A process and apparatus for feeding dewatered sludge into a reactor for thermal disposal, in which process and apparatus dewatered sludge with a water content of less than 85% is subjected to a temperature-pressure treatment after exiting from a thick-matter pump and prior to its atomization within a disposal reactor. In the temperature-pressure treatment the temperature is adjusted to more than 150.degree. C. and the pressure is adjusted to be equal to or greater than the water vapor/saturation pressure at these temperatures.