With the finalization of U.S. Environmental Protection Agency's (USEPA's) Ultraviolet Disinfection Guidance Manual, utilitiesface the complex process of evaluating the relative benefits and challengesassociated with ultraviolet (UV) disinfection. Among these issues are lamp sleevefouling, its probability of occurring at a given location, and the efficacy of variousfoulant removal methods. In this study, long term fouling for a medium pressurereactor utilizing a mechanical-only abrasive sleeve cleaning system was examined.A 4-lamp, medium-pressure UV disinfection reactor was operated for 15 monthsdownstream of a conventional water treatment plant treating a blend of CaliforniaState Project water (SPW) and Colorado River water (CRW). Prior to UVdisinfection, the water was treated by a conventional treatment plant consisting ofraw-water ozonation, coagulation, flocculation, sedimentation, and biologically-active,anthracite-sand filtration. During this time the UV sleeve cleaning systemwas active and water chemistry conditions were periodically recorded. Afterremoval from the reactor, spatial distribution of sleeve UV transmittance wascharacterized and composition and quantity of lamp sleeve exterior foulingmaterials were identified.Significant exterior, and interior, sleeve fouling was discovered. The interiorfoulant was confirmed to consist of relatively high concentrations of calcium,magnesium, sulfur, and phosphorus in two of the four sleeves. Sleeve UVTmeasurements identified a reduction in transmittance from 92% (typical for cleanquartz sleeves) to less than 10% in some locations. After removal of both theinterior and exterior foulants, UVT was still low, indicating a permanent reduction insleeve UVT, perhaps by quartz solarization. While lamp sleeve exterior foulingoften depends on water chemistry and operating conditions, sleeve interior foulingmay be influenced by different issues, such as lamp materials, handling of lampsand sleeves during installation, and orientation (vertical vs. horizontal) of sleevesduring use. A mineral saturation index model was created to investigate thepossible impact on fouling of changes in water oxidation reduction potential. Includes 9 references, tables, figures.
