Emissions of NO, N2O, NO2, SO2 and CO were measured during oxy-fuel combustion of sewage sludge and a reference fuel (bituminous coal) in a 12 kW bench-scale CFB combustor. Combustion tests were conducted at temperature of 850 degrees C in air (base case) and O-2 + CO2 mixtures with oxygen concentrations 21, 30 and 40%vol. The effects of oxygen concentration in oxidizing atmosphere and fuel type on gaseous emissions are evaluated. Instantaneous and average emissions of NO, N2O and SO2 for the combustion of sewage sludge in all atmospheres were much higher than those for the combustion of reference coal. As the oxygen concentration in O-2/CO2 atmosphere increases, NO and SO2 emissions increase while N2O and CO concentrations decrease. The fractional conversions of fuel-N to NOx and N2O are calculated and compared for both fuels. Despite the high content of nitrogen in sewage sludge, the total conversion ratios of the fuel N to NOx and N2O for sewage sludge were much lower than those for coal. (C) 2020 Elsevier B.V. All rights reserved.