Effects of architectural changes and inoculum type on internal resistance of a microbial fuel cell designed for the treatment of leachates from the dark hydrogenogenic fermentation of organic solid wastes

Abstract

A new design of a single chamber MFC-A based on extended electrode surface (larger σ, specific surface or surface area of electrode to cell volume) and the assemblage or ‘sandwich’ arrangement of the anode-proton exchange membrane- cathode (AMC arrangement) and a standard single chamber MFC-B with separated electrodes were tested with several inocula (sulphate-reducing, SR-In; methanogenic, M-In, and aerobic, Ab-In) in order to determine the effects on the internal resistance R int and other electrical characteristics of the cells. In general, the R int of the new design cell MFC-A was consistently lower than that of the standard MFC-B, for all inocula used in this work. Resistances followed the order R int,SR-In < R int,M-In ≪ R int,Ab-In. These results were consistent with reports on reduction of ohmic resistance of cells by decreasing inter-electrode distance. Also, the volumetric power P V output was higher for the MFC-A than for MFC-B; this was congruent with doubling the σ in the MFC-A compared to MFC-B. Yet, power density P An delivered was higher for MFC-A only when operated with SR-In and Ab-In, but not with M-In. The MFC-A loaded with SR-In showed a substantial improvement in P V (ca. 13-fold, probably due to the combined effects of increased σ and decreased of R int) and a 6.4-fold jump in P An compared to MFC-B. The improvement was higher than the expected improvement factors (or algebraic factors; 6.5 improvement expected for P V due to combined effects of increase of σ and lowering the R int; 3.25 improvement expected for P An due to lowering the R int). Our results point out to continuing work using the two-set, sandwich-electrode MFC and sulphate-reducing inoculum as a departing model for further studies on effects of inoculum enrichment and electrode material substitution on cell performance. Also, the MFC-A model seems to hold promise for future studies of bioelectricity generation and pollution abatement processing leachates produced during biohydrogen generation in dark fermentation processes of organic solid wastes.