Dual Porosity Filtration (DPF) is designed for sedimentation-based removal of suspended solids (SS) and adsorption-based removal of dissolved contaminants from stormwater runoff. It consists of shallow (10 mm) low-porosity layers for contaminant retention, interlaid with high-porosity layers for horizontal, gravity-driven flow. First proof of concept was obtained in a 10 m by 60 m pilot plant receiving stormwater runoff from 1.3 hectares of trafficked area in Copenhagen. The pilot plant contains two versions of DPF-designs, a cheaper one with 6 pairs of low- and high-porosity layers (‘DPF-6-layers’), and a more expensive one with 18 such pairs (‘DPF-18-layers’). Both versions are designed for a flow capacity of 9 m3/h. The DPF-designs were tested on the basis of 25 rain events. Flow proportional event mean concentrations showed the concentration of SS to be on averaged reduced from 123 mg/L in the inlet to 10.4 mg/L in the outlet from the DPF-6-layers, and 1.4 mg/L from DPF-18-layers, Zn from 98 to 29 and 12.5 μg/L, Cu from 25 to 12.2 and 9.6 μg/L, Cr from 18 to 10.9 and 10 μg/L, Pb from 9 to 1.0 and 0.2 μg/L, and P from 178 μg/L to 47.4 μg/L and 38 μg/L, respectively for the DPF-6-layers and DFF-18-layers. Based on the observed hydraulic performance and contaminant removal rates the concept of DPF appears to hold a potential for treatment of road runoff to high water quality standards. Cu and Cr fate must be further studied. Suggestions for optimized full scale DPF-designs are given.
Keywords: heavy metals, phosphorus, pilot plant, road runoff, suspended solids