Development of a relationship between olfactory response and major odorants from organic wastes

Determination of an averaged human olfactory response as odour concentration to odours by instrumental means has been sought to simplify on-site measurement and reduce cost. Different concentrations of hydrogen sulphide, 4-methyl phenol, ammonia and acetic acid were used to simulate livestock waste odour. A second-order uniform precision rotatable central composite statistical design identified 31 odour mixtures to establish a human olfactory response model. An odour panel containing eight people was selected according to recognised criteria. They had an average age of 43.3 years. A multiple linear regression model accounted for 74.1% of the variance, with a decreasing order of influence of hydrogen sulphide > 4-methyl phenol>>acetic acid within the bounds of the model described. Surprisingly, 4-methyl phenol concentration produced a negative effect on the olfactory response. To enable better fitting of the complex olfactory response radial basis function, neural network modelling was used to account for 88% of the variance. With pig manure odours outside the studied concentration range the network model did not function. Predictions using the linear regression model were on average 20% less than observed values. These findings demonstrate that this approach is appropriate to determine the odour concentration from pig manure using the main odorants.