Validation of Alternate UV Disinfection Wavelengths
DRAFT 9/15/15
Assumptions:
1. Rotavirus is still representative pathogen for UV treatment of drinking water by POE and POU.
2. Alternate UV wavelengths within range of 240 – 280 nm.
3. UV sensors can operate within this wavelength range.
4. Q-beta phage may have similar UV response to Rotavirus in both RED and log reduction.
5. MS-2 does not correlate to rotavirus for log reduction response to UV.
Goals of Validation Study:
1. Evaluate the ability of Q-beta to represent Rotavirus for UV disinfection systems.
2. Evaluate RED versus log reduction.
3. Evaluate UV inactivation response within wavelength range.
4. Evaluate the effect of alternate UV wavelengths on UV absorbant used.
Test Plan Design
Rotavirus and Q-beta will be combined into a single challenge at levels that will allow a 6 log reduction
to be demonstrated. The test water shall be set to 70% +/- 1% UVT. Evaluation of the systems shall only
be conducted under optimal steady state conditions, the instant on or overheating aspects of the
system design are not part of this validation.
Collimated beam studies of both organisms shall be conducted following the procedure in NSF/ANSI
Standard 55.
Multiple runs with both organisms shall be performed using each of the UV absorbants to evaluate the
ability of the UV sensor to correlate to the effective dose with various UV absorbance profiles and UV
wavelengths.
Test Units
Two types of test units shall be used: a low pressure mercury lamp system and an alternate UV
wavelength system with a UV output between 265 – 280nm. The systems shall be designed so that a
mean 40 mJ/cm2 dose can be achieved at 70% UVT transmittance. The systems should be designed for
a flow rate of less than 4 Lpm to simplify the equipment required to perform the test. If possible, both
systems should include a through the water UV sensor with output indication.
Test Organisms
Rotavirus (source and specification needed)
Q-beta (source and specification needed)
Test Water
Shall meet the specification currently present in NSF/ANSI Standard 55.
UV Absorbants
PHBA
Acetylsalicylic acid (aspirin)
Others?
Analytical Methods
(need to be specified)
Test Method
a) The test equipment shall be configured so that both test units can be operated using the same
influent and if possible, concurrently.
b) The test water shall contain a minimum of 106 of each organism and the appropriate UV
absorbant at 70% UVT (254nm).
c) The test water shall be sampled and confirmed to meet the test water requirements of
NSF/ANSI 55 for each batch prepared.
d) The test units shall be energized and allowed to warm up (if needed) with test water without
organism present.
e) Test water with the organisms present shall be introduced to the test units at the manufacturer
specified flow rate to achieve 40 mg/cm2 dose.
f) Microorganism samples shall be collected after a minimum of 10 unit void volumes has passed
through the test unit.
g) Influent microorganism samples shall be collected from immediately prior to the inlet of the test
system(s).
h) Perform steps e through g three times to generate samples in triplicate for each test water
configuration.
i) Repeat entire test procedure (a through h) for each UV absorbant.
Reporting
The report shall contain the following:
1. Collimated beam study for each organism.
2. Chemical analysis summary of all batches of test water.
3. Operational observations including flow rates, sensor readings and observations of test unit
functions.
4. Analysis results for all microbial samples (influent and effluent).
5. UVT analysis results
6. Deviations and interpretations of test plan.
Background and Rationale for Validation Choices
Alternate UV sources generate UV disinfection wavelengths in addition to or other than 254 nm that is
generated by low pressure mercury lamps. These sources could be single narrow band, broad band or
multiple band UV generators. The USEPA Microbiological Purifier Guide Standard is still the baseline or
referent for evaluating POU and POE products for microbiological performance and requires a minimum
of 4 log reduction of viruses. Currently, the determination whether the 4 log reduction virus reduction is
achieved by POU or POE UV systems is by correlating the UV dose required to achieve 4 log reduction of
UV resistant pathogens. When this was developed for NSF/ANSI 55, rotavirus was identified as the most
resistant common pathogen that was present in water supplies with a UV dose of 30 – 34 mJ/cm2
required to achieve 4 log reduction of rotavirus. The method of using biodosemetry was established as
a method to determine whether the minimum dose was achieved in the device under test. The baseline
dose has changed over time and is currently at 40 mJ/cm2 in NSF/ANSI Standard 55.
The weakness of this method is that UV sources do not all emit radiation at the same wavelength and
the susceptibility of pathogens and surrogate organisms to inactivation is not linear as the UV
wavelength varies and can vary between organisms. The collimated beam study is dependent on a
254nm source, so the log reductions generated based on the 254nm dose may not correlate the
response of the pathogen at the wavelength that the device is inactivating the surrogate organism.
Since the established dose (40 mJ/cm2) was generated using data primarily from UV sources at 254nm,
this dose will most likely not be relevant at other wavelengths. This has been compensated for by the
use of correction factors, however, it would be desirable to use a direct measurement of the
susceptibility of a pathogen to inactivation instead of through an indirect measure of dose. Of course, it
is greatly preferred to use a surrogate organism that has similar characteristics as a class of pathogens
and is safer and easier to analyze.
Another issue that is causing problems in the evaluation of UV POU and POE systems is the
advancement of multiple technology POU and POE treatment products. NSF is seeing more POU and
POE drinking water technologies that combine multiple technologies (UV with absorption and
mechanical filtration) and it has become much more difficult to conduct biodosemetry since in many of
these products the technologies cannot be isolated and tested separately. If UV inactivation could be
evaluated by log reduction instead of biodosemetry these products could be evaluated with the other
technologies present and yield relevant results.
I have reviewed the WRF prepublication report on evaluation on medium pressure (MP) lamp systems
for LT2 compliance. This study included UV sensitivity studies for crypto, giardia, adenovirus, MS2,
T1UV, QB, T7m, and T7. They also looked at UV sensor limitations as well as issues with quartz sleeves.
Below is a summary of findings that appear to be relevant to this effort:
1. Sensitivity variations versus wavelength between the tested organisms was extremely variable
below 240nm (over 6X variation at 200nm).
2. Sensitivity above 240 nm was more limited with peak sensitivities occurring between 260 and
270 nm with T7 and T1UV being the most sensitive (+50%) and all others grouping much closer
together.
3. Surrogates and pathogens have very different relative sensitivities to UV below 240 nm where
there appears to be much less variation above 240nm.
4. Broad band UV sensors seem to have an effective UV detection range of 240 to 280nm. Report
stated that no effective on-line UV sensors were available for wavelengths below 240nm.
5. UV of natural waters seem to show significant deviations below 240nm in absorbance
depending on the NOM present with little variation above 240nm.
Based on these observations, it appears that we will need to limit the range of UV output that we can
evaluated under the protocol, perhaps a range of 240 – 280 nm.
These observations also raise the question regarding what UV absorbant to use for evaluating UV
systems. If a system has multiple bands of output or output that is beyond the range specified that
output could skew the results of the study. It may be beneficial to use a UV absorbant that blanks out
UV wavelengths below 240 nm to minimize the possibility of this effect.
I have included the UV absorbance versus wavelength graphs for PHBA which is currently specified in
NSF/ANSI standard 55 and acetylsalicylic acid (aspirin). Aspirin has a very strong and steep absorption at
wavelengths below 240 nm and may be useful to blank these wavelengths. It also has a relatively flat
absorbance between 250 and 280 nm which may also be beneficial, but may be too low to be effective.
PHBA (parahydroxybenzoic acid)