DisinfectionQuestion 1 of 12

A plant using UV disinfection has recently started failing E. coli limits even though the UV lamps are on, alarms are clear, and UV intensity readings are similar to last month. Operators notice secondary effluent turbidity has increased from 2 NTU to 12 NTU, and final effluent TSS has increased from 8 mg/L to 28 mg/L. Which explanation best describes why disinfection performance is dropping and what the operator should focus on first?

A) The UV system is producing the wrong wavelength; the fix is to change lamp type to a different wavelength because turbidity does not affect UV systems.B) The UV contact time is too short; increasing the channel detention time is the main correction, similar to chlorine contact basins.C) Higher turbidity/TSS is blocking or shielding organisms from UV light, reducing UV transmittance; focus on improving upstream solids removal (clarifier/filters) and cleaning sleeves.D) The UV system is too weak for the flow rate; the primary fix is to add more lamps or increase lamp power regardless of effluent quality.

Practice Disinfection Questions