to provide a strong guarantee for membrane pollution control and extension of MBR operational period.QQ is a metabolic behavior that exists between microorganisms,in which the bacteria with QQ function can secrete a quenching enzyme that can decompose the signal molecules that are used for the communication among microorganisms.As a result,the metabolic activities of microorganisms,the secretion of extracellular polymers(EPS)and their adhesion and accumulation on the surface of membrane modules are inhibited,thereby retarding membrane fouling.The QQ effect has been proven to be a promising technology for controlling Ae MBR membrane biofouling.If it can be applied to control membrane pollution in Ae MBR treating industrial wastewater,it could be a big step forward.The results show that Alginate(poly-vinyl alcohol)-Powder activated carbon-QQ strain(APQ)could significantly mitigate Ae MBR biofouling(45 days)compared with Control-MBR without beads(10 days).At the same time,APQ beads could effectively reduce the EPS content and acyl homoserine lactone(AHL)concentration in the biocake,and delay the adhesion rate of the biofilm on the membrane surface,thus showing a higher biofouling mitigation effect.By adding APQ,a significant reduction in inherent membrane resistance was also observed.The QQ activity test confirmed that the used APQ beads still had a high potential of AHL degradation,indicating that it can be used for membrane biofouling control in the long-term operation of Ae MBR.Investigating the dynamics of microbial communities in Ae MBR is also crucial for characterizing the mechanisms towards membrane fouling control.In the sludge mixture,the top three phyla Betaproteobacterials,Rhizobials,and Sphingobacteriales did not show significant differences between the absence and the presence of APQ bacteria.At the genus level,the abundance of Ferruginibacter decreased in the APQ-MBR,which is considered to be an important evidence for reducing membrane fouling.In the biocake,the abundance of Methyloversatilis which could play an important role in the biofilm formation process decreased in the APQ-MBR.In addition,co-occurrence network analysis suggested that C4-HSL was significantly positively correlated with various bacteria such as norank-f-AKYH767,unclassified-f-Burkholderiaceae,Hyphomicrobium,and Legionella.Although numerous studies demonstrated that QQ is an effective method to control membrane biological pollution in Ae MBR,it is still unclear whether QQ is feasible in An MBR.Microbacterium sp.a facultative anaerobic strain with QQ function was embedded in alginate-embedded beads(QQB)and employed in a laboratory-scale An MBR to study its potential for membrane fouling control.Compared to the Control and vacant bead(VB)stages,the operating time of the An MBR reactor with QQB addition was extended by about 6-8 times before reaching the predetermined maximum transmembrane pressure(TMP).Before the occurrence of"TMP jump",the concentration of AHL in the effluent in each stage was high.But compared with Control,the AHL in the biocake of QQB stage was significantly reduced.The addition of QQB also significantly reduced soluble microorganism(SMP).The EPS,especially protein of EPS,of the biocake in the QQB stage was reduced by 39.73%-80.58%.Meanwhile,a significant change in the organic functional groups was observed in the biocake compared with that of Control stage,in which the biopolymer(BP),building block(BB),and low molecule weight(LMW)content in the biocake in the QQB stage significantly decreased compared to the control stage.The QQ technology achieved satisfied membrane biofouling control in the An MBR,but the effluent N and P nutrients still needs to be further removed.Therefore,forward osmosis(FO)was used to achieve concentrated recovery of effluent nutrients.The influence of the effluent from different phases of An MBR on FO membrane biofouling was examined,and the results showed that the effluent from QQB stage can also reduce and slow down the biofouling of FO membrane.QQ technology was successfully applied to control An MBR membrane biofouling,in which a good membrane biofouling control effect was achieved without affecting the effluent water quality and methane production.The addition of swarm sterilization would certainly influence the native ecosystem.Studying the effect of QQB on microbial community in sludge mixture and biocake in An MBR is important for exploring the mechanism of QQ and mitigation of membrane biofouling.First,the changes in the microbial community of the sludge mixture and biocake showed that the addition of QQ strain increased the overall abundance of fermenting bacteria and acetogenesis.Among them,the abundance of Gram-negative acetogenesis decreased,and conversely,the abundance of Gram-positive acetogenesis increased significantly.Second,the addition of QQ strain resulted in the increase of the abundance of Treponema.There are two methanogenesis mechanisms using H₂/CO₂ in the QQB stage.One is to directly convert H₂/CO₂ to methane by hydrophilic methanogen,and the other is that H₂/CO₂ is first converted into acetic acid by Treponema,and then used by the acetogenic methanogens for methane production.In addition,the addition of QQ strain did not have a significant influence on the abundance of Methanobacterium and Methanoseatea(p>0.05)in the bulk sludge.While the abundance of Methanobacterium increased in the biocake during the QQB stage,the abundance of Methanosaeta showed no difference in the biocake during the VB and QQB stages.Meanwhile,adding embedded beads with different QQ strain dosage to the anaerobic system to investigate its effect on methane production.The results showed that the amount of QQ bacteria added positively correlated with methane production,but negatively correlated with the consumption rate of acetic acid.In addition,the content of EPS and AHL in the system did not show apparent differences among the different dosages of QQ strain.