Effect Of Nonionic Surfactant On The Sorption Behavior Of DDT Onto Jiaozhou Bay Sediment

Surfactants and other organic pollutants are transported into water system through the release of industrial and domestic wastewater, which results in an combined pollution. DDT is a kind of typical persistent organic pollutant. Although its use in agriculture has been banned in China in 1983, unfortunately, it,s still widely distributed in environment because of its persistence, chemical stability and bioaccumulation. Nonionic surfactants are used wildly in industries of food, chemical, and washing due to the characteristics of dispersion, emulsification and wetting effects. The existing of non-ionic surfactants in the ocean can change the physicochemical propertis of sediment/water interface, thus it has an effect upon the migration of organic pollutants.In this thesis, the sorption kinetics and thermodynamics of Tween20 and/or DDT were studied in the system of sediment-artificial seawater. Furthermore, the effects of temperature, salinity and the properties of sediment were also investigated. The main results are as follows:(1) The sorption kinetic process of Tween20 and/or DDT on the sediments was proven to follow the pesudo-second-order kinetic rate equation. The sorption rates were favorably influenced by the decreasing initial Tween20 concentration and increasing temperature. The sorption activation energy of Tween20 was 17.75 kJ·mol^-1, which indicated that the sorption process was mainly a physics one. Tween20 could accelerate the sorption rate of DDT onto sediment in the experimental concentrations.(2) The sorption isotherms of DDT on sediment could be described by the Freundlich isotherm. The results showed that Tween20 with the initial concentrations of 5, 10, 30 and 80mg·L^-1 could enhance the sorption capacity of DDT (C0: 0.1411 mg·L^-1～1.129 mg·L^-1) and linearized the isotherms of DDT onto sediment. When the initial concentration of Tween20 was 160 mg·L^-1, the formation of micelles of Tween20 enhanced the aqueous-phase concentration of the DDT thereby decreasing its sorption on sediment compared to the single system.(3) Studies on impact factors of the sorption indicated that sediment enhanced its capacity to absorb DDT with decreasing temperature, increasing salinity and decreasing sediment particle sizes in both single and combined systems. For DDT sorption on the sediments with different treatments, KF(HCl treatment)> KF(H2O treatment) > KF(H2O2 treatment). In the presence of 30 mg·L-1 Tween20, the sorption capacity of DDT onto HCl treatment sediment was lower than that in the single system. While for the H2O2 treatment sediment, the sorption capacity of DDT was higher than that in the single system.(4) Estimation of thermodynamic parameters indicated that the sorption behavior of DDT was a spontaneous, exothermic and entropy-increasing physical one. The existence of Tween20 caused the∣ΔG(?)∣and∣ΔH(?)∣values higher andΔS(?) value smaller during the DDT sorption process.(5) The sediment and DDT-sediment complexes were characterized by FTIR spectra. It was confirmed that the sorption was resulted form hydrogen bonds formation between DDT molecules and the C=O, phenolic and alcoholic O–H groups of sediment.