Abstract

UVT is defined as the percentage of incident light that passes through the sample.¹ It will be decreased by particulate material and by dissolved compounds that absorb at 254 nm. For our purposes the main thing to be concerned with is dissolved organic compounds. Other absorbing compounds include nitrate, nitrite, bromide, thiosulfate, ferrous iron, chloramines, chlorates, chlorites and ozone. For purposes of monitoring life support systems all of these compounds are undesirable in excess so a reduced UVT would be undesirable no matter which of these compounds is the cause. In systems using bromine as a disinfectant bromide levels may prevent use of this technique.

Marine mammal life support systems commonly use oxidants such as chlorine and ozone as disinfectants to reduce the risk of infectious disease and to meet regulatory requirements for controlling coliform levels. Oxidants added to water with high levels of Normal Organic Matter (NOM) can produce by-products of disinfection that could be harmful to the animals. In potable water production NOM is reduced by filtration, coagulation, flocculation and sedimentation to keep from exceeding allowed levels of trihalomethanes, haloacetic acids, bromate and chlorate. A primary component of NOM is Dissolved Organic Carbon (DOC) and controlling DOC will help to improve the water quality.

Measuring DOC especially in saline waters requires special equipment so samples must be submitted to properly equipped laboratories. In water with chloride the equipment used for freshwater may not be accurate because chloride interferes with some testing methods. The best instruments use a high temperature platinum catalyst and a laboratory grade clean gas supply and are expensive to purchase and maintain. A surrogate test which changes directly with changes in DOC is UVT. In a given water system the UVT changes closely follow changes in DOC making it a useful test for monitoring the adequacy of water treatment.² In potable water production systems UVT has been found helpful in monitoring for disinfection by-product formation potential. Published literature often uses UV absorbance at 254 nm to report these measurements. This formula allows conversion:

UVT = 100 * 10^A₂₅₄
Where UVT = UV transmittance at 254 nm
A^₂₅₄= Absorbance at 254 nm

Ultraviolet radiation at 254 nanometers is used for disinfection purposes. The reason for using this wavelength is that low pressure mercury lamps produce radiation at a peak of 253.7 nm and this is near the Maximum absorption of UV by DNA and RNA of 260 nm. The disinfecting effect of ultraviolet radiation is believed to be due to damage to DNA and RNA. UVT is commonly measured to determine the suitability of UV radiation for disinfection of particular waters. Equipment and techniques for measuring UVT at 254 nm are readily available.

I have used an instrument purchased from Real Tech³ designed to measure UVT in monitoring a system with Harbor Seals (Phoca vitulina) and California sea lions (Zalophus californiensis) in a chlorinated system using NaCl with Specific gravity of 1.021. Clinically I have seen correlation with reduced UVT and ocular irritation. By monitoring UVT and increasing back washing of filters and water changes whenever the UVT went below 88% episodes of ocular irritation have been reduced.

UVT can be measured with any UV spectrophotometer⁴ or with the compact and less expensive Real Tech or similar machine. No reagents are required so no waste is produced.

* Presenting author

References

1.  Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule. Washington, DC: U.S. Environmental Protection Agency, Office of Water (4601), EPA 815-R-06-007; November 2006.

2.  Junzhi Zhang, Jianwei Yu, Wei An, Juan Liu, Yongjing Wang, Youjun Chen, Jia Tai, Min Yang. Characterization of disinfection byproduct formation potential in 13 source waters in China. Journal of Environmental Sciences. (China) 2011;23(2):183–188.

3.  Real Tech Inc., 1375 Hopkins Street, Whitby, ON L1N 2C2, Canada.

4.  Organic Constituents UV Transmission (UV-254). DOC316.53.01305. Hach Company, PO Box 389, Loveland, CO 80539, USA; September 2010.