Abstract: A method of and an apparatus for cleaning crude gas, particularly waste gas from a mineral fibre production plant and contaminated with phenol and/or formaldehyde and/or the products of condensation thereof, wherein the crude gas is sprayed with a circulated washing liquid enriched with micro-organisms, some of the impurities contained in the crude gas being in this way agglutinated, the washing liquid being collected in a storage tank and the impurities contained therein being at least partly degraded by the micro-organisms which are themselves subjected to an activation process, and wherein, after it leaves the spraying tower, the crude gas sprayed with the washing liquid is passed through the electric high-voltage field of a wet film precipitator in which the aerosols are separated and fed to the storage tank or collecting tank. The cleaned gas has substantially lower emission levels than previously and is odorless and colorless.