Anaerobic digestor

A “significant” leak from the £3.7m anaerobic digestion system at Harper Adams University is a setback for Britain’s fledgling on-farm biogas industry.

Critics will argue that if an accident can happen to a flagship system like the one at Harper, the same can happen to similar digesters on farms elsewhere.

Emergency services worked through the night to contain the spill on the university farm at Newport, Shropshire, on 19-20 February.

Anaerobic digesters are capable of turning vast amounts of food and farm waste into green energy – and can play a key role in slurry management.

The system at Harper has been held up as a blueprint for farmers and others wanting to harness the benefits of anaerobic digesters.

But while the technology has been used for years in countries such as Germany, the concept has proved a more difficult sell to a skeptical public in Britain.

Some plants have been approved, such as this one in East Anglia.

Others have faced stiff opposition, such as this one in Cheshire, with concerns over environmental impact often cited as a reason for plans to be rejected.

Backed by the academic community, one aim of the Harper system is to show that anaerobic digestion can be safe, efficient and environmentally friendly.

The Harper system uses 11,000 tonnes of dairy and pig slurry – as well as up to 12,000 tonnes of food waste that would otherwise have gone in to landfill.

Bacteria break down the organic matter in a tank releasing biogas. This biogas is in turn used to create heat and electricity.

Producing energy in this way is saving more 13,000 tonnes of CO2 every year, offsetting campus carbon emissions more than three times over.

The by-product of this system is valuable in itself. Digestate is recycled into a liquid fertiliser and compost reducing reliance on manufactured fertilisers.

It is this digestate that leaked from a storage tank at Harper.

While different to raw slurry and food waste, digestate can still be a serious pollutant, which can cause de-oxygenation and kill fish and invertebrates.

The Harper leak is a reminder that anaerobic digestion can bring significant environmental risks as well as benefits.