Removal Mechanisms And Combined Pollution Effect Of Estrogens In Urban Water Body

With the development of urbanization, more and more pollutants were discharged into urban water system. Although most pollutants could be removed during the process of water self-purification and water treatment, certain micro-pollutants could exist long-term in urban water. Estrogens, as one typical endocrine disrupting compounds, not only have the persistence and refractory characteristics, but also could lead to the endocrine disorders and feminization of animal even at ng/L levels, so it brings about a big threat to the urban water quality assurance and ecological security. Aiming at the typical estrogens in urban water, purpose of this study was to solve the key scientific problems, such as the pollutant status, removal mechanisms and combined pollutant effects existed in urban water system.Solid phase extraction (SPE) followed by GC-MS/Yeast Estrogen Screen (YES) assay were used to determine the pollution status of estrogen in Songhua river water. Total estrogen content in river water was in the range of 6.59-30.97 ng/L, average value was 17.23 ng/L. Natural estrogen estrone (E₁) and 17β-estradiol (E₂), which were mainly from urban sewage, contributed most of all estrogens. Nonylphenol (NP), octylphenol (OP) and bisphenol A (BPA) were detected in all sampling sites, whose contents were in the range of 236.3-1068, 3.1-256 and 13-207 ng/L, and mean values were 512.8, 34.1and 52.8 ng/L, respectively. They were mainly from domestic sewage and industrial wastewater, and the contents were much higher than that of estrogen; Estrogenicity of Songhua river water detected by YES was in the range of 0.50-26.16ng/L, which was in the same pollution level with other river, but it also existed potential problems of ecological security in Songhua River.Removal characteristics of estrogen in wastewater by sewage treatment plant (STP) were also investigated. Average concentrations in influents and effluents ranged from 6.3 (EE₂) to 1725.8 ng/L (NP) and from 2) to 368.5 ng/L (NP), respectively, and mean removal efficiencies were in the range of 16.9 (DES)-94.4% (E₃). 6.4- 46.1% of estrogen was removed during primary treatment, and adsorption on solid particles was assumed as the main removal mechanism. Removal efficiencies of anoxic and aerobic biological treatment units were ranged from -30.2% to 62.2% and from -8.3% to 83%, respectively. EEQ in influents and effluents were in the range of 21.7-54.7 ng/L and 3.5-29.6 ng/L, respectively. The overall EEQ removal efficiencies were in the range of 15.6-92.8%, and biological treatment was crucial to EEQ removal. Total estrogenicity increased after primary treatment due to deconjugating of estrogen compounds by the microbial activity. EEQ of chemical calculation was larger than the results of YES assay, with a ratio value of 3.94±4.00 in all water samples.Removal mechanisms of estrogens in urban water system, including activated sludge adsorption, aerobic and anaerobic biodegradation, was investigated in lab experiments. Adsorption equilibrium of estrogen was achieved in 5.0 h and adsorption process followed the pseudo-second-order model. Thermodynamics analysis revealed that estrogen adsorption onto inactivated sludge was spontaneous, enthalpy-driven, entropy-retarded, and mainly physical adsorption. pH, ionic strength and coexisting organic matters could affect adsorption capacity of estrogen onto sludge, and estrogen equilibrium adsorption amount increased under acidic conditions and low ionic strength, but decreased in presence of coexisting organic matters. Modified Freudlich model could describe adsorption isotherms of estrogen on diferent sludges, and adsorption capacity followed a linear relationship with organic carbon content in sludge. There was almost no hysteresis effect in desorption. Adsorption capacity decreased with increasing of sludge concentration, but removal efficiencies increased; Addition of organic solvent in eluent could improve estrogen desorption efficiency. Aerobic biodegradation of estrogen followed first-order degradation kinetics, and did not depend on the initial estrogen concentration. It was found that E₁ was a main by- product in E₂ degradation. Sludge concentration and temperature could evidently affect E₂ degradation, and temperature coefficient was calculated as 1.05. Kinetic equation of E₁ accumulation in E₂ degradation was also established. Anaerobic degradation process of estrogens included fast and slow degradation stage, which all followed first order degradation kinetics. Degradation rate constant of estrogens decreased linearly with increase of initial estrogen contents, and increased linearly with increase of sludge contents.Compared with AO process, AAO process had advantages in removal of both conventional index and estrogen. The order of estrogen removal was E₂>E₁>EE₂. Decay rate of EEQ in AAO was higher than AO for 22.59%. EEQ calculated from chemical analysis was higher than EEQ determined by YES assay, and the ratio of them was 1.57±0.62. With HRT increasing, estrogen removal rate in AAO increased firstly, but decreased then. SRT also affected estrogen removal evidently, but optimized SRT for removal rate of each estrogen was different. Mass balance indicated that contributions of each removal mechanism on estrogen removal existed great difference for different kinds of estrogen.Estrogen could be removed in certain extent by both UV and UV/H₂O₂, and degradation processes followed pseudo-first order kinetics. Kinetic constants of UV degradation increased from 0.0054 to 0.2753 min^-1 with UV intensity increase. Addition of H₂O₂ could improve estrogen degradation rate. Kinetic constants of UV/H₂O₂ showed positive correlation to UV intensity and H₂O₂ contents, however negative to initial EE₂ contents. A regression model was developed for pseudo-first order rate constant as a function of UV intensity, H₂O₂ contens and initial EE₂ contents. At the initial condition of [EE₂]₀=2.63 mg/L, [H₂O₂]₀ =5 mg/L and I0 =2.669 W/m², more than 95% of estrogenicity was removed after 40 min irradiation and parent compound EE₂ was mainly responsible for observed estrogenicity. Acidic (pH 2-4) and alkaline (pH 10-12) medium benefitted EE₂ photodegradation, but addition of anions inhibitted it, inhibition effect of anions was in the order of HCO₃^->NO₃^->Cl^-. Addition of 5 mg/L methanol and bisphenol A could reduce photodegradation rate constant of EE₂ by 84.31% and 72%, respectively.Combined pollution effect of estrogen was investigated by using the YES assay established in our lab. Estrogenicity of eight estrogen chemicals was in the order of E₂>EE₂>DES >E₁>E₃>OP>NP>BPA; Binary combined effect of estrogen was investigated in the mode of equal molar ratio and equal toxicity. Results indicated that only the combined system of EE₂ and E₁ presented antagonism effect, and the other combined systems all presented synergy effect. In equal-toxicity multiple combined systems, EC₅₀ value of each estrogen in mixture was all smaller than that of each component acting alone, and all presented synergy effect. The types and degrees of combined action effect were related to the kinds and contents of each estrogen component in the mixture.