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Adapted ventilation may reduce ammonia, odor from pig housing

TAGS: Swine
swine barn in Iowa in autumn_DarcyMaulsby_iStock_Thinkstock-464580998.jpg DarcyMaulsby/iStock/Thinkstock
Numerical simulations provide insights about swine barn ventilation that were not possible by experimentation alone.

The Flanders Research Institute for Agriculture, Fisheries & Food (ILVO) in Belgium announced that researcher Rafael Tabase recently defended his doctoral project, "Impact of Ventilation on Ammonia & Odour Emissions from Pig Housing," which examined improved ventilation regimes, specifically in modern pig houses — the so-called underfloor air distribution system (UFAD).

"In principle, with interventions that cost absolutely nothing, we can reduce the odor from an ordinary Flemish pig stable with a slatted floor by 34% and the ammonia emission by 11%," said Tabase, who is also affiliated with the University of Ghent in Belgium.

For the measurements, he combined two newly developed models and an experimental test platform where he mimicked the air movements in the house without the need for live animals to be present. Finally, he also validated his findings in the fattening pig house at the "Pig Campus" operated by ILVO, the University of Ghent and HoGent in Melle, Belgium.

"Numerical flow mechanics is now a mature discipline that can be used in many applications," added Michel De Paepe, a University of Ghent professor who served as an adviser/promoter to Tabase. "In this research, by means of well-validated numerical simulations, insights were obtained about ventilation of pig houses that were never obtained by experiments alone."

The methodological work is, therefore, highly innovative and can be used in follow-up research into the various interactions between internal airflows and emission surfaces, ILVO said in its announcement.

Advisers Bart Sonck and Peter Demeyer with ILVO are already looking ahead to further research.

"From Tabase's experiments, we conclude that there is still progress to be made in avoiding undesirable air exchanges between manure pit and barn space. At the same time, we need to continue to work on a construction-technically improved barn system in which critical parameters such as manure residence time, ammonia formation and the emission surface in the barn are used," Sonck and Demeyer said. "Examples of this are systems in which the solid manure and urine are immediately separated and removed. This prevents the emission problem from occurring at the source."

Fewer emissions without additional costs?

In terms of emissions of ammonia, odor, greenhouse gases and particulate matter, intensive pig farming is subject to European Union directives and regional regulations, ILVO said. In order to apply the European emission regulations, so-called "best available techniques" (BATs) have been described, but in many cases, they are quite costly, complex or work on only one pollutant (or even drive up other emissions).

"Pig farmers are looking for cheaper and easy to control emission reduction techniques, which can supplement their already applied BATs (such as low-emission barn construction concepts)," Tabase said. "My doctoral research focused on reducing air emissions by adapted ventilation in pig houses with UFAD, a concept that is present in two-thirds of recent Flemish pig houses. Computer simulations suggested that you could reduce the emissions there by adapted ventilation to avoid air exchange with the manure pit."

By experimenting with alternative ventilation regimes (such as a different "setting temperature" for the house, different percentages of the minimum and maximum ventilation, a variable setting according to the phase in the fattening round), Tabase discovered that good effects can be achieved by optimized ventilation control, ILVO said in its announcement.

"For example, increasing the so-called setting temperature from 23°C to 25°C led to a reduction of 29-43% of the average ammonia emission per hour," Tabase said. In addition, the air temperature in the ground channel proved to be a determining factor.

Methodology for specialists

To calculate the effects of the alternative ventilation regimes, Tabase used mathematical and physical modeling in combination with practical measurements.

For the indoor climate of the house, a steady-state simulation model was developed, and for estimations of ammonia transport from the manure pit and from the floor, a computational fluid dynamics (CFD) model was developed.

An experimental test platform was also developed at the Pig Campus in Melle. Two pig compartments were equipped with pig models and a urea spraying system.

"We simulated the heat production of the animals with artificial pigs and mimicked the urination of the pigs by spraying a urea solution on the fully slatted floors," Tabase said.

Ultimately, he said the findings were validated in full-scale field experiments in which ammonia, odor and greenhouse gases (methane and nitrous oxide) were continuously measured. Pig performance was also monitored.

Different building concept is needed

Correct adjustment of a ventilation system requires a great deal of skill, ILVO said, noting that it becomes particularly delicate in order to control ammonia, odor and greenhouse gas emissions all at the same time.

"The research certainly gave a promising result for odor," Sonck said. "We also saw a reduction in ammonia, but further research is needed here. I am thinking of heating the soil channel in winter so that there is no cold air in the manure pit or cooling in summer so that the ventilation flows can be reduced."

When it comes to practical applications, the researchers remain cautious. "The greatest added value of Raphael Tabase's research lies in the methodological development of good tools, which can be used even more widely in the future. As far as current practice is concerned, however, we have to remain realistic: Unfortunately, in this building concept, it remains very difficult to achieve significant and demonstrable emission reductions in practice. The internal airflows and the risk of the so-called well exchange are different for each barn, and they are also very subject to the temperature of the air inlet.

"In addition to looking for solutions for existing UFAD-ventilated barns, we must, therefore, also focus on the design of new barn concepts. A better option may be a preventive approach closer to the source, where you focus on the quick separation of solid manure and urine," Sonck added. "This prevents ammonia formation, together with smaller manure residence times and emission surfaces in the barn."

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