• N 2 nanobubbles (NBs) can readily decrease a dissolved oxygen (DO) level to 99.9% DO removal, a level unattainable by conventional N 2 gas bubbling. The NBs-driven DO removal is highly effective across a broad range of initial DO levels, up to ∼ 49 mg/L. While CO 2 NBs can reduce DO levels to ≤ 0.03 mg/L, the results indicate N 2 NBs are superior due to the inherent physicochemical properties of the gas. Mechanistically, NBs significantly alter gas exchange dynamics by enhancing gas transfer and Ostwald ripening, leading to O 2 outgassing as NB gas dissolves into the water. The experimentally observed DO removal efficiency aligns closely with our first-order numerical simulations, which account for the diameter and number density of the generated NBs. Furthermore, our method is reversible, allowing DO levels to naturally re-equilibrate under atmospheric conditions. These findings highlight that NBs offer a promising, environmentally friendly, and cost-effective approach for dissolved gas replacement, opening new avenues for sustainable water treatment.
Kioka et al. (Fri,) studied this question.