(569q) Economics of a Macroalgae Biorefinery: (How) Can It be Viable?

Macroalgal biomass is generally considered as a prospective feedstock for biofuel production as it offers a number of benefits [1-4] including: 1) it is an abundant renewable carbon source, 2) its growth does not require arable land, fertilizer or fresh water, 3) it is not a primary food crop, 4) it grows rapidly (e.g., 2,960 dry MT/km²/yr [2]). The presence of significant quantities of polysaccharides (i.e., laminarin, alginate, and small amounts of other sugars) and sugar alcohols (i.e., mannitol), the absence of a secondary cell wall (i.e., no lignin) and the low levels of hemicellulose make certain species of brown macroalgae (e.g., Saccharina Latissima) particularly attractive for the production of biofuels [5]. Successful deployment of macroalgae-based biorefineries, however, depends on their economic viability at industrial scale. With that in mind, the key objective of this study was to carry out a detailed technoeoconomic analysis (TEA) of this process to understand the economic potential and cost drivers of macroalgal biorefineries.

In this work, a detailed process model for a macroalage-to-ethanol biorefinery was built. Given the current status and possible technological advances, several scenarios were constructed by varying key process and economic parameters. These include: 1) macroalgae price ($50 to 200/dry MT), 2) overall yield (50 to 80%), 3) solids loading in hydrolysis (5 to 20%), and 4) enzyme loading (10 to 20mg protein/g polysaccharide). With a delivered macroalge price of $100/MT, depending on the maturity of the other process parameters (i.e., yield, solids, and enzyme loading), the Minimum Ethanol Selling Price (MESP) was observed to be in the range of $3.6-$8.9/gal. Overall, the price of macroalgae and the yield remain key parameters in determining the economic feasibility of the biorefinery. For instance, the feedstock price needs to be less than $50/MT to ensure MESP is lower than $3/gal (at 80% yield) and with every $50/MT increase in the price of macroalgae, the MESP would increase by $0.6-1/gal (for the yield range studied). Solids loading was observed to be as significant as the yield as it affects both the capital and operating expenses. In addition to the macroalgae-to-ethanol biorefinery configuration, we have studied other configurations that could possibly improve the economics of biorefinery – these additional configurations include the possibility to co-produce alginate and ethanol.

 

References

1.           Jung KA, Lim S-R, Kim Y, Park JM: Potentials of macroalgae as feedstocks for biorefinery. Bioresource technology 2013, 135:182-190.

2.           Roesijadi G, Jones S, Snowden-Swan L, Zhu Y: Macroalgae as a biomass feedstock: a preliminary analysis, PNNL 19944. Pacific Northwest National Laboratory, Richland, WA 2010.

3.           Wargacki AJ, Leonard E, Win MN, Regitsky DD, Santos CNS, Kim PB, Cooper SR, Raisner RM, Herman A, Sivitz AB: An engineered microbial platform for direct biofuel production from brown macroalgae. Science 2012, 335:308-313.

4.           Adams JM, Gallagher JA, Donnison IS: Fermentation study on Saccharina latissima for bioethanol production considering variable pre-treatments. Journal of applied Phycology 2009, 21:569-574.

5.           Li K, Liu S, Liu X: An overview of algae bioethanol production. International Journal of Energy Research 2014.