Project: Ammonia and odour abatement methods for the NI pig industry

Area of Expertise:

Project objective: To assess ammonia and odour abatement methods for the NI pig industry

Main conclusions:


Nitrogen in faeces is mainly present in the form of protein while nitrogen in urine is mainly present in the form of urea. The main source of NH3 is the rapid hydrolysis of urea by the enzyme urease.  Depending on the acidity of the slurry Urea is converted to either ammonium or ammonia. This reaction happens rapidly when urea comes in contact with urease. 


The main compounds within pig odour are:

  • Short-chain acids. C4 and C5 straight chain and branched chain acids, especially butanoic acid, pentanoic acid and 3-methylbutanoic acid. These compounds have unpleasant odours of faeces or rancid cheese.
  • Sulphur compounds. These compounds can be difficult to measure, but when recorded are at levels likely to contribute to odour. Hydrogen sulphide is especially odorous but methylmercaptan and related sulphides and disulphides are also involved. H2S smells of rotten eggs while the other sulphur compounds smell of rotten vegetables.
  • Phenols. 4-Methylphenol makes a major impact but phenol and 4‑ethylphenol are likely also to contribute. The compound, 4‑methylphenol, has a faecal odour whilst the other two have a pungent aromatic smell.
  • Indoles. 3-methylindole and indole are highly odorous compounds with odours of faeces. 3-methylindole, also known as skatole, is responsible for the characteristic odour of pig slurry.
  • Amines. Trimethylamine and ammonia contribute to the odour in pig houses but in most cases are not the major odour compounds. 


Key abatement strategies specifically targeted at ‘animal/house’ include:

  • Dietary – reducing CP content (and increasing Fibre content) as well as inclusion of some feed additives
  • Slat and tank design : concrete slats with notches or protruding edges with gap widths of max 30 mm show better results in favouring manure drainage and decreasing emissions. Separating faeces from urine under the slat is a very effective way of reducing ammonia (and sometimes odour) emissions however slope gradient and cost effectiveness needs further investigation.  Lastly the frequent removal of manure and flushing of pits, though labour intensive, does effectively reduce ammonia and odour emissions.  However, infrastructure costs will be incurred.
  • Use of acid scrubbers and Biofilters are effective, however work is required to design and manufacture them in a way that their maximum potential could be availed of.  However these scrubbers can be expensive to install, maintain and run.


The cost effectiveness of each is difficult to rank as cost will be dependant on the current situation and options available to different farms but it is suggested dietary manipulation will be the easiest and most cost effective initially.  However to reduce ammonia and odour emissions to levels required it is highly likely at least one additional abatement method is required.  Air scrubbers and tank design alterations appear to be the two abatement methods with most research conducted and therefore confidence in the success of these strategies is high.  However, both will increase the cost of infrastructure and that cost will be dependant on the options available to different farms.  Furthermore, whilst air scrubbers are effective, the cost of maintain and run the equipment is an ongoing expense which also need to be considered.

Overall, although there is a body of scientific evidence with regard to ammonia emissions, there remain gaps in the knowledge and further work is required.  However, the evidence gaps with regard to odour emissions from pig facilities as well as the impact of abatement strategies on odour emissions are vast.  As such it is difficult to provide scientific guidance in this area without further research being conducted.

These reports are now complete but over the last few months the relationship between odour analysis techniques has been questioned.  This review did not aim to address the ‘pros and cons’ of odour measurement techniques but it is an area where greater understanding is required in order to assess the usefulness of studies using different odour measurement techniques.