H.A. Elliott

Operator Exposure to Hydrogen Sulfide from Dairy Manure Storages Containing Gypsum Bedding

Dairy manure storages containing gypsum-based bedding have been linked anecdotally with injury and death due to presumed dangerous levels of gases released. Recycled gypsum products are used as a cost-effective bedding alternative to improve animal welfare and provide agronomic benefits to manure recycled back to the land. Sulfur contained in gypsum (calcium sulfate) can contribute to hydrogen sulfide (H2S) gas formation under the anaerobic storage conditions typical of dairy manure slurry. Disturbance of stored manure during agitation releases a burst of volatile gases. On-farm monitoring was conducted to document conditions during manure storage agitation relative to gas concentration and operator safety. One objective was to document operator exposure to H2S levels; therefore, each operator wore a personal gas monitor while performing tasks associated with manure storage agitation. Data from three dairy bedding management categories on ten farms were compared: (1) traditional organic bedding, (2) gypsum bedding, and (3) gypsum bedding plus a manure additive thought to reduce H2S formation and/or release. Portable meters placed around the perimeter of dairy manure storages recorded H2S concentrations prior to and during 19 agitation events. Results show that farms using gypsum bedding produced higher H2S concentrations during manure storage agitation than farms using traditional bedding. In most cases, gypsum-containing manure storages produced H2S levels above recognized safe thresholds for both livestock and humans. Farm operators were most at risk during activities in close proximity to the manure storage during agitation, and conditions 10 m away from the storage were above the 20 ppm H2S threshold on some farms using gypsum bedding. Although H2S concentrations rose to dangerous levels, only two of 18 operators were exposed to >50 ppm H2S during the first 60 min of manure storage agitation. Operators who are aware of the risk of high H2S concentrations near gypsum-laden manure storages can reduce their exposure risk by working upwind and away from the H2S plume within a closed tractor cab.

Protocols for Reliable Field Olfactometry Odor Evaluations

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 it 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. Nasal Ranger® Field Olfactometer (NRO) instruments were used to collect 3096 individual D/T observations at livestock facilities in central Pennsylvania. Twelve to 16 observations were collected at each sampling station using multiple assessors, capturing four concurrent readings each. The multiple-assessor repeat observation (MARO) technique revealed that the reproducibility of D/T observations (across assessors) was more precise than replicate observations by individual assessors (repeatability). Observations were significantly (P<0.0001) influenced by odor source distance, wind direction, barometric pressure, and wind velocity. Power analysis showed that the 16-sample MARO using NRO 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 odor panelist variability. This study shows that MARO field olfactometry can reliably estimate odor D/T differences, even with weather variations. It is noteworthy, however, that the greatest numbers of observations (n= 85-91) are needed at D/T levels of 7 to 15 (to achieve 95% confidence), precisely the range used to define nuisance odor conditions in some states.

Amendments For Short- And Medium-Term Mitigation Of Odor Emissions From Dairy Manure

Simple and low-cost amendments are popularly used to reduce odor emissions from manure storage and handling. Seven promising products were selected for study after a preliminary screening of 22 dairy manure amendments that represented different modes of action. One feed-through additive was evaluated. Reported results are from manure stored at two temperatures (10 and 20oC) for short- and medium-term periods (3 d and 30 d). Amendment was added to 2-kg dairy manure slurry (1:1.7 feces:urine; 11% total solids) following the manufacturer recommended rates. Two samples of each product were evaluated along with duplicate untreated manure slurry. Odor emissions were estimated by six qualified odor assessors following an international standard method for Triangular Forced-Choice Olfactometry. Odor quality characterizations included hedonic tone (pleasantness), supra-threshold odor intensity, and odor character. None of the amendments significantly reduced odor emissions for all study conditions. There were amendments that demonstrated significant odor reduction under certain conditions: 31% reduction (P=0.032) for acidic (abandoned) mine drainage sediment after 3 d at 20oC; a proprietary microbial/enzyme powder, a proprietary aerobic/facultative microbial mixture, and proprietary mixture of chemicals in isopropyl alcohol significantly reduced odor by 26 to 47% after 30 d at 20oC. Hyssopus and peppermint essential oils increased odor detection by 29 to 65% after 30 d at 10oC but improved odor character descriptors. Odor decreased by 20 to 88% for all treatments and temperatures by simply storing the manure for 30 d. All treatments had unpleasant to extremely unpleasant hedonic tone described as offensive, earthy, medicinal, and fishy. Odor emission was correlated to hedonic tone but more intense odors were perceived as more unpleasant.

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 timeconsuming, 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 (α=0.05) 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.