# Sorption of Organic Electrolytes and Surfactants from Natural Waters by Heterogeneous Membranes
## 1 Introduction  
Pollution of water bodies poses a major threat to humans and aquatic ecosystems. Population growth is leading to climate change. Greenhouse gas emissions from industrial enterprises significantly contribute to global warming, rising global temperatures and lower air quality.  
The quality of human life and health depends on the state of the environment [1; 2; 3; 4; 5; 6], the quality of food and drinking water [7; 8; 9], and the level of economic development of the country [10; 11]. These indicators determine the sustainable development of each country. Sustainable development involves the development of methods to prevent water pollution. One way to prevent water pollution is to effectively treat wastewater before it is discharged.  
The growing scale of production, especially in the chemical industry, and the widespread use of surfactants as floatation agents, emulsifiers, foaming agents, synthetic powders and soaps, shampoosand shower gels, lubricants, etc., [12; 13; 14; 15; 16; 17] increasingly demand the development and application of reliable methods for demineralization of wastewaters to prevent environmental pollution by mineral substances and surfactants [18; 19; 20; 21]. Despite the high removal efficiency during wastewater treatment, their high consumption volumes mean that a certain part will always end up in aquatic ecosystems, and surfactants have been found in sea waters and sediments [22; 23; 24; 25; 26].  
One of the most reliable and effective methods for demineralization of wastewaters is the electrodialysis method [27; 28; 29; 30; 31; 32] (Figure 1).  
The essence of the method is that as a result of applying an electric field, there occurs a decrease in the concentration of the solution in some chambers (desalination) and an increase in concentration in others [33; 34; 35; 36; 37], due to selective permeability of the membranes with respect to individual ions [38; 39; 40; 41; 42]. However, during the long-term operation of electrodialysis plants, the process of desalination of solutions deteriorates due to sedimentation on the surface of the membranes and \"poisoning\" (loss of selectivity) of the membranes (see Figures 2 and 3), which is a result of the sorption of organic substances [43; 44; 45; 46; 47]. Along with this, the study of the interaction of ion-exchange membranes with solutions of surfactants is also of special interest, since membranes are used in the purification of medicinal and biological preparations which, in most cases, are surface-active substances (surfactants) [48; 49; 50; 51; 52; 53]. The behavior of large organic ions in the membrane [54; 55; 56; 57] is of considerable interest in connection with the problem of modeling, in particular, biological cell membranes [58; 59; 60; 61].  
Figure 1: Scheme of electrodialysis [33].  
Figure 2: Ion-exchange membrane: (**a**) anion-exchange membrane, (**b**) cation-exchange membrane (these are directly those membranes that we have in the laboratory and on which we carried out experiments).  
The objective of the paper is to study the sorption characteristics (exchange capacity, sorption isotherms, moisture content) of the MA-40 and MK-40 ion-exchange membranes in solutions of simple (NaCl, MgCl\({}_{2}\), Na\({}_{2}\)SO\({}_{4}\)) and organic (sodium benzenesulfonate C\({}_{6}\)H\({}_{5}\)SO\({}_{3}\)Na-NaBS and naphthalene-2-sodium sulfonate C\({}_{10}\)H\({}_{7}\)SO\({}_{3}\)Na-NaNS) electrolytes and in a solution of the surfactant, cetylpyridinium chloride C\({}_{16}\)H\({}_{33}\)NC\({}_{5}\)H\({}_{5}\)Cl \(\cdot\) H\({}_{2}\)O-CPCI.