Anoxic Biotreatment Cell (Abc) for Removal of Nitrate and Selenium From Mining Effluent Waters

Abstract

Removal of nitrate from mining and other industrial and municipal effluents is often required to meet water discharge limits, and state and federal nondegradation standards for surface water and groundwater. To meet the need to remove nitrate from low-temperature waters, a technology termed the Anoxic Biotreatment Cell (ABC) was developed by Hydrometries, Inc. beginning in 1995. A large demonstration-scale ABC operating at a metal mine in Montana since early 1996 has consistently removed over 90 percent of the incoming nitrate when operated at design conditions. Typical results were 95 percent nitrate removal at a flow rate of 130 gallons per minute (gpm) and a water temperature of 12°C. The reactor also operated successfully at flow rates as high as 160 gpm and water temperatures as low as 2'C. The initial reactor was modified in 1997 to reduce downtime and to increase capacity to approximately 400 gpm. A 200-gpm ABC to treat water with higher nitrate concentrations (llO mg/L as N) has successfully operated at another mine site since 1997. Removal of low concentrations of metals and sulfate have also been demonstrated in a full-scale ABC application. The ABC has removed selenium in continuousflow column experiments, from approximately 1.2 mg/L to less than 0.1 mg/L. The ABC is less costly than alternative treatment technologies because it: a) is simple in design, construction and operation, b) is effective at cold water temperatures, and c) does not generate a waste stream. The system can be designed to treat a variety of flows, concentrations, water temperatures and water qualities.