## 4 Conclusions  
In this study, volcanic rock and coconut shell activated carbon were used as the test filter materials, with quartz sand serving as the control filter material, to investigate the pollutant removal performance of both single and mixed filter materials. Through multiple tests of rainwater quality at the test site during the early stages of the experiment, the results indicated that turbidity, NH\({}_{3}\)-N, TOC, and Cr(VI) in the rainwater exceeded the standard levels. The test water with corresponding pollutant concentrations was configured to simulate local rainwater. The pollutants in the rainwater were removed using BSF technology, and the influence of different filter materials on pollutant removal was analyzed. The conclusions are as follows:  
(1) As single filter materials, volcanic rock and coconut shell activated carbon significantly outperform traditional quartz sand in terms of turbidity, ammonia nitrogen (NH\({}_{3}\)-N), TOC, and hexavalent chromium (Cr(VI)) removal efficiency. Specifically, volcanic rock demonstrates superior turbidity retention, efficiently intercepting suspended particles in water to ensure clear water quality. Coconut shell activated carbon exhibits stronger adsorption performance for ammonia nitrogen, total organic carbon, and hexavalent chromium, significantly enhancing the removal of these pollutants and effectively improving water quality conditions. Comparative analysis of the experimental data shows that both volcanic rock and coconut shell activated carbon significantly surpass the treatment effects of quartz sand filter media in their respective areas of expertise, highlighting their unique advantages in water treatment. (2) Mixed filter materials show a significant improvement in removing pollutants compared to single filter materials. For instance, when the mixing ratio was 1:3 (71.51 \(\pm\) 0.64%), the average efficiency of this material in removing total organic carbon was approximately 0.96 percentage points higher than that of coconut shell activated carbon (70.55 \(\pm\) 0.42%), \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Early Stages of Operation**} & \multicolumn{3}{c}{**Remove the Stable Period**} \\ \hline  & **Turbidity** & **NH\({}_{3}\)-N** & **TOC** & **Cr(VI)** & **Turbidity** & **NH\({}_{3}\)-N** & **TOC** & **Cr(VI)** \\ \hline
1 & 83.87 \(\pm\) 1.11\% & 69.07 \(\pm\) 1.43\% & 29.81 \(\pm\) 0.32\% & 14.56 \(\pm\) 6.09\% & 93.28 \(\pm\) 0.25\% & 97.55 \(\pm\) 1.25\% & 49.62 \(\pm\) 0.70\% & 68.46 \(\pm\) 2.89\% \\
2 & 91.46 \(\pm\) 0.99\% & 80.10 \(\pm\) 2.63\% & 43.34 \(\pm\) 1.25\% & 42.29 \(\pm\) 5.00\% & 97.36 \(\pm\) 0.08\% & 98.77 \(\pm\) 0.99\% & 70.55 \(\pm\) 0.42\% & 93.39 \(\pm\) 1.69\% \\
3 & 86.47 \(\pm\) 0.36\% & 86.82 \(\pm\) 2.53\% & 51.80 \(\pm\) 0.21\% & 61.30 \(\pm\) 5.37\% & 94.93 \(\pm\) 0.26\% & 98.90 \(\pm\) 0.42\% & 68.60 \(\pm\) 0.42\% & 90.60 \(\pm\) 2.08\% \\
4 & 88.19 \(\pm\) 0.65\% & 86.81 \(\pm\) 1.10\% & 53.49 \(\pm\) 0.65\% & 68.40 \(\pm\) 3.99\% & 94.50 \(\pm\) 0.25\% & 99.15 \(\pm\) 0.59\% & 70.97 \(\pm\) 1.00\% & 91.42 \(\pm\) 1.26\% \\
5 & 87.94 \(\pm\) 0.61\% & 88.97 \(\pm\) 1.11\% & 54.97 \(\pm\) 1.08\% & 72.19 \(\pm\) 4.93\% & 94.37 \(\pm\) 0.33\% & 99.27 \(\pm\) 0.03\% & 71.51 \(\pm\) 0.64\% & 93.63 \(\pm\) 1.83\% \\
6 & 92.71 \(\pm\) 0.42\% & 88.25 \(\pm\) 1.11\% & 52.86 \(\pm\) 0.64\% & 63.99 \(\pm\) 9.36\% & 97.45 \(\pm\) 0.12\% & 99.14 \(\pm\) 0.62\% & 70.87 \(\pm\) 0.67\% & 90.86 \(\pm\) 1.33\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The average pollutant removal rate (mean \(\pm\) standard deviation) of BSF Reactors \(1^{\#}\) to \(6^{\#}\). and coconut shell activated carbon demonstrated the best removal effect among single filtering materials. This increase is still within the standard deviation range, indicating that under the conditions of this experiment, the synergistic effect of the mixed filter material does not significantly exceed the performance limit of the single filter material. Conceptualization, X.M., H.Z. and D.M.