Combined Sorption Behaviors Of CTAB And DDT On Marine Sediment

Although environmental pollution caused by single contaminate happened frequently, with the rapid developments of agriculture and industry, a great variety of anthropogenic organic pollutants enter marine environment and constitute combined pollution systems.In these combined systems,there are mutual interactions among each of these pollutants, which may make the behavior of each pollutant different from that of the one existing singly.This combined effect between various pollutants has attracted much attention of environmentalists.Dichloro diphenyl trichloroethane (DDT) is a persistent organochlorine pesticide, which has been extensively used between 1960s and 1980s.Although their usage has been banned or severely restricted for the past decades,DDT and its metabolites can be still detected in water, sediment and animals due to their persistence, bioaccumulation and biomagnifications.Quaternary ammonium compounds (QACs) have a wide range of commercial and consumer uses.Wastewater containing QACs has been finally discharged to coastal waters, besides a great harmness to the ecosystem, these surfactants simultaneously affect the fates of coexist contaminants.Therefore,investigation on the combined sorption behaviors of pollutants on sediments is realistically significant to study their transference deeply.In this thesis, the surface charge properties of sediment, the sorption kinetics and thermodynamics of cetyltrimethylammonium bromide (CTAB)and/or DDT are comprehensively studied in the system of sediment-artificial seawater. Furthermore,the effects of environmental factors such as temperature, salinity and pH are also investigated. The main results are as follows:1)The sediment has a quality of negative permanent charge and their specific surface sites (Ds) in three ionic strengthens(0.001,0.01,0.1 mol·L-1 NaNO3) are between 4.58-5.15 sites·nm-2. 2)The sorption kinetic process of CTAB and/or DDT on the sediments has been proven to follow the pesudo-second-order kinetic rate equation.The sorption rate of CTAB increased with increasing temperature, while first increased and then decreased with increasing initial concentration.The sorption of DDT was accelerated remarkably with the addition of CTAB.3)The sorption isotherms of CTAB or DDT on sediment can be described by the Freundlich isotherm. The results showed that CTAB with the initial concentrations of 5, 20,50 mg·L-1 could remarkably enhance the sorption of DDT (C0:0.057～0.915 mg·L-1) and linearized the isotherms of DDT. However. DDT with the initial concentrations of 0.457 and 0.915 mg·L-1 did not affect the sorption extent of CTAB (C0:10～160 mg·L-1) in the experiment.4)The effects of environmental factors,such as temperature, salinity and pH,on the sorption of CTAB and/or DDT were obvious.The sorption capability was increased under higher salinity and decreased temperature for the sorption of CTAB and/or DDT in both single and combined systems.As for CTAB in the single systems,the sorption capability also increased with increasing pH.5)Estimation of thermodynamic parameters indicated that the sorption behavior of CTAB and DDT was spontaneous (ΔGθ<0) and exothermic (ΔHθ<0) with an increase in the degree of freedom (ΔSθ>0).In the presence of 20 mg·L-1 CTAB,sorption of p,p'-DDT and o,p'-DDT have relatively more negativeΔGθ,ΔHθand less positiveΔSθ.