## 2 Application of Membranes in Contamination Situations
### Groundwater Contamination
[94] investigated the effect of membrane pore size and surface properties on membrane performance. The study included four fully aromatic polyamide membranes with different physicochemical properties, including three commercially available NF membranes, i.e., NF90, ESNA1, and ESNA1-LF2-LD and one commercially unavailable membrane M#1. All four membranes were hydrophilic, with the M#1 membrane being the most hydrophilic, with the support layer of a polysulfone or polyamide active layer different from the other membranes and with the smallest pores. The research results showed that the pore size and surface charge, hydrophobicity, thickness of the active layer and roughness are important factors for the membrane operation. These properties can significantly affect water permeability and/or arsenate rejection. On the other hand, the pore size and surface charge are not significantly affected by the membrane size and surface charge. The results showed that the pore size and surface charge are significantly affected by the membrane size and surface charge. other hand, the reaction environment was also important, including the pH value of the solution. The most optimal conditions for the rejection of arsenate were obtained at about neutral pH [94]. Modifications with the use of nanoparticles with high oxidation potential, such as zero-valence iron nanoparticles (nZVI), are widely used. The use of nZVI integrated into the structures of membranes allows to prevent agglomeration and reduces the likelihood of secondary pollution. On the other hand, however, their mechanical strength is limited, which is critical for the long-term operation and regeneration of membranes [95]. [PERSON] et al. [95] developed a high molecular weight double crosslinking method to improve the mechanical strength of polymeric electro-spun nanofiber membranes. Polyacrylic acid is one of the main high molecular weight (PAA, Mw = 450,000) polymers of nZVI [95; 96; 97] immobilization that has been double cross-linked by adding polyvinyl alcohol (PVA) and Fe(II) or Fe(III). PVA was added as a covalent cross-linking agent, while the iron particles acted as an ionic linker. The obtained results indicated that the Fe(III) -based PVA-PAA-nZVI membrane showed a high potential for the long-term filtration process and allowed for a higher degree of Cd ion removal from groundwater [95]. Groundwater more and more often, apart from metals, contains higher and higher concentrations of nutrients that come from crops, landfilled waste, or leachate. Nutrients migrate with rainwater into the soil, undergoing transformation, depending on the chemical, physical and biological characteristics of the environment. Contamination of groundwater with nutrients poses a threat to human health, as in many areas these waters constitute a reservoir of drinking water. Therefore, a lot of work is focused on the removal of various forms of nitrogen and phosphorus. Among others, [PERSON] et al. [98] carried out studies on NO\({}_{3}\)' removal using a PA nanofiltration membrane modified with poly(sodium 4-styrene sulfonate) (PSS). The research results show that the most optimal system, for which the nitrate rejection rate of 88.8% was obtained, was at the PSS concentration of 1.5 mg/L and the permeate flux of 27.0 L/m\({}^{2}\).h. The influence of the initial nitrate concentration and solution pH on the effectiveness of nitrate removal through the modified NF membrane was investigated. It was found that the nitrate rejection rate was further enhanced by PA/PSS at a lower pH, while the membrane permeate flux improved as the pH increased. The initial concentration of nitrates had little effect on both the rate of nitrate rejection and the discharge from the membrane [98]. In addition to nutrients, pesticides also pollute groundwater. [PERSON] et al.