Trace metals and PAHs discharge from ships with Exhaust Gas Cleaning System (EGCS)

With the new global sulphur shipping emission regulations of International Maritime Organization (IMO), remarkable increase of exhaust gas cleaning systems (EGCS) installations was noted recently. EGCS, also known as “scrubbers”, is an alternative technical solution reducing air emission of sulphur oxides, appeared as an attractive, less-expensive solution for many ship companies. EGCS allows ships to continue to use low-cost, high-sulfur heavy fuel oil (HFO) and consequently the shipping industry remains main market for HFO. In the scrubber, the ship exhaust gas is washed out by a high flow rate of the seawater and this process results in the effective reduction of sulphur air emission and in the discharge overboard into surrounding environments of a large amount of polluted washwaters. The resulting discharged washwaters contain a chemical mixture of acidifying and eutrophying substances and toxic pollutants such as heavy metals and polycyclic aromatic hydrocarbons (PAHs), which together with SOx are effectively washed out from the ship exhausts. The use of scrubbers generates thus a new stream of shipping liquid wastes, which will dominate metals and PAH discharges from ships. In this context, there is a growing need to elaborate and improve the methods for evaluation of pollutant discharge through scrubbers and the routine monitoring of this chemical pollution transferred from air to marine waters. In the present report the focus is given primarily on emission discharges of heavy metals and PAHs that is two groups of ship exhaust contaminants, which were less studied and regulated. In essence, the proposed method for scrubber emission discharge evaluation, is built on the same basis as approved methods developed for green-house gases (GHGs) and main shipping air pollutant emission inventories. In this respect, the proposed approach is based on the estimates using pollutant emission factors, washwater volumes and flow rates, assumed scrubber trapping efficiencies, ship fuel consumption and energy demand. The case study of the metals and PAHs discharge estimation is proposed for the model Ro-Pax ferry - one ship scenario and its real-world operation between two ports Marseille and Ajaccio (France). A larger scale projection is also presented, consisting of the potential pollutant discharges by EGCS of 11 Ro-Pax ships fleet also operating in the Gulf of Lion and the Ligurian Sea basins, between mainland France and Corsica. Furthermore, building on the recent work by Osipova et al. (2021) on the global assessment of the mass of washwater discharges from vessels using scrubbers, our report provides various scenarios of washwater and pollutant loads into French Exclusive Economic Zone (EEZ). The calculations are presented for the entire French EEZ as well as the French Mediterranean EEZ and its ports in the Gulf of Lion (GoL) and Corsica. It appears that in France about 75 % of scrubber washwater discharges occur beyond territorial sea of 12 nautical miles, whereas 15 % is released in the territorial seas (TS), 6 % in internal waters (IW) and 4% in their ports. The distribution of pollutant loads will follow washwater discharges. Pollutant quantities amounting to hundreds and thousands of kilograms of main metals (V, Fe, Ni, Zn) and PAHs discharged annually by a given fleet of 11 Ro-Pax ships into the Western Mediterranean Sea come into the same category as other large-scale environmental inputs and emissions of these compounds. The estimated annual EGCS potential loads to the Gulf of Lion and the Ligurian Sea compare to the amounts of vanadium, nickel and ƩPAH16 dumped with major oil spills or to the Rhone river annual flux of PAHs entering the Gulf of Lion. These estimates clearly indicate that ship scrubber washwaters may represent significant source of pollutants entering the western Mediterranean Sea