What is Anaerobic Digestion?

Anaerobic digestion is a complex biological process involving the breakdown of organic matter in the absence of air in large, sealed and insulated vessels with controlled heating and mixing.

Food waste enters a sealed building where it is processed into a liquid porridge, and then pumped into the anaerobic digestion plant. It is here that bacteria feed on the food waste and produce biogas. Biogas is captured and used as a fuel in CHP engines or sent through a gas filter and sent directly to the gas grid.

The digestate or biofertiliser produced undergoes pasteurisation to ensure that any pathogens are destroyed and is stored in large lagoons ready to be applied twice a year on farmland. The use of this high nutrient biofertiliser replaces the use of fossil-fuel derived fertilisers and ensures a complete loop of carbon and energy capture.

The process

Food waste enters site

Food waste arrives by truck at the waste reception building

Food waste separated

Solid waste is chopped up. All plastic and packaging is removed by screens and liquid is added to turn it into a slurry. Liquid waste goes straight into the buffer tank.

The buffer tank

The liquefied waste is stored in here while the initial Anaerobic Digestion (AD) process of
Hydrolysis takes place.

Pasteurisation

The waste flows into pasteurisation tanks and is heated to 70°C for an hour to kill any bugs, using spare heat from the generators.

Digestion

Our two digesters can hold up to 4,500m3 of feedstock each. Pasteurised feedstock enters the tank with gas being blown through to keep the process flowing. In here billions if bacteria convert the calorific fraction of the feedstock into methane.

Electricity generation
(combined heat and power)

The methane piped from the digesters is used to fuel combined heat and power units which
generate electricity.

Carbon capture

The digested feedstock, which is an inert and odourless slurry, is stored in large lagoons on
our farm and is the perfect fertiliser for our farm crops. It is rich in a whole range of nutrients, particularly nitrogen.

Heat capture

A lot of heat is produced by the generators which is not used for heating the digesters.

Back to the land

The digested feedstock, which is an inert and odourless slurry, is stored in large lagoons on
our farm and is the perfect fertiliser for our farm crops. It is rich in a whole range of nutrients, particularly nitrogen.