Abstract

Microbial selenium reduction was investigated for application in the removal of selenium from industrial waste water. This paper presents the results of the development of a routine ICP-MS method for the determination of inorganic selenium species in microbial-treated industrial waste water. For the speciation of water soluble inorganic selenium species (selenate and selenite) two different anion exchange columns were compared. The column separation performance for the determination of selenium was investigated for both inorganic and some organic selenium species. The increase in sensitivity for selenium after the addition of carbon-containing solutions was investigated by the addition of increasing amounts of ethanol to the eluent. The optimum addition level of 2% v/v ethanol resulted in a sensitivity enhancement factor of 5 under the given instrumental settings of the ICP-MS. The ICP-MS instrument showed good long-term stability (3% over 40 h), as shown by the analysis of two independent control standards after every 10 samples with addition of arsenobetaine as the internal standard. The different selenium species showed the same signal sensitivity, resulting in a quantification limit of 1 µg l⁻¹ per species. Over 600 microbial-treated waste water samples were characterized for selenate and selenite content. A selenium compound present in some of the samples could not be identified. No evidence of DL-selenocystine and DL-selenomethionine and DL-selenoethionine could be found. The microbial removal of selenium from industrial waste water was at first hampered by the presence of nitrate (denitrification) and the partial reduction of selenate was observed after the complete removal of selenite to the metallic form.