The purpose of this research is to design a device which can treat highway runoff, especially runoff during initial rainfall with high pollution intensity, by connecting it with the draining grid sink of a drainage ditch on a highway, through which runoff flows. Porous polypropylene (PPL) particles were used as a treatment agent. The device treated highway runoff during initial rainfall by filtration and adsorption. It had a capacity to treat highway runoff in an area of 7.0 m × 20.0 m when rainfall intensity was up to10 mm/hr. Two cases of rainfall intensity were set for the experiment: 5 and 10 mm/hr. The relationships between the efficiency of SS and COD removals and the rainfall intensity were investigated. Using artificial highway runoff with constant flow and SS concentration, results of 70% or more of SS removal with 5 mm/hr and 50% or more with 10 mm/hr were obtained. COD removal efficiency was about 90% of SS removal efficiency. This device was effective to remove non-point source pollutants in runoff on highways.

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