The Wolfson Centre for Bulk Solids Handling Technology

Fifty shades of grey and most of it plastic

(Posted on 09/05/18)

The industry must limit plastic pollution from grey water waste streams with the same regulatory control it has in place for sewage, says ACO Marine

Grey water, that is to say domestic waste other than sewage, is largely unregulated. Yet it can form the larger percentage of water discharged overboard by ships. On the other hand, sewage, which is arguably less environmentally harmful, is subject to very stringent regulatory control.

Grey water is defined as waste water from domestic or commercial sources that has not come into contact with toilet waste – typical sources of grey water are bathrooms, kitchens and laundry operations. Black water – sewage – is tightly regulated, by IMO and other bodies. But there are no international regulations for grey water discharge, and this is seen by many as a significant omission from the MARPOL convention.

There is a point of view that grey water is potentially more environmentally harmful than sewage. Black water, after all, is basically organic. But grey water can contain oils, fats, detergents, chemicals and greases, not to mention plastics.

Mark Beavis, Managing Director of ACO Marine, is mindful of the present outcry about plastic waste in the oceans, resulting from David Attenborough’s award-winning Blue Planet documentaries and other shocking depictions in the media of sea creatures rendered helpless by floating plastic and the ‘Great Pacific Garbage Patch’ – a floating island of plastic waste reputed to be twice the size of France.

“Scientific research has shown that even supposedly clean water contains significant amounts of microplastics and nanoplastics. Much of this results from the breakdown of larger plastic items. A lot has its origin in cleaning liquids and pastes, facial scrubs, toothpaste, shampoos and similar products. This is a relatively new phenomenon, but there is a move to ban the use of plastics in such products. Several countries, including the UK, have already prohibited the manufacture of toiletries and cleaning products containing plastic particles,” says Beavis.

“However, the fact remains that there is no international legislation to prevent the discharge of grey water waste into the oceans. Black water is regulated, but grey water is not. Some special areas – like the Baltic - have rules dealing with all types of waste from ships, but these are market-driven, not regulatory, as such.”

Beavis explains that the existing regulation, MEPC 227(64), although entering into force as recently as January 2016, effectively deals only with sewage effluent standards and treatment, and is itself based on outdated 1970s legislation.

“Even the revisions over the years have failed to address the issue of grey water,” he says. “We need to get up to date. The only way we can limit these harmful discharges from ships is by legislation, and this can only be introduced by the IMO with the support of manufacturers.”

He adds that this is not just a commercial initiative by ACO Marine: “All responsible manufacturers of water and waste treatment systems are singing the same song.”

The current media focus is on plastic pollution, but grey water from ships and other sources contains many other elements which can cause untold harm to the marine environment, and which need to be dealt with effectively before the waste water can be discharged. Laundry waste, for examples, contains fibres, which should be filtered out. But another one of oceans greatest enemies, according to Beavis, is grease.

“While MEPC 227(64) lays down requirements to limit the discharge of oils, there are no IMO standards for the separation of grease from galley water,” he says. “To my mind this is an oversight. The industry needs performance standards to work to, so that shipboard wastewater treatment systems can be optimised for effective grease separation.”

Earlier thinking was that simple grease traps would be sufficient. These are traditionally small in-line entrapment boxes with a weir to hold back floating grease and oils. Although they may work in land-based systems, they are still limited in dealing with neutrally buoyant substances, or denser solids which can pass under the discharge barrier. And, despite standards existing for land-based grease separators, there are none applicable to the more challenging application of a moving ship.

“In the current absence of any performance standards, responsible manufacturers need, as a minimum, to match or exceed the land-based standards,” says Beavis. “These are covered in DIN V4040-2/99, and rated at EN1825, or better still at EN1825+. These ratings define limits for lipoid content of any discharge from the separator.”

But such grease traps require opening, emptying and cleaning, often on a daily basis, a task which is often not undertaken frequently enough, if at all. “The only viable solution is to fit fully-enclosed self-cleaning grease separation technology which can be maintained by ships’ engineers in the same manner as other machinery,” adds Beavis.