| Nitrogen and phosphorus are key nutrients that result in water eutrophication. As the development of biological nutrients removal technology, a new technology with advantages of simple process, high efficiency and less energy consumption will be prevalent in domain of nutrients removal technology. In this sudy, a membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was operated to improve the nitrogen and phosphorus removal abilities by optimizing the operational modes and adjusting the operational parameters. The performances of MBMBR on nitrogen and phosphorous removal, the sludge characteristics and membrane fouling were examined in different operational modes.Firstly, the performances of MBMBR and a conventional membrane bioreactor (CMBR) on nutrients removal and membrane fouling were compared at different influent COD/TN ratios. Compared with CMBR, MBMBR demonstrated a good performance on TN removal via simultaneous nitrification and denitrification (SND) at different influent COD/TN ratios. Even running at low COD/TN ratio (COD/TN= 8.9) with 7.58 mg TN/L-h, TN removal efficiencies were maintained above 70.0%, and the TN removal efficiency via SND was 89.1%. Membrane fouling was more serious in MBMBR than in CMBR. Since the overgrowth of filamentous bacteria in MBMBR resulted in severe cake layer, which would do great harm to membrane filtration. An intermittently-aerated mode was conducted to achieve SND via nitrite in the aerobic MBMBR. Results demonstrated that intermittently-aerated mode was an effective approach to achieve nitrition. Intermittently-aerated time is an important factor for achieving short-cut nitrification and the COD/TN ratio is another key factor for achieving TN removal. Batch tests indicated that under the intermittently-aerated mode, short-cut nitrification was achieved because the activities of NOBs were inhibited.Sequencing batch moving bed membrane bioreactor (SBMBMBR) performed well on nitrogen and phosphorus removal at different COD/TN ratios. The TP removal was closely correlated with the length of anaerobic phase and aerobic phase. When anaerobic time and aerobic time were both 2 h, the average TP removal efficiency reached to 84.1%. DO in aerobic phase was an important factor affecting nutrients removal, and the optimal DO was about 3 mg/L in SBMBMBR. Fluorescence in situ hybridization (FISH) results of microbes showed that in the inner layer of the biofilm, there existed only a small amount of NOBs and PAOs because of the low DO concentration. While for the outer layer of the biofilm and the suspended biomass, a large quantity of AOBs, NOBs and PAOs were observed. An anoxic phase was introduced with external nitrate or nitrite addition between anaerobic phase and aerobic phase to study the capability of denitrifying phosphorus removal. Results indicated that better capability of denitrifying phosphorus removal was observed with nitrite addition than that with nitrate addition. A series of batch tests using different type of election acceptors also indicated that compared with nitrate, nitrite is the more capable type of electron acceptor for denitrification phosphorus removal technology. The denitrifying bacteria were suggested to outcompete PAOs for competing limited carbon source. When influent carbon source was deficient, the exist of nitrate would indeed effect biological phosphorus release and finally result in a reduction of the TP removal efficiency. Batch tests indicated that neither nitrifying bacteria nor PAOs showed evident predominance for competing limited DO. In SBMBMBR, the ceiling inhibition concentration of nitrite was 50 mg/L. Furthermore, results indicated that the sequencing batch operation mode can reduce membrane fouling.
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