Under the present investigation phytoremediation of mercury and arsenic from a tropical open cast coalmine effluent was performed. Three aquatic macrophytes Eichhornia crassipes, Lemna minor and Spirodela polyrrhiza removed appreciable amount of mercury and arsenic during 21 days experiment. Removal capacities of these macrophytes were found in the order of E. crassipes > L. minor > S. polyrrhiza. Translocation factor (shot to root ratio of heavy metals) revealed low transportation of metals from root to leaves leading higher accumulation of metals in root as compared to leaves of the plant. It was evident from plant tissue analysis that mercury and arsenic up take by macrophytes had deteriorated the N, P, K, chlorophyll and protein content in these macrophytes. Correlations between removal of arsenic and mercury from mining effluent and its increase in plant parts were highly significant. Results favoured selected species to use as promising accumulator of metals.

Temporal changes in microbial community function (enzymatic activities) and structure (phospholipid fatty acids) were studied in a post-mining chronosequence of coal discard sites of different rehabilitation ages. The objective was to determine whether temporal changes in microbial community function and structure were related to rehabilitation age or management practices. No trends consistent with the rehabilitation ages (1 to 11 years) of the respective sites were observed. A canonical correspondence analysis showed that sites clustered according to the time of sampling irrespective of their individual rehabilitation ages. Sites sampled in 2002 clustered together, while sites sampled in 2004 and 2005 clustered separately from the 2002 sites. This corresponded with a change in management practices applied after 2002. Dehydrogenase, β-glucosidase, acid phosphatase, and alkaline phosphatase activities for all sites were higher after 2002. Urease activities were lower after 2002, with the exception of Site 3 (4 years old in 2002). Phospholipid fatty acid data showed significant (p < 0.05) differences between sites of different rehabilitation ages over the study period. There was a decrease in microbial biomass in all sites from 2002 to 2004 but an increase in 2005. Fungal to bacterial abundance ratios for all sites decreased over the study period. The proportion of the total microbial community comprised of Gram positive bacteria increased from 2002 to 2005. These data show the value of microbial community function and structure to elucidate management effects that may not be apparent through traditional assessments of rehabilitation status such as aboveground indicators.

A biological source treatment (BST) technique using remote sensing and biogeochemistry has been developed to address acid mine drainage (AMD) at its source. The BST technique utilizes down-hole injections of microbial inoculum and substrate amendments to establish a biofilm on the surface of metal sulfides (AMD source material). The treatment results in an elevated groundwater pH (from acidic to circum-neutral levels) and prevents further oxidation of AMD source material. The first 2 years of an ongoing field study of the BST technique at a reclaimed coal mine in central Tennessee (USA) has produced successful results. For instance, the water chemistry in a monitoring well down-gradient from injection wells has improved substantially as follows: the pH increased 1.3 units from 5.7 to 7.3, the dissolved (0.45 μm-filtered) iron concentration decreased by 84% from 93 to 15 mg/l, the conductivity decreased by 379 μS/cm, and sulfate decreased by 78 mg/l. Electromagnetic induction surveys were conducted to identify AMD source material and monitor BST performance by measuring changes in subsurface resistivity throughout the site. These surveys revealed a treatment zone created between injection wells where the resistance of contaminated groundwater from up-gradient AMD sources increased as it flowed past injection wells, thus, suggesting this technique could be used to treat AMD sources directly or to intercept and neutralize sub-surface AMD.