# High Rate Stormwater Treatment for Water Reuse and Conservation--Review
## 4 Incorporation of Different Filter Media to Enhance the Removal of Specific Pollutants
[49] also explored using permeable reactive barriers and various additives, including zeolites and wood-derived biochar, for use in the substrate component of green roofs. An inclusion of 20% zeolite in the substrate material led to lower total-P concentrations (by in-exchange and adsorption). In another field study by [PERSON] et al. [50] in Nantes, France, two swales received stormwater runoff from roofs. Naturally, sources of silt loam soil were used to make one swale. The other consisted of a central sand filtration area surrounded by silt loam embankments. This study aimed to assess the removal efficiencies for four micropollutants, including zinc (Zn), polycyclic aromatic hydrocarbons (PAHs) such as pyrene and phenanthrene, and glyphosate. [PERSON] et al. [50] found that the standard swale reduced micropollutants in infiltrated water by 35% to 85%, and overflow water concentrations were between 65-100% by adsorption. In contrast, the filtering swap achieved reductions of 67% to 90% for Zn and at least 89% for the other micropollutants, demonstrating that filtering swales were more effective than standard ones. Water treatment residuals (WTR), produced during the drinking water purification process when aluminum- or iron-based coagulants are used, have emerged as a promising filter medium for removing phosphorus and heavy metals [35]. Several field investigations utilizing WTR in various low-impact development (LID) facilities have been conducted recently, as detailed in Table 6.  
In a field study, [PERSON] et al. [43] tested the effectiveness of WTR in a bioretention system over a two-year period. The WTR medium performance was compared to a control setup that included washed gravel, pea stones, sand, and compost. While both media demonstrated reductions in all phosphorus species, the WTR medium consistently showed greater removal rates. [PERSON] et al. [35] also examined aluminum-based WTR in a field experiment conducted over 6 months focused on phosphorus and heavy metal removal (Cu, Pb, and Zn) from stormwater that ran off a car park situated in New Jersey, USA. Throughout 12 storm events, WTR granules effectively lowered dissolved phosphorus, copper, and zinc, as well as total concentrations of phosphorus, copper, lead, and zinc. This highlights WTR's potential as a filter medium that can divert waste from costly landfill disposal. [PERSON] et al. [44] demonstrated that drinking water treatment residuals (DWTR) are effective in reducing all tested phosphorus species, concluding that DWTR is a viable option for phosphorus removal. Woodchips, produced from tree chipping, have also attracted interest as a filtering material in low-impact development (LID) methods for stormwater treatment (see Table 6). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Filter Material Used** & **GSI** & **Pollutants Removed** & **References** \\ \hline Lightweight aggregates (LWA) & Green roof & Total-P & [49] \\ Sand & Swales & Zn, PAHs and glyphosate & [50] \\ Water treatment residuals (WTR) & bioretention & Different P species, and total-N & [43] \\ Woodchip with sand, and gravel & Infiltration trench & SS, Different P- species, and total-N & [45] \\ Woodchip & bioreactor and aeration & nitrate & [41] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Different filter materials incorporated on GSI method (modified from [PERSON] [38]). In a study using stormwater from roads and parking areas, [PERSON] et al. [45] observed that pre-treatment effectively captured silt or sand in quantities ranging from 9% to 92%, with nitrogen and phosphorus levels higher in silt than in sand, thereby enhancing nutrient removal. Zeolites were also field-tested for heavy reduction of metal (see Table 6). In a pilot-scale study in Sydney, Australia, [PERSON] et al. [39] used natural Australian zeolites along with basalt in a permeable pavement system (PPS). They evaluated the removal of five heavy metals (Cd, Cu Ni, Pb, Zn) from synthetic stormwater.