Adsorption-desorption study of selected pesticides and a typical dye in different soils and their removal by high cost activated carbons and low cost materials based on statistical response surface methodology

Abstract

The adsorption-desorption study of bromophos methyl [O, O- dimethyl – O - (2, 5 dichloro-4 bromophenyl) phosphorothioate], quinalphos [O, O-diethyl O-2-quinoxalinylphosphorothioate], pretilachlor [2- chloro-2’,6’-diethyl-N-(2-propoxyethyl)-acetanilide]and a typical dye congo red (CR) [Dinatirum-3, 3 ¢-[[1, 1 ¢-biphenyl]-4, 4¢-diylbis (azo)] bis(4-aminonaphthalin-1-sulfonat) on five soils from different Greek locations with varying physical and chemical properties were studied by batch equilibration method. Adsorption isotherms fitted well to the Freundlich equation than Langmuir isotherm equation for all compounds. Regression analysis between Freundlich adsorption coefficient (Kfads) andvarious soil properties indicated that soil organic matter content plays a controlling role inthe adsorption of these pesticides on the soils. But on the other hand, clay content plays animportant role for congo red adsorption. Desorption isotherms also conformed well to theFreundlich equation and there was a hysteresis effect in all the soils. The Freundlich Kfdesvalues were higher for the soils with the highest organic matter percent for studiedpesticides and for CR the highest Freundlich Kfdes was observed for the soils with thehighest clay contentPesticides are being applied to agricultural lands all over the world for increased cropproduction as well as for greater yield in order to meet the demand of world increasingpopulation. However, at present, misapplication, carelessly disposal or storage of emptypesticides and containers into the environment is a major source of drinking watercontamination in all over the world. As consequences, the accumulation of pesticides infood and drinking water has been generally recognized as dangerous, and the long-termpersistence and toxicity of pesticides in groundwater is potentially responsible for causingvarious kinds of human diseases. In the same way, synthetic dyes are indispensable to thetextile and dyeing industries. Textile and yarn dyeing industries are discharging theiruntreated waste water into the natural streams. So, the surface water body is nowvulnerable, aquatic life is endangered and users are facing serious health problems due tocontamination by hazardous chemicals from those industries. So it is an urgent need tosearch low-cost materials and efficient methodology for the removal of these pesticidesand dye effluents from the waste water. Adsorption is the most widely used methodologysince the beginning of this century for the treatment of these hazardous substances fromaqueous matrices.This PhD study tried to removal of above mentioned hazardous compounds fromaqueous solution onto different adsorbents from diverse origin. The adsorbents used in thepresent study were used tea leaves (UTL), Neem leaf powder (NLP) and saw dusts (SD) aslow cost materials; as well as activated carbon produced from olive seed (OSACs), ricehusk (RHACs) and sugarcane bagasse (BAGACs) used as high cost materials. At first,kinetic studied were performed for all adsorbents in order find equilibrium contact timeand describe the kinetic models. An approach of statistical design of experiments based onresponse surface methodology (RSM) was used to develop response model and desirabilityfunction was then used for simultaneous optimization of all affecting parameters in orderto achieve the highest removal% of all compounds. Finally, removal capacities of alladsorbents were determined by developing isotherms, considering all optimized factors.The results indicated that all adsorbents followed either Langmuir isotherm model orFreundlich model and the kinetic study showed all data for all adsorbents fitted by pseudosecondorder kinetic model. All the low cost materials used in this study are locallyavailable as well as economically feasible and there have no alternative use, moreover,proposed adsorbents do not require any pretreatments but showed high removal capacity incompared to activated carbons. The developed model using RSM can be providing afurther insight for potential use of other processes, especially industrial water treatmentsystem.