The functional principal of biofilters was recognized and used back in the 1920’s to clean contaminated exhaust gas. Over the past decades, the technical implementation has been optimized for a multitude of uses. A biofilter is a simple and cost effective way to clean odorous exhaust gas. Microorganisms in the biofilter break down the odorous substances into harmless components, such as carbon dioxide and water. If odorous substances are present in the exhaust gas of the sewage sludge dryer, the highly saturated exhaust gas of the dryer offers the ideal prerequisites for oxidizing these. The harmful substances are transferred into the condensation range of the gas in the aqueous phase. The water in the exhaust gas forms the habitat for the microorganisms. Those microorganisms that discover the best living conditions through the harmful substance and which use the harmful substance in the air as a source of carbon and energy are established.

The boifilter consists of a container with a woodchip filling as the filter substrate. If necessary, it is incorporated after the dryer into the exhaust gas flow of the dryer. As the exhaust gas is already at the condensation point when leaving the dryer, complete condensation is achieved through the further cooling when flowing through the biofilter, which in turn forms the ideal breeding ground for microorganisms.

Odorous substances are almost completely oxidized as a result.