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This paper summarizes a five-month pilot study conducted with the San Francisco Public UtilitiesCommission (SFPUC) Water Quality Division undertaken to confirm what was expected to be a lowfouling potential of Hetch Hetchy water, given the low level of organic and inorganic constituents, and toevaluate potential operations and maintenance issues associated with the full-scale ultraviolet (UV) disinfectionfacility that SFPUC was concurrently planning. The scope and testing plan was not developed as aquantitative and comprehensive evaluation of the mechanisms of UV fouling.Testing was conducted at SFPUC's Tesla Portal Disinfection Facility, which serves as the primarydisinfection station for the unfiltered Hetch Hetchy supply. The pilot units were supplied with unfilteredwater upstream of any disinfection, but the pH had been raised to approximately 9.2 on average at anupstream lime addition facility.The project utilized two custom-modified UV fouling reactors with nominal chamber diameterof 8 inches. One was equipped with a single 3.6 KW, medium pressure (MP) UV lamp and a secondequipped with four 150W low pressure high output (LPHO), and four 350W low pressure high outputamalgam (LPHO-Amalgam) lamps. Due to space and water supply constraints, the reactors wereconnected in series, with water flowing through the LPHO/LPHO-Amalgam reactor and then into the MPreactor. The study was composed of five testing phases. Phase 1 was conducted from July 13 to August 6, 2007to evaluate baseline fouling during summer season. Phase 2 was conducted from August 13 to September11, 2007 to evaluate potential impacts of MP lamp ballast power output on fouling rate. Phase 3 wasconducted from September 11 to October 9, 2007 to evaluate potential impacts of water flow rate onfouling rate. Phase 4 was conducted from October 22 to November 13, 2007 to evaluate potential impactsof pH adjustment (to about 8.5 using CO2) on fouling rate. Phase 5 was conducted from November 14 toDecember 13, 2007 to evaluate baseline fouling during late fall season. Includes 19 references, tables, figures.

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Edition: Vol. - No. Published: 11/01/2008 Number of Pages: 20File Size: 1 file , 910 KB