Performance of Mixed Organic Substrates during Treatment of Acidic and Moderate Mine Drainage in Column Bioreactors

Abstract

Mushroom compost, wood chips, sawdust, cow manure, and rice straw were characterized and tested in three combinations as prospective substrates during the treatment of acidic (pH 3) and moderate (pH 6) mine drainage in 3.5 L column bioreactors operated for 167 days, at 3 days of hydraulic retention time. Mixtures gave comparable performances in each pH condition with satisfactory efficiencies. After less than a 2-week acclimation period, bacteria became active, as indicated by a pH increase and sulfide production. Dissolved organic carbon (DOC) consumption was higher in acidic condition, whereas sulfate removal mainly occurred in the early reaction period. There were significant differences in the sulfate and DOC results from acidic relative to moderate mine drainage columns. Aluminum was readily removed (nearly 100%) by all the reactors. Iron removal was better for acidic (98–99%) than for moderate (73–85%) mine drainage. Manganese, mostly leached out from substrate materials, prevailed in early reaction times, followed by a steady decrease toward the end. Results demonstrate the potential utility of mixed substrates for enhancing the performances of bioreactors for mine drainage treatment. However, longer lasting times of DOC would characterize the moderate mine drainage condition.