Abstract
The Delphi technique is a means of aggregating the judgement of a panel of experts in order to improve the quality of decision-making. This paper provides a case study of the technique by undertaking a three-round Delphi study to determine a package of best available techniques to reduce nitrogen emissions from a poultry unit under the Integrated Pollution Prevention and Control Directive (IPPC). Forms of nitrogen addressed included ammonia (NH
3), nitrous oxide (N
2O) nitrogen oxides (NO
x
), dusts and nitrate (NO
3
−), with the study providing a means to prioritise the pollution concerns on different spatial scales.
The priority pollutant issues were the contribution of NH
3 to eutrophication, the global cooling effect of NH
4
+ aerosol, the role of NH
4
+ as a vector for atmospheric transport of NO
x
and SO
2, the contribution of N
2O to global warming, and NO
3
− leaching. Reduced nitrogen (NH
x
) was rated as a priority on all scales, while N
2O and NO
3
− were rated as priorities only on global and local scales, respectively. The study indicated the need for abatement techniques at each stage of poultry rearing and waste management, with particular attention to reduce NH
3 emissions, reflecting the priority pollutant concerns. Measures identified by the panel include maintenance of dry litter, low emission removal of litter from housing and storage of litter under cover. Once the litter has left the farm, this should either be used as a biofuel for electricity generation or rapidly incorporated into agricultural soils. The amounts and timing of manure application should be tuned to crop needs.
Uncertainties in the Delphi technique limit its suitability as a stand-alone decision making tool. However, the Delphi technique proved useful in identifying priority pollutant issues, areas of agreement, disagreement and where information is lacking. This demonstrates its use when dealing with the complex issues of prioritising pollution issues and abatement approaches.