Making Biodiesel From Algae

An AlgaeLink growing system harvests algae to make ethanol and biodiesel

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An attractive candidate for full-scale biodiesel production, algae is easy to produce and requires less land than many other plant sources commonly used for making fuels. Also, with a composition containing about half lipid oils, algae appear to be a rich resource as a biofuel feedstock.

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.

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. Some companies build closed bioreactor plants near energy plants to recycle extra carbon dioxide 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.