This study investigated the removal of methylene blue and methyl orange dyes from aqueous solutions containing these dyes. The process of wastewater treatment involved a combination of adsorption processes performed using UV/H2O2/TiO2 and fly-ash adsorbent prepared from sunflower seed pulp. In this study, first the effect of UV/H2O2/TiO2 process parameters including initial dye concentration (10–30 mg/L), UV lamp power (0–30 W), hydrogen peroxide concentration (100–500 mg/L), and titanium dioxide concentration (10–50 mg/L) were investigated (under a process time of 75 min and adsorbent concentration of 2 g/L). In optimal conditions, the percentage of removal of methylene blue and methyl orange dyes were 96.43% and 83.60%, respectively. After the optimization of the parameters of UV/H2O2/TiO2 process, the processing time and adsorbent concentration were investigated. The results indicated that when performing the process under the process time of 150 min and the adsorbent concentration of 2 g/L, the removal of methylene blue dye exceeded 99%. In addition, the removal of methyl orange dye under the process time of 300 min and the adsorbent concentration of 10 g/L exceeded 99%. At the end of the study, an assessment was carried out using quasifirst-order and quasisecond-order kinetic models and the results indicated that both kinetic models had a high level of accuracy for modeling the adsorption of methylene blue and methyl orange dyes on fly-ash adsorbents prepared from sunflower seed pulp.
