Experiments have been carried out to get an understanding of the effect of DO, C/N ratio and pH on the performance of a bench scale membrane bioreactor (MBR) in simultaneous nitrification and de-nitrification. It was found that under the conditions of MLSS in the range of 8000–9000mg/L and temperature of water in the MBR of 24°C, influent COD and NH3-N in the range of 523–700mg/L and 17.24–24mg/L respectively, the removals of COD, NH3-N and TN were 98%,99% and 60%; 96.5%,98% and 75%; 96%,95% and 92%; 90%,70% and 60% respectively at DO of 6, 3, 1 and 0.5mg/L. It was also found that the changes in C/N ratio and pH in a certain range have a slight effect on COD removal but have significant influence on the removal of NH3-N and TN. The results showed that only under the conditions that each ecological factor was maintained relatively steadily, simultaneous nitrification and de-nitrification proceeded smoothly. It was found that when C/N ratio was 30, the influent pH 7.2, the temperature of water in MBR 24°C and DO 1mg/L, as optimum conditions, the removals of COD, NH3-N and TN were 96%, 95% and 92% respectively. In addition, mechanism research on simultaneous nitrification and de-nitrification in MBR has been conducted as well.

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