Biofuel from Algae: The Pros and Cons of Pond Scum – ThomasNet News

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Algae in a biofuel reactor.

Biofuel isn’t a new concept; it’s pretty ancient, in fact. The earliest humans to make their own fire used biofuel when they placed wood, dung, grass, and other distinctly organic fuels. Biodiesel, a distinctly more modern and complicated prospect, isn’t new, either. It’s a little known fact that Rudolf Diesel, the German inventor of the diesel engine, originally designed his prototype engine to run on peanut oil. It wasn’t until the Industrial Revolution that large-scale fossil-fuel oils became the blood of industry.

As we approach a point of peak oil – the point at which fossil fuels become scarcer and more expensive (and some argue that we’ve already passed that point) – the interest in biodiesel has been revived. Producing fuel from food products, however, has been morally controversial from the beginning. As the planet’s population and demand for food grows, it becomes more unconscionable for the wealthier nations to waste food products like corn, soy, sugar cane, and rapeseed, as well as food cultivation space, on filling their gas tanks.

To mitigate wasted food and land, in recent decades there has been a rising interest in cultivating biofuel from algae. In pursuit of low-cost, scalable, green, and clean biodiesel, research organizations in institutions both private and the public have put a lot of time and money into algae research in an effort to advance a technology that could produce transportation fuel on a large scale.

It simply makes sense: as anyone who has ever had a fish tank knows, algae is ridiculously easy to grow. There are many kinds of algae: complicated, multicellular forms (think seaweed), as well as simple, single-celled forms (think pond scum). It’s hardly a fussy plant, and producing large quantities of it doesn’t exactly require a green thumb. What’s so compelling about algae is that it contains a high amount of fatty molecules that are similar to vegetable oils, and these fats can be rather easily converted to a biofuel that can act as a drop-in replacement for petroleum-based gas, diesel, and jet fuel.

The Pros of Algae-based Biofuel

One of algae’s major attractions is that unlike corn for ethanol or soybeans for biodiesel, algae can be grown in places unsuitable for food cultivation, which takes away the wasted space drawback by making use of non-arable, nutrient-poor land that won’t support conventional agriculture.

Algae can be grown in ponds, tubes, or even large bags provided it gets the right combination of vitamins, minerals, and sunlight. It doesn’t require soil or even freshwater to grow, and when cultivated in large quantities, algae can produce more energy per acre than any land crop, making it the most energy-efficient plant for biodiesel production: far more efficient than corn, sugar cane, or soy. And unlike row crops, which are dependent on growing seasons, algae can be grown at any time of year, since ideal growing conditions can be easily simulated.

In addition, it requires no freshwater for irrigation and no application of petroleum-based fertilizers. Algae can thrive in desert ponds using high-saline water from aquifers that can’t be used for traditional crops. Many species of algae can even grow in wastewater from treatment plants and water that contains nitrates, phosphates, and other pollutants. In fact, algae ponds and cultivation facilities are often located as close as possible to wastewater or pollution sources, since algae thrives on both carbon and bacteria.

Like most other biodiesels, algae is also essentially carbon-neutral. While it does emit carbon while it’s burned, it absorbs carbon as food during its growing cycle (like all plants), which means that its net carbon figure is zero. Algae is estimated to have a greenhouse gas footprint that is 93% less than conventional, petroleum-based diesel.

The Cons of Algae-based Biofuel

While algae-based biofuel may use far less land and have a higher energy yield than other biodiesel crops, its production also requires more energy and water (albeit not necessarily freshwater) than plant sources such as corn. It also has higher greenhouse gas emissions, since the production of the final product is more complex and therefore more energy-intensive. While many kinds of algae are easy to cultivate, the species of the plant that contain the most fats are most suitable for biodiesel, and these specialized lipid-producers are a bit fussier than ordinary algae.

Another challenge arises in the final algae-based biodiesel product: it simply doesn’t flow well at lower temperatures. In a paper entitled, “Production and Properties of Biodiesel from Algal Oils,” research chemist Gerhard Knothe of the U.S. Department of Agriculture’s Agricultural Research Service made “unexpected” findings when it came to actually use algae biodiesel. He found that many, if not most, of biodiesel fuels derived from algae, have “significant problems” when it comes to their ability to flow well at lower temperatures (referred to as “cold flow”). In addition, he found that algae biofuels degrade more easily than other types of biofuels. Knothe recommended that these cold flow issues might be solved by blending the algae fuels with other fuels or possibly special additives to improve flow.

While algae biodiesel product is largely carbon-neutral, critics point out that it still requires carbon, and that carbon is derived from petroleum-based sources, which means that algae cultivation is still essentially dependent on petroleum. Ironically, algae biofuel could actually be a victim of its own success: were it to supplant petroleum-based fuels on a large scale, it would its most important source of carbon dioxide required for production.

The cultivation of algae (like the cultivation of most other plants) requires large amounts of phosphorus as a fertilizer, and while it’s not an oft-discussed topic, the world is currently on the brink of a peak of availability of Earth’s finite phosphate resources. “Peak phosphorus,” as it’s called, is the point in time at which the maximum global phosphorus production rate is reached. According to some researchers, Earth’s phosphorus reserves are expected to be completely depleted in 50 to 100 years, and peak phosphorus will be reached by the year 2030 (this is a fairly scary prospect for global agriculture, not just for algae production). To succeed, large scale algae production will need to reduce its use of phosphorus and find ways of reusing what it does require. The need for phosphorus in cultivation has been called by Forbes “The Achilles Heel” of algae biofuel.

Many critics also point out that the world simply can’t produce enough algae through natural photosynthesis to sustain the world’s need for fuel. Natural photosynthetic algae can produce about 2,000 gallons of fuel per acre per year today: far short of world demand, and far short of what scalable biofuel production requires to be economically feasible. For this reason, new production methods are being sought by the companies trying to make algae biofuel work better.

Methods of Production

There are two ways to grow algae for biodiesel. The earliest efforts involved growing algae in open ponds, which is easier and more intuitive, but far more difficult to keep at the right temperature, and requires workers to pump a steady supply of carbon dioxide into them. These open ponds also leave the water and the algae open to the possibility of contamination by native plants that wind up competing with the high-lipid algae for nutrients.

To solve this problem, some researchers have pursued a closed-tank bioreactor, which grows algae inside a contained environment in which ideal growing conditions can be artificially maintained. This way, researchers can ensure they are only growing the strains of algae they want: the high-lipid, high-yield plants.

While closed bioreactors solve some of the problems of open ponds, they come with their own set of challenges: namely, higher costs thanks to more specialized equipment and more intensive energy needs.

This article was originally written by Tracey Schelmetic in 2013 and was updated by the Thomas team in 2020.

Image Credit: Chokniti Khongchum / Shutterstock

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