A gas treatment appliance and a gas treatment process are provided. The proportion of tar is decreased in a product gas formed on the gasification of carbonaceous feedstocks. The product gas or synthesis gas formed on the gasification of carbonaceous feedstocks is generally highly polluted with tar. This tar-polluted gas is exposed to a solid support substrate which is a support for bacteria which degrade tar. Suitable bacteria are, in particular, bacteria that occur in biogas-generating processes. The bacteria contained in the solid support substrate convert at least some of the tars and polycyclic aromatic hydrocarbons (PAHs) contained in the product gas into shorter-chain hydrocarbon compounds and methane which are not an industrial problem, and so their proportion is reduced in the product gas leaving the support substrate. In this manner the tar pollution in a synthesis gas or product gas can be reduced in a simple and inexpensive manner.
