T11 PM Developments in Bioremediation of Acid Mine Drainage Wastes
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 343-344

(LEN-1122-315836) Optimization of bioremediation processes for selenium contaminated wastewaters using anaerobic granular sludge.

Lenz, M¹, Gmerek, A¹, Lens, P.N.L.¹, ¹ Department of Environmental Technology, Wageningen University

ABSTRACT- One component in the "cocktail" of environmental hazardous substances contained in mine drainage is selenium (Simmons et al., 2002). The importance of selenium in environmental research is related to the fact that it shows only a marginal line between the nutritious optimum (as an essential element) and toxic effects upon exposure. In order to treat metal contaminated wastewaters, different physical/chemical and biological processes have been investigated. During the process of dissimilatory metal reduction, bacteria conserve energy by transferring electrons originating from the degradation of organic compounds, H2 or elemental sulfur to soluble oxy-anions of metals, which form a solid phase and thus can be removed from polluted waters This process can be used in order to convert selenate and selenite to elemental selenium. Selenium conversions are influenced by sulfate, but literature gives contradictory information about these influences. Hockin et al. (2003) describe the reduction of selenite to elemental selenium as a combination of a biological and chemical process (via biogenic sulfide). Bebien et al. (2002) state that uptake of selenate uses sulfate-permease. Both findings described make the stimulation of selenium oxyanion conversion possible by stimulation of sulfate reducing bacteria (SRB). On the other hand selenate is described to be a specific inhibitor for SRBs. Consequently, an intensive investigation of the influence of sulfate on selenium conversions is necessary. Therefore anaerobic granular sludge originating from an Upflow Anaerobic Sludge Blanket (UASB) Reactor was tested towards its removal capacity for selenium. In this study, optimization of the process by stimulating the activity of SRB was investigated by testing different feeding patterns for sulfate. Special attention was given to the influence of the redox-potential. Selenate reduction was slightly higher, when sulfate reduction in the granules was stimulated. Furthermore, it was shown that 0.5 mM selenate is indeed highly toxic to sulfate reduction.

Key words: sulfate reducing bacteria, dissimilatory metal reduction