What Happens to Food Waste on a 4,300-Passenger Cruise Ship?

On a lower deck of the 4,300-passenger Sun Princess, the latest and largest addition to the Princess Cruises fleet, I’m exploring a behind-the-scenes area where massive stainless steel 'stomachs' grind and use bacteria to break down food waste, transforming thousands of pounds of leftovers into a thick, environmentally friendly slurry. Meanwhile, another large machine, nicknamed the 'Hungry Giant' by the crew, dehydrates bones, fruit peels, and other items that would ruin a home garbage disposal, turning them into a substance resembling coffee grounds.

The odors in the disposal zones match what you’d expect from the remnants of meals served at the ship’s 30 restaurants and bars. The sounds resemble a bustling laundromat. Together, these cutting-edge technologies significantly lessen the environmental impact of food waste on the ocean and what is sent to landfills.

Cutting Down on Food Waste Begins with the Cruise Ship Menu

Princess Cruises’ parent company, the nine-brand Carnival Corporation, is committed to minimizing food waste as part of its sustainability initiatives—an effort echoed across cruise lines, all striving for ambitious climate goals in the coming years. Proactive measures include reducing the volume of leftovers, utilizing AI technology to monitor and assess guest dining patterns. Crew members also keep a close eye on what’s left on plates, enabling unpopular dishes to be removed from the menu.

Sami Kohen, the vice president of food and beverage at Princess Cruises, emphasizes that minimizing food waste starts with the selection of dishes served and their presentation. He was aboard the Sun Princess in late April for a voyage from Rome to Barcelona, just like I was.

On the new ship, featuring a magnificent glass dome above an indoor/outdoor pool, an intimate theater for circus acts, and a family-friendly amusement area, guests can savor exquisite sushi and premium beef in specialty restaurants (for an additional fee). Additionally, revamped dining room menus, developed in partnership with chefs from the Culinary Institute of America, offer diverse culinary experiences. An all-American diner serves breakfast all day among other options.

Kohen argues that providing enticing culinary styles and varied cuisines throughout the ship helps cut down on waste. “You consume what you crave at that moment,” he remarks.

Behind the scenes, the waitstaff and kitchen team sort leftover food into color-coded containers (vegetables in one, meat with bones in another), which are then weighed to monitor food waste levels. Kohen states, “On this ship, we are taking greater strides to minimize food waste than any hotel in Las Vegas.”

Innovative food waste disposal techniques on the new cruise ship

With thousands of passengers and crew on board, leftovers are inevitable, which is where the cutting-edge biodigester machines come into play. Carnival Corporation officials noticed these machines in hotels and event spaces a few years back and realized their potential for maritime use.

The biodigesters—13 of which are installed on the Sun Princess—function like human stomachs, utilizing a natural bacterial process to decompose uneaten food. This not only significantly reduces the volume of waste but also lessens the ocean's burden for food waste breakdown. Additionally, the company has substituted plastic balls previously used to cultivate and disseminate bacteria in the digestion process with more natural peach pits. The resulting mixture is mostly decomposed when released at sea; international regulations permit cruise ships to dispose of ground food waste at least 12 miles from shore.

These machines operate around the clock. “The digesters need constant feeding, just like your own stomach,” explains Biagio Del Vecchio, environmental officer on the Sun Princess.

For more challenging solid foods like bones, animal fats, and fruit and vegetable skins, Carnival Corporation has recently introduced dehydrators—over 60 are now in operation across the Carnival fleet of more than 85 ships. These dehydrators use heat to eliminate excess moisture from leftover food, resulting in a dry mass resembling coffee grounds, which can be conveniently disposed of on land. Carnival Corporation claims that these dehydrators can reduce food waste offloaded by up to 90 percent. Although the odorless grounds are currently sent to landfills, there are plans to explore repurposing options, such as using them as a sustainable energy source or as fertilizer.

The Outcomes

Through its food waste management technology and various initiatives, Carnival Corporation reports a reduction of over 40 percent in food waste per person compared to a 2019 baseline, already surpassing its 2025 targets. The company aims for a 50 percent decrease per person by 2030, also based on the 2019 figures.

The Sun Princess, which navigates the Mediterranean during the summer and the Caribbean in the winter, is the first ship in the Princess Cruises fleet to operate on liquefied natural gas (LNG), recognized as the cleanest-burning fossil fuel available at scale. Furthermore, the vessel is designed to adapt to alternative fuels as they emerge, demonstrating that significant progress is achievable, even among the world’s largest cruise ships.