The SAARUS project, funded under the German federal research grant 03SX483A from 1 June 2019 to 30 November 2022, aimed to optimise marine scrubber technology for the reduction of harmful ship emissions. The consortium combined the industrial expertise of SAACKE GmbH in Bremen, a leading manufacturer of wet scrubbers, with the scientific capabilities of the Chair of Piston Engines and Combustion Engines at the University of Rostock. SAACKE supplied the scrubber unit, its control system and the necessary measurement instrumentation, while the university provided the 1‑cylinder research engine, a dedicated test rig, and the analytical facilities for exhaust sampling and data analysis. The project was coordinated through regular on‑site visits and online meetings, and a cost‑neutral extension of the project period was granted to accommodate delays caused by the COVID‑19 pandemic, allowing the third measurement campaign to be completed successfully.

Technically, the project achieved the scaling and installation of a full‑scale wet scrubber on the research engine, including a sampling station in the sump, a wash‑water tank, and storage for the collected water. Two measurement campaigns (MK 2 and MK 3) were conducted to evaluate the scrubber’s performance under realistic operating conditions. The scrubber’s SO₂ removal efficiency was investigated by varying the packing material in the wash tower and by testing configurations without packing. The influence of the quench process on the removal rate was also quantified. These studies demonstrated that the choice of packing and the quench strategy significantly affect the required wash‑water volume and the overall space requirement of the scrubber, providing a basis for future optimisation of marine installations.

Particle removal was a central focus of the study. While wet scrubbers are known to reduce total suspended particulates (TSP), the fine‑particle fraction (≤ 0.5 µm) remains largely unremoved. The project measured a mass‑based particle removal efficiency of approximately 80 % for the overall particulate load, but the target of 90 % removal for particles with a cut‑size of 0.2 µm was not achieved. Detailed size‑distribution analyses revealed that particles in the 0.1–1 µm range, which are considered highly toxic, were largely retained in the exhaust stream. Consequently, the consortium investigated a range of downstream filter technologies—both electrostatic precipitators and mechanical filters—to capture the fine‑particle fraction that the scrubber alone cannot remove. Preliminary results indicate that the addition of a post‑scrubber filter can bring the overall fine‑particle removal close to the desired 90 % threshold, although this adds complexity and space requirements to the system.

In addition to SO₂, the scrubber also reduced other regulated pollutants such as NOₓ, volatile organic compounds (VOCs), and particulate matter, contributing to lower atmospheric emissions in compliance with IMO MARPOL Annex VI regulations. The project’s findings highlight that while wet scrubbers effectively mitigate sulfur oxides, their ability to control fine‑particle emissions is limited, underscoring the need for integrated solutions that combine scrubber technology with efficient downstream filtration. The collaboration between SAACKE and the University of Rostock successfully bridged industrial implementation and academic research, delivering actionable data that can inform the design of future marine emission control systems and support the development of regulatory standards for fine‑particle emissions from ships.