RP26: Biofilters
Source: gov.uk (2025-10-27)

Find out about eligibility and requirements for the biofilters item.

This item is part of Capital Grants 2025. You must read the Capital Grants 2025 guidance (https://www.gov.uk/government/publications/capital-grants-2025) to understand the rules and how to apply. If you’re applying for this item as part of a Countryside Stewardship Higher Tier (CSHT) application, you must read the CSHT applicant’s guide (https://www.gov.uk/government/publications/countryside-stewardship-higher-tier-csht) to understand the rules and how to apply.

How much you’ll be paid

£2,026.14 per unit.

How this item benefits the environment

The biofilter degrades pesticide residues that result from pesticide handling activities. They help prevent pesticides from entering drains or water bodies, helping to reduce the risk of water pollution.

This item can help you protect, recover and improve biodiversity on your land.

Where you can use this item

You c an only use this item in areas targeted for the reduction of water pollution from agriculture.

You cannot use this item:
- within 10 metres (m) of a watercourse
- within 50m of a spring, borehole or well which is not used to supply water for domestic use or food production without prior agreement from the Environment Agency (https://www.gov.uk/government/organisations/environment-agency#org-contacts)
- within 250m of a borehole used to supply water for domestic use or food production purposes without prior agreement from the Environment Agency
- in an area that’s designated as a Groundwater Source Protection Zone 1 (https://www.gov.uk/guidance/groundwater-source-protection-zones-spzs) without prior agreement from the Environment Agency
- without relevant advice, consents or waste management licence from the Environment Agency
- on historic or archaeological features identified in your Historic Environment Farm Environment Record (https://hefer-data.org.uk/) (HEFER)
- on areas of wildlife interest identified on your Farm Environment Record (FER) or on MAGIC (https://magic.defra.gov.uk/MagicMap.aspx)
Catchment Sensitive Farming (https://www.gov.uk/guidance/catchment-sensitive-farming-reduce-agricultural-water-pollution) provides advice where there are water quality or flood risk issues linked to farming.

Get permission to use this item

You’ll need to get advice, consents and any required permits from the Environment Agency (https://www.gov.uk/guidance/check-if-you-need-an-environmental-permit) before you start work. You also must make sure you can comply with theT32 exemption (https://www.gov.uk/guidance/waste-exemption-t32-treatment-of-waste-in-a-biobed-or-biofilter) requirements.

What you must do to use this item

You must install a biofilter that:
- meets the requirements of the T32 waste exemption for the treatment of waste in a biofilter
- is either constructed as set out below, as in your approved feasibility study or implementation plan, or bought as a ready-made, purpose-built biofilter kit
- when constructing the biofilter you must use 3 brand new chemical-resistant impermeable containers which are typically a minimum volume of 800 litres
- store pesticide washings in additional containers next to or below the 3 biofilter containers, or in an underground storage tank that collects washings from a pesticide handling area
- cut the tops off the intermediate bulk containers (IBCs), leaving the corners intact
- insert wire mesh lining in the base of each biofilter container
- cover the lining with a permeable membrane
- install a layer of pea gravel over the membrane so that the drainage outlet to the container below is not blocked – the pea gravel should be at least 10cm deep
- make a biomix by mixing one part peat-free compost, one part topsoil and 2 parts straw (wheat or barley) by volume
- allow the biomix to compost for 30 to 90 days before filling the containers
- fill the IBCs with biomix , leaving a 10cm gap at the top for piping
- allow the biomix to settle, then top up to a volume of at least 0.6 cubic metres of biomix in each one
- stack the 3 containers vertically into a tower on a flat concrete base, ensuring the structure is stable – if the biofilter is not covered, replace the top of the uppermost container to prevent rainfall from getting in
- install pumps, pipes and a hose to pump washings from the initial storage container or tank to the top biofilter container and on to the biomix through a piped ring distribution system – this is to ensure the washings are well dispersed across the surface of the biomix
- allow the washings to flow by gravity through the pipes to the biofilter containers below
- pump discharge from the bottom container to a storage tank or directly for drip irrigation onto a vegetated area
- build a concrete bund at least 100 millimetres (mm) high around the biofilter or construct in a bunded farm building
You must not treat more than 15,000 litres of pesticide washings (excluding rainfall) in any 12-month period.

Evidence you must keep

You must keep and provide with your claim:
- photographs of the site during the different stages of construction or contracts, invoices or other documents confirming the technical specification for the completed works
- photographs of the completed works in place and installed
- any consents or permissions connected with the work
You must keep and provide on request:
- receipted invoices or bank statements where a receipted invoice is unavailable
- photographs of site before works start
- documents including records of treatment in the biobed associated with the T32 exemption for the treatment of waste in a biobed or biofilter registered with the Environment Agency
Read the record keeping and site visit requirements in the Agreement holder’s guide: Capital Grants, Higher Tier capital grants and Protection and Infrastructure grants (https://www.gov.uk/government/publications/agreement-holders-guide-capital-grants-higher-tier-capital-grants-and-protection-and-infrastructure-grants-2025) for more information.

If you’re applying for this item as part of a Countryside Stewardship Higher Tier (CSHT) application, read the record keeping and site visit requirements in the CSHT agreement holder’s guide (https://www.gov.uk/government/publications/countryside-stewardship-higher-tier-csht).

Other capital items you can use with this item

You can use this item with these items:

RP27 Sprayer or applicator load and washdown area (https://www.gov.uk/countryside-stewardship-grants/sprayer-or-applicator-load-and-washdown-area-rp27)

RP28 Roofing (sprayer washdown area, manure storage area, livestock gathering area, slurry stores, silage stores) (https://www.gov.uk/countryside-stewardship-grants/roofing-sprayer-washdown-area-manure-storage-area-livestock-gathering-area-slurry-stores-silage-stores-rp28)

Advice to help you use this item

The following advice may help you to use this item, but you do not have to follow it to get paid. It’s not part of this item’s requirements.

British Standards

Check to make sure the work meets relevant British Standards (https://www.bsigroup.com/en-GB/products-and-services/standards/).

Choosing a location

Put the biofilter where you can use it safely. For example:
- away from thoroughfares
- against a wall or other surface where it’ll be well-supported
- outside or in a farm building that’s not used for livestock, feed or food storage
For best results, locate it close to the pesticide handling and washdown area.

Using biofilters

Biofilters are suitable for use on holdings generating smaller volumes of pesticide washings. For example, where the pesticide handling area is roofed so rainfall does not fall on the area or where crops are grown in glasshouses.

Where larger volumes of pesticide washings are generated, a biobed is more appropriate. See RP24: Lined biobed plus pesticide loading and washdown area (https://www.gov.uk/countryside-stewardship-grants/lined-biobed-plus-pesticide-loading-and-washdown-area-rp24) or RP25: Lined biobed with existing washdown area (https://www.gov.uk/countryside-stewardship-grants/lined-biobed-with-existing-washdown-area-rp25) instead.

Read more information about pesticide handling areas and biobeds including sizing and volume calculations on the Voluntary Initiative website (https://voluntaryinitiative.org.uk/water/biobeds/).

Maintaining the biofilter

Add fresh, pre-composted biomix to the biofilter to maintain its depth. The biomix should remain moist but not waterlogged (use irrigation if necessary). Take care to not allow the container to overflow. Replace the biomix every 5 years. You’ll need a U10 (https://www.gov.uk/search?q=U10+exemption&filter_organisations%5B%5D=environment-agency) or U11 (https://www.gov.uk/search?q=U11+exemption&filter_organisations%5B%5D=environment-agency) exemption to spread the biomix. Only use the biofilter to treat pesticide washings.