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What is the basic principle of biological nitrogen removal?
Biological nitrogen removal is controlled by artificial methods according to the principle of nitrogen cycle in nature. Firstly, the nitrogen-containing organic matter in sewage is transformed into ammonia nitrogen, and then it is transformed into nitrate nitrogen by nitrifying bacteria under aerobic conditions. This stage is called aerobic nitrification. Then, under anoxic conditions, nitrate nitrogen is transformed into nitrogen to escape under the energy provided by denitrifying bacteria and external carbon sources. This stage is called anoxic denitrification. The whole biological denitrification process is a decomposition and reduction reaction of nitrogen, and the reaction energy is obtained from organic matter. In the process of nitrification and denitrification, the factors affecting nitrogen removal efficiency are temperature, dissolved oxygen, PH value and carbon source. In the biological nitrogen removal system, the growth rate of nitrifying bacteria is slow, so it is necessary to have enough sludge age. Denitrifying bacteria grow mainly under anoxic conditions, and sufficient carbon source is needed to provide energy to promote denitrification smoothly. Therefore, nitrification and denitrification in biological denitrification system need to meet the following conditions:
1. Nitrification stage: sufficient dissolved oxygen, DO value above 2mg/L, suitable temperature, preferably 20℃, not lower than 10℃, long sludge age and suitable PH conditions.
2. Denitrification stage: nitrate exists, DO value is about 0.2mg/L under anoxic condition, carbon source (energy) is sufficient, and PH condition is suitable.
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