Thermal drying experiments of tannery sludge were conducted in a sludge paddle dryer.The drying characteristics of sludge

emission characteristics of flue gases and condensed water quality were analyzed.The result indicated that three kinds of volatile compounds

i.e.

ammonia

volatile fatty acid (CHCOOH

CH3CH2COOH) and alkane (heptane) were found in the thermal drying process.The water content of sludge decreased by increasing the temperature of heat-transfer oil.The concentration of volatile compounds and the COD value of condensed water were also influenced by the hydrolysis and decarboxylation in this process.The concentration of volatile compounds was measured before and after condensation.It was found that condensation could markedly reduce the emission of gaseous pollutants.