# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 4 Biofouling Mitigation and Advanced Cleaning Technologies
### Advancements in Water and Wastewater Treatment
Overall, the results showed that NBs provide an environmentally friendly and efficient way to control biofouling in agricultural water distribution systems. [PERSON] et al. [86] examined the impact of NB aeration on the structural characteristics and functionality of two typical microbial aggregates: biofilm and activated sludge. According to the key findings, aeration with NBs greatly increased oxygen availability, resulting in a 10.58% increase in total nitrogen removal. Larger activated sludge flocs and thicker biofilms were the result of applying NBs, which also improved the structure of microbial aggregates by increasing extracellular proteins and polysaccharides up to 3.40 times for the biofilm and 1.70 times for the activated sludge. Furthermore, NBs changed the functional substance composition of the aggregates, especially the oxygen-sensitive groups, and confocal laser scanning microscopy showed a more consistent biofilm morphology. This study also found that activated sludge required more adaptation than biofilms, while sludge settleability was initially harmed by low NB ratios and was improved by higher ratios. Overall, the study showed that aerating NBs improves the structural development and oxygen utilization of microbial aggregates, which increases the effectiveness of wastewater treatment. [PERSON] et al. [101] discussed how ozonation and MNB technology can be used to treat wastewater, with an emphasis on the oxidative potential of ROS generated by different-sized ozone bubbles. The results showed that smaller bubbles, which tend to contract and collapse, help produce hydroxyl radicals (\(\bullet\)OH) but do not produce H\({}_{2}\)O\({}_{2}\). With a longer lifespan than traditional bubbles, this study demonstrated that ozone MNPs improve disinfection by efficiently reducing the time required to sterilize _E. coli_ in reclaimed water. The oxidative capacity of MNPs is greatly enhanced by the continuous generation of \(\bullet\)OH at their gas-liquid interfaces, which makes them more effective than larger ozone bubbles at disinfecting pathogen-laden biofilms. This study showed the potential use of ozone MNPs to effectively treat drinking water and wastewater, providing a clean technology solution for a range of water purification requirements. [PERSON] et al. [102] discussed how ethanol-water exchange is used to form surface NBs (SNBs) on hydrophilic and hydrophobic surfaces, highlighting the impact of the exchange rate on the NBs' density and size. The findings demonstrated that on hydrophilic surfaces, like mica, and hydrophobic surfaces, such as highly oriented pyrolytic graphite (HOPG), higher exchange rates result in smaller and more numerous SNBs. According to the research, NBs that formed on HOPG were wider and more numerous than those that formed on mica, and their heights varied less. These observations can be explained by the suggested mechanisms of diffusion-driven growth and nonuniform nucleation. Enhancing our knowledge of SNB generation and stabilization could lead to improved applications in fields such as surface cleaning, where it is crucial to remove biofilms and contaminants. Controlling the ethanol-water exchange rate can improve the effectiveness of cleaning procedures and interfacial reactions, thereby increasing the potential applications of SNBs across a range of industries. [PERSON] et al. [103] developed a CuO-modified Al\({}_{2}\)O\({}_{3}\) ceramic membrane (CuO/Al\({}_{2}\)O\({}_{3}\) CM) for the sol-gel method of wastewater treatment. By changing the charge characteristics and increasing the hydrophobicity of the membrane, the CuO coating facilitated the accumulation of H\({}^{+}\) ions, which aided the collapse of MNPs in neutral aqueous solutions. High-temperature sites created by this collapse activated the CuO particles, producing ROS,  
Figure 14: The anti-biofouling mechanism of NBs. Crystal morphologies were revealed by scanning electron microscope at 900 h. Reproduced with permission from [100], CC-BY-NC-ND license, Copyright © 2020, the authors.