Novel dissolved oxygen distribution model of a full-scale aeration tank for a municipal wastewater treatment plant in a cold climate region

Aeration is the most energy-intensive process in wastewater treatment plants (WWTP). Seasonal variation in hydraulic flow and load has a significant effect on WWTP’s aeration energy efficiency. High flow and temperature variations are common in cold climate regions, and with climate change increasing, extreme weather events will accentuate these situations. The prediction of oxygen mass transfer is crucial for minimizing the energy consumption of the aeration tank. This study presents a computational fluid dynamics model for a turbulent flow regime, simulating the hydraulics and dissolved oxygen (DO) concentration distribution of two phases, water and air bubbles, in a full-scale, as-built activated sludge tank. Model validation error was less than 15%. Different seasonal flows and temperatures were investigated by fixing liquid side oxygen mass transfer coefficient (k_L) to 0.7 × 10^–5 m/s and initial bubble diameter (d_B) to 0.0025 m in the gas phase. The results show that variating hydraulic flow causes noticeable differences in DO distribution and higher flow could be more effective levelling in DO gradients. More even DO distribution could result in using up to a 10% lower DO setpoint value, using 3% less air for the same treatment result, thus lowering aeration energy cost.