Determination of major biogeochemical processes in a denitrifying woodchip bioreactor for treating mine drainage

• At the Kiruna iron ore mine in northern Sweden, mine drainage and process water contain elevated concentrationsof nitrate (NO3−) from the use of ammonium nitrate fuel oil explosives. In order to investigate thetreatment capacity of a denitrifying woodchip bioreactor technique for the removal of NO3− through denitrification,a bioreactor was installed at the mine site in 2015 and operated for two consecutive years. Neutral-pHmine drainage and process water containing 22 mg NO3−-N and 1132 mg SO42− (average) was passed throughthe bioreactor which was filled with a reactive mixture of pine woodchips and sewage sludge, at treatmenttemperatures ranging between 0.8 and 17 °C. At bioreactor temperatures above ∼5 °C, NO3− removal proceededto below detection limits (0.06 mg N L−1) without substantial production of nitrite (NO2−), ammonium(NH4+), nitrous oxide (N2O), or methane (CH4). The relative production of NH4+ and N2O to the NO3− reducedincreased as bioreactor temperatures decreased below ∼5 °C. Based on the resultant changes in alkalinity andpH from the production of bicarbonate (HCO3−) and carbonic acid (H2CO3), a stoichiometric mass balancemodel indicated that denitrification, nitrate reduction to ammonium (DNRA), sulfate reduction, and fermentationwere the major biogeochemical processes controlling pH, alkalinity and nitrogen, sulfur and carbonconcentrations in the system. It is suggested that fermentation changed from being mainly butyrate producing toacetate producing with time, triggering a decline in biogeochemical process diversity and leaving denitrificationas the sole major electron accepting process.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

Nyckelord

Denitrification

sulfate reduction

DNRA

woodchip bioreactor

temperature

biogeochemical processes

mine drainage

nitrogen

denitrifikation

sulfatreduktion

DNRA

bioreaktor med träflis

temperatur

biogeokemiska processes

gruvvatten

kväve

Hydrology

Hydrologi

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