<p>Sewage sludge is mixed with organic material such as woodchips in a three screw mixer so that moving masses are created in the mixing compartment, there being a shearing action at the interfaces between the masses. The mixer includes the mixing compartment and a holding compartment into which dewatered sludge is continuously charged. There is a gate between the compartments which is opened when it is desired to convey sludge from the holding compartment to the mixing compartment. The shearing action results in the organic material being coated with a thin layer of sludge without the formation of dewatered sludge lumps which would rot instead of composting.</p>
