TEXTE Environmental Impacts of Exhaust Gas Cleaning Systems for Reduction of SOx on Ships — Analysis of status quo 
Report compiled within the framework of the project ImpEx 
Den Boer and Hoen (2015) describes that NOx emissions from diesel engine exhaust gas 
typically consist of 90-95% nitrogen monoxide, which is insoluble in water, while the nitrogen 
dioxide fraction is soluble in water. Therefore, during the scrubbing process only 5-10% of the 
NOx from the exhaust can be removed (Den Boer and Hoen, 2015; United Kingdom, 2006). 
In the report of the GESAMP Task Team (Linders et al. 2019), it is stated that most of the 
reviewed studies confirm the limited capacity of EGCS to remove NOx from the exhaust and 
show nitrates concentrations well below the EGCS Guidelines. The report concludes that the 
potential for significant increase of primary production and eutrophication appears to be low (in 
alignment with the conclusion of US EPA, 2011) and notes that part of the exhaust NOx 
emissions would end up in the sea, independent of the use of an EGCS. 
Table A-4 shows nitrate concentrations for EGCS discharge water from OL systems in the range 
<0.033 - 22.3 mg/L and from CL systems <4.4 - 290 mg/L. It should also be considered that due 
to the application of the IMO regulations for NOx reduction (Regulation 13 of MARPOL Annex 
VI), the concentrations in the EGCS discharge water might be expected to be much lower, 
because the NOx removal takes place before SOx removal. 
In order to compare the nitrate discharge criterion (60 mg/L, normalized to a specific flowrate 
of 45 m?/MWh) to other land-based regulations, the German Wastewater Directive 
(Abwasserverordnung, AbwV) was considered. There, total nitrogen is regulated for municipal 
wastewater (13 - 18 mg/L, equivalent to 57 - 80 mg NO3/L) and industrial waters, but is not 
regulated for discharge waters from scrubbing of flue gases from combustion plants. 
6.5 Water additives and other substances 
The current “2015 EGCS Guidelines” and the drafted “2020 EGCS Guidelines” consider a 
regulation for EGCS making use of chemicals, additives, preparations or relevant chemicals 
created in situ. According to the Guidelines, in such cases an additional assessment is required, 
and could take into account the “Procedure for approval of ballast water management systems 
that make use of active substances (G9)” (resolution MEPC.169(57)), to determine if additional 
discharge criteria are required. Those water additives and other substances could be alkali 
solutions for pH control or coagulants and flocculants for the removal of suspended solids in the 
water treatment. That would cover mainly CL systems. 
6.6 Sampling points and sampling procedures 
The current “2015 EGCS Guidelines” contain neither any requirement for sampling points for 
EGCS discharge water nor guidance for sampling procedures. The drafted review now contains a 
brief text passage indicating that the location of sampling points should ensure 
representativeness of the sampled water as well as a detailed guidance for sampling and 
analysis of EGCS discharge water as an annex. 
6.7 Inconsistency of regulations for closed loop systems 
The current “2015 EGCS Guidelines” are more stringent for CL systems in some aspects than for 
OL systems. As mentioned above, the turbidity limit value is fixed and independent of the 
specific flowrate. This leads to CL systems to be designed with efficient water treatment units to 
reach compliant turbidity values. The limit value for PAHypne is normalized, except for specific 
discharges in the range 0-1 m*/MWh, where the threshold is set at 2,250 ug/L. This would apply 
to CL systems (0.1 - 0.3 m?/MWh), and implies more stringent values than for OL systems. 
Nevertheless, the limit value for PAHs does not imply an actual restriction for both type of EGCS 
systems. 
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