Study ‘puts to bed the myth’ about open-loop scrubbers

Indeed, scrubbers are seen as critical systems in bridging the gap to carbon-neutral fuels in shipping’s decarbonisation.

A scrubber system reduces SOx emissions from combustion engines to air by spraying alkaline water into the exhaust gas flow. An open-loop scrubber uses the natural alkalinity of seawater for neutralising the exhaust emissions, and the drained wash water containing the washed-out substances and particles are discharged into the sea, sometimes after filtering and buffering with seawater. Scrubber water monitoring equipment is used to verify the discharge water complies with discharge standards for PAH, turbidity and pH.

The study, Ecotoxicity testing and risk assessment of wash water from open loop scrubbers, addresses the concerns that the discharge water from scrubbers, while infinitely low in concentrations of substances that might be considered hazardous, ’might’ produce an unexpected toxic cocktail.

DHI was appointed to undertake the ecotoxicity assessment in accordance with GESAMP guidelines. DHI is an independent and not-for-profit organisation that specialises in water quality assessments and operates globally. To date, DHI has dealt with over 50% of the US Coast Guard requirements for ballast water management system approvals.

Ecotoxicity is a GESAMP requirement for assessing the risk arising from toxic substance preparations in BWMS and also in anti-fouling systems.

Discharge water was taken from four ships operating in northern Europe with open-loop scrubbers. The samples were homogenised and presented to different levels of marine organisms including algae and crustaceans in a stepwise process, culminating in testing the toxicity with fish. The steps towards assessing the possible toxicity to fish were possible because at no stage were the measured assessment parameters exceeded.

The final step in the risk assessment is the translation of the data to the real-life situations of several scrubbers discharging into a port or into a busy sea lane. In all cases, the risk of ecotoxicity was well below the unacceptable level.

Mr Gregory commented that the study gives certainty to ports, harbours and other authorities about the acceptability of operating open-loop scrubbers in their jurisdictions. EGCSA is seeking partnerships with ports to undertake more studies to provide ongoing assurance that ecotoxicity of the open-loop scrubber wash water remains at a safe level to discharge into the marine environment.

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