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All You Need to Know About Graywater Discharge from Ships

Spoiler alert: it is some really gross stuff

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© sgbirch / Flickr

Ships generate waste like sewage and graywater as a normal part of operations. We all know what sewage is, but what about graywater? The International Maritime Organization defines it as “the drainage from dishwater, shower, laundry, bath and washbasin drains.” At first glance, this may not seem as bad as drainage from toilets (i.e. sewage), but surprise, it is! While people understand the dangers (and let’s face it, the general grossness) of untreated sewage, few realize that untreated graywater can be just as nasty.

In fact, the U.S. Environmental Protection Agency (EPA) reports that untreated graywater has similar characteristics to domestic sewage, and can even have higher concentrations of certain components. For example, fecal coliform concentrations in untreated vessel graywater are one to three times higher than untreated domestic wastewater! And graywater may contain harmful chemicals, pathogens, bacteria, metals, food waste and problematic nutrients.

So what does this mean for the marine environment?

Like sewage, graywater discharges into the marine environment can lead to oxygen depletion, spread pathogenic bacteria and viruses and increase nutrient levels in the surrounding ecosystem. Higher nutrient levels can lead to toxic algal blooms and dead zones that can cause harmful disturbances throughout food chains. People consuming food from the sea can contract a range of illnesses from contaminated waters, which is of particular concern in the Arctic considering the number of indigenous peoples whose diet is heavily dependent on marine species.

Where is graywater discharged in the ocean coming from?

While most ships generate graywater, passenger vessels are responsible for the majority of these discharges, since more people mean more sewage and graywater. The EPA found sewage discharge rates on passenger vessels to be 8.4 gallons per day per person, while graywater discharges total anywhere from 45 gallons per day per person to 65 gallons per day per person.

What is being done about this?

Essentially nothing. While international law regulates sewage discharges to some extent, there is no international law to regulate graywater. Ships can discharge untreated graywater in most waters of the world. My home state of Alaska is one of the few places that regulate graywater from large passenger vessels. Large cruise ships are bound by law to use advanced wastewater treatment systems to treat both graywater and sewage before discharging in state waters, and to meet sampling, reporting and monitoring requirements to ensure compliance. Even with these rules in place, cruise ships have been caught illegally discharging, and the funding for the monitoring that exposes violations is under threat.

What next?

The first step to action is education. Understanding that graywater is as nasty as sewage is a start. Once we gain that understanding, and demonstrate that treatment options exist, we will be steps closer to further regulating graywater. Ocean Conservancy will continue to work with our community partners and other stakeholders to ensure graywater is recognized and regulated as the not so pleasant discharge it is.

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