The term third generation biofuel has only recently enter the mainstream it refers to biofuel derived from algae. Previously, algae were lumped in with second generation biofuels. However, when it became apparent that algae are capable of much higher yields with lower resource inputs than other feedstock, many suggested that they be moved to their own category. As we will demonstrate, algae provide a number of advantages, but at least one major shortcoming that has prevented them from becoming a runaway success.
Fuel Potential of Third Generation Biofuels
When it comes to the potential to produce fuel, no feedstock can match algae In terms of quantity or diversity. The diversity of fuel that algae can produce results from two characteristics of the microorganism. First, algae produce an oil that can easily be refined into diesel or even certain components of gasoline. More importantly, however, is a second property in it can be genetically manipulated to produce everything from ethanol and butanol to even gasoline and diesel fuel directly.
Butanol is of great interest because the alcohol is exceptionally similar to gasoline. In fact, it has a nearly identical energy density to gasoline and an improved emissions profile. Until the advent of genetically modified algae, scientists had a great deal of difficulty producing butanol. Now, several commercial-scale facilities have been developed and are on the brink of making butanol and more popular biofuel than ethanol because it is not only similar in many ways to gasoline, but also does not cause engine damage or even require engine modification the way ethanol does.
The list of fuels that can be derived from algae includes:
Diversity is not the only thing that algae has going for it in terms of fuel potential. It is also capable of producing outstanding yields. In fact, algae have been used to produce up to 9000 gallons of biofuel per acre, which is 10-fold what the best traditional feedstock have been able to generate. People who work closely with algae have suggested that yields as high as 20,000 gallons per acre are attainable. According to the US Department of Energy, yields that are 10 times higher than second generation biofuels mean that only 0.42% of the U.S. land area would be needed to generate enough biofuel to meet all of the U.S. needs. Given that the U.S. is the largest consumer of fuel in the world, that is saying something about the efficiency of algal-based biofuels.
Cultivation of Third Generation Biofuels
Another favorable property of algae is the diversity of ways in which it can be cultivated. Algae can be grown in any of the following ways.
- Open ponds – These are the simplest systems in which algae is grown in a pond in the open air. They are simple and have low capital costs, but are less efficient than other systems. They are also of concern because other organisms can contaminate the pond and potentially damage or kill the algae
- Closed-loop systems – These are similar to open ponds, but they are not exposed to the atmosphere and use a sterile source of carbon dioxide. Such systems have potential because they may be able to be directly connected to carbon dioxide sources (such as smokestacks) and thus use the gas before it is every released into the atmosphere.
- Photobioreactors – These are the most advanced and thus most difficult systems to implement, resulting in high capital costs. Their advantages in terms of yield and control, however, are unparalleled. They are closed systems.
Note that all three systems mean that algae are able to be grown almost anywhere that temperatures are warm enough. This means that no farm land need be threatened by algae. Closed-loop and photobioreactor systems have even been used in desert settings.
What is more, algae can be grown in waste water, which means they can offer secondary benefits by helping to digest municipal waste while avoiding taking up any additional land. All of the factors above combine to make algae easier to cultivate than traditional biofuels.
Third Generation Biofuel Feedstock
One of the major benefits of algae is that they can use a diverse array of carbon sources. Most notably, it has been suggested that algae might be tied directly to carbon emitting sources (power plants, industry, etc.) where they could directly convert emissions into usable fuel. This means that no carbon dioxide would be released from these settings and thus total emissions would be reduced substantially.
As with everything, algae have a down side. In this case, the downside is large and if it cannot be solved, is a deal breaker. Algae, even when grown in waste water, require large amounts of water, nitrogen and phosphorus to grow. So much in fact that the production of fertilizer to meet the needs of algae used to produce biofuel would produce more greenhouse gas emissions than were saved by using algae based biofuel to begin with. It also means the cost of algae-base biofuel is much higher than fuel from other sources.
This single disadvantage means that the large-scale implementation of algae to produce biofuel will not occur for a long time, if at all. In fact, after investing more than $600 million USD into research and development of algae, Exxon Mobil came to the conclusion in 2013 that algae-based biofuels will not be viable for at least 25 years. What is more, that calculation is strictly economical and does not consider the environmental impacts that have yet to be solved.
A minor drawback regarding algae is that biofuel produced from them tends to be less stable than biodiesel produced from other sources. This is because the oil found in algae tends to be highly unsaturated. Unsaturated oils are more volatile, particularly at high temperatures, and thus more prone to degradation. Unlike the fertilizer requirements above, this is a problem that has a potential solution.