UV or EC? Choosing the right ballast water management system for the environment – and your business profile

How “real” are type approval tests?

Believe it or not, the type approval process for ballast water management systems can lead to environmental risk – at least in the case of electrochlorination (EC) systems. Prepared challenge water is used to test both UV and EC systems, but the test results differ in how well they reflect real-world operation.

What EC testing overlooks

During EC system type approval, prepared challenge water is used to evaluate the target concentration for the oxidizing disinfectant that renders organisms non-viable – plus the holding time and/or the addition of chemicals needed to neutralize the total residual oxidants (TRO) before discharge. This target concentration is then applied uniformly, wherever the vessel sails.

The problem is that oxidants are consumed by more than living organisms. All natural waters have their own “oxidant demand”, which means the rate at which TRO is consumed depends on the amount and types of organic carbon they contain. However, the water’s oxidant demand isn’t measured during type approval – nor is it monitored by ballast water management systems in operation.

As a result, the disinfectant generated by an EC system may be consumed faster or slower in real life, depending on where the vessel sails. When the ambient oxidant demand differs from the demand in the prepared challenge water used during type approval, the result can be non-compliant treatment, the damaging release of unneutralized TRO and/or the formation of harmful disinfection by-products (DBPs). These risks apply even if the EC system is operated perfectly – and despite the IMO G9 final approval process that applies to systems using active substances.

UV testing vs real life

For UV ballast water management systems, which use no active substances, the situation is different. During type approval testing, the correct UV dose is coupled to the intensity of UV light that reaches a fixed UV sensor. Since the same sensor setup is used in operation, the relationship between intensity and dose never changes – even if the water does.

This means that UV performance is consistent. In fact, if the system has effective power management, it can safely decrease the UV light applied in clear water conditions. The intensity is maintained, but less energy will be used to make the ballast water compliant.

Avoid non-compliance and the risk of regrowth

Overlooking factors like oxidant demand when type approving electrochlorination (EC) systems puts ballast water compliance at risk. If the challenge water has a low oxidant demand, it will result in a lower target concentration being validated. As a result, the vessel’s discharge may be non-compliant in global waters with a high oxidant demand. In the real world, the “correctly” dosed disinfectant may be consumed before all organisms are rendered non-viable – a de facto underdose that jeopardizes aquatic ecosystems.

Risks can multiply within the tanks

Even when EC systems make the ballast water compliant, regrowth in the ballast tanks can make it non-compliant again. Unlike UV systems, EC systems only apply treatment when the ballast water is pumped in. Since the concentration of total residual oxidants (TRO) decreases over time, the few organisms that survive treatment may be able to regrow during a longer voyage. So, water that was once compliant may be non-compliant when it is discharged.

UV systems resolve this issue. Their UV dose is matched to the ambient water, and most systems treat the water again during ballast water discharge. If any regrowth occurs after uptake, the problem is therefore removed when the water is deballasted. Moreover, UV treatment disrupts the DNA of microorganisms, which means that even if they should survive for a short while, they will not be able to reproduce.

Combat organisms inside the vessel – not outside it

When managing ballast water with electrochlorination (EC) systems or others that use active substances, too much is just as problematic as too little. Nevertheless, in presented samplings, one-third of the systems using active substances have exceeded the maximum allowable discharge concentration (MADC) for total residual oxidants (TRO).

There could be many explanations, such as malfunctioning TRO sensors or problems dosing the neutralizing chemicals. In some cases, it could even be due to the ambient water having a lower oxidant demand than the challenge water during type approval, which would make the “correct” dose of neutralizing chemicals insufficient in practice. But whatever the cause, the risk to the environment is troubling. The concern is shared by nearly three in four experts from Global TestNet, a global network of experts working with ballast water management system testing, in their submission to MEPC regarding the experience-building phase (EBP) associated with IMO Ballast Water Management Convention.

Replacing one problem with another?

The high TRO discharge levels are a topic of discussion among experts, because today’s IMO D-2 discharge standard doesn’t include TRO limits. Although EC systems have a set MADC, no exceedance can be detected during Port State Control inspections, which only look at D-2 parameters. As the rules stand, vessels with EC systems may harm aquatic life without knowing it.

Unfortunately, using more neutralizing chemicals isn’t the answer. An excess of TRO-reducing chemicals can lead to bacterial growth and oxygen depletion, which also harm aquatic ecosystems. A recent study by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP)-Ballast Water Working Group (BWWG) points this out.

The simplest and surest way to avoid the problems of active substances is to select a UV ballast water management system.

Be aware of disinfection by-products (DBPs) and their risks

Perhaps an even bigger concern than high discharge levels of total residual oxidants (TRO) is the formation of disinfection by-products (DBPs) by electrochlorination (EC) systems. DBPs arise through the oxidation of organic matter and other substances present in natural water. Since they aren’t broken down by TRO-neutralizing chemicals, they remain in the water even after neutralization, where they can have an acute or chronic impact on the aquatic environment. The potential for bioaccumulation has not been fully ruled out.

The number and type of DBPs created depend on the water composition. Because seawater often contains bromine, commonly formed DBPs include bromoform, dibromoacetic acid and bromoacetonitrile, which have been linked to cancer and mutation.

Doesn’t IMO G9 mean that EC systems are safe?

To assess their impact on safety, health and the environment, ballast water management systems using active substances are evaluated according to IMO G9. Theoretically, the IMO G9 final approval process should keep toxicity within safe limits.

However, IMO G9 testing is done with prepared challenge water, containing dissolved and particulate organic carbon as defined by the regulations. In real life, DBP formation is influenced by the more diverse types of organic carbon and ions in the water, as well as by temperature and holding time. Since these factors all vary, so will the DBPs actually formed by EC systems – and thus the toxicity of the water discharged into the environment.

The disparity between assessed toxicity and real-life DBP measurements has been highlighted in recent MEPC submissions. In a submission to MEPC 81, Australia noted that measurements of two DBP groups – trihalomethanes (THMs) and haloacetic acids (HAAs) – are significantly higher than those reported in relevant approval documents. This was echoed in Denmark’s submission to MEPC 82, and it was strongly reiterated in Australia’s follow-up submission to the same meeting. The latter called for an audit of DBP concentrations relative to those stated in type approvals, as well as for MADCs to be considered for both THMs and HAAs.

Removing filters adds to DBP risks

Despite the growing concern, the risks connected with DBPs may be increasing rather than decreasing. In recent years, there has been a trend to remove the filter from ballast water management systems that use active substances. While the intent is to boost operational efficiency, the unintended consequence may be a drastic increase in DBP load.

The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP)-Ballast Water Working Group (BWWG) has acknowledged the risks in removing filters, but it has yet to specify how they should be handled. Denmark built its submission to MEPC 82 on the non-confidential part of the approval papers submitted to GESAMP-BWWG, presenting a study of four ballast water management systems whose filters have been removed. For all four systems, the DBP concentration in the discharge water increased significantly after filter removal. In the worst case, it was 299 times higher.

In a post-MEPC 82 Riviera webinar, Mouawad Consulting chief executive Jad Mouawad noted the elevated DBP levels seen in certain regions. He pointed especially to the potential consequences in low-salinity and closed marine environments, and he urged caution when it comes to filterless systems. “Filters do more than just remove organisms,” Mr Mouawad said. “They reduce the risk of harmful chemical interactions that could create toxic by-products.”

Could type approvals in ballast water management be improved?

As explored previously, the approval of electrochlorination (EC) systems raises many concerns that don’t apply to UV systems. Not surprisingly, questions like these have been raised by marine industry experts during the experience-building phase (EBP) tied to the IMO Ballast Water Management Convention:

• How can ballast water management systems be evaluated equally – and more correctly – during type approval?
  Could type approvals of EC systems reflect real-life performance as well as those for UV systems, for example by assessing the oxidant demand in the challenge water?
• How do we avoid solving one environmental problem by creating another?
  Given the documented high discharge levels of total residual oxidants (TRO) from EC systems, should TRO limits be enforced by Port State Control as part of the IMO D-2 standard?
• Have some key environmental risks been overlooked?
  As knowledge continues to grow about the fate and toxicity of disinfection by-products (DBPs), should IMO G9 be further revised – and perhaps re-applied to older systems?

Crew health and safety matter too

Ballast water management concerns the marine environment, but sustainability is a wider picture that also involves vessel crews. Both should be protected.

On vessels with electrochlorination (EC) systems, the oxidizing disinfectant is produced within the system itself. However, crews must still handle the chemicals for neutralizing total residual oxidants (TRO). Those chemicals pose their own health and safety risks, which means strong routines are needed with regard to storage, protective equip¬ment and crew training.

Since UV systems use no active substances, no chemicals are involved at any point during treatment. Crew training is still vital for compliant ballast water management, but no risks are added to the crew environment.

Protecting the environment is good business

By choosing sustainable ballast water management technology, you give your customers a stronger reason for choosing you. As the marine industry becomes greener, selecting UV treatment increases your competitive power. It shows customers and others that:

• You value sustainability and consider your impact carefully
• You choose compliance without active substances
• You avoid uncertain outcomes and questionable by-products
• You work towards the environmental goal – not just the rules

A green profile pays in more ways than one

The arguments above can strengthen your environmental credibility, making it easier to obtain green certifications – or more favourable loans. When you consider that UV treatment can also mean less CAPEX Land lower OPEX, the business decision becomes even easier.

UV technology – always the clear choice for Alfa Laval

Alfa Laval was first with a commercially available ballast water management system, launching Alfa Laval PureBallast in 2006. But we started by considering the issues. When PureBallast development began in 1997, we targeted a simple, effective solution with no unwanted environmental impact. UV technology was the natural answer.