This standard covers the treatment of waste gas/exhaust air containing gaseous air pollutants, aerosols and notably odorants. The described biodegradation of the pollutants is accomplished under aerobic conditions by micro-organisms colonizing on solid support media. This standard gives an overview of waste gas streams that have been successfully treated and/or pollutants that have been effectively degraded in biofilter systems. It addresses the criteria to be considered for the proper design of the biofilter system, discusses performance evaluation criteria and presents production processes in which biofilters have become successfully established for waste gas treatment.