Ballast Water Treatment at Muddy Water Ports
India has been advocating for port-based mobile treated ballast water delivering facilities called BWTBoats since 2013. Given the recent real-world experiences with the challenges of ballast water treatment at muddy water ports and the forthcoming financial burden for ship owners to comply with the 2020 sulfur cap, a port-based treatment model - BWTBoats - could be a viable solution to avoid the cost of retrofitting ballast treatment systems aboard ships.
Twist in BWM convention implementation
At recent MEPC & PPR sessions, IMO discussed the issue of contingency measures in the event that a ship's ballast water is non-complaint after use of onboard treatment systems. In response to this, South Korea submitted a paper (MEPC 71/4/21) which is eye opening for industry. They claim that systems are not working properly in ports with challenging water quality (PCWQ) i.e. muddy water ports. According to the report, during ballast uptake of muddy water, systems are clogging or ballasting operations are delayed beyond unexpected limits due to frequent start/stop back-flushing.
For this circumstance, the Korean authors suggested an onboard contingency measure in which it is advised that in PCWQ, treatment systems should not be used and untreated water ballast be taken on board as it is. The ship would then exchange this water on the high seas or mid-ocean with water treated by the ship's BWMS.
Canada (PPR 5/23/2) has raised concerns over the possibility that this would be a breach of BWM convention, as the water would be taken aboard untreated in port (Article 2 section 8 BWM convention). In addition, it is unclear whether the discharge port will accept this. As per Article 2 section 8 of the BWM convention, it is better to avoid as much uptake of source water species and sediments through treatment at source port only for regular ballast water management.
Testing of type approved BWMS in real-world sediment loads
Over a detailed investigation with Global TestNet (the association of global testing facilities), we found that these systems are mostly tested at real world biological loads (i.e. species) but not at real world sediment loads (i.e. ppm or mg/l of sediment). The IMO G8 performance guidelines only specify sediment condition as >50 ppm (and >24 ppm for the USCG). In the real world, the total suspended sediment (TSS) load can be as high as 1000 ppm.
In a statement, Global TestNet said that "testing extreme TSS value during land-based biological efficacy tests would not be possible because the extreme TSS values would impair the biology of the organisms during the tests, rendering the tests invalid. Therefore, the group agreed that filters should be tested against high level of TSS outside the protocols for biological efficacy testing and agreed to generate a Filter Test Protocol for the evaluation of filter robustness to TSS levels that are reflecting real world scenarios." This means that systems that are type approved with IMO G8 guidelines or USCG guidelines may not work efficiently if PPM loads are higher, which can happen at various ports with challenging water.
Problem is not with technology but with location and usage
According to filter experts, the 50-micron size filters used in almost all type approved BWTS are not failing, but they are taking an extended time for ballast operations in high suspended sediment conditions (100 to 1000 ppm). To treat ballast on board at a faster rate, like the 500m3/hr to 10000m3/hr required during nonstop ballasting operations, multiple filters with big catchment area and continuous back flushing would be required. This is not possible aboard ships due to space constraints and capital requirements.
Alternatively, port based mobile treated water delivering facilities - BWTBoats - could provide 10 times more catchment area at the seachest suction to avoid frequent back flushing. BWTBoats could be purpose-built with many series of modular filters as redundancy, thereby ensuring reliable clear ballast delivery to ships at all times.
Recent design developments in the BWTBoat concept have not only brought down its capital requirement by half, but have also removed the need for any retrofitting or deck connection at all for the receiving ship to take on treated ballast water from the BWTBoat. Thus the ships can receive any water flow from 10 to 10,000 m3/hr seamlessly, without any delay and retrofitting costs. It acts like an external plug-in to the sea-chest of the ship during ballast uptake.
Muddy water ports paves the way for BWTBoats
Both the Korean and Canadian papers have referenced the possibility of receiving clear ballast from port-based treated ballast water delivering facilities, e.g. BWTBoats. An Indian submission (MEPC 71/4/25) gives details about treated water delivering facility as a contingency measure when systems installed on ships are not working at ballast uptake ports.
BWTBoats have a unique business model as a full off-board BWTS option, but ships would have to be able to rely on a network of such facilities at all ports, wherever they call. Now BWTBoats can provide an additional benefit by providing the option to provide filtered water up to 50 microns to ships at muddy water ports. Ships fitted with their own BWMS (UV or chlorine or any other type) can use the filtered water provided by BWTBoats, then treat it further using the ships BWMS. In the case of filtered water, one BWTBoat is independent of another, as ships would be using the BWTBoat filtration service at muddy water ports only and depend on their own BWMS at other ports.
Mr. Sandip Patil is a surveyor with the Research and Innovation Center of the Indian Register of Shipping (IRClass).
Disclaimer: The views in this article are the author’s personal opinions and are not necessarily shared by any organization.
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