In recent years, an increasing spotlight has been placed on the management of livestock slurry.

From storing it to spreading it, from compliance to its utilisation, the focus on slurry has intensified.

Many farmers would like to have additional slurry storage capacity, but inflated building costs can quickly hamper such ambitions. What if there was another way? Well, this is where slurry separation can play a role.

What is slurry separation?

Quite simply put, slurry separation is a process which involves the removal of the solid, fibrous segment before returning the liquid segment to a storage tank.

Although taking place in a very limited capacity in Ireland up to now, the concept is becoming more common and an increasing number of farmers are keeping a close eye on such systems.

Different types of technology are available when it comes to slurry separation.

Some examples include screen separation, membrane separation, decanting centrifugation and press separation. Separation using a press is the most popular method.

To demonstrate how such a system works, Vogelsang Ireland recently held two demonstrations using a mobile setup. The first on an anaerobic digester in Tyrone and the second on a suckler farm near Mullingar.

How does it work?

Before starting the separation process, the slurry needs to be a well agitated soupy material. To put it into perspective, it needs to be agitated to the same degree as if you were going to spread it using an umbilical system fitted with a LESS applicator.

The slurry is sucked from the slatted tank using a conventional slurry hose and fed into the separator using a progressive cavity positive displacement lobe pump.

Like the majority of slurry tankers on the continent, the system utilises such a pump which works on pressure, and can be operated bi-directionally, rather than vacuum which is common in Ireland.

Such a supply pump is required in order to keep the system consistently running at 0.2 bar in the negative, to maintain suction.

The slurry is fed through a RotaCut macerator, which is the system’s first line of defence. Equipped with three blades, the macerator is designed to chop the fibres in the slurry, with a stone trap designed to catch stones and any foreign debris.

From here, the slurry continues its journey up through the elevator to the XSplit separator. This is where the actual separation takes place. The slurry is fed into the press screw.

Essentially, the slurry is forced against a screen, which sees the liquid fraction squeezed through and escape downwards via gravity through a discharge pipe at the bottom of the separator.

The solid fraction

The remaining solid fraction is then pushed out at the end of the separation cylinder. At the demonstration, a dump trailer was parked under the unit to collect the fibrous solids, but this could easily be positioned on a dung pit, etc.

Although building slurry equipment for many years, Vogelsang took the wraps off its latest XSplit separator less than two years ago. The big selling point was its new design, which rather than pressing the slurry against the drive shaft seal, allows it to exit via a gap that lies between the separating cylinder and the motor, with the fundamental aim of reducing maintenance costs.

Vogelsang was using a 2mm screen on this separator, which it claims is the screen of choice based on usage in cattle slurry across Europe. However, screen sizes can be altered.

The liquid element

As mentioned, the liquid fraction escapes downwards via gravity through a discharge pipe at the bottom of the separator.

A displacement pump then sends the liquid out through a four-inch lay flat hose, where it is pumped to a second storage tank.

Vogelsang claims this pump has the capability to pump the liquid fraction in the region of 100m.

Alternatively, the liquid can be gravity-fed from the separator right the way through to the secondary tank, which will work out significantly cheaper. This will be farm-specific.

Automation

The system can be operated in manual or automatic mode. The control panel on this system is very much overkill, but regulates the entire system.

On the control panel, the speed and pressure of each major component such as the pump and the inlet macerator are being continuously measured. If an issue arises, it will be picked up through safety sensors which provide a failsafe.

Through a modem or by hotspotting mobile data, remote diagnostics are available, which connect the operator directly to an engineer in the factory in Germany.

Power and throughput capacity

The unit we went to see was being powered by a 70kVA diesel generator. The system requires a three-phase electrical supply, which will alienate some farms. However, a suitably powered generator (minimum output of 50kVA) will allow farmers get over this stumbling block.

The demonstration unit we visited has a throughput capacity of 50m³/hr.

Vogelsang recommends that, in Irish conditions, it operates at around 30rpm to 40rpm which offers a throughput of 35m³/hr. The lower throughput is in a bid to increase the machine’s lifespan by reducing stress on componentry such as the electric motors. To put this into perspective, a direct conversion from 35m³ would equate to 12.4 tonnes/hour.

Vogelsang claims the XSplit can achieve a dry matter of up to 40% with the solid fraction.

Mobile unit

When we look at such technology from a cost perspective, you often wonder is there an opportunity for contractors to provide such a mobile service.

To set up the likes of this mobile unit on farm, it would take around one hour, and once finished, it would take around an hour and a half to wash down and prepare the unit to get on the road again.

It’s also worth noting that such systems aren’t suited to all farmyards. You need to have an empty tank or lagoon to offload the liquid fraction of the separated slurry.

In an ideal situation, the farmyard would have an overground slurry storage tank or a lagoon, where the cow tanks could be separated and pumped into.

Manufacturers claim that slurry separators have the potential to increase slurry storage by 20% to 30%. This is undoubtedly the big selling point.

The separated liquid fraction is also easier to spread and is absorbed into the ground quicker, causing less ammonia loss, less leaf contamination and less potential run-off.

With current compliance meaning many farmers are required to apply slurry using LESS methods, reduced fibre in the slurry would help to resolve the issue of lines remaining on the ground as can often be the case after applying slurry after first-cut silage, or if slurry is applied and a prolonged dry spell occurs.

Storage

Like farmyard manure, the separated solid fraction must be stored in an area where the run-off can be collected.

On the continent, we see this type of material often being recycled and used for green bedding.

However, we haven’t got confirmation back on whether or not the Department of Agriculture, Food and the Marine or Bord Bia are in favour of this in Ireland.

The XSplit separator itself is priced at around €24,000 plus VAT. However, the unit featured in this article, which comes with all the bell and whistles and the actual trailer unit is priced at north of €120,000 plus VAT.

It is worth noting that this is a top-of-the-range outfit, which wouldn’t be required for most Irish applications.

Screw press slurry separators are now being funded by TAMS III under the Animal Welfare, Safety and Nutrient Storage Scheme (AWNSS). As per the TAMS III documentation, the unit must be a fixed investment.

Capacity

The units are costed based on their capacity in m3/h throughput. The unit featured has a throughput capacity of up to 50m3/hr. Based on the TAMS III document, the calculation of a reference price is as follows: y=20.146(50) + 30,875 which equates to €31,882.30.