Study On Anoxic/Aerobic MBR For Treatment Of Industrial Wastewater Containing High Strength Carbon And Nitrogen Concentrations

The membrane bioreactor (MBR), a combined process of biological treatment with advanced membrane separation, is a new technology for wastewater treatment. In this dissertation, a laboratory scale anoxic/aerobic MBR was tested for treatment of industrial wastewater containing high strength carbon and nitrogen concentrations. Its operational performance and microbial characteristics, as well as membrane fouling and fouling cleaning methods were investigated. The following results have been obtained:By continuous runs under different operational conditions, pollutant removals of the system were investigated. With no sludge discharge, the simultaneous carbon and nitrogen removals were investigated when HRT of MBR was 15h, l0h and 6h, respectively. COD, NH4+-N and TN removals were high at different HRTs of MBR. The COD, NH4+-N and TN removal rates increased linearly with increase influent volumetric loading rates. When SRT was 16d, denitrification efficiencies at different return flow ratios were compared, and the suitable value was 4. At condition of sludge discharge, two types of MBR: suspended growth type and adhesive growth type were compared. Adhesive growth type of MBR was found to be more effective to remove ammonia nitrogen than the suspended growth type of MBR. In addition, nitrogen transformation in bioreactors was also investigated.By experiments at different operational conditions, microbial characteristics in MBR were investigated. With no sludge discharge, sludge concentration increased with the decreased HRT in MBR. Thesludge activity for nitrification (OURN) was higher than that for organic carbon oxidation (OURo), but both decreased with time. When SRT was 16d, sludge concentration stabilized at about 13g/L. OURr and OURo increased obviously, but OURN decreased. After carriers added, suspended sludge concentration decreased and stabilized at 11 g/L. And ORTr and OURo in the adhesive growth type of MBR was lower than that in the suspended growth type of MBR, but OURN was higher in the adhesive growth type of MBR than before. In addition, average particle diameter in MBR was lower than conventional activated sludge process. Extracellular polymers(ECP), which is microbial metabolic products, was higher in the high biomass concentration MBR than that in the low. And the higher ECP can aggravate membrane fouling.By the investigation of membrane permeability change with the time in a continuous test, membrane permeability, the fouling characteristics and its cleaning methods were studied. It was found that the membrane permeability could be improved by selecting appropriate operational parameters: suction time and membrane flux were studied. Resistance of sludge cake layer was the most factor in the decreasing of membrane flux. In addition, at different operational conditions, the relationship between the quantity of sludge deposited and dissolved organics on the membrane surface was also studied. Based on experimental results, a quantitative relationship between membrane filtration resistance R2o at filtration time of 20 minutes, SS concentration and supernatant COD of mixed liquor was deduced as R2o=9.129E(+9)*COD04497SS10189. Ultrasonic cleaning and chemical cleaning were used for cleaning fouled membrane, and chemical cleaning was more effective. The investigation of molecular weight distribution in the cleaning membrane water showed that dissolved organics with micro-molecular weight were main pollutants for gel layer on the membrane surface and in the pore of the membrane.