How food waste is used in anaerobic digestion

Food waste can be used in anaerobic digestors to generate gas or electricity, alleviating demand for non-renewable sources of energy to power and heat homes and businesses, while also diverting waste away from landfill. Here we explore how much food is wasted in the UK and globally, and how it can be used for energy.

The scale of the food waste problem

Globally, food waste is a big problem. According to the Food and Agriculture Organisation (FAO), 1.6 billion tonnes of food is wasted each year on our planet. The carbon footprint associated with this is equal to 3.3 billion tonnes of CO2 being released into the atmosphere every year. The FAO estimates that most food waste ends up in landfill, where the methane emitted represents one of the largest sources of greenhouse gas (GHG) emissions from the entire waste sector.

In the UK, the food waste problem is very similar to the global situation. In their most recent estimate, the Waste and Resources Action Programme (WRAP) stated that 9.5 million tonnes of food is wasted annually in the UK. However, the trends are starting to move in the right direction, as highlighted in our manifesto progress report, with a 7% reduction in food waste per person reported from 2015 to 2018.

It is also encouraging that from 2023 all household food waste in England will be collected separately. This means it can be directed away from landfill to be used or processed more appropriately, enabling a transition towards a more circular economy.

Processing food waste using anaerobic digestion

Once collected from the household or business, there are various ways in which food waste may be processed, all of which are preferable to burying it in landfill where it will gradually emit methane directly into the atmosphere.

Anaerobic digestion (AD) is a method by which food waste can be broken down to release biogas. This can be upgraded to produce biomethane, which is then injected into the grid to heat homes. Alternatively, biogas may be used to power a combined heat and power (CHP) engine, generating electricity and heat, which may be used to heat local buildings or greenhouses.

For more information on the AD process, see our blog post on how it all works.

AD can use various types of material, called feedstock, to produce biogas. Many digestors are powered by waste produced in agricultural processes, such as manure, slurry or surplus straw. However, food waste is also a very useful feedstock, and has the added benefit that it diverts the waste away from landfill to produce energy.

Types of food waste

Not all food waste is the same. WRAP identified that 70% of food that is wasted could have been consumed, while 30% is inedible. Some food is wasted before it leaves the farm, such as fresh produce that fails to meet retailer specifications for size, shape or colour. Of the food which is wasted after it has left the farm, 70% is classed as household food waste, with the remainder split between the retail, manufacturing, hospitality and food service industries.

Any type of food waste can be used in AD. The type of waste chosen as a feedstock depends on the specific waste challenges in an area. For example, an AD plant on a farm growing root vegetables could use the produce which does not meet retailer requirements. Meanwhile an AD plant near to an urban area where household food waste is collected separately, could offer the local council a solution for processing the food waste collected.

Privilege Finance has funded a variety of projects using different types of food waste. For example, Wardley Biogas in the north east has contracts with a multitude of local businesses which send their food waste to be digested, including Newcastle Football Club.

The route to decarbonisation

Using food waste to generate energy using the AD process can help reduce carbon emissions associated with the most difficult to decarbonise sectors, such as heating, transport and agriculture. The ‘Biomethane – a pathway to 2030’ report, which was launched by ADBA earlier this year, shows how the right policy environment will enable AD to make a real contribution towards the decarbonisation of the UK economy.

Ensuring unavoidable food waste is used in AD will help create a more circular economy, reduce the volume of waste ending up in landfill, while generating renewable energy.







Food waste