| Membrane bioreactor（MBR）has been given increasing attentions because of their high quality effluent,small footprint and the separation of HRT and SRT.Nevertheless,mechanical aeration and membrane fouling have become main contributions to operational costs,which prevent the technology from wider applicability.In recent years,the interest in algal-bacterial processes has increased due to its high nutrients removal without mechanical aeration.However,it is still a challenge to prevent the algal-bacterial biomass washout from the system which would impair the effluent quality and destroy the system stability.Thus,a novel algal-sludge bacterial MBR（ASB-MBR）system constructing by introducing algal-sludge bacterial system in a MBR was proposed in our study.In this study,the particular objectives were:（1）to investigate the biological characteristics of algae and bacteria,the performance of wastewater treatment and membrane fouling（2）to explore the effects of algal-bacterial symbiosis and algae on the sludge properties and microbial community structures（3）to clarify the mechanisms of membrane fouling mitigation and nutrient removal improvement in ASB-MBR.3000 lux light intensity,1:5 algae/bacteria and 12h/12h light/dack are considered to be the optimum operation condition.During the long-term operation,the removal efficiencies of COD,NH4+-N,TN and PO43--P was 4%,11.7%,6.1%and 12.8%higher than those of C-MBR,respectively.The result of statistical analysis displayed that the symbiotic relationship between algae and bacteria play more important role rather than either of single species for nutrients removal.Compared with C-MBR,the increasing rate of biomass and the SOUR of glucose,starch and NH4+-N in ASB-MBR was increased by 26.6%,38.6%,37.05%and 54.24%,respectively.Moreover,the rate of algal production oxygen was 28.65%higher than that of algal original inoculation.Those indicated the improvement of microbial biological activity and the establishment of algal-bacterial symbiosis.The increasing rate of TMP in ASB-MBR was decreased 48.11%compared with that of C-MBR indicated the mitigation of membrane fouling.Compared with C-MBR,the zeta and floc size of ASB-MBR was decreased by24.58%and 22.09%,respectively implied the enhanced flocculability of algal-bacterial flocs.Additionally,the growth of the filamentous bacteria was inhibited in ASB-MBR which shortened the time of substance interchange between flocs and surrounding leading to the improvement of nutrients removal.The value of Ro,AR,FF in ASB-MBR were all closed to 1,demonstrating the homogenization and spheroidization of floc.All phenomena happened would prevent the tendency of flocs’s from adsorpting on the membrane and controlled the formation of cake layer.Meantime,algae adhered to bacterial surface which promoted the substance exchange between bacteria and algae resulted in the enhancement of the microbial activity.Moreover,the S-EPSpr/S-EPSps was 38.89%higher than that of C-MBR.The concentration and the pr/ps of B-EPS was decreased by 24.6%and 32.61%,respectively,in ASB-MBR.The hydrophobicity of algal-bacterial flocs was weaken,which reduced the trend of flocs’s accumulation on the surface of membrane.Compared with C-MBR,the NCST of ASB-MNR was decreased by 33.82%.Besides,more pores,lower roughness and the clustered channel distribution were observed in cake layer of ASB-MBR.The content of S-EPS and B-EPS was decreased by 15.01%and 17.07%,respectively,in ASB-MBR.The content of metal ion was reduced leading to the decrease of the complexes ion bridging.Those changes would contribute to improve flocs filterability and decrease the cake layer accumulation in ASB-MBR.Additionally,the bacterial diversity and evenness was decreased in ASB-MBR,which suggested the enrichment of a well-defined internal structure and the formation of more stable state.Meantime,the relative abundance of Planctomycetes,Proteobacteria and Bacteroidetes was increased by 8.44%,5.51%and 1.64%,respectively,in ASB-MBR.The Phreatobacter sp.and Aminobacter sp.were enriched,which were verified as a promoting bacteria facilitating the algal growth.While,the Verrucomicrobium sp.and Streptococcus sp.,causing membrane fouling,were reduced in ASB-MBR.The IOD of PAO,AOB and NOB was 30.3%,33.1%and 13%higher than that of C-MBR,respectively.Maybe algae have a positive effect on the growth of funtional bacteria,which was in accordance with the improvement of N,C and P removal in ASB-MBR.The functional algae communities have also changed after culturing with bacteria.It was found that the main class of algae were Chlorophyceae,Trebouxiophyceae,Ulvophyceae,Dinophyceae and Mediophyceae in ASB-MBR.The relative abundance of unidentifiedchlorophyceae increased from2.07%to 43.32%.The relative abundance of Acutodesmus sp.was decreased from95.27%to 50.06%.Besides,the Chlorella sp.（“luxury”uptake of phosphorus）and the Auxenochlorella sp.（mixotrophy algae）were enriched in ASB-MBR.The variation of algal community would have a growth benefit in algal-bacterial consortia and play a direct role in the improved performance of ASB-MBR.In summary,ASB-MBR was successfully established to achieve effective wastewater treatment and membrane fouling mitigation because of the symbiotic relationship and the algal-bacterial flocs formation in this study.It has a great significance for MBR’s widespread used because of the efficiency and energy-saving. |
