Water Quality Status And Typical Organic Pollutant Adsorption Behavior On Sediment In Mekong River In Laos PDR

The Laos section of the Mekong River has played an important role as a source of irrigation and production and living for local residents and agriculture.The soil in the Mekong River provides protection for crop growth,and its sediment provides habitat and nutrients for the growth of aquatic animals and plants.Organic pollutant pesticides have the effect of preventing pests and promoting agricultural development,so the demand in agriculture is huge.The irrational use of pesticides has led to the entry of a large number of pesticides into the water environment.Soils and sediments eventually become a gathering place for pesticides,which ultimately poses a serious threat to human health through bio-enrichment.Therefore,research on the behavior of typical organic pollutants in the environment has attracted wide attention.In this study,nitrobenzene and diuron were used as representative organic pollutants.The adsorption of nitrobenzene and diuron in the sediments of the Mekong(Luang Prabang,Kerman,and Vientiane)in Laos was studied by batch experiment.Kinetics and adsorption thermodynamics and initial concentration,particle size and pH factors,and through the fitting of adsorption kinetics and thermodynamic parameters,reveal the adsorption mechanism,aiming to understand the sediments in the Mekong River in Laos,p-nitrobenzene and diquat The adsorption situation of Long has provided basic data for the prevention and control of organic pollutants on the sediments of the Mekong River in Laos,and laid the foundation for scientific prevention and control.The adsorption kinetics and adsorption thermodynamics of nitrobenzene on the Mekong River sediments,as well as the initial concentration,particle size and pH,the specific conclusions are as follows:(1)Kinetics of nitrobenzene adsorption:The adsorption rate of nitrobenzene on Mekong River sediments was higher than that of Mekong River sediments at 0 h and 5 h,but decreased within 6~14 h.The adsorption process of nitrobenzene in Mekong sediments accords with the quasi-second order adsorption kinetic model.The adsorption process includes surface adsorption,internal diffusion of particles,and diffusion of external liquid film.Nitrobenzene adsorption thermodynamics:The adsorption curves of nitrobenzene on Lubri Bran and Kerman deposits are roughly consistent with the L-type adsorption isotherms,while the adsorption curves of the phenanthrene deposits for nitrobenzene conform to the S-type adsorption isotherms.?G~?<0,?H~?>0,?S~?>0,indicating that the adsorption ofnitrobenzene by the Mekong sediment is a spontaneous endothermic process,and the system chaos is intensified during the endothermic process.(2)Influencing factors:(1)The effect of different initial concentrations on adsorption:When the initial concentration of adsorbate is small,the adsorption rate is slow.When the initial concentration is medium concentration,the adsorption rate increases,the concentration of nitrobenzene increases,and the adsorption rate increases significantly.(2)Effect of particle size on adsorption:The smaller the particle size,the larger the particle surface area and the more the adsorption point,so the adsorption amount of organic matter will be larger.Different particle sizes showed the difference of adsorption amount.The sediment with the particle size of 300 mesh had the largest adsorption capacity to diuron,and the adsorption with the particle size of 100 was the smallest,indicating that the smaller the particle size,the larger the adsorption amount.(3)Effect of pH on adsorption:Different pH has a great influence on the adsorption of nitrobenzene on the sediments of the Mekong River.When the pH is in the range of 3-5 and 8-10,the adsorption amount of nitrobenzene in the sediment varies with pH.Increasing and increasing,when the pH is in the range of 5~8,the adsorption amount remains unchanged with the increase of pH.The results show that the adsorbate inhibits the adsorption of nitrobenzene on the sediment under acidic conditions and promotes the adsorption of nitrobenzene on the sediment under alkaline conditions.The relevant adsorptions of diuron on the Mekong River sediments are as follows:(1)Dynamic adsorption of diuron:The adsorption equilibrium reached 20 h,and the fitting results show that the adsorption of diuron is more in line with the internal diffusion model of the particles.Adsorption thermodynamics of diuron:The Freundlich isotherm equation has the best fitting effect on the adsorption data of diuron.The?G~?<0,?H~?>0,and?S~?>0 indicate that the adsorption of diquat on the Mekong sediment is a spontaneous endothermic process,and the system chaos is intensified during the endothermic process.(2)Influencing factors:(1)Influence of initial concentration of diuron:When the initial concentration of adsorbate is small,the adsorption speed is slow.When the initial concentration is medium concentration,the adsorption rate increases,the concentration of diuron increases,and the adsorption rate increases significantly.(2)Influence of different particle sizes:The results showed that the adsorption of 300 mesh sediments on diuron was the largest,and the adsorption of 100 mesh sediments on diuron was the largest.As the particle size of the sediment increases,the amount of sediment particles in the Mekong River decreases with diuron.(3)The effect of different pH values:In the pH range of 3~10,the adsorption amount of diuron increases first and then decreases;when the pH value is in the range of 7~10,the adsorption capacity increases with the increase of pH value.Constant.The results show that the weak acid conditions are conducive to the adsorption of diuron by sediments.In summary,the adsorption equilibrium time of nitrobenzene and diuron on the sediments of the Mekong River in Laos is relatively short,and the increase in temperature is beneficial to the adsorption of nitrobenzene and diuron on sediments.The increase of summer temperature is more favorable for the control of organic pollutants in the Mekong River,which makes the mobility decrease to some extent.The concentration of target organic pollutants has a greater impact on its adsorption,indicating that the control of organic pollutants should be controlled at the source.In addition,the particle size of the sediment and the pH of the system also have an effect on the organic pollutants.