Research On Trace Organic Pollutants Removal From Tai Lake Basin By Advanced Oxidation Processes

Emerging contaminants have posed a major threat to drinking water safety. A variety of Pharmaceutical and Personal Care Products (PPCPs) and Endocrine Disrupting Chemicals (EDCs) have been detected at a range of concentrations through water bodies in China. It was known that many of these compounds are recognized as carcinogenicity, teratogenicity, and mutagenicity contaminants, which have been accumulating and enriching in natural environment, imposing negative even harmful impact on health of human as well as other species. What make it worse is that these organic matters can hardly degraded by conventional treatment technologies. Among these technologies, the advanced oxidation process has been wildly researched and applied because this technology has fast reaction rate, mild reaction condition and high mineralization ability. A research on degradation characteristics of coexistence system of steroid estrogen and sulfa antibiotics by the ozone-based and ultraviolet-based advanced oxidation processes was carried out, besides the degradation mechanism, influence factors, degradation pathways and biological toxicity.Steroid estrogen and sulfa antibiotics can be removed effectively in ozone and ultraviolet system. The degradation of sulfa substance by ozone rely mainly on direct oxidation of O3 molecules, while the degradation of steroid estrogen, indirect oxidation of hydroxyl radicals (·OH) can not be ignored. Three sulfa antibiotics have good light degradation activity, and can be degraded by ultraviolet alone. The light degradation activity of steroid estrogens is poor, except estrone. Compared to UV and O3 alone, the target pollutants can be mineralized completely in the UV/H2O2 system. The degradation of each contaminant in coexistence system fitted first-order kinetic model.The influences of operational parameters and water qualities on each reaction processes were studied. Increasing the ozone or UV dose can improve the degradation of organic pollutants, while increase in the initial concentration of target compounds would worsen the degradation efficiency. Essentially, the ratio of ozone (UV) dose to concentration of target compounds determined the degradation efficiency. For O3 process, the solution pH exerted effect on the degradation from two aspects. First, the solution pH can change the proportion of direct ozonation and indirect ozonation involved in the degradation process. Second, the solution pH can influence the dissociation state of target compounds which show different reactivity towards ozone. For UV/H2O2 process, the solution pH can influence the dissociation state of target compounds which have different photolysis activity mainly. Common ions in water impose complex influence on advanced oxidation process, via accelerating or inhibiting OH reaction. Humic acid imposes negative influence on each reaction system.According to the results obtained by GC-MS analysis, OH could attack hydrogen atom in benzene ring or in the cyclic hydrocarbon firstly when steroid estrogen was degraded by each advanced oxidation process, generating hydroxyl followed by carbonyl and carboxyl, which were further mineralized completely. Based on the results of intermidiates analysis by LC/MS/MS method, it can be concluded that a large amount of intermidiates were formed during the O3 and UV processes. Unforunately, these intermidiates kept partial or intact functional groups contined in the parent moleceulars. Degradation intermidiates by O3 mainly include hydroxylation products, oxidation of amino, amino replaced by hydroxyl, sulfur nitrogen bond rupture, and methyl oxidized to carboxylic acid. Degradation products of sulfa antibiotics by UV and UV/H2O2 are similar, they include hydroxylation products, amino oxidation for nitro, sulfonyl product removing sulfur, nitrogen bond rupture, carbon carbon double bond adduct and heterocyclic ring opening.The change of estrogenic activity of estrogens during each oxidation processes was investigated with yeast estrogen screen. The result shows that each oxidation process can effectively reduce the estrogenic activity. However, the intermediate products of estrogens presented estrogenic activity, and hence the removal of estrogenic activity was shown to be lagging behind of the removal of estrogens. The biotoxicity evolution of sulfa antibiotics during each oxidation processes was investigated with chlorella toxicity test. The result shows that the intermediate products of sulfa antibiotics have stronger biological toxicity than its body. The ozone degradation products own antioxidant properties and can not be further degradation by ozone. Although its toxicity enhanced in the process of degradation by UV/H2O2, however, biological toxicity can be removed eventually along with the mineralization of background material.