Evaluation of a high-moisture stabilization strategy for harvested microalgae blended with herbaceous biomass: Part II - Techno-economic assessment

The seasonal variability in algal biomass production and its susceptibility to rapid degradation increases uncertainty in algal productivity and increases risks to feedstock supply for conversion. During summer months when algal biomass productivity is highest, production could exceed conversion capacity, resulting in delayed processing and risk of biomass degradation. Drying algae for preservation is energy-intensive and can account for over 50% of the total energy demand in algae preprocessing. In comparison, wet stabilization of algae eliminates the need for drying, and blending with herbaceous biomass allows for the utilization of the silage industry's existing harvest, handling, transportation, and storage infrastructure. A storage facility co-located with the algae production and conversion operations was designed in this study to stabilize algal biomass produced in excess of conversion capacity during summer months for use in the winter when algal biomass production is reduced. Techno-economic assessment of ensiling algae and corn stover blends suggest it to be a cost effective approach compared to drying. In a high algal biomass productivity scenario, costs of wet storage ($/liter diesel) were only 65% of the cost of drying. When a reduced algal biomass productivity scenario was considered, the stored blend was able to cost-effectively provide sufficient biomass such that winter production in the algal ponds could cease, meanwhile incurring only 91% of the costs of drying; such an approach would facilitate algal biomass production in northern latitudes. Furthermore, the wet storage approaches require only 8-10% of the total energy consumption and release only 20-25% of the greenhouse gases when compared to a natural-gas based drying approach for microalgae stabilization.