Our utilization of fossil fuels has increased dramatically within the past 100 years as our needs for energy and transportation have risen. Evidence suggests that the burning of fossil fuels has contributed to the increased concentration of atmospheric carbon dioxide; this in turn leads to greater heat insulation and towards increased average global temperatures.  To compound this problem, fossil fuels are a finite, non-renewable resource and are necessary for society to function normally. Microalgae biodiesel has the potential to address these issues because combustion of this fuel would produce essentially no net increase in atmospheric carbon dioxide and because microalgae are quite robust, requiring minimum energy input and handling.
Microalgae are single-cell organisms and depending upon species, may live alone or in aggregates. Since some species possess a growth cycle of a few days, microalgae can reach maturity much faster than any other photosynthesizing plant. Having a quick growth rate offers many different advantages. Microalgae utilize carbon dioxide to produce sugars, and with such a fast growth rate, can act as a carbon dioxide reservoir.  This means even without harvesting the microalgae for its lipids to make biodiesel, we could theoretically utilize microalgae to reduce atmospheric carbon dioxide.
Research has shown that up to 40% of the body mass of microalgae consists of fatty acids (lipids); using this figure, estimates have shown that per acre, microalgae produces 200 times more lipids than the best terrestrial plants. These lipids/oils are then converted into biodiesel.  This could potentially reduce the need to convert corn, grain, and other important food crops into ethanol or biodiesel. This is important because in one review, it's been projected that the cost of producing biodiesel from vegetable oil and oilseed could cost up to US $0.54-0.62 per liter and US $0.30-0.69 per liter, respectively assuming all the correct infrastructure has been laid down beforehand; this shows the lack of economic feasibility for these biodiesel sources.  Additionally, because the microalgae are simply converting the carbon dioxide in the air into sugars and lipids, combustion of these organic products would result in essentially no net increase in atmospheric carbon dioxide, meaning carbon neutrality. More important, microalgae biodiesel contains up to 20 to 50 times less sulfur then petroleum based diesel, reducing the production of sulfur dioxide upon combustion and reducing the occurrence of acid rain. 
In addition to reducing air pollution, biodiesel is biodegradable unlike petroleum based diesel fuels.  This allows for much safer clean ups in the case of large spills and reduces environmental impact. One more attractive feature of microalgae biodiesel methyl esters is that it can improve the lubricity of diesel fuel blends. Using just 1% biodiesel by mass in fuel blends can reduce friction wear and tear on engines by as much as 30%, thus prolonging engine life. 
Microalgae biodiesel faces many potential economic/socio-political barriers that need to be properly addressed before any wide-scale implementation can occur. One instance of this dynamic is the utilization and acquisition of land dedicated for biodiesel production. This potentially means seizing of farmland or converting forests in order to make biodiesel production facilities.  According to one British Petroleum statistic, we consume 31 billion barrels of crude oil per year, and we would need to match this in terms of biodiesel production assuming the demand for more oil does not increase.  One estimate shows that 2.5 acres of microalgae can produce as much as 46 tons of oil per year.  We get a better idea of the consumption rate by converting this into barrels
|× 0.9072 tonnes/ton × 7.333 bbl/tonne||=||122.5 bbl/acre|
and then dividing this into the world consumption:
|31 x 109 bbl
|=||2.5 x 108 acres|
That means using as much as 250 million acres of land dedicated to microalgae production to meet current world demand.
To add to the dilemma, microalgae biodiesel will degrade in the presence of oxygen. Once oxidation has been initiated, a process called polymerization may occur in which the lipid molecules begin to aggregate, forming solid clumps instead of remaining as a liquid.  Coupled with the fact that microalgae biodiesel is biodegradable, this will pose a great problem for long term storage capabilities. Another technical issue that arises is the fact that biodiesel, including microalgae biodiesel, in general has lower energy content then petroleum based diesel due to oxygen content; this will lead to lower gas mileage.  They tested sunflower biodiesel and regular diesel using a 2.5 kW diesel engine. The engine's maximum power produced using petroleum diesel was found to be 53 kW at 4000 rpm, but using biodiesel, this dropped by 5% to about 50 kW at 4000 rpm. This means that at the same engine speed, the amount of energy being released is lower, meaning a greater fuel consumption rate in order to get the same output.
One last technical challenge that remains is how to deal with the waste products after harvesting the lipids from the microalgae. Suggestions have been made to use the waste products as feed for livestock or to allow bacteria to consume it and thus produce methane, another source of fuel. 
In summation, biodiesel derived from microalgae is a promising alternative to fossil fuels due to carbon neutrality, the fast growth rate of microalgae, and better engine life time. At the same time, it faces many hurdles including social, political, economic and technical issues. Microalgae biodiesel may not be the cure-all to our energy dilemma, but it represents a step in the right direction as we continue to pursue a clean, renewable fuel.
© 2010 Christopher Bruner. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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