As aircraft are bound (still) to a liquid fuel (it has the most energy content per weight) alternative resources need to be converted into liquid fuels. The industry needs to consider which source is the best for biofuel, it needs to be relalitively easy to 'harvest' compared to fossil fuel, with no impact on human food or water supply whatsoever and must be environmently friendly.

Aircraft engines still cannot run on water but, indirectly, this water can be and is a source of algae. And these algae have a high yield compared to other biomass sources which makes them very interesting to the energy industry. A big advantage of many biofuels over 'normal' fuel types is that they are biodegradable, and if spilled harmless to the environment.

The aviation industry is working hard at reducing fuel consumption, mainly by better engine design, newer cleaner fuels and better aerodynamics and aircraft design.

Environmental Issues

Like any user of petroleum based fuel, the aviation community is aware of the results of using fuel on the environment. To date aviation is responsible for about 2% of man made CO₂ in the atmosphere and a number of studies and industry efforts are active to reduce fuel consumption even further and search for alternative and clean fuel options.

But what about the climate?
Wikipedia: "Existence of the greenhouse effect as such is not disputed. Naturally occurring greenhouse gases have a mean warming effect of about 33°C (59°F), without which Earth would be uninhabitable. On Earth, the major greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect (not including clouds!); carbon dioxide (CO₂), which causes 9-26%; methane (CH₄), which causes 4-9%; and ozone, which causes 3-7%".

Aviation and the environment
Our atmosphere is a layer of gases surrounding our planet and it is kept there solely by its gravity. It contains about 78% nitrogen; 21% oxygen; 0,93% argon; 0,038% carbon dioxide (CO₂), some minute amounts of other gases and a variable amount (average around 1%) of water vapor (resulting in clouds and rain). This complete mixture is known to us as air.

Off all the CO₂ emitted in the atmosphere (0,038%) only 3% is of human origin (0,00114%). Worldwide aviation emissions causes only 2% of all man made pollution in the atmosphere (0,0000242%). Taxing fuel will not help, people will always keep traveling. CO₂ emmissions trading will probably do more if we can avoid long legal battles.

Lets not forget that aviation is one of the most (if not the most) economic method of transportation. There are no real alternatives as of yet. Cleaner fuels are being developed right now and this will increase the advantage aviation has on other forms of transportation.

Energy sources

Energy can be found on this planet in all kinds of forms: in direct sunlight, plants, animal waste, forest residue, algea and a lot more. The source of this is the sun, but as current solar cells do not have a high yield, we need to tap into a converted form of solar energy.

Fossil fuel is still a relatively easy to find form of energy, but it is not readily renewable (it took the planet thousands, millions of years to create it). We need another form that is renewable, cheap, has high energy content, easy to obtain and friendly to the environment.

The only source that will not compete with food supply and other energy sources is algae. Algae fuel, commonly known as algal fuel is a third generation biofuel made from algae, aka pond scum. Compared with second generation biofuels (made from food sources), algae are high-yield still high-cost (30 times more energy per acre than terrestrial crops) feedstocks to produce biofuels.

Algae love CO₂! It is food for them and they thrive on it. It is therefore not neccessary to store this gas underground to keep it out of the atmosphere. Algae farms can use it to accelerate production and using fuel based on algae is then neutral for the climate (with regard to CO₂).

Biofuel

At present biodiesel (and its gasoline counterpart) is able to reduce emissions from a diesel or jet engine without any major changes in the engine itself. Just use it and enjoy the benefits. It can be mixed with JET fuel too and test with a King-Air has shown much cleaner exhaust gasses with almost equal performance.

Biodiesel is CO₂ neutral

A Delfin L-29 has been flying on biodiesel (made from waste oil) since October 2007 as a test aircraft. The fuel was produced by BioDiesel Solutions of Sparks, Nevada. This aircraft is type rated to use anything from heating oil, JP-4 and JP-8; and as such is ideal for testing purposes.

Biodiesel has been known to improve engine performance with much enhanced lubricity and reduction of emissions. It is very easy to use, nontoxic, biodegradable and contains almost zero aromatics and sulfur. At the moment the main biodiesel users are mass transit, trucking, marine, military, automotive and other sectors such as mining. Aviation will soon be one of them too.

In 1998, a study was sponsored by both the U.S. Department of Energy and the U.S. Department of Agriculture, which determined biodiesel reduces net carbon monoxide by 78 percent when compared to normal petroleum diesel. Biodiesel's carbon cycle is the cause of this. The carbon monoxide released into the atmosphere when biodiesel is burned is recycled by growing plants, which are later processed into fuel. So nothing is added to the atmosphere.

A number of airline companies are starting tests (early 2008) with bio- or GTL synthetic produced JET fuel to assess the performance and gain experience in running engines on these new fuels. Air New Zealand is testing with Jatropha oil as a source for synjet. These Jatropha-seeds are toxic and using this as fuel (like algea) will not impact food supply.