Drawing of biofilters are shown in the paper. For odour removal from pig housing, 50 cm thick of material is used and the biofilter can treat 290 m3/h of air per m2 of filter. Garbage compost and fibrous peat have been tested and the peat seems to be the best filter material as the porosity is high and the pressure demand is lower. Higher pressure demand will increase energy cost as the ventilator have to work harder to push the air through the biofilter. Such biofilter are relatively to maintenance however to assure good operation conditions de-dusting has to be done before the air enters the filter material and this material has to be kept moist (generally only during dry periods as the air coming from the building is relatively humid). No cost appreciation is given.