# High Rate Stormwater Treatment for Water Reuse and Conservation--Review
## 4 Incorporation of Different Filter Media to Enhance the Removal of Specific Pollutants  
[PERSON] [38] reviewed various stormwater treatment facilities using different filter media in field and pilot-scale applications to address stormwater pollutants (Table 5). These media were implemented in GSI systems, including green roofs, bioretention areas, and swales. They improved the removal of specific pollutants by enhanced adsorption and filtration. In a pilot-scale study by [PERSON] et al. [39], the removal of heavy metals by a permeable pavement system (PPS) was tested using basalt and zeolite as the filter media. This study examined the removal of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) from synthetic stormwater over an 80-h period, simulating rainfall in Sydney, Australia over a 10-year period. The results showed that basalt removed between 38% and 67% of the total heavy metals tested by adsorption. Biochar has proven effective in laboratory studies as a filter medium for removing various stormwater pollutants [47, 48]. This solid material, composed of carbon and ash, is produced through the thermochemical treatment of organic matter in an oxygen-limited environment, such as during pyrolysis. Additional research has included pilot-scale and field experiments (Table 6). [PERSON] et al. [40] carried out simulated field tests over roughly 14 months using sand alone and a sand-biochar blend to examine _Escherichia coli_ removal with natural stormwater. In another pilot study, [PERSON] et al. [41] employed biochar in a multi-step treatment system designed to address various pollutants. The process began with a sand filter spiked with iron for phosphate removal, followed by a woodchip bioreactor and an aeration step to eliminate nitrate. This was followed by columns filled with sand amended with iron, biochar, and/or manganese oxides to capture trace metals and other harmful substances. This system was tested with real stormwater runoff over 8 months. [PERSON] et al. [41] observed nearly complete nitrate removal in the bioreactor, though phosphate removal in the iron-enriched sand was less effective, resulting in breakthrough conditions. During the first four months, columns containing sand combined with biochar and manganese oxides removed 80% of metals and organic pollutants. The researchers suggested that, in their specific study environment, nutrient removal might be effective for about a decade, while organic compound removal could be less durable. Additionally, lightweight aggregates have been investigated as filter media in green roofs (see Table 6). The removal mechanisms were adsorption and filtration. [PERSON] & [PERSON] [42] identified dredged lightweight aggregates (LWA) as an effective filter medium for green roof applications. These aggregates, typically produced from materials that would otherwise end up in landfills, offer a sustainable solution. \begin{table}
\begin{tabular}{c c} \hline \hline
**Filter** & **Reference** \\ \hline Basalt & [39] \\ Biochar & [40] \\ Biochar & [41] \\ Light-weight aggregates (LWA) & [42] \\ Sand & [41] \\ WTR & [43] \\ WTR & [35] \\ WTR & [44] \\ Woodchips & [45] \\ Zeolites & [39] \\ Zeolites & [46] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of media used in filters (modified from [PERSON] [38]). [PERSON] et al. [49] conducted a study involving 32 pilot-scale green roofs in New Jersey, USA from 2017 to 2022, which spanned all four growing seasons and included 38 storm events. The objective was to evaluate phosphorus contributions to roof runoff from sedimentated roofs. The growing medium consisted of 90% LWA, made using either pumice or expanded clay, with compost being the other alternative. Their findings revealed a decrease in total phosphorus (total-P) concentrations in the effluent over time, indicating green roofs can effectively retain phosphorus within them by filtration. [PERSON] et al.