Abstract: Backwash water containing radioactive cruds of a non-filter aid type filter of the primary cooling water system of an atomic power plant is treated by leading the backwash water directly, or supernatant obtained by removing coarse cruds by settling in advance, to a waste resin settling tank for backwash water containing waste ion exchange resin powder from filter-demineralizer of the condensation-purification system of the atomic power plant, mixing the backwash water or the supernatant with the backwash water from the filter-demineralizer in the tank, thereby allowing the cruds contained in the backwash water or the supernatant onto the waste ion exchange resin powder, and settling the crud-adsorbed waste ion exchange resin powder, thereby separating and removing the cruds from the backwash water from the non-filter aid type filter. Recycle of fine cruds can be eliminated with enhanced percent crud removal, and recycle time of backwash water can be shortened.

Abstract: A method of and a system for removing miniuscule solid particles from liquid wherein the liquid to be processed is supplied to one end of at least one filter element which may be a porous tube filter open at opposite ends and formed with a multiplicity of tiny openings in its wall having a first surface and a second surface. The liquid flows along the first surface and a portion thereof is passed through the tiny openings from the first surface side to the second surface side because of the latter being under lower pressure than the former, to be drawn off as filtrate. The rest of the liquid or a concentrated liquid portion flows out of the other end of the filter element. The flow velocity F of the liquid flowing along the first surface and/or the flow velocity f of the filtrate through the tiny openings is controlled such that the ratio F/f can be kept at a predetermined value.