A panel consisted of six participants; each had three bags in a set to sniff. The screening of qualified panelists was in accordance with Taiwan EPA recommendations and was performed based on accurate determination of five smell standards.
The dilution ratio started at 10 then progressed to 30, 100, 300,1 000, etc., in sequence. Each dilution ratio was tested twice by the six panelists for a total of 12 answers. The test was complete when the number of the correct answers was less than six. Odor concentrations were calculated by the formula (1), and it indicated the dilution ratio of pure air volume required to dilute sampled odorous air to an odor-free threshold point. The regulatory standards ofthe Taiwan EPA are 50 OC in industrial and agricultural regions and 10 OC in residential area.