Abstract: There is disclosed an apparatus for the electrochemical treatment of a liquid medium, which allows the production of a sterilizing solution as well as the decontamination and purification of liquid mediums from toxic organic substances and other impurities. The apparatus contains a diaphragm-shaped electrolytic midstream cell, a feed line for the liquid medium being processed, a cathodic outlet line for carrying the liquid medium out of the cathode chamber to a place of collection or discharge, an anodic outlet line for carrying the liquid medium out of the anode chamber into a catalytic reactor for breaking down active chlorine, an exit line for carrying the liquid medium to the place of collection, and a bypass line, an additional exit line and a flow switching device. The apparatus can also be equipped with a flow switching device, a connecting line, a midstream expansion tank, a purification filter and other components.