Step 2 of 4•16 minutes read
Different Ballast Water Treatments (D-2 Compliance)
There are over 70 Ballast Water Treatment Systems (BWTS) approved by IMO. Most used systems use UV, Electrolysis in different ways, and also Ozone. UV stands for approximately 50%, followed by Electrolysis and then Ozone. When using this method, the Ballast Water is treated most of the time before it enters the tanks.
D-2 process.
UV-Treatment
When the water is about to enter the tanks, the first step is to filter the water to eliminate the most significant particles. By having the first step with filters, the UV light will have a better chance of effectively neutralising the possibly harmful organisms. This means that when the water has passed the filter, it then passes through the UV light system. In many cases, when using this method, the water gets treated on its way out. It is run through the UV light system to give it an extra chance of really making sure that there are no active and harmful organisms about to enter the new ecosystem.
- It is very effective, and there is a good chance that no harmful organisms or bacteria are released into the oceans.
- BWTS that are based upon UV light are not affected by the water's salinity or temperature.
- There are also no added substances that will be released, such as chlorine.
- There is a technical lifespan that needs to be considered when installing the system.
- It needs to be monitored and maintained to ensure that the system performs as it should.
- Poor UV transmittance will affect the system's performance so it will be expensive to buy.
- It could also be considered a con that organisms get killed instead of released.
Electrolysis-Treatment
When the water first is about to enter the tanks, the first step of the treatment is to filter the Ballast Water to eliminate the largest particles, just as when one uses UV as BWTS. When electrolysing seawater, hypochlorite, an ion that acts as an acid and bleach substance, is generated. This substance attacks the organisms and neutralises them. Hypochlorite is considered a pollutant and is not allowed to be discharged into the sea unless it has been neutralised by another chemical or sufficiently decomposed.
In most cases, the process uses seawater directly. The method requires that the entire flow of Ballast Water passes through the hypochlorite generator. The generator then uses a side stream to electrolysis it, just a small portion of the Ballast Water. This is then used to produce this concentrated disinfectant stream, consisting of among other things, hypochlorite, which is then injected back into the Ballast Water. The electrolysis depends on the length of exposure to get satisfactory treatment.
This method requires water with relatively high salinity; this method is inconvenient for vessels that operate in freshwater or water with low salinity. When sailing through these sorts of waters, an alternative substance could neutralise the organisms, such as chlorine.
The cons of this method are that it does not work when sailing through waters with low salinity. There is also a risk that the hypochlorite is not neutralised before being re-released into the ocean, which would lead to even more harm to the environment. Also, the process of electro-chlorination generates hydrogen and chlorine gases that are both explosive and toxic. Again, since there are acids involved in the process, the system needs to have high resistance against corrosion and other problems that can occur with it. To get an efficient electrolysing of the water, it needs to be at least 15° Celsius.
Ozone-Treatment
This sort of BWTS is very similar to the Electrolysis type BWTS. The treatment uses a chemical treatment, in this case, ozone. Ozone, just as with hypochlorite, neutralises the harmful organisms in the Ballast Water. Ozone-type BWTS is mainly composed of an air compressor, air reservoir, ozone generator, and ozone reservoir. The ozone generated by the system is injected into the main ballast line. The substance attacks the organisms and neutralises them.
Ozone is considered a pollutant and is not allowed to be discharged into the sea unless it has been neutralised by another chemical or sufficiently decomposed. Some sorts of ozone BWTS require a neutralisation, but that depends on the system's construction and does not apply to all systems. The overboard discharge must be continually monitored, and the system must control the amount of neutralising substance that has been added. Since ozone is so toxic, the ozone BWTS needs to be fitted with safety systems. This is to prevent exposure to potentially toxic gas for both the environment and the personnel on board.
Ozone systems provide a flexible installation profile. This is because of the lack of a mechanical filter and the side-stream method used in the electrolysing method. This offers flexible installation. Just as with Electrolysis type BWTS, this method can affect the Ballast Water for a more extended time since the reaction occurs within the tanks.
The system typically requires lots of auxiliary systems. This means that ozone systems take up a lot of space, especially compared to a UV system. The system also involves the multiple processes involved in generating and diluting ozone gas and the air and oxygen storage tanks need to be incorporated.
Testing the Ballast Water
When testing the Ballast Water, a sample is taken. A sample is defined as "a smaller, manageable version of a larger group. It is a subset containing the characteristics of a larger population". The testing could be performed by the crew or by the responsible authority. IMO guidelines regarding testing state that:
Samples should be taken from the discharge line, near the point of discharge as practicable, during ballast water discharge whenever possible. The advantage of sampling the ballast water in the discharge line is that this is most likely to accurately represent the concentration of substances and organisms in the actual discharge, which is of primary concern in assessing compliance with the discharge regulations. Other sampling arrangements may be necessary in cases where the ballast system design does not enable sampling from the discharge line.
In-tank sampling should only be used if ballast water treatment occurs on uptake before or while ballast water is in the tank. If any part of the treatment process occurs during the ballast water discharge, then in-tank sampling will be inappropriate. An exception to this is when tanks are emptied through direct overboard discharge valves, as in upper-side wing tanks, rather than through the ballast pumps. In such cases, tank sampling may be an appropriate approach.
There are several suitable instruments and equipment for testing the Ballast Water. You must make sure that you are familiar with your equipment so that accurate sampling and testing can be achieved and data can be logged correctly to prove compliance.