HEAVY METAL AND NUTRIENT REMOVAL FROM STORMWATER RETENTION POND BY VETIVER GRASS (CHRYSOPOGON ZIZANIOIDES): PLANT GROWTH CHAMBER STUDY

With increasing water scarcity and population explosion in the 21^st century, stormwater has been gaining attention as a valuable water resource for water reuse and groundwater recharge in the past decade. However, pollutants such as heavy metals and nutrients commonly found in urban stormwater hinder the reuse of stormwater as a water resource. Among many stormwater Best Management Practices (BMPs), stormwater retention pond has been long implemented to provide peak flow attenuation during storm events and removal of suspended solids through physical settling processes. However, its effectiveness in removing dissolved contaminants such as metals and nutrients are limited. Therefore, retrofitting the stormwater retention pond to enhance its pollutant removal performance is imperative to stormwater harvest and reuse. In this study, the heavy metal and nutrient removal performance of vetiver grass (Chrysopogon zizanioides, a non-invasive, high-biomass nutrient- and metal hyperaccumulating perennial grass) from stormwater was evaluated, which served as the first step toward designing a floating treatment platform (FTP, manmade ecosystem that uses plants growing on floating supporting) for implementation in a stormwater detention pond. During a 30-day study in a plant growth chamber, vetiver grass (4% w/v) was grown hydroponically in the pond water collected from a local stormwater retention pond with the exaggerated dissolved concentrations of Cu, Pb, Zn, and P. The removal of metals (Cu, Pb, and Zn) started immediately and continued for the study period. P concentration in water was found to increase at the beginning of the study and subsequently decreased after 5 days. Rapid removal was observed between day 5 and day 15. Within 30 days, vetiver grass removed 80% Cu, 96% Pb, 97% Zn, and 87% P. To further evaluate the removal performance of FTP with hydroponically grown vetiver grass, mesocosm studies will be conducted. Overall, this study showed that vetiver grass could be effectively integrated with FTP and deployed as a retrofit for stormwater retention ponds to generate clean water for stormwater reuse.