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ILVO Press Release - Tuesday, January 2, 2018

Improved performance of chemical and biological air scrubbers in pig barns achieved after simple adjustments

For the last 10 years, Flanders has required farmers to install a low-emissions system in all newly-built conventional (non-organic) pig and poultry housing. In her doctoral research (Ghent University/ILVO) about the efficiency of ammonia reduction in the currently-available chemical and organic air scrubbers, particularly in pig barns, Caroline Van der Heyden has identified the extent to which the systems lose their scrubbing efficiency when the air flow rates, acid levels or other parameters become suboptimal. “Air scrubbers operate completely automatically using sensitive sensors. Consistent maintenance and recalibration is a must,” says Caroline Van der Heyden.

Using these doctoral results, this is the first time in Flanders that a mathematical model has been made that can isolate the different factors that ultimately lead to the amount of ammonia removed from the air. ILVO now has made a unique test installation for air scrubbing available, where the acid levels, settings, air flow rates, thickness of the scrubber packets and so forth. This installation makes it possible to perform complex experiments and measurements.

Caroline Van der Heyden doctoral research:
“Operation and characterization of air scrubbers for the emission reduction of ammonia, hydrogen sulphide and greenhouse gases from animal housing facilities”.
The public defense took place on 21 december 2017 in Ghent, Belgium.
Promotors: Prof Dr. ir. Eveline Volcke of Ghent University en Dr. ir Peter Demeyer of Flanders Research Institute for Agricutulture, Fisheries and Food (ILVO).

Legal context

European and regional air quality policy in the last decennia has increased pressure on pig and poultry farmers to limit their farms’ emissions.
Since 2004 Flanders has required all newly-built (non-organic) pig and poultry barns to limit their ammonia emissions, i.e., according to one of the accredited ag construction systems on the official list. This list is approved by the Minister of Agriculture based on advice of the Scientific and Administrative Team. The reference work performed at ILVO provides the technical-scientific support. An air scrubbing system for barn air must achieve an ammonia reduction of 70%
Van der Heyden’s doctoral research is situated in the context of emission measurements that are important for Flanders in relation to the NEC guideline and the current ammonia reduction plan (PAS in Dutch) in the framework of Europe’s Natura 2000.

Air scrubbers technically gauged and easier to optimize

To reduce the impact of barn emissions and the potential hinder for those living close to the farm, farmers often install an air scrubber (chemical or organic). Both types of air scrubbers have dozens of variants available on the market. They remove ammonia and other pollutants (odor, particulate matter) from the outgoing air, then converted via acidified water and subsequent chemical and/or biological reactions.

Two unique extra methods to measure air scrubbers and to help develop them are now available:

  1. A powerful mathematical model that can predict the air scrubbing on a series of parameters using the values.
  2. A “pilot” air scrubber mounted on the buildings of the ILVO-UGent pig campus, where researchers can adjust the installation to record the effects on performance under practical circumstances. The installation makes it possible to vary the acidity of the water, the air flow rates, the thickness of the scrubber packs, etc.

“The two tools are useful, either combined or separately, for further scientific work but also for the policymakers and developers of air scrubbers.

To determine the amount of ammonia removed, there is now – for the first time – a continuous measuring system that records data during an entire fattening period. Up to now, only point measurements were done. The variations in day vs. night, size of the animals, animal behavior, barn management and other factors can be related to the air scrubbing data. In pigs the ammonia emissions in the barn air increase linearly (and not exponentially) during the fattening cycle.

For a few air scrubbers, the entire exhaust surface – several square meters – was mapped. Some differences in air scrubbing were noted depending on the measurement location within the exhaust area. To measure the ammonia reduction even more precisely, the outgoing air must therefore be measured in several places.

Performance of chemical air scrubbers can be improved by working with the correct flow rates

Using measurement campaigns and model simulations, the influence of the incoming air conditions and the design and control of the installations on the air scrubber performance were controlled. A rather logical result appeared: higher airflow rates result in a lower ammonia removal efficiency, because the air stays a shorter time in the scrubber. The incoming air temperature has little influence on the efficiency.

A literature study reveals that chemical air scrubbers are now capable of capturing up to 95% of ammonia from the air. The biological air scrubbers achieve a maximum rate of 80-85%. It is also clear that in both systems, important amounts of particulate matter and odor particles are removed during the scrubbing process. “That research was outside the scope of this doctorate, but the optimization of a combined air scrubbing is a challenge for future research,” say the promotors.

Performance of biological air scrubbers can be improved using inoculation and pH controls

In the biological air scrubbers, Caroline Van der Heyden studied the ammonia reduction efficiency in function of the acidity (pH) and the nitrogen components in the scrub water. The effect of nitrification on these two parameters could identify them via model simulations and measurements. An important observation is the risk that biological installations can convert between 2-5% of the ammonia into laughing gas (N2O), a damaging greenhouse gas. And that the installations can acidify. The precise cause is not known but it is preventable using a control system with built-in acid and base dosages.

The functionality was mapped and is favorable. By balancing the pH to 6.5, a more complete conversion of ammonia to nitrate in the scrub water can be achieved. This system does result in a limited increase in the ammonia removal efficiency, but it also increases the cost of the system. This makes it less desirable in practice.

Another strategy to improve the functionality of a biological air scrubber is to inoculate them with active sludge from a water purification plant. Active sludge is available free of charge at most water purification plants and adding it to the air scrubber does add extra work. “Inoculation results in a more appropriate microbial population in the installation, faster start-up of nitrification, less nitrite accumulation and thus lower emissions of N20,” says Van der Heyden. The functionality of the installation is thus optimized and the greenhouse gas emissions are limited.


The current technology behind chemical and biological air scrubbing in pig barns can be optimized by careful maintenance and recalibration. The functionality of biological air scrubbers in pig barns can be improved via inoculation with active sludge from a water purification plant. A thorough training for the farmer to better understand and maintain the installation together with the installer is thus recommended.

In conclusion, there are many ways to improve the effectiveness of air scrubbers: biological air scrubbers can improve the odor reduction without compromising the ammonia reduction. Chemical air scrubbers are stronger in the combination of ammonia and particulate matter.


Greet Riebbels, ILVO Communication,, 32 486 26 00 14
Caroline Van der Heyden, PhD,
Peter Demeyer, ILVO Technologie en Voeding (promotor),, 32 472 93 62 91
Prof. Eveline Volcke (promotor), Ghent University, Dept of Green Chemistry and Technology- Biosystems Control Group,, +32 9 264 61 29