Effect of bubble sizes on oxygen transfer efficiency of nano- and micro-sized bubble clouds for improving aquatic environments

In our groundbreaking experiments, we contribute to the potential of micro-nano bubble technologies to aerate hypoxic environments. Our exploration reveals that the oxygen transfer efficiency (OTE) of nanobubbles (NBs) solution surpasses that of microbubbles (MBs) solutions. Specifically, the volumetric oxygen transfer coefficient K_La for MBs and NBs were explored to be 0.0804 and 0.1410 min⁻¹ at 16 °C, respectively. We discovered exceptional oxygen transfer rate (OTR) of NBs due to large surface area, long retention time, and slow rising velocity. Additionally, the coalescence and collapse of NBs were evaluated through classical Derjaguin-Landau-Verwey-Overbeek theory, emphasize high OTE of NBs. The effect of initial oxygen concentration was explored, insist on micro-nano bubble applications. Analyzing the OTR of NBs in Dongjin River and Saemangeum Lake waters revealed salt level and organic matter significantly impacting OTE of NBs. Through the consideration of the effect of salinity and environmental factors, we calculated actual oxygen transfer rates for fresh and brackish water, exhibiting OTE of 49% and 59%, respectively. Our study not only highlights the effect of bubble size on OTR but also emphasizes the practical applicability of micro-nano bubble technologies, offering calibration factors for treating hypoxic areas in the aquatic environments.