Separated slurry offer to NI farmers

A consortium of businesses that have come together to develop a long-term vision to deal with excess nutrients from agriculture, would like to hear from farmers interested in taking part in the project.

The consortium, which comprises mid-Ulster-based companies, CEMCOR, Road Safety Contracts and Tobermore, along with animal nutrition company, Alltech, is being led by the Centre for Competitiveness (CfC), an independent, not-for-profit organisation.

Back in October 2024, the project was awarded £4m from phase 2 of the DAERA-led Sustainable Utilisation of Livestock Slurry programme. It aims to reduce excess phosphorus (P) from livestock slurry getting into NI waterways. The same £4m award has also been made to Dundonald-based Blakiston Houston Estates to take forward a similar initiative.

Mid-Ulster

Outlining the mid-Ulster-based project at a meeting with farmers last Thursday night in Cookstown, Dr James Young from the CfC said the long-term solution for excess P is to take separated slurry solids to a new biorefinery.

At this facility, the separated solids will be used as a feedstock for anaerobic digestion, producing biomethane gas as well as low-carbon cement and bricks.

The resultant digestate is then processed and transformed into an exportable product, which is high in P.

However, any new biorefinery will be a major capital investment and it is still in the early planning stages. In the meantime, the CfC is keen to demonstrate the potential for mobile separation of slurry, gather data and validate results. Ultimately a market for a high P fertiliser will have to be found, outside of NI.

“We want to work with willing farmers to determine what the economic value is,” Young said. “ We want to get to a point where the cost meets value, so that it is zero cost to you.”

In other words, what is being offered to farmers is that CfC representatives come out to your farm with mobile slurry-separation equipment. The solids fraction is taken away to AD plants that have partnered with the CfC, and used as a feedstock. What is left behind is a liquid product which is easily spread using low-emission slurry spreading equipment.

Value

The value of the separated slurry as a feedstock for AD is dependent on a number of issues, including the nutrient content of the slurry.

That has to be set against the cost of slurry separation, but in practice, the whole process is much more likely to be cost neutral to the farmer if it is slurry from an intensive indoor dairy system, than low-input sucklers.

For those farmers who do work with the CfC, Young said the consortium will calculate all the figures, so the farmer knows how much P has left the farm, as well as carbon in the form of slurry solids.

“It will alleviate the need to export slurry and the dreaded paper acres.

“There will also be a reduction in carbon footprint.

“There is an opportunity to work with us to give agriculture a good name. This is about compliance, sustainability and environmental opportunity,” said Young.

He confirmed that the first mobile separator will be available for use from March 2025 and “there will be more units coming on board”.

There is no doubt that the liquid fraction left behind after slurry is separated is much easier stored and then spread.

Initial analysis of data coming from the DAERA sustainable utilisation of slurry programme shows that separating slurry creates a space saving in tanks of 13%. In addition, 24% of the P in the fresh slurry is recovered in the separated solids, along with 16% of the potassium, 17% of the nitrogen and 39% of the carbon.

Feedstock

When it comes to the value of separated slurry as a feedstock for AD, the data shows it has a biomethane potential over three times that of raw slurry.

However, it is still significantly behind grass silage, with a biomethane potential that is 58.3% of low-quality grass silage and 31.8% of high-quality grass silage.

Since 2010, the amount of soluble phosphorus (P) in NI waterways has been going in the wrong direction and a key cause of that is excess P from agriculture, AFBI researcher Chris Johnston told last Thursday’s meeting.

That excess P is mainly from bought-in concentrate feed, which ends up in livestock slurry and ultimately leaches into lakes and rivers.

According to Johnston, the average farm in NI now has a P balance of around 11.5kg/ha/year, whereas a balance of just 5.5kg/ha/year is necessary to sustain plant growth and animal performance – it equates to a surplus of around 6,000t P annually in NI farming.

“If we can significantly reduce that excess P, over time, we can significantly improve water quality,” he said. Ultimately, he maintained that the key in the overall project is to harvest off P from digestate and export it out of NI.