IC 9389 Passive Treatment Of Coal Mine Drainage

Passive methods of treating mine water use chemical and biological processes that decrease metal concentrations and neutralize acidity. Compared with conventional chemical treatment, passive methods generally require more land area, but use less costly reagents and require less operational attention and maintenance. Currently, three types of passive technologies exist: aerobic wetlands, organic substrate wetlands, and anoxic limestone drains. Aerobic wetlands promote mixed oxidation and hydrolysis reactions, and are most effective when the raw mine water is net alkaline. Organic substrate wetlands promote anaerobic bacterial activity that results in the precipitation of metal sulfides and the generation of bicarbonate alkalinity. Anoxic limestone drains generate bicarbonate alkalinity and can be useful for the pretreatment of mine water before it flows into a wetland. Rates of metal and acidity removal for passive systems have been developed empirically by the U.S. Bureau of Mines. Aerobic wetlands remove Fe and Mn from alkaline water at rates of 10-20 and 0.5- 1.0 g. m-2? d-1, respectively. Wetlands with a composted organic substrate remove acidity from mine water at rates of 3-9 g. m-2? d-1?. A model for the design and sizing of passive treatment systems is presented in this report.