PHYTOREMEDIATION OF HEAVY METALS FROM LEACHATE THROUGH DIFFERENT SPECIES OF GRASSES

Abstract

Phytoremediation is considered more cost effective than other techniques with lesser disadvantages than physical and chemical techniques. It is gaining popularity in academic as well as practical field. Grasses have been used widely to remediate contaminants from wastewater. Municipal solid waste leachate has never been treated with grasses, especially with Rhodes grass. A series of pot experiments was performed to investigate the contaminant uptake from municipal solid waste leachate by Chloris gayana (Rhodes grass) grown in combination with commonly used grass varieties i.e. Vetiveria zizanioides (Vetiver grass) and Pennisetum purpureum (Elephant grass). Leachate used for the experiments had high values for chemical oxygen demand, pH, electrical conductivity, nitrates, and phosphates (i.e. 5,163 mg/L, 8.5, 9 mS/cm, 182.1 mg/L, and 6.4 mg/L, respectively). The results showed that all the grasses significantly reduced the values of chemical oxygen demand, electrical conductivity, nitrates, and phosphates up to 67, 94, 94, and 73% respectively. The metals showed a significant decrease too, which included Zinc (97%), Copper (89%), and Manganese (89%). Comparatively, Rhodes grass remained efficient for Zinc, Elephant Grass for Copper, and Vetiver grass for Manganese. Rhodes grass showed good results in diluted leachates, whereas in concentrated leachates Rhodes grass did not flower and the biomass was also decreased. In Vetiver grass, root and shoot lengths decreased with increasing leachate strength, but the biomass does not change. This shows that the increased uptake of contaminants enhances the mass per unit length of each plant. The study revealed that the Rhodes grass can be used for low strength leachates, especially for metals. The application of combination of these grasses can further improve contaminant removal by constructed wetlands.