Sandia LabNews

Going really green: Algae could fuel future

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Algae is one of several potential fuel sources being looked at to help solve the global energy crisis. It is attractive on several fronts: It’s easy to produce, it can be grown in regions that aren’t used for food, and it doesn’t need to compete with the same water used in crop irrigation. Most important, algae is rich in oils that can be used in biodiesel production.

“Biofuels derived from algae present an opportunity to dramatically impact US energy needs for transportation,” says Grant Heffelfinger (8330), who leads Sandia’s biofuels program.

It turns out, though, that for every advantage, there are disadvantages. For starters, understanding and characterizing the finicky mixture of oils, proteins, and hydrocarbons found in various species of microalgae is an enormous challenge. Second, the extraction of oils from the algae and their subsequent conversion into biodiesel fuels in an economically feasible way represent additional barriers.

Those challenges, however, are in the crosshairs of Sandia researchers involved in a Laboratory Directed Research and Development (LDRD) effort titled “Microalgal Biodiesel, Feedstock Improvement by Metabolic Engineering.” Led by molecular biologist Todd Lane (8321) and using advanced molecular biology techniques largely unavailable in years past, the effort’s aim is to create more effective harvesting, extraction, and conversion techniques for algae and the fuel-friendly oils they produce.

Starving algae

Algae, Todd says, yields the same kind of oils produced by certain vegetables and plants used for biodiesel conversion (as well as animal fats). The chemical composition of these oils includes triacylglyceride, or TAG, which is the key to the conversion to biofuel.

But algae only produces TAGs under very specific environmental conditions, or triggers, a scientific challenge that Todd and his colleagues are addressing.

“Algae only produce TAGs when they need to, basically as a storage defense mechanism, much like humans store fat,” says Todd. “We’re trying to trick the algae into thinking it’s continually experiencing starvation conditions so it will produce oils without interruption.” Once that hurdle is overcome, he says, “you’ve then opened the door to many possible growth and recovery techniques.”

Sandia has been looking at two microalgal organisms, Phaeodactylum tricornutum and Thalassiosira pseudonana, the genomes of which were recently sequenced by DOE’s Joint Genome Institute in northern California. The LDRD project’s intent, says Todd, is to take advantage of the new genetic information to better understand the processes involved in the formation of oils, then eventually to manipulate those processes to produce larger quantities of those oils.

Characterizing the oils, says Todd, involves both proteomic analysis (where the organisms are taken apart and the proteins separated onto gels) and transcriptional analysis (looking at the genes that are expressed even before the organism transitions into starvation conditions). Todd calls this important work the “molecular fingerprinting” of the oils contained in the algae, with the hope that researchers can soon use the information to engineer larger quantities of oil.

The LDRD team has recently completed a significant milestone where it compared the different metabolic routes of oil production in multiple strains of algae by tracking their accumulation as a function of time and environment. The results have produced new insight into the mechanisms of nutrient starvation in algae, and will serve as the basis for engineering the algae into robust oil producers. These findings were presented at an international conference on phycology (the scientific study of algae), and the team has just submitted a paper to the Journal of Applied Phycology that summarizes their conclusions.

Extraction: squeezing the oil out

There are several tried and true methods for extracting oils from algae, including mechanical, chemical, thermochemical, plasma, and microwave techniques. Most traditional methods are not considered to be long-term solutions. The mechanical approach, for example — which involves pressing algae to squeeze out the oil, much like the process for producing olive oils from olives — is highly power intensive and not scalable.

Sandia, Todd says, is mostly focused on the chemical approach, whereby solvents with a biological affinity toward oils are used, acting somewhat like a chemical sponge to “pull” the oils from the algae. This approach, which Sandia believes may be scalable, is fraught with its own obstacles, most notably the fact that the most effective solvents aren’t particularly good for the environment.

But a closed and highly controlled facility, similar to an oil refinery, might be able to handle the operation at an industrial level. “Refineries already produce these kinds of chemicals,” says Todd, “and we’d also be taking advantage of existing chemical engineering and systems engineering infrastructure.” Using the same technology by which hydrocarbons are distilled and separated to separate oils from algae and create “bio crude,” he says, would be a logical and easier way to move toward algae-based transportation fuels.

Another focus of the microalgal LDRD project is the “dewatering,” or drying, of the algae, an important consideration since this step — necessary for the conversion into fuel — is highly energy intensive and thus estimated to represent nearly 50 percent of the current processing cost. Sandia is also examining ways by which algae can be grown and harvested in the first place.

“Algae is easy enough to grow, but it’s expensive to do in a way that’s robust and scalable,” says Todd.

Two years into the three-year microalgal LDRD project, Todd says he and his colleagues have already come to a vastly better understanding of the starvation process that is so critical for the efficient production of oils derived from algae. These results will help build the genomic and biotechnology toolboxes that will be required for the optimization of algal oil production at the massive commercial scales required to meet the transportation fuel demands of the US.

“The simple goal with this project is to improve the yield of oil in these organisms (P. tricornutum and T. pseudonana), then go back and analyze what we’ve done and see if we can apply it to other organisms,” says Todd. Such an achievement, he says, could then be applied to other, more commercially viable organisms, adding considerably to the scientific knowledge base necessary for long-term algae-to-biofuels production.