Ultraviolet light (UV) can treat extremely turbid ballast water, as long as the treatment system is engineered to the highest of standards. Unfortunately, misconceptions about UV’s ability to treat poor quality water are common. However, UV disinfection is extensively proven to treat wastewater, and, in most cases, wastewater is of poorer quality or lower UV transmittance (UVT) than ballast water.
What is UV Transmittance (UVT)?
UVT is the ratio of light entering the water to that exiting the water. Simply put, water with high UVT (e.g., 90%) is relatively clear, allowing more UV light to reach the organisms you are trying to treat. As water quality decreases, the UVT is reduced (e.g., 50%) which in turn reduces the amount of UV light that is able to penetrate and provide treatment.
Every Port is Different
No matter where in the world your vessels trade – whether it’s clear seawater or turbid fresh water – your ballast water treatment system has to work. And, as you know, water quality varies from port to port and day to day.
Different water quality parameters become more or less important depending on the type of ballast water technology used. In the case of Electrochlorination systems, the salinity, temperature and organic content of the water will have a dramatic impact on the overall efficacy of the system. For UV systems, UVT is the most important parameter impacting the effectiveness of the system.
High UVT Values Limit System Applicability
A conventional ballast water treatment system – utilizing a land-based-designed UV system (i.e., designed to treat drinking water with 85% UVT) – won’t be able to provide the same treatment performance in lower UVT (e.g., 50%) water. More equipment would be required to provide the same level of performance, and more equipment means increased power draw and space requirements.
Many existing IMO Type Approved systems have been tested in higher clarity water (high UVT). It is expected that these systems will not be approved to treat lower clarity waters than to what they have been tested to under USCG regulations. The UVT value will be noted on the Type Approval certificate, significantly limiting the applicability of the system in poorer water qualities. In addition, alarms will be noted in equipment logs every time the UVT value of the ballast water falls below the minimum to which it was tested. Multiple alarms are likely to draw increased attention from Port State Control. The best way to reduce your risk is to utilize a ballast water treatment system that has been tested to low UVT values.
Dispelling The UVT Myth
The Trojan Marinex BWT system is tested and approved to one of the lowest UVT values in the industry, under full flow conditions. This dispels the myth that UV cannot be used in the poorest of water qualities.