The Difference Between Oil Interceptors and Oil Water Separators

Oil Interceptors and Oil Water Separators sound like the same type of equipment and the terms are often used interchangeably. However, there are several major differences between the two.

Oil Interceptors

Oil Interceptors are designed to be installed in-line with drains and other plumbing where water containing limited quantities of grease, oil, solid sediments, and other liquid contaminants can be essentially filtered. The oils and solids are intercepted by the design and construction of the Oil Interceptor unit. Internal baffles and chambers in the unit diffuse the flow of water, forcing solids and heavier sludge to settle in collection baskets. Non-emulsified oils, grease and other light density substances rise to the surface of the water in the chambers, allowing the water to continue to flow through and out of the unit. The oils will need to be regularly skimmed from the surface of the water and the solids collection containers will need to be manually emptied on a regular basis.

Oil Interceptors are primarily designed for smaller applications such as foodservice kitchens, automotive service stations, and small to mid-sized manufacturing facilities. Oil Interceptors prevent oils and solids flushed or drained with waste water from contaminating main water lines external to the application location. In foodservice applications, oil interceptors are also called “grease interceptors” and “grease traps”.

Oil Water Separators

In contrast with Oil Interceptors, Oil Water Separators are designed for use on larger volumes of water with a higher water flow rate. As the water and non-emulsified oil flows through the unit, parallel corrugated plates force the oil droplets suspended in the water to combine and increase in size relative to the water, allowing gravity to work more efficiently to separate the oil from the water. An Oil Water Separator essentially uses intervening materials and media in the flow of liquid inside the unit. Heavy sludge and solids falls to the bottom and are pumped out. Water continues to flow through the unit. The flow process forces the enlarged oil droplets to rise to the surface of the water and collect with other oil droplets for removal. Coalesced oil floats to the top of the unit, being lighter in density than the water.

The entire oil water separation process of Oil Water Separators can be applied to very large volumes of water and waste oil, such as at industrial facilities, large asphalt parking lots, fueling facilities such as gas stations, and military installations with multiple waste oil and sludge sources. These units are typically underground but are also available as above ground systems. Oil Water Separators are designed for use in large applications beyond the size of most foodservice establishments.


It’s all about the water flow rate and the volume of oil-laden waste water.

Oil Interceptors (grease traps and interceptors) are primarily for smaller volumes of water, flowing at a moderate rate, with a smaller ratio of oils, grease, and solids to water. They use baffled chambers to slow down the water and separate the contaminants.

Oil Water Separators are made for use on large volumes of water flowing at a fast rate, containing a substantially higher amount of oils and contaminants. The separation process is primarily an agitation of particles created by the flow of the water through and over the internal media in the unit.

Note: Neither of these equipment types can impact chemically-emulsified oils, which have been altered by detergents, soaps, and other chemicals. Emulsified oils will still be interspersed in the main volume of water and will exit both types of equipment into drains, sewers, etc.