A method for treating effluent containing dissolved or suspended solids includes directing the effluent containing dissolved or suspended solids to a reactor and oxidizing at least a portion of the dissolved or suspended solids in the reactor with an oxidizing agent. Oxidation is carried out at a temperature ranging between approximately 20° C. and approximately 350° C. and at a pressure ranging between approximately 1 bar and approximately 160 bar. A gaseous phase and a liquid phase form within the reactor during oxidation. The method includes separating the gaseous phase from the liquid phase and heating the effluent in the reactor with the heat produced from the oxidation of the dissolved or suspended solids.