Biofilters are built so that the polluted air is led through the filter media. Often the polluted air is mixed with air from room-ventilation before entering the top of the bio filter. As the air passes down through the filter media, specific micro-organisms will decompose the odorous compounds into CO2 and water. The detention time may vary, but it is typically 25-35 sec. depending on the complexity of the odorous compounds.
The filter is humidified as required by means of a sprinkler system, as it is important to control the humidity to obtain maximum cleaning effect. Contrary to traditional biofilters the water and the air move in the same direction, and this leads to the possibility of watering the filter media while the filter is in operation. In cases where the water and the air move in opposite directions, only the upper part of the filter media will be sufficient humidified.