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Improve air quality with siting, mitigation strategies

PD Editor Karen Lee Published on 20 November 2013

Odor and air emissions are ever-present on dairy farms and continue to hold the attention of local, state and national regulation agencies.

Earlier this year, Rick Stowell from University of Nebraska – Lincoln gave two presentations on the topic at the Midwest Manure Summit in Green Bay, Wisconsin.



He outlined a number of ways dairies can better manage air quality from implementing best management practices, evaluating risk during siting and adding mitigation strategies.

“There’s no such thing as a typical dairy, but there are such things as typical activities on dairy farms,” Stowell said.

Associated with most dairy farms are livestock facilities, feed storage, manure storage and fields where manure is applied.

Each area has its own emissions to manage. For example, with land application of manure, there is going to be odor, greenhouse gases and particulate matter.

Stowell’s first piece of advice is to prioritize the areas of the farm where emphasis should be placed to mitigate emissions.


Dairy producers should also determine which air quality issue takes precedence.

He set the order of concern from highest to lowest as odor, ammonia, greenhouse gases, and other gases and dusts. Of course, some dairies could rank these differently depending on their situation.

According to Stowell, odor deserves a lot of attention because every dairy farm produces odor.

“A lot of dairy farmers are too close to it to realize there is an odor,” he said. “We know odors can evoke complaints. Odors are bad for business.”

In some cases, odor is doing the communication for a dairy operation, which can drive a wedge between the dairy and its neighbors, open the door for litigation and be a distraction for the farm’s management.

Odor has been known to draw unwanted attention and scrutiny to dairy farms. “This is a sustainability issue,” he said. “The next generation will take on that baggage.”


Ammonia emissions are a growing environmental concern. From the Chesapeake Bay to an expanding reach of regulations, more agencies are taking a look at ammonia.

Greenhouse gas emissions is an area of misperception and uncertainty. Overall, animal agriculture is a small player to greenhouse gas emissions in the U.S., and there is very little support in Washington, D.C., for animal agriculture to report its greenhouse gas emissions, he said.

Producers should focus their concern on odor and ammonia emissions.

Best management practices
One tool to help dairymen evaluate their farm’s emissions and determine where reductions can be achieved is with the National Air Quality Site Assessment Tool (NAQSAT).

Using this online tool, producers can enter their farms’ information to see particular areas where air quality can be improved and then make changes within the online program to see what best management practices have the greatest impact.

“In my book, land application is where it’s at in terms of priorities for odor,” Stowell said.

Both injection and incorporation for manure application have been shown to effectively reduce emissions. Keeping the manure low, either with subsurface agitation of manure lagoons or a low profile with land application and irrigation, will result in less drift and attention.

Don’t forget to monitor the weather; avoid calm days and the stillness of dusk or dawn for manure applications. Don’t irrigate on days when winds are greater than 10 miles per hour.

Communicate with neighbors in advance to show appreciation for their interests, like neighborhood parties, and to convey the efforts you will take to minimize the impact on them.

Stowell’s second priority is the facilities, as they can be a potential chronic source for odor; however, most dairies do well at getting manure out of the facilities quickly.

Dairy producers can also influence ammonia emissions through the ration that is fed. A ration that overfeeds protein leads to higher ammonia emissions.

Proper manure collection, transfer and storage can also help a farm cut down on odor and ammonia emissions.

Facility siting
Odor is generally the No. 1 air quality concern in terms of siting dairy facilities. Stowell said it can be challenging to control, is primarily a local issue and is especially problematic for new facilities.

A big part of addressing odor is understanding the local area and learning who are the farm’s neighbors.

“Odor is really hard to look at objectively,” Stowell said. “The bottom line is while we can come up with a prescribed separation distance in one county, you can go to another area of the state where there will be very little likelihood it will be accepted.”

Advanced planning tools may be required by the state, county or township and can help with this process. These will help a dairy producer identify risk levels through setback differences.

Stowell cautioned not to ignore the risk associated with what’s beyond the risk zone as well as taking the time to identify which of the residences within the risk zone may be problematic.

Mitigation efforts
There are a number of techniques farms can use to reduce the generation of odor, ammonia emissions, greenhouse gases and particulate matter.

• Mechanical separation alone is ineffective, Stowell said, mentioning it only removes 30 percent of solids. Additives, like polymers, can be used to get more of the solids out, but those can be expensive, he said.

• Anaerobic digestion can reduce the odor-generating compounds by 60 to 80 percent, but that can be subject to substrates from off-farm sources that are added in. Digesters are also effective at reducing greenhouse gases; however, there is higher potential for ammonia loss.

• There are two types of wastewater treatment available. The low-tech treatment lagoon can be managed as a lagoon, but Stowell said it is less effective in cold climates.

Plus, it results in high nitrogen losses. High-tech systems, similar to municipal treatment systems, can clean wastewater with very little odor, but it does require good pre-treatment of manure for solids reduction.

• Aeration allows a farm to break down organics aerobically. This has been shown to emit very little odor with fewer undesired gas emissions such as methane and ammonia.

• There are a number of manure additive products on the market today, but according to Stowell, no one has been able to prove any of them consistently work in a laboratory setting.

Due to the variability with bacteria in the manure, he conceded there are probably some instances where it does work in practice.

• Composting is a way to reduce odor in comparison to stockpiling, but it does require additional management.

In addition to reducing odor, there are a few options to capture and destroy emissions.

• Permeable covers slow air exchange at the manure surface but eventually allow gas to come through. In general, it can achieve a 50 percent odor reduction.

• Impermeable covers seal the surface and keep gases from escaping. The built-up pressure does need to be pulled off and destroyed, typically using a flare or as low-grade fuel.

• Biofilters are one of the most effective treatments for odorous air, achieving an odor reduction of 90 percent, but they do have limited applications on dairy farms, Stowell said.

• Vegetative buffers help if you’re not going to prevent emissions. These divert and dilute by moving air up. There is very little benefit from an emission control standpoint, but it does help because people like trees. “It’s a perception issue, and odor is very largely a perception issue,” he added.

In closing, Stowell said, “good siting of facilities can alleviate many potential odor challenges.” For existing dairies struggling with odor and other emissions, implementing more best management practices or employing a new way to mitigate emissions could be beneficial. PD


Karen Lee
Progressive Dairyman