Effects Of Photochemical Pretreatment On Humic Acid And Its Coagulation In Drinking Water Treatment

Humic acid is one of the main components of organic matter in natural water.High concentrations of humic acid will bring lots of problems, such as smell and microbial growth, inceased cost of mixed coagulation reagent consumption and to the formation of disinfection by-products（chloroform, haloacetic acids, chlorinated hydrocarbons）, which increase the risks of carcinogenic and mutagenic in drinking water. So how to effectively remove humic acid has been concerned by more and more researchers. On the basis of previous studies, this paper investigated the effects of photochemical pretreatment on humic acid and its coagulation. The main results are as follows:（1） The effect of UV radiation on the removal of humic acid was significant. When the illumination time was 600 min, the TOC and UV254 removal rates were 64.51% and 93.10%. The analysis shows that the humic acid is oxidized to a small molecule organic matter after UV radiation, such as carboxylic acid, alcohol, fat and so on. Under different pH conditions, the removal rate of TOC of humic acid solution was also different under UV irradiation. The results showed that the effect of UV radiation on the removal of humic acid was better under acidic conditions. And the neutral condition is more conducive to coagulation. By comparing the changes of Zeta potential of the humic acid solution after coagulation with different light time, it showed that the longer the Zeta potential of the humic acid solution, which more close to the isoelectric point and easier to agglomerate.（2） Photocatalytic experiments were carried out using TiO₂ fixed load. Compared with the humic acid solution, the removal rate increased when the illumination time was 180 min, the TOC removal rate increased by 6.32%, and the UV254 removal rate increased by 13.8%. The results showed that the photocatalytic pretreatment technology of TiO₂ fixed carrier not only showed a better removal efficiency in the photocatalytic oxidation stage, but also showed a stable high removal rate in the coagulation stage. Compared to the TiO₂ powder, the TiO₂ fixed carrier has a wider application range and the removal efficiency is more stable.（3） The efficiency of iron photocatalytic technology can improve the photocatalytic efficiency.Without iron, the removal rate of TOC is 18.72% when the illumination time is 120 min, at the same time, the removal rate of UV254 was 21.89%,While adding iron, humic acid removal rate of TOC is 21.5% when the illumination time is 120 min, at the same time, the removal rate of UV254 was 29.7%.This is because in the light of the effect of radiation, part of iron oxidation. Iron ions produced·OH by oxidation reduction. It promoted the decomposition of humic acid in water samples, and improved treatment efficiency.The EPR technique was carried out to detect the humic acid water samples, which indicated that the three kinds of pretreatment technology can produce strong oxidizing·OH. And by FT-IR detected in the light after 60 min of illumination, 1274cm-1, alcohol C-O stretching vibration enhancement, suggesting that light to make the structure of humic acids made changes, humic acid occurred in the decarboxylation reaction to produce the alkanes, alkenes, alcohols and a cyclic anhydride and other small molecule organic matter. Technology of humic acid mixed coagulation effect analysis showed that different pre treatment, humic acid solution in the pre processing process is oxidation of small organic molecules, including the ability to mix coagulation removal of small molecule acid, so in the pre processing stage oxidation ability is stronger, it is possible for coagulation.