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 
6 Deficiencies of the EGCS discharge guidelines 
This chapter analyses the current deficiencies on the discharge water quality criteria as 
presented in the “2015 EGCS Guidelines” as well as the drafted “2020 EGCS Guidelines”. This 
literature review could not establish any underlying documentation resulting in the 
determination of the limit values referenced by the IMO EGCS Guidelines, especially for turbidity 
and PAHpne. Thus, it is questionable whether the criteria in section 10 of the EGCS Guidelines 
ensures the protection of the marine environment in the short and long term from acute and 
chronic effects. In fact, the discharge criteria have been defined generally intended to prevent 
acute effects occurring in the aquatic environment (GESAMP, 2009) and is supposed to be 
revised as more data becomes available on the contents of the discharge and its effects, taking 
into account any advice given by GESAMP (MEPC, 2008a; MEPC, 2009; MEPC, 2015). US EPA 
(2011) indicated that the guidelines limits may be inadequate for metals and PAHs. 
6.1 pH criteria 
The current “2015 EGCS Guidelines” and the drafted review allow to select one of the two 
following requirements for the EGCS discharge water: 
1. pH > 6.5 at the discharge, but during manoeuvring and transit a ApH < 2 (difference 
between inlet and overboard discharge) is allowed, or 
pH limit value for the discharge that ensures achieve pH > 6.5 at a distance of 4 m from 
the overboard discharge point with the ship stationary. The overboard pH discharge 
limit can be determined either by means of direct measurement, or by using a 
calculation-based methodology. 
The first point indicates two cases setting more stringent pH criteria in port than during 
manoeuvring or in transit (ApH < 2 indicates a minimum of roughly 5.0 - 6.3, assuming seawater 
pH ranges 7.0 - 8.3) (GESAMP, 2009). Dilution is allowed in order to achieve these requirements. 
This measure, while supposed to prevent acute harmful effects to the ecosystem, does not 
prevent acidification effects in the long term. Duliere et al. (2020) modelled the acidification 
effects of EGCS discharge water obtaining high effects (equivalent to 10 to 50 years acidification 
effects due to climate change) in areas of high traffic density as well as in the vicinity of large 
harbours and recommended to follow the precautionary principle. 
In the report of the Correspondence Group (MEPC 56/4/1, United States, 2007) to develop the 
first discharge criteria, it was suggested not permitting the discharge of EGCS discharge water in 
those ports, harbours and estuaries where pH is a concern, instead of only restricting pH. United 
Kingdom (2006) proposed that the pH at the point of discharge should not deviate more than 0.2 
units below the pH at the sea water inlet. Lange et al. (2015) proposed that the pH in the 
discharge should be no more than 0.5 units below the value of the surrounding water. 
In addition, the assumption of 2.2 mmol/L for alkalinity and 8.2 for pH in the calculation method, 
allowed under the second requirement, may not be conservative because EGCS discharges may 
occurred in waters with lower pH and lower buffer capacity. 
6.2 PAHs and oil content 
The current “2015 EGCS Guidelines” and the drafted review set a normalized limit for PAHs 
given in phenanthrene equivalents for the difference between the inlet and discharge 
concentrations: 2.25 g PAHyne/MWh. In the drafted “2020 EGCS Guidelines”, however, the limit 
value for discharge water from temporary storage is fixed in 50 ug PAHpne/L regardless the 
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