The emission characteristics of volatile compounds (VCs) during municipal sewage sludge (MSS) and paper mill sludge (PMS) drying process were investigated through experiments conducted on a lab-scale tubular drying furnace and a pilot-scale paddle dryer, respectively. The result indicated that five kinds of VCs, i.e. CO2, NH3, C7H16 (n-heptane), volatile fatty acids (VFAs) and CH4 were emitted during the drying process. It was found that the NH3 and CO2 were the primary compound released from the MSS drying process. In the case of the PMS, the VFAs and CO2 were the main compounds released. The temperature and water content of sludge had great effects on the emission rates of NH3, C7H6, CO2 and VFAs. The pH and chemical oxygen demand (COD) of condensate from the paddle dryer were also studied. It showed that pH and COD of condensate from MSS were much higher than that from the PMS, and that the higher COD value of the MISS condensate interrelated to the higher ammonium and sulfur content of it. (C) 2008 Elsevier B.V. All rights reserved.