Urban Runoff Treatment by Natural and Magnetite-Modified Zeolites in Packed-Bed Columns

Infiltration-based devices are increasingly used to tackle pollution carried by urban runoff, one of the most common nonpoint sources of nutrients and heavy metals in water bodies. This work is aimed at improving, through a Fe₃O₄ coating, the depollution potential of synthetic urban runoff (SUR) of a natural mordenite-type zeolite (NZ). First, it was found that the modified zeolite (Fe₃O₄-Z) had higher cation exchange capacity and specific surface area (measured by methylene blue adsorption) than NZ. Then, infiltration tests were carried out in columns packed with either NZ or Fe₃O₄-Z. Fifteen SUR feeding cycles were conducted, and the concentrations of the pollutants studied (N-NH₄⁺, N-NO₃⁻, PO₄³⁻, Mn²⁺, and Pb²⁺) were measured at the inlet (C₀) and at the outlet (C) of the columns. Breakthrough curves were plotted for each pollutant, which were modeled by the Thomas, Yoon-Nelson, and Adams-Bohart equations; the latter best represented the experimental data. The nonparametric Kruskal–Wallis test indicated that the mean removal efficiency of N-NO₃⁻, Mn²⁺, and Pb²⁺ did not show significant differences (α = 0.05) between the two packing materials, while N-NH₄⁺ and PO₄³⁻ were removed with significantly different efficiencies (α = 0.05) following the packaging material. According to the modeling results, Fe₃O₄-Z exhibited higher maximum adsorption capacities than NZ for the five pollutants studied, all with longer times to material depletion (except for Pb²⁺). These findings imply that Fe₃O₄-Z would have a longer lifetime than NZ in real urban runoff infiltration-based systems, which could constitute efficient control devices for nutrients and heavy metals.