Put less emphasis on outdoor field demonstrations and more on basic biology

Much work remains to be done on a fundamental level to maximize the overall productivity of algae mass culture systems. The bulk of this work is probably best done in the laboratory. The results of this program’s demonstration activities have proven the concept of outdoor open pond production of algae. While it is important to continue a certain amount of field work, small scale studies and research on the

basic biological issues are clearly more cost effective than large scale demonstration studies.

і Take Advantage of Plant Biotechnology

We have only scratched the surface in the area of genetic engineering for algae. With the advances occurring in this field today, any future effort on modifying algae to increase natural oil production and overall productivity are likely to proceed rapidly. The genetic engineering tools established in the program serve as a strong foundation for further genetic enhancements of algae.

і Start with what works in the field

Select strains that work well at the specific site where the technology is to be used. These native strains are the most likely to be successful. Then, focus on optimizing the production of these native strains and use them as starting points for genetic engineering work.

і Maximize photosynthetic efficiency.

Not enough is understood about what the theoretical limits of solar energy conversion are. Recent advances in our understanding of photosynthetic mechanisms at a molecular level, in conjunction with the advances being made in genetic engineering tools for plant systems, offer exciting opportunities for constructing algae which do not suffer the limitations of light saturation photoinhibition.

і Set realistic expectations for the technology

Projections for future costs of petroleum are a moving target. DOE expects petroleum costs to remain relatively flat over the next 20 years. Expecting algal biodiesel to compete with such cheap petroleum prices is unrealistic. Without some mechanism for monetizing its environmental benefits (such as carbon taxes), algal biodiesel is not going to get off the ground.

Look for near term, intermediate technology deployment opportunities such as wastewater treatment.

Excessive focus on long term energy displacement goals will slow down development of the technology. A more balanced approach is needed in which more near term opportunities can be used to launch the technology in the commercial arena. Several such opportunities exist. Wastewater treatment is a prime example. The economics of algae technology are much more favorable when it is used as a waste treatment process and as a source of fuel. This harks back to the early days of DOE’s research.

Photosynthetic organisms, including plants, algae, and some photosynthetic bacteria, efficiently utilize the energy from the sun to convert water and CO2 from the air into biomass. The Aquatic Species Program (ASP) at SERI[1] was initiated as a long term, basic research effort to produce renewable fuels and chemicals from biomass. It emphasized the use of photosynthetic organisms from aquatic environments, expecially species that grow in environments unsuitable for crop production. Early in the program, macroalgae, microalgae, and emergents were investigated for their ability to make lipids (as a feedstock for liquid fuel or chemical production) or carbohydrates (for fermentation into ethanol or anaerobic digestion for methane production). Macroalgae (seaweeds) are fast-growing marine or freshwater plants that can reach considerable size; for example, the giant brown kelp can grow a meter in 1 day and as long as 60 m. Emergents are plants such as cattails or rushes that grow partially submerged in bogs or marshes. Macroalgae and emergents were found to produce small amounts of lipid, which function mainly as structural components of the cell membranes, and produce carbohydrate for use as their primary energy storage compound. In contrast, many microalgae, (microscopic, photosynthetic organisms that live in saline or freshwater environments), produce lipids as the primary storage molecule. By the early 1980s, the decision was made to focus ASP research efforts on the use of microalgal lipids for the production of fuels and other energy products. The studies on the growth and chemical composition of macroalgae and emergents will not be discussed in this report. However, interested readers are referred to reports by subcontractors J. D. Ryther, Harbor Branch Foundation, Florida (seaweeds), and D. Pratt, from the University of Minnesota, St. Paul (emergents) listed in the Bibliography.

Microalgae, like higher plants, produce storage lipids in the form of triacyglycerols (TAGs). Although TAGs could be used to produce of a wide variety of chemicals, work at SERI focused on the production of fatty acid methyl esters (FAMEs), which can be used as a substitute for fossil-derived diesel fuel. This fuel, known as biodiesel, can be synthesized from TAGs via a simple transesterification reaction in the presence of acid or base and methanol. Biodiesel can be used in unmodified diesel engines, and has advantages over conventional diesel fuel in that it is renewable, biodegradable, and produces less SOX and particulate emissions when burned. The technology is available to produce biodiesel from TAGs, and there are growing biodiesel industries both in the United States and Europe that use soybean or rapeseed oil as the biodiesel feedstock. However, the potential market for biodiesel far surpasses the availability of plant oils not designated for other markets. Thus, there was significant interest in the development of microalgal lipids for biodiesel production.

Microalgae exhibit properties that make them well suited for use in a commercial-scale biodiesel production facility. Many species exhibit rapid growth and high productivity, and many microalgal species can be induced to accumulate substantial quantities of lipids, often greater than 60% of

their biomass. Microalgae can also grow in saline waters that are not suitable for agricultural irrigation or consumption by humans or animals. The growth requirements are very simple, primarily carbon dioxide (CO2) and water, although the growth rates can be accelerated by sufficient aeration and the addition of nutrients. A brief overview of the characteristics of the major microalgal classes can be found in Section II. A.2.

A major undertaking by ASP researchers in the early stages of the program was to identify candidate microalgal species that exhibited characteristics desirable for a commercial production strain. Resource analyses carried out by SERI (discussed in Section III. C.) indicated that the desert regions of the southwestern United States were attractive areas in which to locate microalgal-based biofuel production facilities. This, in part, dictated the required strain characteristics. These characteristics included the ability of the strains to grow rapidly and have high lipid productivity when growing under high light intensity, high temperature, and in saline waters indigenous to the area in which the commercial production facility is located. In addition, because it is not possible to control the weather in the area of the ponds, the best strains should have good productivity under fluctuating light intensity, temperature, and salinity.

A multi-faceted effort was carried out to:

• isolate microalgae from a variety of saline habitats (including oceans, lakes, ponds, and various ephemeral water bodies),

• screen those isolates for the ability to grow under a variety of conditions,

• analyze the biochemical components of the strains (especially with respect to lipids), and

• determine the effects of environmental variables on the growth and lipid composition of selected strains.

This effort involved in-house researchers and subcontractors from academia, industry, and other government laboratories. Section II. A.1. documents the efforts of SERI in-house researchers in the area of microalgal strain isolation and screening. It also describes the methodologies developed and employed during the isolation, screening, and characterization phases of the work. Section II. A.2. describes parallel efforts conducted by SERI subcontractors. An account of the history and current status of the NREL Microalgae Culture Collection is presented in Section II. A.3.

Although the collection and screening efforts produced a number of viable candidate strains, no one algal strain was identified that exhibited the optimal properties of rapid growth and high constitutive lipid production. Many microalgae can be induced to accumulate lipids under conditions of nutrient deprivation. If this process could be understood, it might be possible to manipulate either the culture conditions, or to manipulate the organisms themselves, to increase lipid accumulation in a particular strain. Therefore, studies were initiated both at SERI and by

ASP subcontractors to study the biochemistry and physiology of lipid production in oleaginous (oil-producing) microalgae. Work performed by several ASP subcontractors was designed to understand the mechanism of lipid accumulation. In particular, these researchers tried to determine whether there is a specific “lipid trigger” that is induced by factors such as nitrogen (N) starvation. Subcontractors also studied ultrastructural changes induced in microalgae during lipid accumulation. They also initiated efforts to produce improved algae strains by looking for genetic variability between algal isolates, attempting to use flow cytometry to screen for naturally-occurring high lipid individuals, and exploring algal viruses as potential genetic vectors. The work performed by ASP subcontractors is described in Section II. B.1.

Although some of the efforts of the in-house SERI researchers were also directed toward understanding the lipid trigger induced by N starvation, they showed that silica (Si) depletion in diatoms also induced lipid accumulation. Unlike N, Si is not a major component of cellular molecules, therefore it was thought that the Si effect on lipid production might be less complex than the N effect, and thus easier to understand. This initiated a major research effort at SERI to understand the biochemistry and molecular biology of lipid accumulation in Si-depleted diatoms. This work led to the isolation and characterization of several enzymes involved in lipid and carbohydrate synthesis pathways, as well as the cloning of the genes that code for these enzymes. One goal was to genetically manipulate these genes in order to optimize lipid accumulation in the algae. Therefore, reseach was performed simultaneously to develop a genetic transformation system for oleaginous microalgal strains. The successful development of a method to genetically engineer diatoms was used in attempts to manipulate microalgal lipid levels by overexpressing or down-regulating key genes in the lipid or carbohydrate synthetic pathways. Unfortunately, program funding was discontinued before these experiments could be carried out beyond the prelimilary stages.

Cost-effective production of biodiesel requires not only the development of microalgal strains with optimal properties of growth and lipid production, but also an optimized pond design and a clear understanding of the available resources (land, water, power, etc.) required. Section III reviews the R&D on outdoor microalgae mass culture for production of biodiesel, as well as supporting engineering, economic and resource analyses, carried out and supported by ASP during the 1980s and early 1990s. It also covers work supported by DOE and its predecessor agency, the Energy Research and Development Administration (ERDA), during the 1970s and some recent work on utilization of CO2 from power plant flue gases.

From 1976 to 1979, researchers at the University of California-Berkeley used shallow, paddle wheel mixed, raceway-type (high-rate) ponds to demonstrate a process for the simultaneous treatment of wastewater and production of energy (specifically methane). Starting in 1980, the ASP supported outdoor microalgal cultivation projects in Hawaii and California, using fresh and seawater supplies, respectively, in conjunction with agricultural fertilizers and CO2. The two projects differed in the types of algae cultivated and the design of the mass culture system, with the project in California continuing to develop the high-rate pond design, and the Hawaii project studying an (initially) enclosed and intensively mixed system. From 1987 to 1990, an “Outdoor Test Facility” was designed, constructed and operated in Roswell, New Mexico, including two

1,000 m2 high-rate ponds. This last project represented the culmination of ASP R&D in large-scale algal mass culture R&D. These studies are described in Section III. A. Some supporting laboratory studies and development of an “Algal Pond Model” (APM) are also reviewed at the end of that section. The conclusion from these extensive outdoor mass culture studies was that the use of microalgae for the low-cost production of biodiesel is technically feasible, but still requires considerable long-term R&D to achieve the high productivities required.

Section III. B. reviews the resource assessments, for water, land, CO2, etc., carried out by the ASP, primarily for the southwestern United States. These studies demonstrated the potential availability of large brackish and saline water resources suitable for microalgae mass cultures, large land and CO2 resources. They suggest that the potential production of microalgae-derived biodiesel may represent more than 10% of U. S. transportation fuels, although full resource exploitation would be significantly constrained in practice. Several engineering and economic cost analyses were also supported by DOE and the ASP, and these are reviewed in Section III. C., including recent work by the ASP and DOE on power plant flue gas utilization for greenhouse gas (CO2) mitigation.

The overall conclusion of these studies was that in principle and practice large-scale microalgae production is not limited by design, engineering, or net energy considerations and could be economically competitive with other renewable energy sources. However, long-term R&D would be required to actually achieve the very high productivities and other assumptions made in such cost analyses. Section III. D. provides recommendations for future research that could make this technology commercially feasible.