## 2 Application of Membranes in Contamination Situations
### Contamination of the Soil Environment  
Soil contamination poses a serious threat to human health. Dangerous and ubiquitous pollution is caused by, among others, heavy metals polluting water, soil, feed, and food [46; 47]. Moreover, large amounts of waste and the intensive use of chemicals, especially in agriculture, in recent decades have resulted in a significant threat to ecosystems [48]. The main factor influencing the quality of soil is human activity, incl. operation of mines, storage of industrial or municipal waste. For example, in 2018, according to Eurostat data, 5.2 t of waste were generated per capita [49]. Unfortunately, not all waste is recycled and a significant part of it is deposited in landfills, and in the case of hazardous waste, also in burial grounds. Therefore, soil contamination with CBRN substances mainly occurs near landfills, in areas of intense industrial activity, or in the case of an accident. It should be emphasized that soil contamination has a direct negative impact on human health [50]. Due to the high and constantly increasing level of environmental contamination, there is a need to search for effective techniques and engineering methods for purifying or utilizing sewage and other waste streams that pollute the soil. Depending on the type of contamination, various methods of soil reclamation and protection are used, which can generally be divided into chemical, physical, and biological methods [51]. Depending on the type of pollution and the purpose of the reclamation works, membrane technologies are also used, including geomembranes as barriers to seal landfill areas. Due to the structure and raw materials of which geomembranes are made, these are divided into:  
1. Flat membranes made of oxidized asphalts or modified with polymers (poly (vinyl chloride) polyvinyl chloride PVC), or terpolymer obtained from ethylene-propylene-diene rubber monomers (ethylene propylene diene rubber EPDM or high density polyethylene HDPE). 2. Extruded HDPE membranes. Due to their chemical structure, synthetic geomembranes are resistant to most chemicals and also have good resistance to biological degradation and good mechanical strength. Geomembranes are used in places where protection of the natural environment against contamination is required:  
* petrol stations and their storage facilities,
* sewage treatment plants,
* oil boiler rooms,
* rainwater sedimentation tanks,
* hazardous substances reloading yards,
* recycling yards for scrapped vehicles,
* drainage ditches at road bodies,
* sealing municipal waste landfills, and
* broadly understood agrotechnics. It is very important to choose the right geomembrane material taking into account its application. Multi-criteria decision making (MCDM) provides useful selection tools and has been applied successfully to select geomembranes [52]. Various materials used for the production of geomembranes were tested and it was found that HDPE is the most appropriate. In contrast, PVC is the least useful material for the production of geomembranes. Geomembranes are commonly used to protect soil against leakage of hydrocarbons and other petroleum substances that have a significant impact on the environment and can pose a serious threat to both humans and other forms of life in the polluted environment [53]. Contamination with petroleum hydrocarbons constituting persistent organic pollutants, which include many organic compounds such as polycyclic aromatic hydrocarbons (PAHs), is characterized by high stability, which problematizes their degradation and causes them to remain unchanged in the environment for a long time [54]. The presence of these substances in the ecosystem is usually related to anthropogenic sources that cause significant environmental problems, namely ecological and social disasters around the world. Geomembranes are used to limit leakages from tanks or landfills and to remove and prevent the further spreading of pollutants released during accidents and disasters. Currently, HPDE membranes are most commonly used [7].