| Organic pollution, especially organic micropollution, has been nowadays known as a distinct characteristic of water pollution. Chemical treatment of surface water and groundwater polluted by biodegradable and nonbiodegradable organic chemicals can eliminate harmful and toxic compounds from the water and improve water resource quality. Since advanced oxidation processes (AOPs) can mineralize the organic pollutants to CO2, H2O and inorganic ions or convert them to readily biodegradable intermediates and it can be used to nearly all organic compounds, studies during recent years have shown that the methods are very promising in the water treatment and have received increasing attentions.Nitrobenzene and 4-nitrophenol, carcinogenic and mutagenic compounds, are common toxic and bio-refractory compounds in industrial and agriculture wastewaters. Quinoline, a typical one of the polycyclic aromatic nitrogen heterocycles, is thought to be potentially carcinogenic. Quinoline is often found at location associated with oil shale, coal processing and at wood treatment sites due to the discharge of industrial wastewater. Nitrobenzene, 4-nitrophenol, quinoline and reactive brilliant orange K-R were chosen as the model compounds to study the degradation of organic pollutants by homogeneous advanced oxidation process, UV/H2O2, and heterogeneous advanced oxidation process, photoelectrocatalytic oxidation.In the homogeneous advanced oxidation process, this paper is the first one to systematically study the degradation kinetics, influencing factors and degradation mechanisms of nitrobenzene, 4-nitrophenol and quinoline by UV/H2O2. The main conclusions are as follows:(1) It was found that the hydroxyl radical generated by the decomposition of hydrogen peroxide under the UV irradiation was the direct reason that causednitrobenzene, 4-nitrophenol and quinoline to degrade. The degradation of nitrobenzene, 4-nitrophenol and quinoline by UV/H202 process accorded well with the pseudo-first order kinetics.(2) It was found that acidic conditions were more favorable to the degradation of nitrobenzene and 4-nitrophenol while the degradation of quinoline increased with the increase of pH values. With the increase of hydrogen peroxide in a lower concentration range, the degradation of nitrobenzene, 4-nitrophenol and quinoline by UV/H2O2 process will be significantly improved. However, the degradation rate of organic pollutants will be retarded sharply for the increase of hydrogen peroxide to a larger concentration. It was found that anion ions such as HCO3-, NO3- and Cl- in aqueous solution all slowed down the degradation rate of nitrobenzene, 4-nitrophenol and quinoline.(3) The degradation rate of TOC was slower than that of parent compounds, which showed that organic pollutants were not mineralized to CO2 and H2O directly but converted to some intermediates firstly, then complete mineralization was achieved. The variation of pH in the system also indicated the formation of organic acids.(4) Intermediates identified during nitrobenzene degradation are as follows: monohydroxylated compounds, phenol and nitrophenols; multihydroxylated compounds, hydroquinone, dihydroxylated benzene, dihydroxylated nitrobenzene and trihydroxylated benzene; ring-cleavage compounds, ethylmine, 2-butenedioic acid and 2-hydroxy-hexandioic acid; oxidation by-products, 1,3-dinitrobenzene and 4,4'-dinitrobiphenyl. Intermediates identified during 4-nitrophenol degradation are as follows: hydroquinone, dihydroxylated nitrobenzene, trihydroxylated benzene and ring-cleavage compound, 2-butenedioic acid. More than one monohydroxylated quinoline was obtained during the degradation of quinoline by UV/H2O2 process, butAbstract8- and 5-hydroxyquinoline from the attack at the benzene ring by hydroxyl radical are predominant. In addition, several multihydroxylated quinoline, e.g., dihydroxylated quinoline and trihydroxylated quinoline are also detected and the ring-cleavage intermediates of quinoline...
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