A two-stage biofiltration system with a rusty iron reactor followed by a conventional biofilter to remove H2S and methyl ethyl ketone (MEK) from an air stream under ambient temperature and pressure was developed. Experimental results indicated that rusty iron efficiently catalyzed the oxidation of H2S by 02 in air. A properly designed reactor removed nearly all of H2S, and the biofilter was protected from acidification, which was expected if H2S was allowed to enter the biofilter. A model was developed to simulate the removal of H2S in a rusty iron reactor and to provide a basis for design and prediction. A comparative experiment showed that, in treating air containing both H2S and MEK, the performance of a two-stage biofiltration system was stable during the experimental period, while a single biofilter had declining efficiencies for H2S and MEK removal in the same period.