Spent activated carbon (SAC) from wastewater treatment plants is not allowed to be regenerated in Taiwan, and landfill is the only legal way for disposal. Owing its high heating value, SAC can be a potential source of energy from waste. In this study, SAC is used as the fuel in a vortexing fluidized-bed combustor. The combustion characteristics and pollutant emissions are investigated at various operating conditions. Results show that the primary gas flow rate and in-bed stoichiometric oxygen ratio have a significant impact on the bed temperature. The bed temperature increases with the in-bed stoichiometric oxygen ratio, while the bed temperature decreases significantly with the primary gas flow rate. In comparison to the primary gas flow rate and excess oxygen ratio, the in-bed stoichiometric oxygen ratio plays a dominant factor for the combustion fraction in the bed zone and CO/NOx emissions. The combustion fraction in the bubbling-bed region increases, while the CO emission decreases significantly with the in-bed stoichiometric oxygen ratio. In this study, all NOx emission concentrations are within the limit of Taiwan Environmental Protection Agency (EPA) regulations.