Abstract: A system and reactor vessel for electrical treatment of a fluid medium are described. The fluid medium to be treated comprises various industrial or domestic waste waters. The reactor vessel is provided with a housing being closed from one side thereof by a removable closure carrying secured thereon electrodes. The electrodes are electrically connected to the source of electrical power, wherein the closure is adapted for assembling with and disassembling from the housing such that the closure could be conveniently separated from the reactor vessel together with the electrodes to provide easy access to electrodes for inspection, replacement, repair, cleaning or for other type of maintenance.