This is going to strongly depend on the type of bacteria that you are encountering. Are you seeing aerobic or anaerobic bacteria? Are they general heterotrophic, acid producing, or sulfate reducing?

For oil applications, UV will not penetrate far enough into the matrix to ensure inactivation. I think that a gamma radiation source (less dangerous than it sounds, can be used to treat food) is the best bet. Barring that, maybe ultrasonic lysing would work.

There are some chemical additives, e.g. 2-(Thiocyanomethylthio) benzothiazole or Methylene bis (thiocyanate), but they may affect refinery operations dramatically.

Would this be aerobic bacteria? If so removing the oxygen dissolved in the oil and from the head space in the tank may be an economical and low toxicity solution.

UV exposure may help eliminate some bacteria.

Adding chemical compounds (for example: bleach) to the medium may affect the nature and integrity of the oil, ultimately use of the oil. Therefore, you may want to consider method(s) that will not affect the future use of the oil. Headspace nitrogen, and UV light may provide conditions that prevent bacteria to flourish.

This is going to strongly depend on the type of bacteria that you are encountering. Are you seeing aerobic or anaerobic bacteria? Are they general heterotrophic, acid producing, or sulfate reducing?

For oil applications, UV will not penetrate far enough into the matrix to ensure inactivation. I think that a gamma radiation source (less dangerous than it sounds, can be used to treat food) is the best bet. Barring that, maybe ultrasonic lysing would work.

There are some chemical additives, e.g. 2-(Thiocyanomethylthio) benzothiazole or Methylene bis (thiocyanate), but they may affect refinery operations dramatically.