Hakai Magazine

Coastal science and societies

Ships off the coast of Fujairah in Gulf of Oman at sunset
The United Nations’ International Maritime Organization is taking steps to reduce the emission of harmful sulfur oxides from ships. Photo by Justin Kase zsixz/Alamy Stock Photo

Ships Scrub Up to Meet New Pollution Standard

A new international limit for sulfur emissions is prompting a shift toward a controversial technology.

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by Lina Zeldovich

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If you live in a coastal city with a large port, January 2020 might bring you a bit of fresh air. The ships arriving at your docks should be puffing out cleaner exhaust with significantly less sulfur.

The burning of ship bunker fuel emits gases called sulfur oxides (commonly called SOx), which can cause respiratory problems and lung disease and can react with the water in clouds to create acid rain. The United Nations’ International Maritime Organization (IMO) is lowering the maximum allowable sulfur content in bunker fuel from 3.5 percent to 0.5 percent, starting next year. This new, tighter limit will help avoid an estimated 570,000 premature deaths worldwide from 2020 to 2025, according to a study submitted to the IMO by Finland in 2016.

While this new limit may be good news for the health of people and the environment, the shipping industry is finding the deadline hard (and expensive) to meet. And some environmental organizations are questioning whether the cheaper solutions are safe for marine ecosystems.

One option for shipping companies is to switch to low-sulfur fuel. But shipping companies say this more refined fuel is expensive and still needs to be tested for safety and efficiency. Another option, approved by the IMO, is to install a scrubber: a device that uses either water or chemicals, or both, to turn sulfur oxides in exhaust into sulfuric acid, and then into disposable sulfate salts. With the deadline looming, says Christopher Fee, general manager of environment and sustainability at Oldendorff Carriers, some ship operators are scrambling to get in line for scrubber installation.

Scrubbers can also be a significant expense, particularly for smaller companies and ships. “[Our ships] cost 25 million dollars, so if you add a five-million-dollar scrubber on it, it changes things,” says Marc Gagnon, director of government affairs and regulatory compliance at Fednav Limited, a Canadian shipping company. Ram Vis, president and CEO of the international technology company Viswa Group, which manufactures scrubbers and tests fuels, says that a retrofit for a typical 290-meter-long bulk carrier such as a Panamax ship (which just fits through the Panama Canal) costs US $2-million. That’s cheaper, he notes, than the additional expense from a couple of years’ worth of low-sulfur fuel.

In part because of cost, some companies opt for open-loop scrubbers, which discard some of their waste water into the ocean en route. These are typically cheaper and smaller than closed-loop scrubbers, which store their discharge in tanks for disposal in port. Some ships simply don’t have space for that, Gagnon says. The Exhaust Gas Cleaning Systems Association reported that, of the 1,500 ship exhaust scrubbers installed or on order as of May 2018, 63 percent were open-loop.

But some countries, including China and Singapore, recently banned the use of open-loop scrubbers in their waters because of environmental concerns.

Lucy Gilliam, aviation and shipping officer at Transport and Environment, a Belgium-based environmental NGO, says that open-loop scrubber discharge may alter ocean water chemistry; prior studies have expressed concern over increasing ocean acidification. Plus, the discharge may contain heavy metals or other contaminants. There are many different models, she notes, and there isn’t enough research to compare them. “Not all scrubbers are the same and the industry hasn’t been good at sharing data,” she says. A German report to the IMO noted that “a significant quantity of chemical substances will be emitted to the marine environment” by open-loop scrubbers, and concluded that more effort should be taken to monitor scrubber discharge.

Industry-led organizations consider the technology safe. The Clean Shipping Alliance (CSA) 2020 tested the effluent from open-loop exhaust gas cleaning systems on more than 50 cruise ships and concluded the scrubbers were “effective and safe,” according to CSA executive director Ian Adams. Fee notes that “after sodium and chloride, sulfate is the most common naturally occurring ion found in seawater.” So, he says, “there is no cause for concern.” He adds that many other countries, like the United Kingdom and Australia, approve their use.

While the debate continues, shipping companies continue to install scrubbers, while also testing new, low-sulfur fuels, for the tens of thousands of ships in the global merchant fleet. “For a very large shipping line, with a global network, it makes sense to have a combination of these solutions,” says Giles Broom, spokesperson for the Mediterranean Shipping Company.