Which circumstance allows for the processing of oily water through OWS?

The processing of oily water through an Oily Water Separator (OWS) is governed by regulations designed to protect the marine environment from oil pollution. The correct choice, which specifies an oily mixture processed through the OWS not exceeding 15 PPM (Parts Per Million), aligns with these regulations.

The OWS is designed to remove oil from water to a level that meets environmental standards before the treated water is discharged overboard. A concentration of 15 PPM is often recognized as a limit set by various international standards, such as those from the International Maritime Organization (IMO). Discharging water with oil content above this limit can be harmful to marine life and ecosystems, which is why strict control of the discharge is critical.

This limit is lower than another commonly referenced threshold of 30 PPM, which is often associated with other operational allowances but does not reflect the acceptable discharge limit after processing through an OWS. As such, while both figures are relevant in discussions about oily water discharge, only the 15 PPM limit pertains specifically to the treated discharge from an OWS that complies with regulations. Therefore, identifying that the mixture must not exceed 15 PPM emphasizes the regulatory compliance required for environmental protection.

The emphasis on clarity in the other options