Date
9/6/2020

Category
Marine

Posted By
Göran Stenmark

The purpose of any ballast water management system (BWMS) is to neutralize a ship’s ballast water from aquatic organisms and to prevent these from spreading into new, foreign ecosystems when the ballast water is discharged into new parts of the world. One of the most prominent BWMS on the market is the electrochlorination (EC) system. In this article, we are going to delve deeper into how an EC system and its most vital components work.

What sets different ballast water management systems apart is how the ballast water is treated after passing through the initial filter (since most systems use a filter to remove parts and organisms bigger than 50 microns). Generally, a system works so that during ballasting, seawater is loaded into the ship with the help of pumps. The water then usually passes through a filter, after which it passes a treatment step to be fully cleansed from living organisms and sediments. This step in the process is what separates one system from the other, as different systems use different treatment methods.

HOW AN ELECTROCHLORINATION SYSTEM WORKS

In an EC system, the water flow goes through an electrochlorination cell where water molecules and the salt in the seawater are decomposed according to the model H2O + NaCl + energy = NaClO + H2. The sodium hypochlorite molecule (NaClO) is the active ingredient that disinfects the ballast water and kills the microorganisms that have passed the initial filter. The electrochlorination cells, in turn, are powered by the rectifier.

Once the water has passed through the treatment system, the ballast water tanks are filled with the treated water – preventing any organisms from spreading into foreign waters. When de-ballasting, the Total Residual Oxidant (TRO) content is measured, and if it is too high, the ballast water is neutralized, e.g. by adding sodium bisulfite, so that no sodium hypochlorite is discharged into the sea.

IS IT POSSIBLE TO SAY THAT ONE PART OF THE SYSTEM IS THE MOST IMPORTANT? 

A ballast water management system is only as good as its weakest link, and all components are equally important for the system to work properly. The filter is critical because if it doesn’t work or gets clogged, the water flow is reduced, and the ballast water tanks can’t fill up. The system’s ability to purify the water is largely dependent on the amount of hypochlorite in the water, which is measured by the TRO sensors. If the sensors malfunction or break, the system doesn’t work. Hence, the TRO sensors are also considered critically important.

Then there is the rectifier, which feeds the electrochlorination cells with energy, similar to a heart pumping blood to vital organs and muscles. If the rectifier stops working, the system goes into cardiac arrest, to use the heart analogy. Finally, we have the control system. If the control system stops working, it doesn’t matter if all other components are functional – because the system would be braindead.

If you look at which components run the greatest risk of breaking or malfunctioning, it would probably be the ones carrying the heftiest workload: the filters, TRO sensors and the rectifier. Hence, it is very important that these components are of high quality and designed to keep operating if a problem were to occur.

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