Food Waste to Feed-Stock Chemicals, Using Microbial Consortia and Bio-Hybrid Fuel Cells

Tuesday, 3 October 2017: 10:00
National Harbor 10 (Gaylord National Resort and Convention Center)
D. M. Mackie, J. P. Jahnke, M. S. Benyamin, H. M. LeFors, and C. J. Sund (Army Research Laboratory)
Some microorganisms secrete abundant amounts of diverse enzymes, either naturally or through genetic engineering, that can break down components of food waste (or biomass generally). Simple sugars are thereby produced in solution, where fast-fermenting microorganisms can metabolize them much faster than the secretory microorganisms, producing biofuels. (For example, consortia of the mold Aspergillus oryzae and the yeast Saccharomyces cerevisiae on uncooked rice achieve concentrations of 13% ethanol in 10 days at room temperature.) Secretor-fermenter consortia can be directly coupled with fuel cells (FCs), producing electricity and feedstock chemicals. However, long-term operation of such “bio-hybrid FCs” (BHFCs) requires strictly preventing the microorganisms and FC from harming themselves and each other. This can be accomplished by using gas stripping to continually and selectively extract the (volatile) biofuel from the fermentation medium, and to vapor-feed the FC. This protects the FC from the (non-volatile) catalyst poisons in the fermentation. This also protects the consortium from any harmful FC products (e.g., acetic acid) and from build-up of biofuels, which are inhibitory at high concentrations. We first show that power densities for vapor-fed direct ethanol fuel cells (DEFCs) are comparable to those for liquid-fed DEFCs, with power densities greater than 2 mW/cm2 obtained (orders of magnitude higher than microbial FCs). We then show that mold-yeast-DEFC BHFCs fueled with glucose (or rice) can operate for long periods with no maintenance other than adding water and food. With the right conditions and DEFC, the effluent can be acetic acid at high concentrations and with few impurities. Other effluents from BHFCs are possible, depending on the organisms, food, and FC.