R. E. Nicolai

DAILY VARIATIONS IN ODOR AND GAS EMISSIONS FROM ANIMAL FACILITIES

Seven different animal facilities were studied to determine daily variations in emissions of odor, ammonia, and hydrogen sulfide. Air samples were collected every two hours over a 12-hour period during the day for odor and gas measurements from these facilities. A nursery building had the highest emission rates for odor and hydrogen sulfide (max: 50 OU · m 3 /s/m 2 and 140 µg/s/m 2 , respectively). The naturally ventilated swine finishing building had the highest ammonia emission rate (max: 170 µg/s/m 2 ). The data also showed that there was no significant difference in average ammonia and hydrogen sulfide concentrations over the 12-h sampling period for all the animal facilities. Ventilation rates play a key role in determining the emission rates of aerial pollutants from animal buildings. However, when comparing the overall odor and gas emissions among animal buildings with different sizes, it is necessary to consider building sizes in addition to ventilation rates.

Quality assured measurements of animal building emissions: Odor concentrations

Abstract Standard protocols for sampling and measuring odor emissions from livestock buildings are needed to guide scientists, consultants, regulators, and policy-makers. A federally funded, multistate project has conducted field studies in six states to measure emissions of odor, coarse particulate matter (PM10), total suspended particulates, hydrogen sulfide, ammonia, and carbon dioxide from swine and poultry production buildings. The focus of this paper is on the intermittent measurement of odor concentrations at nearly identical pairs of buildings in each state and on protocols to minimize variations in these measurements. Air was collected from pig and poultry barns in small (10 L) Tedlar bags through a gas sampling system located in an instrument trailer housing gas and dust analyzers. The samples were analyzed within 30 hr by a dynamic dilution forced-choice olfactometer (a dilution apparatus). The olfactometers (AC’SCENT International Olfactometer, St. Croix Sensory, Inc.) used by all participating laboratories meet the olfactometry standards (American Society for Testing and Materials and European Committee for Standardization [CEN]) in the United States and Europe. Trained panelists (four to eight) at each laboratory measured odor concentrations (dilution to thresholds [DT]) from the bag samples. Odor emissions were calculated by multiplying odor concentration differences between inlet and outlet air by standardized (20 °C and 1 atm) building airflow rates.

Evaluation of INPUFF-2 Model for Predicting Downwind Odors from Animal Production Facilities

This article presents data evaluating an air dispersion model, INPUFF-2, in predicting downwind odors from animal production facilities. According to the Wilcoxon Signed Rank Test, the model is able to predict the downwind odor levels at distances of 100, 200, and 300 m from odor sources with confidence of 95%, 92%, and 81%, respectively. At farther distances, such as 400 and 500 m, the accuracy of prediction by the model is significantly reduced. This reduction could be due to the reduction in the nasal sensitivity of human sniffers for low levels of odors at such distances, which increases the errors in differentiation. Further research on methods of evaluating air dispersion models for a long range is needed to determine the performance of models. In addition, it was found that INPUFF-2 model can predict downwind odor concentrations as measured in units of odor threshold from either a single or multiple sources with confidence ranging from 81 to 90% based on the Wilcoxon Signed Rank Test.

AMMONIA REMOVAL DURING BIOFILTRATION AS AFFECTED BY INLET AIR TEMPERATURE AND MEDIA MOISTURE CONTENT

Biofiltration is a promising technology for minimizing odor and gas emissions from livestock buildings. A laboratory experiment investigated N accumulation and N transformations to better understand how biofilters remove airborne NH3. Total-N accumulated in the media accounted for only 29% of the N removed by the biofilter after 1160 h. The fate of the remaining N is unknown. Nitric oxide (NO) gas emission accounts for only a small part (<2%) of the difference, and no N was lost via leaching. Microsite denitrification to dinitrogen (N2), nitrogen dioxide (NO2), or nitrous oxide (N2O) may explain some of the discrepancy, but further research is needed. An attempt to determine N transformation rates was not successful due to continuous modeled circular N transformations. Despite these unexplained N fates, this experiment showed that biofiltration can effectively remove NH3 levels from exhaust air.

Dynamic olfactometry variability in determining odor dilutions-to-threshold

When conducting research on odor abatement technologies, a weak link has been the inability to place a precise quantifying number on odor strength that can be accurately reproduced within the same laboratory and between laboratories. Olfactometry is one of the most accepted means for evaluating odor samples. However, insufficient effort has been made to determine variation between or among individual panelists. This study was designed to analyze three odor sample strengths over a three-day period by two odor panels, each composed of eight panelists. Three sample strengths were presented randomly to each panelist three times within each session. Whole-panel variation ranged from a 22% to 50% difference in reported odor units for the same sample, depending on sample strength. Using two different airflow rate calibrations resulted in a 9% to 28% difference in odor units for the same sample, depending on sample strength. Panelist variation ranged from 4.3- to 7.1-fold, depending on sample strength, although panelist standardization slightly reduced this variation. Sample order had no effect on odor strength determination. A learning curve for individual panelists appeared to exist, as odor unit evaluation for later observations were 3.8 and 4.1 times greater than similar evaluations for the first samples. Variation between panelists is approximately the same as variation among evaluations done by the same individual; efforts should be made to reduce both these variations. To be able to detect differences in odor concentrations between control and treatment samples, large reductions in odor concentrations with several air samples are needed to accurately detect a significant reduction in odor.

DEVELOPMENT OF THE OFFSET MODEL FOR DETERMINATION OF ODOR-ANNOYANCE-FREE SETBACK DISTANCES FROM ANIMAL PRODUCTION SITES: PART I. REVIEW AND EXPERIMENT

The objective of the study was to develop a science-based model, OFFSET (Odor from Feedlot - Setback Estimation Tool), to establish setback distances from animal production sites based on the use of an air dispersion model (INPUFF-2) and the actual odor emission data from these sites. Extensive research was conducted to obtain representative odor emissions from various animal facilities and to evaluate the air dispersion model. Odor emissions were measured from 280 animal buildings and manure storage units on 85 farms in Minnesota during 1998 to 2001. The geometric means of the odor emission rates for each type of odor source were obtained to represent odor emissions of that source. The efficiencies of some odor control technologies were summarized. The air dispersion model was evaluated for short-distance (<0.5 km) odor dispersion prediction against the odor plumes measured by trained field assessors on 20 farms and also for long-distance (4.8 km) odor dispersion prediction against odor data recorded by trained resident observers living in the vicinity of livestock operations in a 4.8 × 4.8 km rural area. The relationship between odor detection threshold and intensity was obtained for swine and cattle odors in order to convert odor intensity to detection threshold. The results indicated that the INPUFF-2 model was capable of simulating odor dispersion downwind from animal production operations for low-intensity odors. Six stable or neutral weather conditions that favor odor transport were identified, and their historical occurrence frequencies in all 16 directions at six weather stations in Minnesota were obtained. The occurrence frequencies of these weather conditions were used to determine odor occurrence frequencies in the OFFSET model.

DEVELOPMENT OF THE OFFSET MODEL FOR DETERMINATION OF ODOR-ANNOYANCE-FREE SETBACK DISTANCES FROM ANIMAL PRODUCTION SITES: PART II. MODEL DEVELOPMENT AND EVALUATIONS

The OFFSET (Odor from Feedlots - Setback Estimation Tool) model was developed to estimate the setback distances from animal production sites in Minnesota. It is based on odor emissions taken from field measurements and an evaluated air dispersion model. The odor emissions of a site were estimated using odor emission rates that were the geometric means of odor emissions measured from 280 animal buildings and manure storage units on 85 farms in Minnesota. The odor-annoyance-free intensity level was set at 2 (faint odor) on a 0 (no odor) to 5 (very strong odor) intensity scale. An evaluated air dispersion model, INPUFF-2, was used to calculate setback distances from various animal farms for the set odor-annoyance-free level under six weather conditions that favor odor transport. Setback distances are presented in a graphic form as well as mathematically as a function of the total odor emission factor and the desired odor-annoyance-free frequency of the neighbors. Odor-annoyance-free frequencies between 91% and 99% are based on the average weather data for Minnesota from 1984 to 1992. Suggestions for odor-annoyance-free frequency selections are given. The OFFSET model also deals with residences located in different directions from a livestock site. Additionally, it can determine the odor occurrence frequency of a residence surrounded by several livestock sites. Comparing the setback distances obtained from the OFFSET model and the odor events reported by the resident observers, it was found that the OFFSET model does not overpredict odor transport distances under very stable weather conditions. By comparing the OFFSET predictions with the odor complainers’ distances from swine farms, it was clear that their residences had high odor occurrence frequencies. The OFFSET model was also evaluated by comparing odor occurrences documented by the resident odor observers in the vicinity of eight livestock farms. It was found that although the model may describe the average neighborhood intensity correctly, a high variation in the observed odor intensities existed for all levels of predicted intensities calculated from the OFFSET. Further research is needed to improve the accuracy of OFFSET and also to improve the field odor measurement method by the resident observers to obtain reliable odor occurrence data. By comparing OFFSET with four other existing setback guidelines, it was found that the distances required by the other models fell in or below the 91% to 98% annoyance-free curves of the OFFSET.

EVALUATION OF THE INFLUENCE OF ATMOSPHERIC CONDITIONS ON ODOR DISPERSION FROM ANIMAL PRODUCTION SITES

A 4.8 . 4.8 km (3 . 3 miles) grid of farmland in southern Minnesota was selected to observe odor dispersion from animal facilities as affected by atmospheric conditions. Nineteen trained resident–panelists living within or adjacent to the grid monitored odor events from June to November 1999. The panelists used a numerical 0 to 3 intensity scale (0 being no odor and 3 very strong odor) to assess the odor strength. A weather station was set at the center of the grid to collect weather data including temperature, relative humidity, solar radiation, wind speed, and wind direction. Odor emissions from the farms were also measured. Odors were detected more frequently in the summer than in the fall. However, very strong odors (intensity 3) were most common in the fall as a result of the removal of manure from storage basins and pits and the subsequent application of this manure onto cropland. A large majority of odor events (71%) were reported during either moderately or slightly stable atmospheric conditions (atmospheric stability classes E and F) during the evaluation period. This predictable response was further verified by the high occurrence of odor events (approximately 50%) during periods of low wind velocities (under 2.5 m/s). This result was consistent for all odor strengths (faint to very strong) identified by the reported intensities. Thus, for this particular location and animal facilities, the frequency of odor occurrences has an inverse linear relationship to the wind velocity. However, 35% of the strong odors (intensity 3) were reported under atmospheric stability class D, which indicated that neutral atmospheric condition with high wind speeds could also result in strong odors at the ground observing level.

Swine manure storage covers for odor control

Twenty-one, 750-L (200 gal) polyethylene tanks were filled with swine manure. Air samples were collected 24 and 48 h after each manure addition. The samples were tested for odor strength using a dynamic olfactometer and for hydrogen sulfide concentration using a Jerome® meter. The experimental design consisted of a randomized block design containing three blocks (replications) of seven treatments. The seven treatments included no cover (control), straw mat, vegetable oil mat, straw/oil mat, clay ball mat, PVC/rubber membrane, and geotextile membrane. Statistical analysis indicated that all three main effects—cover treatment, collection period, and time after manure addition—significantly (5% level) affected odor units and hydrogen sulfide concentration. Considering all air collections, the six covers reduced odor units and hydrogen sulfide concentration at various points in the study, but not in a consistent manner. The straw mat and PVC/rubber membrane significantly reduced both odors units and hydrogen sulfide concentration consistently 24 h after manure addition during the first three collection periods. Mixing vegetable oil with straw appears to increase longevity of the cover as compared to straw only. The vegetable oil layer, when mixed with the manure, produced a distinctively offensive non-swine odor. The clay ball mat reduced emissions, although not as well as other covers. A geotextile membrane may be a possible cover choice, since the fabric is self-floating and the biofilm that grew on the mat could self-seal the cover. A straw mat (possibly including vegetable oil) and PVC/rubber membrane appear to be the most effective covers in reducing both odors and hydrogen sulfide. Oil alone should not be used as a cover.

Partial Biofiltration of Exhaust Air from a Hybrid Ventilated Deep-Pit Swine Finisher Barn

A strategy for providing partial biofiltration of a critical minimum amount of ventilation air (CMVR) from a hybrid ventilated swine finishing facility was developed and tested. The CMVR, defined as the minimum treated exhaust air that suppressed nighttime curtain opening movement, was set at 81 m3 h-1 pig-1 with the intention of providing enough fan ventilation to suppress inlet curtain movement during stable atmospheres, providing biofiltering for a high percentage of exhaust air. Two side-by-side 300-head hybrid ventilated deep-pit swine finishing rooms were used for this research, one room as the control (CTL) with the other treatment (TRT). The TRT room was fitted with a wood-chip based biofilter for scrubbing the CMVR. In terms of total room emissions, the TRT room had an average odor emission 37% less than the CTL room. Ammonia emission was 58% lower for the TRT room as compared to the CTL room. The results presented indicate that a strategy of partial biofiltration can result in significant reductions in odor and ammonia emissions when applied to hybrid ventilated swine finishing barns.