| The membrane bioreactor (MBR) process for wastewater treatment consists of a bioreactor and a membrane filtration unit for the separation of biomass that replaces solids separation in a secondary clarifier. It has many advantages such as high concentration of mixed liquor suspended solid (MLSS), little surplus sludge, high removal efficiency of pollutants, stable and high quality of effluent, convenient management, easily achieving automation etc. Many studies on treatment of household sewage and various industrial wastewaters, the optimization of operational conditions, the factors on the removal of pollutants and the mechanism of membrane fouling have been performed, however, membrane fouling is still one of the important problems that prevent the wide application of MBR. Immobilization technology which has developed since the 1970's also has many advantages of high cell density, long reaction time, little lost bacteria quantity and easy separation of liquids and solids. In this dissertation, the feasibility of treating seawater toilet-flushing sewage with immobilization technique and MBR has been studied.This dissertation concludes the treatment of seawater toilet-flushing sewage with immobilized microorganisms and MBR. An immobilization technique, "polyvinyl alcohol-boric acid" (PVA-H3BO3), is used for the preparation of immobilized microorganisms. The suitable entrapping agents such as sodium alginate, active carbon, silicon dioxide, calcium carbonate and their proportion are determined according to the strength of immobilized pellets and the removal efficiency of pollutants. The optimum conditions of removing pollutants with immobilized microorganisms are found according to the removal efficiency of NH3-N and CODCr under different temperature, pH, MLSS, and Cl- concentration. Primary experimentalresults shows that the concentration of silicon dioxide is 10g/l, the concentration of calcium carbonate is 1.25g/l, the ratio of activated sludge to entrapping agents solution is 1:4 and the cross-linking time is over 24 hours. The orthogonal experiment results show that the optimum concentration of polyvinyl alcohol, sodium alginate and active carbon is 80g/l, 4g/l and 10g/l. It has been also shown that the removal efficiency of NH3-N and CODcr is high at the temperature of 30°C,after 10 hours; the removal efficiency and the resistance to the shock of acids and alkalies are increased during the pH range of 4—10; the suitable concentration of immobilized activated sludge is 75g/l. Tests in successive fluidized bed reactor show that the immobilized pellets are stable during a long time of running, and the concentration of NH3-N and CODcr in effluents meets the integrated wastewater discharge standard II. Scanning electron micrographs show that the reticular structure that the prevents the losing of immobilized microorganisms can be seen.In this dissertation, aerobic submerged MBR is used for treating seawater toilet-flushing sewage. By optimizing the operational conditions of MBR, the average hydraulic retention time (HRT) of 4h, the concentration of MLSS of 68g/l, the aeration flowrate of 461/min, the suction time of 10 minutes and the suction suspended time of 3 minutes are obtained. The results show that the existence of Cl" has no effect on the removal of CODohki and NH3-N, however the removal efficiency of CODcr slightly decreases with the increasing concentration of Cl*. The MBR system is stable, efficient and has good quality of effluents under the conditions of high concentration of MLSS. The turbidity of the effluents is less than 1FTU and the removal efficiency is greater than or equal to 97.8%. In this MBR system, the concentration of CODCr, CODohki, TOC, BOD5 and NH3-N in effluents is less than or equal to 61mg/L, 8 mg/L, 8mg/L, 12mg/l and 1.6mg/L and the removal efficiency accordingly is greater than or equal to 85.7%, 97.4%,93.0%, 92.0% and 96.9%. The quality of effluents meets the integrated wastewater discharge standard I . Although the removal efficiency of most of pollutants is excellent, the removal efficiency of total phosphorus is low in the MBR. When the average influent concentration isapproximately 10mg/l, the highest removal efficiency is 21.2%. The membrane flux clearly decreases under condition of high MLSS. Simple physical methods contribute little to the remediation of the flux after many days, so chemical methods are necessary. The chemical methods help to abate the membrane fouling and keep a stable flux for a long time. Irreversible membrane fouling occurs in MBR during running. When immobilization technique is combined in this MBR, the result shows that it is not only helpful to abate membrane fouling and increase membrane flux, but also increases the removal efficiency of total nitrogen and total phosphorus.
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