Nitrification of arsenic-containing mining waters

The oxidation of arsenic-containing minerals in mine sites results in the spreading of arsenic into the environment. In gold mining, arsenic often co-occurs with ammonium deriving from the degradation of cyanide used for gold recovery. In the present work, batch bioassays were used for assessing the feasibility of maintaining nitrification in presence of arsenic. Ammonium was completely oxidized even at total As concentrations up to 100 mg/L. At 150 and 200 mg/L of dissolved As, nitrification was partially inhibited resulting in 75% of ammonium oxidation. As(III) was chemically oxidized to As(V) during the first 3h alleviating nitrification. Candidatus Nitrospira defluvii and other species belonging to Nitrospirae were the main nitrifying microbial species revealed by PCR/DGGE analyses. In summary, microorganisms tolerated high As levels making nitrification a potent process for ammonium oxidation in mining waters.