(71d) Optimization and Mechanism Analysis of a Wastewater Treatment Plant – Towards Energy-Saving and High Nutrient Removal

Wastewater treatment plants have historically been operated to remove biological oxygen demand (BOD) and nutrients (e.g., fixed nitrogen and phosphorus). However, the complex microbial interactions that are integral for maintaining and optimizing treatment processes remain unclear. Here we investigated the performance of a wastewater treatment plant along with different operational modes in various configurations for process optimization and mechanism analysis. The wastewater treatment plant was operated in Modified Ludzack-Ettinger (MLE) single-feed mode, anoxic-oxic-anoxic-oxic (AOAO) step-feed mode and modified- Johannesburg (Mod-JHB) step-feed mode with a membrane bioreactor (MBR) to optimize nutrients (i.e., nitrogen and phosphorus) removal efficiency and the functional microorganisms’ abundance (i.e., anammox bacteria, ammonia-oxidizing bacteria). The highest nitrogen removal efficiency (98.5±0.8%) and the highest phosphate removal efficiency (76.8±0.5%) were achieved in the Mod-JHB step-feed mode with an internal sludge recycling ratio of 200% and an anoxic/anaerobic step-feed volume ratio of 3:1. Based on the mass balance analysis, in the Mod-JHB step-feed mode, aerobic simultaneous nitrification and denitrification (SND) process (in aerobic zones) and the anammox process (in the anaerobic zone) were identified to be responsible for 34.2% and 42.9%, respectively, of total inorganic nitrogen removal. Microbial community analysis demonstrated that a higher fraction of anammox bacteria (0.66±0.01% and 0.13±0.02% in anoxic and swing zones, respectively) can be achieved under continuous supply of limited oxygen concentrations (< 0.1 mg/L) with step feeding under Mod-JHB mode. This project, therefore, provides a practical experience for the start-up of a WWTP aiming for high nutrients removal efficiency and energy-saving.