Biodegradation by bacteria seems to me a good start. You have a lot of parameters to take into account such as salinity, heavy metal content, biocide, surfactant, demulsifiant, corosion inhibitor, temperature, and concentration of oil in the produced water. Base the treatment on waste water treatment plant is a way to look at the problem. Could you be more precise about the produced water?
Though your question does not really provide any precise specifics, I will suggest that you use bio-adsorbents (eg. treated rice husk) to clear the plumes of contaminants, Afterwards, you could use simple sand, sawdust, and probably clay filtration to filter. After these steps, any other water treatment test could be used to make the water more cleaner.