Combined algal processing: A novel integrated biorefinery process to produce algal biofuels and bioproducts

TLDR

Integrated biorefineries that produce multiple products are essential for commercializing microalgal biofuels, and dilute‑acid pretreatment efficiently hydrolyzes carbohydrates to sugars while enhancing lipid extractability and generating a protein fraction for other uses. This study develops a simplified Combined Algal Processing (CAP) approach to increase total energy yield from microalgae. CAP feeds whole acid‑pretreated algal slurry directly into fermentation, then sequentially recovers ethanol and lipids from the broth via thermal treatment and solvent extraction. CAP utilizes nearly all fermentable sugars for ethanol without compromising lipid recovery and, according to techno‑economic analysis, cuts microalgal biofuel cost by $0.95 GGE (a 9 % reduction) compared to the previous scenario.

Abstract

The development of an integrated biorefinery process capable of producing multiple products is crucial for commercialization of microalgal biofuel production. Dilute acid pretreatment has been demonstrated as an efficient approach to utilize algal biomass more fully, by hydrolyzing microalgal carbohydrates into fermentable sugars, while making the lipids more extractable, and a protein fraction available for other products. Previously, we have shown that sugar-rich liquor could be separated from solid residue by solid–liquid separation (SLS) to produce ethanol via fermentation. However, process modeling has revealed that approximately 37% of the soluble sugars were lost in the solid cake after the SLS. Herein, a Combined Algal Processing (CAP) approach with a simplified configuration has been developed to improve the total energy yield. In CAP, whole algal slurry after acid pretreatment is directly used for ethanol fermentation. The ethanol and microalgal lipids can be sequentially recovered from the fermentation broth by thermal treatment and solvent extraction. Almost all the monomeric fermentable sugars can be utilized for ethanol production without compromising the lipid recovery. The techno-economic analysis (TEA) indicates that the CAP can reduce microalgal biofuel cost by $0.95 per gallon gasoline equivalent (GGE), which is a 9% reduction compared to the previous biorefinery scenario.