The Problem

Climate change and global warming have been buzzwords since this millennium started. What humankind couldn’t do in 2000 years was done with the advent of modern technology in the last 200 years. With the marvels of science and technology, we dived into the deepest oceans, flew across the highest mountains and explored other planets. These feats came at the cost of overexploiting fossil fuels and polluting the environment with greenhouse gasses, plastics etc. leading to an increase in average global temperature, rise in sea levels and melting of glaciers.

It's time we move towards sustainable development by using alternative energy sources. We are focusing on the transportation sector, mainly the aviation industry as it is one of the major culprits of CO₂ emissions. While the world is moving towards electric vehicles, not much is done about flights as they can operate only with high energy density(HED) fuel. Air transport has made our lives so much easier and faster that there is no going back. The problems that ensued due to the COVID-19 pandemic, are a testimony to our irreplaceable dependence on the aviation industry.

Further, India is soon going to host one of the largest aviation industries in the world.^[1]

A Step Towards the Solution

Sustainable Aviation Fuel as the Solution

The aviation industry’s net-zero carbon emissions target is focused on delivering maximum reduction in emissions at source through the use of Sustainable Aviation Fuel (SAF).

SAFs are liquid fuels which can reduce the CO₂ emissions by upto 80%. It can be produced through various sources (feedstocks) fats, oils, agricultural residue etc. SAF can be considered sustainable because it does not require any incremental resource usage and does not promote environmental challenges such as deforestration, soil productivity loss or biodiversity loss, whereas fossil fuels add to the overall level of CO₂ by emitting carbon that had been previously locked away. SAF recycles the CO₂ which has been absorbed by the biomass used in feedstock during the course of its life.

Problem of Feedstock

Airlines have committed to net-zero emissions by 2050 at the 77th International Air Transport Association (IATA) annual general meeting in 2021 to contribute to the Paris Agreement of limiting the global temperature rise to 1.5 degrees Celsius. IATA estimates that SAF could contribute of 65% reduction in emissions to reach net zero by 2050. This will require a massive increase in production of SAF in order to meet the demand.

The reason why SAF has not been able to reach its maximum potential in terms of production is because the feedstock becomes limiting to produce SAF on a commercial scale. With the increasing number of mandates put by international policies and governments on airlines, feedstock availability becomes crucial.^[20]

Current Solutions

There are 7 technologies approved by ASTM currently. Out of these the prominent ones include Hydrotreated Esters and Fatty Acids (HEFA) pathway^[21], Alcohol to Jet pathway (ATJ)^[22], Fischer-Tropsch synthesis^[23] (FT) and Power to Liquid^[24] (PtL).

Fig 7: This depicts the expected cost of SAF production through various pathways in the years to come

Out of these, the HEFA technology is the most suitable because of its established production because the cost of production of HEFA is expected to be the lowest out of these.

The currently used feedstock for the HEFA pathway is Jatropha oil and Used Cooking Oil (UCO) but it continues to remain limiting in the production of SAF through this pathway. While production cost is estimated to be the lowest in case of HEFA due to the industrial set up required and the technology used for the same, it is important that the feedstock be available in surplus to scale up the production of SAF.

Jatropha and its Problems

Oil Consumption in India

The implementation of The National Mission of Biodiesel policy in 2003 in India happened within the biofuel hype that supported renewable energy use around the globe, specifically in the transportation sector, which is responsible for the second largest share (23%) of global carbon dioxide emissions. One of the main goals behind India’s biofuel policy was to reduce the country’s dependence on energy imports. India covers 26% of its total primary energy consumption from crude oil, of which around 80% is imported. Diesel remains the most-consumed oil product in India, accounting for 39% of petroleum product consumption in 2019, and is used primarily for commercial transportation.

Another important motivation included the goal of reducing CO2 emissions, although we have way lower per capita emissions when compared to the global average, we still account for 7% of it.^[2]

Jatropha Curcas

Jatropha curcas is a plant native to South America which now grows naturally in tropical and subtropical areas around the world. The mature Jatropha curcas seeds are 212 cm in length and may easily be cracked to extract the oil. Toxins such as phorbol esters, curcin, trypsin inhibitors, lectins, and phytates are present in such high amounts in seeds making it highly unfit for consumption without detoxification.

Its great potential to produce biofuels was first realised at the turn of the 21st century, with many experiments done to assess its economic feasibility, heralding it as a “magical biodiesel plant” and being “pro-poor”. The then-Indian President Dr. APJ Abdul Kalam praised the positive properties of the shrub. He planted it on the presidential estate, met with farmers to encourage them to go for the crop and was also seen riding a Jatropha oil-fueled vehicle. Many felt that the plant would actually change their fates.

The Tamil Nadu Agricultural Institute did experiments showing the high economic viability of extracting Triacylglycerols from Jatropha Curcas to be used directly as biodiesel without further processing.

Initial claims about the Jatropha plant were:

• Jatropha had a high oil yield even under marginal conditions.
• It was not prone to many common pests and diseases.
• It was drought-tolerant and did not require a lot of irrigation.
• Farmers could reclaim wastelands that can be converted into Jatropha plantations.
• It was said to be suitable for soil erosion control and prevention.
• Its seed cake could be used as organic fertilizer and as a high-quality livestock feed.

These claims disillusioned farmers, policymakers, and the general public to believe that:

• Achieving energy security,
• Revitalizing marginal and degraded lands, often referred to as wastelands, and
• Addressing rural poverty through job creation and sustainable biofuel production

were all possible with J. curcas plantations.

However, when this plant left the rich controlled environment of the institute and was tried to grow on semi-arid lands, the results could not be reproduced. Further, the plant had generally lost popularity due to its low yield under unfavorable conditions.

Due to the anticipated environmental advantages, large-scale Jatropha plantations have been established in other Asian nations as well, notably Indonesia and China, as well as in African and Latin American countries.

But How Much was Achieved?

The so-called “Global Market Study on Jatropha” published by Global Exchange for Social Investment (GEXSI) commissioned by the World Wide Fund for Nature (WWF) in 2008, claims that (with no reference to back these up) the area that has been or will be planted under Jatropha: close to 1 million hectares at the time of report writing, 5 million hectares in 2010 and 13 million hectares in 2015.

With the cherry-picked evidence and discursive practices for biofuel promotion, especially Jatropha, the government of India had then sanctioned millions of hectares of government wastelands for the cultivation of the plant, but there was a catch.

For them to reach their goal of the biodiesel blending targets set in the Indian Biofuel Policy, it could be only done by converting 4-5% of the land of our country (around 14-17 million hectares), which quite obviously, wasn’t available. In a country, where 2/3rds of the land is under agricultural practices, this paved the way for severe anti-biofuel discourses which stressed on the food vs fuel conflicts.

Coming to the environmental effects of planting Jatropha, Reinhard and Achten concluded that J. curcas cultivation has a higher impact on acidification and eutrophication than the use of fossil fuels. Thus, the environmental burden might be shifted from global warming to other environmental impacts if biofuels are used instead of fossil fuels.^[3]

Methods of Production

Many approaches are being used in order to improve the process by extracting the highest amount of oil from the Jatropha curcas seed at the lowest possible cost including Mechanical extraction (cold press technique and expeller-pressed method), solvent-based extraction (Soxhlet extraction method) and a few new technologies in oil extraction have been established, including supercritical fluid extraction, ultrasound-assisted extraction, and microwave-assisted extraction.^[4]

Engine Performance and Emissions

In short, aviation fuel benefits from

Jatropha oil possesses a unique chemistry of constituent fatty acids, a high cetane rating, and low sulfur content, making it the perfect candidate for aviation fuel purposes.

Further, the increasing proportion of Jatropha biodiesel in the diesel–biodiesel blend reduces hydrocarbon (HC) emissions^[5].It was reported^[6] when compared to diesel fuel, an increase in biodiesel percentage results in a reduction in HC emissions of 14.91–27.53 percent. Lower HC emissions are usually observed at full load conditions than other load conditions^[7].

Economic Viability of Jatropha Biodiesel Production

It was reported^[8] that based on a yield of 2000 kg per year from mature trees, yearly operational expenditures for 1 ha of Jatropha curcas are estimated to be about 200USD. Picking and post-harvest processing make for a large number of total expenses, they said. Thus annual expenditures are strongly reliant on production. Because Jatropha curcas growing requires a lot of labour, it’s difficult to achieve or sustain economic viability. Jatropha curcas can be intercropped with annuals, perennials, or trees which boosts soil productivity acts as a soil cover and gives instant extra revenue to farmers.^[8]

Although large scale plantations of Jatropha have been done in various agro-climatic regions of the world, the growth performance, seed yield and oil content of the plant were far lower than expected . An expected seed yield of 4-5 mg ha 1 yr 1 was considered to be commercially viable for a Jatropha-based biofuel program and an average seed yield of 3.75 mg ha / yr with an oil content of 30–35% and oil yield of 1.2 mg ha / yr is better than the yield profile of other important oil seed crops such as soybeans^[9][10]. However, the actual seed yield reported from various countries like India (0.5–1.4 mg ha / yr ), Belgium (0.5 mg ha / yr ), South Africa (0.35 mg ha / yr ) and Tanzania (2 mg ha / yr ) was less than the expected level.^[11][12]

Our Solution

Our project, ‘JetroEco’, answers the questions raised by the usage of conventional fuel, like the impact on ecology, and also provides a better way of producing biofuels, one that doesn't have a lot of obstacles.

We plan to clone the two major thioesterases of Jatropha curcas - JcFatA and JcFatB (which are responsible for synthesizing 91% of Jatropha oil's fatty acid content) into an oleaginous yeast Yarrowia lipolytica

• We are trying to clone Jatropha curcas thioesterases (JcFATA and JcFATB) into Yarrowia lipolytica so that it can act on acyl ACP/CoA to convert them into fatty acid with a composition of that of Jatropha oil.
• To increase the yield of these fatty acids, we are trying to delete two genes - FAA1 (which takes the fatty acids to the beta-oxidation pathway) and ALK2 (which converts fatty acids to fatty alcohols).
• We plan on integrating ScRAD52, recombinase, from Saccharomyces cerevisiae into the genome of Y.lipolytica to increase its rate of homologous recombination for genomic integration.
• We plan to introduce a photodecarboxylase enzyme CvFAP from Chlorella variabilis to convert the fatty acids into hydrocarbons (alkanes and alkenes).
• This will ensure that minimal chemical processing of our product is required, as all the steps until production of hydrocarbons are done in vivo.

Our Chassis

We chose the model oleaginous yeast, Yarrowia lipolytica for its high production rate and accumulation of lipids relative to its dry weight as compared to other yeast organisms like the commonly used Saccharomyces cerevisiae. Furthermore, its genome has been mapped and there are multiple genetic tools available which are specific to Yarrowia lipolytica. With the high oil producing capacity of this chassis, we wish to upscale the production of the superior Jatropha-based jet fuel.