Holistic assessment of ship scrubbers, with emphasis on the marine environment

Doctoral thesis, 2024

The ocean is essential, providing life support, food and recreation and ocean economy is projected to grow, implying more human activities and ocean claims. A key player in ocean economy is the shipping sector, both as an industry on its own and as a prerequisite for the development of other ocean-based sectors. The daily operations of a ship exert multiple pressures on the environment, affecting climate change, human welfare and ocean health.
As shipping can trigger change in environmental state which may cause negative impact on both the environment and human welfare, there is a need to get a complete perspective of the environmental impacts associated to ship activities. The DAPSIR framework offers a structured approach to assess the cause-effect relationship of society (Drivers, Pressures), environment and human welfare (State, Impact) and policy (Response). The overall aim of this thesis is to assess pressures, changes in environmental state and impacts on the marine environment following the wide-scale use of scrubbers, an aftertreatment technology to reduce sulphur oxide emissions to the atmosphere by spraying the exhaust with (sea)water, producing large volumes of heavily acidified and contaminated water that is discharged to the marine environment.

The results show that, in comparison to the use of distillate fuels, ships running on residual heavy fuel oil with a scrubber have much higher emissions of metals and polycyclic aromatic hydrocarbons (PAHs) (Paper I) and the discharge of scrubber water can result in one of the largest anthropogenic pressures of certain metals and PAHs on the marine environment (Paper II). When multiple shipping activities are included in the impact assessment, results show that three out of four ports are subject to unacceptable cumulative environmental risk and that scrubber water discharge and leakage of copper from antifouling paint have the largest contribution (Paper III). By applying computational models to fill the experimental ecotoxicological data gap, the risk and impact assessment of substances commonly found in scrubber water could be extended. Examples of substances, previously unaccounted for, are alkylated PAHs that show substantial contribution to the toxicity and environmental risk associated to scrubber water (Paper IV). The economic perspective shows strong economic incentive to install scrubbers, with potentially high socio-economic costs related to the discharge of hazardous substances in scrubber water discharge (Paper V).

It is possible to quantitatively assess activity, pressure and state, while extending the analysis to impact is a challenging task. Despite the challenges, the results from this thesis show that the use of scrubbers is not a sustainable technology and that the use of scrubbers could favour lock-ins in unsustainable patterns of development, enabling the continued use of residual heavy fuel oil.