## 3 Benefits of Biochar Amendment in Green Roofs
### Runoff Quality Improvement
\begin{tabular}{c} **Concentration** \\ **without Biochar** \\ **(mg/L)** \\ \end{tabular}  & \begin{tabular}{c} **Concentration** \\ **with** \\ **Biochar (mg/L)** \\ \end{tabular}  & \ \begin{tabular}{c} **Load without** \\ **Biochar (mg/L)** \\ \end{tabular}  & \begin{tabular}{c} **Load with Biochar (mg/p)** \\ \end{tabular}  \\ \hline  & & & & & & & \\  & & &  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Reference** & **Approach** & **Substrate** & **Biochar Setup** & **Pollutant** & **Concentration** & **Concentration** & **Coal without Biochar** & **Load without** & **Load with Biochar (mg)** \\  & & & & & **(mg/L)** & **Biochar (mg/L)** & **Biochar (mg/L)** & & & \\ \hline  & & & & & 0.9 275, 260, 220, & & 0.0029, 0.085, 0.8, 0.05, & & & 0.0029, 0.085, 0.8, 0.05, & \\  & & & 1-2 mm & & & \(\phantom{0}\) and \(\phantom{0}\) /6.7, 7.6, 7.65 & & 0.12, 0.15, and \\  & & & & & 84 and 29 & & 0.05 (\(\mathrm{m}^{-2}\)) \\ \multirow{4}{*}{[89]} & \multirow{4}{*}{Pilot-scale} & Porous aggregates, & & & & 0.8 27, 240, 190, & 0.008, 0.085, 0.075, 0.65 & 0.0035, 0.1, 0.9, 0.7, and & \\  & composed & 2.8-4 mm & Mg (first & & 473/0.75, 7.5, & 0.023, 0.001, & 0.27/0.0014, 0.015, \\  & organic matter, & & & flush/second & 85, 88, and 31 & 0.23, 0.02, and & 0.17, 0.006 (\(\mathrm{m}^{-2}\)) \\  & and fine sand & \multirow{2}{*}{Unprocessed 1-2 mm} & & & 0.85, 25, 280, 185, & 0.075 (\(\mathrm{m}^{-2}\)) & 0.0021, 0.06, 0.7, 0.4, and \\  & & & 1-2 mm & & & 0.16, 0.0011, 0.009, 0.18, & \\  & & & & & 110, 78, and 30 & 0.13, and 0.05 (\(\mathrm{m}^{-2}\)) & 0.015, 0.07, 0.4, and \\  & & & & & 0.7 (\(\mathrm{m}^{-2}\)) & 0.021, 0.06, 0.7, 0.4, and & \\  & & & & & & 0.16, 0.0011, 0.009, 0.18, & \\  & & & & & & 0.13, and 0.05 (\(\mathrm{m}^{-2}\)) \\ \multirow{4}{*}{[90]} & \multirow{4}{*}{Pilot-scale} & \multirow{4}{*}{Pilot-scale} & \multirow{4}{*}{Pilot-scale} & \multirow{4}{*}{NA} & \multirow{4}{*}{TN (lowest and highest)} & \multirow{4}{*}{0.05 and 1.47} & \multirow{4}{*}{0.18 and 2.09} & \multirow{4}{*}{NA} & \multirow{4}{*}{NA} \\  & \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Reference** & **Approach** & **Substrate** & **Biochar Setup** & **Pollutant** & **Concentration** & **Coordination** & **with** **Biochar (mg/L)** & **Load without** **Biochar (mg/L)** \\ \hline
[94] & Pilot-scale & Local soil, perlite, and vermiculite & Rice husk/Maze strux (10\(\sim\)20\% \(\
icefrac{{}}{{\sigma}}\)) & TN & 103.68 & 26:21-52.77/10.12-3.97 & \\ \cline{3-6}  & & & & & TP & 0.27 & 0.22-0.57/0.58-1.07 & NA & NA \\ \cline{3-6}  & & & & & Organic carbon & 94.47 & 101.76–59.41/52.45–26.73 & \\ \hline
[95] & Pilot-scale & & & & TN (at the beginning/the end) & 27:2-32.8/0.5–0.7 & & \\ \cline{3-6}  & & & & & & and & \\ \cline{3-6}  & & & & & & & \\ \cline{3-6}  & & & & & & & \\ \cline{3-6}  & & & & & & & \\ \cline{3-6}  & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cont. As previously discussed, biochar possesses physiochemical properties that help retain a variety of heavy metals and nutrients such as total nitrogen (TN) and total phosphorous (TP), thereby enhancing soil fertility [96]. The primary mechanisms through which biochar captures pollutants are adsorption, cation exchange, and biotransformation [72; 90; 97]. Furthermore, biochar indirectly improves runoff quality by improving plant performance, which leads to higher water and nutrient uptake by plants [89; 92]. Adding biochar to GR substrates in [64] effectively reduced the nutrient loads in GR runoff as compared to non-biochar GRs. Specifically, in sodium GR test modules, biochar evenly spread on the substrate surface reduced the loads of TP and TN from 40 and 580 mg/m\({}^{2}\) to 35 and 550 mg/m\({}^{2}\), respectively. For meadow GRs, TP and TN loads were reduced from 45 and 700 mg/m\({}^{2}\) to 41 and 560 mg/m\({}^{2}\), respectively. The effect was even more considerable in the case of biochar at the bottom of the substrate.