Researchers from North Carolina State University
and West Virginia
University have developed
a new technology that can reduce air pollutant emissions from some chicken and
swine barns, and also reduce their energy use by recovering and possibly
generating heat.
Specifically, the research team designed, built, and evaluated a
proof-of-concept unit that incorporates a biofilter and a heat exchanger to
reduce ammonia emissions from livestock barns, while also tempering—or heating
up—the fresh air that is pumped into the barns.
The pollution removal component uses a biofiltration mechanism, in which
polluted air is passed through an organic medium, such as compost or wood
chips, that contains bacteria. Those bacteria interact with the pollutants and
break them down into harmless or less harmful constituents. Biofiltration also
allows recycling of nitrogen because when the “spent” medium is applied on
cropland, the nitrogen becomes available to the crops. However, biofiltration
also introduces additional costs for animal agriculture operations. The
researchers hope to defray those costs by reducing an operation’s energy
consumption.
Here’s how their prototype works: warm, polluted air from the livestock
facility enters the biofilter, and some of the heat is transferred to the heat
exchanger. When fresh air from outside is pumped into the building, it passes
over the heat exchanger, warming it up.
The prototype not only helps recover heat from the facility, it also
produces its own heat. This heat is generated within the biofilter when
heat-producing biochemical reactions occur—for example, when the ammonia is
converted into nitrate by bacteria. The heat from the biofilter is also routed
to the heat exchanger.
Maintaining the appropriately high temperature is important for chicken and
swine operations, because it is essential for rearing chicks and piglets to
maturity.
“The technology is best suited for use when an operation wants to vent a
facility that has high ammonia concentrations, and pump in cleaner air in
preparation for a fresh batch of chicks or piglets—particularly in cold
weather. It is also suitable for use when supplemental heat is required for
raising the young animals,” says Sanjay Shah, PhD, an associate professor of
biological and agricultural engineering at NC State and lead author of a paper
describing the research. For this to be feasible, it would be necessary to
replace a couple of the conventional cold weather ventilation fans with
higher-pressure fans. Shah explains that the technology is not compatible with
summer ventilation using tunnel-fans, because of the high cost and choking
effect on the fans.
Shah says the researchers focused on ammonia removal because: it is released
from chicken and swine houses in large quantities; it contributes to nutrient
loading problems such as hypoxia; it is an indirect contributor to greenhouse
gases (GHGs) because it can break down in to the potent GHG nitrous oxide in
the ground; and because it is a precursor to very fine particulate matter,
which contributes to haze and public health problems, such as asthma.
Researchers showed that their design is effective under real-world
conditions, operating their prototype in a 5,000-bird chicken house. The prototype
removed up to 79% of ammonia and reduced the energy needed to maintain the
necessary temperature in the facility—recovering as much as 8.3 kW of heat.
“We plan to continue working to improve the system design in order to make
it even more efficient,” Shah says.
The paper, “Coupled Biofilter – Heat Exchanger Prototype for a Broiler
House,” is published in Applied Engineering in Agriculture.
