Phytoremediation of Cr(VI) in wastewater using the vetiver grass (Chrysopogon zizanioides)

Abstract

In this study, the phytoremediation of Cr(VI) in wastewater using vetiver grass (Chrysopogon zizanioides) was investigated. The influence of parameters such as initial concentration, grass density, and solution pH was evaluated. The toxicity of Cr(VI) to the grass was observed at concentrations ≥ 30 ppm as demonstrated by the drying up of the aboveground biomass of the plants. High grass density (15 vetiver slips) resulted in faster and more efficient Cr(VI) removal regardless of the initial concentration. However, faster removal (100% in 26 d) was attained for the 5 ppm solution compared to 82% removal in 30 d for the 30 ppm Cr(VI) solution. Cr(VI) remediation was favored under acidic conditions with 100% removal being attained within 20 d for the 30 ppm solution. The distribution of Cr(VI) within the grass structure was also investigated. At low initial concentrations, most of the chromium was located in the subterranean component of the plants. However, as the concentration increased, the roots became saturated, and more Cr was accumulated in the leaf mass fraction (LMF). The results thus far have indicated that vetiver grass is a viable option for phytoextraction. Additionally, results showed that vetiver grass could be used in the phytostabilisation of heavy metal in aqueous solutions. The accumulation of the metal in the leaves indicates the possibility of utilising vetiver grass in the extraction and recovery of the metal for reuse by burning and reprocessing of ash. The latter is common practice in other industries such as the mining and refining of platinum and other platinum group metals (PGMs).