Statistical Confidence of Field Olfactometry and Biosolids Odor Assessment

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.