黄河水体颗粒物对3种多环芳烃光化学降解的影响

研究了、苯并(a)芘、苯并(ghi)3种多环芳烃在黄河水体中的光化学降解规律,探讨了黄河泥沙和黄土2种颗粒物对多环芳烃光化学降解的影响.结果表明:①当水体不含任何颗粒物时,多环芳烃的光降解符合一级反应动力学规律,且反应动力学常数随污染物初始浓度的降低而增加;3种多环芳烃的光降解速率与分子的吸收光谱相关.②黄土通过对光强的阻碍作用和其中所含腐殖质的光敏化作用影响多环芳烃的光化学降解,这2方面的共同作用导致不同浓度黄土所产生的影响不同.黄土浓度为0.1g/L或5g/L时促进了和苯并(a)芘的光降解;黄土浓度为5g/L时促进了苯并(ghi)的降解.当水体含有黄土时,多环芳烃的光降解符合二级动力学规律.③对多环芳烃光化学降解起主要作用的是黄土中存在的溶解性腐殖质,非溶解性腐殖质的作用不大.④由于黄河泥沙在河水中长期存在,泥沙中的溶解性腐殖质都已溶于水中,泥沙主要通过对光强的阻碍作用影响水体中多环芳烃的光降解,使光降解速率随泥沙浓度的增加呈幂指数降低.

Effect of Particles on the Photodegradation of PAHs in Natural Waters of the Yellow River

Photodegradation of chrysene, benzo(a)pyrene and benzo(ghi)perylene in natural water of the Yellow River was studied using simulation sunlight. The effects of particulates on the photodegradation were explored. Several results arose from this study: (1) The photodegradation of PAHs can be fitted with first-order kinetics when no particulates exist in water system, and the first-order constant increase with the decrease of initial concentration of PAHs. The photodegradation rates of the three PAHs are related to their molecule absorption spectrum. (2) The presence of loess exerts two kinds of effects on the photodegradation of PAHs, which include the inner filter effects and the photosensitizing effects of humic substance in Loess. These two opposite effects lead to the difference of net effects among different contents of loess. When the loess contents are 0.1 g/L and 5.0 g/L, the presence of loess stimulates the photodegradation of chrysene, benzo(a)pyrene. When the loess content is 5.0 g/L, the presence of loess stimulates the photodegradation of benzo(ghi)perylene. In addition, the photodegradation of PAHs can be fitted with the second-order kinetics when there is loess in the water system. (3) The dissolvable humic substances in loess can accelerate the photodegradation of PAHs while the indissoluble part cannot. (4) Since the dissolvable humic substances in the suspended solids of the river have been dissolved in water, the addition of suspended solids to the water system can only cause the decrease of photodegradation rate of PAHs due to its inner filter effects, and the photodegradation rate decreases with the suspended solid content as a power exponent function.