Dark Water: Thanks to exhaust scrubbers, while ships are polluting the air less, their water-pollution footprint is rising

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May 19, 2021 6:45 AM

As India embarks on its Sagarmala programme, it will need to keep in that it can’t allow one kind of pollution to mutate into another in the name of green action.

Against this backdrop, as India embarks on its Sagarmala programme, it will need to keep in that it can’t allow one kind of pollution to mutate into another in the name of green action.

A move to reduce pollution of the air by ships, ironically, seems to be driving up water pollution, notes a report in Science. Sulphur from ships’ exhaust is a significant contributor to ozone depletion. International Maritime Organization’s (IMO’s) Suplhur 2020 vision estimates that the capping standards for sulphur content in ships’s fuel will lead to a 77% drop in overall sulphur oxide emissions from ships—an annual reduction of 8.5 million tonnes of SOx.

On January 1, 2020, the IMO, a UN body, started the enforcement of a rule banning sulphur-heavy fuel. Since sulphur-light fuel can be very expensive, it allowed ships to install exhaust scrubbers that use high-volume, high-speed, water spray to absorbs pollutants from the exhaust.

There are two types of scrubbers—open-loop ones that dumps the scrubber wastewater into the sea/at the port and closed loop ones that treat the wastewater before dumping. A the time of adopting the new norms, it was hoped that more ships will get fitted with closed-loop scrubber systems.

While the ban on sulphur-rich fuel has driven up fitting of scrubbers—250 ships in 2015 versus 4,300 ships in 2021—data from early last year showed the scrubbers were overwhelmingly open-loop. Both kinds of scrubbers have led to the dumping of 10 gigatons of scrubber wastewater containing dangerous pollutants and toxic chemicals, including carcinogenic hydrocarbons.

This has endangered not just sensitive marine ecosystems along the most popular sea routes, but also threatens human health through seafood-consumption. Against this backdrop, as India embarks on its Sagarmala programme, it will need to keep in that it can’t allow one kind of pollution to mutate into another in the name of green action.

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