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Water Science & Technology Vol 65 No 10 pp 1875–1881 © IWA Publishing 2012 doi:10.2166/wst.2012.030 The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludgeJan Bartacek, Fernando G. Fermoso, Frank Vergeldt, Edo Gerkema, Josef Maca, Henk van As and Piet N. L. LensPollution Prevention and Control Care, UNESCO-IHE, P.O. Box 3015, 2601 DA Delft, The Netherlands E-mails: j.bartacek@unesco-ihe.org; jan.bartacek@vscht.czDepartment of Water Technology and Environmental Engineering, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic Sub-department of Environmental Technology, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands and Instituto de la Grasa (C.S.I.C.), Avda. Padre García Tejero 4, 41012 Sevilla, Spain Department of Agrotechnology and Food Sciences, Laboratory of Biophysics and Wageningen NMR Centre, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands ABSTRACT Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA]2−) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations. Keywords: anaerobic granular sludge; bioavailability; essential metals; magnetic resonance imaging; metal speciation; metal toxicity; UASB reactor eProduct: Buy this article for £24.00 (IWA MEMBER PRICE: £18.00) All prices include VAT. For customers where VAT should not be applied, the VAT amount will be removed upon payment |
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