An engineer at the University of Michigan has developed a nonthermal plasma reactor that removes viruses and other pathogens from airflow
By Jackie Clark
A researcher and innovator at the University of Michigan has developed a system that can inactivate airborne porcine reproductive and respiratory syndrome (PRRS) virus. In lab testing, the nonthermal plasma reactor removed or inactivated 95 per cent of the virus from the airflow, according to a March 10 university release.
The technology is well suited for the swine industry.
“We arrived at the swine market for a couple of reasons,” Dr. Herek Clack, associate professor in the department of civil and environmental engineering at the University of Michigan, told Farms.com.
“Much of what we’ve developed is designed to address the actual and perceived shortcomings of particle filters,” he explained. “A conundrum that you really can’t get around with conditional particle filters (is that) the more thoroughly they remove particles, the less air you can get through them.”
Pig barns need adequate fresh air flow, with exceptional filtration, to optimize herd health.
“Once we started looking at applications that needed to move large volumes of air but still needed high degrees of performance in terms of protecting against whatever the particles are in the air, that really led us to animal applications in general and swine in particular,” Clack said.
The technology works similar to a flame at an oil refinery used to combust waste gases, except it’s nonthermal.
“It’s essentially kind of a cold flame,” Clack said.
“If you place an electrode at a high enough voltage in air … you get a glow, and that glow is a plasma. It’s where the air is being ionized,” he explained. At that location, oxygen and nitrogen in the air that are usually present as two bonded oxygen or nitrogen molecules, are being broken apart into individual molecules. Water vapour present will also break down into its molecular hydrogen and oxygen components.
“Those fragments, called ions or rapid radicals, are a very potent component of the air right where that plasma’s being formed. They are very reactive,” he added. “Because they are not stable species, they tend to react very quickly with anything, including the surface of bacteria and viruses.”
Though results have shown a high percentage of inactivation of the PRRS virus after being run through the nonthermal plasma reactor, the exact mechanism of that reduction is still debated.
“We have not yet proven one mechanism over another,” Clack said. “We believe it’s these oxidizing radicals … that are sterilizing in their effects.”
Some other scientists think that the plasmas generate UV light, and that contributes to sterilization effects, however Clack doesn’t believe that has much impact.
His theory is that the viruses, or other unwanted particles, react rapidly with the fragments in the plasma, which are fuelled by the high-voltage electrode. Those reactions have the inactivation or sanitizing effect on the virus.
If we go back to our oil refinery flame comparison, this also makes the reaction simpler to control.
“In a flame you’re fuelling the combustion event with the fuel, whereas here with a nonthermal plasma, what’s driving the plasma is that high voltage. It’s not self-propagating; it can’t run away like a flame could,” Clack explained.
In swine production systems “we’ve identified three locations where this conceivably could be installed,” he said. The nonthermal plasma reactor could be installed in barn air intake points, to protect the pigs inside from airborne pathogens outside. The reactor could also be used at air exhaust points, which could help in isolating disease events. Removing PRRS or other viruses from barn exhaust would protect livestock in nearby barns on the same farm or neighbouring facilities.
Additionally “you could also install it for example in a pit fan exhaust,” Clack explained. “We have a colleague at Michigan State that has shown that the PRRS virus can survive in the manure pit, and when you pump out the manure pit those aerosols can have viable PRRS virus in it.”
This application may also help reduce smell pollution from pig farms.
The air filtration technology holds promises for human health and other animal diseases as well.
Though it can’t prevent direct animal-to-animal transmission within a barn or insect vectors, the nonthermal plasma reactor can help “where there’s concern about an airborne disease,” Clack said.
Airborne diseases may spread directly from viruses shed in animal breaths, coughing or sneezing, or through pathogens that attach to dust in the air.
Swine production systems are the ideal candidates for this technology because of the high investment in biosecurity and confined nature of production, however, there may be application opportunities in the poultry industry. Cows typically don’t spend enough time in a confined, environmentally controlled setting for the reactor to prevent airborne illness, Clack explained.
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