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At the end of 2013 the estate commissioned a farm based anaerobic digestion plant. The unit takes crops grown on the estate to produce electricity, heat and biofertiliser. A plug-flow system was selected on the basis of it’s low profile, meaning it’s visually un-obtrusive to it’s surroundings.

 

What is Anaerobic Digestion?

 

Anaerobic Digestion (AD) is a natural biological process where organic material is broken down by bacteria. It is similar to composting but differs in that it takes place in the absence of oxygen. The process occurs naturally in swamps and bogs and also takes place in landfill sites.

AD is a 4-stage process: hydrolysis, acidification, acetogenesis & methanogenesis. These are long words which basically describe the reason why cows have four stomach compartments.

 

An Anaerobic Digester is a device for optimizing and controlling the digestion process to produce:

• biogas (made up of around 60% methane, 40% CO2 and small amounts of hydrogen, hydrogen sulphide, nitrogen, and water vapour).

• Bio-fertiliser (digestate).

 

The technology has been widely adopted across Europe. In Denmark there are a number of farm co-operative AD plants which produce electricity and district heating for local villages. In Sweden biogas plants have been built to produce vehicle fuel. In Germany and Austria, encouraged by favourable government renewable energy policies, there are several thousand on-farm digesters treating mixtures of manure, energy crops and restaurant waste, with the biogas used to produce electricity.

 

The Cranford AD plant produces 2.2GW of electricity annually, enough to power over 500 homes, and generates 3000 tons of bio-fertiliser; the latter is then spread back over the farm generating a valuable source of soil nutrient and thereby reducing our dependency on imported nitrogen based fertiliser.

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