Effect of temperature on the nitrogen removal efficiency of anammox reactor under high salty stress

The temperature of sewage is usually limited by seasons and regions, and it is difficult to achieve the optimal temperature conditions required for anammox reaction in cold regions. In order to investigate the effect of temperature on the denitrification performance of anammox reactors under high salt conditions, a UASB reactor was used for continuous flow experiments at a salinity of 15 g/L. The experiments were conducted under the conditions of medium temperature (34 ℃), gradually decreasing to low temperature (16 ℃), activity recovery, and gradually decreasing to medium low temperature (22 ℃). The stable operation of the reactor at different stages was analyzed. The results showed that the average removal rates of \mathrmNH_4^+ -N and \mathrmNO_2^- -N in the reactor at 34 ℃ were 88.92%, 96.47%, respectively. When the reactor temperature dropped to 16 ℃, the removal rates of \mathrmNH_4^+ -N and \mathrmNO_2^- -N were only 25.14% and 30.96%, respectively. In the activity recovery stage, the reactor performance was restored by gradually increasing temperature, adding 0.2 mmol/L glycine betaine, and 20% mass ratio of fresh anammox granules in sequence. The average removal rates of \mathrmNH_4^+ -N and \mathrmNO_2^- -N were 88.18% and 94.33%, respectively. After performance recovery, the reactor was gradually cooled down again and stable operation at 22 ℃ was achieved by extending HRT, with \mathrmNH_4^+ -N and \mathrmNO_2^- -N removal rates of 82.14% and 87.03%, respectively. The research showed that microorganisms under high salinity consumed more energy after temperature reduction, leading to a decrease in particle size and EPS content. Extending HRT could alleviate salinity stress after cooling. After the temperature rose, the sludge performance could be restored, and the addition strategy of glycine betaine and fresh anammox granules was effective in restoring activity.