An Inovative MBR Process Comnined With Biosorption Pretreatment And Its Membrane Fouling Mechanism

In the present work, based on the fact that heteotroph and nitrifier have distinctfilterability properties, an MBR system combined with a biosorption pretreatmentwas developed to obtain a stable wastewater treatment performance, whilst toalleviate membrane fouling by means of process adjustment. The MBR system(marked as R1) and a conventional MBR (marked as R2) operated side-by-side up to6months to evaluate the stability and capability of membrane fouling mitigation.Meanwhile, the suspended sludge properties in terms of MLSS, EPS, SMP and theircomposions, under different operantion conditions were comprehensively analyzedto reveal their correlation with membrane fouling velocity and extent.Both R1and R2were operated in a lab-scale, and the treatment performanceresults showed that these two systems have rather high remove effectiveness ofCOD and ammonia from wastewater. The COD removal efficiency in R1and R2was92.7%and90.4%, and the NH4+-N removal rate was93.7%and88.1%,respectively.The pretreatment in R1as biosorption can effectively reduce the occurrencefrequency of membrane fouling. In detail, the MBR in R1undertakes three foulingcycle throughout the experimental phase, indicating that the average foulingfrequency is up to62days. In constrast, five fouling cycles occurs in R2and theaverage fouling frequency is more than35days. Therefore, it is deduced that about40%of membrane fouling velocity can be alleviated by the biosorption pretreatment,which would effectively reduce the cost on membrane cleaning. The relative lowmembrane fouling rate in R1mainly attributes to the large abundance of nitrifiers inbulk and correlated sludge properties. As that nitrifying bacteria have a betterfilterability than heterotroph, the large abundance of nitrifiers accompanying with alow C/N in R1would improve the filterability of sludge mixture in R1. Moreimportantly, through a long-term examination, found that，the average EPS in R1and R2was14.8mg/L and34.5mg/L, the average SMP was25.1mg/gMLSS and36.7mg/gMLSS respectiviely, R1has consistently lower SMP and EPS contentcompared with those in R2, which may be deemed as another important reason ofdifferent fouling evolution velocity.To determine the major foulants in MBRs, a comparative and systematicanalysis of the correlative relationship between the sludge properties parameters andTMP evolution rates was conducted. It is found that all TMP evolution curve havetwo step profile, as described as TMP slow growth in the beginning and TMP jumpin late phase. Throughout these two steps, both SMP and EPS content showed positive correlation with TMP evlution rate. However, the Pearson’s correlation ofSMP and TMP evolution rate was higher than that of EPS with TMP rate, implyingthat SMP was more likely to be the major foulant in MBRs. More detail, the proteinsand polysaccharides in SMP and EPS affected membrane fouling in a different level,while the proteins in EPS and the polysaccharides in SMP take more important rolesin membrane fouling, rather than other components. Besides, membrane foulingevolution would also been influenced by operational conditions. The membraneresistance decreased with the decreasing of MLSS or increasing of the cross flowvelocity. Hence, to maintain a proper MLSS in bulk and cross-flow velocity inbioreactor are evtually important to control membrane fouling in MBRs.