Background
Microbial fuel cells (MFC) and microbial electrolysis cells are electrical devices that treat
water using microorganisms and convert soluble organic matter into electricity and
hydrogen, respectively. Emerging cellulosic biorefineries are expected to use large
amounts of water during production of ethanol. Pretreatment of cellulosic biomass
results in production of fermentation inhibitors which accumulate in process water and
make the water recycle process difficult. Use of MFCs to remove the inhibitory sugar and
lignin degradation products from recycle water is investigated in this study.
Results
Use of an MFC to reduce the levels of furfural, 5-hydroxymethylfurfural, vanillic acid, 4-
hydroxybenzaldehyde and 4-hydroxyacetophenone while simultaneously producing
electricity is demonstrated here. An integrated MFC design approach was used which
resulted in high power densities for the MFC, reaching up to 3700mW/m2 (356W/m3 net
anode volume) and a coulombic efficiency of 69%. The exoelectrogenic microbial
consortium enriched in the anode was characterized using a 16S rRNA clone library
method. A unique exoelectrogenic microbial consortium dominated by -Proteobacteria
(50%), along with -Proteobacteria (28%), -Proteobacteria (14%), -Proteobacteria
(6%) and others was identified. The consortium demonstrated broad substrate
specificity, ability to handle high inhibitor concentrations (5 to 20mM) with near complete
removal, while maintaining long-term stability with respect to power production.
Conclusions
Use of MFCs for removing fermentation inhibitors has implications for: 1) enabling higher
ethanol yields at high biomass loading in cellulosic ethanol biorefineries, 2) improved
water recycle and 3) electricity production up to 25% of total biorefinery power needs.