Technical Publications

Odour Measurement Using An Efficient And Reliable
Dynamic Olfactometer

Jurn Wei Chai, Lawrence C C Koe, School of Civil & Environmental Engineering, Nanyang Technological University

EXECUTIVE SUMMARY

Odour nuisance has become a major environmental issue in Singapore with increasing level of development and rising living standards. Odour annoyance affects the population directly and the quality of the air is first assessed with the noses of the people and a bad smell is often regarded as an indicator for possible health risks. The local environmental authorities is driving a more serious approach and attention to assess and tackle the odour problems caused by odour generating facilities such as wastewater treatment plants and poultry farms.

The reliability of odour measurement is a fundamental issue in odour assessment. The use of dynamic olfactometry is widely regarded as a favoured method for quantifying odour. In this method, a series of diluted odour sample over a range of concentration is delivered to a group of odour panelists who represent the general population for determining the odour thresholds. The device used to deliver the dilute odour sample to the odour panelists is known as an olfactometer. Inter-laboratory studies involving different commercial olfactometers and standards have shown disappointing reproducible results as the olfactometers vary significantly in their design and yield different odour threshold values for the same sample. In recent years, emphasis has been directed towards standardising equipment and techniques of odour sampling and measurement so that results can be compared between laboratories and between different olfactometers with some degree of reliability.

This paper describes the development and testing of a new generation, computerised olfactometer, named the Odormat, which was developed at the Department of Civil Engineering, National University of Singapore. The Odormat has two sniffing ports and uses the “binary forced-choice method”, with odourless air being presented to the panelists through one port and diluted, odorous air through the other. In the odour evaluation procedure, the Odormat presents the panelists with a choice of two air streams at 20 L/min through the two sniffing ports. One air stream contains the diluted odour while the other an odour-free reference gas. The panelists are asked to sniff from each port and select the port from which the perceived odour is presented. The panelists are also required to nominate the confidence level of their selection by choosing from three categories: guessing, inkling, or certain.

The Odormat is designed to enable odour concentrations of air samples to be measured in an efficient and high quality controlled procedure such that results are reliable and accurate. All air flows and control valves are electronically operated with high precision. The incremental changes in air flows and analysis of the responses from the odour panel are automated by a computer software. The Odormat is built to ease the process of odour evaluation with a fully integrated automatrion to minimise human errors. The usable dilution range of the Odormat is 4 to 262144. The repeatability and accuracy of odour measurement for the Odormat are tested to satisfy the stringent requirements in the CEN (Committee European de Normalisation) Standard. Odour measurement conducted using the Odormat was found to be highly similar and comparable with another commercial dynamic olfactometer that conforms to the CEN standard for olfactometry.