How to Operate an Oily Water Separator (OWS) on Ship?

An oily water separator clears the bilge water of oily content to bring it inside the acceptable range to discharge it overboard. An oily water separator is a machinery for such importance that it is handled by only the 2nd or chief engineer. (However, the duty engineer might also be asked to operate under supervision)

Operating an Oily Water Separator

An oily water separator can only be operated when the ship is sailing and en route. According to MARPOL, the oil content of the effluent must be less than 15 ppm and the ship has in operation an oil discharge monitoring and control system and oily-water separating/filtering equipment.

Oily Water Separator

In case of failure to follow any of the above mentioned rules, the ship will be fined and stopped, and the chief or 2nd engineer can even be imprisoned.


Because of such high risks, operating an oily water separator should be done with utmost precision to minimize the risks of marine pollution. Though a “How to Operate?” guide is always posted near the oily water separator, there are few points to be kept in mind and followed to prevent any mistake.


Operating Procedure

The following points are to be followed while operating OWS.

1) OWS overboard manual discharge valve is to be kept locked and keys are to be kept with the chief engineer. Open the lock and overboard valve. Open all the other valves of the system.

2) Open the desired bilge tank valve from which the oily water mixture is to be discharged from OWS.

3) Open air if the control valves are air operated.

4) Switch on the power supply of the control panel and OCM unit.

5) Fill the separator and filter unit with fresh or sea water to clean up and prime the system till the water comes out from vent of second stage.

6) Start the OWS supply pump which is a laminar flow pump and one that will supply the oily water mixture to OWS.

7) Observe the OCM for ppm value and keep checking sounding of bilge tank from where OWS is taking suction and of the OWS sludge tank.

8 ) A skin valve/sample valve is provided just before overboard valve and after the 3-way valve. Keep a check on the sample for any effluent and clarity.

9) Keep a watch on the ship side at the overboard discharge valve.

10) After the operation, Switch off the power and shut and lock the overboard valve. Keys to be handed over to the chief engineer.

11) Entry to be made by chief engineer in the Oil Record Book (ORB) with signature of operating officer, chief engineer and the master.

If you liked this article, you may also like to read- What is oil spill at sea & Fighting oil spill on ship


Do you have info to share with us ? Suggest a correction

Subscribe To Our Newsletters

By subscribing, you agree to our Privacy Policy and may receive occasional deal communications; you can unsubscribe anytime.

Web Stories


  1. Good Suggestions , to add ,It is alaways a good practice to test the 15 PPM alarm to ensure it is operational before starting the OWS. Some ship owners have fitted white boxes in the OWS discharge line to record the start, flush , stop time & oil content trend of effuluent being pumped overboard. It is also possible to record the position at start & during the entire period the OWS is operational if GPS feed is provided. Need to check the functioning of whitebox OCM as well. Engineers should record the correct timings in ORB as there could be errors in recorded timings & timings in Whitebox data.

  2. Thank you for your good information.i am a marine engineering student in kenya in the TECHNICAL UNIVERSITY OF MOMBASA.i am very greatful.

  3. Additional information: Nowadays, oily water separator are equip with additional monitor with memory and printer to know the time and position when the equipment was started and stopped. So, we cannot escape or lie about the use of this equipment.

  4. please add the details on correct way of testing 15ppm monitor. some are telling that it is enough to insert the cleaning brush into the sensing chamber to simulate the alarm. is this the correct method?

  5. How to test 15 ppm monitoring device is working properly or not? Thanks in advance

  6. which of the area prohibided start ows, and how meny mile must be nearest land

  7. Too much thanks for giving knowledge.If possible please teach us how oil content monitering system works.

  8. @Anug: Glad you found it useful. Please check this article -

Leave a Reply

Your email address will not be published. Required fields are marked *