The removal capacity of biological air filters is often limited by the mass transfer from the gas to the liquid phase. In order to optimize this mass transfer we have developed a new biofilter concept based on parallel tubes. The filter is furthermore characterised by the use of counter-current flow, fresh water supply without recirculation, high air velocity and a special filter material that distributes the water underneath the biofilm with the help of capillary action. In this way the filter is able to reduce contaminants that are hardly soluble in water. The filter has been tested at three different pig facilities for treating ammonia and malodours compounds. The capacity was up to 12.000 m3. h-1 with a specific gas flow of 4.000 m3. h-1 pr. m3 of filter material. Nitrogen mass balances were made for all facilities and showing good correlation between incoming ammonia and the outgoing metabolites. The filters achieved a removal efficiency for ammonia up to 99 % with an average of 76 %. For malodorous compounds such as acetic acid, formic acid, propionate, benzoic acid, p-cresol, phenol, 3-hydroxy-2-butanone, 2.3-butanedione and hydrogen sulphide the removal efficiencies were between 80 and 100 %. Hardly water soluble components like methanethiol, dimethyl sulfide and methane was reduced by 7-9 %. In relation to the greenhouse effect the degradation of methane fully compensate the nitrous oxide emission from the filters. These results were achieved with a pressure drop and water consumption similar to existing technologies, but with a smaller specific surface area and lower construction and operation costs. Moreover, the filters showed no signs of clogging, even after 14 months of operation.
Ikke Angivet, 2007
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International Congress on Biotechniques for Air Pollution Control, 2007