| Conventional biological nutrient removal process exist some problems such as system complex, large footprint, high investment, ect. Short-cut nitrification and denitrification, simultaneous nitrification and denitrification are novel biological nutrient removal technologies. The processes have many advantages, such as energy saving, less sludge and less footprint, ect. So these new technologies are being paid more and more attention by environmental engineering scientists.In this paper, simultaneous nitrification and denitrification was studied in the Membrane Bioreactor (MBR) and simultaneous nitrification snd denitrification via nitrite was studied in the Hybrid Submerged Membrane Bioreactor (HSMBR). From the experiments I get the main conclusion as follows.(1) According to the experimental results, the paper has proved that Simultaneous nitrification and denitrification (SND) can occur concurrently in Activated Sludge System and MBR. Compared SND in the Activated Sludge System with SND in MBR and found that the MBR has a higher removal efficiency of COD, ammonia and TN than the Activated Sludge System. As a whole, In the MBR is easier to realize SND than activated Sludge System, and the effect is better.(2) The experimental results in Activated Sludge System and MBR showed that DO is a limiting factor to SND, C/N is a key factor to SND, and pH is a important factor to SND. According to the experimental results, The efficiency of simultaneous nitrification and denitrification is the best when DO concentration is 0. 8mg/L～1. 0mg/L and pH is neutral to alkalescent. With reduction of COD/TN, the TN removal efficiency becomes lower. But the TN removal efficiency increasing with enhancing F/M. Moreever, F/M is another key factor impacting on the SND, and F/M is 0. 15～0. 36kgCOD/kgMLSS·d for best efficiency of simultaneous nitrification and denitrification in MBR when DO concentration is 0. 8mg/L. In the research, the optimal technological conditions for SND process in MBR are determined, under which the DO is about 0. 8ppm, C/N value is about 10, F/M is 0. 34kgCOD/kgMLSS. d, and pH is neutral to alkalescent. (3) According to the experimental results, the influence mechanism which DO and C/N affect on SND is consistent in Activated Sludge System and MBR.(4) HSMBR treating nitric wastewater can realize simultaneous nitrification and denitrification via nitrite, and NO2-—N accumulation efficiency is 50. 9%～80. 3%, TN removal efficiency is 37%～74. 5%. System of simultaneous nitrification and denitrification via nitrite can operate till one month, but it can not be long term stable.(5) The fundamental reason of simultaneous nitrification and denitrification via nitrite in HSMBR is that nitrogen oxidation bacteria compete out nitrite oxidation bacteria during the process of adapt to temperature,DO,pH,FA.(6)The COD, ammonia and total nitrogen(TN)removal efficiency were studied in the paper at low DO concentration in single-stage anoxic/aerobic Hybrid Submerged Membrane bioreactor treating wastewater with high ammonia concentration. The experimental results showed that the COD and ammonia average removal efficiency reach respectively 94. 4% and 92. 8%, when DO is 0. 5～1. 0mg/L. Because of the low influent COD/TN ratio (=2. 01), the TN average removal efficiency was only 69. 4%, while TN removal efficiency could be increased by 17. 7% with the nitrite accumulation ratio increasing from 60. 5%～67. 1% to 83. 5%～86. 4%. Moreover, SND via nitrite at low DO level could be realized.(7) Under the conditions of SND, the denitrification seemed to be rate-limiting step. Meanwhile, based on the analysis and processing of data of SND, the kinetic model of SND was constituted, and nitrate saturation coefficient KNO3 was deduced according to the experimental results. It was found KNO3 on the conditions of SND was greater than that of denitrification process in general model for single-stage activated sludge system, and SND was deeply understood from quantitative aspect.
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