Full Description

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) dictates that for a drinking water treatment plant(DWTP) to receive credit for ultraviolet (UV) inactivation of chlorine resistant pathogens such asCryptosporidium and Giardia, validation testing must be performed to demonstrate that theUV reactor equipment delivers the required dose. This paper summarizes an extensivebioassay validation program undertaken at the DVGW testing center in Germany with theobjective to evaluate the performance of two closed-vessel UV reactors for the disinfectionof drinking water. A cross-flow in-line reactor and an axial-flow bottom-through-top reactoroperating with 4-kWatt medium pressure lamps were tested using the UV intensity set-pointmethod and Bacillus subtilis spores as a pathogen indicator. The paper reviews the impact ofkey design parameters on the disinfection performance as measured during bioassayvalidation testing. Key design parameters evaluated include sensor to sleeve distance,approach hydraulics, reactor inlet and outlet configuration and doped versus non-dopedsleeves. It was determined that optimization of sensor to sleeve distance is vital to yieldingmaximum reactor performance. Increasing the initial sensor to sleeve distance producedbeneficial results. Under conditions where the inlet pipe diameter was smaller than thediameter of the cross-flow reactor, the resulting approach hydraulics yielded a high inletvelocity, described as a core jet, and subsequent degradation of performance. Theimplementation of a stilling plate restored performance to some extent particularly with lowflow conditions. No significant impact on reactor performance was observed by using dopedversus non-doped sleeves. Careful consideration and optimization of the design parametersoutlined herein is a vital component of any reactor validation program, ensuring that UVreactors can deliver the proper UV dose over a wide range of water quality and flowconditions experienced at water treatment facilities. Includes 4 references, tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 16File Size: 1 file , 1.6 MB