RP26: Biofilters

Find out about eligibility and requirements for the biofilters item.

How much will be paid

£990 per unit.

Where to use this item

Available for Mid Tier and Higher Tier

Only in areas targeted for the reduction of water pollution from agriculture

Where this item cannot be used

  • within 10m of a watercourse
  • within 50m of a spring, borehole or well
  • within 250m of a borehole used to supply water for producing domestic food without prior agreement from the Environment Agency (EA)
  • on historic or archaeological features or areas of wildlife value identified on the Farm Environment Record (FER), the Environmental Information Map or the HEFER
  • without relevant advice, consents or waste management licence from the Environment Agency (EA)

How this item will benefit the environment

The biofilter will degrade pesticide residues that arise from pesticide handling activities. This will help prevent pesticides from entering drains or water bodies, which will help reduce the risk of water pollution.


Agreement holders will need to install a biofilter. This should be constructed either as set out in the approved Feasibility Study or Implementation Plan, or as described below and which to meet the T32 exemption.

To construct a biofilter applicants must:

  • use 3 new, chemical-resistant impermeable containers - these will typically be 1000 litre intermediate bulk containers (IBCs) stacked vertically
  • store pesticide washings in additional containers next to the IBCs, either before or after treatment
  • alternatively, pump the washings directly from an underground storage tank that collects washings from a pesticide handling area
  • cut the tops off the IBCs, leaving the corners intact
  • insert wire mesh lining in the base of each one
  • cover the lining with a permeable membrane
  • install a layer (at least 10cm) of pea gravel over the membrane so that the drainage outlet to the container below is not blocked
  • make a biomix by mixing one part peat-free compost, 1 part topsoil and 2 parts straw (wheat or barley) by volume
  • allow the biomix to compost for 30 to 90 days before filling the IBCs
  • 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 0.5 cubic metres of biomix in each one
  • stack the 3 IBCs vertically into a tower on a flat concrete base
  • 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 tank to the top biofilter container and on to the biomix through a piped ring distribution system
  • allow the washings to flow by gravity through the pipes to the containers below
  • pump discharge from the bottom container to a storage tank, or for direct irrigation through a perforated hose on a vegetated area
  • build a concrete bund at least 100mm high around the biofilter
  • meet the requirements of the T32 waste exemption
  • meet relevant British Standards - examine copies of the most up-to-date standards for guidance

Do not treat more than 15,000 litres of pesticide washings (excluding rainfall) in any 12 month period.

Keeping records

Agreement holders will need to keep the following records and supply them on request:

  • any consents or permissions connected with the work
  • receipted invoices, or bank statements where a receipted invoice is unavailable
  • please see the record keeping and inspection requirements as set out in the Mid Tier manual for more detail

Agreement holders will need to keep the following records and supply them with the 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

Before applying, applicants must seek advice from the EA and obtain any consent that may be required to carry out the planned work. Applicants must check whether they are in a Groundwater Source Protection Zone 1 area with EA. Applicants will have to send the following with their application:

This item can be used on the same area as the following items:

Advice and suggestions for how to carry out this item

The following section gives advice on carrying out this item successfully but does not form part of the requirements for this item.

How to choose a location

The biofilter should be situated where it can be used safely, for example:

  • away from thoroughfares
  • on a flat concrete base
  • against a wall or other surface where it will be well-supported

The biofilter can be placed in a farmyard or building or under a roof. It can also be placed it on areas of land, or farm buildings, that are not used for production. For best results, it should be located close to the pesticide handling and washdown area.

How to maintain the biofilter

Fresh, pre-composted biomix should be added to the biofilter to maintain its depth. The biomix should remain moist, using irrigation if necessary. Care must be taken not to allow the container to overflow. The biomix should be replaced every 5 years. A U10 or U11 exemption for spreading waste will be required to spread the biomix. The biofilter should not be used to treat hazardous waste.

Further information

More information about pesticide handling areas and biobeds, including sizing and volume calculations, is available from the Voluntary Initiative

Catchment Sensitive Farming (CSF) operates in parts of the country where there are water quality issues linked to farming. The scheme provides farmers with free advice and training. See guidance for further information on CSF support.

See the Mid Tier manual or Higher Tier manual to find out more about the scheme and how to apply.

Published 2 April 2015
Last updated 10 March 2017 + show all updates
  1. Updated for 2017 applications.
  2. Information updated for applications in 2016
  3. First published.