Field-scale denitrifying woodchip bioreactor treating high nitrate mine water at low temperatures

摘要

A field-scale woodchip bioreactor was installed at the Kiruna iron ore mine (northern Sweden) for the removal of NO_3 in mine and process water originating from the use of ammonium nitrate based explosives. Over a period of two years, the woodchip bioreactor removed an average incoming NO concentration of 22.o±o.3 mg N L~(-1) to below detection limits (0.06 mg N L~(1)) at bioreactor temperatures above 5°C and hydraulic residence times between 1.9-2.6 days. As the hydraulic residence time in the system was decreased to 1 day and/or the bioreactor temperature decreased to below 5°C, NO_3~- removal was incomplete. The bioreactor acted as an overall sink and source of NO, and NH_4~+, respectively, with low level ammonium production (< 1 mg N L~(-1)) observed during the test period. The direct application of a woodchip bioreactor for the removal of NO_3 in leachate produced from waste rock deposits in subarctic climates is limited by the variability and timing of leachate production.