Capturing carbon dioxide "at source" to combat pollution caused by maritime transport. The trial launched in recent months at the ports of Los Angeles, Long Beach and Oakland by Californian startup Stax Engineering has attracted considerable interest — a test that many have already described as a "breath of fresh air in the fight against maritime pollution". We are talking about a barge several tens of metres long equipped with a flexible 90-metre arm that captures and filters the exhaust gases of container ships docked in port.

A solution that works almost like an enormous kitchen extractor hood where the harmful emissions generated by the engines are drawn into the barge's filtration system through a network of pipes, filters and pumps — a solution that could represent an effective way to reduce the environmental impact of maritime transport.

The barge removes 99 per cent of the particulate matter emitted by ships

The system is powered by low-sulphur diesel and is designed to capture and filter exhaust gases not only from large ships but also from cars, removing 99 per cent of particulate matter and 95 per cent of nitrogen oxide. The filtration process ends with the release into the air of a mixture that includes low levels of CO2 and water vapour.

Once fully operational, the system could represent a significant step forward in the fight against maritime pollution. At least for as long as the enormous container ships (up to 400 metres in length) remain docked in port. Which is precisely where pollution causes the greatest damage, affecting major American port cities such as Los Angeles, Long Beach and Oakland, through which approximately half of all United States container imports pass.

California's regulations to reduce maritime transport emissions

According to the Environmental and Energy Study Institute, the ports of Los Angeles and Long Beach alone (practically a single entity, given that they are separated by just a handful of kilometres) produce around 100 tonnes of pollutants per day, an amount greater than the emissions of 6 million cars. An enormous figure, which prompted the California Air Resources Board to issue regulations requiring certain ocean-going vessels to reduce their emissions by at least 80 per cent while at berth.

The most viable solution currently available remains connecting ships to onshore electrical power via a dedicated cable (cold ironing), which would allow diesel engines to be switched off during port stops, thereby improving air quality with a significant reduction in local emissions. Implementing the technology and setting up the infrastructure to electrify port quaysides "is a challenge that will take time," said Mario Cordero, chief executive of the port management company of Long Beach. Ships, as well as terminals, must in fact be adapted to allow shore power connection, requiring substantial investment. The solutions being examined to reduce the impact of maritime transport are numerous.

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According to CEO Mike Walker, the alternative already available to cold ironing could be the aforementioned Stax system, adaptable to all those ships that are not yet set up for a plug-in connection to onshore power sockets; it is estimated that currently only around 15 per cent of the container ships docking in the United States could adopt this solution.

In the ports of Los Angeles and Long Beach alone, where the Stax system is being trialled, the CO2-capturing barge could, once fully operational, reduce emissions from up to 140–150 ships per year. A small figure compared with the almost four thousand merchant and passenger vessels that dock at these terminals every year.

The alternative? Capturing carbon dioxide from ships on the open sea

While the CO2-capturing barge in California is delivering good results, work is also under way in Italy in this direction. Ecospray, an Italian company specialising in integrated solutions for the sustainable reconversion of maritime and land-based industries, has developed a filtration system that acts on the capture and storage of CO2 from ships — in this case not while docked at the quayside but during navigation.

In this case the research focuses on two technologies that act on the chemical absorption of carbon dioxide exiting from ships' funnels through the use of amines or calcium hydroxide. In both cases these are solutions that make it possible to capture up to 80 per cent of the CO2 emitted while under way, as demonstrated by a test carried out in 2023 on a commercial vessel after two years of trials.

The choice between which of the two technologies for CO2 capture developed by Ecospray is more effective also depends on the type of vessel and the characteristics of the route it must travel. The impact of maritime transport is a significant factor in the context of global mobility: based on data provided by the European Union on the emissions of ships that have operated within the Community area, a vessel of 6,000 gross tonnes emits almost 7 million tonnes of CO2 in a year.

Taking into account the data provided by Brussels, according to which around 10,800 ships of over 6,000 gross tonnes operate worldwide, Ecospray estimates that it would already be possible to capture up to 2,000 tonnes of CO2 per single voyage.

The ocean is the planet's largest carbon reservoir

Oceans absorb around 25–30 per cent of global CO2 emissions. While on one hand this phenomenon purifies the air and limits global warming, on the other it leads to an increase in water acidification. Among the possible solutions to address the problem is a pilot project to capture carbon dioxide from seawater. In practice this involves a system capable of providing solutions for the liquefaction of CO2 in collaboration with Captura, a United States company founded within the California Institute of Technology (Caltech). Captura in turn is collaborating to build a pilot CO2 capture system of one thousand tonnes per year at the Equinor facility in Kårstø, on the western coast of Norway.

Delivery of the liquefaction system by Ecospray for the pilot plant is scheduled for the third quarter of 2024. Here is how it works: once the CO2 has been captured, the seawater is removed, liquefied and purified using Ecospray technology. The same will then be used for the commissioning of the Northern Lights facilities, the world's first open-source infrastructure offering CO2 transport and storage services.