Statistical Confidence of Field Olfactometry and Biosolids Odor Assessment
Abstract:Specific gasses (odorants) are often poorly correlated with odors, which require human perception. Thus, olfactometry is used to quantify odors, which commonly contain a complex mixture of offensive compounds. Laboratory-based dynamic olfactometry is expensive and time-consuming, and is accompanied with sample container/ preservation issues. Field olfactometry provides real-time measurements at lower detection levels, but is influenced by environmental factors. This study explores the use of field olfactometry for quantifying dilutions-to-threshold (D/T) of environmental malodors. Field olfactometer instruments were used to collect 3096 individual D/T observations at various livestock facilities in central Pennsylvania. Twelve to 16 observations were collected at each station using multiple assessors, capturing four concurrent readings each. The multi-assessor repeat observation (MARO) technique found the reproducibility of D/T observations (across assessors) was more precise than replicate observations by individual assessors (repeatability). Observations were significantly (αα0.05) affected by assessor n-butanol sensitivity and source distance. Fluctuating wind speed and direction influenced odorant-fresh air mixing and resultant D/T readings. Power analysis showed that the 16 sample MARO field olfactometry method achieved 95% odor panel confidence with a power value of 0.90 at lower-D/T (2,4) and upper-D/T (30, 60) levels. Mid-range D/T settings of 7 and 15 exhibited the greatest panelist variability. This investigation found that MARO field olfactometry can reliably detect odor D/T differences; however, the greatest numbers of observations are needed at D/T levels of 7 to 15, precisely the values used to define nuisance odor conditions in some states.
Two studies were subsequently conducted to investigate the MARO methodology for biosolids odor emission quantification. First, an odor-ring technique was employed to assess the influence of storage time on malodors from surface-applied biosolids. The multi-assessor/ repeat-observation methodology was also used to investigate the potential for off-site odor nuisance episodes at the Philadelphia Biosolids Recycling Center. Summary findings from these studies are presented to illustrate the value and practical implications of using FO in high-value decision-making.
Keywords: D/T; MARO; Reproducibility; biosolids odors; dilutions-to-threshold; field olfactometry; livestock odors; multi-assessor repeat observation; odor nuisance; odor-ring; power analysis; repeatability
Document Type: Research Article
Publication date: January 1, 2010
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