- Modern cruise ships, accommodating thousands of passengers, produce substantial waste. While older practices involved dumping untreated sewage into oceans, contemporary ships treated sewage extensively before release.
- Treatment processes, including bioreactor aeration, membrane filtration, settlement, disinfection, and storage, ensure the removal of contaminants.
Cruise ships manage human waste (black water) and grey water through onboard treatment plants, ensuring safety and adherence to environmental regulations. Cruise lines are also addressing food waste, utilizing grinders and incinerators, with efforts to reduce wastage through technology and revised dining practices. Despite improvements, cruise ships still deposit treated sewage into oceans, prompting the industry to enhance sustainability measures, reports Cruise Mummy.
Treatment process
Cruise ships get rid of human waste by treating it extensively in an onboard treatment plant. Leftover solids are either processed once the ship returns to shore or incinerated onboard, while the treated liquids are then dumped in the ocean where suitable.
Black water – this is the heavily contaminated water from toilets and urinals
Grey water – this comes from drains, such as showers, basins, and baths – it’s still unclean water, but it doesn’t contain harmful sewage
Here’s the process that sewage goes through on a cruise ship in the onboard treatment plant
1. Bioreactor Aeration Chamber
The first step for sewage on a cruise ship is to enter an aeration chamber. This chamber is filled with bacteria that work to break down some of the organic compounds in sewage that contaminate it, removing them from the wastewater.
2. Membrane Filtration System
After aeration, the wastewater is passed through a filtration system which will capture a lot of the solid impurities. These solids are passed back through the aeration chamber to further break them down – the aim is to remove as much of the contaminants as possible through bacteria.
3. Settlement Chamber
In the settlement chamber, the remaining solid materials are captured. This is done via settlement – the sludge-like solids sink to the bottom of the chamber and are captured for further re-processing, while the liquids move into the next stage.
At this stage, all solid materials will eventually be removed from the sewage, once they have been passed through the first three steps multiple times. The solid matter will be a lot lower in volume than when it first entered the plant, and it will now be incinerated in a low-emission incinerator, minimizing the release of harmful chemicals. It may also be stored until it can be disposed of properly when the ship returns to port.
4. Disinfection Chamber
The liquids that remain following the settlement chamber are passed into a disinfection chamber where UV radiation is used to remove the remaining pathogens and chemicals. At this stage, the water is almost as pure as tap water, although you still shouldn’t drink it, since actual cruise ship tap water has to go through stringent, certified tests.
5. Storage Tank
Once the sewage has been completely processed, it will enter a storage tank until it can be disposed of, either on land or released into the sea at a safe distance from the shore.
A large cruise ship typically has 1.5 tonnes per day of food scraps to dispose of.
Each galley has a grinder that purees the food waste. Then, at night, when the ship is out at sea, the food waste is discharged into the ocean below the waterline. Fish and other marine animals often follow the ship, feeding on the scraps.
Sometimes, food waste collected on a cruise ship is treated through a dehydrator to remove moisture, and then once all liquid has been removed it is incinerated. This is considered the safest, most environmentally friendly option for cruise ship food waste.
To reduce the environmental impact of food waste (and the cost) cruise ships take great strides to minimize the amount of waste they produce.
It’s not just about how food waste is disposed of, too, but also how it can be reduced in the first place. After all, wasted food is wasted money from a cruise line’s perspective, so anything they can do to reduce the amount of wastage being created not only helps the environment but also helps their bottom line.
Some of the methods used to tackle food waste include:
1. Getting Rid of the Midnight Buffet
Just like skeet shooting, and hitting gold balls off the side of the ship, the midnight buffet is an old cruise line tradition that you don’t see on ships anymore.
It’s a nice idea – being able to pop along for some midnight snacks and choose from a wide range of foods – but realistically most guests were either asleep or still full from dinner, so the buffets would just create unnecessary waste.
Cruise ships do still have buffet restaurants but they tend to close between 8 pm and 10 pm on most ships. For those who get hungry later, there’s usually somewhere to grab a bit to eat later on, whether that’s a cafe or a small section of the buffet with a few sandwiches and cakes.
Some cruise lines including Carnival and Royal Caribbean have started to work with artificial intelligence technologies to help manage menu options and food production, in a bid to reduce wastage.
AI is still an emerging tech but if cruise lines can use it to predict when certain meals are going to be needed and to manage the freshness of ingredients, there could be some fantastic strides in the reduction of food wastage.
3. Charging for Additional Courses
In most cruise dining rooms you can order as many dishes as you want. Stuck between two or three options on the menu? You can just order them all.
Beyond wastage, cruise lines are also looking at other environmentally friendly technologies that could be better for the environment and either be more profitable in the future or ensure that people are still happy to cruise. Fuel technology advancements, such as Royal Caribbean’s investment in biofuel, are one of the prominent areas of research.
How Much Waste Is Dumped by Cruise Ships?
It’s worth clarifying that typically human waste refers to toilet water, but there are different types of water on a cruise ship that must be disposed of…
It’s estimated that an average cruise line dumps around 30,000 gallons of sewage into the ocean each day. Larger ships will be above this average, but specific figures are never released.
As a guide, a four-minute shower uses around 8 gallons, while a toilet flush uses just under 2 gallons. So for 3,000 guests, that’s one toilet trip and one four-minute shower each day – it’s not as much as it might sound.
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Source: Cruise Mummy
