Study On The Photodegradation Of Dissolved Organic Matter At Low Temperature

In this study,dissolved organic matter(DOM) in the Xihe River in Shenyang was fractionated using XAD resins into 5 fractions: hydrophobic acid(HPO-A), hydrophobic neutral(HPO-N), transphilic acid(TPI-A), transphilic neutral(TPI-N) and hydrophilic fraction(HPI). The photodegradation of DOM fractions in ice under natural solar radiation was investigated. The results showed that the photodegradation of five DOM fractions in ice occurred under solar radiation, and the photodegradation degree of HPO-A was the highest. The UV-254 removal rates of HPO-A, HPO-N, TPI-A, TPI-N and HPI in ice were 43.4%, 44.15%, 45.9%, 55.0% and 58.8%, respectively. after 80 h solar radiation. The reductions of fluorescent materials in ice which resulted from photodegradation were significant. Except for aromatic protein-like fluorescent materials(Ⅰ) in HPO-A, the photodegradation degrees of all types of fluorescent materials in DOM fractions were higher than those of the bulk organics represented by dissolved organic carbon(DOC). The removal rates of fulvic acid-like and humic acid-like fluorescent materials in DOM fractions which resulted from photodegradation were higher than those of soluble microbial byproduct-like and aromatic protein-like fluorescent materials. The reductions of as well as the productions of trihalomethanes(THMs) precursors occurred in the photodegradation of DOM fractions in ice. The photodegradation resulted in the decreased content of THMs precursors in HPO-A, as well as the increased content of THMs precursors in TPI-N. On the other hand, the changes in the content of THMs precursors in the other three fractions were related to solar irradiation time.In addition, this study done a specially research on the regular of the photodegradation of transphilic acid(TPI-A), which is one of the components of dissolved organic matter, under natural solar radiation. The Influencing factors containing p H, concentration of Fe Cl3, concentration of KNO3, initial DOC and concentration of KCl with various levels, which made a difference on photodegradation of TPI-A in ice under natural solar radiation was investigated. The results showed that, compared with the neutral,acid/alkalinity circumstances promoted the he remove of DOC, UV-254 and SUVA of TPI-A in ice occurred under solar radiation. Further more, the function of alkalinity circumstances was much than acid circumstances in removing of DOC or UV-254. Increase of p H in alkalinity circumstance or decrease of p H in acid circumstance promoted the he remove ofSUVA. alkalinity circumstance availed the remove of fluorescent substances of TPI-A much than acid circumstance.Ultra alkalinity circumstance(p H=11.0) reduced the formation of trihalomethane. Fe Cl3 increased the amount of fluorescent substances little. But the incremental quantity caused by Fe Cl3 with different concentration was not obviously. KNO3 affected odd DOC obviously. The bigger the Concentration of KNO3 was, the more DOC was removed.The higher rate of remove of DOC reached 87.5%. KNO3 with too higher concentration was not benefit for the remove of fluorescent substance. The optimum concentration of KNO3 promoting the remove of fluorescent substance was 0.1μg/L. The effect which original made on odd DOC was most obviously. The lower the original concentration of DOC was, the lower the odd concentration of DOC was, the higher the rate of the remove of DOC was, the lower the rate of the remove of fluorescent substance was, and the higher the Specific Trihalomethane Formation Potential was. The DOC with low original concentration availed the remove of SUVA. The optimum concentration of Fe Cl3, KCl promoting the remove of DOC was 8.0mg/L, 5.0g/L, and the corresponding removing rate reached82.8% and 86.8% respectively. The optimum concentration of Fe Cl3, KNO3 promoting the remove of UV-254 was 1.6mg/L and 0.1μg/L respectively, and SUVA was too. The optimum concentration of Fe Cl3, KNO3 and KCl promoting the remove of Trihalomethane Formation Potential was 16.0mg/L, 0μg/Land 0g/L respectively. The optimum concentration of Fe Cl3, KNO3 and KCl was 16.0mg/L, 0μg/L and 0g/L respectively.