18 September 2023

The decarbonisation potential of anaerobic digestion

Anaerobic digestion is an environmentally friendly and cost-effective way of turning organic waste into clean energy, diverting food and crop waste away from landfills and repurposing it to create biogas and biomethane.

As a great example of circular economy – and a powerful way to reduce greenhouse gas emissions – anaerobic digestion holds real potential to help us accelerate the green energy transition. Yet, only a small part of the UK’s food waste is currently being recycled in this way.

To understand why this is the case and what can be done to improve the status quo, we talked to Christer Stoyell, Managing Director of Severn Trent Green Power.


The size of the challenge

Did you know that if food waste was a country, it would be the third largest contributor of carbon emissions? It’s hard to believe, but the UK produces about 9.5 million tonnes of food waste each year, with only 30% of it being classified as inedible parts.

This is not only a waste of valuable resources – it also represents a big environmental problem. When rotting in landfills, food waste – as well as other organic waste, such as crop residue – produces methane that is released into the atmosphere. However, methane is about 80 times more potent than carbon dioxide at trapping heat into the atmosphere, meaning its effects on global warming are far worse.

Luckily, technology has come to the rescue, and modern anaerobic digestion plants are able to break down organic waste and trap the resulting gas to use it for domestic and industrial heating.

This is what water utility Severn Trent is doing with its renewable energy division: Severn Trent Green Power:

“Severn Trent Green Power was set up about ten years ago to allow Severn Trent to self-supply some of its water and wastewater treatment sites with clean energy,” explains Christer. “It was also created to allow Severn Trent to expand horizontally into the technology of anaerobic digestion – which was already used to treat sewage sludge – and enter non-regulated markets by using different feedstocks, such as food and crop waste.”

Thanks to its investment in anaerobic digestion, Severn Trent Green Power is now able to treat food waste from local authorities and commercial customers and repurpose it to create biomethane. This can then be injected into the gas grid, or used for combined heat and power engines.


Working towards an ideal world scenario

Not only does anaerobic digestion divert food waste away from landfills – it prevents harmful emissions from being released into the atmosphere, while providing the local community with clean, reliable fuel.

But how does it work, exactly? Organic waste – such as food waste, crops residue, sewage sludge or manure – is fed into a tank where bacteria break it down in the absence of oxygen, releasing gas. Essentially, the process mimics our bodies’ ability to eat and digest, but the gas that is produced as a result is trapped and put to use.

“In an ideal world there would be no food waste and I would be out of business,” comments Christer. “But the reality is that there will always be food waste. So, we want to make sure that every drop of it will be used to generate renewable energy rather than go to landfill, because it would cost more money to dispose of it that way, and it would be far worse for the environment.”


A look at the future

“Currently, only about 20-25% of our food waste is being repurposed through anaerobic digestion, so there is huge untapped potential,” continues Christer. “As part of the Environment Act, there is legislation in place that, at some point in the future, will mandate all local authorities and businesses to separately collect food waste.

“What is taking a bit longer than all of us had hoped for, is to get clarity on the exact dates of when this is going to take effect. The single biggest thing we can do to try and increase the amount of renewable gas coming from food waste is to have policy clarity from the Government.”

Christer suggests that only legislative clarity on long-term policy will allow local authorities to confidently allocate capital and resources to a separate food waste collection.

He adds that another major hurdle to overcome is the necessity to bring together a high number of utilities and stakeholders to effectively incorporate anaerobic digestion into our decarbonisation plans.

Finally, he suggests that the successful implementation of anaerobic digestion at a national level should start with small, local clusters. This would speed up deployment, and would allow for better chances to build relationships among businesses at all nodes of the value chain.

As we move forward with plans to inject more biomethane into the gas grid, Christer has two main wishes:

“My biggest wish is policy clarity,” he states. “The  other big one has to do with connections to the electricity grid. The speed of connecting new renewable assets to the power grid can be a challenge, with lengthy time frames. If we could speed that up, I think it would make a big difference.”

To learn more about the role of anaerobic digestion in the decarbonisation of gas, you can listen to Christer’s Q&A with Victoria Mustard, Xoserve’s Decarbonisation Strategy Lead.

Listen to the podcast

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To learn more about how Xoserve supports the decarbonisation of gas, take a look at our decarbonisation knowledge centre.

If you have any feedback, questions or suggestions for our Decarbonisation Team, please email us.

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