Algae Biofuel as an Alternative Energy Source

Small aquatic organisms could help fight our worst energy challenges.

Test tubes rack with micro algae

Santiago Urquijo / Getty Images

Algae biofuel—which refers to converting the energy produced by plant-like photosynthetic organisms into biodiesel—has been proposed as an alternative energy source since the early 1950s.

The idea gained momentum during the 1970s energy crisis—which actually ended up spurring more growth in the commercialization of solar technology—and even into the 1980s and 1990s with support for the U.S. Department of Energy’s Aquatic Species Program (ASP).

The ASP put about $25 million toward research with a goal of producing oil from microalgae from 1978 to 1996, testing thousands of different species on their nutrients, CO2 concentrations, and any engineering challenges that could come from mass-producing algae for the purpose of fuel. By the mid-1990s, however, due to a combination of financial barriers and the rise of cheap oil, the program was terminated.

In recent years, the global demand for fuel, environmental concerns, and the threat of “peak oil” have reinvigorated interest in algae-based biofuel both in the United States and around the world.

What Are Algae?

The term “algae” covers a diverse array of aquatic organisms that are capable of producing oxygen through photosynthesis (absorbing light from the sun and CO2, turning them into energy and carbohydrates).

There are estimated to be anywhere from 30,000 to over 1 million species of algae. The algae used in biofuel production is typically of the chlorophyceae variety, a type of aquatic unicellular green algae known for its high growth rates.

Rebirth of Algae Biofuel and Subsequent Setbacks

Promoted as an answer to the negative financial and environmental impacts of traditional oil production, algae biofuel development had substantial amounts of money invested by large companies.

These companies ran into a fair amount of limitations once it came time to retain productivity at a large scale, mainly due to the high expenses of providing enough light and nutrients to keep the farms healthy. Paired with yet another decrease in oil prices, most companies chose to cut their losses and pull the plug on algae biofuel research.

Today, the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office supports technologies to produce biofuels. Specifically, the Advanced Algal Systems program performs research and development to lower the costs associated with producing biofuels from algae.

So far, the program’s Pacific Northwest National Laboratory has developed a process to turn algae into bio-crude oil in just minutes, while participating researchers at the Scripps Institute of Oceanography have made breakthroughs in the metabolic engineering of algae to improve yields of energy-storing fat molecules used in biofuel production.

Although major corporations like Shell and Chevron had previously invested in algae biofuel research and development, pretty much all of them (with the exception of ExxonMobil) have stopped actively pursuing it in recent years.

How Algae Contribute to Climate Change Mitigation

According to a 2020 study published in the Smart Innovation, Systems and Technologies book series, biological methods using algae could be one of the most efficient and economical CO2 sequestering technologies. Algae farms may consume up to 1.8 kilograms of CO2 per kilogram of biomass, while the resulting bioproduct can be used for multiple products outside of simply biofuel.

How Efficient Are Algae Biofuels?

Production of micro algae for regenerative power

fotografixx / Getty Images 

Studies testing different ratios of traditional diesel fuel mixed with algae biodiesel have shown that blends of 30% biofuel are slightly more efficient compared to diesel fuel.

In a 2017 study published in Renewable and Sustainable Energy Reviews, engine exhaust gas (nitrogen oxide) showed no significant difference between fuels, though carbon monoxide was reduced by 10% when the algae biofuels were used.

Algae biofuel can be used by most diesel cars without major changes to the engines or infrastructure—the issue lies in the ability to produce algae biodiesel at a commercial scale.

Algae Biofuel Pros and Cons

Algae are a fast-growing, easy-to-cultivate, renewable resource, and they also have multiple uses outside of biofuel. Hydrocarbons from algae biomass can be used in different varieties of products such as fertilizers and industrial cleaners. Plus, cultivated proteins can be used for both human and animal feed.

Perhaps most importantly, algae absorb CO2 from the atmosphere.

On the other hand, research is still lacking when it comes to algae biofuel, and there are some concerns over human exposure to algae-derived toxins, allergens, and carcinogens from GMOs, since algae are commonly genetically modified.

Algae also have a large water demand, often necessitate fertilizers, and can have high costs.

Still, many of the barriers keeping algae biofuel from the mainstream are being addressed by top minds and researchers. Chemists from the Technical University of Munich, for instance, are currently working on methods to grow algae using saltwater rather than freshwater. Similarly, researchers from the University of California Riverside are studying ways to grow algae for biofuels using solar-generated electricity.

How to Extract Oil From Algae

Not surprisingly, there are numerous ways to remove the lipids, or oils, from the walls of algae cells. But you may be surprised to learn that none of them are particularly earth-shaking methods. For example, ever hear of an olive press? One of the ways for extracting oil from algae works very much like the technique used in an oil press. This is the simplest and most common method for extracting oil from algae and yields about 75% of the total available oil from the algae plant.

Another common method is the hexane solvent method. When combined with the oil press method, this step can yield up to 95% of available oil from algae. It utilizes a two-step process. The first is to utilize the oil press method. Then, instead of stopping there, the leftover algae is mixed with hexane, filtered and cleaned to remove all traces of the chemical in the oil.

Used less frequently, the supercritical fluid method can extract up to 100% of available oil from the algae. Carbon dioxide is pressurized and heated to change its composition into both a liquid as well as a gas. It is then mixed with the algae, which turns completely into oil. Though it can yield 100% of available oil, the plentiful supply of algae, plus the additional equipment and work required, make this one of the least popular options.

An AlgaeLink Algae growing system that is harvested to make ethanol and biodiesel. Producing oil from algae in this way is much more efficient than from growing traditional plant oil crops like oil seed rape. It also has the benefit that it does not take

Construction Photography / Getty Images

Growing Algae for Biodiesel

The methods used for promoting algae growth in a particular way to yield the most oil are more diversified than the extraction processes. Unlike practically universal extraction methods, growing algae for biodiesel varies greatly in the process and method used. It is possible to identify three primary ways to grow algae, and biodiesel manufacturers have worked hard to tweak these processes to customize and perfect the growing process.

Open-Pond Growing

One of the easiest processes to understand, open-pond growing is also the most natural way to cultivate algae for biodiesel production. As its name implies, algae are grown on open ponds in this method, particularly in very warm and sunny parts of the globe, with the hope of maximizing production. Though this is the simplest form of production, it has serious drawbacks, like comparatively high potential for contamination. To truly maximize algae production this way, water temperature needs to be controlled, which can prove very difficult. This method is also more dependent on weather than others are, which is another impossible to control variable.

Vertical Growth

Another method for growing algae is a vertical growth or closed-loop production system. This process came about as biofuel companies sought to produce algae faster and more efficiently than they could with pond growth. Vertical growing places algae in clear plastic bags, which are stacked high and covered as protection from the elements. These bags allow exposure to sunlight from multiple directions. The extra light is not trivial, as the clear plastic bag allows enough exposure to increase production rates. Obviously, the greater the algae production, the greater the amount of oil to extract. Plus, unlike the open pond method that exposes algae to contamination, the vertical growth method isolates algae from it.

Closed-Tank Bioreactor Plants

The third method of extraction biodiesel companies utilize is closed-tank bioreactor plants, a method of growing algae inside that increases already high oil production levels. Indoor plants are built with large, round drums that can grow algae under near-perfect conditions. Algae can be manipulated into growing at maximum levels in these barrels, even to the point of daily harvests. Understandably, this method results in very high outputs of algae and oil for biodiesel. Closed bioreactor plants can be built near energy plants to recycle extra carbon dioxide rather than polluting the air.

Biodiesel manufacturers continue to hone the closed container and closed-pond processes, with some developing a variation known as fermentation. This technique cultivates algae that "eats" sugar in closed containers to spur growth. Fermentation is attractive to growers because it provides complete control over the environment. Another advantage is that it doesn't rely on weather or similar climatic conditions to be viable. However, this process has researchers mulling over sustainable methods to obtain enough sugar to maximize algae production.

Originally written by
Lori Weaver
Lori Weaver is a freelance writer covering renewable fuel and green transport technologies, as well as food and feed issues in the agricultural sector.
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