AWWA WQTC62606

The appeal of ultraviolet (UV) irradiation as an efficient method of drinking waterdisinfection continues to expand, stimulated by regulations limiting chemical disinfectionbyproducts and mandating improved disinfection of surface waters. Sleeve foulingmechanisms, including precipitation of dissolved minerals, interfere with the disinfectionprocess by absorbing radiation that would otherwise pass through quartz lamp sleevesand into the water being treated. Previous anecdotal observations have linked lamp sleevefouling to high water mineral content, and specifically to high concentrations of themetals that are most often found in the lamp sleeve foulant matrix: iron and calcium. However, the effects of oxidation/reduction (redox) potential on fouling behavior havenot been examined in detail. In this study,a commercially produced, enclosed, low-pressure high-output (LPHO) reactor was usedwith three groundwater treatment facilities to classify lamp sleeve fouling characteristics.All three facilities were characterized by high concentrations of ionic constituents that are commonly found in inorganic foulant matrixes from UV systems. At two of the facilities,fouling experiments were conducted at several locations within the system to allowexamination of the effects of the introduction of oxidizing chemicals (chlorine andoxygen) on fouling dynamics.Although high inorganic ion concentrations were measured in all source waters used inthis research, fouling dynamics were highly variable. Fouling rates generally werehighest when source waters contained high concentrations of inorganic foulantconstituents, and when they were experiencing (or had recently experienced) rapidincreases in redox potential. It is hypothesized that these increases in redox potentialresulted in rapid changes in the solubilities of some metal-ligand combinations, therebypromoting fouling. Moreover, it is hypothesized that the formation of these foulants wasaccompanied by co-precipitation of other metals and anionic ligands that may not havebeen otherwise influenced by changes in redox potential.Collectively, the results of these experiments indicate that fouling behavior is stronglyinfluenced by source water composition, including redox potential. Decisions regardingthe location of UV reactors within treatment operations should take this behavior into account. Includes 11 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

16

File Size:

1 file , 800 KB