INSTEAD of spreading animal waste on the land and having it run into our lakes and rivers, we could use it to produce electricity, biomethane (‘renewable gas’) and “sustainable” fertiliser.

That was the tantalising, if slightly unappetising, promise of a UUP motion passed almost unanimously by the Assembly on Monday. Only the TUV raised on objection.

The motion called on the Executive to deliver this vision by developing a strategy for anaerobic digestion “as a matter of urgency”.

Similar signals have recently been emanating from the agrifood industry. There is a push on to promote this approach.

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Anaerobic digesters are vats of fermenting animal and food waste – they can take this from kitchen bins as well as from farms.

Biomethane comes out of the top, which can be burned to generate electricity or fed into the natural gas network and piped to our homes. Heat can also be captured for nearby buildings.

Digesters already produce about 4% of Northern Ireland’s electricity and small amounts of biomethane have been added to our gas supply since 2023.

What is left at the bottom of the digester is a sludge called digestate that can be used as fertiliser.

Most of it is liquid that can be spread directly onto the land. The remaining solids are more often used as a sort of compost to improve soil. These are high quality, valuable products.

It sounds too good to be true because it is. Digestate still contains all the nutrients – mainly ammonia and phosphorous – that cause slurry to pollute our lakes and rivers.

To be fair to the UUP, it is not suggesting digestate has no nutrients. A fertiliser would be pointless without them.

The party is using the term ‘sustainable’ to mean fertiliser made in Northern Ireland from renewable resources, as opposed to imported or manufactured from fossil fuels.

The final line of the Assembly motion asked the Executive to encourage investment in technologies that remove the nutrients from digestate, to “directly tackle surplus phosphorus and ammonia challenges”.

These technologies are well established and widely used, including in several advanced plants here.

It is reasonably straightforward to remove the ammonia and dispose of it safely or sell it for other uses, although the commonest other use is still making fertiliser.

That leaves the phosphorous, the main cause of the algal blooms in Lough Neagh and elsewhere.

Extracting it is more difficult and destroying it is impossible: phosphorous is an element.

Sometimes it is buried in landfill, although this has to be done carefully. There are a few industrial processes that can make use of it.

However, the usual way to dispose of phosphorous-laden digestate is to export it as a solid fertiliser to somewhere not (yet) overly polluted by it.

Such places are becoming harder to find. Europe is already polluted and has its own digestate surplus.

Shipping solid fertiliser further afield is often uneconomic and in any case the rest of the world is catching up with Europe’s pollution and surpluses.

Like Stormont, everyone is counting on exporting their excess nutrients.

The UUP motion referred to creating a “circular system” of waste, energy and food security, but what it really set out was a circular argument about getting rid of slurry in a way that does not get rid of the problems caused by slurry.

The motion was circling around the fact that Northern Ireland simply needs to produce less slurry. There is no other way to significantly reduce its impact on our environment.

That means less livestock and poultry, barring some technical miracle.

Canadian scientists created an ‘enviropig’ two decades ago that dissolved phosphorous in its saliva, reducing the amount in its manure by 70%.

The project was cancelled due to consumer and regulatory resistance over genetic modification.

If there is a technical miracle, we may also need a political miracle to make use of it.

The EU has effectively banned genetically modified livestock and we have to follow its rules under the Windsor Framework.

Northern Ireland’s farming industry must be aware of the limitations of anaerobic digesters.

In 2019, it emerged farmers here had been the victims of an RHI-type scheme to install waste-to-electricity digesters.

There were serious financial and legal consequences when the equipment failed to perform as expected.

This scheme was said to have contributed substantially to ammonia pollution of our water and air, which is the highest in the UK and Ireland.

It is a sign of desperation that the farming lobby is now promoting digesters as the answer to slurry pollution.

The UUP looks foolish or cynical to be shovelling this out on their behalf.

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