(359c) Co-Product Recovery in Wet Anaerobic Storage to Reduce the Cost of Algae Biomass for Fuels and Chemicals Production

Seasonal variation in algae biomass productivity requires storage to ensure a constant feedstock supply to a biorefinery for year-round fuels production. Wet anaerobic storage instead of drying as a means of preserving algae biomass has been shown to reduce the cost of algae biofuels by as much as $0.32/GGE. The low oxygen environment of wet anaerobic storage encourages the growth of lactic acid bacteria, which produce lactic acid, reducing the pH and inhibiting the growth of other microorganisms and thus preserving the biomass. These organic acids (lactic, succinic, and acetic acids) could potentially be recovered as a co-product to reduce the cost of algae biomass production. A two-stage membrane filtration process was developed to recover succinic acid from Scenedesmus biomass that accumulated 40% of its dry weight as succinic acid during storage. The first membrane consisted of a microfiltration membrane to separate soluble organic acids from the microalgae biomass after which a nanofiltration membrane (MW cutoff of 90 Da) was used to concentrate organic acids. The nanofiltration membrane achieved a succinic acid rejection rate of 95% and a transmembrane flux of 10 L m^-2 h^-1. Techno-economic analysis was utilized to assess the impact storage byproducts could have on the cost of algae biomass when succinic acid was accumulated to 40% (w/w, dry basis) in storage through two different scenarios. The first applied the value of succinic acid as a credit toward the cost of algae biomass and provided high-acid biomass directly to a biorefinery. The second scenario utilized the two-stage filtration process to first recover organic acids from stored algae before providing low-acid biomass to a biorefinery. The minimum biomass selling price could be reduced by 20% when acid-rich biomass was provided directly to the biorefinery, while recovering storage co-products first could reduce MBSP by 9%. This study demonstrates that wet anaerobic storage, in addition to enabling the year-round operation of algae biorefineries, reduces the cost of producing fuels and chemicals from algae biomass by increasing its value.