Changes In Characteristics Of Microbial Community Structure In A/O-MBR And Relation To Membrane Fouling

Nowadays, as a new efficient wastewater treatment technology. Membrane Biological Reactors(MBRs) has been attracted much more attention. Membrane fouling is a major obstacle to the wide application of MBRs.Nowadays, scholars studied MBR fouling by focusing on the fouling factors, such as sludge characteristics, operational parameters, membrane materials and feedwater characteristics and so on. However, the complex nature of membrane foulants, activated sludge and the microbial community structure is the main cause that puzzles us, the causes of MBRs membrane fouling is still very confused, and there were some conflicting conclusions. For further illustrated the fouling mechanisms, using aerobic-oxygen membrane bioreactor (A/O-MBR) disposal synthetic wastewater,investgate MBR operating performance under different SRTs(10d,30d,60d), the relationship between changes of microbial community structure and the metabolites.In the study, the average removal rate of COD and NH4+-N were all above 96.0% and 98.0% and the effluent concentration of pollutants reached municipal wastewater treatment plant emissions level A standard (GB18918-2002). It can be seen that there were no obvious influences on the removal of COD and NH4+-N under different SRTs. After the reactor gained sustainable status under different SRTs, the average removal rates of TN were 66.2%,57.2% and 67.7%, separately. The effluent TN were under 20mg/L. Though SRTs were different, the systems all obtained higher total nitrogen removal rate.Microbial community structures in the mixed liquor were clearly different along with the change of SRT. With the increased of membrane fouling, there were significant trend of microbial communities changed from aerobic bacteria to anaerobic bacteria. The research indicated when the SRT designed for 60d, there were the most complex microbial community structure in the reactor. Aeromonas spp of aerobic bacteria, Anaeromyxobacter of anaerobic myxobactena and Aquimonas vorai bacteria of photosynthetic bacteria were identificationed in aerobic bank, indicating that aerobic microbial community was a complex system, there was anoxic or anaerobic micro-environment. Microbial community structure of the surface sludge layer on membrane was generally more complex than bio-film on the membrane surface. Myxobacterium emergenced in the operation of SRT 60d and the final run of SRT 10d, which could biodegradated a variety of macromolecules substances such as protein, lipids and so on. Though EPS, SMP concentration decreased in the reactor.The trend of SMP in aerobic mixed liquor under different SRT were all increased firstly and then decreased; The trend of EPS change differently with the difference of SRT. Using SPSS software statistical analysised the experimental data, the result indicated that the filtration resistance was significantly related to the SMP and EPS, but the significance of SMP decreased with the increasing of SRT; The significance of the filtration resistance with EPS and SMP was the strongest when SRT designed for 30d, membrane fouling was the most seriously; Carbohydrate was the main membrane fouling material when the SRT was 30 and 60d, while the contribution on membrane fouling of protein was slightly larger than carbohydrate when SRT was 10d.