Factors Affecting Simultaneous Nitrification And Denitrification In Sequencing Batch Reactor

Nitrogen is an important pollutant which results in water eutrophication and environmental pollution. Sewage denitrogenation has been paid comprehensive attention to all over the world. Traditional biodenitrification technics have such common shortcomings as long process flow, big floor space, great capital cost etc., so people attached much importance to studyng new denitrogenation theories and technics, one of them, simultaneous nitrification and denitrification (SND), is widely focused on because of it's virtues of energy-saving,less sludge production and small floor space etc..A lot of progress in SND uner lab-scale has been maken by scholars in and abroad, but SND is still not very clear in many ways such as concept, mechanics, occurrence, impact factors, how to implement and its engineering application etc.. SND as a new concept and theory, a number of studies should be done to validate its correctness in theory and feasibility in actual application.Under different conditions (for example DO, COD/NH₄⁺-N and MLSS )effects of SND were investigated in a sequencing batch reactor(SBR) with single-stage aerobic treatment in artificial sanitary waste in this thesis. The rule of SND and its feasibility in engineering were discussed and the mechanics of SND was preliminary studied. The conclusions as follows:Under the conditions that initial COD concentration was about 400mg/L, initial NH₄⁺-N concentration was about 40mg/L, MLSS in the reator was maintained at around 3000mg/L, DO was controlled at the concentration of 4mg/L, 2mg/L and 0.5mg/L respectively by adjusting aeration. The COD removal efficiency reduced a little as the DO decreased; the NH₄⁺-N removal efficiency had a bigger reduction as the DO decreased, it was closed to 100% when DO was 4mg/L and only about 90% when DO was 0.5mg/L; DO had an important influence to total nitrogen removal efficiency, the lower DO was, the lower effluent total nitrogen concentration and the higher the total nitrogen removal efficiency were, when DO was 0.5mg/L, the total nitrogen removal efficiency was maximum to 75%.Under the conditions that initial NH₄⁺-N concentration was about 30mg/L, MLSS in the reator was maintained at around 3000mg/L and DO was controlled at a high concentration of more than 6mg/L, the influent COD/NH₄⁺-N ratio was respectively controlled at 2, 5 and 10, the higher concentration of influent COD, the more apparent was the phenomenon of SND and the higher the total nitrogen removal efficiency. Conclusions was drawn from the experiment that there might be exist heterotrophic nitrifiers and aerobic denitrifiers in activated sludge, they had a little contribution to the denitrification process because of their small amount.Under the conditions that initial NH₄⁺-N concentration was about 30mg/L, initial COD concentration was about 300mg/L, DO was maintained at 2mg/L during aeration process, MLSS was respectively maintained at around 2000mg/L and 4000mg/L, the higher concentration of MLSS, the more apparent was the phenomenon of SND and the higher the total nitrogen removal efficiency.