The use of hay and sawdust to promote the removal of selenium and nitrate in coal mine drainage: A saturated up flow column experiment

A saturated up-flow column experiment was conducted to compare the ability of locally-available organic amendments (hay and sawdust) to foster reducing conditions and attenuate permit-exceeding concentrations of sulfate, nitrate, and selenium in effluent from a British Columbia coal mine. Mine effluent was continuously passed through columns containing one or both amendments mixed with mine-sourced rock, and indicators of organic decomposition and redox conditions were quantified in influent and effluents. Over the 180-day trial, effluent from hay-amended columns exhibited the highest removal of target parameters (up to 99.9%, 98.6%, and 77.5% removal of nitrate, selenium, and sulfate, respectively), although performance decreased over time, suggesting possible long-term performance concerns. In contrast, sawdust-amended columns fostered only partial denitrification and no sulfate removal, which could be linked to the more recalcitrant nature of the organic matrix. Effluents from all columns amended with organics would require further treatment before discharge to a receiving environment.