Petroleum refining industry
Petroleum refining industry requires plenty of water for all its production needs. Accordingly, it requires a well-established water supply and wastewater treatment system. Wastewater pollutants in this industry (oil depots, service stations, etc.) include motor gasoline, diesel fuel, fuel oil, gas oil, lubricants, etc. Oil products in sewages are mainly in freely state and form films or layers on the surface due to the lower density as compared to water. They require mechanical cleaning (sand traps, grids, oil catchers etc.), then pressure flotation, using coagulants with or without flocculants. This is due to the regulations on maximum contamination levels, whereby oil content in purified water of petroleum refining plants returned to biological treatment facilities should not exceed 25 mg/l.