| Abstract The use of ultraviolet light disinfection technologies continues to increase
dramatically in the number of installations for treated wastewater disinfection, and is
now experiencing a much broader application. UV is now considered a viable
technology alternative for the disinfection of Combined Sewer or Sanitary Sewer Overflows
(CSO/SSO), treated wastewater for reuse, and is under consideration by EPA as a primary
disinfectant for potable supplies. In Europe, UV is widely applied to drinking waters.
With this increasing interest in the technology, a need to assess, and in some cases,
validate the ability of commercial UV disinfection systems to reliably meet desired
treatment goals has emerged. Such a process allows the regulatory community, design
engineers and municipal officials to objectively compare competing UV technologies, from
conventional systems that use standard low-pressure mercury-vapor lamps to those with
advanced, high output mercury lamps, or alternative UV radiation sources. Such
verifications provide a level of comfort that a given technology configuration will
provide adequate protection of public health.
Several programs and sets of protocols have been developed to demonstrate and/or validate
the disinfection capacity of commercially available UV systems. These include the
U.S. Environmental Protection Agency's (EPA) Environmental Technology Verification (ETV)
program and the pending guidance and protocol prepared by the National Water Research
Institute (NWRI) and the American Water Works Association Research Foundation (AAWARF) for
drinking water and reclaimed wastewaters. In Europe, Austria and Germany have instituted
verification procedures for UV applications to drinking waters.
These initiatives are standardizing and codifying protocols that HydroQual and others have
been applying for nearly two decades in conducting biodosimetry assessments of commercial
UV systems, commonly referred to as "bioassays;" an empirical procedure that
quantifies the UV dose delivered by a particular system. The procedure correlates the
response (e.g., log survival ratio) of an indicator organism, such as the MS2 coliphage
that is in common use in the industry, with an accurately measurable dose delivered by a
validated collimated beam apparatus in the laboratory. This same culture is then used to
challenge a commercial UV system operating over a range of flows and water quality levels.
The dose that is delivered by the system is then inferred from the indicator
organism's response and the correlation to dose that had been developed in the laboratory.
With such varied entities developing these protocols, conflicting requirements have
emerged, even when the same goals are targeted. This paper will address and compare
these protocols with respect to their objectives, approach and specific testing
requirements. More importantly, observations, experiences, and lessons learned from
transferring "protocols and guidance" to a technically defensible, logistically
practical and cost-effective test program will be highlighted.
Currently, two equipment verifications are being carried out by HydroQual on commercial
systems under the EPA's Environmental Technology Verification (ETV) Wet-Weather Pilot.
Additionally, standard UV dose assays have been conducted with an MS2 phage for a
number of manufacturers and test plans have been developed to implement the National Water
Research Institute's new guidance for UV applications to reuse and drinking water
disinfection. Selected results from these test programs will be presented to address
key issues regarding the growth, storage and enumeration of MS2 phage, effective quality
assurance, in-field sampling and logistics, hydraulic measurements, lamp-age factor
testing, and cleaning mechanism evaluations. Validation of the dose-response
collimator equipment and procedures will also be discussed, including the effects of
mixing, sample depth, collimator length, radiation uniformity and transmittance. The
reproducibility of these results will be discussed, as well as the impact of the inherent
variability of the assay procedure on the design sizing of a system.
Overall, the discussion will focus on specific insights gained and "lessons
learned" that will be helpful in the design and conduct of future UV equipment
validations. |
