AWWA WQTC60686

The objective of the AwwaRF Tailored Collaboration Optimzation of UV ReactorValidation is to improve the existing tools for UV reactor validation, thereby optimizing systemsizing (reducing costs) while maintaining public health protection. This is being achievedthrough 3 main initiatives. The first involves finding a better challenge microorganism.The organisms most frequently selected for use in these tests are MS-2 coliphage (in theUnited States) and Bacillus subtilis spores (in Europe). Because these microorganisms aremuch more resistant to UV light than many waterborne pathogens, an uncertainty factor, termedthe "RED bias", is required (USEPA, 2003b). Use of a RED bias safety factor can lead to over-sizing of hydraulically well-designed UVsystems. The goal of this work was to identify and evaluate microbial surrogates whoseinactivation characteristics better match the target pathogen(s), thereby reducing the requiredRED bias value. The second initiative involves finding a better UV-absorbing compound. During reactor validation, low UV transmittance at 254 nm (UVT) water conditions aresimulated by the addition of UV-absorbing chemicals to the feed water. The most commonlyused UV-absorbing compounds are coffee (NWRI/AwwaRF, 2000), flourescein (ÖNORM, 2002)and lignin sulphonate (DVGW, 1997). For a given UVT, the UV absorbance spectra of coffee,flourescien and lignin sulphonate differ substantially from that of water treatment plant (WTP)waters. This difference impacts both dose delivery and monitoring with UV systems equippedwith medium-pressure (MP) lamps. This necessitates the use of an uncertainty factor to accountfor this difference in conditions between the test and the WTP. This safety factor is termed the"polychromatic bias."The second goal of this project is to identify and validate sources of NOM for loweringUVT during validation to reduce or, if possible, eliminate, the polychromatic bias factor. The third initiative involves investigating the impact of lamp and sleeve aging on dose delivery. Spectral shifts in the UV output of MP lamps (Phillips, 1983) and the UV transmittance oflamp sleeves (Kawar, 1998) with aging has been reported. Very significant visual changes havebeen observed in drinking water pilot studies (Mackey, 2004) and at many wastewater treatmentplants. The degree of spectral shifts in lamp output and sleeve UV transmittance withcommercial UV reactors used in drinking water applications is not known. If significant, there willbe a need to restrict sensor response or use appropriate safety factors to account for theseeffects. For this reason, this third task involves the characterization of the UV output of new andaged (during standard operation at a water or wastewater plant) UV lamps and sleeves.This paper summarizes the interim results of this on-going study and theimplications for the adoption of new validation tools in full-scale applications. Includes 10 references, tables, figure.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

8

File Size:

1 file , 470 KB