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What slurry dewatering technology could mean for dairy farmers

Gelli Aur College farm, Carmarthenshire, is trialling a system which removes water from slurry, making it easier to store and spread.

 

Farmers Guardian finds out what this technology could mean for dairy farmers...

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The slurry produced by the 500-cow herd at Gelli Aur has until now been stored in three tanks with a capacity of approximately one million gallons.

 

The new treatment plant, made from marine-grade stainless steel with a galvanised framework, is positioned next to two of those tanks and visually demonstrates the advantages of dewatering and purifying slurry.

 

Two small heaps of compressed slurry sit beneath the two filtering systems on trial. The material is a tenth of its original volume because the water has been extracted and it is 30-40 per cent dry matter (DM).

 

Once the holding area is full this stackable material is scooped up and stored in a covered area, ready for spreading.

 

Technology such as this could be eligible for support from Wales’ new £6m Sustainable Production Grant (SPG) as this new round of funding aims to address on-farm nutrient management and storage.


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The equipment is not cheap but, set against reduced storage and spreading costs, the cost benefits stack up, says Gareth Morgan, whose company, Swansea-based Power & Water, developed the system.

 

“The initial investment could be greater than for storage but over the course of three to four years the costs become comparable when spreading and fertiliser savings are factored in,” he says.

 

The price, he says, will depend on a farm’s needs.

“Each farm has different criteria. The treatment unit at Gelli Aur will not necessarily work on another farm of similar herd size.”

 

The project calculates the annual savings for a 500-cow herd system would be £16,908 on bagged fertiliser, due to the higher nutrient content of the compressed slurry. Reusing the water and the savings on applying it to land would result in further cost savings of £32,296.

 

And it is not just the advantages for nutrient storage and management which need to be considered, Mr Morgan says. Compressing slurry reduces air and water pollution.

 

“The material which is spread onto the land has a higher nutritional content and it is not wet so there is not the same risk of run-off,” says Mr Morgan.

 

Running the plant consumes energy, though just how much is being evaluated in the trial, but it only uses power when it is processing.

 

The equipment at Gelli Aur has only been operational since the end of August, processing 35 tonnes of slurry a day, and further work is needed to get the filtered water clean enough for discharge into local watercourses or reused on the farm but this outcome is in reach, says Mr Morgan.

 

“The treated water does need analysis before being discharged,” he adds.

The system works by pumping the slurry in its original form from the cubicle housing into a separator.

 

There are two separation systems being trialled at Gelli Aur. One uses centrifugal force to push out the solids while the other, a screw press filter, forces slurry through a mesh screen.

 

Compatible

 

Some farms already have this equipment. For instance, screw presses are used for producing green bedding from slurry and it could be incorporated into the new plant, if compatible, to keep down the cost, says Mr Morgan.

 

“The centrifuge system is more energy intensive but produces higher density solids while the screw press is more cost-effective but there is not as much separation. We will establish which produces the optimum results,” he explains.

 

Once the slurry has been through the separator, the filtered liquid is about 4-5 per cent dry matter and passes into another part of the plant where a patented system of oxidation breaks down the ammonia to nitrogen and hydrogen and removes those remaining solids which are routed back to front-end of the treatment process and added to the compressed slurry beneath the separator.

 

The £1.1m trial at Gelli Aur, funded by the Welsh Government through the Rural Development Programme, will run for two years, but Mr Morgan says if his company can show the system works, then it is feasible it could be up and running on other UK farms within two months, tailored to herd size.

Farmer opinion

Farmer opinion

Although the trial is in its early stages, Gelli Aur farm manager John Owen says the potential for the industry is enormous, allowing farms to become more sustainable by making better use of their nutrients.

 

“Dairy farming has become more intensive in recent years but technology has not moved forward at the same pace as this intensification. With this system we are using new technology which has been used in other sectors in agriculture and making better use of the nutrients we produce.

 

“It will go a long way towards alleviating contamination of watercourses and other issues around pollution.”

 

Mr Owen says scale is not a barrier to rolling it out to farms.

 

“This is going to be appropriate to all sizes of dairy farms; it is not just about the big herds, it is suitable for everyone. If it was not it would not make much of a difference to overall water quality.”

 

The next stage could be pasteurising and pelleting the compressed slurry, providing a transportable fertiliser product which farmers who have an abundance of slurry could sell to regions with less livestock.

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