APPARATUS FOR MEASURING OIL LAYER THICKNESS IN STILL STANDING TYPE OIL-WATER SEPARATING TANK, STILL STANDING TYPE OIL-WATER SEPARATING TANK USING THE SAME AND OIL-WATER SEPARATING METHOD

PROBLEM TO BE SOLVED: To precisely and quickly measure the thickness of an oil layer in oil-containing wastewater by providing a water column manometer communicated with the liquid in an oil-water separation tank, a means for measuring the water level of the manometer, and a means for measuring the height of the liquid level in the oil-water separation tank. SOLUTION: At first, an oil-containing wastewater injection valve 5 is opened to inject the oil-containing wastewater in an oil-water separation layer 1. At this time, a water injection valve 34 of a water column manometer is opened and water is supplied in order to prevent contamination of the water column manometer with oil and water. At the time when a means 31 for measuring the height of the liquid level of the oil-water separation layer I detects a prescribed height h2 as the liquid level height H of the oil-water separation layer 1, the oil-containing wastewater injection valve 5 and the injection valve 34 are closed and the separation layer is left still for a sufficient time to separate the oil by floatation separation and the water level h1 of the water column manometer. Then, the thickness D of the oil layer is calculated based on the equitation I from the difference (d) of the liquid level height h2 of the oil-water separation layer 1 relative to the liquid level H and the water level h1 of the water column manometer 20, the previously measured or set specific gravity γ2 of the oil, and the specific gravity γ1 of water.