Effect of exogenous K+ addition on the denitrification efficiency of high salinity wastewater treatment by anammox process at medium and low temperature: In-depth study

In this study, high-salinity wastewater was treated by the anaerobic ammonia oxidation (anammox) process at medium and low temperature. Under the dual stress of salinity and low temperature, the anammox process was strengthened by exogenous addition of K+. Fast start-up of the anammox reactor was performed in 90 days. MLSS and MLVSS was 8388 mg/L and 7511 mg/L, respectively. The MLSS/MLVSS ratio was as high as 0.90 after the successful start-up of the reactor. The effects of sludge particle characteristics and denitrification efficiency with respect to gradual salinity gradient domestication at medium temperature (30 °C) was done. 30 g/L salinity stress inhibited the denitrification efficiency of the reactor. With the increase of salinity, the content of soluble extracellular polymeric substance (EPS) gradually increased and there was a sharp increase at 20 g/L salinity. The total nitrogen (TN) removal load was 0.64 kg/(m3·d) at low temperature (15 °C) and salinity 20 g/L with TN removal efficiency 88.81%. Under low temperature conditions, biomass and nitrite significantly inhibit the denitrification efficiency. Also, PS/PN ratio increases by 0.39 and the sludge granularity becomes worse. Static batch and continuous flow tests were performed to explore the effect of exogenous addition of K+ on the denitrification performance under anammox resistance salinity in the short-term and long-term experiments. Under the salinity stress of 6 g/L, X (compared to anammox activity) can be increased by 35.76%. With the increase of K+ concentration under medium and low temperature and high salinity, the denitrification efficiency first increased and then decreased. 5 mmol/L K+ was the best promotion point under medium temperature (30 °C) and high salinity (30 g/L), the TN removal efficiency was 86.22%, which was 10.88% higher than that of 0 mmol/L K+ intervention. The nitrogen removal rate (NRR) was increased from 0.83 kg/(m3·d) to 0.95 kg/(m3·d) increased by 10.87%. Under the optimal promotion point, 10 mmol/L K+ for low temperature (15 °C) and high salinity (20 g/L) the TN removal efficiency was 92.60% increased by 3.94%. Inhibition phenomenon appeared in 20 mmol/L K+ under medium and low temperature conditions.