[Realization of Short-cut Nitrification in a CAST Process at High Temperature and Its Phosphorus Removal Performance]

A synthetic wastewater was employed to investigate the realization of short-cut nitrification and its phosphorus removal performance in a CAST reactor operated at 22℃, 25℃, and 28℃. The results showed that TN removal of the system was stable and higher than 80% at different temperatures, and NH₄⁺-N removal performed well. When the temperature was at 22℃ and 25℃, nitrite accumulation was not observed in the system and the phosphorus removal rate were 94.3% and 86.9%, respectively. When the temperature was increased to 28℃, nitrite accumulation efficiency in the reactor reached 87.2%, implying the system achieved a stable short-cut nitrification. In addition, in the short-cut nitrification stage at high temperature (28℃), the phosphorus release and uptake capacity of the system decreased. The anaerobic phosphorus release/COD consumption (P/C) ratio was much lower compared those at 22℃ and 25℃. However, the phosphorus removal performance of the reactor did not deteriorate at this stage. The phosphorus removal rate was 68.9%, indicating that a sufficient carbon source in the influent could not only guarantee the removal of TN, but also detoxify NO₂^- to reduce its inhibitory effect on the phosphate accumulating organisms (PAOs). The batch tests of phosphorus uptake by the sludge under different temperature conditions revealed that O₂, NO₃^-, and NO₂^- could all be used as electron acceptors for phosphorus uptake. The aerobic phosphorus uptake rate was higher than that with NO₃^- and NO₂^- as electron acceptors. The phosphorus uptake rates of O₂ and NO₃^- as electron acceptors were also found to be negatively correlated with temperature.