A method for the production of heat comprises composting solid organic waste, preferably in admixture with sewage sludge, and burning the composted waste, for example in a kiln for calcining an inorganic calcinable material. The composted waste preferably has a water content of less than 20% by weight, more preferably from 10 to 20% by weight. The organic waste is preferably composted in a rotating drum preferably for an average residence time of from 12 to 48 hours. The invention also provides a method for producing a fuel by composting a solid organic waste as described above and the fuel produced thereby. The composting is suitably carried out in a rotating drum having festoon chains arranged therein to serve as mixing lifters or flights.