Sand Filtration Enhanced by Various Reactive Materials for Bioretention Cell Design Considerations

Various reactive treatment materials were evaluated to enhance sand filtration of dissolved species common in stormwater runoff: ${\mathrm{NO}}_3^{-}$, ${\mathrm{PO}}_4^{3-}$, ${\mathrm{Cu}}^{2+}$, ${\mathrm{Pb}}^{2+}$, and ${\mathrm{Zn}}^{2+}$. Fly ash and iron oxyhydroxide mine drainage residuals were blended with sand at 5% (FA5.0) and 7.5% (MDR7.5) by mass and packed into laboratory columns. Additionally, minus 30 mesh particle sizes of proprietary peat products APTsorb and bioAPT were each packed without blending with a succeeding sand layer (APT-S and BIO-S). Pollutant removal performance was evaluated by pumping synthetic stormwater (SS) through packed up-flow columns without recirculation. The control material was 100% sand (SAND). Target SS concentrations included $1.5\mathrm{mg}/\mathrm{L}{\mathrm{NO}}_3^{-}$ as N, $0.5\mathrm{mg}/\mathrm{L}{\mathrm{PO}}_4^{3-}$ as P, $25\mathrm{\mu g}/\mathrm{L}{\mathrm{Cu}}^{2+}$, $30\mathrm{\mu g}/\mathrm{L}{\mathrm{Pb}}^{2+}$, and $100\mathrm{\mu g}/\mathrm{L}{\mathrm{Zn}}^{2+}$. FA5.0 and MDR7.5 both removed over 84% of P. SAND, APT-S, and BIO-S removed limited total P and total dissolved P, while BIO showed a net export of up to 30% P. All columns removed greater than 75% and 89% of ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Zn}}^{2+}$, respectively. APT-S removed the greatest ${\mathrm{Pb}}^{2+}$, at over 84%. None of the columns exhibited consistent ${\mathrm{NO}}_3^{-}$ removal greater than 10%.