(86d) Adsorption Studies of Endosulfan, Chloropyrifos and Monocrotophos Pesticides From Aqueous Solution Using Activated and Unactivated Cocoa Pod Husk

Increased agricultural practice and pesticide application has resulted in the contamination of natural environments with different kinds of pesticides. The removal of toxic pesticides such as Endosulfan, Chloropyrifos and Monocrotophos by inexpensive biomaterial termed biosorption requires that the substrate displays high pesticide uptake and suitable mechanical properties for the applied remediation technique. The kinetics, intrparticulate diffusivities and adsorption isotherms for the adsorption of Endosulfan, Chloropyrifos and Monocrotophos onto activated and unactivated cocoa pod husk was investigated. The amount of the pesticides adsorbed increased as time and initial concentration was increased. Endosulfan and Chloropyrifos was maximally adsorbed at about 60 minutes with 37.0 and 37.25 mg/g respectively onto activated cocoa pod husk. The trend of the sorption capacity was found to be Chloropyrifos > Endosulfan> Monocrotophos for both activated and unactivated cocoa pod husk. Activation of the husk improved the sorption capacity. The mechanism of sorption of the pesticides followed particle diffusion model. The pseudo-first order and pseudo-second order kinetic equations were used to model the adsorption kinetics with the pseudo-second order giving a better fit to the sorption experimental data, as seen from the correlation coefficients (R2) which ranged from 0.2457 to 0.7913 for pseudo-first order and 0.9417 to 0.9980 for the pseudo-second order model. Among the three adsorption isotherms used, Dubinin-Radushkevich isotherm gave a better fit with R2 values ranging 0.6438 to 0.9639; followed by Freundlich isotherm (0.1101 to 0.9583) and then the Langmuir isotherm (0.0065 to 0.9797). The sorption process was found to be a chemisorption process as seen from the apparent energy of adsorption. Therefore, this study shows that activated and unactivated cocoa pod husk could be used to remove pesticides from aqueous solution and also established the mechanism of sorption.

Key words: Bioremediation, Adsorption, Pesticides, Kinetics, Isotherms.