This paper presents a new reactor for the biological trickle bed process in biological waste gas treatment. Clogging of the support is permanently avoided by 1. use of rotating support packing units; 2, a defined liquid regime in the start-up, operating, and cleaning phases, 3. continuous measurement and monitoring of the immobilised biomass. A uniform biofilm over the support surface is produced by optimised liquid distribution by spray jets and utilisation of support rotation. Cleaning is accomplished by liquid shear forces produced by jets. The time-controlled operating regime is accomplished with the aid of on-line quantification of the immobilised biomass. The resulting new quality of process control in biological gas treatment is demonstrated by experimental results on gas pressure drop, liquid holdup, and degradation rates. The practical relevance of this reactor prototype has been demonstrated by its use in a mobile pilot experiment with real gas emissions.