product is tested again for quality and purity before being released for sale to the public. REOB The sludge ("residue") associated with engine oil recycling, which collects at the bottom of re-refining vacuum distillation towers, is known by various names, including "re-refined engine oil bottoms" (abbreviated "REOB" or "REOBs"). A report from the U.S. Federal Highway Administration (FHWA) states that: The oil in a car engine... contains a variety of additives to enhance the vehicle’s performance. These include polymers, viscosity modifiers, heat stabilizers, additional lubricants, and wear additives. The REOB contains all the additives that were in the waste oil as well as the wear metals from the engine (mainly iron and copper). These additives include zinc dialkyldithiophosphate, which contains zinc, sulfur, and phosphorus; calcium phenate, which contains calcium; and molybdenum disulfide, which contains molybdenum and sulfur. Some producers of asphalt for paving have—openly or secretly—incorporated REOBs into their asphalt, creating some controversy and concern in the traffic engineering community, with some experts suggesting it reduces the durability of the resulting pavement. See also Vegetable oil recycling Vehicle recycling References External links Recycleoil.org American Petroleum Institute Energy Efficiency and Recycling at the American Petroleum Institute Motor oils Vehicle recycling Recycling by product Water pollution