Activated Persulfate Decolorization Of Dye Wastewater Containing Cl~- Or Cr(VI)

Advanced oxidation technologies, in which peroxydisulfate (PS) or peroxymonosulfate (PMS) is used as oxidant, came forth recently for the degradation of non-biodegradable contaminants. In other side, the high saline condition makes printing and dyeing wastewater more difficult to decontaminate. In this study, azo dye Acid Orange 7 (AO7) was chosen as a model contamination to study its degradation rate by heat, UV, or metal activated peroxide oxidation (PS, PMS and H₂O₂) in the solutions containing Cl^-. The influential factor and radical mechanism were also studied. Specific studies are as follows:1) The AO7 degradation rate of UV activated peroxide (PS, PMS and H₂O₂) oxidation in seawater (NSW) was studed. The results indicated that PS, PMS and H₂O₂ can be activated by UV (254 nm) in NSW, but can not be activated under UV (365 nm) except PMS. Moreover, UV activated PS could not only decolorize AO7 in visible spectrum but also in the ultraviolet spectrum.2) High-temperature wastewater constitutes one of the largest groups of organic compounds that represent an increasing environmental danger. The goal of this section is to use the high-temperature wastewater as heat resource to activate PS to degrade contamination in wastewater containing Cl^-. The result indicated that high-temperature can activate PS to degrade AO7. The presence of Cl^- has little effect on the degradation of AO7.3) The aim of this experiment is to study the degradation of AO7 by PS and H₂O₂ under Fe²⁺ activated method. The results showed that AO7 can be degraded in the three systems (distilled water: DW; simulated seawater: SSW; seawater: NSW) by H₂O₂, but can't be removed by PS in NSW. In Fe²⁺ activated H₂O₂ system, the degradation order is DW > SSW > NSW. The radical quenching experiments demonstrate that·OH plays a dominant role in the Fe²⁺ activated method.4) In this section, the PMS and NaClO were used as oxidants to compare the degradation of AO7 and Rhodamine B (RhB) by Cl^-/PMS and that by NaClO. The results show that Cl^- is an effective activation method. Cl^- activated PS could degrade AO7 rapidly. As the increasing of concentration of Cl^-, the degradation rate increases. The radical quenching experiments demonstrate that HClO plays a dominant role in the degradation of AO7 in Cl^-/PMS system.5) In this section, we have studied the oxidation capacity of the PMS/Cr(Ⅵ) redox system and the removal of Cr(Ⅵ) by 2st-stage which involves the reaction between H₂O₂ and Cr(Ⅵ). PMS was expected to be activated by Cr(Ⅵ) to degrade AO7 and used to low down the pH value of the solution in the oxidation process since it can dinegative H+. Afterwards, H₂O₂ was then used as a reductant to completely remove Cr(Ⅵ) from solution in the acid entironment benefitting from the 1st-stage. The result indicated that Cr(Ⅵ) can activate PMS and then degrade AO7. The use the acid condition making from the 1st-stage can completely removal Cr(Ⅵ) by H₂O₂ instead of adding other acid.