Removal of ammonium and nitrate from cold inorganic mine water by fixed-bed biofilm reactors

Nitrogenous compounds, e.g. ammonium and nitrate, from various sources in extractive industry are often discharged with mine water to the aquatic environment. Ammonium and nitrate in blasting agents can dissolve in water from undetonated explosives and the nitrogenous compounds can negatively affect receiving water bodies. In this laboratory study, the removal of ammonium and nitrate from cold inorganic mine water was achieved by fixed-bed biofilm reactors at temperatures as low as 5 °C. Water from two underground mines was treated for ammonium removal in a nitrifying bioreactor. Ammonium concentration was from 2 to 83 mg NH4+–N/l. The sodium and chloride ion content was up to 0.8 and 2.2 g/l, respectively. At 5 °C, nitrification of up to 98% was reached at load of 0.33 g NH4+–N/m2/d. The highest applied load was 2.42 g NH4+–N/m2/d. The feed to the denitrifying bioreactor contained 12 to 86 mg NO3-–N/l. The anoxic methanol-fed denitrifying bioreactor reached up to 95% nitrate removal at loads as high as 0.91 kg NO3-–N/m3/d and in combination with an anoxic unit a surface load of 4.26 g NO3-–N/m2/d was applied at 5 °C. This is the first report on high-rate removal of ammonium and nitrate from cold inorganic mine water by fixed-bed biofilm reactors at low temperature.