EXISTING guidelines for scrubber operations need to be reviewed and strengthened with a view to banning the sulphur abatement technology altogether, a study by the International Council on Clean Transportation concludes.

The council’s November 2020 assessment of air emissions and water pollution discharges from ships with scrubbers found that the technology substantially reduced sulphur dioxide emissions.

However, carbon dioxide, particulate matter and black carbon emissions were higher than using marine gasoil and there was no guarantee that scrubber discharges, while compliant with International Maritime Organization guidelines, were safe, the report said.

The Washington DC-based organisation recommended that governments take unilateral action to ban the use of open-loop and closed-loop scrubbers in their jurisdictions. Some 29 countries have already taken this step.

The council also called for a scrubber ban on newbuildings, harmonising of rules for scrubber discharges, and for the equipment to be phased out on existing vessels.

Some 4,300 vessels have scrubbers installed. That allows them to use cheaper, higher-sulphur fuel oil while still remaining compliant with international regulations introduced on January 1 that mandate lower-sulphur marine fuel used by the international merchant fleet.

“Scrubber discharges from both open-loop and closed-loop systems usually comply with IMO guidelines,”  the report said. “We question whether complying with the IMO guidelines should be taken as evidence that scrubbers are doing no harm to the aquatic environment.”

The review cited a 2019 study that found some 35m tonnes of scrubber discharge water was emitted off the British Columbia coast, some 90% from cruiseships.

Even though some scrubbers were so-called ‘closed loop’ and stored sludge waste, it ultimately ended up in landfill as hazardous waste, according to the ICCT.

“Scrubbers can substantially reduce SO2 emissions, with emissions from ships using 2.6% sulphur Heavy Fuel Oil with a scrubber averaging 31% lower than 0.07% sulfur Marine Gasoil,” the study said.

“We also found that scrubbers seem to somewhat reduce CO emissions by 11% on average, although the mechanism by which this occurs deserves further investigation.

“For other pollutants, including CO2, PM, and BC, using HFO with scrubbers results in higher emissions than Marine Gasoil.

“Average CO2 emissions were 4% higher using HFO with a scrubber compared with MGO. On a life-cycle basis, well-to- wake CO2 emissions are expected to be 1.1% higher than using MGO.”

The ICCT said that the IMO had opportunities to strengthen scrubber discharge guidelines in 2009, 2015 and 2020 but member states declined, citing too little scientific evidence to revise them.

“We recommend that individual governments continue to take unilateral action to restrict or prohibit scrubber discharges from both open-loop and closed loop systems,” the report said.

“We also recommend that the IMO focus on harmonizing rules for scrubber discharges including where, when, and even if those discharges should be allowed, and to do so with urgency.

“The IMO should consider prohibiting the use of scrubbers as a compliance option for newbuild ships and work to phase out scrubbers installed on existing ships. This is because we have found that using HFO with scrubbers is not equivalently effective at reducing air pollution compared to using lower sulphur fuels, such as MGO.”

Environment and Climate Change Canada funded the study.