Discoloration of simulated textile effluent in continuous photoreactor using immobilized titanium dioxide: Effect of zinc and sodium chloride

In the present research, the optimization of the photocatalytic degradation of simulated textile effluent containing two pollutants (Methylene blue (MB) and Zinc) consisted of studying the variation of four parameters, namely initial MB concentration ([MB]_I, mg/L), zinc concentration ([Zn²⁺]_I, mg/L), sodium chloride concentration ([NaCl]_I, M) and flow rate (Q, mL/min) through a design of experiment using the response surface methodology approach. Results showed that MB degradation depends by order of importance on NaCl concentration > MB concentration > ionic zinc concentration > flowrate. Modeling results presented a good concordance between predicted and experimental values with acceptable correlation coefficients (R² = 0.9879 and R² (adjusted) = 0.9773). Desirability function was applied on the second-order polynomial equation to determine the optimal experimental condition for fastest total photocatalytic degradation and it was identified as follows: For a maximal target of 85.91% and a desirability of d = 1.0, [MB] = 75 mg/L, [Zn²⁺] = 45 mg/L, [NaCl] = 0.125 M and Q = 500 mL/min. Moreover, results showed that zinc had a good affinity to cellulose material and contributed on enhancing the photocatalytic activity in terms of degradation. Mineralization of the dye was assessed for the optimal conditions using the TOC method. Moreover, special attention was also paid to better understand the effect of inorganic pollutant, scavenging effects of different molecules such as EDTA, isopropyl alcohol and CCl₄ were examined and discussed.