Abstract: A method of treating fluids containing impurities by means of an electrochemical reactor consisting of at least one pair of opposed main electrodes, a power source capable of generating an alternating current connected to the main electrodes, and a plurality of auxiliary electrodes disposed between the main electrodes which are uniformly arranged in a mutually close relationship. The auxiliary electrodes may be disposed on the surfaces of nonconductive supports so as to form a macroporous mixed filler layer between the main electrodes. Control of the electrochemical reactions is achieved through the choice of electrocatalytic materials on the surfaces of the auxiliary electrodes and materials dissolved in the fluid to be treated.