Beef study measures gas emissions, dust
By KAREN SCHWALLER
SIOUX FALLS – More than 300 people from nine states attended a conference in Sioux Falls, S.D. on Nov. 21 to hear the results of a two-year study regarding air emissions in beef mono-slope buildings and compare various types of beef facilities.
The study was done cooperatively by South Dakota State University, Iowa State University, the U.S. Department of Agriculture-Agricultural Research Service and the University of Nebraska-Lincoln.
It began in August 2010 and ended in October 2012. Its purpose was to gather baseline data for levels of gas emissions and particulate matter, or dust, from beef mono-slope facilities, evaluate the effects of two different manure handling systems (packing and scraping) on air quality and comparte building and management practices that may reduce gas emissions.
The study was conducted in four barns-two in northwest Iowa and two in northeast South Dakota. All barns were 100-feet-wide, were of east-west orientation and had southern exposures. Two barns used a scrape system – all bedding and manure removed weekly and replaced with fresh bedding. Two used a pack system – where the bunk aprons and edges surrounding the pack are scraped weekly.
Bedding was added weekly with the pack system, and the pack remained in place within the pen until cattle were marketed.
Air temperature, relative humidity and wind speed were monitored in various locations in the north and south wall openings. Measurements were taken over every season, recording the results of ammonia, hydrogen sulfide, methane, carbon dioxide and nitrous oxide.
Dust was measured over two five-day periods in April and June 2011 at one of the pack barns. Each of those periods included three days of routine operation and two days with a bedding event. In the scrape barns, 24-hour dust collections occurred at least twice during each monitoring period between August 2010 and December 2011.
Results showed gas concentrations of hydrogen sulfide, ammonia and methane were considerably higher in the pack barns than in the barns were manure and bedding were scraped weekly. Gas concentrations peaked between 7 a.m. and 9 a.m. and again between 8 p.m. and 9 p.m.
The study concluded that those times coincided with increased animal movement, urination, feces elimination and disruption of the manure or pack surface-along with low wind speeds at dusk and dawn.
As air flowing through the barn decreased, gas concentrations increased. When southerly winds occurred, concentrations measured in the north wall opening (serving as the air outlet) were higher than in the south wall opening.
For northerly wind events, the south wall opening had higher gas concentrations. Both confirmed that incoming outdoor air picks up gas and dust as it moves across and out of a barn.
Researchers said their assumsions that south opening of a mono-slope facility contains less gas emissions were challenged, because their studies found that gas concentrations on the south side, on average, were higher than at the north sides for comparable wind speeds.
Results determined that some mixing and back-drafting occurred in the south wall opening for both northerly and southerly winds.
Their studies showed a significant increase in hydrogen sulfide concentration with increasing temperature in both the pack and scrape barns, but that increase was greater and more variable for the pack barns. Ammonia concentration also increased with rising temperatures in the pack barns.
When manure is handled in the barns, ammonia and hydrogen sulfide emission rates for the pack barns were more variable than for the scrape barns.
Studies showed that it could be attributed to the effects of the age and condition of the bedding/manure pack. The deeper the pack, the higher the internal pack temperature.
This, researchers said, could increase gas production. Hydrogen sulfide production can be promoted with increasing pack depth and temperature, leading to anaerobic conditions.
Particulate matter is of concern to researchers because of its effects on animal and human health. PM that is small enough can enter the human esophagus, and even the human lung, and can also create serious animal and human respiratory health issues if not controlled.
PM was collected from scrape barns and measured at least twice during each monitoring period, during routine operation and bedding events. PM was collected from one pack barn for three days each in April and June 2011 and only included hours of routine operations.
Concentrations of PM that are most dangerous to humans were similar in the two scrape barns. During routine operating time, those concentrations were slightly lower for the pack barn. However, during bedding events, the PM concentration was considerably higher in the pack barn.
Concentration for the most dangerous levels of PM for both pack and scrape barns were lower or within the range of values reported for open feedlots.
The study showed total suspended PM was significantly higher during the bedding events than during normal operation in the pack barn. Dust composition was more constant in the pack barn, but dust concentration in the pack barns during routine operation were considerably lower than reported for open feedlots, while concentrations measured during bedding events were, on average, slightly higher than for open feedlots.
Studies showed that since bedding events in mono-slope barns are short, PM concentrations quickly return to baseline levels.
As ventilation goes, studies showed that as ambient wind speed increased, the airflow through the barns typically increased in a linear pattern.
They stated an example using an 11-mile-per-hour south wind, showing that there were approximately 10 to 70 air changes per hour for closed curtain conditions – 1 to 2 feet open – in all four barns, and 160 air changes per hour with curtains open at 7 feet.
Studies showed that increased concentration of gases occurred in the barns when air movement was decreased, but since the emission rate depends on both the concentration and airflow rate, the reduced rate of airflow through the barn resulted in decreased emission rates of ammonia, hydrogen sulfide and methane.
The teams said they concluded that, among other outcomes, gas concentrations in beef mono-slope buildings are similar to, or a little higher than, open feedlots and vary with temperature, and that improved air quality inside these facilities can be obtained by removing manure more frequently.
Rick Stowell, associate professor and a UNL Extension ag engineer, encouraged producers to follow environmental regulations for air quality and manure containment before and after construction, specifically for herds of 1,000 head or larger.
He said the list of Environmental Protection Agency standards for hazardous air pollutants numbers 180, but that list does not include the major gases generated by livestock facilities.
He said the list could be amended, and that it could open cattle operations to additional regulatory laws.
In order for this to not happen, Stowell said beef producers as a whole should concentrate on managing dust, air flow and manure sources.
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