Dear Mary, Good question, ...

Dear Mary,

Good question, the oil is the dangerous pollutant for aquatic life, it shield the oxygen transfer into depth of water.

Step by step process for oil water separation when oil quantity s more then gravity system to be used and hen centrifuge oil disc separation etc. following are the process, Centrifugal separation is another process of separating two fluids with contrast in densities. Imparting centrifugal motion creates two streams namely the less dense oil which orients itself along the rotational axis and the denser fluid (water) which orients around the stream of less dense fluid. 

1. Gravity separation
2. Oil disc separation
3. Centrifuge separation by density
4. Skimmer system
5.  Microbubble technology. 
6. partition gravimetric method 
7.  Dean-Stark Method to separate oil and water. 
8. Membrane-based filtration systems. 

To separate oil from water, add a solution of soluble ionic salt to the solution. Distillation, which involves boiling and condensing the water, is another option, as well as partially freezing the oil and water combination and discarding one-fourth to one-third of the unfrozen water.

Regards,

Prem Baboo