Odor Ratings System Estimates Setbacks

University of Minnesota researchers have developed an odor ratings system called Odor From Feedlots Setback Estimation Tool (OFFSET). The system estimates the setback distance from animal production sites by determining the site's estimated odor emissions.

All odor sources at the site are identified. OFFSET selects the odor emission number on a per-square-foot basis, determines the total surface area of a barn or manure storage unit, credits any odor-control technology and then calculates the total odor emission factors for each source.

OFFSET includes: - A database generated from emissions measurements at 260 animal buildings and manure storage units from 1997 to 1999;

- An air dispersion model, and

- Average weather data for Minnesota from 1984 to 1992.

First, the total odor emission factor is determined for a production site. Buildings and manure storage units are considered, along with species, housing types and sizes, manure storage types and sizes and odor control technologies used at the site.

The OFFSET database is then used to assign an odor emission number for the barns and manure storage. Hog barns with deep pits, pull plug or scraper systems and natural or mechanical ventilation are assigned a 23. Open front barns with concrete lots get an 8. Hoop barns get a 2, and farrowing barns with flush systems and mechanical ventilation get a 10.

Manure storage is also assigned an odor emission number (OEN). Earthen storage basins are a 20, first cell lagoons a 4, and second cell lagoons a 1. Settling tanks are a 50 OEN.

In addition, odor-control factors are assigned numbers. Biofilters on building fans are a 0.1. Geotextile covers and 2 in. of straw covering manure are a 0.5. If no odor control technology is used, a value of 1 must be assigned to the odor source.

Those numbers are then plugged back into Table 12. The emission area is simply the physical size of the buildings and/or manure storage units.

Finally, the odor emission factor is calculated by multiplying the values in columns B, C and D and dividing by 10,000. The values in column E are added up to obtain the total odor emission for that site.

The total odor emission factor (sum of column E) is then plotted on the horizontal axis of Figure 1. The vertical axis is the distance in miles. Based on the odor annoyance percentage desired, the setback distance is determined.

OFFSET defines an annoyance-free odor level as an odor intensity of 2 on a 0 to 5 scale. Odor intensity 2 is a faint odor that an average person might detect if attention is called to the odor but would not annoy the person. Odor intensity 3 would be readily detected and probably regarded as a nuisance.

Figure 1 shows a family of odor annoyance-free curves. The curves represent odor annoyance-free time for the prevailing wind direction from the site from mid-April to mid-October. They are based on meteorological data and the U.S. Department of Agriculture/Environmental Protection Agency-INPUFF2 air dispersion model. For example, 99% annoyance-free means 99% of the time, at the indicated distance from the site, people are not expected to receive an odor above an intensity rating of 2. The remaining 1% of the time, seven hours/month, individuals may smell odors higher than odor intensity 2.

Researchers: Larry Jacobson and David Schmidt, University of Minnesota. Phone Jacobson or Schmidt at (612) 625-9733 or e-mail Jacobson at jacob007@umn.edu.

Hydrogen Sulfide Emission Levels Studied

National Pork Producers Council (NPPC) research shows producers often exceed the 1999 Minnesota statute for hydrogen sulfide (H2S) emissions when agitating and pumping out manure pits.

Until new feedlot regulations were implemented in October, the H2S emissions standard allowed producers to exceed the 30 parts per billion (ppb) - a 30-minute average - of H2S threshold once in any five-day period or the 50 ppb threshold once a year. Under current regulations, Minnesota producers are allowed to request a 21-day exemption during manure handling.

The researchers monitored ambient air H2S levels downwind from facilities on six farms of varying size in Iowa, Illinois and Minnesota.

The MDA Scientific Chemcassette Single Point Monitors (SPM) were located at 50-ft. and 100-ft. intervals downwind from the manure pits during agitation and pumping of manure. Each monitoring station included two SPMs, one with 1 to 90 ppb-H2S range and the other with 50 to 1,500 ppb-H2S range.

Researchers recorded temperature, relative humidity, wind speed and direction to track the role of weather conditions on transport of H subscript 2S downwind from barns.

Figure 2 shows the H2S concentrations during agitation and pump out at 50, 100 and 200 ft. downwind from manure pits. On average, most H2S concentrations dropped or were below 30 ppb at 100 ft. and beyond. Peak H2S concentrations at 50 ft. were measured an average of 3.2 hours after the start of agitation and ranged from 0 to 8 hours. The maximum total number of 30-minute average measurements greater than 30 ppb averaged five times and ranged from three to nine times.

Researchers point to key findings in this study, including: peak H subscript 2S concentrations during agitation and manure removal are not sustained at high levels for extended periods of time; peak ambient H2S concentrations measured are not considered harmful and H2S concentrations drop significantly when agitation is finished.

Researchers: Carrie Tengman, NPPC. Phone Tengman at (515) 294-9604 or e-mail tengmanc@nppc.org.

Pit Additives Reduce Hydrogen

University of Minnesota researchers conducted research on reducing hydrogen sulfide (H2S) emissions by adding chemicals before manure pit agitation and pumping. They found that hydrogen peroxide is the most cost effective of seven chemicals for reducing H2S emissions.

First, researchers identified seven chemicals that can reduce H2S emissions. Calcium hydroxide, ferric chloride, ferrous chloride, ferrous sulfate, hydrogen peroxide, potassium permanganate and sodium chlorite were identified in bench-top experiments.

Dosage curves to reduce H2S emissions from 20% to 90% were developed for each chemical. From these curves, the researchers determined the amount and cost of chemical needed to reduce 50% of emissions. Hydrogen peroxide (H2O2) and potassium permanganate (KMnO4) appeared to be the most cost-effective chemicals. Cost/cubic meter of manure was $0.074 for H2O2 and $0.062 for KMnO4.

Next, the researchers conducted a lab test of H2O2 and KMnO4 by testing the chemicals in manure-filled columns. In half of the columns, chemical addition and testing of H2S emissions started six minutes before agitation began. In the other half of the columns, chemical addition, testing of H2S emissions and agitation began simultaneously.

Researchers found no statistical difference in concentrations when air sampling began, so the data was pooled. Table 13 lists the mean H2S concentrations for the period 10 to 20 minutes after chemical addition. With KMnO4, H2S concentrations decreased as planned. But with H2O2, there was no statistical difference between the 30% and 90% reduction, indicating less H2O2 was needed to reduce emissions than was used in the lab trial.

Finally, researchers conducted a field trial in two identical 41-ft. by 200-ft. deep-pitted finishing barns. One barn was used as a control, the other to test the effect of H2O2 on H2S emissions. A concrete wall divided the pit under each barn.

Researchers used a single treatment of 110 gal. 30% H2O2 with the goal of a 70% reduction in H2S emissions. Total treatment cost was $1,100 or about $1/pig.

In the first compartment, 55 gal. of the H2O2 was poured into the pump out port and allowed to mix into the manure during agitation. H2S concentrations were 240 parts per million (ppm) at 30 minutes, 25 ppm after 70 minutes, and 3 ppm after 90 minutes.

In the second compartment, 55 gal. of the H2O2 was divided into half. One-half was evenly distributed on the manure surface by pouring it through the slots and the other half was poured into the pump out port and agitated into the manure. H2S concentrations were 100 ppm after three minutes, 28 ppm after seven minutes, 11 ppm after 15 minutes, and less than 1 ppm after 30 minutes.

H2S concentrations from the control barn (agitated without chemical addition) remained at 250 ppm throughout the two-hour sampling period. The maximum concentration the instruments can read is 250 ppm.

Researchers: Dick Nicolai, David Schmidt and Larry Jacobson, University of Minnesota. Phone Jacobson or Schmidt at (612) 625-9733 or e-mail jacob007@umn.edu or schmi071 @umn.edu.