Effect of bubble size on oxygen transfer during aeration of integrated wastewater treatment systems

In integrated wastewater treatment systems(IWTS), aeration accounts for the most energy-intensive process. However, the quantitative influence of initial bubble diameter (d₀ = 1-4 mm) on aeration efficiency remains insufficiently characterized. This study employs computational fluid dynamics coupled with the Population Balance Model (CFD-PBM), incorporating an oxygen transfer model to predict the impact of d₀ on oxygen transfer efficiency in the aerobic tank. Results reveal that dissolved oxygen (DO) distribution exhibits a clear dependence on d₀. Specifically, a d₀ of 2 mm not only maintains a high oxygen transfer rate (k_La = 6 × 10^-3 s^-1), but also significantly enhances the vertical uniformity of DO distribution. The oxygen transfer coefficient (k_L) is influenced by both flow field and d₀, with the latter playing a more dominant role. For small-scale IWTS (depth ≤1 m), a d₀ of 2 mm is recommended as the optimal aeration design parameter, as it achieves an optimal balance between oxygen transfer efficiency and DO distribution uniformity.