Remediation of acid mine drainage-impacted water by vetiver grass (Chrysopogon zizanioides): A multiscale long-term study

Abstract

Acid mine drainage (AMD) is an acidic discharge from mining sites that contains elevated levels of metals and sulfate (SO42−). AMD can inflict health and environmental dangers through metal toxicity and physical stress. Current methods for AMD treatment, including chemical or passive biological treatments, are often non-sustainable owing to expense, require continuous maintenance, or are unsuitable for prolonged treatment. Our ultimate goal is to develop a cost efficient and sustainable floating treatment wetland system using vetiver grass (Chrysopogon zizanioides). Year-long large- and small-scale hydroponic experiments were used to determine the effectiveness of vetiver for treating AMD-impacted waters from the Tab-Simco mine site in southern Illinois. For the large-scale mesocosmic study, vetiver rafts were suspended in 100-gallon containers. Water quality was monitored by chemical analysis of samples every 28 days and at the end of the experiment (364 days); plant health was monitored by measuring changes in biomass and recording visual changes in root and shoot coloration and morphology. There was higher net removal of Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), SO42− (28%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). Metals were mainly localized on the root surface as Fe plaques, whereas Mn and Zn showed greater translocation from root to shoot. Furthermore, toxicity characteristic leaching procedure showed that vetiver biomass was not hazardous waste as a result of metal accumulation. From the small-scale experiment, there was near complete removal of SO42− (91%) and metals (90–100%) with the exception of Pb (15%) and Cu (0.0%). These experiments demonstrate that vetiver can effectively remediate AMD-impacted waters over an extended period of time.