Mitigating measures for odor emissions

Literature study

In the framework of the reference tasks for the Environment, Nature and Energy policy area, a literature study was made of mitigating measures for odor emissions that can be applied in existing pig and poultry houses in Flanders. This study gives an overview of the scientific research carried out internationally on these measures. It concerns measures that can be applied relatively easily and without major additional costs in most existing stables.

(In Dutch) Milderende maatregelen voor geuremissies afkomstig van bestaande varkens- en pluimveestallen in Vlaanderen (pdf - aangepaste versie sinds 30/09/201


This letter applies to existing pig or poultry stables (i.e. stables that are not constructed according to the list of low ammonia emission stables), which in the past have given rise to complaints about odour nuisance and of which, at the time of (re)licensing, it is judged that the company is causing an unacceptable odour nuisance for local residents.

The purpose of the circular is to list the current and economically feasible technical and organizational measures for limiting odor emissions at existing pig and poultry houses.

The circular forms an assessment framework for the licensing authorities so that the uniform treatment of (re-)licensing applications of pig and poultry farms is promoted across the provinces and the legal certainty of the farmers concerned is guaranteed.

This letter is also a practical guide for farmers who are confronted with odor nuisance complaints when submitting their license application. In this way, they can already proactively include a number of measures in their permit dossier.

The measures to be taken will be determined in consultation with the competent administration. The steps to be followed within the framework of a (re-)application for a permit can be found in the circular (5. Step-by-step plan).

Omzendbrief (pdf)


For many of the measures imposed, the implementation of a standard procedure is a prerequisite. In certain cases the application of the standard procedure must be recorded and kept in a logbook. The standard procedure and the logbook must be kept at the disposal of the supervisors at all times. On this site examples of the various standard procedures and logbooks are made available (click on the measures below). In specific cases and with the consent of the licensing authority these examples of standard procedures and logbooks may be deviated from.

Mitigating measures for pig farms (in Dutch)

A-V1 Optimalisatie van het ventilatiesysteem
A-V2 Intensief en regelmatig reinigen van de stal bij all-in of all-out systemen
A-V3 Voederen volgens de behoeften van de dieren
A-V4 Goed brijvoedermanagement als dat van toepassing is
A-V5 Voederverliezen beperken en deze regelmatig verwijderen
B-V1 Beperken van de mestverblijftijd in de stal

Mitigating measures for poultry houses

A-P1 Optimaliseren van het ventilatiesysteem
A-P2 Intensief en regelmatig reinigen van de stal

Fully strewn houses

A-P3 Geschikt strooiselmateriaal kiezen (aangepaste versie sinds 30/09/2013)
A-P4 Nat en samengeklit strooisel verwijderen en vervangen door vers strooisel
A-P5 Drinkwaterverlies beperken

Not-fully strewn houses

A-P6 Frequente afvoer van mest naar gesloten opslag

Mitigating measures for outside the stall

B1 Kadaverkoeling
B2 De ventilatie-uitlaat verhogen
B3 Aanleggen van een windsingel
B4 Een windbreekmuur installeren

Question and answer

Question 1: Among the mitigation measures for pig houses, the first measure is "optimize the ventilation system". What if some of the existing pig houses are still ventilated naturally? Should we assume that this is no longer possible, and that in other words, the naturally ventilated stables must be adapted to mechanical ventilation?

The measure that is currently in the circular concerns stables that are already equipped with a mechanical ventilation system. With these stables specific problems can occur which occur less or not at all with naturally ventilated stables, such as excessive ventilation, pollution of the ventilation system. With natural ventilation, the standard package can also be applied with the specified reduction percentage.

Some comments for those who want to switch to mechanically ventilated houses:

For swine barns and piglet barns, converting from natural ventilation to well-dimensioned mechanical ventilation can also be profitable for the farmer, since the climate in the barn will usually improve. In sow stalls, however, this does not always provide a benefit, and is also often more difficult to achieve.

Bedded stalls are better ventilated naturally rather than mechanically.

In the case of naturally ventilated stalls, it will have to be determined on a case-by-case basis whether converting the stall to a mechanically ventilated one will improve the situation for the people affected. It is possible, for example, that there are nuisance occupants at very close distances and that the installation of a mechanical ventilation system with ventilation shafts on the roof will reduce the nuisance at very close distances. If, for example, the people who are bothered are not very close to the house and they end up in the plume of the mechanical ventilation, this can lead to more odour emission than with the naturally ventilated house. In addition, one must also consider the visual aspect of the ventilation ducts. It can cause a psychological effect on the neighbours and they will experience odour nuisance more quickly.

The cost of converting to mechanical ventilation depends very much on the existing situation. Both mechanical and natural ventilation are BAT measures. Converting an existing house from natural ventilation to mechanical ventilation is not always BAT.

If the house has to be renovated anyway (new roof and windows) this can be taken into account more easily. Otherwise it can lead to high costs.

Question 2: A reduction for windbreaks is only possible for "the existing part" of the farm. For the new stables this reduction cannot/may not be applied. How is this possible?

The circular has been drafted to tackle odour problems around existing stables. It cannot be the intention that the circular ensures that a windbreak can no longer be applied to new stables. However, the question is how much of a reduction can be counted on when applying a wind wall around a new stable. At the moment this aspect has not yet been included in the EIR cell's guidelines book on animals. LNE is currently discussing the added value of a windbreak.

May we point out that it is a measure that requires quite some time before there is any effect, if it still has to be implemented. It is rather a measure that in the last order of consultation can still give some positive result.

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