(125b) Biodiversity Enhances Multifunctionality in a Life Cycle Assessment of Microalgal Biofuel Production

Life cycle assessments (LCAs) comparatively analyze and interpret the sustainability of fuel production pathways and are imperative for improving energetic efficiencies and reducing environmental impacts. Accuracy and interoperability within the field of algal biofuel LCAs have proven challenging due to variance in empirical data collection, methodologies, models, and specious ecological assumptions. Here, we describe a contiguous well-to-wheel LCA for the production of algal biofuel that employs an ecologically based growth model to study the impacts of biodiversity on life cycle sustainability metrics. Our approach incorporates data from collaborative publications that considered algal cultivation in indoor mesocosms under two temperature regimes as well as growth in outdoor ponds. The studies integrate empirical input parameters from each stage of algal biofuel production, including elemental composition of algae and biocrude, phosphorous and nitrogen nutrient use efficiencies, as well as biomass and biocrude yields for mono-, bi-, and poly-cultural algal cultivation. Under optimal laboratory growth conditions, we found that Selenastrum capricornutum, a dominant species in biomass accumulation and culture stability, yielded an energy return of 0.99 and emissions of 122 kg CO₂eq/MBTU. However, upon translation to outdoor ponds, a biculture of S. capricornutum and Chlorella sorokiniana outperformed all other culture compositions with an energy return of 0.60 and emissions of 167 kg CO₂eq/MBTU. Despite markedly worse life cycle metrics, the success of the biculture over the best monoculture arose due to an unprecedented and beneficial multifunctionality between input parameters. Our results necessitate the consideration of ecological constraints within LCAs as well as the propensity of select algal polycultures for favorable energetics and reduced emissions during scaled biofuel production.