Air washers not only reduce emissions of ammonia from livestock sheds - Yang Zhao discovered during his PhD research - they also filter out particulates and germs. However, they don't do this good enough.
Zhao measured the levels of bacteria, dust particles and ammonia present in the air in the sheds before and after the air was cleaned with three different air washers. It seemed that the air washers not only trapped 70 to 100 percent of the ammonia present, but also 46 to 85 percent of bacteria and 50 to 90 percent of particulates. A combined air washer with three successive cleaning steps was the most efficient.
Zhao's findings are important because fine particles in barn air can carry germs, explains researcher Andre Aarnink: 'It seems that Q Fever is spread through the air. A recent study in the United States shows that the PRRS virus in pigs can be spread through the air.' Yet, very little is known about the transmission of germs through the air, says Aarnink. 'It is difficult to measure germs in the air.' For this reason, there is currently no law to prevent the spread of air-borne diseases, although there are rules concerning the movement of humans, animals and vehicles to and from an infected farm.
Current air washers are suitable for reducing dust particles, but are not yet able to tackle the spread of diseases. 'A reduction of particles by 70 percent is already quite a lot', says Aarnink, 'but germs can be present in large quantities in animal sheds; will even a reduction of 90 percent be good enough? For infectious animal diseases, you would want this to be 100 percent.' With the knowledge gained by Zhao, producers of air washers can now make even better appliances, feels Aarnink, to trap even more germs. 'Techniques already exist for reducing particulate matter and germs successfully, but these are only used in office buildings at present. Their introduction into animal sheds hasn't happened yet.'
Zhao defended his thesis successfully on 20 April under Professor Mart de Jong of Quantitative Veterinary Epidemiology and Professor Peter Groot Koerkamp of the Farm Technology Group.