The use of micro-nano bubbles in groundwater remediation: A comprehensive review

Micro-nano bubbles (MNBs) are minute bubbles with diameters on the micrometer and nanometer scale. Along with small size, MNBs have a large specific surface area, high zeta potential, long residence times in water, and high oxygen transfer efficiency. These attributes make MNBs more effective than conventional macro-bubbles in air sparging for groundwater remediation purposes. This paper aims to review recent research on the generation and properties of MNBs, and its implementation as a groundwater remediation technology. The MNB generation techniques are categorized while the factors to choose bubble generators are analyzed. Methods for characterization of MNB properties, including size and zeta potential, are also summarized. We further discuss properties and controlling factors of MNBs’ size, mass transfer, rising velocity, zeta potential, transport and generation of hydroxyl radicals in water. We summarize recent findings related to the use of MNBs technologies for remediation of contaminated groundwater bodies. Finally, the current challenges and limitations of MNBs application for groundwater remediation are discussed.