| Haloacetic acids (HAAs) are common organic pollutants in drinking water or other aqueous systems. HAAs are disinfection byproducts (DBPs) produced in sterilization or bactericidal process such as chlorination. Typical HAAs are monochloroacetic acid (MCAA), dichloroacetic acid (DCAA),trichloroacetic acid (TCAA), monobromoacetic acid (MBAA), dibromoacetic acid (DBAA), tribromoacetic acid (TBAA), bromodichloroacetic acid (BDCAA), chlorodibromoacetic acid (CDBAA) and bromochloroacetic acid (BCAA), among which DCAA and TCAA account for the biggest proportion in chlorination process. Due to their high carcinogenic, teratogenic and mutagenic properties, HAAs present great threats to hunman health and environmental quality. It is therefore of great significance to study the formation characteristics and the effective methods for elimination of HAAs.In this thesis, we selected DCAA and TCAA as the target pollutants, and discussed the formation and degradation of HAAs. Major results and conclusions are as follows:(1) Methods based on gas chromatography or ion chromatography for the determination of HAAs have been established. Under the optimized conditions, the detection limits and recoveries for gas chromatography were 0.48～0.621μg/L and 86.92%～108.0%,;and those for ion chromatography were 12.58～14.16μg/L and 71.7%～100.19%,respectively. Both of the two methods are satisfactory for determination of HAAs in dringking water.(2) The formation of HAAs in aqueous system was simulated by adding humic acid as the model organic precursor with sodium hypochlorite as the disinfectant.The experimental results indicated that the yield of HAAs was directly proportional to the concentration of humic acid and the available chlorine.In addition, the yield of HAAs enhanced with increasing reaction time and tempreture in a certain range, and it declined with decreasing pH value.(3) HAAs in aqueous solution were degraded by photo-Fenton oxidation. Effects of reaction time, Fenton reagent dosage, initial pH and light intensity on removal efficiencies of HAAs were investigated. A preliminary study on degradation kinetics of HAAs was also conducted. The best conditions were confirmed as following:light intensity of 500W/m, Fe2+ concentration of 1.0 mmol/L, H2O2 concentration of 5.0 mmol/L, reaction time of 60 min and initial pH of 4.0. Under these conditions, the degradation efficiencies of DCAA and TCAA with an initial concentration of 100μg/L were 90.32% and 87.77%,while they were 75.34% and 68.80%, respectively, when the initial pH was 7.0.A significant synergistic effect of light intensity and Fenton reagent was observed. It was ascertained that degradation of HAAs obeyed a pseudo first-order kinetics with apparent activation energies of 52.42 kJ·mol-1 and 56.46 kJ·mol-1 for degradation of DCAA and TCAA,respectively.(4)Ultrasonically assisted reductive degradation of HAAs with zero-valent iron (Fe0) was reported in this work. The influences of solution pH, dosage of iron, reaction temperature and time, and the initial concentration of DCAA (or TCAA) on the degradation were studied. It was determined that the best conditions were:Fe dosage of 4.0g/L, initial pH of 4.0, and reaction temperature and time of 25℃and 4h, respectively. Under these conditions, the degradation efficiencies of DCAA and TCAA with an initial concentration of 50μg/L were 82.01% and 87.33%,respectively. When the initial pH was 7.0, the degradation efficiencies of DCAA and TCAA with the same initial concentration of HAAs were 82.01% and 87.33%,respectively. It was confirmed that ultrasonically assisted reductive degradation of HAAs with Fe0 also obeyed a pseudo first-order kinetics with rate constants of 0.1550min-1 and 0.3418min-1 for degradation of DCAA and TCAA,respectively.
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