Green energy

Anaerobic digestion can help airports become more environmentally friendly and reduce their carbon footprint, writes the World Biogas Association’s Jocelyne Bia.

As countries prepare for a post COVID-19 recovery, aviation will resume, and the industry will once again be questioned about its impact on the environment and called upon to reduce its carbon footprint.

Many feel that now is the time to seize the opportunity to ‘build back better’, creating a greener global economy. Indeed, the UN, EU, International Energy Agency and some leading economists and businesses have been calling for world governments to embed decarbonisation and renewables into plans to kick-start the economy.

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 AD 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. 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 CO2e emissions are prevented.

A key benefit of AD treatment is that 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.

Sustainable airports

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, airports 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, Airport Authority 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 wintery 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.