Enhancing nitrogen removal and reducing aeration energy for wastewater treatment with intermittent Modified Ludzack-Ettinger process: A field demonstration

Previously an enhanced nitrogen removal process, i.e., intermittent Modified Ludzack-Ettinger (iMLE), was developed by incorporating intermittent aeration into the MLE process. In this research, a field demonstration of iMLE process on enhancing nitrogen removal was conducted in Shenzhen Guangming Wastewater Treatment Plant (WWTP) at a daily treatment capacity of 25,000 m3/d. Results indicated that, when operating the iMLE process with dissolved oxygen (DO) based control mode, its effluent chemical oxygen demand (COD) and ammonia concentrations were consistently less than 30 mg/L and 1.5 mg/L, respectively, similar to the original two-stage Anoxic/Oxic (A/O) process with continuous aeration. Even though the influent had insufficient organic matter (BOD5/TN = 2.5), the effluent TN concentration in the iMLE was still consistently below the new limit of 10 mg-N/L, with an average and removal rate of 6.1 +/- 1.0 mg-N/L and 78%, respectively. This performance was similar to that in the two-stage A/O process equipped with step feed and external carbon addition. Without the addition of external carbon in the iMLE process, it saved approximately 0.16 Chinese yuan for one cubic meter of wastewater treated. In addition to eliminating external carbon addition, the iMLE process decreased the air consumption by 20-30%, which would also reduce operation cost. Therefore, the iMLE process operated with appropriate DO control could reduce chemical cost and aeration energy use synergistically, which provides a cost-effective approach for WWTP upgrade.