Operating the Oily Water Separator

1. Before anything else — is the discharge permitted?

No operation begins until the legal position is settled. The conditions themselves, with their exceptions and the Special Areas, are in When You May Discharge. What has to be confirmed, in order, before a pump is started is:

• the ship is on passage, not in port and not manoeuvring;
• the ship is at least 12 nautical miles from land;
• the ship is not in a Special Area — or, if it is, that the plant is capable of below 15 p.p.m. and the alarm and automatic stopping device are fitted and working;
• the oil content monitor, the alarm and the automatic stopping device are all operational.

If any one of those fails, the water goes into the bilge tank instead. There is no third option.

2. The operating sequence

This is the full sequence as it is worked on board. It is written in order and should be learned in order.

1. Inform the bridge, so that the timing and the ship's position are noted, and take the Chief Engineer's permission.
2. The overboard manual discharge valve is kept locked, with the key with the Chief Engineer. Open the lock and the valve, and open all valves in the presence of the Chief Engineer.
3. Close the drain valve, and open all the other necessary valves.
4. Open the bilge tank valve from which the mixture is to be drawn.
5. Open the air supply if the control valves are air operated.
6. Switch on the control panel and the oil content meter unit, and the oil discharge monitor and alarm system.
7. Run the pump, taking suction first from the sea chest, to fill the separator with sea water. Watch the shell pressure while filling. Prime until water comes from the second stage vent.
8. Open all vents and cocks to release air, then close the vent.
9. Open the steam heater valves and maintain about 60 °C. Separation depends on temperature; this step is not optional.
10. Flush the oil content meter with fresh water for at least 5 minutes before putting the monitor into operation, then change over from fresh water to the sampling line.
11. Change the pump suction over to draw from the bilge tank.
12. Start the oily water separator supply pump.
13. Watch the oil content meter for the p.p.m. reading, and check the soundings of the bilge tank and the separator sludge tank.
14. Check the sample from the sampling valve — which is fitted just before the overboard valve and after the three-way valve — for effluent condition and clarity.
15. Keep a watch on the ship's side at the overboard discharge valve. A discharge is visible; if anything shows, the operation stops.
16. Regularly check the interface through the test cocks. If the lower test cock shows oil, open the drain valve until the upper test cock shows water, then shut the oil valve.
17. After the operation — flush the system with sea water, flush the oil content meter with fresh water, switch off the power, shut and lock the overboard valve, and hand the keys back to the Chief Engineer.
18. Enter the quantity, the time and the ship's location in the Oil Record Book, signed by the operating officer, the Chief Engineer and the Master.

The steps that people get wrong

• Step 7. The vessel is filled with clean sea water before any oily mixture is admitted. Starting with an empty vessel and oily water gives the automatic controls nothing to reference.
• Step 9. Running cold produces poor separation, a high reading, and a tripped discharge. The separator will appear faulty when it is simply cold.
• Step 10. The fresh water flush of the monitor is what keeps the optical cell clean and the zero reference honest. Skipping it is the usual cause of a monitor reading that drifts.
• Step 17. The key goes back to the Chief Engineer and the valve is relocked. Leaving it open is the failure that turns every subsequent mistake into a pollution offence.

3. When the alarm sounds

If the alarm operates: open the oil drain cocks and check the oil control level, then stop the pump. Nothing else.

The mechanism behind it — what the three-way valve has already done to the discharge, and why the oil has to be drawn off before the machine will work again — is in Oil Content Monitoring, section 4. What belongs in an operating procedure is only the order of the operator's actions, because that is the part that has to be right the first time.

4. The Chief Engineer's control of the operation

The authority for the discharge rests with the Chief Engineer, and the sequence reflects that:

• the operating engineer informs the Chief Engineer and asks permission;
• the Chief Engineer selects the position for the discharge, having taken the ship's position from the bridge;
• the operation proceeds with him present for the valve work;
• the regulation governing the discharge is his responsibility to confirm.

In port, it is not allowed at all.