PROBLEM TO BE SOLVED: To make a long oil-water separating area and a long water tank unnecessary by providing an oil film detector installed in a treated water tank and a second valve installed in a recirculation line having one end connected to a part between a treated water tank and a first valve installed in a treated water line and another end connected to an inflow water tank. ;SOLUTION: Oil concentration of treated water 12 which has flowed into an inflow water tank 1, has subjected to oil separation in an oil-water separating area 4 and has reached a heated water tank 2 after passing through an guiding plate 3 is normally detected by an oil film detector 8. If the detected oil concentration is not higher than a specified value, a valve 10b is opened and a valve 10a is closed to discharge the treated water out of a system. If the detected oil concentration exceeds the specified value, the valve 10b is closed and the valve 10a is opened to return the treated water 12 to the inflow tank 1 via a recirculation line 9 in order to separate oil component in the oil-water separating area 4 and recirculated until water quality falls within a specification. By this constitution, length of a water tank is greatly reduced.;COPYRIGHT: (C)1999,JPO
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