Fixed Bed Adsorption of Water Contaminants: A Cautionary Guide to Simple Analytical Models and Modeling Misconceptions

This contribution is intended as a specific review of the modeling approaches used to describe breakthrough curves of water contaminants and as a cautionary guide to some common and persistent modeling misconceptions. Its intended audience is early career researchers working in the area of adsorptive water remediation. First, typical data- and mechanism-driven models are discussed. A brief description of numerical fixed bed models with multiple curve broadening mechanisms (axial dispersion; intraparticle diffusion; film mass transfer; reaction kinetics) is presented. Particular attention is paid to analytical fixed bed models constructed for linear and nonlinear trace systems. Because these models assume that a single curve broadening mechanism is operative, their functional forms are relatively simple. Examples of spreadsheet calculations with these models are provided. A summary describing several egregious misconceptions associated with the use of two phenomenological models based on reaction kinetics (Bohart–Adams and Thomas) and one empirical model (Yoon–Nelson) to fit breakthrough curves is presented. In many previous studies, the three models have been used blindly, resulting in meaningless findings. The author hopes that this article will help the early career researcher avoid repeating the same mistakes.