Superfund Innovative Technology Evaluation (SITE)
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As part of the Superfund Innovative Technology Evaluation (SITE) Program, the U.S. Environmental Protection Agency (EPA) evaluated passive water treatment (PWT) technologies for metals removal from acid mine drainage (AMD) at the Summitville Mine Superfund Site in Southern Colorado.
PWT technologies have been demonstrated to be effective in removing high concentrations of metals (aluminum, copper, iron, manganese, and zinc) from AMD. These systems supply alkalinity to the mine drainage along with aeration to precipitate metals such as aluminum and iron as oxides and hydroxides (oxyhydroxides). The technology is waste-stream specific, requiring characterization of all organic and inorganic constituents. Two technologies were evaluated for this project: the Successive Alkalinity Producing System (SAPS), a PWT technology, and the Aquafix treatment system, which is a semi-passive treatment technology.
In consideration of the severity of the AMD quality at the Summitville site, an iron settling pond pretreatment system was constructed upstream from the SAPS pond. This pond provided a means to aerate the AMD, allowing oxidation and precipitation of ferric ion prior to SAPS treatment. From the Reynolds Adit collection sump, AMD was delivered as influent to the SAPS at a rate of 5 gallons per minute (gpm). This influent was aerated by passage through a spray nozzle to atomize the AMD as it settled into the pond. The iron, and potential co-precipitated metals, settled to the bottom of this pond prior to delivery into the SAPS.
The SAPS consists of a pond that contains three sections or layers: ponded water, compost, and crushed limestone. AMD effluent enters the pond just above the compost layer and flows down through the compost and limestone. Discharge from the SAPS enters a settling pond approximately 2 feet below the pond surface. Discharge from the settling pond was routed to a rock drain or limestone channel for final treatment (polishing).
The Aquafix system consists of a water wheel mechanical distribution system for addition of alkaline material to the AMD; ideally, the treated drainage stream would be delivered to a settling pond. The Reynolds Adit collection sump provided AMD influent for the Aquafix system at a rate of 19 gpm. Due to a lack of sufficient surface area at the site, Baker tanks were used in place of settling ponds. The Aquafix machine provides the addition of lime at a rate proportional to the AMD flow rate. After the lime has been added, the AMD is routed through a rock drain to promote mixing and dissolution of the lime and aeration of the AMD, which causes the metals to precipitate.
The results of the PWT technology evaluation demonstrated that the treatment systems removed the metals from the AMD. Removal efficiencies ranged from 11 percent to 97 percent for the SAPS, and as much as 97 percent to 99 percent for the Aquafix treatment system.
Economic data indicate that the costs for both the SAPS and Aquafix systems is $0.005 per gallon for the 25 gpm systems.Contact