Experimental and theoretical insights into advanced removal of the refractory cibacron green H3G dye by UV/chlorine innovative oxidation process

The discharge of highly persistent Cibacron Green H3G (CG-H3G) dye by textile factories poses a significant threat to both environmental and human health. In this study, the UV/chlorine advanced oxidation process was successfully used to degrade and mineralize this dye. The synergism resulted from coupling 254 nm irradiation UV and low chlorine dosage was assessed at various solution pH (5-10) and liquid temperature (up to 50 degree celsius) for a range of chlorine dosage (50-200 mu M). In only 5 min, 85 and 100 % of CG-H3G (20 mg/L) were eliminated with high synergy indexes of 4.34 and 6.3 for 100 and 200 mu M of dissolved chlorine, respectively. Besides, 45 and 72 % of the initial TOC were mineralized after 30 and 60 min of photoirradiation with 100 mu M chlorine. The synergistic treatment was more efficient as chlorine dosage increased (in the range 10-200 mu M), and solution pH and temperature decreased (pH range: 5-10, temperature range: 20-50 degree celsius). Cl-2 center dot(-) and center dot OH/Cl center dot radicals were identified as the key oxidants degrading CG-H3G with contributions of 35 % for {center dot OH + Cl center dot}, 65 % for Cl-2 center dot(-) at 100 mu M of chlorine, and 25 % for {center dot OH + Cl center dot}, 75 % for Cl-2 center dot(-) at 200 mu M of chlorine. The contribution of Cl-2 center dot(-) increased by 10 % chlorine dosage increase from 100 to 200 mu M, whereas the contribution of {center dot OH + Cl center dot} decreased by 10 %. Finally, the different project's results were analyzed by adopting a simulation approach, where the concentration profiles of the different reactive species generated during chlorine photo-activation (specifically at steady state) was related to the degradation outcomes. This analysis provides an easier understanding of the degradation mechanism that occurs in the UV/chlorine process when applied to treat refractory textile effluents in deionized water.