Enhanced removal of total nitrogen and total phosphorus by applying intermittent aeration to the Modified Ludzack-Ettinger (MLE) process

Abstract

In the conventional preanoxic Modified Ludzack-Ettinger (MLE) process, the nitrified mixed liquor cannot be completely returned to the preanoxic zone for denitrification. In this study, we applied intermittent aeration to the MLE process to enhance denitrification and total phosphorus (TP) removal. Pilot-scale test results indicated that, when treating municipal wastewater with a carbon (represented by five-day biological oxygen demand) to total nitrogen (TN) ratio (e.g. C/N ratio) of 2.4 or greater, the effluent ammonia, TN, and TP were generally less than 0.5 mg-N/L, 5 mg-N/L, and 0.5 mg-P/L, respectively. The removal efficiencies of both TN and TP were approximately 90%. Under extremely low temperature of 9.3 °C and low C/N ratio of 1.6 conditions, this process still removed 76% of TN and 56% of TP. Compared to the conventional MLE process, the implementation of intermittent aeration significantly improved TN and TP removal and also saved aeration energy by 10%. Existing MLE plants can be easily upgraded to this intermittent aeration mode to achieve enhanced nutrient removal while saving energy.