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TECHNICAL REPORTS

Heavy Metals in the Environment

Bioconversion of Selenate in Methanogenic Anaerobic Granular Sludge

^a Sub-department of Environmental Technology, Wageningen University, P.O. Box 8129, EV Wageningen 6700, The Netherlands
^b National Research and Development Institute for Environmental Protection, Splaiul Independentei 294, Bucharest 77703, Romania
^c Laboratoire des Géomatériaux et Géologie de l'Ingénieur; Université de Marne la Vallée; Institut Francilien des Sciences Appliquées, Bât. IFI; 5, Boulevard Descartes-Champs sur Marne; 77454 Marne La Vallée, Cedex 2, France

^* Corresponding author (piet.lens{at}wur.nl)

Received for publication November 30, 2005. The capacity of anaerobic granular sludge to remove selenate from contaminated wastewater was investigated. The potential of different types of granular sludge to remove selenate from the liquid phase was compared to that of suspended sludge and contaminated soil and sediment samples. The selenate removal rates ranged from 400 to 1500 µg g VSS^–1 h^–1, depending on the source of biomass, electron donor, and the initial selenate concentration. The granular structure protects the microorganisms when exposed to high selenate concentrations (0.1 to 1 mM). Anaerobic granular sludge "Eerbeek," originating from a UASB reactor treating paper mill wastewater, removed about 90, 50, and 36% of 0.1, 0.5, and 1 mM of Se, respectively, from the liquid phase when incubated with 20 mM lactate at 30°C and pH 7.5. Selenite, elemental Se (Se^o), and metal selenide precipitates were the conversion products. Enrichments from the anaerobic granular sludge "Eerbeek" were able to convert 90% of the 10-mM selenate to Se^o at a rate of 1505 µg Se(VI) g cells^–1 h^–1, a specific growth rate of 0.0125 g cells h^–1, and a yield of 0.083 g cells mg Se^–1. Both microbial metabolic processes (e.g dissimilatory reduction) as well as microbially mediated physicochemical mechanisms (adsorption and precipitation) contribute to the removal of selenate from the Se-containing medium.

Abbreviations: VSS, volatile suspended solids • Se^o, elemental selenium

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