The microbiology of passive remediation technologies for mine drainage treatment

Water draining abandoned mines or mine sites is often acidic and contains relatively high concentrations of dissolved metals and sulfate. Such water (AMD) arises from the oxidative dissolution of sulfidic minerals, such as iron pyrite (FeS2), exposed by mining activities. As AMD production can occur over a very long time scale, passive remediation systems are becoming increasingly important in the treatment of this wastewater. The passive remediation technology of choice to treat AMD from coal mines and coal spoils is compost wetlands. Using molecular-based techniques (based mainly on the 16S rRNA gene), we have followed, from the start-up phase, the changes in microbial populations of wetlands filled with different compost materials. While differences in the populations of the wetlands were evident initially, the populations converged as the wetlands aged. Microbes found to dominate in the early stages of operation were mainly cellulolytic, while sulfate-reducing microbes were detected in the later stages. The microbial composition data are being compared with those from mature wetlands to gain a fuller understanding of the evolution of microbial populations in compost wetlands.