Taking extra steps to clean up bilge water

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There’s a space at the lowest level of a ship’s insides where a dark liquid mixture collects. It has a suitably unattractive name – the bilge – and the nasty soup that collects there is called bilge water.

It’s mainly just that – water, mostly fresh, some salt. Darkening it are oil and oily chemicals, cleansers and other fluids that make their way to the bilge from the ship’s mechanical operations and some onboard drains. A buildup of bilge water can cause stability problems for a ship, as well as give off potentially toxic fumes, so it must be removed. But global standards forbid dumping untreated bilge water at sea.

The International Maritime Organization, a United Nations agency whose responsibilities include preventing oceanic pollution, allows only an infinitesimal,  amount of bilge-borne contaminants to be released at sea: 15 parts per million (ppm).

Because it’s hard to visualize a ratio of that size, those who conjure with such numbers liken it to 15 drops of oil in 50 liters (more than 13 gallons) of water. Another way to picture it is as 15 inches out of 16 miles. Or 15 cars in a bumper-to-bumper traffic jam nearly 2,500 miles long.

Royal Caribbean’s self-imposed standard of ABC – Above and Beyond Compliance – makes that ratio even harder to grasp. RCL ships treat bilge water until oily contaminates measure only 5 ppm, or three times less than what is allowed by law.

“All Royal Caribbean ships have onboard what is called an OWS or oily water separator,” says Nick Rose, RCL’s environmental regulatory lead. “The OWS treats onboard bilge using different filtering processes.”

After most of the oily content rises to the top of the bilge water in treatment holding tanks, it’s skimmed off into separate sludge tanks. Once in a port with an approved waste contractor, the ship offloads this sludge for reuse in pavement, as fuel for energy generators, or for other recycling.

Before the sludge-free water is released from the OWS, it passes through three progressively finer filters, the last of which is activated carbon, which will remove more pollutants.

“Once it goes through these levels of filtration media,” Rose explains, “if it meets our company standards, it is then sent either overboard through another monitoring device called the ‘white box,’ or it is stored onboard until it is ultimately discharged through the ‘white box.’”

Fleetwide installation of this “white box,” the final component of RCL’s bilge water treatment protocol, was completed in 2009. The computer-controlled device, locked in a cage to prevent tampering, is set to release bilge water only if it meets or beats RCL’s stringent standard of 5 ppm or less oil content.

Rose said the only reason for RCL ships to store treated bilge water is if they are less than 12 nautical miles from land, RCL’s self-imposed minimum allowable discharge point.

In 2014, processed bilge water discharged from RCL ships averaged less than 1.5 ppm of contaminants – only a car-and-a-half in that 2,500-mile traffic jam.