A process for the treatment of sludge which produces a dry sludge free of pathogenic and non-pathogenic microorganisms enriched with nitrogen which can be used as a fertilizer, and which uses as raw materials: elemental sulfur, formaldehyde, ammonia, urea, chlorine, and sulphuric acid, and comprises the steps of feeding the sludge into a pre-dryer into which is fed a hot gas stream containing sulfur trioxide produced by the combustion and catalytic oxidation of sulfur with air and finally completely drying the sludge by feeding it into an ammoniator.
