Selenium speciation in anaerobic granular sludge

Abstract

Chromatographic (IC-CD, GC-FID) and spectroscopic (XRD) techniques that allow the specific determination of several selenium species present or formed during bioremediation processes of selenate contaminated drinking, ground, or wastewaters have been established. The developed techniques are shown to be applicable in determining selenium species in the range of target concentrations for emissions and are thus appropriate to characterize bioremediation processes. The applied techniques offer advantages regarding short analytical times without loss of satisfactory accurateness towards more sophisticated methods. By means of IC-CD, selenate and selenite can be detected specifically to concentrations far below allowance levels for metal finishing industries (20 µg L⁻¹ selenate, 40 µg L⁻¹ selenite) within 16.0 min. Thus, the removal of selenate from the liquid phase by anaerobic granular sludge was quantified by IC-CD, and the concomitantly formed red precipitates were analysed by XRD. Hexagonal elemental selenium was found to be present in the XRD analysis. Even if the precipitate contained iron and zinc, as shown by ICP-OES, no iron- or zinc-containing selenium minerals were detected by XRD. The GC-FID method described determines dimethylselenide and dimethyldiselenide at a detection limit of 1 ng and 2 ng, respectively, without further chemical derivatization within 7.4 min. Thus, the GC-FID offers adequate detection of two major volatile organic selenium species potentially formed during bioremediation of selenium contaminated waters.

Keywords:

• Selenate
• Selenite
• Elemental selenium
• Dimethylselenide
• Dimethyldiselenide
• UASB

Acknowledgements

We greatly acknowledge Geert Meijer, for the assistance in developing the IC method, and Hillion Wegh, for the support during the development of the GC method. We thank Dr. Marcel Giesbers, for the conduction of the XRD analysis, and Lar Iglesias, for proofreading the manuscript.