Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 1. Equilibrium parameters

This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (∼5 μg L−1 to ∼500 μg L−1 at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L−1 for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1-5 mg L−1) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites (KL ∼ 103 L mg−1) which are 10-20 less present in a carbon surface than lower reactivity sites (KL ∼ 10 L mg−1), according to the qm values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g−1 and 190 mg g−1. This theoretical value is very close to the experimental qm values obtained when using linearized forms of Langmuir, Tóth and Fritz-Schluender models.