How to power tomorrow’s aeroplanes? It’s a question that many, from large aircraft manufacturers to university research teams, are grappling with. The plan is to detoxify aviation’s image as one of the foremost causes of emissions and fight back against those who claim that the industry’s damage to the environment outweighs the benefits of air travel.

Some of the ideas emerging are highly imaginative. Of course, not all will come to fruition, but the bandwagon is picking up speed. However, a word of caution about biofuel: as an energy source it is not without its critics – with many pointing to the potential for environmental harm caused by deforestation and the use of land that could otherwise be used for food production. That is important to remember when picking through the evolving initiatives.

‘Grassoline’ – more than just animal feed

That lawnmower waste in the garden could be much more valuable than first thought.

“Until now, grass has mainly served as feed for animals. We can get more out of grass: due to its vast abundance, it is an attractive source to produce organics such as aviation fuel,” said scientist Way Cern Khor, at Ghent University, earlier this year.

Khor and colleagues from Ghent’s Center for Microbial Ecology and Technology have, they claim, developed a way to turn grass into biofuel. The science bit goes something like this: grass is pre-treated to increase its biodegradability, before bacteria is used to convert the sugars in grass into lactic acid. The Ghent University website adds: “The lactic acid can already serve as an intermediate chemical to produce other compounds such as biodegradable plastics (PLA) or fuels. In this case, the lactic acid is converted into caproic acid which was [then] further converted into products such as decane, [which] can be used as fuel.”

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The idea is very much in its formative stage; only a few drops have been produced in a lab. Khor added: “If we can keep working on optimising this process, particularly in cooperation with industrial partners, the efficiency will come up and feasibility will follow. And maybe in a few years we can all fly on grass.”

From the kitchen, to the plane

In 2015, a Boeing 737, in use by Chinese airline Hainan Airlines, travelled from Shanghai to Beijing on a 50/50 mix of conventional jet fuel and biofuel derived from waste cooking oil collected from restaurants in China. Hainan said at the time that it was “showing that aviation biofuel can play a safe and effective role in China's air transport system.”

"Maybe in a few years we can all fly on grass."

The biofuel was supplied by Chinese oil refiner Sinopec. Zhenhai Refining and Chemical, a subsidiary of Sinopec, intends to start construction on a full-scale production plant to mass produce the biofuel sometime next year.

Reports suggest it could be sold to airlines operating long-haul flights. A spokesperson for Zhenhai Refining told the South China Morning Post: “The flight [Boeing 737] was a one-off; just for show. The plant, however, means long-term business.”

IATA’s alternative fuel plan

Not so much a single idea here, but more of a wide-ranging programme to push the use of alternative fuels. The International Air Transport Association (IATA), which represents 275 airlines, has set an ambitious target of a 50% net emissions reduction by 2050 compared to 2005, with one key plank being the commercialisation of biojet fuels.

The Sustainable Alternative Aviation Fuels Strategy (SAF) is the framework by which the IATA hopes to meet its target. SAF includes biojet fuel produced from oil crops such as jatropha, camelina and algae, as well as from wood and waste biomass.

In the SAF roadmap documentation, it describes how the first flight using a SAF blend took off in February 2008, when a Virgin Atlantic plane travelled from London Heathrow to Amsterdam using 20% biodiesel from coconut and babassu oil, which is extracted from the babassu palm found in the Amazon region of South America.

Also listed in the roadmap are three ‘pathways’ approved for SAF in commercial aircraft: Fischer-Tropsch, which converts solid biomass to a synthetic gas and then “processes the gas into a mixture of hydrocarbons including road and aviation fuels”; Hydrotreated Esters and Fatty Acids, which works by converting oils into fuel in a similar way to how crude fossil oil is refined; and Renewable Synthesized Iso-Paraffinic – fuel from “hydro-processed fermented sugars”.

Alaska’s alcohol-to-jet biofuel

Just over a year ago, two Alaska Airlines flights, departing from Seattle to San Francisco and Washington D.C., respectively, used something known as alcohol-to-jet biofuel, produced by Gevo, a renewable chemical and biofuel company.

The 20% biofuel blend was made by capturing the protein and fibre in non-edible field corn to create animal feed. Gevo then fermented the starch in the corn into isobutanol – a similar process to that which is used to make ethanol. Finally, the isobutanol is converted into a renewable jet fuel.

"Alaska used a 20% biofuel blend."

Glenn Johnston, Gevo’s executive vice president of regulatory affairs, said last year: “The amazing part about this is that you can make something like a carbohydrate into jet fuel and not have to change the plane at all.”

As for the environmental aspects, Alaska Airlines claimed last year that if it could replace “20% of its entire fuel supply at Sea-Tac Airport” with the biofuel, “it would reduce greenhouse gas emissions by about 142,000 metric tons of CO2.”

Not content with that, Alaska Airlines has also completed a commercial flight using waste tree limbs and wood scraps. The flight, from Seattle to Washington, D.C., took place in November last year, using a 20% blend sourced from forest projects in the Pacific Northwest region.

Virgin and industrial waste: five years in the making

Since 2011, and following on from the 2008 flight between London Heathrow and Amsterdam, Virgin Atlantic has been working with a company called LanzaTech to produce fuel from steelworks waste gases. Last September the breakthrough came when it was announced that 1,500 US gallons of jet fuel had been manufactured.

Labelled a “real game changer” by Virgin founder Richard Branson, Lanzanol, as the fuel is known, could result in carbon savings of up to 65% when compared to common jet fuel, according to Virgin.

Virgin says on its official website that LanzaTech believes it could retrofit the Lanzanol process “to 65% of the world’s steel mills.” This, it adds, could potentially produce 30 billion gallons of ethanol worldwide, for around 15 billion gallons of jet fuel per year.