Removal Of Endocrine-disrupting Compounds (EDCs) In Domestic Wastewater

Endocrine-disrupting compounds (EDCs) constitute a class of persistent organic pollutants with high toxicity, bioaccumulative property and significant negative impacts on human health and the environment. The detection rate of EDCs in the environment increased significantly because of the development of modern industry. Domestic wastewater reused as main supplement water has become an inevitable trend to relieve water shortage. However, it is necessary to pay more attention on the ecological risk of reuse water owing to EDCs remained in domestic wastewater. Therefore, it not only has important theoretical guiding significance, but also has important practical value to study on removal of endocrine-disrupting compounds (EDCs) in domestic wastewater.This study is the main research content of Science and Technology Project in Colleges and Universities of Shandong Province (Grant No. J11LB18). Three typical classes of EDCs named polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalic acid esters (PAEs) were chose as the studied objects. The distribution and removal laws of typical EDCs in each unit of the sewage treatment plant were analysed. α-Fe2O3 nanocatalysts dedicated to photo-Fenton processes have been prepared by a hydrothermal method. The nanostructure and morphology of the catalysts were characterised by XRD (X-ray diffraction), TEM (transmission electron microscopy) and SEM (field-emission scanning electron microscopy). In addition, fixed bed reactor applied activated carbon loaded with α-Fe2O3 nanocatalysts for photo-Fenton catalytic oxidation was designed and developed. The operating parameters of the fixed bed reactor for photo-Fenton process were optimized. Furthermore, the removal efficiency of the three classes of EDCs in clarifier effluent treated by the prepared reactor was determined. And the reaction mechanism of photocatalytic degradation of EDCs pollutants was discussed. The main research works and results included:(1) The detection analysis methods of the PAHs, PCBs and PAEs in environmental samples using GC-MS-MS were established. The solid phase extraction methods, GC separation conditions and MS conditions of the three classes of EDCs were determined respectively. The distribution and removal laws of typical EDCs in each unit of Guangda Water (Jinan) Co., Ltd. sewage treatment plant were analysed. Six kinds of PCBs, four kinds of PAHs and six kinds of PAEs were discovered in each water treatment stage. Furthermore, the concentrations of dichlorobiphenyl, trichlorodiphenyl and tetrachlorobiphenyl were higher, and the concentrations of four kinds of PAHs had no distinction, but the concentration of DEHP was the highest of 6 kinds of PAEs. The EDCs content in water samples in summer was higher than that in winter, but sludge samples were opposite. Both the concentration of EPCBs and benzo(a)pyrene in plant effluent were higher than surface water environmental quality standards limits, and the benzo(a)pyrene content exceeded one order of magnitude. The concentration of DEHP in plant effluent was the highest of 6 kinds of PAEs, but it not exceeded surface water environmental quality standards limits. The EDCs content in sludge samples was much higher than that in water samples, but it was lower than the agricultural standards limits. The removal efficiency of EDCs treated by traditional sewage treatment process was low, and parts of EDCs just transferred from water to sludge by adsorption.(2) Based on our previous studies, new-type α-Fe2O3 nanocatalysts dedicated to photo-Fenton oxidation have been successfully synthesized by a hydrothermal method without any additional organic reagents or templates. The prepared α-Fe2O3 nanoparticles with a mean size of 70 nm possess a typical cubic morphology, and the size distribution of these nanocubes is narrow, and the dispersibility is also good. Both effect of reaction temperature on the morphology of nanocrystals (from irregular to cubic nanoparticles) and effect of reaction time on the phase of the products (products containing α-FeOOH phase for lack of reaction time) were also studied. The optimum reaction temperature and time of this hydrothermal route were 180℃ and 6 h, respectively. The efficiency and rate of photo-Fenton oxidation by using synthesized α-Fe2O3 nanocatalysts got significantly improved comparing to the traditional photo-Fenton oxidation, and it reduced 40% of the dosage of FeSO4-Fe at the same time. Compared to commercially available Fe2O3 particles, the catalytic activity of the prepared α-Fe2O3 nanocatalysts was greater, and the UV-utilize rate of the reaction system achieved higher, and the efficiency and rate of organic pollutants degradation got also significantly improved.(3) A fixed bed reactor for photocatalytic oxidation process adopted baffles and corridors has been developed for this study. The water flow in the reactor adopts gravity-flow style and no circulating. The light source is UV, and the carriers of α-Fe2O3 nanocatalysts are coconut shell activated carbons. The modification method of activated carbons is HNO3 oxidizing treatment combined with N2 reducing treatment, and nanocatalysts are loaded on activated carbons by high-temperature adsorption. The reactor body has a length of 107cm, a width of 45cm, a height of 38cm, an actual depth of 25cm, a single-corridor width of 15cm, and a reaction volume of about 120L. The optimum operating conditions of this reactor were pH of 3.0, H2O2 dosage of 40.0mmol/L, CAC dosage of 800g, FeSO4 dosage of 1.8mmol/L and hydraulic retention time of 150min, respectively. Furthermore, the removal efficiency of phenol in simulated wastewater treated by the photocatalytic reactor got higher than 90% under the optimum operating conditions, and the operational stability and reliability of the reactor were great.(4) The removal efficiency of three classes of EDCs treated by the prepared reactor was significant, and all of the concentrations of benzo(a)pyrene, ΣPCBs and EPAEs in reactor effluent were lower than surface water environmental quality standards limits. According to the experimental results, we concluded that the removal efficiency of naphthalene was the highest, followed by fluoranthene, anthracene and benzo(a)pyrene lower. The removal rate of PCBs decreased by the number of substituted biphenyl chlorine atoms increasing, and considering chlorine atom substituted 1 or 1’ as a reference position, PCBs containing symmetrical chlorine atoms in relative positions were more refractory to be degraded, and conversely, PCBs containing ortho or meta-substituted chlorine atoms were more degradable. The PAEs contained simpler side chains were easier to be oxidized than the ones contained complex side chains. The removal rate of PAHs, PCBs and PAEs treated by the reactor were 87.20%,82.52% and 86.60%, respectively.(5) In the a-Fe2O3 nano-photocatalytic Fenton oxidation system, many electron-hole pairs were generated in α-Fe2O3 nanocatalysts excited by light. The EDCs were oxidized to various organic radicals directly by photogenerated holes, and the radicals were then converted to small molecules or CO2 and H2O. At the same time, the EDCs were also attacked by hydroxyl radicals generated via reactions of photogenerated electrons and various substances in the solution. Besides, the Fenton reactions mainly occurred in flowing water to enhance the system’s oxidation capacity. Furthermore, the concentration of pollutants was concentrated by adsorption of the modified activated carbons to obtain enrichment on the carbon surface area. A cyclic process of nanocatalysts loaded activated carbon adsorption, surface diffusion, photocatalytic degradation, situ regeneration, and readsorption was formed in order to create the collaborative effect of adsorption and photocatalytic oxidation. The degradation mechanism of coupling nano-α-Fe2O3 photocatalytic Fenton oxidation and adsorption was established for deep purification of water.