Using a mechanical slurry separator to manage your slurry
What farmers and land managers must know about slurry separators, storing and applying separated materials.
Applies to England
What slurry separators do
They divide slurry into liquid and more solid organic manure. The liquid remains slurry. If you can stack the more solid material, you can treat it differently to slurry.
You can keep the materials in separate stores and apply them to land at different times depending on soil and crop need. This could make your organic manure easier to:
- store because it reduces crusting and build-up of solid matter in slurry stores
- move around the farm
- apply to meet soil and crop need because the separated materials have different ratios of nutrients
Some separators can produce a stackable material that is dry enough to reuse as animal bedding. This is called recycled manure solids (RMS). You must notify the Animal and Plant Health Agency and follow certain conditions if you plan to use RMS as bedding for dairy cattle.
If you use a weeping wall, it will not produce a material dry enough to stack. You must store and manage both materials as slurry.
If you use chemicals like coagulants with mechanical separation, you may need an environmental permit. Check with the Environment Agency if you are unsure.
What mechanical slurry separators you can choose from
To find the right system for your farm consider:
- the type of slurry you produce based on your herd composition, feed regime and type of animal bedding
- how you manage slurry
The main mechanical separators are:
- screw press which uses an Archimedes screw surrounded by a robust fine mesh screen to compress the solid and filter out liquid
- rotary or roller screen press which pumps slurry into a revolving perforated metal drum
- decanting centrifuge which uses high rotation speeds to separate solid and liquid and is often used with coagulant chemicals
You can install sand lanes after a mechanical separation to remove sand from the slurry. This can prevent the build-up of sand in your slurry store, reducing how often you dredge the store. You must follow conditions if you wash used sand-based animal bedding for reuse and spread wash waters for irrigation.
Rules you need to follow when calculating your slurry storage capacity
Slurry is defined as “liquid or semi-liquid matter composed of excreta produced by livestock while in a yard or building (including that held in wood chip corrals); or a mixture wholly or mainly consisting of livestock excreta, livestock bedding, rainwater and washings from a building or yard used by livestock, of a consistency that allows it to be pumped or discharged by gravity at any stage in the handling process” by the Water Resources (Control of Pollution) (Silage, Slurry and Agricultural Fuel Oil)(England) Regulations 2010 (SSAFO).
The amount of slurry storage you need depends on where your farm is and the type of livestock you keep.
All farms that produce slurry and spread it on their land must have at least enough storage to hold all the slurry produced in any 4 month period and comply with Farming Rules for Water (FRfW).
If your farm is in a Nitrate Vulnerable Zone (NVZ), you need at least:
- 5 months slurry storage for cattle, sheep, goats, deer and horses
- 6 months slurry storage for pigs and poultry
You must have enough storage to meet these requirements without the separator. This will make sure you have enough storage if the separator fails or needs maintenance.
You can use slurry separators to further reduce pressure on your stores once you meet legal minimum standards. By diverting only the liquid to the store, you can:
- free up extra capacity in your stores
- safely manage the stackable material in a separate store or location
Collect and separate slurry
Collect your slurry in a reception pit before separation.
The pit must be large enough to hold all the slurry you are likely to produce in a two-day period, including any rainfall. You should have an alarm system and a contingency plan to prevent overflow.
You may need to install the separator on a gantry to allow the slurry to pass through it. You must fit the gantry with an access ladder and platform to allow safe inspection. You should be able to secure or lock this to prevent unauthorised access.
Store slurry
Once your slurry has passed through the separator, the liquid will remain slurry. You must transfer it to a slurry store built to comply with the minimum capacity and build standards required by the SSAFO regulations.
You should cover your slurry stores with an impermeable cover. This minimises ammonia loss and prevents rainwater from entering the store.
Collect and store stackable material
You must collect and store the stackable material on an impermeable surface to prevent leaching into the soil. If liquid leaks from stackable material, you must capture it and divert it to your slurry store. To prevent stackable material getting wet and turning back into slurry, you should:
- keep it under an impermeable cover such as a tarpaulin or in a barn
- not store it in an uncovered field heap, except for short periods when preparing to spread the material to land
If material does get wet again, you must store and manage it as slurry.
As with all organic manure, you must not keep the stackable material within:
- 10 metres of inland freshwaters or coastal waters, including those that are seasonally dry
- 50 metres of any spring, well or borehole
Spread your separated materials to meet soil and crop need
Slurry separation creates materials containing different ratios of nutrients. For example, the amount of readily available nitrogen may be higher in the liquid. Managing the materials separately could help you meet more of your soil and crop need through organic manures. This can reduce the need for artificial fertilisers. When you apply nutrients, you should:
- use a nutrient management plan
- regularly test your separated materials and soil to calculate how much to apply and plan timing
You cannot spread liquid with high readily available nitrogen during closed periods in Nitrate Vulnerable Zones, even if there is a soil and crop need. As with all slurries and liquid digestates, you should apply the liquid using low emission spreading equipment (like trailing hose or shoe or injection) rather than surface broadcast (splash plate). This reduces ammonia pollution and helps retain more nutrients in the soil.
The stackable material contains more organic matter and may contain more of the phosphate. In some areas, high levels of phosphate in soil means you have to export material. Using a separator helps make this phosphate easier to transport. If stackable material remains high in readily available nitrogen, you cannot spread it during closed periods in Nitrate Vulnerable Zones, even if there is a soil and crop need.
Last updated 25 October 2023 + show all updates
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Update to the spread your separated materials to meet soil and crop need section. Clarification that using low emission spreading equipment reduces ammonia pollution.
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First published.