Effective economic methods are needed to control offensive odours arising from the storage and landspreading of slurries and solid manure and from livestock buildings. Odour concentration in air can be determined through the use of a dynamic dilution olfactometer and a panel of people. The use of micrometeorological or wind tunnel techniques, enable rates of odour emission to be calculated during and after spreading wastes on land.
The highest rates of emission occur during and for the first few hours after spreading. These rapidly decline to much lower levels, which normally persist for 2-3 days with small diurnal fluctuations, reflecting changes in wind speed and possibly, air temperature. A wide range of animal, management and environmental factors influences rates of emissions. Methods for reduction include anaerobic digestion or aerobic treatment of slurries prior to storage, direct injection into soil or, on arable land, rapid incorporation by ploughing or rotavation. There is less information on odour emissions from livestock buildings which are often much greater than those from land, especially from mechanically ventilated pig and poultry houses. Frequent removal of wastes, or cleaning exhaust air by means of a biofilter or bioscrubber can be effective in reducing these emissions.
Relationships between odour concentration and odour intensity (the perceived strength) suggest that, in many instances, >90% reduction in concentration is needed for effective abatement.