Selenium Treatment of Mine Water Effluent in a Fluidized Bed Reactor (FBR)

摘要

A pilot study was conducted to evaluate Selenium (Se) removal from a surface coal mineeffluent stream by a biological fluidized bed reactor (FBR). FBR treatment technology is wellproven for nitrate and perchlorate removal and utilizes heterotrophic facultative bacteria that useoxidized selenium species as electron acceptors and reduce them to elemental Se underanoxic/anaerobic conditions. The FBR pilot demonstrated consistent dissolved Se reduction tobelow the required NPDES discharge limits (4.7 μg/L monthly average limit and 8.2 μg/L dailymaximum) during eight weeks of steady-state operations. However, the average total Se was11.6 μg/L, which is above the discharge limit. Tertiary treatment (e.g., media filtration,clarification, etc.) of the FBR effluent will be required to remove the Se-containing suspendedsolids to achieve compliance for total Se. Full-scale design also would require influent heating tomaintain the minimum reactor temperature in the range of 50 to 55 °F during winter months anda tertiary treatment step to reduce the residual excess soluble effluent biochemical oxygendemand (BOD) to acceptable discharge levels. Results of the pilot study were used to definegeneral design parameters such as hydraulic retention time (HRT), electron donor (organiccarbon) dosage, nutrient requirements, and sludge production for full-scale FBR design.