Apparatus for treating a fluid, which comprises: - at least one pair of electrode layers power supplied by power supply means to different polarities, facing each other, separated by a spacing distance delimiting at least one passage chamber susceptible of being traversed by at least one first fluid flow containing ionized particles and exerting hydraulic pressure on at least one first wet surface of said electrode layers; - retention means, adapted to transmit a mechanical counter-pressure on said at least one pair of electrode layers in order to prevent their moving away; characterized in that each said electrode layer of said at least one pair of electrode layers comprises: - at least one metal conduction layer electrically connected to said power supply means and provided with at least one first contact surface; - at least one first impermeable layer of graphite, which: - is arranged as a sealing cover on the first contact surface of said metal conduction layer, as a separation of said metal conduction layer from said first fluid flow; - is provided with said at least one first wet surface directed towards said passage chamber and with a first dry surface compressed, by the hydraulic pressure exerted by said fluid contained in said passage chamber, directly in adherence against the first contact surface of said metal conduction layer, in order to distribute the current of said power supply means from said metal conduction layer to said first impermeable layer of graphite. - at least one pair of electrode layers power supplied by power supply means to different polarities, facing each other, separated by a spacing distance delimiting at least one passage chamber susceptible of being traversed by at least one first fluid flow containing ionized particles and exerting hydraulic pressure on at least one first wet surface of said electrode layers; - retention means, adapted to transmit a mechanical counter-pressure on said at least one pair of electrode layers in order to prevent their moving away; - at least one metal conduction layer electrically connected to said power supply means and provided with at least one first contact surface; - at least one first impermeable layer of graphite, which: - is arranged as a sealing cover on the first contact surface of said metal conduction layer, as a separation of said metal conduction layer from said first fluid flow; - is provided with said at least one first wet surface directed towards said passage chamber and with a first dry surface compressed, by the hydraulic pressure exerted by said fluid contained in said passage chamber, directly in adherence against the first contact surface of said metal conduction layer, in order to distribute the current of said power supply means from said metal conduction layer to said first impermeable layer of graphite. - is arranged as a sealing cover on the first contact surface of said metal conduction layer, as a separation of said metal conduction layer from said first fluid flow; - is provided with said at least one first wet surface directed towards said passage chamber and with a first dry surface compressed, by the hydraulic pressure exerted by said fluid contained in said passage chamber, directly in adherence against the first contact surface of said metal conduction layer, in order to distribute the current of said power supply means from said metal conduction layer to said first impermeable layer of graphite.