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Food Waste and Anaerobic Digestion (AD)

Anaerobic Digestion (AD) process uses feedstocks to produce biogas, which is a mixture of methane and carbon dioxide and also digestate, a biofertilizer. In this article we’ll look in more detail at the types of materials that can be used as feedstocks, what the biogas and digestate can be used for and how this technology can be used to help reduce our carbon emissions and reliance on fossil fuels.
A lit up gas cooking ring
© University of York/BioYorkshire

Anaerobic Digestion (AD) process uses feedstocks to produce biogas, which is a mixture of methane and carbon dioxide and also digestate, a biofertilizer.

In this article we’ll look in more detail at the types of materials that can be used as feedstocks, what the biogas and digestate can be used for and how this technology can be used to help reduce our carbon emissions and reliance on fossil fuels.

Food Waste

We all waste far too much food – around 180kg per person per year, or the weight of an adult reindeer! There are lots of good ideas out there to encourage us to consume or use up the one third of food we throw away that could still be eaten. When food waste ends up in landfills it decomposes and creates methane, which is harmful to the environment. Sending food waste to an AD plant changes it from a waste to a source of renewable energy.

Sewage Sludge

Yorkshire Water use sewage sludge to convert human waste into biogas as part of their ambition to become net zero carbon by 2030. They’ve even used the electricity to power their own pub called ‘The Number Two Tavern’.

Biogas can also be ‘upgraded’ (by removing carbon dioxide and other contaminants) to produce a renewable natural gas called biomethane which can be used to power buses and cars:

This is an additional video, hosted on YouTube.

Grass Clippings and AD

Research at the Biorenewables Development Centre is looking at the potential for using clippings and mowings from nature reserves and other wildlife habits in AD and assessing the potential this offers for effective biodiversity management and as a source of income to offset conservation costs. The Biorenewables Development Centre also worked with STRI, the world’s leading sports surface solution provider to assess the potential of turf clippings for AD. This offers an opportunity for thousands of tonnes of clippings to be converted into green energy.

So, how can the products and processes associated with AD help reduce our reliance on fossil fuels?

Power Generation from AD

Small biogas plants offer the potential to generate low-cost energy that can be used on site for cooking and lighting.

Biogas can also be injected into the national grid and directly replace energy derived from fossil fuels. The carbon released into the atmosphere from the combustion of biogas replaces that removed from the atmosphere when the feedstock was grown, making the process carbon neutral.

Transport

As mentioned above, upgraded biogas, biomethane, can replace petrol and diesel in transport. Italy has over 885,300 vehicles that are gas powered according to a 2019 report from the European Biogas Association. In the UK there’s even a fleet of trucks powered by biomethane made from sausage rolls! and in May 2021 Royal Mail announced that it is adding 29 biogas trucks to its fleet in the north-west of England.

Wastewater Treatment

Using anaerobic digestion to treat waste water and sewage sludge is an effective way of treating a large volume of organic matter. The water treatment plant featured in the recent BBC programme on ‘The Secret Science of Sewage’ processes the waste of 8 million people and collects 32,000 litres of waste water a second, every day!

Fertiliser

The digestate produced during the AD process can be used as a natural fertiliser to enrich and nourish the soil. According to the Italian Biogas Association, Italy produces up to 30 million tonnes of digestate per year, resulting in a 400 million Euro saving on fossil fertilisers.

Would you consider driving a car powered by biogas?

© University of York/BioYorkshire
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