Brief background on fossil fuels, biofuels, and greenhouse gasses.

What are fossil fuels?

Fossil fuels are carbon based geological deposits.  When organic matter is buried, decays, and is compressed for millions of years it transforms.  They can form crude oil, natural gas, or coal.   They are called fossil fuels because they are essentially made up of fossils of organic material that has transformed.  Instead of the carbon being released into the atmosphere, it has been captured in these forms.

So, what’s the problem with burning fossil fuels?

The main problems with burning fossil fuels for energy are threefold.

1.       Mining the fuels is “dirty”.  Simply put, oil spills; mining for coal involves ripping the tops off mountains, and “fracking” for natural gas is possibly the worst things we can do to contaminate our drinking water.  This is a very interesting topic, but we will not focus on it here.

2.       Burning fossil fuels (burning anything for that matter) releases greenhouse gasses into the environment.

3.       Fossil fuels are not pure substances and have many contaminants that also are spewed into the atmosphere (eg. sulfur in coal)

What are biofuels?

Simply put, biofuels are fuels that you make from living things, or their byproducts.  As an example, wood is among the simplest biofuels.  Since biofuels are grown, they have an inherent sustainability in their production.  In contrast to fossil fuels, bio fuels are replenishable, and can be grown well after fossil fuels are scarce.  Biofuels are traditionally broken down into three categories called first, second and third generation.

1) First generation biofuels are made from the sugars of edible plants.  Some of the most common examples are corn, beets and sugarcane.  The sugars or starches from these plants are fermented to produce enthanol.  Although the technology is there, turning edible crops into fuels can be a bit troublesome as a world where people are going hungry.  Given our finite resources (water, land, phosphorous etc.) it is not a socially responsible system.  Food crops are also not as energy dense as other crops that can be farmed, if the goal is simply to produce fuel.  

2) When using non-edible agricultural products such as wheat straw and corn husks for biofuels they are known as second generation biofuels.  Benefits include using parts of plants that cannot feed people as a source of fuel.  The extraction process is more expensive (financially and in terms of energy), however, they do not have the pitfalls of using food for fuel.  The sugars are not readilly available (they contain complex carbohydrates instead) as they are in first generation biofuels so they must undergo extensive treatment to "extract" a useful fuel.

3) Although algae could be looked at as a second generation biofuel, its efficacy is so promising that they are generally considered in a category of their own, called third generation biofuels.  Not only does algae grow fast, it contains a relatively large concentration of lipids (fats) and can be extracted with moderate ease.  A significant amount of the fats can be expeller extracted (like olive oil) and even more can be extracted using a recoverable solvent.  The algae extraction products known as "green crude" is very similar to crude oil chemically, thus can be turned into a biodiesel with moderate ease.  The main limitation for algae is phosphorous, which is a vital nutrient for growing the food we eat.  Although this is a problem for all biofuels, the rate at which algae can be grown, combined with the lipid content and ease of extraction make it such a strong candidate for fueling our transportation fleet.  Phosphorous limitations become more important with algae because it is seen as having such enormous potential, but unfortunately we need an enormous amount of phosphorous to utillize it.  Currently it is very energy intensive to recover the phosphorous from the algae waste; hopefully easier methods are discovered.

What are greenhouse gasses and why do they matter?

Greenhouse gasses act just like the glass in a greenhouse.  In a greenhouse the light enters, but when it reflects off the ground some of it gets trapped, thus leading to heating of the enclosed area.  Gasses are like other materials in the way that dense objects sink while less dense objects float (think of a balloon on water).  Greenhouse gasses such as carbon dioxide are denser than air, thus they sink near the surface. Being that they sink, greenhouse gasses accumulate near the surface.  They act as a lens and trap the heat close to the surface in the same way the glass in a greenhouse does.  There are many different greenhouse gasses which vary in how effective they are at trapping heat.

What causes these greenhouse gasses to accumulate? What does it have to do with fuels?

When burning hydrocarbon fuels (coal, oil, gasoline, diesel, natural gas etc.) the main products of combustion are water vapor and carbon dioxide.  Although carbon dioxide is not the strongest greenhouse gas (methane is about 21 times more effective), we release an extremely large amount of it into the atmosphere, which makes the effects large.  The most prominent source, is from combustion.  Combustion is how we obtain roughly ¾ of the electricity in this country, and almost all of the energy fueling cars and trucks.

It's great that biofuels are sustainable, but wouldn't burning them release greenhouse gasses as well?

This is an important question, and the answer helps illustrate the importance of biofuels.  As discussed earlier, combusting hydrocarbons releases carbon into the air, even if they are derived sustainably (so yes, even biofuels produce greenhouse emissions when burned).  The important distinction is that biofuels by their nature used carbon from the atmosphere to be produced, and the carbon would be released upon their decay.  Photosynthesis (which is the reaction that enables plants to grow) uses carbon dioxide as a reactant (ingredient), and releases oxygen as a product (a simplified view, but true nonetheless).  This process uses carbon in the air and uses it for growth.  If you have ever wondered where the “stuff” of a plant comes from, it’s the carbon from photosynthesis!  So, when burning a biofuel, it has a somewhat net neutral effect on the amount of carbon in the atmosphere.  It is a bit more complicated than that, as they need energy to be grown, transported and processed.  Ideally in the future all of our energy needs will be met using carbon-free sources, however, that is a long time away.  In the near future it is imperative  that we figure out ways of reducing our carbon emissions on the planet.