BACKGROUND: Biofilters are suitable to treat industrial emissions polluted with volatile organic compounds(VOCs), responsible for photochemical smog and depletion of the ozone layer. This study analyzes the performance of a biofilter with Macadamia ternifolia nutshells as a carrier material treating air streams contaminated with ethylbenzene under mesophilic conditions with continuous feeding. RESULTS: The biofilter was operated continuously for 5 months applying several inlet loads (IL), empty bed residence times ;(EBRT) and temperatures. At a temperature of 303 +/- 1 K removal efficiencies (RE) higher than 90% were obtained for ILs lower than 85.6 gm(-3) h(-1) and 70.6 gm(-3) h(-1) at an EBRT of 150 and 90 s. The yield coefficient resulted in 0.73 g of dry biomass formed per g of ethylbenzene degraded. Michaelis-Mentens half saturation parameter Km and maximum volumetric elimination rate r(m) were calculated for EBRT of 90 s, Km = 0.28 +/- 0.09 gm(-3) and r(m) = 89 +/- 11 gm(-3) h(-1), and 150 s, Km = 0.72 +/- 0.18 gm(-3) and r(m) = 117 +/- 15 gm(-3) h(-1). CONCLUSIONS: The experimental data shows that a biofilter with Macadamia ternifolia nutshells (waste material in Thailand) as a carrier material is a good option for air treatment in tropical areas with typical temperatures varying from 292 to 313 K, using ethylbenzene as a test substrate. (C) 2012 Society of Chemical Industry