| In recent years, because of the industrial, agricultural and urban pollution, the quality of drinking water sources becoming worse and worse. Various organic matters exist in the original water, including natural organic matter and synthetic organic compounds. And the humic acid, which accounts more than50%for the total organics in the natural water, can produce disinfection byproducts as precursor in chlorinated water, which are harmful to people. So it is important to move HA from the source water. UV/H2O2has grown to be a widely-used water treatment technology in the past20years. It has a good effect in handling of organic pollutant because of its strong oxidizing ability. On this basis, this paper studied the degradation of HA by UV/H2O2and the whole study can be divided into the parts as follows: the effect factors on the degradation and mineralization of HA, the oxidation characteristics of the degradation process, as well as the mechanism analysis. Comparing with other AOPs such as single ozonation and having further optimal design with orthogonal experimental.The factors effect was studied by analyzing the UV strength, the dosage of H2O2, the initial concentration of HA, the pH of solution and the UV irradiation intensity in the water, etc. on the effect of degradation. The result shows that: the removal efficiency was gradually increasing to some extent with the increase of H2O2dosage within a certain range, but there exist an optimum dosage of H2O2; the increase of UV strength can enhance the degradation of humic acid; the lower of the initial concentration of HA, the faster of the degradation; the degradation can be effective in a wide pH range and neutral or weakly acidic conditions is more conducive to HA degradation; as to the dosing way of H2O2, multiple steps addition of H2O2is superior to one-time dosing. All the reaction kinetics fitted the Langmuir and Freundich equation first-order well.The experiments show that the UV/H2O2system can be effective in decomposing HA with55.3%and77.9%removal rate at reaction time of60min/120min. The degradation process has an overall removal of UV254and chroma but not obvious of the TOC and CODMn, which means that the process is not a complete oxidation of mineralization, just from the big humic acid molecules into small molecule. The removal of disinfection byproduct precursors is more than80%and no bromate is produced in the reaction, which can effectively solve the problem of disinfection byproducts in drinking water.The fluorescence analysis was adopted to explain the mechanism of the· OH oxidation. The tert-butanol and HCO3-have an inhibition in the reaction of HA degradation, the more of the free radical scavenger, the stronger of the inhibition. All this shows the oxidating reaction follows the free hydroxyl radical pathway.The comparing experiment with other AOPs showed that:in the initial period of the reaction, the removal efficiency of single ozonation increased more quickly than UV/H2O2, but the continued removal efficiency is becoming flat, even less than that of the UV/H2O2system. Both of UV/H2O2, O3, O3/H2O2, UV/H2O2/O3have an effective removal of humic acid, changing the structure and character, which is reflected in higher removal rate of chroma and UV254. The removal of TOC and CODMn is not obvious. And the combined AOPs display better than UV/H2O2or O3.Finally, analyzed by the orthogonal experimental design, the most important factor is reaction time, and the follows:the reaction time, the initial concentration of HA, the dosage of H2O2, and finally the UV light intensity. |
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