Construction Of Quorum Quenching Beads Core-shell Structure And Its Capacity For Membrane Biofouling Control

Membrane bioreactors(MBRs),as a highly efficient wastewater treatment technology,has the advantages of excellent biological treatment effect,easier for the separation of biomass and smaller occupation area and have become one of the most promising treatment technologies for now.However,the membrane fouling in MBR,especially the membrane biofouling,limits its further development.Quorum quenching(QQ)technology,based on quorum sensing(QS),has been proved to be an efficient method to mitigate biofouling in MBRs.Moreover,many studies have certified that QQ beads composed of sodium alginate and QQ bacteria have shown wonderful biofouling mitigation and reduced the extracellular polymeric substances(EPS)contents in MBR.But,pure bacterial sodium alginate beads(SAs)with low mechanical strength and poor chemical stability cannot maintain a long-term stable operation in MBR.Therefore,they are not worthy of practical application in engineering.In this paper,in order to enhance practicability of SAs and promote its further development in membrane fouling inhibition,chitosan and polyacrylonitrile(PAN)were chosen to strengthen SAs and constructe core-shell structure of QQ beads by coating sodium alginate cores,and then extend their service life,improve their practical performance,enable them to keep QQ ability stably in MBR for a long term,mitigate biofouling at last.We prepared three types of QQ beads with same cross-linked algiante cores successfully: SAs with single chitosan layer(SA-Cs),SAs with single PAN membrane layer(SA-Ps)and SAs with both chitosan and PAN membrane layers(SA-C-Ps),and pure SAs.The results indicated that the microcapsules coated with PAN membrane layer showed excellent performance in terms of chemical stability(preventing bacteria leakage from the microcapsules),physical stability(increasing service life)and hardness work(higher mechanical strength).And confocal laser scanning microscopy(CLSM)images demonstrated that there were less dead bacteria in the microcapsules coated with both chitosan and PAN membrane layers than those coated with only PAN membrane layer for the reason that chitosan layer in layer by layer(LBL)structure can protect bacteria entrapped in alginate cores from the hurt caused by the process of coating PAN membrane layer.At the same time,the vacant microcapsules coated with PAN membrane layer presented more efficient antibiofouling ability than those not in the physical washing test.The QQ activity experiment showed that coating membrane layers(especially the PAN layer)did affect the material transfer in the beads during a short time,and reduced QQ activity compared with SAs.But,the PAN layer expressed obvious assistance in terms of maintaining the long-term QQ ability of QQ beads.And the QQ active composition was also investigated,it was found that the AHL adsorption of QQ beads mainly occurred in the first 10 min(during this period,the degradation and adsorption of AHL were caried out simultaneously),and then reached the the end of adsorption,whereafter the QQ activity was dominated by the degradation.Meanwhile,the impact of chitosan and PAN layer on AHL adsorption of QQ beads was negligible.After comprehensive comparison of three types of QQ beads,the SA-C-Ps were chosen to have a MBR operation,and the result showed that SA-C-Ps could significantly mitigate membrane fouling,inhibit the formation of biofilm and reduce EPS contents in MBR.Besides,we found that exogenous dosing of QQ bacteria would not affect MBR performance and activated sludge performance,so MBR can still work as usual.All the above proved that SA-C-Ps are with great potential in MBR mitigation biofouling.