Purpose
There is already considerable operational experience with the UV
disinfection of drinking water globally and in the UK. Other
countries have developed UV disinfection regulations and guidance
manuals (ÖNORM 2001 and 2003; NWRI-AWWARF 2003; DVGW 2006; USEPA
2006) and several industry organisations have produced survey
reports (e.g. UKWIR, AWWA) that provide detailed recommendations
for the proper installation, maintenance, and operation of UV
disinfection systems as well as cost summaries (Cotton et al. 2005;
Bolton and Cotton 2008; Camm et al. 2008). The intention of this
Policy Position Statement (PPS) is neither to re-state these
previous recommendations nor to challenge any of them. Rather, this
PPS is intended to set out CIWEM's current position on the UV
disinfection of water supplies in light of the recent amendment to
the Water Supply (Water Quality) Regulations and make
recommendations for consideration in the UK water industry
context.
CIWEM's Position on UV Disinfection
UV disinfection is now an established primary disinfection
process that is recognised to be an effective treatment against a
range of waterborne pathogens, including certain chlorine-resistant
pathogens (e.g. Cryptosporidium), although it is less effective
than chlorine against viruses. UV disinfection, properly
implemented in conjunction with other treatment processes as part
of an overall multi-barrier treatment strategy, can serve as an
effective treatment for the control of certain microbial pathogens
and may be the most appropriate treatment in some situations.
Key Recommendations for the UK Water Industry
(i) There is currently no regulatory instrument in
the UK to provide specific guidance on the proper installation,
operation and maintenance of UV disinfection systems. With the
recent amendment to the Water Supply (Water Quality) Regulations,
it is recommended that the additional disinfection barrier provided
by UV disinfection should be taken into account in current and
future Drinking Water Safety Plans (Camm et al. 2008).
Update: In February 2010 the Drinking
Water Inspectorate published an ultraviolet disinfection guidance
document entitled
"Guidance on the use of Ultraviolet (UV) irradiation for the
Disinfection of Public Water Supplies".
(ii) Proper dose monitoring and regular system maintenance are
crucial for effective UV disinfection performance. UV
disinfection systems installed in the UK should be properly
validated, using standardised procedures, within their intended
normal operating ranges (e.g. flow rate, UV transmittance) to
ensure a consistently achieved adequate UV dose with a justified
margin of safety. It is the responsibility of the UV system
manufacturer to provide validation documentation as well as
instructions for the ongoing maintenance of the system (e.g. lamp
replacement, sensor calibration).
(iii) A recent UKWIR report estimates that appropriately
designed UV disinfection systems typically use less than 20 kWh/Ml
of energy, versus 250-500 kWh/Ml typically for high lift pumping,
and energy use by UV disinfection is comparable with, or less than,
that for alternative treatment options of ozonation or membrane
filtration for Cryptosporidium control (Camm et al. 2008). While
overall energy consumption by water treatment facilities is
certainly an important consideration in the UK water industry,
energy usage on its own should typically not be a justification for
ruling out UV disinfection as a viable treatment process option for
a given treatment works.
(iv) UV disinfection should be considered as one component
in an overall multi-barrier treatment strategy rather than a
cure-all. For example, UV disinfection is most effective when
turbidity is reduced upstream, e.g. by conventional coagulation,
flocculation, sedimentation, and/or filtration. This is to prevent
suspended particles from blocking the pathway between the UV light
and target pathogens. Also, UK practice requires that a chemical
disinfectant must be added post-UV disinfection to provide a
secondary disinfectant residual for the distribution
network.
(v) Selection of UV disinfection for a particular treatment
works needs to be considered on a site-specific basis, taking into
account water quality, associated treatment and the nature and
magnitude of the microbial challenge.
Context
Ultraviolet (UV) disinfection involves the application of
germicidal UV wavelengths to water, which damages microbial cell
components and thereby prevents cell replication and renders
pathogens harmless. UV disinfection has been proven to inactivate
certain chlorine-resistant pathogens such as Cryptosporidium as
well as a range of other waterborne pathogens. Applied at
conventional UV doses, there is little to no known formation of
regulated disinfection by-products associated with UV disinfection,
which is an advantage over chemical disinfectants (e.g. chlorine,
ozone). The increasing number of applications of UV disinfection in
several countries throughout the world over the past decade
(especially in North America, Europe) has led to the development of
cost-competitive, optimised UV disinfection system designs that can
be applied to a range of treatment plant sizes, from small
groundwater systems up to water supplies for major cities (e.g. New
York City). UV disinfection in the UK to-date has been mostly
restricted to smaller groundwater sites (<10 Ml/d) (Camm et al.
2008).
A recent amendment to the Water Supply (Water Quality)
Regulations for England and Wales came into force on 22 December
2007 (2007 Statutory Instrument No. 2734) and has direct relevance
to the future of UV disinfection in the UK. Specifically, section
26(5) of the amendment defines an "adequate treatment process" to
now include any "process of blending or purification treatment
which removes or renders harmless the value of concentration of any
property of, organism or substance in, water, so that supplies do
not constitute a potential danger to human health". The inclusion
of the words "or renders harmless" removes a previous obstacle to
the implementation of UV disinfection in water supplies, since UV
disinfection inactivates microorganisms (e.g. Cryptosporidium)
without physically removing them (e.g. as in membrane
filtration).
The Chartered Institution of Water and Environmental Management
(CIWEM) is the leading professional body for the people who plan,
protect and care for the environment and its resources, providing
educational opportunities, independent information to the public
and advice to government. Members in 97 countries include
scientists, engineers, ecologists and students.
References / Further Reading
Bolton, J.R. and C.A. Cotton. (2008). The Ultraviolet
Disinfection Handbook. American Water Works Association (AWWA),
Denver, CO, USA.
Camm, R., Ferrere, P., Hall, T., and G. Stanfield. (2008). UV
Inactivation of Cryptosporidium. UK Water Industry Research (UKWIR)
Report 08/DW/06/20. UKWIR, Queen's Gate, London.
Cotton, C.A., Passantino, L., Owen, D., Bishop, M., Valade, M.,
Becker, W., Roopesh, J., Young, J., LeChevallier, M., and R. Hubel.
(2005). Integrating UV Disinfection into Existing Water Treatment
Plants. American Water Works Association Research Foundation
(AWWARF), Denver, CO, USA.
DVGW. (2006). UV Devices for the Disinfection of the Water
Supply. German Standard W 294-1, 294-2, 294-3.
National Water Research Institute (NWRI) and American Water
Works Association Research Foundation (AWWARF). (2003). Ultraviolet
Disinfection Guidelines for Drinking Water and Water Reuse. NWRI,
Fountain Valley, CA, USA.
ÖNORM (2001). Plants for Disinfection of Water Using Ultraviolet
Radiation - Requirements and Testing: Low Pressure Mercury Lamp
Plants. Austrian Standard 5873-1.
ÖNORM (2003). Plants for Disinfection of Water Using Ultraviolet
Radiation - Requirements and Testing: Medium Pressure Mercury Lamp
Plants. Austrian Standard 5873-2.
United States Environmental Protection Agency (USEPA). (2006).
Ultraviolet Disinfection Guidance Manual for the Long Term 2
Enhanced Surface Water Treatment Rule (LT2ESWTR). EPA 815-R-06-007.
Office of Water, Washington, DC, USA.
September 2008
Revised 2010
Note: CIWEM Policy Position Statements (PPS) represent the
Institution's views on issues at a particular point in time. It is
accepted that situations change as research provides new evidence.
It should be understood, therefore, that CIWEM PPS's are under
constant review, and that previously-held views may alter and lead
to revised PPS's.
