| Advanced Oxidation Processes (AOPs) has been proved to be successfully applied in the treatment of sewage. It can decolorize the wastewater, reduce the toxicity of pollutants, converte the pollutants to be a biodegradable by-product and achieve the completed mineralization of the organic pollutants. The Fenton technology which performed by iron-activated hydrogen peroxide (H2O2) to produce hydroxyl radical (HO·) has been widely investigated in the past few decades. Recently, Sulfate radical (SO4·-) which was produced by the activation of persulfate (S2O82) is applied to the restoration of organic pollutants in water and soil. It is a new technology developed recently at home and abroad. It is also believed to be one of the most promising advanced oxidation technologies.In this study, a new complex of iron introduced to the traditional Fenton reaction. The ferric iron Fe(Ⅲ) and Ethylene diamine-N,N’-disuccinic acid (EDDS) formed the complex named Fe(Ⅲ)-EDDS. It can overcome the main disadvantage of traditional Fenton technology. Because traditional Fenton technology can only performe high efficiency in acidic condition. Simultaneously, EDDS is biodegradable and it is one of the best environment-friendly complexing agents. On the other hand, the transition metal is able to activate S2Og2- to generate SO4·-. Therefore, Fe (Ⅲ)-EDDS will also be applied to activate S2O82- in present study. It is the first research on the utilization of Fe(Ⅲ)-EDDS to activate S2O82- and generate SO4·- at home and abroad.4-tert-Butylphenol (4-t-BP) is chose as a target pollutant in this study. It is widely used as a chemical raw material. It is classified as endocrine disrupting chemicals due to the estrogenic effects. The 4-t-BP degradation rate (R4-t-Bp) is used to indicate the efficiency of the advanced oxidation technologies which are based on Fe(Ⅲ)-EDDS. The main contents and conclusions of this research are shown as follows:In the first part, the character of Fe(Ⅲ)-EDDS and the 4-t-BP degradation efficiency in UV/Fe(Ⅲ)-EDDS system were studied. The results showed that Fe(Ⅲ)-EDDS is a stable complex which was formed by the Fe(III) and EDDS with the molar ratio 1:1. From the photoredox process of Fe(Ⅲ)-EDDS, the formation of hydroxyl radical was confirmed and HO’is the main species responsible for the degradation of 4-t-BP present in aqueous solution. Ferrous ion Fe(Ⅱ) was also formed during the reaction. With the increasing concentration of Fe(Ⅲ)-EDDS,4-t-BP degradation rate increased but inhibited when the Fe(Ⅲ)-EDDS concentration was too high. Indeed, Fe(Ⅲ)-EDDS is the scavenger of HO·. pH value had a significant effect on the degradation efficiency of 4-t-BP and it showed good degradation rate under neutral or alkaline conditions. On the one hand, Fe(Ⅲ)-EDDS presented in the FeL-, Fe(OH)L2-, Fe(OH)2L3-, Fe(OH)4- four different forms under different pH conditions and they had different sensitivity to the UV light; On the other hand, pH value affected the circulation between Fe(Ⅲ) and Fe(Ⅱ). The formation of HO2· and O2·- as a function of pH was also one of the reasons. It was observed that O2 was an important parameter affecting the efficiency of this process mainly due to oxygen is a key factor in the formation of HO·.The second part of the research mainly investigated the 4-t-BP removal efficiency in Fenton-like and photoFenton-like reacton. The results showed that the 4-t-BP removal efficiency in photoFenton-like reaction was much higher than that in Fenton-like reaction. Influence of Fe(Ⅲ)-EDDS concentration and dissolved oxygen concentration on both reactions were the same. With the increasing Fe(Ⅲ)-EDDS concentration, R4-t-BP showed firstly increased and then decreased; The 4-t-BP degradation rate accelerated with the dissolved oxygen concentration increased. However, the effects of H2O2 concentration and pH value on Fenton-like and photoFenton-like reaction were different. With the increasing H2O2 concentration, R4-t-BP increased and then decreased in Fenton-like reaction, whereas R4-t-BP kept increasing in photoFenton-like reaction. When the pH value increased from 2.0 to 9.0, R4-t-Bp showed increasing trend in Fenton-like reaction, while the optimal pH value was 7.5 in photoFenton-like reaction. The target pollutant could be efficiently degraded at neutral pH or even alkaline condition It overcomed significant deficiency of the traditional Fenton reaction. This is the main advantage of this new iron complex.In the third part,4-t-BP was degraded by SO4·- which were produced in UV/Fe(Ⅲ)-EDDS/S2O82- system. The effect of Fe(Ⅲ)-EDDS concentration, S2O82-concentration and pH value on the degradation performance of 4-t-BP was investigated. It was observed that 4-t-BP was degraded efficiently in UV/Fe(Ⅲ)-EDDS/S2O82- system. Accroding to the result of pH effect on both UV/Fe(Ⅲ)-EDDS/S2O82- and UV/Fe (Ⅲ)/S2O82- systems, UV/Fe(Ⅲ)-EDDS/S2O82-system was significantly better than UV/Fe (Ⅲ)/S2O82- system. With the increasing Fe(Ⅲ)-EDDS concentration, R4-t-BP also showed firstly increased and then decreased in UV/Fe(Ⅲ)-EDDS/S2O82- system. When S2O82- concentrations was lower than 1 mM,4-t-BP degradation rate increased with the increasing S2O82- concentration. Steady-state experiments and transient laser flash photolysis experiments were performed to determine the second order reaction rate constant, k4-t-BP, SO4·-,k4-t-BP, HO·, k2-Propanol, SO4·- and kt-BuOH,SO4·were determined as 4.42×109 M-1 s-1,1.61 × 1010 M-1 s-1,6.68 × 107 M-1 s-1 and 7.88 × 105 M-1 s-1, respectively. In the UV/Fe (III)-EDDS/S2O82- system, SO4·- made the major contribution to 4-t-BP degradation, much larger than the contribution of HO·.The fourth part of the research mainly investigated the mechanism of the reactions between4-t-BP and HO’/SO4·-. The reaction pathway was also speculated according to the results of by-products analysis. The results showed that 4-t-BP molecules was degraded through chemistry bond breaking, restructuring, dimerization reaction by the attack from oxidative radicals. Finally,4-t-BP mineralized and converted to CO2 and H2O2. Surprisingly, the 4-t-BP mineralization caused by SO4’" was more efficient than HO·. |
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