## 3 Results and Discussion
### Effect of Salts and Surfactants Presence on DY50 Adsorption  
Industrial wastewaters generated during various technological processes carried out in textile factories, paper and tameries contain auxiliary agents such as salts, acids, bases, surfactants, oxidants and reducing agents. They get into the sewages in the amount in which they were used in the dyeing baths and do not wear out in the dyeing process of the fiber, as opposed to dyes. Depending on the type and nature of the fiber, as well as the intensity of coloration, the amount of dyes and auxiliaries used are different. The compositions of dyeing baths are summarized in Table 5[66; 67]. The main component of the dyeing bath is water characterized by a relatively high surface tension; therefore, it is necessary to introduce surfactants which reduce surface and interfacial tension [66; 67]. The addition of surfactants will cause that water will moisten the fiber surface better, which will facilitate the dyes' contact with this surface. Interactions between the surfactant and the dye molecules in the aqueous solution are of great importance in the process of water treatment and reuse [66; 67; 68; 69; 70]. Therefore, it is necessary to assess the effects of various salt and surfactant amounts on the adsorption of dyes. The influence of auxiliaries on DY50 sorption efficiency on the A21, A23 and A24 anion exchangers was studied using the static method in the systems containing 0.5 g of anion exchangers and 50 mL of DY50 solution of 500 mg/L concentration while the concentration of salts and surfactants changed from 5 to 25 g/L of Na\({}_{2}\)SO\({}_{4}\) or Na\({}_{2}\)CO\({}_{3}\) and from 0.1 to 0.5 g/L of SDS or TX-100. The amount of dye adsorbed by the anion exchanger after 15 min of phase contact time was determined. In the studies a decrease of \(q_{t}\) was observed in the anion exchangers-DY50 systems with an increase of Na\({}_{2}\)CO\({}_{3}\) concentration (Figure 6), however the least pronounced impact of carbonate presence of the uptake effectiveness can be observed for the anion exchange resin of polyacrylic matrix, i.e., A24. The decrease in the sorption capacity together with the increase of sulphate concentration in the system may be caused by competitive sorption of sulfate ions compared with the anionic form of the dye. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Bath Components** & **Light Intensity** & **Deep Intensity** \\ \hline Dye & up 0.5\% & 0.5–3\% \\ Na\({}_{2}\)CO\({}_{3}\) & 05–1\% & 1–2\% \\ Na\({}_{2}\)SO\({}_{4}\) & 4–10\% & 10–30\% \\ Surfactants & up 0.5\% & 0.5–1\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Compositions of baths for dyeing with direct dyes. Figure 6: The effects of (**a**) Na\({}_{2}\)CO\({}_{3}\) and (**b**) Na\({}_{2}\)SO\({}_{4}\) presence on DY50 adsorption on A21, A23 and A24 anion exchangers. The presence of SDS and TX-100 (0.1-0.5 g/L) in the dye solution resulted in an increase in \(q_{t}\) values using the phenol-formaldehyde resin A23 during sorption test as it is characterized by the highest value of the total capacity (1.8 eq/L as declared by the manufacturer), resulting in a larger concentration of the -N(CH\({}_{3}\))\({}_{2}\) functional groups compared to the other anion exchangers (A21, A24). The interactions between dye anion and a surfactant with the same charge contribute to electrostatic repulsion in the aqueous phase and favors adsorption of DY50 anion in the resin phase in dye-surfactant systems. The presence of these surfactants caused a decrease in the dye adsorption on the polystyrene A21 and polyacrylic A24 anion exchangers which suggests that competitive sorption of the anionic surfactant compared to the dye anions is more pronounced, as presented in Figure 7. Therefore, the type of anion exchanger matrix composition plays an important role in dye sorption from solutions containing auxiliaries such as surfactants. Notwithstanding this, the hydrophobic interactions between the DY50 and the SDS or TX-100 are dominate during DY50 adsorption on A23.