Algae-derived gasoline, diesel, and jet fuel sound like the imaginings of science fiction, but a growing number of entrepreneurs, investors, scientists, and policy makers are trying to make them reality. If developed sustainably, the algae biofuel industry may be able to provide large quantities of biofuels with potentially minimal environmental impacts.
But to properly assess the sustainability of algae biofuels, we need a way to see the big picture - to analyze the full life cycle impact of algae biofuel production in the context of issues such as water resource management, land use impact, energy balance and air emissions.
To help address this challenge, NRDC has published a new report entitled: "The Promise of Algae Biofuels", authored by Catie Ryan, a consultant with Terrapin Bright Green. In this report we provide a framework for comprehensive environmental analysis of algae biofuels; identify key ecological issues to be considered across all stages of production; summarize the known and unknown environmental impacts of each production process; and recommend areas for future policy and research.
Valcent's High Density Vertical Growth (HDVG) systems grow algae with only light, water, and air in a closed loop, vertical system of polyethylene sleeves in greenhouses. Photo credit: Valcent Products Inc.
This report's primary objective is to encourage and participate in a growing, industry-wide effort to determine the complete environmental impacts of transforming algae into fuel. We believe it is vital, working with stakeholders across business and non-business sectors, to develop a clear picture of the environmental pros and cons of algae biofuel systems, environmentally preferable algae fuel pathways, and the areas of research needed to mitigate the impacts of algae fuels. Otherwise, much as with earlier generations of biofuel technologies, the economic, technical and political challenges brought on by unsustainable production practices could derail this promising fuel feedstock.
However, despite the need for accurate sustainability analysis, current publicly available data and project experience is insufficient to make quantifiable comparisons among different algae biofuel (or against other fuel) production pathways . This is due primarily to the current state of the algae biofuels industry, which is sprawling and dynamic, exploring innumerable pathways to produce fuels from algae and developing mostly in "stealth" mode. But to avoid getting mired in similar environmental controversy as seen with corn ethanol, the algae biofuel industry must build on the data currently available and move quickly to fill the multitude of remaining information gaps regarding its environmental performance.
We hope NRDC's work on this project serves as one step in a much larger knowledge-building effort.
Our report starts by mapping five theoretical production pathways and explores the associated environmental implications of the individual process steps contained therein. Production generally consists of four linked processes, algae cultivation, biomass harvesting, algal oil extraction, and oil and residue conversion, with different options within each broad category.
Mapping Framework for Potential and Existing Pathways for Algae Biofuel Production Draft
- Cultivation: Algae cultivation at commercial scale (where algae is grown in open or closed systems for downstream usage) could have significant environmental consequences, based on how water, nutrients, land, and light are supplied and managed. At a minimum, the criteria for sustainable cultivation should consider the impact of water, land and genetically modified organism (GMO) usage on biodiversity and ecosystem health, as well as the environmental impacts of infrastructure fabrication, materials toxicity, electricity demands, and waste treatment.
- Harvesting: Harvesting involves recovering, dewatering and drying algal biomass; techniques used vary depending in part on the cultivation system. Most recovery processes require chemical or mechanical manipulation to separate the biomass from the process wastewater. At a minimum, the criteria for sustainable biomass harvesting should consider the potential toxicity of chemical additives, environmental management of output water and the energy and carbon balance implications of energy-intensive drying techniques.
- Extraction: Algal oil extraction (removing oil from the algae biomass) can be achieved via a number of techniques, but there is limited information about the chemical and energy inputs in this process. The criteria for sustainable oil extraction should consider energy inputs and potential environmental toxicity of chemical solvents.
- Conversion: Oil and residue conversion pathways include transesterification, fermentation, pyrolysis, and hydroprocessing (among others). These conversion steps have been employed in conventional biofuel refining for some time, meaning good data is available, although not necessarily related specifically to algae biofuels. The criteria for sustainable conversion should consider potential energy usage and the handling of low-value coproducts or byproducts. In the near term, industry may need to embrace biological services (e.g. wastewater treatment) and high value nonfuel coproducts (e.g. animal feed, nutraceuticals,) to make algae biofuels economically viable. This will further influence calculations surrounding algae biofuel sustainability.
Open raceway ponds with paddle wheels (far right) for circulating the water. Photo credit: Seambiotic, Ltd.
Our report also attempts to determine the anticipated impact of algae biofuel production on several primary ecological resources - water, land, soil, biodiversity and air - as well as its potential energy and carbon balance.
- Water: The effect of algae biofuel production on regional water sources is not fully understood and early emphasis by the algae biofuels industry on water impact could mitigate many potential issues. Concerns include aggregate water consumption, systems discharge and water quality, and reduction of groundwater infiltration. The ability of algae to thrive in and treat wastewater and potentially eliminate the need for agriculturally-based biofuels offers one promising path to mitigate some water issues but further study and technology development is needed.
- Land: Algae biofuels can be produced on non-arable land, which is a strong advantage over agriculturally-based biofuels. However, claims regarding yield per acre are often exaggerated and certain algae cultivation processes could have far more land impact than others. For example open systems will likely have a relatively larger land use footprint than other systems, while heterotrophic systems (which use sugar to grow algae) could have significant indirect land use impacts.
- Soil and Biodiversity: as with all industrial systems using hazardous substances, algae production could contribute to soil contamination, unless non chemical methods are used for harvesting and other processes. Poisoning soil with salt is also a concern for algae cultivated in briny or brackish water. Overall biodiversity could be threatened by producing algae biofuels unsustainably (e.g. through land transformation, water and soil contamination, air pollution and use of alien species)
- Air: similar to soil and biodiversity above, the pathway of biofuel production and the technologies used will determine impact on air quality. One potential area for future research is the impact of evaporation from open pond cultivation on local and regional humidity, and local ecosystems.
- Energy and Carbon Balances: the potential energy and carbon balances of algae biofuels are highly uncertain calculations, and range widely depending on production system, type of biofuel produced, energy savings realized by the coproducts, and so on. In terms of atmospheric greenhouse gas (GHG) concentrations, it is critical to consider the net impact which includes all direct and indirect inputs and outputs from all production processes employed. Terms used in this context such as "sequestration" are particularly problematic, as they take into account actions and emissions that are not within the boundaries of the algae biofuels production system.
Finally, we recommend a number of steps that regulators/policymakers and industry can take to proactively encourage sustainable algae biofuel production.
From a regulatory and policy standpoint, key steps include clarifying roles and responsibilities within government agencies, establishing information resources, specifying sustainability metrics and industry standards, encouraging industry collaboration and assisting in life cycle analysis (LCA) at the fuel product design phase.
The algae industry can proactively address sustainability issues by conducting and publishing techno-economic and life cycle analyses, water balances, and energy and carbon balances; where feasible, adopting low-impact development, operations, and maintenance practices; and improving understanding of how relationships between production processes define resource consumption and management. Finally, together and separately, the public and private sector should use the information from various sustainability assessments to guide research and development to help algae fuels avoid and mitigate environmental impacts.
Ultimately, environmental questions will persist in the production of algae biofuels until sustainable production processes are fully established. By proactively engaging in environmental analysis and full-system life cycle calculations, and identifying, managing, and mitigating potential environmental impacts associated with algae biofuels production, we can help to develop a sustainable biofuels industry and increase the odds of success for algae-based biofuels,