10 Washwater
10.1 Washwater discharge criteria1
10.1.1 When the EGC System is operated in a ports, harbours, or estuaries, 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:
- The discharge washwater should have a pH of no less than 6.5 at the overboard discharge with the exception that during manoeuvring and transit, the maximum difference between inlet and outlet of 2 pH units is allowed.
- During commissioning of the unit(s) after installation, the discharged washwater plume should be measured externally from the ship (at rest in harbour) and the discharge pH at the ship’s overboard pH monitoring point will be recorded when the plume at 4 metres from the discharge point equals or is above pH 6.5. The discharged pH to achieve a minimum pH units of 6.5 will become the overboard pH discharge limit recorded in the ETM.
10.1.3 PAHs (Polycyclic Aromatic Hydrocarbons)
The washwater PAH should comply with the following requirements. The appropriate limit should be recorded in the ETM.
10.1.3.1 The maximum continuous PAH concentration in the washwater should not be greater than 50 µg/L PAHphe (phenanthrene equivalance) 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.
10.1.3.2 The 50 µg/L limit described above is normalized for a washwater flow rate through the EGC unit of 45t/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
|
Fluorescence
|
11.25
|
200
|
– ” –
|
22.5
|
100
|
– ” –
|
45
|
50
|
– ” –
|
90
|
25
|
– ” –
|
10.1.3.3 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
The washwater turbidity should comply with the following requirements. The limit should be recorded in the ETM.
10.1.4.1 The washwater treatment system should be designed to minimize suspended particulate matter, including heavy metals and ash.
10.1.4.2 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.
10.1.4.3 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 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.
10.1.6 Washwater additives and other substances
10.1.6.1 An assessment of the washwater is required for those EGC technologies which make use of active substances, preparations or create relevant chemicals in situ. The assessment could take into account relevant guidelines such as resolution MEPC 126(53), procedure for approval of ballast water management systems that make use of active substances (G9) 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 1 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
10.3.1 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.
1.The washwater discharge criteria should be revised in the future as more data becomes available on the contents of the discharge and its effects, taking into account any advice given by GESAMP.