Preliminary guideline to assess pollution caused by livestock husbandry in livestock buildings

 INTRODUCTION

Livestock farming in Austria is increasingly confronted with questions of environmental protection. Livestock husbandry causes different kinds of emissions. One of them is odour which is a very important component because the acceptance of livestock farming in the vicinity can decrease due to an increase in odour sensation. Some countries have already developed guidelines to address odour from livestock. This paper presents and discusses the new Austrian "Preliminary guideline to assess pollution caused by livestock husbandry in livestock buildings".

GUIDELINE OVERVIEW

Requirements to Apply the Austrian Guideline

 The Austrian guideline presented here serves as a tool to assess airborne emissions resulting from livestock husbandry and the pollution caused by these emissions. It can be used both for projected and for existing livestock buildings. Application of the Austrian guideline results either in calculating a minimum protection distance to the neighbourhood which guarantees a far-reaching protection against odour annoyance or in a comparative assessment of sites of emission sources including the meteorological dispersion conditions at the sites. Which part of the assessment process is applied depends on the land use category in which the pollutant and/or the neighbour is situated. In agricultural areas, for example, livestock husbandry is principally possible and customary. Thus, in these areas higher pollution than in residential areas is reasonable, and a far-reaching protection against pollution via keeping minimum protection distances is not justified.

As an instrument of land use development plans, the Austrian guideline offers the possibility to ensure livestock farming in case of changes of the local land utilisation and cultivation plans by keeping the necessary minimum protection distances. The protection is not only legitimate in case of residential areas against odour pollution from livestock but also for the locations of resident livestock owners against approaching residential areas.

Some requirements have to be fulfilled before the Austrian guideline can be applied. To start the assessment of a given project, a technical description including all necessary maps is compulsory. The technical description has to contain all information which facilitates an agricultural-technical assessment. This includes items like storage of manure, ventilation facilities, the kind of feed etc. Appropriate guidelines and legal requirements must be followed.

To carry out the assessment process, at least the number of animals, their use and the way they are kept, have to be known. Any other information (pollutant source, meteorology, land use categories) leads to a more accurate and as a rule more favourable assessment of the project with respect to the livestock owner, because the factors which have to be calculated are multiplied and, in general, are less than one or equal one in the worst case. This is an essential principle of the Austrian guideline.

Determination of the Source

The pollutant source is determined spatially by a demarcation line which encompasses all odour sources of the farm and quantitatively by the odour number O which is calculated for all the relevant odour sources by

(1)

(2)

Thus, the odour number O is calculated by multiplying the number of animals Z, the animal factor f_A and the technical factor f_T which is a measure of the technical equipment of the livestock building i. Each kind of animals kept is characterised by a specific odour, which is felt differently by people. The possible annoyance of this specific odour is also dependant on the way and the intensity the animals are kept. Thus, the factor O allows for a quantitative estimation of the annoyance by odour. By choosing a common factor for all kinds of animals it is possible to assess also livestock farms where various kinds of animals are kept.

A first assessment of animal buildings without considering the technical equipment results from taking into account the number of animals Z and the kind of animals as well as the way they are kept. By use of the animal factor f_A the odour pollution of an animal caused by its metabolism is accounted for via its weight.

The technical equipment of an animal building is assessed by considering air ventilation, manure treatment, and feeding. The technical factor f_T is calculated via

(3)

The kind of air ventilation (factor f_V) used influences the source strength and the geometry of the source and therefore also pollution in the immediate surroundings of animal buildings. Its importance is stressed by allowing for a large variation of f_V between the values .10 and .50. Natural ventilation via open windows and doors is judged most unfavourable because in this case the livestock building is a diffusive source of odour substances. When a ventilation system is used f_V varies depending on the stack height above rooftop or ground, the outlet velocity, and the outlet direction. The ventilation is judged more favourable the higher the stack and the larger the outlet velocity. In this way a transport of odorants into the wake of the building should be prevented. Outlet openings below rooftop or in the side walls are therefore considered almost as unfavourable as natural ventilation.

Table 1. Scoring criteria to evaluate the odorant emission

Manure treatment (factor f_M) is assessed by taking into account the kind of manure system as well as the air flow pattern in the livestock building. Odour develops mainly from the duration the manure is kept in the building, the use of straw, and the air flow pattern. Odour development inside the livestock building is reduced if manure is removed frequently, straw is used, and air speed above the manure surface is low. Poultry is treated separately. Here, odour emissions are mainly dependant on the consistency of the slurry: the drier, the more favourable the manure system is judged. For all the other animals, a differentiation between solid and liquid manure systems can be undertaken. Mechanical solid manure systems with closed manure removal show the lowest odour emissions. Deep litter systems are judged more favourable if the duration the manure is kept inside the building is short. Liquid manure systems produce odour depending on the frequency of manipulation of the sewage: the less frequent, the smaller is f_M, and thus the more favourable the manure system is judged. f_M varies between .10 and .30.

Feeding (factor f_F) is judged by taking into account the specific odour, the storage and the required manipulation of the feed. Compared to ventilation system and manure treatment, its weight with values between .05 and .20 is lowest.

Estimation of Pollution Around the Source

The odour pollution around the source is assessed by taking into account the wind distribution, orographic influences, and given land use categories. The minimum protection distance depends on these parameters in addition to O.

Data from the nearest weather station are used to estimate the regional wind patterns to determine major odour transport directions and their frequencies. Local flow situations are introduced by assigning a site to one of three categories: plain, slope, or valley. These categories are characterised by different classes of dispersion conditions, with local flow being of distinctive importance. The climatology of the wind direction distribution and the local situation define the dispersion by the factor f_D.

Table 2. Scoring criteria to evaluate the dispersion of odorants by local wind systems.

In the plains, dispersion conditions are dominated by the regional flow. However, odour dispersion is eventually reduced by objects in the neighbourhood, like other buildings or vegetation, which can distort the flow (Lee and Hoard, 1991). Sites on slopes or in valleys experience the influence of periodical slope or valley wind systems (Defant, 1949; Vergeiner and Dreiseitl, 1987; Whiteman, 1990). During daytime, upslope and upvalley winds develop due to solar insolation, accompanied by good vertical mixing caused by thermal turbulence throughout the boundary layer, approximately the first kilometre of the atmosphere. Dispersion conditions are favourable during these periods. At night, downslope and downvalley winds dominate, and vertical exchange is restricted to a very shallow, near-surface layer of mechanical turbulence caused by windshear. Reception of odour is then possible over large distances of at least several hundred meters, depending on the source strength. Thus, the directions of downslope and downvalley winds are judged unfavourable for odour pollution.

The relative frequencies (in %) of the regional wind directions for 8 classes and the points due to the local flow situation (Tab. 2) are added. If calm wind conditions exceed 30 % a surplus is added independent of the direction to the neighbours, because in these cases odour dispersion is assumed to be extremely variable in space and time. In these situations it is not possible to forecast which areas will be affected most from odour pollution. The sum of the points of the regional wind and the local ones are transformed into the dispersion factor f_D for all 8 classes of wind direction (Tab. 3). The value of the dispersion factor f_D is direction-dependant and assumes values between .6 for the most favourable and 1.0 for the most unfavourable directions.

Table 3. Assignment of the sum of points due to the regional wind directions and the local flow situation to the dispersion factor f_D.

Different local land use categories allow for graded claims of protection against odour pollution from livestock husbandry. Protection is highest in recreation and pure residential areas, followed by primarily residential areas where other landuses are also possible and protection therefore is slightly less. The third category comprises mixed land use, commercial and plant areas. Values of the land use factor f_L range between 1 in the first case and .5 in the third; thus, protection is reduced in commercial areas by 50 % compared to pure residential areas. The assessment due to land use is dependant on the direction to the neighbours. In rural areas where livestock husbandry is common no land use factor is defined. In these areas odour pollution is judged by the former-mentioned comparative assessment of sites of emission sources taking into account the calculation of the odour number O and the meteorological conditions for the dispersion of odour.

Calculation of the Protection Distance

The minimum protection distance is that direction-dependant distance which allows for a far-reaching protection against odour pollution from livestock husbandry. Based on the odour number O and including the regional and local dispersion conditions f_D and the land use-dependant protection f_L, the protection distance P is calculated by

(4)

The dependence of the protection distance on O is not linear, as shown in Fig. 1.

Figure 1. Protection distance P depending on the odour number O assuming f_D = 1 and f_L = 1. The final protection distance P can be calculated via f_D and f_L determined in real situations. (E.g. an odour number O = 100 results in P = 250 m; by taking f_D = .8 and f_L = .7, the product f_D ×  f_L = .56, reducing P = .56 ×  250 m to 140 m).