The maritime sector faces increasing regulatory pressure to mitigate sulphur oxides (SOx) emissions, necessitating innovative solutions to minimize environmental impacts. Over recent years, exhaust gas cleaning system (EGCS or “scrubber”) technologies have been extensively studied to mitigate SOx emission, however, yet gaps remain in optimizing scrubber washwater treatment processes to minimize marine pollution. This study examines advanced scrubber washwater treatment technologies deployed on a cruise ship, emphasizing their role in aligning with international standards while preserving marine ecosystems. Using operational and laboratory data, the research evaluates key parameters, including pH, heavy metals, and hydrocarbons, under varying voyage scenarios. Results highlight the efficacy of multi-stage filtration systems, achieving significant pollution reduction and compliance with the MARPOL Convention guidelines. The findings provide actionable insights for sustainable maritime practices and policy formulation.