Benefit of AD units called into question

Claims about the environmental benefits of anaerobic digestion units on large-scale livestock farms are unlikely to be justified, according to the Soil Association.

The organic body says anaerobic digestion units on UK farms only reach a fraction of their potential and their impact on the environment is far from clear.

It also says the economics of anaerobic digestion means livestock farmers are eventually driven to use crops instead of animal waste in the units, causing more environmental damage.

The claims are made in a report commissioned by the Soil Association and the World Society for the Protection of Animals looking at anaerobic digestion units on large-scale livestock developments.

Carried out by an independent consultant, the report was sent to Derbyshire County Council on Wednesday (28 December).

Planners there are expected to make a decision over Midland Pig Producer’s proposals for a 2,500-sow pig unit at Foston in Derbyshire in the next month.

In a letter accompanying the 32-page document, Soil Association policy director Peter Melchett said the Foston unit had been presented as a ‘green’ development because of the addition of an AD unit.

But he said the association and WSPA had serious misgivings about the claims the development would be environmentally friendly.

“There are too many uncertainties in respect of anaerobic digestion units linked to large-scale dairies or pig units for anyone to say for sure that they will lead to an overall reduction in the greenhouse gas emissions from the cows or pigs,” he added.

Among the findings of the report, it claims digestate from AD plants has no greater value as a fertiliser than slurry and that waste from pigs was one of the most uneconomic fuels.

It also said it would be likely the unit would have to switch to maize as its main or sole fuel – as had happened in similar units in Germany for economic reasons – potentially increasing greenhouse gas emissions.

But the report has been slammed for using out-of-date data and attacking a system that could offer multiple opportunities to organic producers.

Richard Crowhurst, of renewable energy website EnAgri, said the document was poorly researched and poorly argued.

“The basic premise of this report – that the Foston pig plant is only being built to provide feedstock for the attached biogas plant – is clearly wrong and designed to divert the debate,” he said.

“Their assertions that plug-flow AD systems do not work is based on one or two experiences in the United States and is akin to saying that because some former organic producers have reverted to integrated production methods, organic farming doesn’t work either.

“A well-designed pig production facility, whether conventional or organic, fitted with efficient manure management and anaerobic digestion will mitigate most, if not all, of the GHG emissions associated with the production of pigs.”

A Midland Pig Producers spokeswoman added: “It is inappropriate for us to comment on views opposing a process that is well-established throughout the country and supported by government departments. We will leave that to the industry representatives.

“We can confirm, however, that our plans have been developed using acknowledged best practice from global sources, supported by the most credible of experts.”

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