| Advanced oxidation technologies, in which peroxydisulfate (PS) or peroxymonosulfate (PMS) is used as oxidant, came forth recently for the degradation of non-biodegradable contaminants. PS and PMS can be activated to generate SO4-·which is also a powerful oxidant and can oxidize most organics in wastewater. The study of activation method is a hot issue. The conventional activation methods consist of heat, UV and metal activation. While some new activation method come forth recently. In this study, azo dye Acid Orange 7 (AO7) was chosen as the model contamination to study the degradation rate, influential factor and radical method under heat and UV activation method (conventional activation method) and CO32- and microwave activation method (new activation method). Besides, the effect of Cl-, which is an efficient quenching reagent, was studied. Specific studies are as follows:1) The three peroxides mentioned above (PS, PMS and H2O2) are similar in structure and they all have O-O bond. On the other hand, they have some difference in structure which results various degradation rates and radical mechanisms under various peroxides activated method. Therefore, the main objectives of this study are: (1) to compare the degradation efficiencies of A07 by these three peroxides (PS, PMS, H2O2) under heat or UV activation condition; (2) to study whether common anions (SO42-, NO3-, CO32-, HCO3-,HPO42-, Cl-) can activate these peroxides and consequently degrade A07. The results show that the order of A07 degradation efficiencies by heat activation is PS >> PMS> H2O2 and the order by UV activation is PS> H2O2> PMS. In the anions activated method, it was found that PMS could be activated by some anions, but PS and H2O2 can not be.2) High-temperature wastewater constitutes one of the largest groups of organic compounds that represent an increasing environmental danger. It is reported that billion tons high-temperature printing and dyeing wastewater discharge every year in china. The goal of this study is to use the high-temperature wastewater as heat resource to activate PS to degrade contamination in wastewater. The result indicated that the higher temperature of wastewater can result in the faster degradation rate. The radical quenching experiments demonstrate that both SO4-·and·OH could degrade AO7 but SO4-·plays the dominant role. Maximum AO7 degradation occurred at pH 7. Heat activated PS could not only decolorize AO7 but also mineralize it.3) The aim of this experiment is to study the degradation of AO7 by PS under UV activated method. The results showed that PS could be activated by UV (254 nm). The higher temperature of wastewater can result in the faster degradation rate and maximum AO7 degradation occurred at pH 7. UV activated PS could not only decolorize AO7 but also mineralize it. The radical quenching experiments demonstrate that both SO4-·and·OH could degrade AO7 but SO4-·plays the dominant role.4) CO32- is common anions in natural water and wastewater. The existence of CO32-, which has been considered as an efficient quenching reagent by competing with radicals, can retard the degradation rate of organic compounds in the AOPs. The main objectives of this experiment are to study the degradation of AO7 by CO32- activated PMS. The results show that CO32-activated is an effective activated method. CO32-activated PS could not only decolorize AO7 but also mineralize it. The radical quenching experiments demonstrate that 1O2 other than SO4-·plays the dominant role.5) Microwave heating can decrease activation energy, reduce reaction time, increase the selectivity of reaction and improve the speed of reaction, and etc. Activated carbon (AC), which is an excellent MW absorbing material, could absorb and convert MW energy into thermal energy. The goal of this experiment is to study degradation of AO7 by microwave activated PS. The results show that the biggest advantage of microwave activation PS is fast. AO7 (up to 1000 mg/L) is completely decolorized within 5-7 min. The present of activated carbon enhance the oxidation of microwave/PS systems, improving the organic matter degradation.6) Cl- is common anions in natural water and wastewater. The existence of Cl-, which has been considered as an efficient quenching reagent by competing with radicals, can retard the degradation rate of organic compounds in the AOPs. The effect of Cl- on the degradation of AO7 by PS and PMS under various activated conditions (UV (254 nm)/PS, Thermal (70℃)/PS, UV/PMS, Co2+/PMS) and the role of active chlorine oxidizers (Cl2-·, HClO) generated from the reaction of Cl- with SO4-·or·OH were investigated by using quenching method. The results show that under UV/PS and heat/PS, Cl- inhibited AO7 degradation due to reaction of Cl- with SO4-·to generate Cl2-·and HClO. Under UV/PS condition, with the increased of Cl-, the amount of HClO increases and the degradation rate accelerates. Under Co2+/PS condition, Cl- can restrain the circulation of Co2+ and Co3+and hinder the formation of SO4-... |
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