Purpose and scope of the third Report
The purpose and the objective of the 3rd Report is to provide both scientific and advisory workers with information and basic facts about:
In the Report, aerial contaminants are divided into three groups and discussed in separate chapters: gases, particles and odour. The basic idea was to describe each contaminant under the headings: Introduction; Production-origin; Dispersion-behaviour; Measurement methods; Effects on animals and humans; Reduction technology and References. The Report contains the following chapters:
Emissions in and from animal buildings must be identified and analyse d in respect of potential detrimental hazardous effects on the atmosphere, man, animals, buildings and environment. The problems must be viewed and solved from a system analysis approach which includes synergetic effects between different compounds, circulation and mass balances. When proposing measures to reduce the release of some emission, it is preferable to look for the best system solution and not merely convert one kind of emission to another. An important strategy is of course to minimise the primary sources of emissions e.g. feed composition and manure handling systems.
Since animal production is global and atmosphere knows no borders, the problems should be solved from an international perspective.
The effect on animals is multifactorial and a direct relationship between air quality factors and animal health can be difficult to measure. However, there is substantial evidence that some gases and particles have a negative effect on the health and productivity of animals. For humans the area factor will affect persons within the building an d also those living nearby. Persons working in animal buildings can develop respiratory p roblems. The general strategy should aim at reducing exposure to aerial contaminants.
Air flow patterns - measurements and theory
Air flow patterns in livestock buildings are important because they influence the distribution of air velocities, temperature, gas concentrations, and release of gases from manure. When examining the release and distribution of gases, the air pattern must be made visible with smoke; methods and equipment are presented. Techniques to measure ventilation rates at the exhaust are examined. The air flow pattern outside livestock buildings is described with a plume model, which is discussed.
Gases covered in the report are ammonia NH3, carbon dioxide CO2, methane CH4, hydrogen sulphide H2S, hydrogen cyanide HCH and carbon monoxide CO. The basic chemical,enzymatic and microbial processes and principles which are involved in the production orforming of the gases are given. Expressions for the production of CO2 and CH4 are given.The behaviour and dispersion of gases within animal buildings and techniques to measure concentrations in, and emissions from, the buildings are presented. Gas distribution caused by density differences is outweighed by the air flow pattern.
Ammonia is given most attention because of tie relative high concentration in livestock buildings and because the emissions contribute to environmental damage both locally and globally. Vegetation, soil, surface and ground water are directly affected by ammonia emissions. 80% of ammonia in the atmosphere originates from agriculture, especially from animal production. High deposition of nitrogen oxides and ammonium contribute together with SO2 and volatile organic compounds to an acidification of both soil and water, which can contribute to changes in the vegetation due to the increased availability of nitrogen (eurotrophication). Chemical, enzymatic and microbial processes transforming nitrogen-containing compounds into ammonia are discussed and following conclusions drawn. Ammonium is readily produced from urea in urine from cattle and pigs and from urine acid from poultry. Production from faeces (organic matter is much slower. Separation of urine and faeces reduces ammonia volatilisation in cattle and pig manure. A pH below 6 would virtually eliminate ammonia emission from manure. Manure storage temperature below 10°C greatly reduces ammonia emissions, as does the absence of air movement above the manure surface.
Odour is characterised by a totally different behaviour as compared to gases and airborne particles. Conflicts between livestock producers and the public concerning dour are now being reflected in laws and regulations to protect the public from malodours generated by livestock units. Nowadays, therefore, there is an acute need for effective methods of odour control and reliable and efficient odour measurements. Odour is the effect of a gas mixture produced by bacterial actions. Only volatile compounds have been identified in piggery waste. Some of them will contribute more to the odour than others.
Since odour is a very complex and subjective phenomenon it cannot be easily expressed in ordinary figures. Odour measurement methods must use three complementary approaches: sensory (the response - odour perception by a panel), chemical (the dose analysed by gas chromatography or spectrometry) and sociological methods (the annovance level assessed by questionnaire). These methods are presented and also discussed critically from the perspective of emission and related annoyance. Empirical models fro distances necessary between livestock buildings and residential areas are reviewed.
Approaches to odour abatement can be made by destroying or inhibiting the bacterial and enzymes responsible for the production of odorous compounds by the use of chemicals, biological-mechanical treatment of the manure (aerobic treatment, separation of manure and urine, etc.), or treatment of the exhausted air. Examples are given of large collective biogas plants constructed as combined energy and environmental plants. Currently 10 large plants are operating in Denmark. Reduction techniques in the ventilation air could be applied using biofilters or scrubbers. Comparisons between methods are made. There is also a survey of the effects of odour control chemicals, stating that not all tested chemicals were effective in reducing odour. Some products may have side-effects on humans, animals and crops, and their use is questionable.
The aerosol mixture in animal houses includes micro-organisms, gas, water vapour and other substances. Dusts are dispersed particles of solid matter in gases which are generated during mechanical processes. Inspirable aerosols are the fraction of airborne particles and droplets which enter the nose and mouth during breathing. Respirable aerosols are the fraction of airborne particles and droplets which, penetrates through the gas exchanges region of the lung, the alveoli. The chapter relates aerosols to dust particles. For intensive buildings the dust sources are: incoming air, feed, bedding, manure and animals. Dust is removed by ventilation air extraction or filtration, settling, and removal with manure.
The opportunity to reduce dust by manipulating ventilation rates is limited, but should not be ignored. However, a significant part of the dust will be removed by ventilation.
Sedimentation in still air follows Stokes Law and dust will deposit on the floor fixtures, etc. The settling velocity for a 2 =E6m diameter particle is 0.12 mm/sec. This explains why smaller particles follow the movement of air. The total amount of airborne dust in livestock buildings at any time is the equilibrium between all sources of dust "production" (included re- suspended settled dust) and the various removal mechanisms (sedimentation and ventilation).
Factors influencing dust production are primarily animal feed and animal activity. Increasing the moisture content of grain before grinding gives an 80% reduction in dust production. Adding fat to the feed can give an equivalent reduction. Airborne dust varies considerably depending on animal activity. Simultaneous measurements of pig activity and dust concentration show that variations in pig activity can explain most of the variation in dust concentration within a building.
The most interesting methods for measuring dust are presented and evaluated. The filter methods (total and respirable) give only average dust concentration and the particle counter gives only relative measurements.
Effects on animal and humans
The main diseases associated with agricultural work, allergic rhinitis and asthma, pneumonitis/alveolitis, organic dust toxic syndromes and bronchitis are described an examples are presented with references from different studies. The relevance of dust to livestock is twofold: most important is damage to the respiratory tract caused by dust particles the second concern involves micro-organisms which cause damage to the respiratory systems.
Some of the information available on the relationship between airborne particles and respiratory ailments remains contentious, although studies have demonstrated significant relationships between air quality factors and the severity of respiratory diseases when variable pathogens are also present. Examples of studies with references which relate to air quality factors and respiratory problems are given.