Evaluation Of Water Treatment Residuals and Vetiver Grass for Treating Acid Mine Drainage

Surface mining is important to our modern way of life and to coal mining in the United States of America. Unfortunately old and new surface mining sites produce a metal-rich acidic solution termed acid mine drainage (AMD), which contaminates water and soil. Acid sulfate soil is unstable and prone to erode, and spreading this acidic sulfate–rich liquid across mine sites may increase the amount of AMD that can be generated. The current study focused on evaluating two affordable passive treatments of AMD and AMD-impacted water which could be used together to construct a semipermeable membrane for erosion control of acidic soils, immobilization of heavy metals, and to increase the pH. The first treatment was the land application of an inexpensive industrial by-product, drinking water treatment residuals (WTRs) to treat AMD with its alkalinity and metal binding affinity. The second treatment, intended for placement behind the WTR to clean metal-contaminated water and provide erosion control was the perennial grass, sunshine vetiver (Chrysopogon Zizanioides). Sunshine vetiver is fast-growing, non-invasive, extremely tolerant of adverse AMD conditions, and a hyperaccumulator of some metals. In this experiment, all the sunshine vetiver grasses were able to grow in the practical mixtures of WTR and AMD-soil considered. With exposure to acidity the investigated WTRs released greater amounts of toxic heavy metals, the RCRA8 metals and aluminum, than ideal for use as a soil amendment on AMD sites.