Ballast water management system filters in less than perfect condition could lead to operational problems, according to Erma First’s managing director Konstantinos Stampadakis.
Research from academic institutes and more than 70% of BWMS manufacturers agree that mechanical separation is essential to ballast water management systems. It is estimated that between 10Bn and 12Bn tonnes of ballast water is transferred around the globe each year, with the potential to carry bacteria, plankton, viruses, small fish, crabs or jellyfish into foreign ecological systems.
In the early days of ballast water treatment, it was assumed that a simple filter/strainer on the intake would prevent most organisms entering the ballast tanks. However, research proved the mesh required would have to be much finer, down to 40 μm, leading to less energy required for disinfection to take place as less disinfectant concentration is produced. Organisms larger than 50 μm are in their adult stage of life and have developed resistance against any form of water disinfection. Consequently, no-filter BWMS utilising active substances require increased total residual oxidants (TRO), such as chlorine, and holding time to avoid the risk of non compliance.
To meet D2 standards without a filter using electrolysis, TRO production should be increased ( >31mg/Lit) [1]. This can be achieved via one or a combination of the below:
Action |
Effect |
Increase the number of electrodes |
More expensive electrode Bigger size Higher energy consumption |
Use special anodes coating to increase electrode efficiency (more chlorine production from the same anode surface) |
More expensive electrode Higher energy consumption |
Electrophoresis* for ballast water does not exist or is unsupported by any scientific or engineering document. It is the chlorine which oxidises the bacteria and pathogens. Organisms in dimensions higher than 40 μm are insensitive to chlorine. As such the only elimination method is either to use a filter, the extreme high TRO concentration or a long holding time to kill such insensitive organisms by starvation.
The absence of a filter leads to a high solid material concentration in ballast water that consumes chlorine at a very fast rate [2]. As such, minimal or no holding time may not guarantee disinfection efficacy and compliant operation when faced with high sediments and turbid seawater.
In addition, a filter protects components’ internal, wet parts. Unfiltered water, which contains various sized solids and debris, consisting of both organic and inorganic material, has a detrimental effect on the lifetime of the anode electrodes at the heart of the electrolysis technology. These anodes usually consist of a precious metal oxide mixture coating applied on a titanium substrate and are highly susceptible to mechanical wear caused by unfiltered water at high velocities[2].
Taking into consideration that in some no-filter BWMS, the electrolyser housing is made of metal, the debris passing through in combination with the high-water velocity effectively sandblasts the housing causing accelerated mechanical wear. This wear in combination with the produced oxidants on site could have a catastrophic effect on the structural integrity of the electrolysers.
Equally important is the ballasting sequence: BWMS without a filter come with a T-strainer with a mesh filter of approximately 3,000 μm retention capacity. If the T-Strainer is clogged, ballasting must be stopped so the internal mesh can be manually cleaned.
Last but not least, is the TRO sampling: With no filter, there will be challenging TRO sampling and analysis procedures, due to large solids in seawater that will result in frequent sensor filter clogging. Moreover, solids affect the efficiency of the photometric sensor measurements.
The above paper was contributed by Erma First. If you have any questions or comments, these should be addressed to: Craig.Jallal@Rivieramm.com.
[1] Sensitivity of barnacle cyprid larvae to chlorine, N H B M Kaag and A C Sneeks, C103/10, IMARES
[2] Marie Deborde , Urs von Gunten, Water Res. 42 (2008), 13 – 51
* Electrophoresis is a separation technique based on the mobility of ions in an electric field
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