10.1 Washwater discharge criteriafootnote
10.1.1 When the EGC system is operated in ports, harbours, or estuaries, the
washwater monitoring and recording should be continuous. The values monitored and
recorded should include pH, PAH, turbidity and temperature. In other areas the
continuous monitoring and recording equipment should also be in operation, whenever the
EGC system is in operation, except for short periods of maintenance and cleaning of the
equipment. The discharge water should comply with the following limits.
10.1.2 pH criteria
10.1.2.1 The washwater pH should comply with one of the following requirements which
should be recorded in the ETM-A or ETM-B as applicable:
- .1 The discharge washwater should have a pH of no less than 6.5 measured at the
ship's overboard discharge with the exception that during manoeuvring and
transit, the maximum difference between inlet and outlet of 2 pH units is
allowed measured at the ship's inlet and overboard discharge.
- .2 The pH discharge limit, at the overboard monitoring position, is the value
that will achieve as a minimum pH 6.5 at 4 m from the overboard discharge point
with the ship stationary, and which is to be recorded as the overboard pH
discharge limit in the ETM-A or ETM-B. The overboard pH discharge limit can be
determined either by means of direct measurement, or by using a
calculation-based methodology (computational fluid dynamics or other equally
scientifically established empirical formulae) to be left to the approval by the
Administration, and in accordance with the following conditions to be recorded
in the ETM-A or ETM-B:
- .1 all EGC units connected to the same outlets are operating at their
full loads (or highest practicable load) and with the fuel oil of a
maximum sulphur content for which the units are to be certified (Scheme
A) or used with (Scheme B);
- .2 if a test fuel with lower sulphur content, and/or test load lower
than maximum, sufficient for demonstrating the behaviour of the
washwater plume is used, the plume's mixing ratio must be established
based on the titration curve of seawater. The mixing ratio would be used
to demonstrate the behaviour of the washwater plume and that the
overboard pH discharge limit has been met if the EGC system is operated
at the highest fuel sulphur content and load for which the EGC system is
certified (Scheme A) or used with (Scheme B);
- .3 where the washwater flow rate is varied in accordance with the EGC
system gas flow rate, the implications of this for the part load
performance should also be evaluated to ensure that the overboard pH
discharge limit is met under any load;
- .4 reference should be made to a sea-water alkalinity of
2,200 μmol/litre and pH 8.2footnote; an amended titration curve
should be applied where the testing conditions differ from the reference
seawater, as agreed by the Administration; and
- .5 if a calculation-based methodology is to be used, details to allow
its verification such as but not limited to supporting scientific
formulae, discharge point specification, washwater discharge flow rates,
designed pH values at both the discharge and 4 m location, titration and
dilution data should be submitted.
10.1.3 PAHs (Polycyclic Aromatic Hydrocarbons)
10.1.3.1 The washwater PAH should comply with the following requirements. The appropriate
limit should be specified in the ETM-A or ETM-B.
10.1.3.2 The maximum continuous PAH concentration in the washwater should not be greater
than 50 μg/L PAHphe (phenanthrene equivalence) above the inlet water PAH
concentration. For the purposes of this criteria, the PAH concentration in the washwater
should be measured downstream of the water treatment equipment, but upstream of any
washwater dilution or other reactant dosing unit, if used, prior to discharge.
10.1.3.3 The 50 μg/L limit described above is normalized for a washwater flow rate
through the EGC unit of 45 t/MWh where the MW refers to the MCR or 80% of the power
rating of the fuel oil combustion unit. This limit would have to be adjusted upward for
lower washwater flow rates per MWh, and vice-versa, according to the table below.
|
Flow rate
(t/MWh)
|
Discharge concentration limit
(μg/L PAHphe
equivalents)
|
Measurement technology
|
| 0-1
|
2250
|
Ultraviolet light
|
| 2.5
|
900
|
– " –
|
| 5
|
450
|
Fluorescence3
|
| 11.25
|
200
|
– " –
|
| 22.5
|
100
|
– " –
|
| 45
|
50
|
– " –
|
| 90
|
25
|
– " –
|
10.1.3.4 For a 15-minute period in any 12-hour period, the continuous PAHphe
concentration limit may exceed the limit described above by up to 100%. This would allow
for an abnormal start-up of the EGC unit.
10.1.4 Turbidity/Suspended Particle Matter
10.1.4.1 The washwater turbidity should comply with the following requirements. The limit
should be recorded in the ETM-A or ETM-B.
10.1.4.2 The washwater treatment system should be designed to minimize suspended
particulate matter, including heavy metals and ash.
10.1.4.3 The maximum continuous turbidity in washwater should not be greater than 25 FNU
(formazin nephlometric units) or 25 NTU (nephlometric turbidity units) or equivalent
units, above the inlet water turbidity. However, during periods of high inlet turbidity,
the precision of the measurement device and the time lapse between inlet measurement and
outlet measurement are such that the use of a difference limit is unreliable. Therefore
all turbidity difference readings should be a rolling average over a 15-minute period to
a maximum of 25 FNU. For the purposes of this criteria the turbidity in the washwater
should be measured downstream of the water treatment equipment but upstream of washwater
dilution (or other reactant dosing) prior to discharge.
10.1.4.4 For a 15-minute period in any 12-hour period, the continuous turbidity discharge
limit may be exceeded by 20%.
10.1.5 Nitrates
10.1.5.1 The washwater treatment system should prevent the discharge of nitrates beyond
that associated with a 12% removal of NOX from the exhaust, or beyond 60 mg/l
normalized for washwater discharge rate of 45 tons/MWh whichever is greater.
10.1.5.2 At each renewal survey nitrate discharge data is to be available in respect of
sample overboard discharge drawn from each EGC system with the previous three months
prior to the survey. However, the Administration may require an additional sample to be
drawn and analysed at their discretion. The nitrate discharge data and analysis
certificate is to be retained on board the ship as part of the EGC Record Book and be
available for inspection as required by port State control or other parties.
Requirements in respect of sampling, storage, handling and analysis should be detailed
in the ETM-A or ETM-B as applicable. To assure comparable nitrate discharge rate
assessment, the sampling procedures should take into account paragraph 10.1.5.1, which
specifies the need for washwater flow normalization. The test method for the analysis of
nitrates should be according to standard seawater analysis as described in Grasshoff et
al.
10.1.5.3 All systems should be tested for nitrates in the discharge water. If typical
nitrate amounts are above 80% of the upper limit, it should be recorded in the ETM-A or
ETM-B.
10.1.6 Washwater additives and other substances
An assessment of the washwater is required for those EGC technologies which
make use of chemicals, additives, preparations or create relevant chemicals in situ. The
assessment could take into account relevant guidelines such as the Procedure for
approval of ballast water management systems that make use of active substances
(G9) (resolution MEPC.169(57)), and, if necessary,
additional washwater discharge criteria should be established.
10.2 Washwater monitoring
10.2.1 pH, oil content (as measured by PAH levels), and turbidity should be continuously
monitored and recorded as recommended in section 7 of these guidelines. The monitoring
equipment should also meet the performance criteria described below:
pH
10.2.2 The pH electrode and pH meter should have a resolution of 0.1 pH units and
temperature compensation. The electrode should comply with the requirements defined in
BS 2586 or of equivalent or better performance and the meter should meet or exceed BS EN
ISO 60746-2:2003.
PAH
10.2.3 The PAH monitoring equipment should be capable to monitor PAH in water in a range
to at least twice the discharge concentration limit given in the table above. The
equipment should be demonstrated to operate correctly and not deviate more than 5% in
washwater with turbidity within the working range of the application.
10.2.4 For those applications discharging at lower flow rates and higher PAH
concentrations, ultraviolet light monitoring technology or equivalent, should be used
due to its reliable operating range.
Turbidity
10.2.5 The turbidity monitoring equipment should meet requirements defined in ISO
7027:1999 or USEPA 180.1.
10.3 Washwater monitoring data recording
The data recording system should comply with the requirements of sections 7
and 8 and should continuously record pH, PAH and Turbidity as specified in the washwater
criteria.
10.4 Washwater residue
10.4.1 Residues generated by the EGC unit should be delivered ashore to
adequate reception facilities. Such residues should not be discharged to the sea or
incinerated on board.
10.4.2 Each ship fitted with an EGC unit should record the storage and disposal of
washwater residues in an EGC log, including the date, time and location of such storage
and disposal. The EGC log may form a part of an existing log-book or electronic
recording system as approved by the Administration.