As the focus of the industry moves gradually from debating legislative semantics to addressing the more pressing and practical aspects of compliance, more and more examples of practical, real-life operation of BWMS are coming to the fore – and in many cases, these reports are not positive.

In our somewhat unique position as shipowners trusted advocate, we hear numerous operational anecdotes each day – providing valuable feedback on the reliability of all manner of BWMS technologies and systems. Whilst many of the issues we hear about can be attributed to a lack of familiarity or training onboard, one thing is for certain – there are still BWMS recommended and installed onboard vessels that are simply not suitable for the vessel’s operation or trading routes.

All BWMS have design limitations, however, until the advent of USCG Type Approval testing, and revised IMO G8 protocols, manufacturers were not obligated to disclose the design limitations of their system – meaning hundreds of owners and operators were investing in technologies that were not fully understood.

It was, and indeed in many ways still is, clear that the lack of independent guidance on design limitations of different BWMS technologies is resulting in systems being installed that are not suitable for particular vessel trading routes or operations – resulting in what a recent ABS report indicated as 43% of BWMS being “inoperable.”

In order to help owners and operators understand some of these design limitations, and facilitate a more robust decision making process on BWMS technology and system options for their vessels, Cleanship Solutions (CSS) has developed a multi-part special editorial series covering the performance truths of different BWMS technologies.

Part 1 is the Ultraviolet (UV) system.


With an estimated 50% market share, Ultraviolet (UV) based ballast water management systems (BWMS) are currently the most popular method of treatment on the market. The appearance of being “well known and trusted technology” combined with simple operation make UV systems an appealing and low cost solution. However, as with all BWMS, UV systems are not necessarily the most suitable option for all vessels, and, indeed, are even more restricted by their suitability, or lack thereof, for particular trading routes and regions.



UV systems are generally considered the most technically and commercially appealing solutions for vessels with ballast flow rates of less than circa 1,500 m3/hr. The primary force behind this consensus is the operational cost of a UV system – which is predominantly driven by power consumption. At lower flow rates, other technologies such as Electro-chlorination systems, despite having lower operational costs, simply cannot compete on a combined CAPEX and OPEX analysis due to their higher capital costs. Whilst in some cases UV systems may still be economically viable beyond those flow rates, the general consensus is that as the ballast flow rates approach the 1,500 m3/hr mark, UV system power consumption begins to become unmanageable and costly, and other technologies become more commercially attractive.


I – Uv Dose & measurement

Ultimately, from the shipowners perspective, the most important consideration of any BWMS, not just UV systems, is the ability to successfully treat the water in a range of geographic locations and water qualities. However, because of the variance in water qualities (and most critically clarity) around the world, and the fact that UV systems are using UV light to treat the water, UV system performance is ultimately related to the clarity of the water being treated.

Fundamentally, the UV exposure that any organism within the ballast water receives is critically related to the amount of UV light that the organism is exposed to. Currently, there are two commonly used measurements associated with this exposure to UV light.

The first measurement is termed “Ultraviolet Intensity (UVI)” which essentially represents the total amount of UV energy that penetrates the water. This measurement is determined by the amount of energy that the UV intensity meter identifies and is specific to each BWMS. However, UVI does not include any relationship to water clarity.

The second method of measurement is termed “Ultraviolet Transmittance (UVT)” which represents the relationship between the UV light and the water clarity. In simple terms UVT indicates how much UV light of particular frequency passes through a water sample of specific water clarity, compared to the amount of light that passes through a pure water sample.

For the purpose of comparison between different UV based BWMS, only the UVT measurement is useful – as it is the only measurement which takes into account the clarity of the ballast water itself.



Water clarity varies significantly between different ports, and can be also be greatly impacted by seasonal or tidal conditions too. For the purpose of comparison of different ports, the UVT value is generally used, and provided as a percentage. As shown in the table below, the range of UVT values in common trading port around world can vary from as low as 49% in Shanghai, China, and 51% in Southampton, England, to as high as 93% in Rotterdam.

 Source: White Paper – MDD00657 1704


Insufficient consideration of the UVT capabilities of the BWMS can ultimately result in a system being installed that is not capable of treating the ballast water in certain ports around the world. Indeed, some well known UV based BWMS struggle with UVT values lower than even 70%, making them broadly unsuitable for a significant proportion of the common ports from the table above.

Unfortunately this issue does not simply result in a deficiency during any port state sampling. Indeed, in many cases we have witnessed, UV systems struggling with the UVT of the ballast water can simply fail to operate due to insufficient UV intensity monitoring within the unit – which is a significant operational issue indeed.

Even those UV based BWMS that do claim to have the ability to operate at low UVT values should be carefully examined, as often this is subject to significantly reducing the ballast water flow rates in order to increase exposure time.


With such variances in UVT around the world, and values in common ports going as low as 49%, it is critically important the shipowners and operators ensure they understand the UVT limitations of any UV based BWMS before making any investment decisions.

Whilst some manufacturers will openly quote their UVT capability, others still insist only on quoting the UVI of their system. For the purpose of any successful benchmarking it is crucial that owners use only the UVT values.

Cleanship Solutions offer comprehensive scrubber feasibility studies for owners, analysing the various options available and objectively determining the most suitable system for any given vessel. We have no commercial ties to any particular manufacturer, meaning we can offer vessel specific recommendations free of any subjective preference…

 For more information feel free to speak to one of our experts using our Expert Program, or get in touch.

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