Last reviewed 13 November 2018

What role does mustard play in air travel? Would you expect to find it in tasty sandwiches or fuel tanks? The answer is, both. But although Qantas has used a 10% mustard blend in its renewable fuels, biofuels generally pose complex environmental challenges. Jon Herbert reports.

Biofuels are part of the clean energy revolution where fuels are grown as renewable crops rather than derived from fossil fuels, and they are in the ascendancy. But despite their low-carbon credentials in aviation and other transport areas, biofuels are facing headwinds.

The problem is that they pose a complex dilemma. While offering natural environmental answers at one level, they are also in direct potential competition with land valued for its food-growing capacity at another. To make the sustainability equations even more complex, other recent studies (which some organic groups disagree with) suggest that intense farming methods are the “least bad option” if used to also protect wilderness areas.

It is argued that by carefully taking certain factors into account — including a well-regulated carbon price, new crop alternatives, realistic logistical factors such as crop-selection, location, transport, processing and distribution costs — biofuels do factor in climate change solutions.

UK biofuel use

In the UK, the Renewable Transport Fuel Obligations (RTFO) Order requires transport fuel suppliers to make sure that a proportion of the fuel they supply comes from renewable sources. Latest data shows that 1621 million litres of biofuel were supplied in 2017–18, some 3% of total road and non-road mobile machinery fuels used. Of these, circa 1306 million litres (81%) meet sustainability requirements; biodiesel methyl ester (ME) — known as biodiesel — accounted for 48%, bioethanol for 47% and bio-methanol for 5%.

Additionally, information shows that the top five countries supplying feedstocks to the UK, including the UK itself, provided 63% of the total sustainable supply (UK feedstocks account for 25%). The most widely reported source for biodiesel was US used cooking oil at 133 million litres; this accounted for 10% of total fuel used and 21% of biodiesel. The most widely reported source for bioethanol was UK wheat — 140 million litres, or 11% of total fuel and 23% of bioethanol.

In terms of greenhouse gas (GHG) savings, the aggregated total was 76% when compared to fossil fuels. However, when emissions from indirect land-use change (ILUC) were included, this figure was reduced to 71%.

Biofuel pros and cons

The case for the best use of crop-growing land is complicated. One argument says that land capable of growing food for a rapidly-expanding world population facing environmental pressures from global warming is at a premium. A counter-view is that the world already produces enough food; problems are not agricultural but economic and political.

Conventionally, biofuels have been derived from the refining of crops like corn, soybeans and sugarcane to produce ethanol. However, one interesting finding is that food crops like corn are not the best for “clean” biofuel production. Instead, species like switchgrass need less water and fertiliser and can be grown on marginal farmlands, so-called because they are not ideal for food production. That is a welcome conclusion.

More detailed work is also being carried out on all the energy inputs involved in biofuel crop production. This includes the addition of fertilisers, the inevitable use of agricultural and haulage equipment, and the energy and financial costs of refinery conversion into finished saleable products which then need to be distributed and vended. For example, marginal lands produce lower yield rates. This means that haulage distances to refinery centres become important if all carbon emissions are included in the calculations through a complete life cycle analysis.

Pollution pricing

Research has also looked at factors such as incentives. These include biofuel prices and the economic cost of GHGs — an effective carbon price. Simply supporting clean energy producers is not seen to be enough; a clean energy premium is needed to drive behavioural changes.

Putting the right price on carbon pollution also sends important signals to biofuel growers that using fertilisers which add to overall carbon emissions is wrong. In other words, the balance of conditions for acceptable biofuel production is quite specific and delicate.

Other research

Two recent study reports also make interesting reading. The first, commissioned by the Government from the Royal Society and the Royal Academy of Engineering, suggests that planting millions of acres of trees and energy crops while also restoring wetlands and coastal habitats, will be essential in ensuring that the UK can become carbon neutral by 2050.

The recommendations intentionally do not involve the immediate development of new technologies, but do include the permanent underground carbon capture and storage (or Bio-energy with carbon capture and storage (BECCS)). Here, experts estimate that all former North Sea oil and gas drilling sites could provide some 20 billion tonnes of storage capacity; the UK would need 75 million tonnes of capacity annually.

The aim is to provide a system that generates some 14% of the UK’s power; equivalent to three large coal-fired plants running on biomass with BECCS. Specifically, the study finds that we should increase the UK’s forest cover by about 40%, import some biomass, plant circa 2.5 million acres of energy crops, restore wetlands and salty marshes, crush silicate rocks to be spread on farmland to absorb carbon dioxide (CO2) (plus a form of charcoal called biochar on farmland) and build more houses with timber.

Depending on geography, biofuel crops could include grasses like miscanthus in some areas but poplar and willow in others. Forests managed for biomass will include rapidly-growing trees like pines and willows.

Importantly, the study authors say a strong price for carbon is vital. Currently, the UK carbon price is circa $25 per tonne but needs to be in the range of $50–100 dollars a tonne.

Intensive farming

The other report published in September by Nature Sustainability ( finds that intensive, high-yield farming counter-intuitively is the best way to satisfy growing food demand while also conserving wilderness areas that safeguard biodiversification. Criticised by organic groups, the report suggests that correctly-managed intensive farming limits pollution and environmental damage.

The researchers, working with 17 international organisations, say that using the limited data available they have accounted for “externalities” like emissions, fertiliser and water use in respect of Asian paddy rice production, European wheat and dairy and Latin-American beef. They conclude that many high-yield systems involve less environmental damage and land use.

Going further, lead-author, Professor Andrew Balmford of the University of Cambridge, says that conserving species “with which we share the planet” means making better use of existing farmland rather than expanding agricultural land use.

To “get smart about high-yield agriculture” the world needs to cut “beef and other high-impact foodstuffs” consumption and make “space for nature”. But this might need incentives for farmers to take land out of production for the “public good” and payments for holding floodwaters and absorbing CO2.

Organic groups have responded that world food production is already adequate but poorly distributed and that the new study does not include high-energy and chemical inputs. They add that organic methods in fact can support 50% more wildlife to higher welfare standards. Soil health is also improved and can capture and hold up an additional 450kg of CO2 per hectare.

Qantas leads but not alone

A Qantas Boeing Dreamliner 787-9 on a scheduled 15-hour passenger service between Los Angeles and Melbourne created a world-first when it used a fuel blend with a 10% component from brassica carinata, an industrial type of mustard seed that farmers grow routinely as a fallow restorative crop in regular crop cycles. The carbon emission saving over the usual flight carbon profile was said to be 7%. Over the fuel’s full life cycle, the emissions saving was rated as 80%.

While invasive crops like palm oil compromise and reduce biodiversity, crops such as mustard are benign and yield 400 litres of aviation fuel, or 1400 litres of renewable diesel per hectare. Their use overcomes the consistency problem associated with processing oil wastes from sources such as fish and chip shops.

Qantas and Jetstar first used a blend of 50% cooking oil in 2012 on internal Australian flights. However, Qantas is not alone internationally. Alaska Airlines has run scheduled flights on a cooking oil blend, as has the Dutch airline, KLM. Qantas’s aim is to use some form of renewable fuel on all its Los Angeles flights by 2020 and hopes to set up an Australian-based biorefinery with Canadian company, Agrisoma Bioscience.

Currently, the biofuel component is capped at 50%; Qantas hopes this can be raised to 100%.


The UK is struggling to meet its legal-binding carbon emissions reduction targets. Replacing conventional fossil-based fuel use with renewable biofuels refined from a range of crop sources is an important tool in the battle, although aviation and, ironically, farming may never reach zero-carbon levels for technical reasons.

However, complex issues are involved. Biofuels are frequently accused of displacing food crops on valuable agricultural land and putting biodiversity at risk. Large palm oil plantations are often cited as a major culprit.

Research indicates that the careful selection of crop species, use of so-called marginal farmland, location and production methods to reduce transport and operational carbon footprints, plus incentives such as carbon pricing, can make biofuels viable.

A number of international airlines are experimenting with different biofuel strategies that are proving to be commercially successful.