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Sulphate reducing bacteria: Cathodic catalyst in membraneless microbial fuel cells

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Sulphate reducing bacteria: Cathodic catalyst in membraneless microbial fuel cells

Questo lavoro evidenzia le correlazioni tra le popolazioni micorbiche anaerobiche ed il ruolo central che i batteri solfato-riduttori possono svolgere nella catalisi del processo catodico in celle a combustibile microbiche alimentate con reflui grezzi di depuratore e acetato di sodio (3 g/L).

Microbial communities operating on electrodes of membraneless microbial fuel cells were sampled and analysed using the fingerprinting molecular technique DGGE (Denaturing Gradient Gel Electrophoresis). The microbial fuel cells were inoculated with raw wastewater coming from a municipal plant of the city of Milan and fed with sodium acetate 3 gL-1. At the end of the test, lasted three months, a cluster analysis based on presence/absence and similarity data showed that species of anodic and cathodic biofilm did not differ significantly. Although the cells were built with air-exposed cathodes, the dominant microbial populations sampled inside the cathodes, as well as on anodes, were anaerobic, in agreement with the almost low-negative open circuit potential of electrodes. Anodic communities shared with the cathodic biofilms Spirochaetes, Sulphate Reducing Bacteria (SRBs) and photosynthetic purple non-sulphur bacteria (PNSs). Geobacteriaceae-related microbial populations were found prevalently in anodic communities, as resulted by the classification of band sequences. The results suggest a central role of SRB metabolism at the cathode, alone or in synergy with the other microrganisms found (Spirochaetes and PNSs).  The anaerobic communities of bacteria operating in membraneless single chamber MFCs, SRBs in particular, seem capable to activate power generation by reactions that involve a cyclic red-ox reactions of sulphur compounds (sulphate-sulphide) through the cathode, as well as the direct oxygen reduction to water. The mechanism of cathodic reaction activation by metabolism of SRBs  is debated [1, 2].

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