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Biofiltration consists of a filter-bed of organic matter serving both as carrier for the active biomass and as nutrient supply, through which the polluted gas passes. The selection of a suitable medium material is of major importance to ensure optimum biofilter efficiency. Peanut shells are an agricultural byproduct locally available in large quantities at a low price in most tropical and sub-tropical countries. A previous study showed that peanut shells are physically and chemically suitable for biofiltration. This paper presents the results obtained during a six month biofiltration experiment using peanut shells as medium and methanol as air pollutant. It is shown that peanut shells are potentially suitable as biofiltration medium, since degradation rates of up to 30 kg MeOH/m(3)d with an empty bed residence time of 19s was obtained. The biofilter showed a good resistance to shock load and no operational problems were observed.

Biotechnology has been applied to find systems to decrease the level of pollution. The main biological systems used in the deodorisation of waste gases are biofilters, biotrickling filters and bioscrubbers. These technologies work at normal operating conditions of temperature and pressure, and therefore they are relatively cheap with high efficiencies when the waste gas is characterised by high flow and low concentrations of odorous compounds. The aim of this work was to study the influence of different parameters (residence time of the gas phase, pollutant loads) of a biofilter and a bioscrubber on removal efficiencies. Ethanol was used as pollutant compound, because it is representative of both volatile organic compounds and odorous molecules. The performances of the two biological systems are presented and discussed. The use of pressure drop monitoring as a tool to control the operation of a biofilter and to obtain optimal conditions in a bioscrubber is proposed.