Swedish industrial power supply company KraftPowercon’s product manager Göran Stenmark considers the pros and cons of UV radiation, electrochlorination and chemical injection ballast water treatment systems
Choosing a ballast water management system (BWMS) can be challenging, especially if you do not know the ins and outs of a specific system, let alone the ever-growing number of systems available on the market. One thing is for sure though: there is no one-size-fits-all when it comes to BWMS. However, some are more suitable than others for your ship and its specific conditions. There are pros and cons in all of the three most common BWMS out there: UV, electrochlorination and chemical injection systems.
Many factors come into play when looking for a suitable BWMS. For starters, there are many available treatment methods out there, from UV radiation, pressure vacuum and heat, to chemical injection, electrochlorination and ozonation. Each method has its advantages and disadvantages, and what is optimal for one ship might not be the best choice for another.
On top of this, there are ship-specific factors that need to be considered before settling on a specific system, such as the size of ship and its ballast water pump capacity. It is also important to consider the ship’s operating route and the water characteristics of said route, as some systems might be incompatible with certain types of water.
Lastly, the system needs to be approved by International Maritime Organisation (IMO) and the US Coast Guard (USCG). Since the Ballast Water Management Convention was ratified in September 2017, all vessels weighing more than 400 gross tons need to be fitted with a compliant and type-approved BWMS.
All systems mentioned above work on the principle of one or a combination of mechanical, physical, or chemical treatment methods. The most prominent BWMS in use today are UV radiation, electrochlorination and chemical injection. While most of these systems work on the principle of running water through a filter, they use different treatment technologies to purify the actual ballast water.
EC systems have a higher capacity for treating larger volumes of ballast water, since the active substance (sodium hypochlorite) is produced on board and can be added to the ballast water flow. The amount of sodium hypochlorite added is linear to the ballast water flow and the maximum water flow is not dependent on the UVT in the same way as a UV system.
EC systems require less power and less footprint compared to UV systems to treat the same water flow. With lower UVT, the difference in power consumption is even greater. UV systems may also need to treat the water on both uptake and discharge. Further, EC systems do not have UV lamps that needs to be replaced regularly, which UV systems do. All in all, this means EC systems have a lower opex since they require less maintenance.
EC systems usually have no hold times, since the entire water flow will be completely treated at uptake and no extra time or additional treatment is needed. This will make the water compliant and with no risk for regrowth of microorganisms.
As opposed to UV systems, the performance of an EC system is not affected by sediments or turbid water. This is because the active substance in an EC system is distributed evenly throughout the entire water flow. When the water is treated by a UV system, the UV light must reach every single drop of water. If the water contains a lot of sediment this can be a challenge, since this reduces the UV transmittance. Increased intensity of the UV lamps will solve this to a certain level, but this will cost in terms of both increased power consumption as well as reduced lifetime of the lamps.
EC systems are dependent on the salt in the seawater in order to work. If the vessel enters a port with freshwater, the system might not work unless seawater is brought in a separate tank from where the active substance can be produced.
EC systems, especially side-stream systems, can be more complicated to install than UV or chemical injection systems and the active substance is a chemical that must be handled in a proper way in order to avoid injury to crew or damage to the vessel.
EC systems emit hydrogen gas because of the chemical reaction when sodium hypochlorite is produced. The hydrogen must be handled in a proper way to avoid risks, usually by using a hydrogen separator and fans that will blow the gas up in the air.
EC systems use a chemical treatment method that could cause corrosion in the ballast water tanks over time, unless they are maintained and coated.
Before the ballast water can be discharged back to the ocean, the Total Residual Oxidants (TRO) are measured and if the level is too high, the oxidant level has to be reduced. This can be done by adding a neutraliser when de-ballasting.
As opposed to EC systems, UV systems work in almost all types of water, as long as the UV transmittance is high enough. EC systems have a harder time in freshwater since they are dependent on saltwater to function properly. This can be mitigated by bringing seawater in a separate tank.
They are cheaper to buy and install (capex), but have higher operating costs (opex) due to higher power consumption and consumables. No chemicals are used that can be a risk for the crew or cause damage to the vessel.
One disadvantage of the UV system is its sensitivity to water quality. Since the entire body of water inside the ballast water tanks needs to be illuminated by the UV light to be fully treated, the system can be inefficient if the water is murky, i.e. the UV transmittance is low.
UV systems have hold times as the UV lights need time to neutralise the organisms.
Low water temperature can reduce the performance of UV lamps, especially low-pressure lamps which might even stop working if the water temperature is too low.
The UV lamps gradually decrease in efficiency when used, which means that they have to be replaced regularly. They can also break, which can lead to a non-compliant BWMS.
As opposed to EC systems, UV systems do not kill all aquatic organisms carried in the ballast water. Rather, the UV lamps make most organisms non-viable, destroying their ability to reproduce. The USCG demands that organisms inside the ballast water tanks are dead before the water is discharged from the tanks, which means a UV system needs to heavily increase its power to be compliant.
UV transmittance is lower on average in freshwater, which might reduce the performance of a UV system.
Chemical injection systems are easy and cost-effective to install on virtually any type of vessel, regardless of the size of the system. They are also easy to scale up, simple in their design, robust and do not have many components that can break.
Chemical injection systems work well in both fresh and saltwater as well as for low-temperature water, since they do not have to produce the active substance on board.
The active chemical substance is purchased separately. Hence, a chemical injection system will have a high opex because of the high costs of the consumables.
Chemical injection systems utilize a toxic chemical solution that is stored on board the ship, which naturally could be a concern from a crew and vessel perspective. Because of this, a chemical injection system might not be an ideal system for all types of ships.
The three technologies discussed are not the only systems available on the market. They are, however, some of the most prominent ones used by shipowners and operators. This does not mean that they have to be the best choice for every ship or operation. KraftPowercon always recommends thorough research and due diligence before picking a system. Help from an expert can be a worthwhile investment to find the best possible solution for the ship’s needs.