Origin of objectionable odorous components in piggery wastes and the possibility of applying indicator components for studying odour development

Many problems are associated with the measurement of objectionable odours from livestock confinement buildings. In principle, odours can be measured only by using techniques which include the human nose. But sensorial techniques have many disadvantages for routine purposes. As an alternative approach many authors have tried to determine odour intensity by measuring the concentration of one or more of the volatile constituents of odorous air. The choice of the compounds to be measured in such an approach is very important. In piggery wastes about 150 volatile compounds have been identified. Most of these compounds are presumed to be products of anaerobic microbial degradation of the waste constituents. The microbial pathways leading to the formation of the various volatile compounds in the wastes are indicated in this paper. In addition, the overall process of the conversion of high molecular waste constituents to low molecular weight compounds is discussed.

Finally, it is suggested that certain volatile waste constituents, which are strongly related to the degradation of protein and/or plant fibre residues, are suitable for monitoring instrumentally. It is concluded that p-cresol and volatile fatty acids to a large extent meet the requirements for such indicator compounds.