Systematic Variation of Membrane Chemistry and Biofilm Composition in Strategic Modifications of Microbial Fuel Cells (MFC) and Other Bio-Electrochemical Systems (BES)

Microbial fuel cell (MFC) technology is under development for electricity production for cleansing of waste waters, but also for direct use of the electricity in bio-electrochemical systems (BES) geared to produce high added value products (e.g. acetate and other complex organics from CO₂).  The presentation will detail systematic examination of the chemical and biological variables in such systems. 

Both cation and anion exchange membranes of a range of controlled thickness as anode compartment and air cathode separator membrane will be outlined, with the accompanying variations in performance of otherwise similar cells.  Both types of membrane can be readily tailored by their production using radiation-induced grafting of appropriately functionalized precursors and subsequent conversion to ionic head groups with accompanying ion-exchange properties.

From extensive studies of a range of closely related MFCs, the role of variations in the composition of anode biofilms in operational MFCs have been characterized and compared to the population in suspension [1].  Film composition has been followed using DDGE, identifying the range of microbes present and variations in film composition during operation.  Diversity of the community has been found to correlate with cell performance, and hence can be used as a predictor of cell behavior [2].

Identification of the make-up of microbial communities in operating MFCs has led to studies of the electrogenic activities of individual strains, and of their interactions when more than one species is present, detecting synergistic or antagonistic relationships.  Data on microbial oxidative activity (metabolic profiling) using a range of substrates and a Biolog instrument (multi-well UV-vis spectrometer) have characterized the behaviors of a range of species (e.g. C. denitrificans and B. graminisolvens) not normally considered of significance for power production in MFCs, both as single strains and in combination.  “Synthetic communities” derived from these studies are indeed active in production of electricity in MFCs, with product analysis carried out by ion chromatography.

 A basic outline of the proposed metabolic profile of a synthetic community has been proposed, with individual species being classified as fermentative or electrogenic.  The presence of fermentative species may lead to higher power output, contrary to previous orthodoxy.

 The potential for use of a complex waste (distiller’s dried grains with solubles, DDGS) for production of electricity or in the bio-electrochemical production of high added value products is also under investigation, with useable power densities being achieved

Acknowledgements The UK’s SUPERGEN Biological Fuel Cells Consortium (8 univeristies) is led by RS and is funded by Research Councils UK (RCUK) under EPSRC grant EP/H019480/1.  Further work in MFC science at Surrey is funded by RCUK under EPSRC grant EP/I004882/1 and BBSRC grant BB/J01916X/1.

References

[1]    N Beecroft, F Zhao, JR Varcoe, RCT Slade, A Thumser, C. Avignone-Rossa.  Dynamic changes in the microbial community composition in microbial fuel cells fed with sucrose. Appl Microbiol Biotechnol. 93, 423 – 437 (2012).

[2]    J.P. Stratford, N.J. Beecroft, R.C.T. Slade, A. Gruning, C. Avignone-Rossa.  Anodic microbial community diversity as a predictor of the power output of microbial fule cells.  Bioresource Technol. 156, 84-91 (2014).