Emission of volatile organic compounds (VOCs) produced during composting of different organic wastes (source-selected organic fraction of municipal solid wastes (OFMSW), raw sludge (RS) and anaerobically digested wastewater sludge (ADS) and animal by-products (AP)) and its subsequent biofiltration have been studied. Composting was performed in a laboratory scale composting plant (301) and the exhaust gases generated were treated by means of a compost biofilter. VOCs concentration in the composting exhaust gases for each composting process ranged from 50 to 695 mg C m(-3) for OFMSW (5:1), from 13 to 190 mg C m(-3) for OFMSW (1:1), from 200 to 965 mg C m(-3) for RS, from 43 to 2900 mg C m(-3) for ADS and from 50 to 465 mg C m(-3) for A-P. VOCs emissions were higher during the beginning of the composting process and were not generally related to the biological activity of the process. These emissions corresponded to an average loading rate applied to the biofilter from 2.56 to 29.7 C m(-3) biofilter h(-1). VOCs concentration in the exhaust gas from the biofilter ranged from 55 to 295 mg C m(-3) for OFMSW (5:1), from 12 to 145 mg C m(-3) for OFMSW (1:1), from 55 to 270 mg C m(-3) for RS, from 42 to 855 mg C m(-3) for ADS and from 55 to 315 mg C m(-3) for AP. Removal efficiencies up to 97% were achieved although they were highly dependent of the composted waste. An important observation was that the compost biofilter emitted VOCs with an estimated concentration of 50 mg C m(-3). (c) 2005 Elsevier B.V. All rights reserved.