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Discharges from exhaust gas cleaning systems on ships

This information sheet summarises the key findings of an environmental risk assessment of scrubber discharges in New Zealand waters. The study was conducted in two phases between 2020 and 2021 by the National Institute of Water and Atmospheric Research (NIWA) on behalf of the Ministry for the Environment.

This information sheet summarises the key findings of an environmental risk assessment of scrubber discharges in New Zealand waters. The study was conducted in two phases between 2020 and 2021 by the National Institute of Water and Atmospheric Research (NIWA) on behalf of the Ministry for the Environment.

Some large international ships use exhaust gas cleaning systems (scrubbers) to reduce the emissions of contaminants, including sulphur oxides, to the air.  Scrubbers can create a washwater, (‘open loop’ systems) or in some cases a concentrated ‘bleed off’, (‘closed loop’ systems) which is then discharged to the marine environment. Some hybrid systems are also in use and can produce either type of discharge. 

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