ELECTRO-BIOCHEMICAL REACTOR (EBR) TECHNOLOGY FOR SELENIUM REMOVAL FROM BRITISH COLUMBIA'S COAL-MINING WASTEWATERS

摘要

The weathering of coal mine waste rock releases iron, calcium, sulfate and associated trace elements like selenium [Se], which are introduced to seepage waters. Nitrogen species, such as nitrate and ammonia, are also found in association with coal-mining drainages mainly due to leaching of residual blasting compounds. Elevated concentrations of Se are a ubiquitous occurrence in coal mining environments in British Columbia, with values ranging from below 50 to over 500 ug/L in site waters. Selenate is the most common form of selenium found in waste rock seepages, and is exceedingly mobile in aerobic fresh waters. A major concern with waterbome Se in British Columbia is the potential for its bioaccumulation in aquatic food chains. Treatment to remove Se from coal-mining wastewaters has proven to be challenging for conventional water treatment technologies. Compounding this challenge, many streams are characterized by high flows and low selenium concentrations. Conventional membrane and ion exchange treatments produce concentrated brine streams that are difficult to treat or require disposal. Conventional biotreatment systems use excess nutrients to provide the required electrons to compensate for inefficient and variable electron availability, as well as to adjust reactor chemistry. The Electro-Biochemical Reactor (EBR) technology provides electrons to the microbes directly at a low voltage potential (1-3 V), supplying a controllable and consistent supply of useable electrons to the system and microbes at low current. In this manner, the EBR technology overcomes the shortcomings found in conventional systems, as it reduces the required nutrient addition and provides a more controllable, efficient, economical, and robust biotreatment system than found in past generations of biological treatment systems. Additionally, the EBR process does not produce excess solids or biomass; therefore, solids management post-treatment is not required. Laboratory EBR bench-scale and on-site pilot-scale systems were used to treat five British Columbia coal mine wastewaters; influent Se concentrations ranged from 35 ug/L to 531 ug/L. Se treatment targets for the tested waters ranged from 5 to 10 ug/L. Mean Se concentrations in EBR effluents ranged from 0.5 ug/L to 1.4 ug/L, while reducing sulfate concentrations. The test data demonstrate that the EBR technology is an effective Se removal option for British Columbia's coal-mining wastewaters.