Pore Blockage Effects on Atrazine Adsorption in a Powdered Activated Carbon/Membrane System. I: Model Development

The mechanism of pore blockage plays an important role in competitive adsorption of trace organic compounds by microporous materials, such as activated carbon. An accurate description of the pore blockage effect of natural organic matter (NOM) on adsorption kinetics is a necessary part in the development of kinetic models for process design and performance prediction. In this study, a bisolute kinetic model based on homogeneous surface diffusion was developed to predict atrazine adsorption in a continuous flow powdered activated carbon (PAC)/membrane filtration system, incorporating the pore blockage effect. In order to elucidate the pore blockage effect, the system used in this study was simplified by representing the pore-blocking fraction of NOM with a single compound, poly(styrene sulfonate) with a nominal molecular weight of 1,800 Dalton. The surface diffusion coefficient of atrazine was modeled as a function of the surface concentration of the pore-blocking compound, which was also calculated by the model. The adsorption process was modeled for PAC application as either a pulse input or a step input; the quality of membrane backwash water was also used as a variable. Part II of this study, which appears in the companion paper, presents the model verification with a bench-scale PAC/microfiltration system, as well as model simulations that show optimal operating conditions for this system.