A comparative bench scale study of oxygen transfer dynamics using micro-nano bubbles and conventional aeration in water treatment systems

Aeration is widely employed in water and wastewater treatment systems. Aerobic wastewater treatment relies significantly on maintaining adequate levels of dissolved oxygen (DO) in water to ensure optimal quality of treated wastewater. Conventional aeration systems, however, require considerable energy usage due to the ineffectiveness of oxygen mass transfer to the treated water. Adopting micronanobubbles (MNB) can improve this limitation due to their high gas-liquid mass transfer rates. This study used micro-nano air bubbles to experimentally determine the volumetric oxygen transfer coefficient (k_La), standard oxygen transfer rate (SOTR), and standard oxygen transfer efficiency (SOTE) of an MNB aeration system and compared them with those of a conventional aeration system. The MNB generation and bubble analysis results showed that the MNB concentration was 10^8–10^9 bubbles/mL, with an average diameter ranging from 100 nm to 2 μm. MNB aeration achieved a maximum k_La of 0.4204 min⁻¹ at an airflow rate of 0.5 ± 0.1 LPM for a 25 L water volume, which was notably higher than the corresponding observed values for the conventional aeration system. Furthermore, MNB aeration demonstrated superior SOTR and SOTE values across all airflow rates tested, achieving a maximum of 139.78 mg/h and 54.33 %, respectively. The findings of this study suggest that MNB aeration, with its enhanced mass transfer characteristics, offers a more energy-efficient alternative to conventional aeration methods, with the potential for higher oxygen transfer rates and improved wastewater treatment performance. Results also indicate that optimal operation at specific airflow rates can increase oxygen transfer efficiency by two folds compared to conventional aeration systems.