Pollutants trapped | Design of the yard, type of trees and wind direction play role in effectiveness
INTERNATIONAL PEACE GARDEN, Manitoba-North Dakota border — Locating intensive livestock operations away from populated areas is one way to keep odour from being an issue.
Trees are another.
Shelter belts known as vegetative environmental buffers (VEB) can trap air pollutants and dust escaping from large-scale hog and poultry barns, said John Tyndall, a professor of natural resource economics at Iowa State University.
He told the Great Plains Windbreak conference that a VEB can reduce by five to 15 percent the odour concentration moving downwind of a barn at a cost of one to three cents per pig.
Read Also
Key actions identified to address canola tariffs
Federal and Saskatchewan governments discuss next steps with industry on Chinese tariffs
However, the reduction depends on many other factors, including weather, tree height and emissions.
The familiar manure smell is made up of more than 400 individual chemicals that are collectively known as volatile organic compounds.
Ammonia is one component, but it’s light and tends to dissipate quickly. Hydrogen sulfide is heavier than air, moves slowly and rarely goes beyond the farm.
The components that stick to dust are the ones that cause the problems. Tyndall said controlling particulate movement will control odour movement.
Changing diet and using feed additives can have a small effect on the volatile organic compounds. Preventing their release through the use of air filters and vent scrubbers can also help.
However, these two methods won’t completely eliminate the problem.
Air will escape and, once it does, landscape features or the hundreds of temperature inversions that occur during the summer can trap it, Tyndall said.
“Once it’s released into the atmosphere and it’s picked up by prevailing winds and it’s moving downwind, there’s sort of this tertiary last line of defence,” he said. “That’s where VEBs come into play.”
VEBs create mechanical turbulence that intercepts the particles that would be carried away from the barn. Heavier particulates drop out of the airstream and land on the leaves and branches of the trees.
“Trees are capable of grabbing and holding onto a tremendous amount of material. We’ve all seen trees along the roadside covered in dust.”
Tyndall said 90 percent of particulates are the right size for trees to grab. Their irregular shape makes it easier, and once the trees are covered, the dust itself is good at grabbing other dust, he said.
One row of trees can do the trick, but several rows are better, he said.
Precipitation helps keep the trees healthy; all that dust isn’t good for them.
Tyndall cautioned that the benefits of shelter belts in odour mitigation are site specific. The design of the yard, the trees and wind direction all have a part to play.
However, he said there is no doubt that they work.
As well, he said research has found the visual screen that VEBs provide lead people to believe the odour isn’t as bad.
“As farms are viewed as being more attractive, perceptions of odour are reduced,” he said.
Focus groups in Iowa said the more trees the better.
“There was high appreciation for the visual response to odour issues,” Tyndall said, noting that other odour suppression methods can’t be seen or appear to be industrial.
In the United States, VEBs are incorporated into the design for new buildings.
Some older facilities weren’t situated properly and adding trees can be challenging, he added.
Problems can arise around snow deposits, ventilation issues if the trees are too close to the barn and visibility issues for large trucks entering and leaving the facility.
Proper design and maintenance are necessary, he said.
