Prediction of wastewater treatment processes in the aerobic tank of integrated equipment using coupled CFD-ASM1_2O modeling.

The substantial spatiotemporal variation of dissolved oxygen (DO) during the aeration process significantly affects the pollutant removal efficiency in wastewater treatment. Traditional monitoring methods often provide non-intuitive results and delayed information. In this study, computational fluid dynamics (CFD) and the Activated Sludge Model No.1 (ASM1) were combined to systematically investigate the reaction processes of wastewater components in the aerobic tank of an integrated wastewater treatment unit under different aeration conditions, with a specific focus on the removal of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), and total nitrogen (TN). An oxygen mass transfer model based on the double-film theory was incorporated into ASM1 to explicitly link gas-phase oxygen to liquid-phase DO dynamics and to refine the representation of aerobic-anoxic reactions, and a population balance model (PBM) was introduced to quantify the effects of bubble coalescence and breakup on oxygen transfer. The CFD-PBM predictions of the aeration flow field were validated against particle image velocimetry (PIV) measurements, with relative errors below 6.49%, and the integrated CFD-ASM1_2O modelwas further calibrated and confirmed using actual wastewater treatment data, showing good agreement in pollutant removal efficiencies. In addition, a specific energy consumption (SEC) index was proposed to evaluate the aeration economy. This study provides a mechanistic link between flow field characteristics, bubble behavior, oxygen transfer, and biochemical reactions, supporting energy-efficient optimization of aeration systems.