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The wonder of waste

Biofuels can be produced from a wide variety of waste products:

To get them from municipal waste, the world's third-largest chemical company, Ineos, uses a simple three-stage process. The waste is first superheated to produce gases. Then, the gases are fed to naturally occurring bacteria, which efficiently produce ethanol. Finally, the ethanol is purified to be blended for use in cars.

Getting them from cheese, is something Ireland's Carbery Group has mastered. The company had far too much whey, in the 1970s, after Ireland's membership of the Common Market. Carbery soon realised that if it removed the whey proteins to put in baby food and sports and nutrition foods, it could ferment and distil the leftover lactose to make ethanol.

There are different theories on how biofuel can best be made from algae, but one method is unique because it is derived from wild algae that naturally inhabits sewage ponds, as opposed to purpose-grown algae. The slime offers great potential because it has such a high lipid density, meaning that a great deal of oil (derived from the human waste in the pond) can be extracted from it to turn into biodiesel. The downside is that sewage treatment facilities are generally limited in size and many do not even have open ponds.

Old tyres can also be turned into biodiesel, using pyrolysis. This essentially returns the high heating value of the rubber and oils that were initially used in the manufacture of the tyres. By carefully controlling the temperature, pressure and oxygen level, more pyrolysis oil and charcoal is encouraged. This oil can then be used as a form of biodiesel.

One US company is making the fuel from the skin of one of America's favourite fruits - oranges. The company behind the newly-owned pilot plant - Xethanol Corporation - explains that citrus waste is rich in pectin, cellulose and hemicellusic polysaccharides, which can be hydrolyzed into sugars and fermented into ethanol.

Last year, two British adventurers successfully made an 8,500km trip driving from the UK to Timbuktu in Mali on a truck that was fuelled by biodiesel made from waste chocolate. Ecotec, the company behind the chocolate-based fuel, explain: "Firstly we use recycled cooking oil as the basis for the biodiesel. Ethanol or methanol are crucial ingredients in making biodiesel, and are used in large quantities. Ecotec has developed a process for converting waste chocolate from a nearby factory into bioethanol on an industrial scale."

Methane-rich cow manure can contribute to the production of biofuels in a number of ways. For example, one site in Wisconsin says it utilises 200,000 gallons per day of cow manure to produce two million gallons per year of ethanol. This is done via a "High Yield Anaerobic Digester" which collects animal waste at dairy feeding locations and then ferments it. The mixture of methane or biogas is collected and further processed in an alcohol conversion unit and distilled into fuel-grade bioethanol. Alternatively, the methane can be used directly as a gas in cars.