Abstract: A process for the thermal treatment of incombustible liquids in a combustion space of a combustion apparatus by contacting the incombustible liquid with a supplementary fuel in the combustion space in the presence of at least one reactive gas. The process of the invention comprises feeding the incombustible liquid and the supplementary fuel into the combustion space (1) at different points, mixing the incombustible liquid with at least one reactive gas and the supplementary fuel with at least one inert gas prior to the contacting, and vaporizing the incombustible liquid and supplementary fuel prior to the contacting in the combustion space. The advantage of this invention is that environmentally harmful waste waters in particular are disposed of by burning these using a supplementary fuel. The required amounts of supplementary fuel are minimal in the process and only small amounts of nitrogen oxides, carbon monoxide and soot are generated.