Conventional oil separators are based on separating oil and water by gravity. The less dense oil floats on top of the denser water. For this process to work properly, the medium must have sufficient residence time in the oil separator. It therefore has to have a certain minimum size. As a rule, the better the oil separator is expected to work, the larger it has to be. However, space is often very limited in industrial plants.

Another limiting factor is the bath chemistry, i.e. the cleaner. If a demulsifying cleaner is used, which is the case in most degreasing baths, it is almost impossible for an oil separator to remove the oil from the bath. The cleaner keeps the oil emulsified, i.e. it remains very stable as small droplets suspended in the water.

The advantage of membrane filtration is that separation takes place via the membrane pore size. This pore size is clearly defined and does not change. The water and the cleaner can pass through the pores, while the oil and particles are retained. This process is independent of the cleaner, temperature, and also the oil and dirt concentration. The resulting filtrate is always free of oil and turbidity.

This makes membrane filtration the more robust and reliable process compared to oil separators for maintaining cleaning baths. These advantages have increased further in recent years through the use of robust ceramic membranes.