Experiment Study On Photo-degradation Of Bisphenol A Enhanced By Algae In Water Source

As lots of endocrine disrupting chemicals (EDCs) being used in the world,water pollution caused by EDCs is becoming much worse. As one kind of EDCs,bisphenol A (BPA) exists widely in water body, which constitutes potential threaton human health and security of ecological system. The transport and transform ofBPA in the environment have caught much more attentions. In natural water body,photo-degradation is one of the most important ways for transformation of organicpollutants. Based on the laboratory conditions and by using a40W ultraviolet (UV)lamp as the light source, this research studied the photo-degradation efficiency anddegradation kinetics of BPA enhanced by four species of algae, i.e., Microcystisaeruginosa, Chlorella vulgaris, Scenedesmus dimorphus and Spirulina sp. as wellas the mixtures of the above mentioned algae species. The effects of pH, lightsource, background constituents and other factor, on the photo-degradation of BPAwere also studied in detail.Exposed to40W UV lamp, photo-degradation of BPA could be enhanced byone single species of algae or the mixtures of algae. When some amounts of onesingle algae species or mixtures were dosed to the reaction liquid, the photo-degradation rates of BPA reduced with the increasing of initial concentration about0.5-2.0mg/L. With BPA initial concentration of1.0mg/L and single species of algaeor the mixtures of algae concentrations of20.40μg/L, as well as reaction time of80min, photo-degradation rates of BPA were90.6%,77.6%,87.1%,85.3%, forMicrocystis aeruginosa, Chlorella vulgaris, Scenedesmus dimorphus, Spirulinasp.,respectively. BPA in the tests with the six ways of mixed algae solution almostcannot be detected.Algae concentration was the important factor which affected the photo-degradation. With the increasing of algae concentration, the photo-degradation rateof BPA was also increased. According to the kinetics analys is, the photo-degradation of BPA in algae solution follows the law of pseudo-first order reactionkinetics. Meanwhile, by studying the effect of pH on photo-degradation of BPA,one can find that the degradation in partial acid and neutral condition was betterthan that of the base condition, which means the photo-degradation efficiency of BPA would be reduced when pH value was more than7. By comparing the photo-degradation effic iency of BPA under40W UV lamp and250W high-pressuremercury lamp, one can also conclude that the photo-degradation efficiency wasbetter under the irradiation of a UV lamp.Fe(OH)3particles in culture medium might be adsorbed to the algae cellsfurther affect the photo-degradation. By washing the algae cells with ascorbic acid,Fe(OH)3particle adsorbed on the cell might be reduced and further thephotosensitization could be also reduced. However, by washing the algae cells withde-ionized water, Fe(OH)3particle might stay in the system and further promote theproduction of hydroxyl radicals by photosensitization, therefore photo-degradationof BPA can be enhanced.By using benzene as the capture agent of hydroxyl radicals, the photo-production of hydroxyl radicals in algae solution was determined by HPLC. Theresults showed that hydroxyl radicals production increased with the increasing ofalgae concentration. With Microcystis aeruginosa concentration of5.29×109cell/Land the reaction time of120min, the production of hydroxyl radicals could bereached0.84mg/L. Under partial acid condition, more hydroxyl radicals could beproduced.The results also showed that the photo-degradation efficiency of BPA in tapwater, distilled water and de-ionized water was different, implying the promotionby the background constituents in tap water. Meanwhile, the effects of humic acid,Cl-, HCO3-on the photo-degradation of BPA in algae solution were also studied.The result showed that certain concentration of humic acid, Cl-, HCO3-can promotethe photo-degradation of BPA, however, higher or lower concentration of thebackground constituents would inhibit the photo-degradation. Under40W UV lamp,the removal efficiency of BPA in the mixtures consisted of algae and Fe3+wasbetter than that in the algae only system. With Fe3+concentration in algae solutionof10μg/L and the reaction time of60min, BPA degradation rate could be reached81.6%, but in the algae only system, BPA degradation rate was only59.6%.