| Pharmaceuticals and personal care products (PPCPs) have been frequently detected at ng/L-μg/L levels (trace concentration) worldwide in the environment. Due to the large consumption of human and veterinary medicines, these compounds can be persistent in aquatic environment. Numerous researches showed that the long-term exposure to low concentration of pharmaceutical compounds has been regarded as the main reason to the change of genes in aquatic organisms, development of bacterial resistance to antibiotics and formation of endocrine disruption. Because of their incomplete removal in WWTPs, PPCPs can enter the aquatic environment through the discharge or reuse of wastewater treatment plants (WWTP) effluents, therefore, it is necessary to explore some new ways to promote their removal efficiency.Clofibric acid (CA) is a metabolite of several lipid regulators consumed by human beings suffered angiocardiopathy problems and is believed as one of the most persistent pharmaceuticals in the environment. CA removal performances under the same experimental conditions by ultraviolet (UV), vacuum ultraviolet (VUV), UV/H2O2 and VUV/H2O2 processes were compared in this study. The influences of various factors including H2O2 amount, initial CA concentration, initial solution pH, anions (Cl-,SO42-, NO3-, HCO3-) and organic matters (humic acid, HA) on CA degradation were performed. In addition, the effect of temperature on CA removal was specially investigated in UV/H2O2 process. The performance of CA degradation in solar/TiO2 and solar/ZnO processes was studied in summer and winter seasons and the effects of temperature, solar light intensity, NO3- and HCO3-, HA and H2O2 on CA photo-catalysis were evaluated. Finally the intermediates in CA degradation during UV, UV/H2O2, VUV, VUV/H2O2 and solar/TiO2 processes were identified by GC-MS and the toxicity of these by-products also assessed. The key findings were summarized as below.(1) All the experimental data well fitted the pseudo-first-order kinetic model. Direct oxidation was the main process in VUV irradiation despite the slight generation of hydroxyl radicals (·OH). In contrast, indirect oxidation of CA by generated OH was the main CA degradation mechanism in UV/H2O2 and VUV/H2O2. CA photodegradation was negatively influenced in both low and high pH conditions. The addition of 20 mg/L HA could significantly inhibit CA degradation, whereas anions (1.0×10-3 and 0.1 mol L-1) showed inhibitive or insignificant effects on CA degradation in all processes except in UV irradiation where they could increase the apparent reaction rate constants. The effects of Cl- and SO42-were less obvious than NO3- and HCO3- anions.The degradation rate decreased 1.8-4.9 folds when these processes were applied to real WWTP effluent due to the complex constituents. In all of the four, VUV/H2O2 showed the most effective process and the CA removal efficiency reached over 99% after 40 min in contrast to 80min in both UV/H2O2 and VUV processes and 240 min in UV process.(2) Higher temperature (10℃-30℃) would favor CA degradation in UV/H2O2 process. When using a real WWTP effluent spiked with 10 mg/L CA over 99% of CA removal could be achieved under T3 (29.0-30.0℃) within only 15 min compared with 40 and 80 min under T2 (19.0-21.0℃) and T1 (9.0-11.5℃), respectively. HA had negative effect on CA degradation in Milli-Q water and this effect was much more apparent under low temperature condition. In addition, the inhibitive effect on CA degradation at both lower and higher concentrations of bicarbonate was observed, and this inhibitive effect was much more apparent at higher bicarbonate concentration and lower temperature condition. On the other hand, at higher nitrate concentration the inhibitive effect on CA degradation under three temperature ranges was observed, and with the temperature increase this negative effect was apparently weakened. However, at lower nitrate concentration a slightly positive effect on CA degradation was found under T2 and T3 conditions.(3) Significant difference in CA degradation in two seasons was observed both in solar/TiO2 and solar/ZnO processes. The two anions (NO3- and HCO3-) adversely affected CA degradation, particularly at high HCO3- concentration. CA degradation slightly increased with 0.5 mg L-1 HA in solar/TiO2 in summer, but significantly inhibited in winter at 20 mg L-1 HA. However, the inhibitive effect of 20 mg L-1 HA on CA removal in solar/ZnO had no remarkable difference in two seasons. The degradation in solar/TiO2/H2O2 was similar to that in solar/TiO2, but inhibited obviously in solar/ZnO/H2O2. When applying photo-catalytic process into WWTP effluent degradation rates were apparently lower comparing to Milli-Q water.(4) Eleven intermediates were detected by GC/MS, of which only three compounds have been reported before by other researchers. Combining with the evolution of the dissolved organic carbon (DOC), Cl- and specific ultraviolet absorption at 254 nm (SUVA254), it could be proposed that cleavage of aromatic ring followed by dechlorination was the mechanism in solar/TiO2 process, while dechlorination happening first and aromatic intermediates accumulated in other processes. The acute toxicity was evaluated by means of P. phosphoreum (T3, spp.) bioassay. It was believed that aromatic intermediates enhanced the solution toxicity and the ring-opening pathway in solar/TiO2 process could reduce the acute toxicity.
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