Microalgal biomass production pathways: evaluation of life cycle environmental impacts

Abstract

BackgroundMicroalgae are touted as an attractive alternative to traditional forms of biomass for biofuel production, due to high productivity, ability to be cultivated on marginal lands, and potential to utilize carbon dioxide (CO2) from industrial flue gas. This work examines the fossil energy return on investment (EROIfossil), greenhouse gas (GHG) emissions, and direct Water Demands (WD) of producing dried algal biomass through the cultivation of microalgae in Open Raceway Ponds (ORP) for 21 geographic locations in the contiguous United States (U.S.). For each location, comprehensive life cycle assessment (LCA) is performed for multiple microalgal biomass production pathways, consisting of a combination of cultivation and harvesting options.ResultsResults indicate that the EROIfossil for microalgae biomass vary from 0.38 to 1.08 with life cycle GHG emissions of −46.2 to 48.9 (g CO2 eq/MJ-biomass) and direct WDs of 20.8 to 38.8 (Liters/MJ-biomass) over the range of scenarios analyzed. Further anaylsis reveals that the EROIfossil for production pathways is relatively location invariant, and that algae’s life cycle energy balance and GHG impacts are highly dependent on cultivation and harvesting parameters. Contrarily, algae’s direct water demands were found to be highly sensitive to geographic location, and thus may be a constraining factor in sustainable algal-derived biofuel production. Additionally, scenarios with promising EROIfossil and GHG emissions profiles are plagued with high technological uncertainty.ConclusionsGiven the high variability in microalgae’s energy and environmental performance, careful evaluation of the algae-to-fuel supply chain is necessary to ensure the long-term sustainability of emerging algal biofuel systems. Alternative production scenarios and technologies may have the potential to reduce the critical demands of biomass production, and should be considered to make algae a viable and more efficient biofuel alternative.

A Review of Environmental Life Cycle Assessments of Liquid Transportation Biofuels in the Pan American Region

“…Most studies considering water consumption are from countries with an extensive and welldeveloped biofuel sector, such as the US and Brazil. Eight analyses were conducted in the United States (ChavezRodriguez and Nebra 2010; Chiu et al 2009Chiu et al , 2012Clarens et al 2010;Mishra and Yeh 2011;Yang et al 2011Yang et al , 2012Zaimes and Khanna 2013), 3 in Brazil (Cavalett et al 2013;Chavez-Rodriguez and Nebra 2010;Ometto et al 2009), 2 in Chile (Iriarte et al 2010(Iriarte et al , 2012, and 1 in Argentina (Emmenegger et al 2011). Water consumption is of particular importance where water scarcity is a prevalent issue (e.g., southwestern US, the northern region of Mexico, and the Norte Grande in Chile all deal with arid climates) and can be a limiting factor.…”

Innovative harvesting processes for microalgae biomass production: A perspective from patent literature

“…The amount of greenhouse gas emissions (GHG) for each method was expressed as the amount of produced CO2 per required energy unit (g CO2-eq MJ -1 ). When no direct data were available, conversion was based on literature studies with the amounts CO2 produced in relation to the distance (g CO2-eq 100 km -1 ), and converted using the formulae: 17] or by dividing the reported amounts kg CO2-eq ton -1 algae by the average microalgal net calorific value (18.5 MJ kg -1 ) ( [18]; [19]). These types of conversions were applied for decanters ( [18]; [19]) and belt filters ( [18]; [20]).…”

“…When no direct data were available, conversion was based on literature studies with the amounts CO2 produced in relation to the distance (g CO2-eq 100 km -1 ), and converted using the formulae: 17] or by dividing the reported amounts kg CO2-eq ton -1 algae by the average microalgal net calorific value (18.5 MJ kg -1 ) ( [18]; [19]). These types of conversions were applied for decanters ( [18]; [19]) and belt filters ( [18]; [20]). Other conversions were based on the reported amount of CO2 emissions per ton biodiesel for disk stack centrifugation ( [21]; [20]; [22]), decanters ( [18]; [19]), chamber filters ( [21]; [19]), inorganic flocculation ( [23]; [24]; [25]) and organic flocculation ( [26]; [24]).…”

“…These types of conversions were applied for decanters ( [18]; [19]) and belt filters ( [18]; [20]). Other conversions were based on the reported amount of CO2 emissions per ton biodiesel for disk stack centrifugation ( [21]; [20]; [22]), decanters ( [18]; [19]), chamber filters ( [21]; [19]), inorganic flocculation ( [23]; [24]; [25]) and organic flocculation ( [26]; [24]). This approach allowed to estimate the amount of greenhouse gas emissions based on literature data across several studies and report it as an interval between minimum and maximum reported values.…”

Design of Sustainable Biofuel Processes and Supply Chains: Challenges and Opportunities

“…This holistic systems approach captures environmental impacts that are outside the purview of the traditional process design boundary. Life Cycle Assessment (LCA) is one of the most common approaches for evaluating the environmental impact of a product or a process over its entire life cycle, and in recent years has emerged as the predominant method for analyzing the environmental sustainability of emerging biofuel platforms [88][89][90][91][92][93][94][95]. LCA considers impacts throughout all stages of the fuel life cycle-from raw material acquisition, to fuel conversion, and final use.…”