AWWA WQTC63976

With the recent Federal Register publication of the Long Term 2 Enhanced Surface WaterTreatment Rule (LT2), improved protection against resistant pathogens is mandated and focus isshifting onto meeting the requirements and practical constraints associated with solution options.One technology well-suited for meeting LT2 guidelines is disinfection by ultraviolet (UV)irradiation, which has proved effective against a range of microbial pathogens. A concern withUV treatment is the potential for performance reductions associated with fouling of the quartzsleeves that encase UV lamps. As mineral and particulate materials accumulate on sleevesurfaces, the effective lamp sleeve transmittance decreases, reducing the efficacy of thedisinfection process. Chemical and mechanical sleeve wiping systems aid in removal of lampsleeve fouling materials, but there can be uncertainty in determining to what extent thesepotentially costly systems may be necessary to ensure adequate UV exposure, and how often theyshould be activated to maintain adequate reactor function. Information is also limited with respectto the fouling effects that could be anticipated if sleeve wiping measures were interrupted.Experiments utilizing a commercial medium pressure (MP) UV disinfection reactor installed atthe City of Albany, New York's Loudonville UV Treatment Facility were conducted to assess theeffects of an interruption to sleeve wiping. The surface water source used had relatively lowconcentrations of the dissolved minerals sometimes associated with problematic sleeve fouling.Effects of sleeve wiping interruption were assessed by monitoring the temporal distribution ofUV dose, and by post-experimental analysis of lamp sleeves. The UV transmittance of both cleanand fouled sleeves was characterized over the germicidal UV wavelength range, and chemicalanalysis of lamp sleeves was performed to quantify metals content on sleeve surfaces. Ananalysis of spatial distribution for sleeve transmittance demonstrated that in this perpendicular-flowMP reactor, fouling was relatively uniform along the length of quartz sleeves. Sleevetransmittance at a wavelength of 254 nm decreased from approximately 92 % to 61% (relative toair) after four weeks. Transmittance data were also collected at other wavelengths relevant toreactors utilizing MP lamps. Flow rate and reported dose data were used to estimate reductions inUV irradiance, and over the experiment duration of 4 weeks, the average reported dose decreasedby 9.5%.Iron was present at the highest surface concentrations in sleeve foulant, which was notable due torelatively low iron concentrations in the source water. Modeling of mineral speciation andsolubility based on source water composition allowed identification of potential contributors tothe foulant that was observed. Comparisons to previous groundwater fouling experimentshighlighted differences in the potential driving forces that influence fouling rate. Includes 11 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

11

File Size:

1 file , 390 KB