It is a fact that oil industry is that biggest industry in all over the world. Because of the recent downfall in world economy like all other industries, the oil industry is also trying to control cost and amounts but it has not been possible. Water is the one of the biggest need of these refineries; the average refinery requires 2.5 gallons of water for every gallon of crude oil processed and in a result of that it will produce at least 8-10 MGD of wastewater without the addition of storm water and sanitary sewer. Just like that, a large refinery will pay the cost of at least 100,000 dollars a day only for water, and all that money lost its worth with waste water. To overcome the situation, oil industries have come up with the concept of decentralized wastewater treatment so that they can improve the water by recycling and make it useful that can help to decrease the amount required for oil refineries.

Oil Refinery Wastewater Treatment also requires a big place and many types of equipment and too much extra care because this waste water has so many harmful containments that sometimes they can ruin the whole environment.

The wastewater originating at the Crude Unit Overhead is one of the larger volumes waste water treating process because that water contains contaminants like petroleum hydrocarbons, ammonia, and organic sulfur. The wastewater treatment has controlled the cost very much because the water gets reused again and again and there is less requirement to put money for water purchasing. Innovative process engineering in conjunction with technological advances in process control of biological treatment of these three major contaminants has made zero discharge of Crude Unit Overhead water cost effective for reuse with internal utilities. In past some years many companies have built plants to treat wastewater and have been able to take a very big control on cost.

The whole process of waste water treatment is consisting of three parts. In the first part with the help of biological technology, oil and grease and other petroleum hydrocarbons get removed from the water. The Newer technology membrane bioreactor (MBR) that has been introduced recently is not a good choice for this application because it requires high maintenance. In the second stage, a submerged fixed film biological reactor get used. The main purpose of this process is to remove all the bacteria which are added with hydrocarbon degraders. There are no moving parts of the reactor other than diffused air supply. This process does produce some hydrocarbon oxidation with additional families of hydrocarbons and because of that, it requires more retention time to complete.

In the final stage, nitrification process helps to remove ammonia. Many people try to do it in the first stage but that is not reasonable because it requires extra time for cell residence. There is particular ammonia that gets removed at this stage; all other type would have been cleaned in the first stage.

The most cost effective methods are the process of low-pressure boiler feedwater, followed by cooling tower makeup, followed by high-pressure boiler feedwater.