Course:CONS200/2021/Aviation, Biofuels, and Sustainability: Is 'Green Travel' any Closer?

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With the advent and rise of globalization, aviation and air travel have become an increasingly integral part of the global economic and transportation systems [1]. Attributable to its massive contributions to employment, international trade, and tourism, the aviation industry continues to produce projections of exponential growth in most regions of the world[1]. As a result, the impacts of aviation including noise pollution, contamination of air quality, and climate change have elevated in relevance alongside environmental concerns[1].

Figure 1. Avation in motion

Contemporarily, approximately 5% of anthropogenic climate change is accredited to the worldwide impacts of the aviation sector, and with passenger transport expected to rise by an additional 4% per year, the strain it imposes onto the environment is only forecast to increase[2]. This consequence is a product of the current propellant system in the aviation domain which is highly dependent on oil-derived jet fuel; an unsustainable fossil-based energy source which emits carbon dense chemical contaminants known to damage the biosphere[1]. In order to significantly reduce greenhouse gas emissions in the aviation domain, biofuels derived from biomass, or plant material and animal waste have become popular potential solutions [3]. As a carbon neutral proxy to conventional jet fuels, biofuels may very well be a salient champion in humanity's time sensitive race against climate change [3].

Interest in supplementing “green travel” has grown steadily in favour of both environmental and economic welfare as the ascent of costs for fossil-based transportation propellants sanctioned competition within the market[3]. This has allowed for the exploration of alternative jet fuels (AJFS), with emphasis on biofuels including ethanol, biodiesel, and microalgae biofuel to surge in demand [3]. The implementation of said alternatives, however, is a complex process as both their economic and environmental performance must be thoroughly evaluated and compared to most effectively construct short and long term international strategies[1].

Nature of the issue or problem

Since the invention of the airplane in 1903 humanity has become deeply reliant on air travel[4]. Air travel supports and makes possible an international network of business and tourism[5]. In 2019 4.3 billion passengers traveled by air globally[5], 58 millions tons of freight was carried by airlines[5], and airlines flew a combined distance of 54 billion kilometers[5]. 65.5 million jobs rely on the airline industry[5], and it’s estimated global impact on GDP is 2.7 trillion dollars[5]. Despite the enormous reliance of the world on air travel, it is a well-known contributor to CO2 emissions, accounting for approximately 2 - 2.5% of total global CO2 emissions according to some estimates,[6]and up to 5% according to others [2]. Efforts are underway to develop alternatives to jet-fuel[7]. Although there are several promising alternatives being researched, at this time none are feasible to replace jet fuel in any short term scenario[6]. Fundamentally, the nature of the problem is that current air travel infrastructure, including the worldwide fleet of airplanes, and the worldwide design of airports and air support systems, are set up to run on fossil fuels. Fossil fuels have been a cost effective way to travel by airplane for decades, but there is an impetus to change because of the impact of air travel on worldwide carbon emissions. The challenge is to develop alternatives to high emitting carbon engines, and to re-design air travel support systems to accommodate this change.

Current remedial action(s)

Current Action and Research Into Cleaner Aviation

The International Energy Agency (IEA) predicts that in the next 20 years the aviation industry will double in size[8]. As the industry continues to grow, airlines[9], scientists, energy companies[10], and governments[11] are allocating more time to advancements in technology that have the potential to cut aviation emissions significantly. Ethanol and Biodiesel are two of the more common sustainable fuels currently being mixed with traditional jet fuel[12], but further research is being done to improve effectiveness and scale up production to compete with kerosene based jet fuel. Production facilities like the Arbios Biotech plant proposed for Prince George, British Columbia[13] are being designed around the world to increase supply which is extremely important for lowering the market price.

Figure 3. Biofuel production facility using wood biomass to form biodiesel

Ethanol (CH3CH2OH)

Made from biomass, a mixture of natural products like wheats, grasses, and food waste, Ethanol is a liquid alcohol[14] used in todays cars, some planes, and other machinery because it produces less harmful greenhouse emissions. Ethanol releases 19-48% less greenhouse gasses and greatly reduce harmful byproducts of burning gasoline[15] such as Polycyclic aromatic hydrocarbons. There are two processes manufacturers choose from when making ethanol; known as 'dry' or 'wet', they differ mainly because of how the biomass is treated during the milling stage[16]. Almost all the ways to make ethanol involve fermentation. The biomass is milled and then boiled with a catalyst to break down large starch molecules quickly (Liquefaction). Another catalyst is added in the next stage (Saccharification) to break down starch into the simple sugar, glucose. When yeast is added (Fermentation) it breaks down the glucose, giving itself energy and giving us ethanol with a purification of about 10-15%. The next step (Distillation and Dehydration) is to purify the ethanol to 95%, the remaining 5% water evaporates or is strained. The final step is to add a small amount of gasoline so that the fuel is undrinkable[17]. The byproducts of this process are distillers grains which can be used to feed livestock, and CO² from the yeast can be collected and sold to carbonated beverage, dry ice, and food companies to name a few[18]. Ethanol can cause problems in airplane engines such as corrosion, damage to rubber engine components, vapour lock[19], and produces 33% less energy than gasoline[20].


A very versatile fuel that can be made from leftover or recycled household vegetable oils and animal fats[21]. Biodiesel has many of the same advantages over gasoline that ethanol has such as producing fewer greenhouse gasses and being less toxic. However it is also renewable, degrades quicker than diesel, and has no harmful manufacturing byproducts[22]. With certain precautions like storing vehicles inside so fuel doesn't freeze and regular maintenance checking engine components, Diesel engines can run on a mix of biodiesel and diesel or B100(100% biodiesel)[23]. The manufacturing process begins when Methanol is added to recycled vegetable oils and animal oils and fats. Either Potassium Hydroxide or Sodium Hydroxide are used as an alkaline catalyst. Crude biodiesel and crude glycerin are the products of the reaction and are both refined separately. By the end you are left with biodiesel, glycerin that can be sold to cosmetic and pharmaceutical companies, and the catalyst that can be recovered from the reaction[24].

Microalgae biofuel

Figure 2. The process of converting microalgae into biofuel through multi-facted cultivation and harvesting

Scientists believe there to be millions of species of aquatic algae that use carbon dioxide to photosynthesize[25]. Unlike Macroalgae which is multicellular, Microalgae are single celled organisms[26]. Unlike ethanol and biodiesel, microalgae biofuel is rarely used. This is because of problems in the lipid extraction process, lack of infrastructure and resources, and tough growing conditions[27]. To meet US oil demand, it is estimated that 30 million acres of water bodies would be required[28]; and to meet the UK's oil demand fertilizer use would increase by 50%, according to Swansea University marine biologist Professor Kevin Flynn (2017). Further research to identify the best algae strain to farm, improvements in technology to make oil extraction cheaper and more effective, as well as harvesting, pond design, and protection are all changes that need to be made before Microalgae biofuel can be commercially viable[29]. The two most common Microalgae production methods are Enclosed photobioreactors and open ponds. An enclosed photobioreactor is a collection of thin tubes, usually around 10cm to maximize photosynthesis, that maintain a constant flow of water using pumps to make sure the algae does not settle. Because photobioreactors are closed systems certain favourable factors can be enhanced or maintained to increase yield up to 13 times over open ponds. When ready for harvesting algae is collected using gravity settlement or centrifuge. Open ponds would not interfere with food crops [30]and are 20-30cm deep and usually setup in a snaking 'raceway' formation[31]. Fertilizers are added ahead of a paddlewheel so they are mixed appropriately[32]. Once the algae is ready for harvesting it is removed from the circuit and the process continues. Because these ponds are open and exposed to the elements it is hard to maintain 'natural' conditions, control evaporation, and increase biomass production because of limited carbon dioxide absorption[33]. With technological advancements and the correct infrastructure Microalgae biofuel could be a viable fuel for planes and other machinery; however, currently there are too many challenges making it hard to compete with other biofuels[34].


During the last century engineers have repeatedly tried to create planes that will run on hydrogen, and although some experiments have been reasonably successful there are still no commercial applications. Advantages of hydrogen fuel cells include high energy content (120 MJ/kg)[35] compared to jet kerosene (43.15 MJ/kg)[36], reaction produces only water, hydrogen is accessible, and planes would produce less noise pollution[37]. Hydrogen fuel cells powering a plane consist of an anode separated from a cathode by an electrolyte membrane. The reaction begins when Hydrogen enters the fuel cell through the anode where its atoms react with a catalyst and split into protons and electrons. Oxygen then enters from the cathode. Positively charged protons pass through the porous membrane to the cathode where negatively charged electrons flow out of the cell and generate electric current. Water is produced in the cathode when protons combine with Oxygen[38]. The production of Hydrogen can have varying amounts of environmental impact, depending on whether electrolysis, gasification, fermentation of biomass, or renewable liquid reforming are used[39]. The limitations of hydrogen include there not being enough infrastructure, airports and airlines would need a constant supply of hydrogen, planes would need to be fitted with larger tanks and the appropriate engines, and the explosive tendencies of the element require extreme caution. Bottom line, research continues to make the transition to aviation powered by hydrogen possible, but it would be expensive and slow.

Options for future remedial action(s)


The future for remedial actions in sustainable aviation include holistic solutions and looking at electrification options. In the past, individual elements of aviation systems were optimized separately from each other. However, the future is looking towards the system as a whole and optimizing elements in relation to each other. For example, instead of designing an efficient engine in isolation of an efficient airframe, you design them both together.[40] Another idea is to use electrical components for the propulsion system in order to alleviate reliance on fossil fuels and take advantage of the fact that electrical systems are much more efficient at converting energy into propulsion than jet fuel.[40] Alejandra Uranga and a company called are working on blown lift technology, which redirects air to generate a very high lift. This is enabled by distributed electric propulsion, which would allow more flexibility and efficiency for shorter flights. In distributed electric propulsion, electrification also allows for thrust to be generated by an array of smaller propulsors rather than the more typical dual engine configurations.[40] It has been found through previous studies that high levels of electrification are extremely good for short missions. This means shorter flights (100 nautical miles) and a smaller passenger load (between 2-20 people) see the largest benefits from electrification.[40] A possible downside to the electrification of aviation travel is the redesign of the whole aircraft in order to take advantage of the technology, and figuring out how to make it work for longer trips with more passengers.


According to an industry roadmap, global aviation emissions are projected to increase by 2030 due to the expected growth in overall flights. Creating policies that limit the amount of emissions produced by aviation could be another option for the future of sustainable air travel. Corsia (short for "Carbon Offsetting and Reduction Scheme for International Aviation"), is an agreement underpinned by the UN designed to help the aviation industry reach an aspirational goal to make all growth in international flights after 2020 “carbon neutral”.[41] Part of the policy is that airlines will have to buy emissions reduction offsets from other sectors to compensate for any increase in their own emissions. The scheme will start with a pilot in 2021 that will last until the end of 2023. 78 countries representing three-quarters of international flights have volunteered to participate in the pilot. Some of these countries include the US, Australia, Canada, Saudi Arabia, Japan, the UK and many other EU countries. Countries that are not participating in this are China, Brazil and India. After the pilot, the first phase will run from 2024 until the end of 2026, and will allow participating countries to join or withdraw at the beginning of any year with notice given. The second phase will run from the beginning of 2027 to the end of 2035 and is mandatory for all members. At the end of each three-year phase, participating airlines will be required to buy offsets for emissions growth above 2020 levels for each of the previous three years.[41] Other policies could reduce the demand for flying. Climate action group Possible is pushing for a frequent flier levy, which would see everyone get one tax-free return flight each year but add a gradually rising tax on any subsequent flights.[42]

Flight Routes

Flights are currently operating on a cost basis, but optimizing them for CO2 levels could help lower future emissions. There is technology that could support this: a company named Sky Breathe has come out with an AI technology which analyses flight operations to reduce fuel. Some airlines, such as AirFrance and Norwegian Airlines, have already signed up to use the software. It uses digital technologies such as Big Data Algorithms, Artificial Intelligence, and Machine Learning to automatically analyze billions of data records to identify the most relevant saving opportunities and provides a series of recommended actions that can reduce the total fuel consumption by up to 5%.[43]


Humanity remains deeply intertwined with fossil fuel based air travel. Although there are several promising alternatives to kerosene-based jet fuel, none are currently scalable to the proportion needed to power the airline industry in the short term. The next 20 years are critical as the airline industry is expected to double in size. There are four main areas of research into biofuels: Ethanol, Biodiesel, Microalgae biofuel and Hydrogen fuel. Ethanol and Biodiesel have proven the most economically viable and are most commonly used at present. Apart from finding sustainable fuels that don't emit as much CO2 as kerosene, there are other avenues of research into aircraft design that may prove useful. One of the barriers to green air travel is that the current infrastructure, including the vast majority of aircraft that currently exist, are designed with fossil fuel propulsion as an assumption. The aircraft and airport as it currently exists will likely have to undergo radical design change to accommodate a future of green air travel.


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  1. Doliente, Stephen; Narayan, A; Tapia, J; Samsatli, N (2020, July 10). "Bio-aviation Fuel: A Comprehensive Review and Analysis of the Supply Chain Components". Check date values in: |date= (help)
  2. (2018). Writing better articles. [online] Available at: [Accessed 18 Jan. 2018].

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