An Oil Content Meter (OCM) is an integral part of all Oily Water Separator (OWS) systems. The OCM continuously monitors how much oil is in the water that is pumped out the exit valve of the OWS system.^[1] The OCM will not allow the oil concentration of the exiting water to be above the Marpol standard of 15 ppm. If it is still above that standard, then the bilge water will be reentered into the system until it meets the required criteria. The Oil Content Meter will sound an alarm if the liquid leaving the system has an unsatisfactory amount of oil in the mixture. The OCM uses light beams to determine how oily the water in the system is. It is determined by this method because oil tends to absorb light whereas other particulates such as soot or sludge would scatter it. The system will then gauge the oil concentration based on a light intensity meter. Oil content meters also have a data logging system that can store oil concentration measurements for more than 18 months.^[1]

If the OCM determines that there is far too much of a type of oil, the OCM needs to be fouled and flushed out.^[2] Running clean water through the OCM is one way it can be cleaned. Also scrubbing the area with a bottle brush is another effective method.^[2]

The new MEPC 107(49) regulations have set out stringent actions that require the OCM to be tamper proof and also the OCM needs to have an alarm that sounds whenever the OCM is being cleaned.^[2]