Sawdust-supported passive bioremediation of western United States acid rock drainage in engineered wetland systems

Economical remediation of acid rock drainage (ARD) at secluded high-altitud e western ore mines is difficult given the current treatment technology. Se veral passive-engineered systems that are based on wetland technology were tested in the laboratory with three western ore mine ARDs (Co, Cu and Fe mi nes) and with a copper leachate effluent. These systems used well-weathered lodgepole pine sawdust as the sole carbon source and mud from a pond at on e of the mine sites as the source of sulfate-reducing bacteria (SRB). Simpl e one pass flow-through systems removed 44% to 99% of the various heavy met als from the Co and Cu mine ARDs and increased the pH from 3 to 7 after 28 days of SRB acclimation with a five-day residence time. Carbohydrate utiliz ation rates were generally low: except for one 437-day run, which consumed 25%, 30% and 21 % of the cellulose, hemicellulose and lignin, respectively. Initial pH, amounts of toxic heavy metals and the degree of predegradation of the sawdust were found to significantly affect both remediation potenti al and acclimation time. Engineered SRB systems, alone or in combination wi th other passive technologies, offer promise for the economical remediation of western US ore mine ARDs.