## 3 Results and Discussion
### Efficient Removal of Heavy Metals in Stormwater Infiltration Facility  
To test the removal of heavy metals by PPG-nZVI beads in remediation system, PPG-nZVI beads as filling materials were paved in the simulated stormwater infiltration pool to examine their removal efficiency on treating the heavy metal solutions including Pb\({}^{2+}\), Cr\({}^{6+}\), Zn\({}^{2+}\), Cd\({}^{2+}\), and Cu\({}^{2+}\). Generally, the treatment efficiency of heavy metals by pool 1 with PPG-nZVI beads layer is superior to pool 2 without beads layer, and the removal efficiency decreased following in the order of Pb\({}^{2+}\)\(>\) Zn\({}^{2+}\)\(>\) Cr\({}^{6+}\)\(>\) Cu\({}^{2+}\)\(>\) Cd\({}^{2+}\) after 3 h operation. As seen from Figure 8, the removal efficiency of Pb\({}^{2+}\) in pool 1 and pool 2 was not significantly different, and the removal rate of effluent of both pools was more than 84%. After operation of the facility, the removal rate of Pb\({}^{2+}\) increased slowly. The reason may be due to that Pb\({}^{2+}\) is more likely to adhere to the surface of the suspended particles than other ions, so that it is easily removed by the filters other than PPG-nZVI beads layer. The removal efficiency of Zn\({}^{2+}\) was significant for both plant pools. The removal rate of Zn\({}^{2+}\) increased from 50%-73% to 69%-78% after adding of PPG-nZVI bead layer. There is also a significant difference between pool 1 and pool 2 in the removal of Cr\({}^{6+}\). The removal efficiency towards Cr\({}^{6+}\) was significant for both plant pools. The removal rate of Cr\({}^{6+}\) by pool 1 is above 75%, while the removal rate by pool 2 without PPG-nZVI beads layers is between 60%-65%. It seems that the removal of Cr\({}^{6+}\) by traditional layers retention such as sand, pumice, and gravel is limited. The addition of PPG-nZVI bead layer could significantly improve the removal rate and effectively reduce the risk of pollution. For Cd\({}^{2+}\), the pool 1 is slightly superior to pool 2. The removal rate of Cd\({}^{2+}\) was between 58% and 68% for both pools. The removal behavior of the pool 1 and pool 2 on Cu\({}^{2+}\) is quite different. The removal rate of Cu\({}^{2+}\) was 2.3 times higher by pool 1 with beads than pool 2 after 3 h operation. Above all, the pool with PPG-nZVI bead layer can effectively handle high-intensity, high-concentration instantaneous water and indicated that the PPG-nZVI beads might be effective sorbents as the filling materials in stormwater infiltration facility in purification of heavy metal contaminated water. The preparation of PPG-nZVI beads requires only chemicals including binder and porous material for the ball formation. The chemicals were all environmental  
Figure 7: XPS spectroscopy of O 1 s for fresh PPG-nZVI beads (**a**) and for PPG-nZVI beads reaction with Pb\({}^{2+}\) (**b**), Cu\({}^{2+}\) (**c**), and Zn\({}^{2+}\) (**d**).  
friendly thus could reduce pollution. The cost of the synthesized sorbents is estimated to be only 0.566 $ per 1000 beads, which could treat 40 mg of heavy metal pollutants in water system. Compared with the nZVI powder, PPG-nZVI beads could greatly improve the effective contact time with the pollutant. Especially when they were applied as the filling materials in stormwater filtration devices, the well-formed beads could allow the polluted water flowing through the filler with good penetration.