Conventional gravity separators use the force of gravity to separate oil and other contaminants from water. This works because oil is less dense or lighter than water. Therefore, when oily water is put into a separator, the oil rises to the top, solids and sediment sink to the bottom and the water is left in the middle. The oil is then skimmed off the top and disposed of, while water is free to flow through an outlet on the side of the tank for further processing or to be released into the environment. Solids and the sediment layer are scraped off the bottom into a sludge pump for disposal.