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A novel water hyacinth based biosorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) removal from aqueous solution

In the current study, a novel low cost biosorbent was developed using water hyacinth root powder for the biosorption of a phenoxy pesticide (2,4-dichlorophenoxy acetic acid) from its aqueous solution. Initially, biosorbents were prepared by systematically modifying the water hyacinth root powder with acid, thermal, ultrasound, thermal-acid and ultrasound-acid treatments. The ultrasound-acid modified biosorbent exhibited superior biosorption capacity over the others with a maximum biosorption capacity of 40.0 mg g–1. For the ultrasound-acid treated biosorbent, three biosorption operation parameters namely biosorbent dosage, solution pH and initial pesticide concentration were varied to obtain their optimal values for maximum biosorption capacity. A maximum removal of 91% was obtained for 4 g L–1 dosage of ultrasound-acid modified biosorbent at pH of 4 in 100 mg L–1 of the pesticide solution. The presence of various sulphur containing functional groups on the surface of ultrasound-acid treated biosorbent might be the reason for the enhanced biosorption capacity. The biosorption kinetic data obtained for different initial concentrations with the optimal values of biosorbent dosage and pH were well fitted to pseudo second order kinetic model indicating chemisorption type interaction. The biosorption equilibrium data was well fitted to Langmuir isotherm model which represent mono layered biosorption. The presence of intra particle and film diffusion limitations for the biosorption were confirmed using two well-known intra particle diffusion models namely Weber and Boyd.