This study investigated the emissions of polycyclic aromatic hydrocarbons (PAHs) from two fluidized bed incinerators (FLBI_A and FLBI_B) and one fixed bed incinerator (FlBI) disposing biological sludge generated from the petrochemical industries in Taiwan. The results of 21 individual PAHs (including low (LM-PAHs), middle (MM-PAHs) and high molecular weight PAHs (HM-PAHs)) were reported. The LM-PAHs mainly dominated the total-PAHs in the stack flue gases, whereas the LM- and HM-PAHs dominated the total-PAHs in the bottom fly, fly ash and WSB effluent. Due to high carcinogenic potencies (= total-BaPeq concentrations) in the bottom ash (195 ng g(-1)) and WSB effluent (20,600 ng L-1) of the FIBI, cautious should be taken in treating them to avoid second contamination. Lower combustion efficiency and elevated fuel/feedstock (F/W ratio for the FIBI led to the highest total emission factor of total-PAHs (38.400 mu g kg(-1)). Lower total-PAH removal efficiencies of wet scrubber (WSB) (0.837-5.89%), cyclone (0.109-0.255%) and electrostatic precipitator (ESP) (0.032%) than those reported elsewhere resulted in high fraction in PAH contributions from the stack flue gases. Lower total-PAH emission factor was found for FLBLA (2380 mu g kg(-1) biological sludge) with higher combustion efficiency compared to those for FLBI_B (11,500 mu g kg(-1)) and FIBI (38,400 mu g kg(-1) biological sludge), implying that combustion efficiency plays a vital role in PAH emissions. (C) 2009 Elsevier B.V. All rights reserved.