Pilot Testing of Selenium Removal in a Surface Coal Mine Water Containing High Nitrate and Selenium Concentrations

Pilot testing of an anoxic fluidized bed reactor (FBR) technology for selenium (Se) removal from runoff water at Teck Coal Limited's Line Creek mining operation was conducted in 2011. Based on pilot testing results, a subsequent conceptual treatment alternatives evaluation identified FBR based treatment to be the most feasible and cost effective technology for full scale application. FBR treatment utilizes heterotrophic facultative bacteria that use oxidized Se species as electron acceptors and reduce them to elemental Se under anoxic/anaerobic conditions. Results from pilot testing of the FBR for Se treatment followed by a Moving Bed Bioreactor (MBBR) for organics polishing are discussed. The FBR was tested at two different hydraulic retention times (HRT) and with two different electron donors (organic carbon) to better understand the impact of these variables on Se removal. With a 60 minute HRT and MicroCg (an engineered organic carbon) as the carbon source, the FBR effluent was able to meet the target filtered Se concentration of ≤10 μg/L. MBBR results confirmed that the system achieved the necessary organics polishing required to meet potential future biochemical oxygen demand (BOD) limit. A liquid-solids separation step would be required between the FBR and MBBR for removal of biological solids containing elemental Se, to prevent reoxidation to soluble Se in the aerobic MBBR. Results of the pilot study were used to define general design parameters such as HRT, electron donor dosage, nutrient requirements, and sludge production for full-scale FBR design.