(551e) Life Cycle Assessments of Algal Biofuels: Extensions Beyond Traditional Algal Fuels Framework
Algae-based biofuels have received considerable interest due to the potential for large volumes of biofuel production using relatively small amounts of idle or retired agricultural lands. However, concerns persist about the environmental impacts of this novel technology as cost-effective and environmentally sustainable technologies are developed and tested. Our recent work within the National Alliance for Advanced Biofuels and Bioproducts (NAABB) research consortium has focused on conducting life-cycle assessment (LCA) studies to investigate key potential scenarios concerning algal biofuels development. Here, we present study results on a selection of the important considerations: cultivation infrastructure impacts, fertilizer choice, non-lipid algal fraction usage, allocation methodology, hydrogen sources, and conversion to other fuel products such as hydrotreated renewable jet (HRJ). Modeling results reflect the high variability inherent in the current data sets. For example, estimated GHG savings for HRJ compared to fossil jet fuel ranged from greater than 40% to negative 50% depending on critical assumptions such as lipid extracted algae (LEA) use and algal biomass drying inputs. Exporting lipid-extracted algae (LEA) as animal feed results in a worsening environmental footprint for algae biofuels. LEA that is re-used on site after anaerobic digestion has considerable value as a source of heat, power, and nutrients, and the benefit from displacing an animal feed in the technosphere does not outweigh the burdens associated with replacing these requirements that LEA can satisfy as an internally used product. Employing algae for nutrient removal in a wastewater treatment plants shows promise for achieving energy savings credits in the algae life cycle, significantly reducing the net GHG emissions for a crude oil derived by fast pyrolysis of wild algae (RTP green fuel). As large tracts of land are converted to algal raceways, direct land-use change impacts can be larger than impacts associated with pond liner deployment or land leveling and preparation, and could result in GHG emission equivalent to one of several important processing stages such as algae dewatering and drying. Our presentation details the methods, assumptions and initial LCA results for these and other scenarios of importance when considering the algae biofuels life cycle.
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