| Membrane-aerated biofilm reactor (MABR), in which bubble-free oxygenation is achieved by gas-permeable carrier, combines membrane technology with biofilm process for wastewater treatment. In MABR, gas/liquid phases are separated, oxygen penetrates through the membrane into biofilm that forms on the outer surface of the membrane. Bacteria in the bifilm subsequently consume the oxygen to efficiently oxidize pollutant in the bulk solution. Despite some advantages, some factors, such as membrane fouling, poor stability and high material cost, restrict its wide application. In this paper, coal-based carbon membranes with low cost are acted as gas-permeable support, and performance of the carbon membrane-aerated biofilm reactor (CMABR) is investigated for wastewater treatment.Feasibility tests were carried out to verify the effectiveness of carbon membrane as both aerator and biofilm carrier. Specific attached biomass on carbon membrane was 0.55gTOC/m2, which exhibited a high degree of bacterial adhesion. Carbon membrane's individual oxygen transfer coefficient (KM) was 0.36 m/h and it was compatible to supply oxygen to the biofilm.Reactor's operation to treat municipal wastewater indicated that removal efficiency of COD, NH4+-N and TN averaged 88ï¼…, 90ï¼…and 78ï¼…, respectively, and specific removal rate could reach 35.6gCOD/m2.d and 9.34gNH4+-N/m2.d. CMABR has huge potential for wastewater treatment and was effective in simultaneously removing COD and TN. In the long term, hydrophobic extracellular polymeric substance (EPS) adhered to pore and played an important role in membrane fouling, which drastically decreased the oxygen transfer coefficient. Alkaline washing was a useful method to remove fouling and good permeability almost recovered after washing.CMABR was utilized to treat inorganic ammonium wastewater and oxygen supply was controlled by adjusting intra-membrane air pressure. The results showed that under the air pressure of 0.017 MPa and 0.015 MPa, the bacteria within biofilm consumed all oxygen supplied through carbon membrane, and at the same time high NH4+-N's removal efficiency was obtained. Under pressure of 0.009 MPa, ratio of NH4+-N and NO2--N in effluent was approximately 1:1, which could be treated with anaerobic ammonium oxidation. The maximum specific removal rate of NH4+-N was 9.7 g/m2.d and it was limited by the amount of bacteria grown onto carbon membrane's surface and by substrate diffusivity. Tests were conducted to investigate the effect of different parameters on reactor's performance and the optimum conditions were determined in terms of intra-membrane pressure, influent COD/N and hydraulic retention time (HRT). Nitrification, COD removal and denitrification efficiency could reach 95ï¼…, 88ï¼…and 92ï¼…, respectively, under the conditions of intra-membrane pressure of 0.025 MPa, influent COD/N of 5 and HRT of 8 h. Reactor's start-up time was decreased to 8 d by hanging biofilm repeatedly. Furthermore, the system displayed good resistance to shock loads and operation of reactor was stable.Microbial composition and spatial distribution in biofilm were analyzed by fluorescence in situ hybridization (FISH) technology. The microscopic images revealed that Nitrosomonas, Nitrosospira and Nitrospira were dominant nitrifying bacteria in the biofilm treating the inorganic ammonium wastewater and occupied above 60ï¼…of the total bacteria number. Ammonia oxidizing bacteria existed throughout the biofilm. Whereas Nitrosospira and Nitrospira formed important population in the biofilm treating wastewater with COD/N of 5, the fraction of which was about 20ï¼…of the total bacteria, and Nitrosomonas was undetectable. A clear stratification of nitrifying bacteria was established within the biofilm, that is, nitrifying bacteria were almost restricted to the inner layer and microorganism other than nitrifier were still present in biofilm's outer layer, which were speculated to belong to denitrifying bacteria based on reactor's running.
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