There are several arguments for and against a U. S. microalgae biodiesel R&D program. One of the more important, and perhaps contentious, issues, is the potential impact of such technologies on U. S. energy supplies, specifically liquid transportation fuels. The review in Section III. C. of the NREL resource analyses for microalgae biodiesel concluded that there is a potential for production of several quads (1015 Btu) of biodiesel fuels in the southwestern United States alone. However, as stated earlier, it will be difficult to find many locations where all the resources required for microalgae cultivation, flatland, brackish or waste waters, and low-cost CO2 supplies, are all available in juxtaposition. And, as also pointed out, the southwestern United States is not the ideal climatic location for such systems. For both these reasons, the resource potential estimated by these resource studies must be significantly discounted.

In the case of utilization of power plant CO2, diurnal and seasonal factors would restrict direct CO2 (e. g., flue gas) utilization to about one-third of the power plant CO2. Even with CO2 capture and transportation (which greatly increases costs), only about half of the CO2 would be useable. With most coal-fired power plants located in the north, or in otherwise unfavorable climates, only a rather small fraction of power plant CO2 resources would likely be captured with microalgae systems in the United States.

A conservative estimate is that microalgae systems would be able to mitigate, directly or indirectly, perhaps only about 1% of current power plant CO2 emissions, supplying an approximately equivalent amount of current transportation fuels. Herzog (1995) argued that such a potential, in fact, anything less than 10%, is not sufficient to justify a R&D effort, and that scarce resources should be devoted only to potentially high-impact technologies, such as the disposal of CO2 in the oceans or geological formations. However, Benemann (1995) countered that such a resource-only argument is too limited, as it ignores the issue of economics and technological risks. For example, the technical feasibility of ocean disposal is far from established, and the costs of such a process are not currently constrained by credible engineering and economic analyses. A balanced R&D portfolio would need to account for such factors. Also, it is inherently more attractive to use and recycle CO2, thus increasing economic activity, rather than to bury it or dump it into oceans. In addition, microalgae CO2 utilization could spin-off other technologies, as in the case of the ASP. Thus, although a decisive role for microalgae fuel production and greenhouse gas mitigation cannot be extrapolated, a modest R&D effort in this area is appropriate in the context of developing many such alternative technologies.

IV. B. I.e. Summary of Major Conclusions from the ASP Microalgal Mass Culture Work

This report cannot do justice to the extensive and long-term R&D effort in applied microalgae mass culture carried out by DOE and the ASP over a 20-year period. Here only a very brief summary of the major conclusions is provided to put into context the recommendations for future R&D, which follow.

Two major conclusions can be derived from the outdoor cultivation projects and engineering/economic analyses under the ASP, and can be briefly summarized:

1. There appear to be no fundamental engineering and economic issues that would limit the technical feasibility of microalgae culture, either in terms of net energy inputs, nutrient (e. g., CO2) utilization, water requirements, harvesting technologies, or general system designs.

2. Productivities, in terms of total biomass and algal lipids (oils) currently achieved during the ASP are substantially higher than those reported and even projected before the ASP, but still well below the theoretical potential, and the requirements for economical viability.

The first conclusion should not imply that all these issues and problems have been solved. It does, however, suggest that the immediate R&D needs are not for engineering designs or cost analysis, or even in the operation of large, outdoor algal mass culture systems. Rather, from the second conclusion, the emphasis of any R&D effort must be on more fundamental and early-stage applied research issues faced in developing very high productivity algal strains. Ideal strains would dominate the pond cultures, achieve near-maximal productivities, efficiently biosynthesize large amounts of lipids, and be easy to harvest.

Another conclusion from the DOE-ASP program is that the only plausible near — to mid-term application of microalgae biofuels production is integrated with wastewater treatment. In such cases the economic and resource constraints are relaxed, allowing for such processes to be considered with well below maximal productivities.