An oil skimmer is a device that is designed to remove oil floating on a liquid surface from oil spills. The effectiveness of a skimmer is highly dependent on the roughness of the surrounding water that it is working on: the more choppy the surrounding wake and water, the more water the oil skimmer will take in along with the oil, rather than take in oil alone. Skimmers can be self-propelled, used from shore, or operated from vessels, with the best choice being dependent on the specifics for the job at hand. Skimmers can be pressed into use for a number of applications other than oil spills, with the correct type to use again being dependent on the nature of the intended application. Examples of possible uses include making skimmers one component of oily water treatment systems, removing oil from machine tool coolant and aqueous parts washers, and collecting fats, oils, and greases as part of wastewater treatment efforts for food manufacturing industries. Oil skimmers are different from swimming pool sanitation skimmers, which are designed for a similar but unrelated purpose. Oil skimmers were used to great effect to assist in the remediation of the Exxon Valdez spill in 1989. Limitation and design factors There are many different types of oil skimmer. Each type has different design features and therefore results in different applications and use. It is important to understand the design features before employing a particular skimmer type. Some factors to consider are: Oil removal flow rate: Alternative Skimmer designs have different oil removal flow rates. Volume removal rates for Oleophilic skimmer types (drum, brush, disc, belt) are comparatively low. Weir type skimmers are capable of very high oil and water removal rates. ASTM F2709 standard establishes the test procedure for determining oil recovery rate (ORR). Oil removal concentration: It is a common misconception that oil skimmers remove concentrated or pure 'oil'; when in fact they remove a mixture of oil and water. In most situations the 'oil' mixture removed is an emulsion of oil and water more like a 'mousse'. Oleophilic and Non-Oleophilic skimmers can provide a more concentrated oil in the removal stream, however still collect entrained water. Effectiveness with different oils: Oleophilic and Non-Oleophilic skimmers are not equally effective with all oil types due to the changing nature of the attraction forces with different oils and materials. Effectiveness with chemicals in the water: Oleophilic skimmers