How bio-waste could fuel your next flight

We all know the world must do more to tackle carbon emissions. The Inter-Governmental Panel for Climate Change’s (IPCC) latest assessment report shows climate change strategies submitted in 2015 by nations during COP 21 in Paris are not adequate to contain global temperature rises within 2-degree celsius limits. The report underlines the urgent need to decarbonize the environment by deploying technology in our daily lives that reduces the carbon intensity of our actions across all spectrums of human activity. The zero-carbon future demands immediate action from all of us.

In October 2021, the global air transport industry committed to achieving net-zero emissions by 2050 – but this will not be an easy task. The average long-haul flight generates more CO2 than the per capita emissions of many countries. A large aircraft such as a Boeing-747, for example, consumes around 4 litres of aviation fuel per second - or about 534 kgCO2e per person for a round trip from New Delhi to London.

To meet this emissions reduction goal therefore, the aviation industry must abate a cumulative total of 21.2 gigatons of carbon between now and 2050. Continuous improvements in operations and infrastructure, and the development of national biofuel policies, could help the sector achieve this aim.

Developing sustainable fuels

An alternative to the current use of fossil fuels by the aviation sector is to use sustainable aviation fuel (SAF). One of the ways SAF can be produced is by using bio-based resources. This could be a major solution to decarbonisation of the aviation industry in the near future. SAF benefits from high greenhouse gas (GHG) savings potential, is based on widely-available feedstock and uses rapidly-maturing technologies to process this feedstock into sustainable fuel.

The technology landscape for production of SAF is changing and many new technologies and pathways are rapidly becoming commericalized. The American Society for Testing and Materials has defined international specifications for SAF and has already approved several technology pathways, including alcohol-to-jet (ATJ), which utilizes agricultural residues and carbohydrate-based feedstock, and hydro-processed esters & fatty acids (HEFA), which uses waste lipids such as cooking oil as feedstock. These are a few of the feedstocks currently certified to produce SAF by the International Civil Aviation Organisation’s Carbon Offsetting & Reduction Scheme for International Aviation.

In India, SAF produced via the ATJ pathway holds great potential due to the surplus availability of feedstock, such as agricultural residues. An estimated 500 million tons of agricultural residues are generated annually in India, out of which a significant amount of agricultural residue is burnt on the field every year. This not only causes severe air pollution and health hazards, but also impacts agriculture productivity.

Producing sustainable fuels – and more

Based on the ATJ pathway, and using agricultural residues as feedstock, a multi-product biorefinery could produce SAF, as well as green hydrogen, ethanol and biobased material such as bio-bitumin as co-products during the refining process. Even converting just 5% of total agricultural residues would yield around 2 billion litres of SAF per year saving around 3 million tons of carbon emissions. Further carbon emission savings could be derived from the billions of high-value low carbon renewable fuels produced as co-products during the refining process.

This will not only contribute to environmental solutions, but will also help to improve the rural economy. Collecting agriculture residues as feedstock for conversion into biofuels could create employment in rural areas and provide an alternative sustainable revenue stream for farmers. In this way, rural entrepreneurship would be supported by the effort to build a robust ecosystem to facilitate supply chains for feedstock, bio-aggregations and transportation.

Additionally, sugary feedstock such as molasses could also contribute to SAF volumes, if they meet the sustainability criteria. Even with 20% ethanol blending mandates in India, there is still likely to be surplus feedstock such as damaged grains or sugary streams for production of SAF.

Scaling up the sustainable fuel production

The technology for production of SAF through an ATJ pathway is a two-step process. Feedstock is first converted into alcohols and then further processed into SAF. The technology for the second step – converting alcohol into SAF – involves standard unit processes that are already used in refineries.

Converting sugary streams and damaged grains into alcohols uses mature technology that has been developed indigenously and commercialised worldwide. The technology for converting agricultural residues into alcohol is also indigenously developed but has yet to be commercialized in India.

Oil companies in India are already planning 12 plants that would convert agricultural residues into alcohol – 4 of these plants are already under construction and expected to be operational in a couple of years. The success of these first plants would pave the way for more capacity to process agricultural residues into alcohol.

Gaining global momentum

There is growing global momentum for use of SAF and it is being driven by national biofuel policies. The US announced plans in September 2021 to provide up to $1.75 per gallon of tax credits to SAF producers, for example. The EU has also proposed a mandate to blend 2% of SAF by 2025, with a gradual increase to 63% by 2050. In India, initiatives such as the National Policy on Biofuels 2018, the Sustainable Alternative Towards Affordable Transportation and national solar and hydrogen missions support the transition towards cleaner energy to achieve the country’s climate goals.

The commercial use of SAF in India will require further strategic policy interventions, however, with incentives needed throughout the value chain and supply chain. Infrastructure must be developed from the logistics of collecting agricultural residues through to delivering SAF to airports. India’s access to rapidly scaling technologies and surplus feedstock for the production of SAF provides it with the opportunity to become a leader in decarbonising the aviation industry. With a series of initiatives to encourage production already in place, we can expect the India’s SAF industry to be ready for take-off very soon.