Full Description

Dose delivery monitoring is the only assurance that an installed ultraviolet (UV) reactor is meeting drinking water disinfection requirements. However, dose delivery monitoring approaches vary significantly with UV vendors. In this paper, CFD-based dose monitoring and UV intensity sensor modeling are used to understand the relationship between dose delivery and dose monitoring. Plots of MS2 reduction equivalent dose (RED) versus measured UV intensity are used to describe two approaches for dose monitoring. In the first approach, the target dose delivery is assured at a given flowrate when the measured intensity is above a setpoint value. This approach is shown to be most effective when the UV intensity sensor is placed at an optimum location where dose is proportional to intensity regardless of lamp power and water UV transmittance. In the second approach, the target dose delivery is assured at a given flowrate when the measured intensity and UV transmittance are both above respective setpoints. This approach works if the UV intensity sensor is relatively close to the lamp. Test conditions required to validate the first approach are shown to differ from those required to validate the second. Plots of MS2 RED versus measured UV intensity are also used to explore dose-monitoring issues with medium-pressure reactors. Large bias errors are shown to occur if the UV absorber used during validation does not mimic the absorbance spectra at a water treatment plant, and if the spectral response of the UV intensity sensor is not restricted to the germicidal region. Monte Carlo simulations are used to explore the impact of random uncertainty in UV reactor validation and on-line monitoring on dose monitoring. Includes 15 references, table, figures.

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Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 17File Size: 1 file , 410 KB