Pretreated algal biomass fermentation generates value-added co-products and high-quality lipids during Combined Algal Processing

Algal biofuel processes are currently hampered by the high costs of biomass production. Converting protein and carbohydrates in post-extracted biomass residues to methane via anaerobic digestion is a low-value approach and only recovers a small amount of energy compared to their original fuel potential. Combined Algal Processing (CAP) helps to mitigate these costs by taking the novel approach of pretreating the harvested algal biomass to release carbohydrates as soluble and fermentable sugars while making lipids more extractable. The released sugars, predominantly glucose and mannose, are available for fermentation to value-added co-products prior to lipid extraction. After fermentation, ethanol or other fermentative co-products and lipids are sequentially recovered from the stillage. We have demonstrated the complete conversion of these sugars to ethanol at >85% yield in less than 18 hours. To investigate the production of higher value fermentation products, we also demonstrated production of succinic acid at 0.54 g succinic acid/g glucose. In addition, pretreated algal biomass is relatively non-toxic compared to pure sugar controls and does not require additional nutrients for rapid and robust fermentation indicating that pretreated algal slurry is a rich source of nutrients and sugars for fermentative microbes. Post fermentation, algal lipids were recovered at >80% yield through hexane extraction of the stillage. In summary, pretreated algal biomass is a readily fermented sugar source that can be utilized for the production of a variety of value-added co-products through fermentation. This process places algal biomass on the path towards economic and sustainable biofuels and bioproducts.