Adsorption isotherms of diuron and hexazinone in drinking water using four agro-industrial residues

Abstract

Materials with high organic carbon content are studied for the removal of herbicides from water, such as activated carbon. Low cost alternatives should be investigated for the substitution of this type of material in the removal of herbicides from water. In this context, the aim of this research was to evaluate four agro-industrial residues (white grape bagasse, corn straw, peanut shell and soybean hull) as adsorbents of diuron and hexazinone in drinking water. Samples of drinking water were collected from sources used for human consumption. Five concentrations (1, 2, 3, 4 and 5 mg mL-1) of each herbicide were added to the potable water samples. Each experimental unit consisted of 10 mL of a solution of water and herbicide with 0.1 g of each agro-industrial residue. Sorption was evaluated using the batch equilibrium method. High performance liquid chromatography (HPLC) was used to determine the amount of herbicide present in the aqueous solution. The Kf (Freundlich coefficient) of diuron was higher (2.99-11.93 mmol(1-1/n) L1/n kg-1) than hexazinone (2.31-4.61 mmol(1-1/n) L1/n kg-1) for all adsorbents used. Diuron percentage sorption was higher with white grape bagasse (51.15%) and peanut husk (52.44%), and hexazinone with corn straw (22.77%) and white grape marc (21.48%), than other agro-industrial waste for both herbicides. Even though the sorption of diuron was more pronounced than that of hexazinone, the sorption values obtained in this study were less than 52.44% and considered unsatisfactory in terms of effective removal from contaminated water.