For vessels operating with an open loop scrubber, also referred to as an Exhaust Gas Cleaning System (EGCS), entering US waters can introduce an additional compliance challenge.
Under the US EPA Vessel General Permit (VGP), vessels discharging scrubber washwater into US waters must meet specific discharge requirements, including limits for pH at the overboard discharge.
For shipowners and operators, this means that an open loop scrubber that is compliant under international requirements may still require additional measures when operating in US waters.
Traditionally, operators have had three main options: switch to compliant fuel, operate the scrubber in closed loop mode or adapt the existing open loop system to meet the required washwater discharge conditions.
For vessels with regular US trading patterns, ME Production offers another way to maintain the advantages of open loop operation:
NaOH dosing of the scrubber washwater.
Understanding the US VGP pH requirements
Scrubbers remove sulphur oxides from the exhaust gas by bringing the exhaust into contact with washwater.
During this process, the washwater becomes acidic.
Under the current US EPA Vessel General Permit requirements, scrubber washwater discharged into applicable US waters must have a pH of no less than 6.0 when measured at the vessel's overboard discharge.
During manoeuvring and transit, an alternative criterion allows a maximum difference of 2.0 pH units between inlet water and the overboard discharge.
This differs from the International Maritime Organization (IMO) methodology, where alternative methods for demonstrating washwater pH compliance may be accepted. As a result, a scrubber approved according to IMO requirements may not automatically demonstrate compliance with the US VGP discharge requirements.
Operators also need to consider state and local requirements, as additional restrictions on scrubber washwater discharge may apply in individual US waters.
Three ways to operate when approaching US waters
When a vessel operating an open loop scrubber approaches waters where the washwater discharge does not meet the applicable requirements, the operator essentially has three options.
1) Switch to compliant fuel
The first option is to stop using the scrubber and change to fuel that complies with the applicable sulphur requirements without exhaust gas cleaning.
This requires the vessel to manage the fuel changeover correctly and means temporarily giving up the economic benefit of operating on high sulphur fuel with a scrubber.
For vessels calling occasionally at US ports, this may be a straightforward solution.
For vessels with frequent US trading, however, repeated fuel switching can affect the overall business case of the scrubber installation.
2) Convert to closed loop or hybrid operation
A second option is to upgrade the scrubber to enable closed loop operation.
In closed loop mode, washwater is recirculated and treated onboard instead of continuously relying on seawater alkalinity and discharging the full washwater flow overboard.
A conversion from open loop to hybrid configuration can provide substantial operational flexibility, particularly for vessels trading globally across several areas with different washwater discharge restrictions.
However, a full conversion also requires additional equipment, integration work and investment.
For vessels whose primary challenge is specifically related to pH compliance during US operation, a full closed loop conversion may provide more functionality than the vessel actually requires.
3) Increase washwaterpH with NaOH dosing
For these vessels, ME Production can provide a more targeted solution.
A NaOH dosing system introduces sodium hydroxide into the washwater system to increase the pH before discharge.
Rather than changing the fundamental operating principle of the scrubber, the solution is designed to allow the vessel to continue operating in open loop while managing the washwater pH required for the relevant operating conditions.
The result is a targeted retrofit aimed at one specific compliance challenge.
For operators with significant exposure to US waters, this can provide an attractive alternative to repeatedly switching fuel or investing in a complete open-to-closed loop conversion.
A targeted solution for US-heavy trading patterns
The right scrubber compliance strategy depends heavily on the vessel's operational profile.
A ship trading globally through several areas with open loop discharge restrictions may benefit from the flexibility of a full hybrid conversion.
A vessel that only occasionally operates in US waters may find compliant fuel changeover sufficient.
But for a vessel spending a significant part of its operation in or around US waters, NaOH dosing can offer a different business case.
Instead of redesigning the complete scrubber configuration, the operator can address the specific washwater pH requirement while retaining open loop operation where permitted.
This makes NaOH dosing particularly relevant when the objective is to achieve compliance with minimal changes to an otherwise functional open loop scrubber installation.
Available for ME Production and NON-ME Production scrubbers
The solution is not limited to scrubbers originally supplied by ME Production.
ME Production can assess both ME Production and NON-ME Production scrubber installations and develop a dosing solution based on the existing system configuration, vessel layout and operational requirements.
This is particularly relevant for vessels with older scrubber installations or equipment from suppliers where modification and aftermarket support may be limited.
The starting point is always the existing vessel.
Before recommending a solution, the scrubber configuration, washwater arrangement, monitoring equipment, available space and trading pattern must be considered to determine the appropriate integration.
NaOH dosing or closed loop conversion?
There is no universal answer.
The two solutions address different operational requirements.
A hybrid or closed loop conversion provides maximum flexibility for vessels operating across multiple jurisdictions where open loop washwater discharge is restricted or prohibited.
A NaOH dosing system, on the other hand, can be a more focused alternative when washwater pH is the primary compliance challenge and the vessel wants to retain open loop operation.
For shipowners, the decision should therefore not begin with the technology itself.
It should begin with the vessel's trading pattern.
Where does the vessel operate? How often does it enter restricted waters? How much time is spent in US waters? What is the cost of switching fuel? And does the vessel need full closed loop capability, or simply a solution to a specific compliance requirement?
Answering those questions makes it possible to select a scrubber upgrade based on the actual operational need rather than installing unnecessary complexity.
Keeping existing scrubber investments operational
Regulations surrounding scrubber operation continue to develop, but that does not necessarily mean that existing open loop scrubbers have reached the end of their useful life.
In many cases, targeted modifications can adapt an existing system to new operational requirements.
ME Production works with scrubber operators to assess existing installations and identify the appropriate path forward, whether that means service and optimisation, a dosing system or a complete open-to-hybrid conversion.
The objective is the same: keep the vessel compliant while maintaining as much operational and commercial flexibility as possible.
If your vessel operates an open loop scrubber and regularly trades in US waters, contact ME Production to discuss whether NaOH dosing could be a suitable alternative to fuel changeover or closed loop conversion.