Negative air ionisation strongly decreases fine dust

The air inside poultry houses generally contains high concentrations of dust, or ‘Particulate Matter’ (PM). In poultry, dust mainly originates from the litter and manure, down feathers, mineral crystals from urine, and feed. The concentration of dust inside poultry houses is directly related to the activity of the birds during light periods, especially in litter housing systems like floor housing for broilers and layers, and aviary housing for layers.

Dust particles are classified in terms of their size or their region of deposition in the human respiratory tract. The abbreviation ‘PM10’ refers to the fine dust fraction with a particle size smaller than or equal to 10 micrometre, whereas ‘PM2.5’ refers to the very fine dust fraction below 2.5 micrometres. These smaller dust fractions are able to pass the nose, mouth and larynx, penetrate into the thorax and some even into the lung tissues, causing adverse respiratory and cardiovascular health effects. For a few decades now, agricultural research has worked on developing measures for the reduction of dust exposure in poultry facilities.

European standards
During the last decade, in Europe, more and more attention has been paid to PM concentrations in the ambient air from a public health perspective. In 2008, the European Union issued directive 2008/50/EC containing limit values for PM10 and PM2.5 in the ambient air of its member countries. As from 1 January 2005, the daily average limit for PM10 was set at 50 μg/m³ with 35 crossings allowed per year. The annual average limit for PM10 was set at 40 μg/m³.

To be able to comply with these limits, measures are needed in the Netherlands to reduce emissions from major sources, including poultry houses. Besides this, the EU-wide ban on traditional cage housing for laying hens results in a shift towards high-dust litter housing systems at this moment. In view of this, the Dutch government commissioned Livestock Research of Wageningen University and Research Centre to develop and test practical and effective solutions for PM emissions from poultry. An overview of the main measures tested, is shown in Table 1.

Electrical-magnetic field
One of these solutions is a commercially available negative air ionisation system for broiler barns. The system is basically composed of three units. A high voltage unit is used to convert the AC of the power supply system to a DC at -30kV and a low amperage to ensure safety. The unit is connected to a system of wires with needle-shaped pins that run along the length of the broiler barn, underneath the ceiling surface, which is extra grounded if needed. The high voltage on the top of the pins creates an electrical-magnetic field between the wires and ceiling and any other grounded surfaces.

Electrons are emitted from the pins and move over the field towards the ceiling, thereby charging dust particles that are encountered. The negatively charged particles then adhere to the grounded surfaces and are removed from the air. During the empty period, the dust load is removed by normal cleaning.

Dust deposition visible
To come up with a ‘proof of principle’, the system was first tested in a small-scale experimental broiler barn of Wageningen UR Livestock Research. This barn is divided into several fully identical rooms, each containing 2,475 broilers, housed on a litter floor. The rooms were equipped with lines with drinker nipples or feed pans, radiator heaters and HF fluorescent lamps. Rooms were ventilated separately, with roof fans and side wall inlets. In two rooms, the system was installed, whereas two identical rooms served as controls.

During two consecutive growing periods, concentrations and emissions of PM10 and PM2.5 were measured weekly, as well as ammonia, odour, greenhouse gases and microorganisms. Besides emissions, technical performance (mortality, feed conversion, water consumption, weight gain), litter quality (dry matter content, friability) and bird exterior (breast dirtiness, breast irritation, scabby hips, hock burns, foot pad lesions) were monitored. Significant effects were only found for PM10 and PM2.5: their emissions over the total growing period were reduced by 38% and 10% respectively. Dust deposition was visible within days as a yellowish colour on surfaces.

The voltage set to -30 kV did not vary along time, over the rearing cycle, but the amperage gradually decreased, due to the insulating effect of the increasing dust layer between wire and surfaces. Because negative air ionisation may result in production of harmful ozone, this was also monitored. Measured ozone concentrations were all below the detection limit of 0.01 ppm.

Over the first days of the rearing cycle, however, ozone could be detected in the ionisation rooms by the human nose, perceived as an intense smell of ‘clean bed sheets or fresh forest air’. As ventilation rates increased along time, this smell could not be perceived anymore, after day five of the growing period.

Desert-like surface
Dutch poultry farmers that are in need of a PM mitigation measure in order to receive an environmental permit, can choose from an official list of approved and tested options, issued by the Ministry of Environment and Infrastructure. To obtain this approval, effectiveness of the system must be validated under field conditions, following a measurement protocol.

This protocol states that at least two farm locations must be used, to include any variations in effectiveness caused by differences between barns. To include any time variations within a barn, six 24 hour measurements must be carried out per barn, balanced over the calendar year and the growing period.

To obtain this approval, the negative air ionisation system was installed at two modern, commercial broiler facilities. At each facility, one barn was equipped with the system, whereas a second, identical barn, served as control. Within days, the deposition of a dust layer was evident on the ceiling and some other surfaces like feed hoppers. By the end of the growing period, the dust layer had built up to an impressive desert-like surface of several centimetres thick (Figure 1). The full set of 12 year-round measurements showed a reduction of fine dust emission over the total growing period of 49% for PM10 and 65% for PM2.5. Again, no clear-cut effects were found on emissions of ammonia, odour or greenhouse gases, nor on litter quality or bird performance. The wires of the system were brought closer to the ceiling every time the amperage dropped below a critical level, indicated by a notification light on the high voltage unit, to maintain its target amperage and effectiveness. After each growing cycle, the barns were cleaned using a high pressure spray gun.

Extensive research
Based on the results of the field study, the system was added to the official list of dust mitigation options by the Dutch Ministry of Environment and Infrastructure. This was also the case for a number of other options, including both in-house and end-of-pipe techniques. From 2007 to 2012, a large number of dust mitigation measures were developed and tested in an extensive research programme at Wageningen University and Research Centre, in cooperation with suppliers of air cleaning techniques. Some measures and techniques tested did not prove to be effective, practically applicable or economically feasible, but in the end, a fair amount of options made it all the way to official approval.