Effects of a partial pit ventilation system on indoor air quality and ammonia emission from a fattening pig room

The investigation was based on a hypothesis that applying an extra pit ventilation system may remove the highly concentrated gases and odours from the headspace above the liquid manure surface. This would improve air quality in the animal occupation zone, and utilising an air purification system to clean the pit-exhaust air may result in a reduction of the total emission from livestock buildings. In the investigations, an experimental fattening room with two pens and 30 pigs was used. The room was equipped with an automatically controlled negative pressure ventilation system with ceiling diffusion air inlet and a ceiling–roof top ventilator as a major exhaust unit. Additionally, an extra pit-exhaust unit was also installed. During the experiments, the major exhaust unit was automatically controlled by the climate computer according to indoor thermal conditions. About 10% of the maximum ventilation capacity was dedicated to the pit ventilation in each of two two-week periods. Ammonia concentrations, in air inlet and outlet, in the headspace above the slurry pit and in the slurry-pit exhaust were measured continuously. We found that the combination of ceiling and pit ventilation resulted in significantly lower ammonia concentrations in the room air (42.6%, p < 0.001) and in the slurry-pit headspace (22.3%, p < 0.001) compared with only ceiling ventilation. Total ammonia emissions increased slightly due to this new combination of ventilation systems. However, using an air cleaning system such as bioscrubber for pit exhaust, reductions in the ammonia emission of 37–53% from pig building might be achieved. The capacity required for the air cleaning needs only be 10% of the system capacity for cleaning all exhaust air. We conclude that indoor air quality can be significantly improved, and emission from the buildings significantly reduced, by utilising partial pit ventilation together with an exhaust air cleaning in pig buildings with ceiling ventilation system, without affecting pigs' behaviour.