Seasonal performance of stormwater biofiltration system under tropical conditions

© 2019 Elsevier B.V. Urbanization rates are increasing in developing countries such as Malaysia. In the tropics, flooding is a major concern, due to high rainfall intensities. In addition to flooding, pollution caused by contaminants contained in urban runoff are also of concern. Biofiltration system as one of the technologies in on-site stormwater treatment, has gained its popularity as part of Water Sensitive Urban Design measures. To date however, studies on tropical biofiltration system are limited in number and scope. This study aims to assess the effect of wetting and drying on performance, since such systems are constantly subject to wetting and drying cycles. In this study, a set of sand-based filter columns were prepared with three different native plant species including Cordyline fruticosa (CF), Graptophyllum pictum (GP), and Cyperus alternifolius (CA). Ten wetting and drying regimes were conducted including 5 wet weather simulations (0, 0, 1, 2, 3 dry days) followed by 5 dry weather simulations (5, 7, 10, 14, 21 dry days). To aid the plants survivability during the dry period, submerged zone was installed in all columns, simulating groundwater table. The results showed that all three plants could survive throughout both wet and dry periods with minimum stress. The overall treatment performance of all column types was satisfactory as the heavy metal concentration reduction was 90% and above while total dissolved phosphorus (TDP) reduction was up to 94%. Although total dissolved nitrogen (TDN) reduction was not as high as TDP (up to 58% reduction), the effluent TDN concentration still met the required receiving water quality standard. Overall, effluent concentration from CF, GP, and CA columns satisfied the requirement of class IIB recreational water standard in Malaysia. It was also concluded that plant CA comparatively performed better than the others in terms of both survivability and pollutants removal aspects.