Evaluation of constructed wetlands for the treatment of diffuse pollutants from various sources: A case in South Korea

The efficiency of constructed wetlands is highly affected by its configuration as well as the influent pollutant characteristics which vary depending on land use. In this study, the treatment performance of different constructed wetlands installed across South Korea was investigated in terms of the effect of land use and other affecting factors. A total of 54 constructed wetlands were installed at 35 locations across South Korea from 2011 to 2019. Among these, 13 were installed in urban areas, 25 were located in agricultural areas, 3 were utilized in industrial areas, 3 were constructed commercial areas, and 10 were placed in livestock areas. The influent BOD/COD ratio in commercial and livestock areas was found to be 0.6, whereas that in agricultural, urban, and industrial areas were comparable at 0.52. In the effluent, the BOD/COD ratios were reduced to 0.54, 0.53, 0.51, 0.47, and 0.43 for the constructed wetlands located at agricultural, livestock, commercial, industrial, and urban areas, respectively. The lower ratios implied that the biological treatment mechanisms in the constructed wetlands are effective. In the case of industrial complexes, the biological treatment mechanisms appeared to be lower due to the high concentration of non-biodegradable organic substances in the runoff. Overall, meaningful results were drawn after the comparison of different pollutant ratios from various land use sources. It was identified that among the studied land uses, it was most difficult to achieve efficient treatment of the runoff from industrial areas using constructed wetlands. Adequate residence time and constructed wetland components such as plants, soil, microorganisms, and structural elements should also be considered in the facility design in order to promote efficient removal of different nitrogen species.