Natural occurring spore-forming sulfate reducers and their influence on the bentonite barrier

To investigate the potential influence of natural occuring microorganisms within the bentonite on its minaralogical properties, we prepared anaerobic microcosm-experiments containing bentonite and a synthetic Opalinus Clay pore-water solution. Two different Bavarian bentonites (a natural and an industrial one) were incubated for one year at 30 °C and 60 °C and analyzed for bio-geochemical parameters and microbial diversity. For stimulation of microbial activity, some set ups were supplied with organics (acetate or lactate) or H2.
Only microcosms containing the industrial bentonite show striking effects. The presence of supplemented lactate or H2 led to the dominance (up to 81 %) of spore-forming Desulfosporosinus spp. – strictly anaerobic, sulfate-redung microorganisms. The respective microcosms show an increase of ferrous iron and a simoultaneous decrease of ferric iron as well as a decrease in sulfate-concentration. Concomitantly, the redoxpotential dropped and hydrogen-sulfide was fomed – leading very likely to the formation of the observed fractures and iron-sulfur precipitations. Furthermore, lactate-containing microcosms show the formation of acetate in the same amount as lactate was consumed. The here mentioned, microbial formed metabolites could affect the dissolution bahavior of minerals and ions within the bentonite and, thus, potentially change the sealant and adsorbent properties of the bentonite barrier.