Study On Mixed Liquor Characteristics In MBR And Its Influence On Membrane Fouling

MBR, as a new highly effective water treatment technology, has attracted the increasing attentions of the researchers. However, a major obstacle to the wide application of MBR is the membrane fouling. This paper, using the submerged hollow-fiber MBR, mainly investigated the effects of sludge age (i.e. sludge retention time, SRT) and filamentous bacteria on mixed liquor characteristics, and the effects of mixed liquor on membrane fouling mechanism. Meanwhile, the regulative technology of MBR is also discussed. The research has significance in its theory and application for effective control of membrane fouling.The main research work of this paper is as follows:The effects of SRT on the extracellular polymeric substances (EPS), the concentration of tightly bound EPS (TB) and loosely bound EPS (LB) and the ratios of protein and polysaccharide in TB and LB have been investigated. The results showed that the total EPS increased and the ratios of protein and polysaccharide in tightly bound EPS (TB) and loosely bound EPS (LB) changed with the extension of SRT, which influenced the surface charge of bacteria, increased the proportion of hydrophilicity base and hydrophobicity base on the surface of bacteria, changed the existence state of bacteria from the instable (R type) to the stable (S type), decreased the Zeta potential and enhanced simultaneously sludge volume index (SVI). Statistical analysis for the main parameters of fouling resistance has been performed by SPSS software, and it was found that the correlation coefficients (rp) were -0.818 for Zeta potential, 0.853 for the concentration of suspended solids in supernatant and 0.832 for relative hydrophobicity, respectively.The microorganism characteristic and the effluent quality of MBR under the different SRTs have been investigated, the model of the sludge multiplication dynamics to forecast the sludge concentration, and the theory basis on controlling SRT of MBR has been proposed in MBR. Microfauna community structure in MBR presented the regular variation along with the SRT extension, which has instructive function to the movement of MBR.Based on the Langmuir theory and the Darcy law, the paper confirmed that polarization resistance and the gel level resistance are the identical nature resistance by theory analysis and correlated them by Langmuir formula. The mathematical model of the micro-filtration resistance was also derived.By the comparison experiments for two MBRs, the effects of the conditions of nitrogen-deficiency and phosphorus-deficiency on the removal efficiency and the bulking of filamentous bacteria have been investigated. The removal efficiency of MBR reduces obviously and filamentous index (FI) is higher, when nitrogen is limited. Filamentous sludge bulking results in higher hydrophobicity in both mixed liquor and membrane surface and lower Zeta potential, which accelerate the pollutant deposition and adsorption on the membrane surface, thus causes the more serious membrane fouling.The research discovered that the supernatant suspended solid concentration (SSs), Zeta potential and relative hydrophobic are main influence factors of membrane fouling. The control of SRT, addition of PAC and the batch operation of flux can control the membrane fouling effectively.