5-07: Bioconversion of brown seaweed into mixed ketones through carboxylate platform processing

One configuration of carboxylate platform processing makes use of an acidogenic digestion process that applies a mixed culture inoculum for conversion of biomass into carboxylic acids. Several advantages of mixed cultures compared to conventional bioprocessing include: non-sterile fermentation, the use of inexpensive tanks, adaptability to a wide variety of feedstocks and no need for added hydrolytic enzymes. The products of mixed organic acid fermentation can then be converted into mixed ketones through neutralization and a thermal deoxygenation process. Finally, mixed alcohols can be generated by hydrogenating the mixed ketones.

Brown seaweed, one of the most abundant biomass resources in the world, was selected as the feedstock in this project, for which mixed ketones will be the final product. The fermentation condition of 37 ℃ with lime pretreatment was demonstrated in previous research as being the most efficient out of four different fermentation conditions: temperatures of 25 or 37 ℃, with or without lime pretreatment. Organic acids and mixed ketones were successfully produced through the acidogenic digestion and the thermo-decomposition processes. Four more fermentation conditions were conducted in a new set of fermentations to test the effect of calcium carbonate as the buffer instead of ammonium bicarbonate and the use of a mixed culture enriched with C. acetobutylicum as an aid to decomposing mannitol, which an abundant carbohydrate in kelp that proved recalcitrant in previous fermentations.

Keywords:  Acidogenic digestion, biofuels, carboxylate platform, macro algae, Saccharina latissima