Development of a hybrid constructed wetland system for treating stormwater runoff from road

ABSTRACT Hybrid constructed wetland (CW) is a combination of various types of wetland that has different water treatment capabilities integrated into a single wetland system. However, most hybrid CWs have been formed in a larger scale, wherein the application of a hybrid CW to a limited space such as an urban area is recommended. Therefore, this study was performed to develop a hybrid CW technology which overcomes the limitations in space. The hybrid CW considered in this study was composed of a forebay, a free water surface (FWS) flow and horizontal subsurface flow (HSSF) wetlands. To evaluate the efficiency and applicability of the technology, a pilot and test-bed scale experiments were performed. The pilot experiment results showed that the removal rate of most the pollutants, including particulate matter, organic matter, and nutrients, were ranging from 3% to 31% in the forebay, 44% to 54% in the FWS CW, and 12% to 19% in the HSSF CW. With respect to the removal efficiency of each pollutant according to the vegetation, a combination of reed and cattail plants showed high removal efficiency for particulate matter and heavy metals. As for the combination of reed and iris, high removal efficiency was observed for the organic matter and nutrients. To evaluate the applicability of a hybrid CW, a test-bed was developed adjacent to a campus road. Monitoring results showed that the removal efficiency for TSS, COD, TN, TP, and heavy metals was at least 60%, which was 10%–0% higher than that of a single CW. In addition, the particle size of particulates removed by the hybrid CW was analyzed, and the result showed that diameter of 8.0–24 μm of the particulates in the inflow were removed.