# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 3 Advanced Applications of NBs in Precision Surface Cleaning
### NBs in Membrane Cleaning
The findings demonstrated that the method by which bubbles prevent fouling is dependent on their size: bigger bubbles (2 mm) limit fouling but do not improve fouling retention, whereas smaller bubbles (<0.05 mm) absorb foulants but may also contribute to a flux drop. According to the study, optimizing the bubble size could result in a compromise between energy efficiency and fouling prevention. Furthermore, two-phase air-water fluxes might enhance impurity retention and reduce fouling; however, the effects vary for submerged hollow fiber membranes and flat sheet membranes. The results emphasized the importance of bubble size and filtration mode in maximizing membrane performance, and further study is required, especially for membranes with big pores. [PERSON] et al. [44] investigated the effects of MNBs on the antifouling, rejection, permeability, and membrane performance. The findings demonstrated that MNBs reduced the flux attenuation, enhanced the antifouling effectiveness by 165.9%, and markedly increased the membrane permeability during filtration. Nanoparticle tracking analysis showed that, because of the aggregation effect of MNBs, contaminants tended to form bigger particles. MNBs improved fouling control by acting as a \"gas bridge\" between contaminants and the membrane surface, inhibiting adherence. In wastewater treatment, this \"gas bridge\" phenomenon offers a fresh strategy for reducing membrane fouling. [PERSON] et al. [48] devised a method to create high-performance ultrafiltration (UF) membranes with high surface porosity and small pore diameters (<20 nm) using NB-assisted nonsolvent-induced phase separation (BNIPS). A small quantity of CaCO\({}_{3}\) nanoparticles was added to the casting solution, which caused a phase inversion in a diluted-acid coagulation bath to produce CO\({}_{2}\) NBs, thereby controlling the microstructure of the membrane. With a skin layer thickness of 80.3 nm, a pore size of 10.2 nm, and a surface porosity of 12%, the resultant membrane was created using 0.3% nano-CaCO\({}_{3}\). At remarkable pure water permeance, it maintained over 99% bovine serum albumin (BSA) rejection, which was 2.5 times greater than that of the control membrane. Compared with commercial and other UF membranes, the BNIPS approach provided higher permeability and selectivity, offering an affordable means of enhancing membrane performance. However, future research should address issues such as possible equipment degradation and nanoparticle dispersion. [PERSON] et al. [49] investigated the effects of adding BNBs to the UF process (Figure 6). The addition of BNBs enhanced the membrane performance, as shown by a notable increase in the permeate flux in both lab and pilot-scale UF tests. In the lab and pilot-scale experiments, the permeate flux rose from 9.27 to 14.57 kg/h\(\cdot\)m\({}^{2}\) and from 6.89 to 9.59 kg/h\(\cdot\)m\({}^{2}\), respectively (\(p<0.05\)). Moreover, the addition of BNBs changed the microstructure of skim milk concentrate (SMC) dispersions and significantly decreased their apparent viscosity. According to the study, adding BNBs improves the efficiency of UF membranes and may result in more effective processing in the food and dairy industries. The two BNB generation methods employed to integrate BNBs directly into the SMC during UF were hydrodynamic and sonic cavitation. Furthermore, when BNBs were present, CLSM pictures of fouled membranes revealed fewer dense membrane fouling layers and decreased particle accumulation. The results demonstrated how BNB technology can be used as an environmentally friendly method to enhance UF membrane performance. Future studies should focus on creating BNB generation systems that can accurately regulate BNB content and size for particular food processing uses. [PERSON] et al. [50] examined the use of NB-assisted backwashing (NBB), a novel technique to reduce membrane fouling in membrane bioreactors (MBRs), which is a significant issue that increases operating costs.