Elimination of pesticides onto granular activated carbon bed in presence of natural organic matter : Development of a protocol associating experiments and numerical calculations in order to simulate competitive equilibria and kinetics of adsorption.
Faced with the persistent contamination of natural raw waters by pesticides, granular activated carbon (GAC) is an efficient treatment, more and more used in drinking water plants. Its performances depend on the equilibria and kinetics of adsorption, on the hydrodynamics of the reactor and on the competition with the natural organic matter contained in raw waters. Within this framework, the aim of this research was double : first to elaborate a protocol in order to acquire equilibrium and kinetic parameters for competitive adsorption and secondly to develop a simulation software for the adsorption onto GAC beds. The theoretical part is based on : (1) the homogeneous surface diffusion model (HSDM) which takes into account both the external mass transfer coefficient (kf) and the superficial diffusion coefficient (Ds) for the adsorption kinetics, (2) on the ideal adsorbed solution theory (IAST) for the competition and (3) on the definition of an equivalent background compound (EBC) for the natural organic matter. The experimental work consists, on one hand, to achieve isotherms with ultra pure water, natural water and natural water diluted with ultra pure water in order to obtain equilibrium parameters. On the other hand, adsorption kinetics are carried out in a differential column batch reactor (DCBR) in order to determine superficial diffusion coefficients. Numerical simulation programs were conceived, written and validated with results found in the literature. Then, they were involved in the global simulation protocol for real GAC filters. For one natural water, this protocol was performed with three pesticides and two granular activated carbons.