Lab Microtunnel Measures Emissions More Accurately

University of Minnesota researchers have built a laboratory microtunnel they say will provide a more accurate picture of hog manure emission reduction technologies.

The lab-based model eliminates season, climate and site variants, and leaves only a true comparison between control and treatment efforts aimed at reducing gas and odor emissions.

Determining gas and odor emissions in a controlled environment will also decrease the cost per sample to about 25% of field samples.

Measuring gas and odor emissions in the field is a challenging process with time and space factors influencing emission rates. Detailed on-farm emission measurements are not easily transferable to other sites with different genetics, feeding programs, manure management systems, geographic areas, etc.

This study focused on developing and testing a laboratory method to study the relationship of manure parameters and environmental conditions to manure emission rates.

A team of investigators developed a lab-scale method using a small aluminum wind tunnel to measure ammonia (NH3), hydrogen sulfide (H2S) and odor. This method was tested using 83 manure samples from 20 livestock farms throughout Minnesota. Findings are summarized in Table 1.

The microtunnel focused on airflow rates representing 0.5 to 2.0 mph wind speeds. The microtunnel was able to consistently detect differences in gas and odor emissions from different manure types, manure sources, manure solid contents and airflow rates. Ammonia emission rates agreed with field emission rates reported. Hydrogen sulfide and odor emission rates were somewhat higher than previous field research.

Those early results show promise for this new laboratory technique in testing gas and odor concentrations found in hog manure, determining emission rates and differentiating manure sources and manure types.

In other work, researchers studied the impact of manure agitation with the microtunnel. Slow stirring without surface disruption reduced ammonia emissions by 30% and increased hydrogen sulfide emissions by 2800%. Eight minutes after stirring slurry stopped, emission rates returned to previous levels.

When diluted manure was measured for emissions, each dilution level lowered gas emissions in a linear pattern. But the odor pattern was more of a bell-shaped curve, meaning that as manure became diluted, some samples attained greater odor strength.

To study the impact of sample storage time on emissions in the microtunnel, manure was stored up to nine days at cold temperatures (40°F) and/or room temperature (72-76°F). Overall, the ammonia emission rate increased about 8%/day when stored at the warm temperature, possibly due to increased microorganism activity. Hydrogen sulfide emissions decreased about 6%/day.

Development and testing of the microtunnel was funded by the National Research Initiative Air Quality Program, Cooperative States Research, Education and Extension Service, USDA.

In future collaboration with Iowa State University, accuracy and repeatability of the microtunnel is being tested for emissions of volatile organic chemicals. The microtunnel is also being modified and tested for its value in determining emission rates from a solid surface (dry manure and soil after manure application).

Researchers: David Schmidt, Chuck Clanton, Blanca Martinez, Ketty Clow and Joe Cummings, Department of Bioproducts and Biosystems Engineering, University of Minnesota; and Jacek Koziel, Department of Agricultural and Biosystems Engineering, Iowa State University. Contact Clanton by phone (612) 625-9218, fax (612) 624-3005 or e-mail

Table 1. Ammonia (NH3), Hydrogen Sulfide (H2S) and Odor Emissions from Various Swine Manure Storage Methods for Gestation and Finishing Buildings
Manure Storage pH NH3
Gestation deep pit
Farm A 7.6 391 241 152
Farm B 7.9 555 143 95
Farm C 7.6 311 261 52
Farm D 7.6 399 258 219
Gestation 1st cell earthen basin
Farm E 7.8 186 4 22
Farm F 7.5 167 41 87
Gestation 2nd cell earthen basin
Farm G 7.8 254 8 67
Farm F 7.9 241 12 32
Finishing deep pit
Farm H 6.3 29 2 38
Farm I 7.8 1119 20 29
Farm C 7.7 816 87 152
Farm D 7.2 306 2 30
Literature ranges: Ammonia: 200 - 400 µg/m2/s; Hydrogen sulfide: 30 - 145 µg/m2/s
*µg/m2/s micrograms/square meter of surface area/second; ou/m2/s odor units/square meter of surface area/second

Surface Aerator Makes Lagoon Odor Reduction Affordable

Preliminary results of a new surface aeration system pilot-tested at a 4,800-head, grow-finish operation show it provides an effective and affordable means of handling odors in lagoons.

The aerator module (Figure 1) features six venturi air injectors, which significantly increases aeration efficiency without altering power consumption.

Increased efficiency results in the establishment of an aerated layer in top lagoon liquid with a constant level of dissolved oxygen of greater than 0.3 mg./L at a depth of 6 in. from the lagoon's surface. This layer functions as a biological cover that prevents odorous compounds from escaping from the liquid, enhancing odor reduction.

In limited trials, the odor detection threshold (ODT) was reduced from around 3,000 to 1,200 in less than 10 days of continuous operation, according to the olfactometry analysis of air samples collected from the lagoon used in the experiment.

Surface lagoon aeration is not new technology. However, unlike earlier systems, the innovative engineering design developed by the University of Minnesota offers an economical alternative. Based on a 4.5-hp motor driving the system 24 hours/day, 365 days/year (with a definitely shorter period in cold climates), the total annual power usage will be 29,565 kWh (kilowatt hours) [24 hour/day × 365 days/year × 4.5 hp × 0.75 kW/hp]. In the equation, 0.75 kH/hp represents both horsepower and kilowatt hours, which are power consumption units.

The relationship between these two units is 0.75 kWh, which is equal to 1 hp. Based on $0.07/kWh and 2.5 production cycles/year, the cost/pig for this treatment is $0.17. As a rule of thumb, the cost for odor treatment should be below $1/pig.

The cost of the whole aeration system is expected to be very affordable to the vast majority of pork producers.

The project is being funded by a research grant from the USDA National Research Initiatives Air Quality Program.

Researcher: Jun Zhu, University of Minnesota Southern Research and Outreach Center at Waseca, MN. Contact Zhu by phone (507) 837-5625, fax (507) 835-3622 or e-mail