This guideline provides information about cleaning waste gas/waste air (WGA) to reduce or eliminate certain pollutants and odours by biological treatment in biofilters. Biofiltration has been used successfully to purify emissions from many different type of industries or productions including livestock production and manure treatment. Many odorant components (organic compounds such as oxygen-containing compounds, sulfur-containing compounds, nitrogen-containing compounds and inorganic compounds such as hydrogen sulphide and ammonia) are degraded in an aerobic process by the activity of the micro-organisms settled on solid carrier substances. Compost, fibrous peat, heather, mixes of these of other organic substances and also lava or porous clay can be used and arranged in layer so the WGA can flow through and be sorbed onto the carrier substances surfaces where the micro-organisms can decomposed its components. To operate properly optimum conditions must be controlled in the biofilter such as WGA concentration and type, type, number and activity of the micro-organisms in the biofilter, temperature, moisture content of the WGA and pH-value. Proper design and construction should be done and particular attention should be given in dimensioning the biofilter and start up and maintenance procedures. The efficiency of the biofilter will be evaluated by the reduction of specific pollutant or of the odour emission using different techniques (gas chromatographic and spectrometric analysis) for the pollutants and olfactometry for the improvement in the odour (VDI 3881 and 3882). The biofilter supplier has to guarantee the assured properties for define operating conditions.

Biofilters are effective for WGA reduction. However this technology, even if not very complicated, involves quite a bit of following up to maintain the proper conditions for micro-organisms activity and WGA reduction. The investment and operation costs of biofilters have also to be evaluated and weighted in the possible solutions for WGA reduction. Important operation cost are associated with the use of biofilters for treatment of waste air from ventilated livestock building as important volume of air has to be blown through the filter.