Illuminating Alternative UV Dosing Strategies
Kim Sayers (R.V. Anderson Associates Limited)

UV systems in Ontario, Canada are commonly designed for a disinfection dose of 40 mJ/cm2 to achieve 2-log, 3-log, and 2-log inactivation of cryptosporidium, giardia, and viruses, respectively. UV dose selection should not be considered only for control of select target pathogens, but also as part of a multi-barrier and/or multi-purpose treatment system to protect against a much broader spectrum of pathogens and other target compounds. Furthermore, cost-benefit analysis and consideration for flexibility for future changes should be incorporated in the UV dose selection process.

This presentation will incorporate key design considerations from three case studies in which the selected design UV dose was not the typical 40 mJ/cm2. The case studies include the Newcastle Water Supply Plant, Cannington Wells, and Decew Falls Water Treatment Plant.

For the new Newcastle WSP, a design dose of 20 mJ/cm2 was selected following a cost-benefit analysis. The remaining 1-log virus required credit is achieved with chlorine, which readily inactivates viruses.

The new Cannington Wells are non-GUDI, which require a minimum of 2-log virus inactivation. The disinfection system was designed to attain 4-log virus inactivation for this facility in anticipation of more stringent regulatory requirements in the future. Following a review of the available validated UV systems for 4-log virus removal, low-pressure high output UV system applying a UV dose of 186 mJ/cm2 was implemented.

For the existing Decew Falls WTP, a conceptual design was completed for an UV system that would be capable of disinfection and future seasonal taste and odour control. During the taste and odour season, the applied UV dose would increase to achieve both primary disinfection and 1 log removal of 2-methylisoborneol MIB.