Investigation of removing orange II azo dye from wastewater through an oxidation process

Rapid industrial growth in Bangladesh, especially in the textile industry, has led to water pollution from toxic azo dyes like orange-II, which are harmful to ecosystems and enter the food chain via irrigation. This study examined the use of chemical coagulation (using \({\text{C}}_{6} {\text{H}}_{11} {\text{NO}}_{4} {\text{X}}_{2}\) and \({\text{FeCl}}_{3} \cdot 6{\text{H}}_{2} {\text{O}}\)) and advanced oxidation process (using \({\text{NaOCl}}\)) to treat orange-II dye for irrigation. However, \({\text{C}}_{6} {\text{H}}_{11} {\text{NO}}_{4} {\text{X}}_{2}\) and \({\text{FeCl}}_{3} \cdot 6{\text{H}}_{2} {\text{O}}\) showed limited effectiveness in removing orange-II dye across various pH (3, 6, 9, and 12) levels. In contrast, \({\text{NaOCl}}\) achieved significant dye removal rates of over 90–99%. The study focused on high color removal, limited \({\text{ClO}}_{2}\) and neutral pH after the test. Variables included \({\text{NaOCl}}\) doses (0.5 ml, 2.5 ml, and 5 ml), orange II dye doses (50 mg, 100 mg, and 150 mg) under different pH (3, 6, 8, 9 and 12) conditions. The manuscript is the first to assess orange-II dye using higher doses (2.5 ml and 5 ml) of \({\text{NaOCl}}\) compared to other studies, as an alkaline chemical to neutralize pH levels post-test. The highest dye removal occurred at pH 9 with similar results at other pH levels except pH 12. However, despite effective color removal, the pH remained alkaline at pH 8, 9, and 12 after the test. Hence, optimal experimental conditions of operational parameters were pH = 3 or 6, 2.5 ml \({\text{NaOCl}}\) dose with 100 mg/L or 150 mg/L dye doses. Further research is recommended on the degradation process, toxicological analysis of the final product, and cost-effectiveness for safe irrigation water.