The future of fuel is ... microalgae?

The future of fuel is ... microalgae?
January 24, 2016


There are currently more than seven billion people living on Earth, and scientists expect that figure to surpass 11 billion by the year 2100. With that figure comes the reality of needing to feed and provide energy for all of those people, while preserving a clean planet for them to live on.

Scientists from Cornell University and Duke Marine Laboratory proposed one possible solution in a recent article in the journal Oceanography; a solution that may seem more like a nuisance than a progressive energy technology. That possible solution is marine microalgae.

Microalgae CulturesMarine microalgae are microscopic plants that live in the ocean and other salt-water environments. To the naked eye, they look pretty much like pond scum: tiny green dots that multiply into what resembles a blanket atop the water or an emerald slurry reminiscent of some super-nutritious juice. These tiny organisms, however, are packed full of oils and sugars that scientists and engineers can convert into diesel and ethanol fuels for transportation as well as electricity generation.

If this story sounds familiar, that’s because it has been told before with a different cast of characters. Switch grass, corn stover and pulpwood have all been investigated as sources of biofuel. Through processes like superheating and chemical catalysis, scientists break down these biomass sources to create fuels and chemicals. Further, as these plants all photosynthesize they remove carbon dioxide from the atmosphere.

For each biomass source, engineers and scientists evaluate how much energy, land, water and effort it would take to produce biofuel from each, and whether they could create enough fuel to make those costs worth it. More recently, scientists have added algae to the list of potential sources and the Marine Algae Industrial Consortium (MAGIC), a team of experts from universities and industry, have begun studying the feasibility of algae. The recent article in Oceanography explores that feasibility and how microalgae compares to other sources.

The first major point of comparison is the amount of land required to cultivate a crop of each fuel source, which is a function of how much useful sugar and oil is in each plant and how close together you can grow them. Previous studies have shown that crops like corn and soybeans can produce a few dozen gallons of oil per acre. Canola, coconuts and palms can produce a few hundred gallons per acre. Microalgae blows them all out of the water, producing between 6,000 and 13,000 gallons of oil per acre. Algae contains between 20 and 50 percent oil and sugar after all the water has been extracted and these microscopic plants can grow so closely together that they can produce plenty of oil.

Microalgae BioreactorZackary Johnson, a molecular biology and marine science professor at Duke and leader of MAGIC calculated that with a little more than 151,000 square miles of microalgae farms, you could meet the energy demand of the United States, and with 800,000 square miles, you could power the world. Granted, 800,000 square miles is almost three times the size of Texas, but if you wanted to use corn you would need every square inch of space on Earth and then some.

Just as important as the amount of land you need is the type of land and algae has the advantage there as well, according to the study. Corn, soy and grass all require arable land, but algae can grow in salt water environments like bays and oceans. Even when the algae are grown in reactors—large channels or tube systems that circulate the algae and nutrients—the reactors do not require arable land. The only requirements are a sufficient temperature and ample sunlight. So algae farms could function perfectly well even in a desert.

Microalgae also do not require as much of some very valuable resources as other biomass sources do. Microalgae take up nutrients like phosphorus and nitrogen far more efficiently than corn and other terrestrial crops do, so they do not require as much fertilizer. Also, since the microalgae grow in salt water, farmers could use sea water or salt water from underground aquifers—useless for drinking or other farming—to grow the algae.

Wherever possible, engineers and scientists try to find some useful byproducts from these fuel sources or use byproducts of other crops as fuel sources. Corn stover is the leftover stalks and leaves from the corn grown for food and agricultural feed, and wood pulp is a byproduct from paper production. Microalgae have their own byproduct as well. They can be up to 60 percent protein, and that protein is useful as food for both animals and humans. According to the study, the amount of algae it would take to power the world would produce 2.4 billion tons of protein-rich food per year, more than 10 times the current global soy protein production.

Microalgae FarmGiven the food, energy, efficiency with valuable resources and ability to remove carbon from the atmosphere, you might wonder why we don't have algae farms everywhere. The reason is that the processes of farming and harvesting the algae and converting it into fuel are energy intensive and expensive.

Imagine you are gardening. You cannot just simply sprinkle seeds in a random patch on the lawn, throw fertilizer at it once in a while and expect a beautiful vegetable patch to grow. The same is true for microalgae. It does not need much in the way of fertilizer, but it has to be mixed in properly. Wastes need to be filtered out, carbon dioxide needs to dissolve into the water and just like a real garden, pests need to be kept out. That is why, in order to produce microalgae on an industrial scale, the algae needs to be grown in a bioreactor.

Bioreactor systems consists of canals and tubes full of microalgae and salt water. Fertilizers are pumped in regularly, as is carbon dioxide to give the algae enough to eat. The water constantly circulates to mix in the nutrients and all of that circulation requires energy and infrastructure, neither of which are cheap.

According to the study, a microalgae farm covering four square miles would cost up to half a billion dollars, putting the total price tag for meeting the world’s energy needs in the hundreds of trillions of dollars. 

Also, those costs are just for building the farms. The process of converting the algae into biofuel is also expensive and energy intensive. Creating biofuels from plants often requires breaking them down in very high temperatures, dissolving them in superheated fluids and/or chemical reactions that need rare, expensive metals as catalysts. Further, this type of chemistry requires that all of the water and salt be removed from the algae. Extensive drying or use of chemical solvents are needed to purify the algae.

All of this requires energy. Johnson suggests that algae farms could be combined with wind or solar installations. Solar energy could be especially useful as the algae farms would need a great deal of sunlight to grow to their fullest potential. Even so, algae farms come at a high cost.

Still, Johnson says, in a world with a growing population and growing needs for food and energy, integrated systems will come to pay for themselves over time, especially when fossil fuels and current farming practices will not last forever.

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.

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