Analysis of microbial diversity of inocula used in a five-face parallelepiped and standard microbial fuel cells

This work had a double purpose: (i) to study the effect of sulphate-reducing (SR-In) and enriched (E-In) inocula on the characteristics of one-chamber standard microbial fuel cell (MFC-S) and parallelepiped cell and (ii) to analyze the bacterial communities in cells operated with either SR-In or E-In. The MFC-S of 150 mL consisted of one-chamber plexiglass cell with electrodes separated 7.8 cm. The MFC-P consisted of a parallelepiped built in plexiglass with a liquid volume of 270 mL. Five faces of this cell were fitted with ‘sandwich’ cathode–membrane–anode assemblages (CMA). The values of internal resistance (Rint) were 4602 and 687 Ω, for the MFC-S loaded with SR-In and E-In, respectively. The values of Rint were 400 and 84, and 292 and 80 Ω for the faces connected in series and parallel and the MFC-P loaded with SR-In and E-In, respectively. Parallel connection of cell faces also significantly improved the electrochemical characteristics of the P cell (higher powers). In general, use of E-In in both types of MFC lead to improved power densities compared to SR-In. Molecular biology analysis of microbial communities showed that the E-In was less diverse than SR-In (in terms of phyla). An electrochemically active bacterium Geovibrio ferrireducens belonging to phylum Deferribacteres was found in the E-In. Predominance of Deferribacteres was observed in the E-In. Members of this phylum were not found in the SR-In.

► We evaluated the effect of two types of inocula on the characteristics of MFCs. ► Molecular analysis showed presence of iron-reducing bacteria in enriched inoculum. ► The enriched inoculum improved the characteristics of MFCs used in this work. ► The 5-face MFC leads to reduction of internal resistances compared to standard cell. ► Low species richness and low-to-moderate evenness of the inocula used in this work.