A microbiological-based air cleaning system using a two-step process for removal of ammonia in discharge air from a pig rearing building

In coming years large livestock farms will have to significantly reduce their emissions of odours, ammonia and dust to the surrounding area. The characteristics of a prototype air cleaning system for emission control in livestock buildings were measured using a pig rearing building. The system uses a two-step process: (1) absorption and (2) nitrification. The absorption process takes place in a scrubber, in which ammonia is removed by a water spray. The nitrification process takes place in water purification unit, in which the ammonia in water is oxidized to nitrites and nitrates using a microbiological process. Scrubbers or spray towers can be installed in ventilation stacks. Water purification unit is a central unit, which recycles water with a controlled pH to the spray towers. In tests, the water purification unit was able to maintain the spray water at pH < 7.5, which enabled 55–95% ammonia removal efficiency. Further development of the system is required to reduce the consumption of water and optimise the microbiological processes in the water purification unit.