Anaerobic digestion can help airports become more environmentally friendly and reduce their carbon footprint, writes Jocelyne Bia.
Before the coronavirus outbreak stole the headlines, the main concern for people and governments around the world was the climate emergency and the need for urgent action.
Like many other industries, the aviation sector was under pressure to reduce its carbon footprint. Airlines were asked to abide by the ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation (Corsia), whilst on the ground, airports sought to make their operations more sustainable. The UK aviation industry had set the tone by establishing a Net Zero by 2050 target for itself.
Then COVID-19 hit, and most global air travel all but stopped overnight, dealing the aviation industry a devastating economic blow.
As countries prepare for a post COVID-19 recovery, two schools of thought are emerging. On one side are those who want to deliver immediate stimulus packages to put businesses back on their feet, irrespective of the climate change agenda. On the other are those who want to seize the opportunity to ‘build back better’, creating a greener global economy.
Indeed, the UN, EU, International Energy Agency, leading economists such as Joseph Stiglitz and Lord Nicholas Stern, and even businesses have been calling for world governments to embed decarbonisation and renewables into their plans to kick-start the economy whilst still fulfilling their Paris Agreement commitments.
For the aviation sector, and particularly airports, getting back to business while delivering sustainability is not incompatible. There are pre-pandemic examples of airports successfully adapting their operations to implement good sustainability practice.
One technology that helps them achieve their greening ambition is anaerobic digestion (AD). By treating food and other organic waste and transforming it into biogas, AD can help establish a low carbon circular economy within the airport, saving both money and greenhouse gases emissions.
How anaerobic digestion works
Anaerobic digestion is the natural breakdown of organic matter, in the absence of oxygen, which takes place in a plant called a digester. This process generates biogas and a bio-fertiliser called digestate.
The ‘green gas’ generated by the AD process can be used for electricity and power or upgraded into biomethane, sometimes called renewable natural gas (see gaphic).
Biomethane is a direct replacement for fossil natural gas, so it is already injected into the gas grid for heat or used as a transport fuel for heavy duty vehicles such as lorries, buses and, in the near future, tractors.
For every 1,000 tonnes of food waste treated through AD, over 1,100MWh of renewable energy can be generated – the equivalent energy of over 107,000 litres of diesel – and 475 tonnes carbon dioxide equivalent (CO2e) emissions are prevented.
A key benefit of AD treatment is that the organic waste that would otherwise emit harmful gases in landfill or through incineration are instead recycled into green resources for hard-to-decarbonise sectors such as heat, transport, waste management and agriculture.
AD is a mature, readily available technology that stands first in the waste management hierarchy to treat waste that cannot be reduced or reused – ahead of composting and energy recovery.
ACI defines airport sustainability as: “A holistic approach to managing an airport so as to ensure the integrity of the economic viability, operational efficiency, natural resource conservation, and social responsibility of the airport”. This definition has been evolving as focus moves from reducing noise, air and light pollution to reducing greenhouse gas emissions.
Even before COVID-19, many airports had made sustainability pledges and understood the benefits of integrating AD and biogas into their processes. As both generators of significant volumes of food waste and heavy users of energy, they are ideally placed to reap the benefits of the circularity of the AD process and its ability to cut their carbon footprint.
Heathrow, for example, which had already set itself a net zero waste policy, is sending some of its food waste to AD, and has just entered a partnership with Engie to use biomethane across all its terminals until 2022.
Meanwhile the Airport Authority of Hong Kong has been collecting food waste for recycling since 2003 – most of it being sent for conversion into biogas. Its collection network now covers 17 airport business partners including restaurants and lounges operating in terminal buildings, as well as airline catering companies, hotels and cargo terminals.
And in North America and Europe airports affected by wintry conditions, biogas-powered snow equipment is used to clear the runways.
These are still small steps towards integrating AD and biogas into an airport’s operations, but they demonstrate the potential of the technology to contribute to the industry’s sustainability agenda.
As world governments look at green answers to the economic downturn caused by COVID-19, the aviation industry can potentially look to AD as an additional solution to emerge back from the crisis whilst still adhering to its green ambition.