Mitigation of variable seasonal productivity in algae biomass through blending and ensiling: An assessment of compositional changes in storage
2019
Wahlen, Bradley D. | Wendt, Lynn M. | Murphy, J Austin | Seibel, Fábio
Microalgae biomass has gained considerable attention in recent years as an attractive feedstock for biofuel production. However, seasonal variability in algae growth presents a challenge to delivering a consistent feedstock supply to a conversion facility. Drying is one approach to preserving algae produced in productive summer months for conversion in winter, but is energy intensive and costly. Ensiling is an alternative to drying that preserves algae in wet anaerobic conditions in the presence of organic acids. We have previously demonstrated that dry matter loss of algae:corn stover blends can be limited to 8% over 35 days using this approach. However, longer storage durations will be required to maintain a consistent feedstock supply to a biorefinery. Furthermore, the impacts to biomass quality that occur during storage are unknown. A Box-Behnken design of experiment was conducted to determine the influence of moisture, soluble sugar, and algae content on dry matter loss of algae:corn stover blends in wet anaerobic storage over a 30-day period. Using one-way analysis of variance (ANOVA) moisture and soluble sugar content were found to significantly affect dry matter loss in storage. The results of experimental design were then used to inform the initiation of a 180 day storage study that evaluated the storage performance and biomass composition of algae:corn stover blends containing 5, 20 or 40% algae. After 180 days of storage dry matter loss ranged from 6 to 17%. A relative increase in nitrogen content of stored blends indicates that protein content was unaffected by storage, while the carbohydrate fraction was most impacted, decreasing by 5–15%. For each stored blend the oxygen content decreased in storage resulting increased higher heating values (HHV). The impact that changes to biochemical and elemental composition of algae:corn stover blends has on biomass conversion to fuels and chemicals is discussed.
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