Reactor for the treatment of wastewater that contains contaminants, for example heavy metals, chemicals, oils, colourants, pigments, textile dyes, inks, bacteria, viruses, by electrolytic means, which reactor comprises: a wastewater reservoir, at least the inside of which is electrically insulating; an inlet for wastewater to be treated; an outlet for treated wastewater; wherein the wastewater is located in the reservoir for a chosen residence time during operation of the reactor; a number of alternately intermeshed mutually parallel vertical metal plates (7; 8) positioned with the same mutual distances between them acting as electrodes with connecting means (9; 10) for the connecting of the plates (7; 8) to a source of electric current, such that the plates (7; 6) are alternately connected with one connection and with the other connection (12; 13) of a central unit, such that, during operation of the reactor, an electric current flows between the plates (7; 8) through the wastewater present in the reservoir, whereby, as a result of electrolysis, a portion of the metal of the plates (7; 8) is ionized and goes into solution in the form of metal ions (M n+, where n is the valency of the metal), hydroxyl ions (OH -) go into solution, and gas bubbles (inter alia H 2) appear on the surface of the plates (7; 8), which gas bubbles rise in the water, altogether such that the contaminants bind to the metal ions, the hydroxyl ions and/or the gas bubbles, whereby clusters form through coagulation, some of which clusters undergo electroflotation and move upwards, whereby they form floating flocs on the water's surface, and others form sediment through precipitation which sinks to the bottom of the reservoir; adjusting means for the adjusting of the mutual distances between the adjacent plates (7; 8), and hence the adjusting of the intensity of the current flowing through the plate (7, 8) electrodes via the water; and removal means for the removing of floating flocs and of the settled precipitate, or at least the facilitating thereof; characterized in that the plates (7, 8) are commonly arranged by means of hinges so as to be pivotable about individual, mutually parallel pivot axes that are determined by the hinges and extend in one flat plane and the plates (7, 8) are pivotable about the axes through the action of the pivot means ( 14, 15, 16, 17, 18, 19) while maintaining their mutually parallel relationship, such that the mutual distance between adjacent plates (7, 8) can be adjusted under the effect of a central unit between a maximum distance, where the plates (7, 8) extend perpendicular to the flat plane determined by the pivot axes, and a minimum distance determined by spacing means. a wastewater reservoir, at least the inside of which is electrically insulating; an inlet for wastewater to be treated; an outlet for treated wastewater; wherein the wastewater is located in the reservoir for a chosen residence time during operation of the reactor; a number of alternately intermeshed mutually parallel vertical metal plates (7; 8) positioned with the same mutual distances between them acting as electrodes with connecting means (9; 10) for the connecting of the plates (7; 8) to a source of electric current, such that the plates (7; 6) are alternately connected with one connection and with the other connection (12; 13) of a central unit, such that, during operation of the reactor, an electric current flows between the plates (7; 8) through the wastewater present in the reservoir, whereby, as a result of electrolysis, a portion of the metal of the plates (7; 8) is ionized and goes into solution in the form of metal ions (M n+, where n is the valency of the metal), hydroxyl ions (OH -) go into solution, and gas bubbles (inter alia H 2) appear on the surface of the plates (7; 8), which gas bubbles rise in the water, altogether such that the contaminants bind to the metal ions, the hydroxyl ions and/or the gas bubbles, whereby clusters form through coagulation, some of which clusters undergo electroflotation and move upwards, whereby they form floating flocs on the water's surface, and others form sediment through precipitation which sinks to the bottom of the reservoir; adjusting means for the adjusting of the mutual distances between the adjacent plates (7; 8), and hence the adjusting of the intensity of the current flowing through the plate (7, 8) electrodes via the water; and removal means for the removing of floating flocs and of the settled precipitate, or at least the facilitating thereof;