Low C / N Shortcut Nitrification And Denitrification Of Factors And System Stability

Adopting sequencing batch reactor (SBR), this experiment studied the influencing factors and system operation stability of shortcut nitrification-denitrification. Nitrite accumulation was studied under the conditions of controlling pH and FA, low DO and low C/N, as well as the factors that had influenced the shortcut nitrification-denitrification system. The organic compounds and ammonia nitrogen removal rate, nitrite accumulation rate and the operation stability of shortcut nitrification-denitrification system were investigated under the conditions of multiple factors combined. What's more, the denitrification capability, impact resistance and operation stability of shortcut nitrification-denitrification system were studied under the impact conditions of high ammonia. The results had some guiding significance to the theoretical research and practical applications of shortcut nitrification-denitrification.Using SBR process had achieved the shortcut nitrification-denitrification process respectively, and the nitrification rate could be maintained above 90%. by controlling pH=8.0±0.1, FA=7.48-8.54mg/L, low DO=1.0-1.5mg/L, The best pH value range of nitrite bacteria and the selective inhibition theory of free ammonia were the theoretical basis to achieve shortcut nitrification-denitrification by controlling pH value. However, OLAND theory and the dynamics difference of two types of bacterias under low DO was the reason of controlling DO to get high nitrite accumulation. Operating the experiment for 80 days under low C/N condition, found that:there were high nitrite accumulation in the SBR system which could be above 35mg/L, the nitrification rate could be maintained at 90%-95%, showing that low C/N condition could achieve shortcut nitrification-denitrification very well, and the system could run very well and be more stable. Under normal temperature and dissolved oxygen concentration, when the wastewater average C/N=3.6 was beneficial to get high nitrite accumulation to achieve shortcut nitrification-denitrification. However, when the C/N<2.8, the high ammonia loading could restrain nitrifying bacteria and nitrite bacteria, when the C/N>5.6, the nitrite bacteria's number and diversity began to reduce, and neither of them could not be beneficial to achieve high nitrite accumulation rate or to achieve shortcut nitrification-denitrification, average C/N=3.6 was the optimum condition to get high nitrite accumulation under low C/N condition. Combined experiment found that the combination control of low DO and low C/N could achieve shortcut nitrification-denitrification stablely,when the DO=1.2-1.4mg/L and low C/N=3.6, and the SBR system maintained a high nitrite accumulation rate and stable operation efficacy. The study broke through the traditional research constraints to obtain a stable nitrite accumulation you should control DO below 1.0mg/L (or 0.5mg/L), which improved the system removal efficiency and expanded the dissolved oxygen controlling range to achieve shortcut nitrification-denitrification, it also showed that the controlling together with low C/N conditions was beneficial to improve the realization extent and operation stability of shortcut nitrification-denitrification process.In order to test the impact resistance of the running system under the low DO and low C/N combination control, the ammonia-resistant impact experiment was studied. After 7 days of high ammonia impact experiment, the results showed that:the effluent ammonia concentration increased slightly, the average concentration changed from 10.8mg/L to 13.2mg/L, but the average removal rate remained as high as 84.6%; After the impact, the average nitrite concentration and nitrosation rate changed respectively from 35.1mg/L and 93.6% to 32.6mg/L and 90.2%, though it declined a little, it kept great adaptability and recovery ability. Through this impact test, it showed that shortcut nitrification-denitrification could not only be achieved effectively under the combination of appropriately low DO and low C/N, but also had long term stable operation, some impact resistance and recovery ability.