It may not be the first thing that comes to mind when you think about cruise ships, but those giant vessels generate a lot of wastewater. Much of that is greywater: liquid waste from things like showers, laundry facilities, dishwashers, bath and washbasin drains.

Greywater may not sound as concerning as sewage (the drainage from toilets and urinals), but a report from the U.S. Environmental Protection Agency (EPA) concluded untreated greywater has similar characteristics to domestic sewage and can even have higher concentrations of certain pollutants. For example, fecal coliform concentrations in untreated vessel greywater are one to three times higher than untreated domestic wastewater! Even worse, unlike sewage, the discharge of greywater is not regulated in most parts of the world, meaning ships can discharge greywater directly into the ocean, without any form of treatment.

Fortunately, that’s not the case in Alaska. Alaska has required both sewage and greywater of large passenger vessels to be treated by Advance Wastewater Treatment Systems (AWTS) for almost 20 years. In that time, the state has sampled greywater and sewage discharge from passenger vessels in its waters.

Ocean Conservancy worked with an outside expert to analyze 19 years of data from Alaska’s sampling program. Earlier this year, we released the results of that analysis in a new report that summarizes lessons learned and offers recommendations for both research needed moving forward and how to improve greywater management both in Alaska and internationally.

What are the report’s conclusions?

First, greywater is gross and cruise ships discharge a lot of it.

Sampling in Alaska confirms that untreated greywater contains bacteria, nutrients, solids and a variety of pollutants, some at levels as high as or higher than raw sewage. These concentrations are high enough to impair human and environmental health. Data reported by ships in Alaska also show that ships discharge greywater at much higher volumes than sewage. Greywater discharge is often eight to 12 times greater than sewage discharge.

Second, advanced wastewater treatment systems can work well.

The required AWTS systems on large vessels are very effective at treating greywater. After ships were required to treat greywater with an AWTS, their fecal coliform levels generally tested below the detection limit. Similarly, solids and nutrients were removed at a high rate.

Third, good results are not automatic.

The mere presence of an AWTS on a ship does not necessarily mean ships treat wastewater to the Alaska standards at all times and in all places. AWTS must be maintained and monitored to ensure good results. The data support the need for performance monitoring of greywater treatment. The data also show that non-AWTS treatments—used by many small cruise ship vessels—have greater variability in their test results.

What next?

With its greater volume and high values of pollutants and bacteria, it is concerning that greywater, unlike sewage, is not regulated internationally or even nationally in many parts of the world.

Data from the Alaska program shows greywater can be treated to safe levels for discharge. Performance monitoring through a sampling of greywater and sewage discharges in Alaska can be used as an example for future requirements on greywater elsewhere in the world.

One important step is to ensure the International Maritime Organization (IMO)—the UN body that regulates international shipping—takes action to address and regulate greywater. The IMO regulates other forms of waste from ships including sewage, ballast water and exhaust gas cleaners. Greywater—with its high levels of bacteria and nutrients and potentially toxic substances—merits the same level of attention. While achieving IMO regulation of greywater will take years of work, Ocean Conservancy will continue to push the importance of such a measure.