Scrubbers on ships: Time to close the open loop(hole)

In January 2020, the International Maritime Organization (IMO) reduced the maximum allowable sulfur content in shipping fuel from 3.5% to 0.5%, except for ships that use exhaust gas cleaning systems, commonly known as scrubbers. By significantly reducing air emissions of sulfur oxides, this policy is expected to improve air quality and save, conservatively, tens of thousands of lives per year. However, more than 4,000 ships have installed or ordered scrubbers to avoid using cleaner, but more expensive, low-sulfur fuels. The figure below illustrates the recent, dramatic increase in the number of ships that are using or intend to use them.

Figure 1
Ships with scrubbers installed or on order. Source: Data from DNV GL Alternative Fuels Insight Platform

This year, about 16% of container ships, representing 36% of container carrying capacity, will have scrubbers installed; the same will be true for 15% of bulk carriers and one in ten oil tankers. What’s the issue? Well, as my colleague Elise Georgeff explains, scrubbers generate contaminated washwater that’s usually dumped overboard, and this raises questions about whether or not scrubbers should be allowed.

Indeed, a growing number of governments have restricted or banned the use of scrubbers, especially in high-traffic areas like ports and canals. For now, though, scrubbers are a legal alternative to compliant fuels in most parts of the world. As I’ll explain, this is a loophole that needs to be closed. Below I lay out a four-step approach that starts by reducing water pollution from the scrubbers we already have and ends with phasing them out completely.

But first, let’s briefly review how different scrubbers work and the risks they pose. Scrubbers come in three varieties: open-loop, closed-loop, and hybrid. Open-loop systems suck in seawater, spray it into the exhaust, and discharge it overboard, often without treatment. Instead of using seawater, closed-loop systems have a tank of alkaline-dosed freshwater onboard. After it is sprayed into the exhaust, the water is filtered to remove solid particles and then recirculated, with a small amount of “bleed-off” water discharged overboard. Hybrid scrubbers can be operated in open-loop or closed-loop mode. About 80% of scrubbers installed on ships are open-loop. Hybrid scrubbers account for about 17% and closed-loop scrubbers account for less than 2%. Open-loop scrubbers are the most popular because they are the least expensive to install and operate. Hybrid scrubbers cost more, but provide a bit of insurance against local restrictions on open-loop scrubber discharges, as they can be switched to closed-loop or zero-discharge mode. Mainly, ships use hybrid scrubbers in open-loop mode to avoid collecting and storing scrubber sludge, which needs to be disposed of on land, for a fee of course. Closed-loop systems are the most expensive and, unlike open-loop systems, continuously collect and store scrubber sludge that must be removed from the recirculating washwater.

Further, despite IMO’s scrubber discharge guidelines for pH, temperature, polycyclic aromatic hydrocarbons, turbidity, and nitrates, studies are showing that scrubber washwater and the pollutants it contains damage ecosystems and harm wildlife. A new study estimates that if 15% to 35% of the fleet (by gross tonnage) operating in the English Channel and the southern North Sea were equipped with open-loop or hybrid scrubbers, each year the pH would drop by between 0.004 and 0.010 pH units, about as much as the ocean acidifies in two to four years due to climate change. Near Rotterdam, the pH decrease was estimated at up to 0.088 pH units per year, which would normally take between 30 and 50 years from climate change.

According to our recent study focused on Canada’s Pacific coast, in 2017, 30 scrubber-equipped ships dumped 35 million tonnes of contaminated washwater near British Columbia, including 3.3 million tonnes within the designated critical habitat for threatened and endangered killer whales. Cruise ships were responsible for 90% of these discharges. Since 2017, the government of Canada more than doubled the size of resident killer whale critical habitat. Under the revised definition, 5.1 million tonnes of washwater were dumped inside these areas. (In the next year, the ICCT will estimate total scrubber washwater discharges worldwide.)

Without a global prohibition, we can expect more and more ships to take advantage of the cost savings of open-loop scrubbers, even if the pace of scrubber installations is temporarily slowed by the coronavirus outbreak. This is because, despite local restrictions, oceangoing ships spend the majority of their time on the high seas, where fuel cost savings quickly accrue. At its next Marine Environment Protection Committee meeting, which could be held virtually later this year, the IMO is expected to approve a new workplan focused on harmonizing the rules for scrubber washwater discharges. This is an opportunity for IMO to decide when, where, or even if scrubber discharges should be allowed.

Here’s my proposal for how IMO should proceed under a scrubber workplan:

Step 1. Prohibit new scrubber installations. No new or existing ship should be allowed to install a scrubber if they don’t already have one installed. All ships should use fuels that comply with the IMO 2020 sulfur regulations.

Step 2. Convert existing open-loop scrubbers to closed-loop. This would allow shipowners who have already spent millions of dollars on scrubbers to continue to use them, but would also dramatically reduce the amount of polluted water that’s dumped overboard. Closed-loop systems discharge less than 1% as much as open-loop systems, but this bleed-off water is acidic and contains a higher concentration of pollutants. So closed-loop scrubbers still pollute.

Step 3. Prohibit closed-loop bleed-off water discharges in places that should be protected. Ships with scrubbers should operate in zero-discharge mode when they are in places that governments agree should be protected. These might include critical habitats for threatened and endangered species, marine protected areas, particularly sensitive sea areas, estuaries, near-shore areas, or in ports.

Step 4. Phase out existing scrubbers over time. Ships with scrubbers do and will continue to have a market advantage over ships without because the fuel cost savings of using high-sulfur heavy fuel oil outweigh the capital, operating, and maintenance costs of the scrubber. If new scrubber installations are prohibited, then it’s only fair that existing scrubber installations be phased out. The IMO should agree on a timeframe for phasing them out.

Except for local restrictions, these changes will require IMO member states to amend the International Convention for the Prevention of Pollution from Ships, better known as MARPOL. This process will take several years to negotiate and, if agreed, an additional two years to become enforceable. In the meantime, countries, states, and ports can prohibit the use of scrubbers in the waters they control. Scrubber washwater discharges are already prohibited in all or parts of China, Singapore, several European countries, the Suez and Panama Canals, California, Connecticut, Hawaii, and in major ports such as Fujairah.

While local actions are a good start, they are not sufficient. The four steps above can serve as a recipe for uniform, global action on scrubbers that closes the open loophole.

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