Why do you want to eliminate ...

Why do you want to eliminate the bacteria?  The bacteria will eliminate the oil and grease, in time. The COD can be lowered with microbes.  We grow them for this use.  A grease separation through flotation and skimming would allow the recovered grease to be sold, if you have a large amount.  Many of the large food processing, and meat processing plants use this method.  Depends on the oil and grease, how you set it up.  I did a steel mill by using both precipitation of heavy tars, and flotation of the light oils.  Both were recovered.  I would have to know more about what else is there and what the full system is about before thinking about using ozone or a halogen: from what you have said, it may not be needed.  

Problems with Oil and grease have sometimes been solved with pH reversal, take it down and then bring it back up.  A high pH in the alkaline range will turn the oil into a soap. 

More needs to be known.  It sounds like a salesman just wanted to sell Ozone. You need to get some specifics.  Type of oil, or oils, grease from what?  what is causing the high COD, besides oil, full water analysis including metals, pH, hardnes (total, Ca, Mg), conductance UMOS, etc.   

Flow rates, and amount of flow, changes in flow, sessional flow, etc. if important.

I hope that helps.