This research provides an equilibrium model for predicting both the emission of gaseous pollutants and the fate of heavy metals during incineration of biologically treated dye sludge in a bench-scale fluidized bed incinerator. Major gaseous pollutants and hazardous trace heavy metals have been also measured under various operating conditions. The predicted values, which were derived by using a thermodynamic equilibrium model, can be used to determine the optimum operating parameters and the risk associated with hazardous waste incineration by means of verifying experimental data. However, prediction of NOx emission using a thermodynamic equilibrium model during incineration of waste was not simple. The reason is that the variation of NOx emission during incineration of waste was affected by the various operating parameters, such as air-fuel ratio (λ(T)), primary air factor (λ(1)/λ(T)), combustor geometry, method of heat release, and preheating of combustion air. According to the distributions of Cr and Pb simulated by the equilibrium model, all of the Cr in the feed was retained in the ash as the solid phase of Cr2CO3. However, most Pb was retained in the ash during incineration as the solid phase of PbSO4, or heterogeneously deposited onto the fly ash as PbO(g) when the combustion gas becomes cool.