Study On Operational Characteristics Of Membrane Bioreactor And Effect Of Soluble Microbial Products On Membrane Fouling

Soluble microbial products, including utilization associated products (UAP) and biomass associated products (BAP), play a key role in membrane fouling.In order to deeply understand the character of SMP, the author adopted labour to simulate the domestic sewage and research the operational state and the character of SMP under the condition of SRT for15d、30d and60d and the membrane pollution mechanism of SMP、UAP and BAP, the main researching contents and results are as following:1、The author adoped three parallel membrane bioreactors and systematically researched the operation of them and membrane pollution state under different SRTs (SRT=15d, SRT=30d, SRT=60d). The result showed that the removel rate of COD was98%, trichobacteria breeded in the membrane bioreactors under SRT for15d, the membrane bioreactors under SRT for60d had more MLSS, the two conditions appeared serious membrane pollution, the TMPof the membrane bioreactors under SRT for30d is under30kPa in the beginning20days,the membrane bioreactors run well and had very good character of activated sludge and activity of germ. Through observing surface morphology of membrane in the AFM, the author found that the membrane under SRT for30d was polluted less significantly and not soundly be covered by sludge.2、The concentrations of SMP and components (Protein and polysaccharide) climbed up and then declined with the extend of SRT. The concentrations in the membrane under SRT for30d was the lowest.Through the research to the molecular weight of SMP, the author found that the substances with big molecular weight increased and the substances with small molecular weight declined. Through fluorescence spectrum analysis to the SMP, the author found that the substances with small molecular weight in the membrane under SRT for30d, such as Humic acid and Fulvic acid, was relative1y few, which also shown that the filter layers on the membrane palyed a good filter ing role for the substances with small molecular weight. 3、Stirred cell filtration was used to study fouling mechanisms of individual SMP components. As the filtration experiments stop, the respective flux decrements were69%and78%for BAP and SMP, the lux decrement of UAP is82%; simultaneously, UAP had higher MFI-UF (1.63×104s/L2) than BAP with a value of4.37×103s/L2, Average MFI-UF index of SMP is close to BAP, which shows that UAP is more likely to cause membrane pollution than BAP; The proteins in UAP and BAP were accounted for45.3%and12.1%, respectively; however, the proteins concentration in permeate decreased to near zero and polysaccharides were effectively retained in a range of26.6%-46.8%due to membrane interception. EEM analysis exhibited that humic-like and fulvic-like compounds had lower retention than proteins; By comparison,the characteristics of SMP in the SRT=30d is similar with BAP, which shows that BAP is the main reactor in this operating conditions.4、MWD results showed that the fouling performances for UAP and BAP filtration were clearly distinct for their different Mw/Mn (BAP permeate=3.2; UAP permeate=20.9). Molecular weights of UAP is more extensive than the BAP, it’s shows the filtering mechanism are different.; Simulation results well indicated that the main fouling mechanisms for UAP and BAP filtration were complete blockage and cake filtration, respectively, further confirming that UAP produced in the cell proliferation phase have higher fouling potential. There are further evidence to show that BAP of SMP in SRT=30d has a larger proportion, as for the simily between SMP and BAP.