The Challenge of Reducing the Sulfur Oxides Emission in the Maritime Transport: Risks Derived from the Discharge of the Scrubber Washwater into the Marine Environment

The emission of sulfur oxides into the atmosphere is one of the major concerns derived from the maritime transport. To reduce their impact on the environment and the human health, the last update of the MARPOL Annex 6 established a limit of 0.5% of sulfur in in the fuel as of 2020. Nevertheless, ships can use fuel with higher sulfur content if they are equipped with an exhaust gas cleaning system, also known as scrubber. In the case of open-loop scrubbers, seawater is put in contact with the exhaust gas and then released into the ocean. This washwater absorbs the sulfur oxides efficiently, as well as other substances such as polycyclic aromatic hydrocarbon (PAHs), and increases int temperature by the contact with the hot exhaust gas. For this reason, the discharge of the washwater may concern to the aquatic environment and compromise the human activities. The objective in this study is to analyze the data recorded by the Continuous Emission Monitoring System of a ship during a series of commercial voyages, with the purpose of determining the potential threats derived from the discharge of scrubber washwater into the ocean. Data revealed that the washwater was discharged at pH below 4, a concentration of PAHs greater than 13 µg/L and temperature 7 °C greater than the recipient seawater. The discharge of washwater is especially concerning during the arrival and departure maneuvers, due to the releasing of acid, PAHs enriched and hot water into enclosed water bodies.