Treatment Process Monitoringhard
A plant uses UV disinfection for final effluent treatment. The UV transmittance (UVT) of the effluent has dropped from 72% to 55% following a storm event. What is the effect on disinfection and what action should be taken?
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Correct Answer
Lower UVT means more UV is absorbed by the water before reaching pathogens; the UV dose delivered decreases and disinfection is compromised; increase UV intensity or reduce flow
UV transmittance measures how much UV light passes through the water. At 55% UVT, significantly more UV is absorbed by dissolved organics and TSS before reaching pathogens, reducing the effective UV dose. The operator should increase UV lamp intensity (if variable), reduce flow through the UV system to increase contact time, or switch to supplemental chlorination until UVT recovers.
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