Disinfection policy for UV with respect to inactivation of viruses

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Query from Jeremy Wood......

"I was just looking at the Ct calculator with a view to adjusting our disinfection policy for use of UV. I expected to see a LRV of ~ 4 for Coxsackie virus as the generally perceived wisdom appeared to be (i.e. the only spanner in the UV works I am always told is Adenovirus with high LRVs for the chlorine limiting pathogens such as coxsackie). So was hoping slotting the relevant numbers/ adjustments in was going to be straightforward with the Ct toolbox providing apt reference/ justification.

However the value coming up for all the viruses is just 2 LRV? Having just checked the report it seems to confirm a value of 2…for “viruses”. If this is the case I’d be interested to hear from others who have installed UV with “marginal” how they have got around this? Have you assumed higher values… If so obviously the Ct toolbox provides a contradiction that it would be good to resolve?"

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3 Replies

Response from Kathleen ...

Response from Kathleen Higgins....... "Not sure if this helps, but a North American Benchmarking reference for you: (reference Ontario Procedure for Disinfection, should align relatively well with USEPA Regulations) Regulations require 4 log removal of virus. Most UV systems will achieve at least 0.5 log virus removal. (reference: USEPA UV Guidance Manual) For 4 log Ct (for a bit of safety built in), At minimum water temperature you would want to design for a Ct of 12. CT Table reference: see https://www.ontario.ca/environment-and-energy/procedure-disinfection-drinking-water-ontario

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Response from Carol ...

Response from Carol Weatherley....... "We have more or less the same approach as Richard - if our catchment risk assessment indicates there is potential for human faecal contamination of the water course then our disinfection strategy states that we can’t have a disinfection credit for UV because of viruses and need to meet Ct target for chlorine. We have one or two remote catchments where there are very few if any properties where we could apply a UV credit but in actual fact we meet the chlorine Ct anyway."

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Response from Richard ...

Response from Richard lake...... "We carry out disinfection on a risk based approach. If there is the possibility of a pathway for viruses to get into the raw water (as determined by the amount of faecal contamination), then we follow UV with Super and Dechlor, with a Ct of 10. Only at sites where there is no history of faecal contamination (which is most of our groundwater sites) do we have UV plus marginal.

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