Anaerobic digestion 

Turning food waste into valuable renewable resources

All of the food waste we collect goes to a network of anaerobic digestion (AD) plants across the UK. This network enables us to take your food waste to a nearby plant, minimising its carbon footprint. AD plants turn organic materials into biogas which is a highly versatile renewable fuel. It can be used to power vehicles, generate heat and power and be fed into the national electricity and gas grids to fuel homes and business premises.

The anaerobic digestion process

Anaerobic digestion is a process in which bacteria break down organic matter such as food waste, without oxygen. As the bacteria consume the food waste, they give off biogas which rises to the top of the digester. This consists mostly of methane, the primary component of natural gas. The solid content of the food waste falls to the bottom of the digestion chamber and this is extracted to make a nutrient-rich organic fertiliser.

In simple terms, the system is much like a huge stomach and, like all stomachs, it requires regular feeding and a healthy balanced diet. To provide just the right recipe for the bacteria, the food must be prepared and have any packaging removed.

Digesters come in a wide range of shapes and sizes and each one is slightly different. Getting the precise mix of nutrients to keep the microbacteria well-nourished and efficient is quite an art which can involve adding ingredients such as manure or other specific trace elements to the feedstock. Getting this right ensures that the plant maximises the energy recovered from the food waste.

Converting biogas into precious renewable resources

Once it is extracted from the digester, the biogas is used to fuel a combined heat and power plant. Most of the gas we produce is used to produce renewable electricity in this way. Any excess biogas is cleaned of impurities to create biomethane so that it will meet the standard required by the national gas grid and can be used to supply households and businesses.

Our flagship anaerobic digestion plant in Aylesbury is ISO 9001 and 14001 accredited. The green energy plant produces enough sustainable energy to power the equivalent of 12,000 homes. The power from this plant is largely used to supply heat and power to the world’s largest net zero carbon dairy.