Scrubbers: Closing the loop; Activity 3. Task 2; Risk assessment of marine exhaust gas scrubber water.

In response to regulations on permitted levels of sulphur emissions from ships an increasing amount of ships are expected to become equipped with exhaust gas cleaning systems, so called scrubbers. The use of scrubbers makes it possible to continue to use high sulphur fuel oil on board. In the scrubbers, the exhaust gases are washed with a scrubber fluid aiming at reducing levels of sulphur dioxide. The fluid passes the exhaust gas once (“open loop scrubber”) or is recirculated (“closed loop scrubber”). This study investigates the potential impact of the discharges from open and closed loop scrubbers on marine ecosystems.

Samples were taken of effluent water from ships with closed loop and open loop scrubbers. The water from closed loop systems is treated before discharge to the marine environment. The waters were tested for toxicity using experimental studies with field collected zooplankton and bottom-dwelling blue mussels. Zooplankton were found to be more sensitive than mussels. A subsequent risk assessment based on the toxicity results and data on discharged volumes together with a simple and static model on mixing in sea water showed that the issue needs further attention specially to protect sensitive and enclosed areas with heavy ship traffic.

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Last updated: 2021-05-05

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