Abstract: A system for at least partially removing a contaminant in a contaminated fluid includes a reaction vessel with a fluid inlet and a fluid outlet. The contaminated fluid is conductable in a fluid flow direction which has at least a component oriented antiparallel to the force of gravity. A fluid supply unit supplies a contaminated fluid through the fluid inlet inside the reaction vessel. The reaction vessel is filled with reactive particles. The fluid supply unit controls a flow velocity of the contaminated fluid between the fluid inlet and the fluid outlet so that the flow of contaminated fluid through the reactive particles generates a fluidized bed of the reactive particles, thereby removing, at least partially, the contaminant in the contaminated fluid by a reaction of the contaminant and the reactive particles. At least 80% of the reactive particles have a size of more than 2 mm.