How phosphorus recovery could change dairy slurry management

As pressure grows on dairy farmers to manage phosphorus more carefully and reduce water pollution, novel technology to remove phosphorus from slurry could offer a game-changing solution.

The technology has been shown to consistently remove 98% of phosphorus.

Makers elentecBio have been working alongside researchers at Harper Adams’ dairy unit in Shropshire to trial the system. Innovate UK has funded the work in partnership with Defra; the NFU Midlands Regional dairy board recently visited to learn more.

See also: What to consider ahead of new slurry regulations

How the technology works

The modular system has been operational at scale at the university since April 2026 and is housed in three, 6m (20ft) shipping containers near the slurry store. Duarte Tito from elentecBio says its modular design means capacity can be increased or reduced to match herd size and slurry processing needs.

Slurry initially passes through a conventional screw-press separator to remove larger particulates above 0.75mm, which contain high levels of phosphorus. The remaining liquid then has a three-step treatment.

Duarte explains that inside the first container, the liquid undergoes electrocoagulation, where an electrical current helps remove suspended solids.

Instead of using potentially harmful chemical coagulants, iron from the electrodes binds with phosphorus.

It is dosed through a series of cartridge-style units and can process up to 3 cu m/hour.

The remaining liquid is then ultrafiltered to remove finer particles, before passing through reverse osmosis in the final shipping container, where it separates water from the remaining nutrients.

This leaves three products:

1. A phosphorus-rich fraction containing over 98% of the original phosphorus entering the unit
2. A phosphorus-stripped liquid containing dissolved nitrogen, potassium and salts
3. High-quality processed water, which could potentially be reused for parlour washdown or cattle drinking water, subject to Environmental Agency approval.

Challenges and costs

The technology does, however, require significant capital investment. For a 400-head milking unit, Duarte estimates the system would cost around £500,000.

Researchers are still establishing its full energy requirements because the demonstration unit is not yet operating continuously. At Harper Adams, the slurry is pumped to the main store, with liquid intercepted at the transfer point.

Duarte says a commercial unit should ideally be installed at the store and run constantly to maximise efficiency. He estimates power demand of 10-20kW during operation, although more precise running cost data is expected by early 2027. Maintenance requirements include replacement components within the electro reactors, plus the cartridges used for iron dosing.

Results and next steps

So far, results show the system consistently removes 98% of phosphorus from the slurry entering the unit. Harper Adams soil scientist Dr Ana Morais Natalio is examining the value of the recovered nutrients by running application trials on Italian ryegrass under a four-cut system.

Ana is comparing phosphorus-rich applications with separated slurry, conventional fertiliser, and water as a control.

Preliminary results show that ryegrass receiving phosphorus outgrew plants under other applications by around 10%.

One possible explanation, she says, is that the recovered phosphorus is more readily available to the plant, although further analysis is needed.

Trials are also under way in spring wheat to assess nutrient uptake and crop yield, as well as potential nutrient leaching and greenhouse gas emissions.

Reducing pressure on slurry and land

For farmers with high soil phosphorus indices or limited slurry storage, Duarte believes nutrient separation could be valuable.

“Farmers are running out of storage capacity and the land bank [to spread slurry]. If phosphorus indices are already high, this technology could enable farmers to export it,” he says.

Under Farming Rules for Water, farmers must plan organic manure applications so they do not create a significant risk of agricultural diffuse pollution, matching nutrient applications to soil and crop requirements.

By separating nutrients, Duarte says they could target nitrogen and phosphorus applications more effectively.

Removing water also helps reduce the overall volume of slurry that needs to be stored, while cleaning water for potential reuse. The next challenge is to concentrate the recovered phosphorus enough to make transportation economical.

Duarte says this will be important to create a circular nutrient system, allowing phosphorus to be exported from farms with surpluses to those with a nutrient requirement.

Barriers to adoption

However, regulation is presently a barrier to adoption. NFU Midlands regional dairy board chairman and national dairy board vice-chairman Robert Davies says the Environment Agency (EA) permitting requirements could prove a significant obstacle.

“The EA classes this as a waste treatment process, so farmers need a permit which costs tens of thousands. But it is not a waste; it is a valuable resource.”

ElentecBio says it is working with the EA to overcome these challenges and is reporting water-quality data to allow farmers potentially to reuse the treated water on farm.

The company is now beginning to deploy the technology to demonstration farms as it works towards wider commercialisation. “We want to have three static units next year and are demonstrating a mobile system for smaller farms over the winter,” says elentecBio chief executive Jayne Brookman.