Modeling of nitrate adsorption and reduction in Fe⁰-packed columns through impulse loading tests

A conventional tracer study using Li⁺ and Cl^- was conducted on four Fe⁰-packed column reactors for nitrate removal. Both Li⁺ and Cl^- showed strong adsorption onto iron media and thus were not ideal tracers for the study. Tests using an impulse loading of nitrate were then innovated to investigate the transport and reduction of nitrate in the reactors. The impulse loading was superposed on a continuous constant feeding of nitrate which generated a steady effluent baseline. A multivariable model incorporating hydraulic dispersion, adsorption/ desorption, and reduction of nitrate was developed and numerically solved. Both Langmuir adsorption and linear adsorption isotherms were separately applied to describe nitrate adsorption on the reactive surface. The parameters of the model were estimated by fitting the model with the response curves from the impulse loading tests. These estimated parameters were consistent with previous studies. Specifically, the modeling results suggest a significant adsorption of nitrate by the iron media, causing an evident retardation effect. The research may lead to new methods for studying the fate of contaminants in porous reactive environments. Journal of Environmental Engineering