# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 3 Advanced Applications of NBs in Precision Surface Cleaning
### NBs in Membrane Cleaning
When added to backwashing to clean membranes, NBs with an average diameter of approximately 150 nm performed better in terms of cleaning than both chemically enhanced backwashing and traditional tap water backwashing. Without changing the microbial activity or sludge characteristics in the MBR, the NBB proved especially successful in lowering reversible fouling and even assisting in the control of irreversible fouling. It was proposed that the NBB increased the fouling layer porosity, which made it easier to remove, although the exact mechanism underlying its improved cleaning effect is still unclear. The findings demonstrated NBB's potential as an effective and environmentally friendly membrane cleaning technique. To make NBB a viable option for fouling mitigation in MBRs, future studies should focus on improving backwashing conditions, examining the effects of various NB properties, and delving deeper into the cleaning mechanisms. [PERSON] et al. [51] created NBs by introducing sodium bicarbonate (NaHCO\({}_{3}\)) into the aqueous phase, which changed the micro-nano structure of the polyamide (PA) rejection  
Figure 6: Proposed mechanism of the bulk NBs on ultrafiltration membrane performance. Reproduced with permission from [49], Copyright © 2022 Elsevier Ltd.  
layer in thin-film composite forward osmosis membranes. To successfully limit reverse solute flux and improve salt rejection, the addition of NaHCO\({}_{3}\) raised the PA layer's surface roughness and encouraged the creation of blade-like and band-like features. Nevertheless, the rougher surface also resulted in greater concentration polarization, which decreased the flow of water. Furthermore, by acting as a proton scavenger and promoting the polymerization of m-Phenylenediamine and trimesoyl chloride, NaHCO\({}_{3}\) enhanced the membrane's ability to intercept salt and its overall efficacy as an FO membrane. [PERSON] et al. [52] offered a novel solution for membrane fouling, which is a significant problem in the treatment of oily wastewater, especially that resulting from offshore oil spills. Superhydrophilic TiSe\({}_{2}\) nanospheres were formed on titanium foam using a one-step hydrothermal process, and an external electric field was used to support a dual antifouling strategy involving in situ aeration and dielectrophoresis. Unlike earlier passive techniques, this approach actively prevented oil droplets from coming into contact with the filtration surface, significantly increasing the fouling resistance by 90%. For four distinct oil-in-water emulsions, the TiSe\({}_{2}\)/TF material showed over 99% separation efficiency, which was maintained even after four months of constant filtration. Additionally, the material demonstrated outstanding endurance with little flux drop. This novel approach offers a viable method to treat oily wastewater from both onshore and offshore sources, laying the groundwork for further studies and real-world environmental water treatment applications. [PERSON] et al. [53] examined the combined effects of heat and NBs produced during the preparation of nanofiltration membranes by introducing acid aqueous catalysts (e.g., NaHCO\({}_{3}\), NaOH, and Ca(OH)\({}_{2}\)). When the acid acceptors reacted with the interfacial polymerization (IP) byproduct HCl, heat was released, and CO\({}_{2}\) bubbles were produced in the case of NaHCO\({}_{3}\). These factors affected the membrane structure and performance. A thicker PA layer and decreased flux resulted from the use of NaOH and Ca(OH)\({}_{2}\), which released more heat. In contrast, NaHCO\({}_{3}\) increased the flux from 20.3 to 28.3 L/m\({}^{2}\) h bar while maintaining a salt rejection rate of 97.7% by encouraging the creation of a rougher PA surface through both heat and bubble release. Furthermore, the presence of acid acceptors facilitated crosslinking, which reduced the negative charge of the membrane. This study provided a better understanding of how the IP process and membrane performance are affected by heat and gas emissions from acid acceptors. [PERSON] et al.