UV Flashcards
UV + cloro
UV would be for primary disinfection of Giardia (also Cryptosporidium, if needed)
Chlorine would still be needed for primary disinfection of virus and secondary disinfection (e.g., chloramine)
Chlorine usage would not significantly change if UV is implemented
Pros de UV + cloro
UV allows the DCB to shrink in size significantly; lower facility and NPV costs
UV is the most effective disinfectant for Cryptosporidium
Implementing UV will provide a higher level of treatment for Denver Water:
Multiple barrier disinfection (UV, free Cl2, chloramine)
Cryptosporidium inactivation (not provided by free Cl2 or chloramine)
Reduced DBP formation (less free Cl2 contact time)
Overall greater public health protection
Implementing UV disinfection at Marston will provide a higher level of treatment, but lower cost given need for DCB replacement
UV dose reqs
Most reactors validated using MS-2
Validation Factors for virus inactivation much lower than for Cryptosporidium/Giardia
UV Dose
0.5-log Virus: UVDGM dose = 39 mJ/cm2
To achieve, requires MS2 RED: 45 – 50 mJ/cm2
0.5-log Giardia: <10 mJ/cm2
Recent research results (Linden et al, JAWWA, April 2009) demonstrate medium-pressure UV even more effective – potential future discussion with State
DBP considerations
EPA’s UVDGM (2006, Page 2-37): “UV light at doses less than 400 mJ/cm2 has not been found to significantly affect the formation of THMs or HAAs upon subsequent chlorination”
Often hypothesized that implementing UV will reduce chlorine use, but chlorine dose controlled by maintaining the desired residual throughout distribution system
Reckhow et al., JAWWA, June 2010: LP and MP UV tested at doses up to 120 mJ/cm2; UV disinfection did not substantially change THM orHAA formation following chlorination; Small reductions in formation observed (always <10%)
