Untapped Potential: Applying Microbubble and Nanobubble Technology in Water and Wastewater Treatment and Ecological Restoration

Abstract

Microbubbles (MBs) and nanobubbles (NBs) refer to bubbles of micrometer to nanometer sizes. Due to several unique attributes, including long-term stability, negative surface charge, and the ability to generate reactive oxygen species, MB and NB technology has garnered significant attention in water and wastewater treatment and ecological restoration. Recently, several studies have shown the beneficial effects of MBs and NBs in membrane defouling, pathogen deactivation, environmental remediation, etc. However, there is limited knowledge of the physical and biochemical interactions between MBs and NBs and microbial communities; the mechanistic roles of MBs and NBs on micropollutants removal during aerobic wastewater treatment and anaerobic digestion; and the engineering limitations on versatility and scalability of MB and NB technology, among others. This review fills this gap by providing a systematic discussion on the fundamentals of MBs and NBs, including their size and concentration, physicochemical properties, and generation methods. The latest advances on MB and NB applications to water and wastewater treatment and ecological restoration are then critically discussed. The review thus identifies the challenges of implementing MB and NB technology and concludes with future research directions for a broader understanding of MB and NB technology.

Ozone Micronano-bubble-Enhanced Selective Degradation of Oxytetracycline from Production Wastewater: The Overlooked Singlet Oxygen Oxidation

“…19,20 In recent years, micronano-bubbles (MNBs, with diameters < 100 μm) have attracted significant attention owing to their unique physicochemical properties. 21 MNBs have large specific surface areas and excellent gas dissolution capabilities owing to their high internal pressure, acting as "gas banks" for the supplementation of more gases, such as oxygen or ozone, to aqueous solutions. In addition, previous studies have reported that numerous • OH are produced during the collapse of MNBs.…”

Combination of ozone-based advanced oxidation process and nanobubbles generation toward textile wastewater recovery

“…The zeta potential in the final residence time of 300 min is reported to be −21.08 ± 0.35 mV with the corresponding distribution is depicted in Figure 6B. The negative value here is assigned to the generated ROS at the bubble interface, which leads to the bubble stability (Ushikubo et al, 2010;Selihin and Tay, 2022;Zhou et al, 2022). Typically, zeta potential value can be associated to the charge of the bubble rather than its density in the water.…”

Nanobubble Reactivity: Evaluating Hydroxyl Radical Generation (or Lack Thereof) under Ambient Conditions

“…Additionally, due to surface charge (−40 to −25 mV under neutral condition) and resulting electrostatic repulsion, NBs do not readily coalesce to form larger bubbles. Consequently, NBs can remain as stable suspension in water for months . Large interfacial area per unit gas volume also enables high mass-transfer efficiencies, which are advantageous for water treatment processes , such as bioremediation (e.g., activated sludge treatment), − dissolved air floatation, − adsorption (i.e., enhanced interaction between the target substances and charged surface of NBs), and advanced oxidation processes (AOPs) that employ gaseous precursors such as ozone. , …”