(Co-)combustion characteristics of sewage sludge (SS), coffee grounds (CG) and their blends were quantified under increased O-2/CO2 atmosphere (21, 30, 40 and 60%) using a thermogravimetric analysis. Observed percentages of CG mass loss and its maximum were higher than those of SS. Under the same atmospheric O-2 concentration, both higher ignition and lower burnout temperatures occurred with the increased CG content. Results showed that ignition temperature and comprehensive combustion index for the blend of 60% SS-40% CG increased, whereas burnout temperature and co-combustion time decreased with the increased O-2 concentration. Artificial neural network was applied to predict mass loss percent as a function of gas mixing ratio, heating rate, and temperature, with a good agreement between the experimental and ANN-predicted values. Activation energy in response to the increased O-2 concentration was found to increase from 218.91 to 347.32 kJ.mol(-1) and from 218.34 to 340.08 kJ.mol(-1) according to the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods, respectively.