Managing odour

Factors contributing to odour nuisances include the frequency (F) of occurrence, the intensity (I) or strength of the odour, the duration (D) of exposure and the offensiveness (O) or character of the odour (Artis 1984; Bulley and Phillips 1980). These terms are collectively described as the FIDO factors.

For piggeries, the rate at which an odour is generated is influenced by shed design, effluent collection and disposal systems, and overall piggery management. The impact of generated odours is influenced by the climate and topography of the land.

Odour generation

The odour generated from piggeries is a result of manure and waste food decomposing. Odour from freshly excreted manure is generally less offensive than odour released from anaerobically decomposing manure.

The decomposition of piggery wastes may occur either anaerobically or aerobically. The compounds produced depend on the oxygen status of the waste and, thus, the process involved in the decomposition.

Aerobic decomposition occurs under conditions where oxygen is available in the system. Under aerobic conditions, the main decomposition by-products are carbon dioxide, water and other compounds (e.g. water soluble, inorganic nitrogen and sulphur-based compounds), which tend to produce little odour (Elliot et al 1978).

Anaerobic decomposition occurs where there is little or no oxygen available to the system. Anaerobic decomposition is a slower and less complete process than aerobic decomposition. Because anaerobic digestion is less complete, the by-products yielded are more complex and subsequently tend to be more odorous (Elliot et al 1978). Some of the by-products of anaerobic digestion, such as volatile fatty acids, phenols and hydrogen sulphide, produce strong odours that may be detected a significant distance from the source (Elliot et al 1978). Other compounds released are odourless (e.g. methane).

Odour dispersion

When air transports an odour from the source, dispersion or dilution of the odour occurs. This results in a declining odour concentration with increasing distance downwind of the source. This reduction in odour concentration depends on the atmospheric stability at the time.

Generally, odour does not disperse and mix as readily at night as it does during the day. Atmospheric stability refers to the potential of air to disperse and is defined using Pasquill Gifford scheme where the atmosphere is categorised from unstable (category A) to stable (category F). Optimum dispersion occurs under unstable conditions. In simple terms, the lower the stability class (closer to A), the greater the odour dispersion and, hence, the lower the potential for odour nuisance (see Table 1).

Table 1. Pasquill's stability categories (adapted from Pasquill et al 1983)
Wind speed (height of 10 m) Day time (incoming solar radiation) Night time (cloud cover)
m/s Strong Medium Slight Mostly overcast Mostly clear
< 2 A A - B B - -
2 - 3 A - B B C E F
3 - 5 B B - C C D E
5 - 6 C C - D D D D
> 6 C D D D D

Separation distance plays an important role in the dispersion of odours from piggeries. Piggeries should be established a sufficient distance from sensitive receptors, such as farm residences and towns, to ensure that dispersion effectively limits odours to acceptable levels and frequencies under the expected range of atmospheric conditions. Under some circumstances, computer modelling of odour dispersion may be required to support an application for a new or expanding piggery development.

Odour sources and management practices

Sheds

Modern piggery sheds generally produce less odour than older styles of piggery sheds. This is primarily due to improved natural ventilation, better construction materials that are easy to clean, and the use of flushing pits rather than static pits.

Management practices that may reduce odour generation in sheds include:

  • Cleaning/sweeping and water-pressure washing lanes, pens and handling areas regularly.
  • Flushing flushed sheds twice daily.
  • Dumping static-pit sheds weekly, or more frequently if possible.
  • Cycling pit flushing or emptying to ensure complete cleaning of the pit.
  • Using recycled effluent liquid to top-up static systems and in flushed sheds to reduce total effluent and odour production.
  • Minimising the use of bactericides in piggery disinfection to avoid detrimental affects on pond flora and fauna.
  • Providing deep-litter sheds with sufficient bedding material to avoid the formation of wet areas.

Drains

Well-maintained, adequately designed drains should not create odour problems. Odour emissions from drains occur when wet manure accumulates in the drain and decomposes anaerobically.

  • Construct drains with smooth concrete, fibreglass or other impervious material in spoon or vee-channel sections.
  • Drains should have a minimum 0.5% slope to ensure non-retention of solids, ease of cleaning and drying between use.
  • Enclosed drains/pipes should have 1% slope and should be flushed with sufficient fluid to self-clean.

Ponds

Anaerobic ponds are an effective method for treating piggery waste. If they are designed and managed correctly, odour generation can be minimised, resulting in fewer odour complaints.

  • Effluent loading needs to be even and must not exceed the design capacity of the pond system.
  • Effluent released from sheds to ponds should be staged to avoid slug or shock loading.
  • Pond active volume should be maintained by regular and planned desludging.
  • Excess pond salinisation should be avoided by the addition of fresh water.
  • Pond pH should be maintained between 6.8 and 8.0.
  • Afterbirth, pig carcasses and foreign material should not be disposed of in ponds.

Covering ponds with supported straw and permeable polypropylene has been shown to reduce odour emissions from anaerobic ponds by up to 90%. This is a relatively new technology in Australia and is currently being researched.

Impermeable pond covers can also be used to eliminate odour emissions from anaerobic ponds. While such systems can be quite costly, bio-gas from the ponds can be flared or converted to thermal or electric energy.

Effluent disposal areas

Irrigation of effluent generates odours through the release of offensive gases and by spray-drift of fine aerosols through the atmosphere.

  • Manage the application or irrigation of piggery effluent so that effluent infiltrates, or is incorporated into the soil soon after application.
  • Avoid surface ponding and effluent irrigation during prolonged wet periods or when runoff would occur following further irrigation.
  • Consider the timing of effluent application including time of day or day of the week (e.g. consider weekends and public holidays), prevailing weather conditions, and working conditions of the pond.
  • Consult neighbours when management practices are likely to cause excessive odour emission.

Carcass disposal

Odour generation may be significant in poorly designed and managed disposal facilities.

  • Design pits to prevent entry of upslope runoff water.
  • Cover the whole carcass with a layer of soil immediately after placement in the pit.
  • If composting is used, cover the carcass with at least 300 mm of sawdust or other composting substrate.

Pond desludging

Sludge is comprised of either completely or partially digested organic matter, which settles out in the anaerobic pond. When sludge is removed from the pond, all of the solids are disturbed and, thus, desludging can be highly odorous.

As desludging is an infrequent but unavoidable event, inform your neighbours before you begin.

Suggested management practices

The measurement of odour generation rate and odour intensity is a developing science. The technology for odour measurement is not suitable for real-time piggery management or regulation. However, it is widely recognised that good design, construction and management practices can minimise excessive odour emissions. Consequently, the following management practices are suggested:

  • Avoid excessive manure build-up in piggery buildings and below floor pit areas.
  • Ensure that external open drains are impervious, with non-earthen base and sides that are kept clean and dry between use.
  • Manage ponds to ensure minimal crusting and an even effluent loading that does not exceed the design capacity of the pond system.
  • Where practical, incorporate piggery solids (sludge and screenings) into the soil within 24 hours of spreading.
  • Manage on-site manure storage and processing areas to avoid odour nuisances.
  • Advise neighbours in advance of any management practices that may lead to odour nuisances.

Other methods of reducing odour complaints

The adage 'out of site - out of mind' holds true for piggeries. Planting trees around existing piggeries or siting new piggeries appropriately will make them less obvious to the public and, generally, reduce the incidence of odour complaints. Properly planted tree buffers also have the potential to enhance odour dispersion, thereby reducing odour nuisance.

Make sure you communicate with you neighbours. Many odour complaints arise from disagreements and misunderstanding.

Complaint recording and investigation

As part of a piggery operator's environmental management plan, a register should be kept of all odour complaints. This register should include time, duration of the event, meteorological conditions (temperature, humidity, wind speed, wind direction) and any changed management or operational practices at the time.

Record the cause of the odour (if known) and any remedial action taken to rectify the problem.

References

Artis, D 1984, 'Legal controls over odour nuisance', Chemistry and Industry, 9:320.

Bulley, NR and Phillips, D 1980, 'Sensory evaluation of agricultural odours: A critical review', Can. Agric Eng. 22:107-112.

Elliot, LF, Doran, JW and Travis, TA 1978, 'A Review of Analytical Methods for Detecting and Measuring Malodors'. Soil Sci. Soc.

Pasquill, F and Smith, FB 1983, Atmospheric Diffusion. Chichester, Ellis Horwood.

Further information

  • Managing a piggery (includes information about welfare considerations, building design, financial management, improving your herd, pig health and diseases, and feed and nutrition)