This study demonstrates that calcium carbonate (CaCO3) allows not only enhancement of the production of CO as syngas, but also reduction of the content of polycyclic aromatic hydrocarbons (PAHs) in the pyrolytic products from sewage sludge. CO2 was formed by the decomposition of CaCO3 in pyrolysis. The CO2 derived from CaCO3 enhanced thermal cracking of volatile organic carbons (VOCs) generated during the pyrolysis of sewage sludge and provided an additional source of C and O, likely enhancing the production of CO at >650 degrees C. In addition, more solid product was converted into gaseous and liquid products by the addition of CaCO3 in the pyrolysis of sewage sludge. This work suggests that CaCO3 can be used as an inexpensive source of CO2 that increases thermal efficiency of the pyrolysis process and reduces the evolution of harmful chemical species such as PAHs during thermal treatment of the byproduct during processing at municipal and industrial wastewater treatment facilities (i.e., sewage sludge). (C) 2018 Elsevier Ltd. All rights reserved.