## 1 Introduction  
Chloride anions are mainly found in oceans, seawater, in the waters of salt lakes, rivers, and surface waters. They are also found in the extensive underground deposits formed by NaCl that have appeared because of the drying up of seas. It occurs as the forms of minerals such as halite (rock salt), sylwin (potassium chloride), and carnallite (hydrated double potassium chloride) [1]. Chlorides are present in all living organisms where they are needed to maintain an appropriate osmotic pressure. In the human body, it is the main component of the physiological solution. Chlorides are a basic ingredient in animal and plant nutrition [2]. Chlorine is one of the macronutrients commonly found in nature. The natural cycle of this element helps to maintain a balance in nature which can be destabilized by human activities. Chlorine compound accumulation in a small area causes negative effects in the environment which requires remediation to achieve a natural balance again. Water contamination by chlorine compounds can be caused by inflow from landfills [3]. Calcium and sodium chlorides are used to defrost roads, which causes a large increase in chlorides in the environment [4]. Over the years, agglomeration practices have influenced water irrigation changes or leachate recirculation changes in urban and agricultural hydrological cycles. In fact, new challenges have appeared in urban and landfill management. Advanced technologies and modeling approaches allow the creation of hydrological modelling tools to mitigate the contamination of groundwater and deep aquifers by various ions such as chlorides [5]. Organic and inorganic pollutants can directly influence the changes in natural element balance e.g., carbon, oxygen, nitrogen, or phosphorous. Dissolved organic carbon is one of the most important elements for microorganisms in their metabolic pathways. Incontaminated sites, the balance between macro- and micro-elements can be destroyed if the concentrations of pollutants increase. In addition, the changes in the amount of dissolved organic carbon from surface and groundflow water may significantly influence biogeochemical cycles [6]. Agricultural production also is an important source of water pollution through releasing chloride ions originating from fertilizers [7]. The rock salt used in farms and on pastures as animal licks also causes an increase in chlorine in ecosystems [8; 9]. Chlorine compounds are used in various branches of industries. One example is the power industry, where transformers filled with oils containing commercial mixtures of polychlorinated biphenyls (PCBs) have been used for years. Defective operation of industrial equipment as well as various types of accidents may lead to soil and water contamination. In this way, chlorine-containing compounds can pollute the environment [10]. Although this element is very widespread around the globe and necessary for the functioning of organisms, its high concentration in aquatic and terrestrial ecosystems may pose a threat to the proper functioning of fauna and flora. Therefore, researchers for many years have been conducting experiments aimed at the effective removal of chlorine from places where its accumulation exceeds permissible doses. There are biological, chemical, and physical methods that are used as fundamentals to study the environmental remediation of polluted sites [11; 12; 13]. Biological processes such as biodegradation and bioremediation are environmentally friendly but often require more time than others to move pollutants from the solution. Biodegradation process technologies use autochthonous microbial communities capable of metabolizing contaminants [14; 15]. Microorganisms (bacteria or fungi) which naturally appear in polluted sites are screened and studied in order to biodegrade toxic compounds and their metabolites. There are many species of bacteria which provide the biodegradation processes in polluted sites. The processes that appear during various stages of the chlorine cycle in nature require different oxygen conditions.