Oil and Water Separators Information

Oil and water separators (oil-water separators, oil water separators) are remediation devices that separate oil from water and/or wastewater. This product area includes both aboveground and underground systems for the containment and treatment of oil-contaminated water. Oil and water separators also include smaller, filtration-type devices that treat wastewater produced by large, oil-lubricated equipment such as compressors. Oil filters that process compressor condensate to a residual oil content of 5 parts per million (ppm) may allow processed water to be discharged in municipal water treatment systems. These oil and water separators can be matched to compressor capacities from 700 to 4500 standard cubic feet per minute (scum), and may be able to separate oil that has become emulsified.


Oil and water separator. Video Credit: WashBaySolutions /CC BY 3.0


Oil and water separators are typically vaults or tanks made of cement. An oily water separator is designed with a series of baffles or coalescing plates built in to the vault that slow down the flow of the incoming water and force oils to float to the surface of the tank. The coalescing plates divide the oil water separator into two sections. The oily water enters the tank through an inlet pipe where sediments settle out to the bottom of the tank. As the oily water passes through the coalescing plates, the oil is attracted away from the water and floats to the surface of the tank. A floating oil skimmer is used to remove the oil from the surface of the water. Floating oil skimmers typically use a series of pumps to draw oily water in and pump clean water out, as well as internal, self-adjusting weirs or dams to hold the skimmed oil. Oil and water separators for smaller applications include a bilge water separator, or marine oil water separator, used to treat oily water from boats, ships, and off-shore oil platforms.


Oil and water separators are used in many industries, from food processing to heavy manufacturing to wastewater treatment and marine applications. Another important use for oil and water separators is in diesel engines. A diesel fuel water separator is a device that removes the background humidity from diesel fuel before the mixture can reach sensitive engine components where the water can cause wear or damage.

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