Study On Flux Enhancement Strategy Of Submerged Osmotic Membrane Bioreactor

The osmotic membrane bioreactor?OMBR?is an emerging innovative technology,which shows broad application prospects in the fields of wastewater reuse and resource recovery due to the technical advantages of high pollutants rejection efficiency,good effluents quality and low membrane fouling propensity.However,problems such as concentration polarization,salinity accumulation,and membrane fouling caused rapid water flux decline during the operation of OMBR and limited its practical application.In this paper,the water flux in submerged OMBR of different operation modes and different combined process were investigated,and the influence factors led to flux decline were analyzed.The main contents and research results are as follows:The FO membrane filtration water flux?J_W?was affected by draw solution?DS?concentration,membrane orientations and the spacer.With the increase of DS concentration,the water flux increased while more draw solutes reversely diffused?J_S?to the feed solution.The value of J_S/J_W which took the two aspects into consideration simultaneously showed that the best filtration performance came when DS concentration was 1.5 mol·L^-1.When active layer of membrane faced the DS?PRO mode?,the initial water flux was higher compared to the situation where active layer of membrane faced the feed solution?FO mode?.However,the water flux decline rate was faster due to the concentrative internal concentration polarization.The addition of the spacer mitigated the concentration polarization,and the flux increases in PRO and FO modes were 3.5%and 12.8%,respectively.The results of wastewater purification by FO showed that the FO membrane enables efficient rejection of TOC and nutrients in wastewater.In addition,membrane fouling during the FO process was mild and reversible,and the flux could be effectively recovered by physical cleaning.Under continuous-flow operation,the salinity in the OMBR reactor gradually increased owing to the membrane rejection and reverse solute diffusion.Due to the accumulation of salinity,the activity of microorganisms in OMBR was inhibited,and the biodegradation efficiency of PO₄^3--P and NH₄⁺-N decreased gradually.In addition,the increase in salinity caused partial cell apoptosis resulted in gradually decreased amount of microorganisms.The particle size of the sludge was also gradually reduced,and more soluble microbial products?SMP?were released due to sludge disintegration,which not only increased the salinity of the mixed liquor but also aggravated membrane bio-fouling,resulting in a rapid decline in flux.After the regulation of intermittent supernatant discharge,the flux decreased relatively slowly,and the activity of the microorganisms and the excretion of SMP in the mixed liquor returned to the normal level.During the operation of R1?AFS-OMBR?and R2?AGS-OMBR?,the average removal efficiency of TOC and PO₄^3--P were maintained above 95%,respectively,while the aerobic granular sludge in R2 can achieved high-efficiency biodegradation of NH₄⁺-N,with average removal efficiency of 77%,significantly higher than 57%of R1.The R2 flux decline rate was significantly less than R1.And at the end of the run,the difference value between R2 and R1 is 1.0 L·m^-2·h^-1.During the whole operation,the concentration of SMP in R2 was generally lower than R1,which results in more content of polysaccharides and proteins in membrane surface bio-fouling layer of R1.The appearance of the bio-fouling layer would decrease the mass transfer efficiency of the membrane strengthening the external concentration polarization,which lead to a more rapid decline in water flux.The results of microbial structure analysis showed that the microbial diversity of the membrane surface was lower than that of the mixed liquor and the microorganisms enriched on the membrane surface were mainly the Proteobacteria and Firmicutes which had the characteristic of better salt tolerance.