[en] Purpose: To effectively obtain clean water of high purity from laundry waste from work clothes or the like worn in the atomic power plant and to increase the concentration factor of the impurities. Constitution: The laundry drain is supplied to a forestage condensation tank through a supply pipe, via a control valve controlled by a level gage so as to always maintain the liquid level constant, and the liquid within the tank is increased in pressure by the fore-stage high pressure pump and supplied to the fore-stage inverse osmosis module. There occurs a phenomenon of inverse osmosis so that water in disposed liquid is urged through a film and discharged from a osmosed water discharge pipe. In this case, the concentration of a surface active agent in the disposed liquid is detected by a flow meter depending on the quantity of osmosed water, and when the concentration exceeds a predetermined level to decrease the quantity of osmosed water, the opening of the control valve is increased and the liquid is discharged from the discharge pipe into the final tank for disposal in substantially similar manner. (Yoshihara, H.)