## 2 Application of Membranes in Contamination Situations
### Surface Water Contamination  
Water pollution is a widespread problem worldwide, and the sources of pollution can be geological or anthropogenic [16]. The types and concentrations of natural pollutants depend on the type of geological materials through which groundwater flows and the type of catchment development. Surface waters moving through different terrains can contain various substances such as magnesium, calcium, chloride, arsenate, fluorine, nitrate, and iron [17; 18]. If naturally occurring elements are present at unacceptable levels, water may be contaminated [19]. Other contaminants are by-products made by humans, industries, and agriculture, including heavy metals, mercury, copper, chromium, lead, and hazardous chemicals, dyes, and compounds such as insecticides and fertilizers. Generally, there are four types of surface water pollution, i.e., inorganic, organic, biological, and radiological. Significant natural contamination of surface water is affected by calcium and magnesium compounds causing water hardness. Other pollutants coming from natural sources, industrial processes, as well as from water supply systems are compounds of fluorine, arsenic, lead, copper, chromium, mercury, antimony and cyanides [20]. The main anthropogenic sources of organic pollutants are pesticides, household waste, industrial waste, etc. [21]. Contamination with organic materials can cause serious health problems, such as cancer, endocrine disruptions, and nervous system disruption [22]. Biological water contamination is caused by the presence of living organisms such as algae, bacteria, protozoa or viruses [23]. Each of them can cause different problems in the water. Radiological contamination is caused by radioactive elements. Sources of radioactive material can be soil or rocks through which water flows or some industrial waste [24]. The erosion of natural deposits of certain (radioactive) minerals can emit radiation (like \(\alpha\) and \(\beta\)). At the same time, radioactive elements, such as U226, Ra226, Ra228, and Rn228 seem to be a bigger problem in groundwater than in surface water. All types of radiological contamination increase the risk of cancer [25]. Depending on the type of contaminants present in the water, they are removed by various methods using both physical and chemical processes. Some of the common methods of water purification are precipitation and coagulation (including water softening and removal of heavy metals, phosphorus, fluoride, arsenic, dyes), distillation, adsorption (often using activated carbon, zeolites, silica gel, or ion exchange resins). Often, depending on the type of contaminants present in the water, hybrid treatment processes combining different methods are also used. Such activities are aimed at obtaining waters of appropriate purity, taking into account not only the efficiency of operation, but also the costs of these processes. Currently, innovative membrane technologies are used more and more often for water purification. In water treatment, the best results are achieved by pressure processes, e.g., reverse osmosis, or electrically driven processes, e.g., electrodialysis (ED) [26]. The basic principle of membrane separation using electrodialysis is similar to the ion exchange reaction [27]. Polymer membranes used in osmotic processes generally have an open porous support layer and a thin, less porous skin layer of the same material. Separation takes place in the epidermis layer, and the carrier is easily permeable to water and substances undissolved in water. In MF/UF membranes, the active part of the membrane is a selective surface layer with pores from 0.01 to 0.2 mm, which is responsible for the efficiency of the filtration process. MF and UF membranes are most often made of polymers, e.g., polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), polypropylene (PP), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).