v>EPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 832-F-99-064
September 1999
Waste water
Technology Fact Sheet
Ultraviolet Disinfection
DESCRIPTION
Disinfection is considered to be the primary
mechanism for the inactivation/destruction of
pathogenic organisms to prevent the spread of
waterborne diseases to downstream users and the
environment. It is important that wastewater be
adequately treated prior to disinfection in order for
any disinfectant to be effective. Some common
microorganisms found in domestic wastewater and
the diseases associated with them are presented in
Table 1.
An Ultraviolet (UV) disinfection system transfers
electromagnetic energy from a mercury arc lamp to
an organism's genetic material (DNA and RNA).
When UV radiation penetrates the cell wall of an
organism, it destroys the cell's ability to reproduce.
UV radiation, generated by an electrical discharge
through mercury vapor, penetrates the genetic
material of microorganisms and retards their ability
to reproduce.
The effectiveness of a UV disinfection system
depends on the characteristics of the wastewater,
the intensity of UV radiation, the amount of time the
microorganisms are exposed to the radiation, and
the reactor configuration. For any one treatment
plant, disinfection success is directly related to the
concentration of colloidal and particulate
constituents in the wastewater.
The main components of a UV disinfection system
are mercury arc lamps, a reactor, and ballasts. The
source of UV radiation is either the low-pressure or
medium-pressure mercury arc lamp with low or high
intensities.
TABLE 1 INFECTIOUS AGENTS
POTENTIALLY PRESENT IN UNTREATED
DOMESTIC WASTEWATER
Organism
Disease Caused
Bacteria
Escherichia coli (enterotoxigenic)
Leptospira (spp.)
Salmonella typhi
Salmonella (=2,100 serotypes)
Shigella (4 spp.)
Vibrio cholerae
Protozoa
Balantidium coli
Cryptosporidium parvum
Entamoeba histolytica
Giardia lamblia
Helminths
Ascaris lumbricoides
T. solium
Trichuris trichiura
Viruses
Enteroviruses (72 types, e.g.,
polio, echo, and coxsackie
viruses)
Hepatitis A virus
Norwalk agent
Rotavirus
Gastroenteritis
Leptospirosis
Typhoid fever
Salmonellosis
Shigellosis (bacillary
dysentery)
Cholera
Balantidiasis
Cryptosporidiosis
Amebiasis (amoebic
dysentery)
Giardiasis
Ascariasis
Taeniasis
Trichuriasis
Gastroenteritis,
heart anomalies,
meningitis
Infectious hepatitis
Gastroenteritis
Gastroenteritis
Source: Adapted from Crites and Tchobanoglous, 1998.
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The optimum wavelength to effectively inactivate
microorganisms is in the range of 250 to 270 nm.
The intensity of the radiation emitted by the lamp
dissipates as the distance from the lamp increases.
Low-pressure lamps emit essentially monochromatic
light at a wavelength of 253.7 nm. Standard lengths
of the low-pressure lamps are 0.75 and 1.5 meters
with diameters of 1.5 - 2.0 cm. The ideal lamp wall
temperature is between 95 and 122°F.
Medium-pressure lamps are generally used for large
facilities. They have approximately 15 to 20 times
the germicidal UV intensity of low-pressure lamps.
The medium-pressure lamp disinfects faster and has
greater penetration capability because of its higher
intensity. However, these lamps operate at higher
temperatures with a higher energy consumption.
There are two types of UV disinfection reactor
configurations that exist: contact types and
noncontact types. In both the contact and the
noncontact types, wastewater can flow either
perpendicular or parallel to the lamps. In the
contact reactor, a series of mercury lamps are
enclosed in quartz sleeves to minimize the cooling
effects of the wastewater. Figure 1 shows two UV
Note: A UV bank is
composed of a
number of UV
modules
Flap gate
level control ~
UV vertical lamp
module with
support rack
Source: Crites and Tchobanoglous, 1998.
(a) adapted from Trojan Technologies, Inc.
(b) adapted from Infilco Degremont, Inc.
FIGURE 1 ISOMETRIC CUT-AWAY VIEWS
OF TYPICAL UV DISINFECTION SYSTEMS
contact reactors with submerged lamps placed
parallel and perpendicular to the direction of the
wastewater flow. Flap gates or weirs are used to
control the level of the wastewater. In the
noncontact reactor, the UV lamps are suspended
outside a transparent conduit, which carries the
wastewater to be disinfected. This configuration is
not as common as the contact reactor. In both types
of reactors, a ballast—or control box—provides a
starting voltage for the lamps and maintains a
continuous current.
ADVANTAGES AND DISADVANTAGES
Advantages
• UV disinfection is effective at inactivating
most viruses, spores, and cysts.
• UV disinfection is a physical process rather
than a chemical disinfectant, which
eliminates the need to generate, handle,
transport, or store toxic/hazardous or
corrosive chemicals.
• There is no residual effect that can be
harmful to humans or aquatic life.
UV disinfection
operators.
is user-friendly for
UV disinfection has a shorter contact time
when compared with other disinfectants
(approximately 20 to 30 seconds with
low-pressure lamps).
UV disinfection equipment requires less
space than other methods.
Disadvantages
Low dosage may not effectively inactivate
some viruses, spores, and cysts.
Organisms can sometimes repair and reverse
the destructive effects of UV through a
"repair mechanism," known as photo
reactivation, or in the absence of light
known as "dark repair."
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• A preventive maintenance program is
necessary to control fouling of tubes.
Turbidity and total suspended solids (TSS)
in the wastewater can render UV
disinfection ineffective. UV disinfection
with low-pressure lamps is not as effective
for secondary effluent with TSS levels
above 30 mg/L.
• UV disinfection is not as cost-effective as
chlorination, but costs are competitive when
chlorination dechlorination is used and fire
codes are met.
APPLICABILITY
When choosing a UV disinfection system, there are
three critical areas to be considered. The first is
primarily determined by the manufacturer; the
second, by design and Operation and Maintenance
(O&M); and the third has to be controlled at the
treatment facility.
Choosing a UV disinfection system depends on
three critical factors listed below.
Hydraulic properties of the reactor: Ideally,
a UV disinfection system should have a
uniform flow with enough axial motion
(radial mixing) to maximize exposure to UV
radiation. The path that an organism takes
in the reactor determines the amount of UV
radiation it will be exposed to before
inactivation. A reactor must be designed to
eliminate short-circuiting and/or dead zones,
which can result in inefficient use of power
and reduced contact time.
Intensity of the UV radiation: Factors
affecting the intensity are the age of the
lamps, lamp fouling, and the configuration
and placement of lamps in the reactor.
• Wastewater characteristics: These include
the flow rate, suspended and colloidal
solids, initial bacterial density, and other
physical and chemical parameters. Both the
concentration of TSS and the concentration
of particle-associated microorganisms
determine how much UV radiation
ultimately reaches the target organism. The
higher these concentrations, the lower the
UV radiation absorbed by the organisms.
Various wastewater characteristics and their
effects on UV disinfection are given in Table
2.
TABLE 2 WASTEWATER
CHARACTERISTICS AFFECTING UV
DISINFECTION PERFORMANCE
Wastewater
Characteristic
Ammonia
Nitrite
Nitrate
Effects on UV
Disinfection
Minor effect, if any
Minor effect, if any
Minor effect, if any
Biochemical oxygen
demand (BOD)
Hardness
Humic materials, Iron
PH
TSS
Minor effect, if any.
Although, if a large
portion of the BOD is
humic and/or unsaturated
(or conjugated)
compounds, then UV
transmittance may be
diminished.
Affects solubility of metals
that can absorb UV light.
Can lead to the
precipitation of
carbonates on quartz
tubes.
High absorbency of UV
radiation.
Affects solubility of metals
and carbonates.
Absorbs UV radiation and
shields embedded
bacteria.
UV disinfection can be used in plants of various
sizes that provide secondary or advanced levels of
treatment.
PERFORMANCE
Gold Bar Wastewater Treatment Plant in
Edmonton, Alberta, Canada
The Gold Bar Wastewater Treatment Plant
(GBWTP) in Edmonton, Alberta, was required to
use disinfection to meet water quality standards for
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contact recreation in Alberta. During that period,
the average and peak design flow rates for this
treatment facility were 82 and 110 million gallons
per day (mgd), respectively. A pilot study was
conducted to review current UV disinfection
systems, effectiveness of lamp intensities, and costs.
UV disinfection was determined to be the most
efficient disinfection system to achieve the required
treatment levels.
Lamp fouling is a potential problem among UV
systems, but with proper cleaning and O&M, it
should not interrupt the system's disinfection
capability. Lamp cleaning at the GBWTP was
achieved by a mechanical wiping mechanism
accompanying each cluster of lamps. Lamps were
cleaned on a regular basis using an in-channel
cleaning system. The safety concerns for both
low-pressure and high-intensity UV systems
regarding exposure to UV radiation and electrical
hazards are low under normal operating conditions.
However, precautionary measures should be taken
when operating high-intensity lamps to avoid
overexposure. The risk was not considered major
by the GBWTP and was outweighed by the
potential savings of using high-intensity UV
systems. At the GBWTP, a medium-pressure,
high-intensity system was found to be more
economical than the conventional low-pressure
systems in both capital and life-cycle costs.
Northwest Bergen County Utility Authority
Wastewater Treatment Plant in Waldwick,
New Jersey
The use of UV disinfection for wastewater
treatment has increased dramatically in the last few
years due to the impact of chlorinated organics from
sewage effluent on receiving waters. Such was the
case with the Northwest Bergen County Utility
Authority (NBCUA) Wastewater Treatment Plant
located in Waldwick, New Jersey. In 1989, the
treatment plant had to convert from chlorination to
an alternative disinfection technology with zero
residual after treatment. This change was brought
about when the "zero residual" regulation was
imposed by the New Jersey Department of
Environmental Protection with the passage of the
Toxic Catastrophic Prevention Act.
Several factors, such as public safety and recent
findings and concerns over the environmental
impact of chemical releases and spills, have led to
more stringent permit requirements for chlorine.
Also, there were other conditions that the treatment
plant had to meet if chlorine use was to continue.
To avoid the escalated costs that could be incurred
and to be in compliance with the new regulations,
the wastewater treatment plant switched to UV
disinfection. The UV system was installed within
the existing chlorine contact tanks, along with an
extension to the existing building for easy
maintenance during bad weather. The UV system at
NBCUA was able to meet fecal coliform levels (200
count per 100 ml) better than chlorination since its
installation in August 1989.
OPERATION AND MAINTENANCE
The proper O&M of a UV disinfection system
ensures that sufficientUV radiation is transmitted to
the organisms to render them sterile. All surfaces
between the UV radiation and the target organisms
must be clean, and the ballasts, lamps, and reactor
must be functioning at peak efficiency. Inadequate
cleaning is one of the most common causes of a UV
system's ineffectiveness. The quartz sleeves or
Teflon tubes need to be cleaned regularly by
mechanical wipers, ultrasonics, or chemicals. The
cleaning frequency is very site-specific, some
systems need to be cleaned more often than others.
Chemical cleaning is most commonly done with
citric acid. Other cleaning agents include mild
vinegar solutions and sodium hydrosulfite. A
combination of cleaning agents should be tested to
find the agent most suitable for the wastewater
characteristics without producing harmful or toxic
by-products. Noncontact reactor systems are most
effectively cleaned by using sodium hydrosulfite.
Any UV disinfection system should be pilot tested
prior to full-scale operation to ensure that it will
meet discharge permit requirements for a particular
site.
The average lamp life ranges from 8,760 to 14,000
working hours, and the lamps are usually replaced
after 12,000 hours of use. Operating procedures
should be set to reduce the on/off cycles of the
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lamps, since their efficacy is reduced with repeated
cycles.
The ballast must be compatible with the lamps and
should be ventilated to protect it from excessive
heating, which may shorten its life or even result in
fires. Although the life cycle of ballasts is
approximately 10 to 15 years, they are usually
replaced every 10 years. Quartz sleeves will last
about 5 to 8 years but are generally replaced every
5 years.
COSTS
The cost of UV disinfection systems depends on the
manufacturer, the site, the capacity of the plant, and
the characteristics of the wastewater to be
disinfected. Total costs of UV disinfection can be
competitive with chlorination when the
dechlorination step is included.
The annual operating costs for UV disinfection
include power consumption; cleaning chemicals and
supplies; miscellaneous equipment repairs (2.5% of
total equipment cost); replacement of lamps, ballasts
and sleeves; and staffing requirements.
Costs have decreased in recent years due to
improvements in lamp and system designs, increased
competition, and improvements in the systems'
reliability.
Medium-pressure lamps cost four to five times as
much as low-pressure lamps. However, the reduced
number of lamps necessary for adequate disinfection
could make medium-pressure lamps cost-effective.
Table 3 A summarizes the costs of some of the lamps
used in UV disinfection. This information was
collected in a study conducted by the Water
Environment Research Federation in 1995 for
secondary effluents from disinfection facilities at
average dry weather flow rates of 1, 10, and 100
mgd (2.25, 20, and 175 mgd peak wet weather
flow, respectively). Table 3B describes the typical
capital and O&M costs that are associated with a
UV disinfection.
TABLE 3A LAMP COSTS FOR UV
DISINFECTION SYSTEMS
Item
UV lamps
1-5 mgd
5-10 mgd
19-100 mgd
Construction cost
for physical
facilities
Range*
($/lamp)
397-1,365
343-594
274-588
(% of UV
lamp cost)
75-200
Typical*
($/lamp)
575
475
400
(% of UV lamp
cost) 150
* Costs are based on a 1993 Engineering News Record
Construction Cost Index of 5,210.
Source: Adapted from: Darby etal. (1995) with permission
from the Water Environment Research Foundation.
TABLE 3B CAPITAL AND O&M COSTS
FOR UV DISINFECTION SYSTEMS
Cost Item
UV System Cost ($)
Capital Costs
Equipment
Structural modifications
Electrical
Miscellaneous
120,000
64,000
20,000
40,000
Total: 244,000
Annual operating and maintenance costs
Energy 3300
Lamps and chemicals 2840
Cleaning 1180
Maintenance 1440
Process control 6240
Testing 4160
Total
19,190
Source: Hanzon and Vigilia, 1999.
REFERENCES
1. Crites, R. and G. Tchobanoglous. 1998.
Small and Decentralized Wastewater
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Management Systems. The McGraw-Hill
Companies. New York, New York.
Darby, J.; M. Heath; J. Jacangelo; F. Loge;
P. Swaim; and G. Tchobanoglous. 1995.
Comparison of UV Irradiation to
Chlorination: Guidance for Achieving
Optimal UV Performance. Water
Environment Research Foundation.
Alexandria, Virginia.
Eddington, G. June 1993. Plant Meets
Stringent Residual Chlorine Limit. Water
Environment & Technology. P. 11-12.
Fahey, R. J. Dec. 1990. The UV Effect on
Wastewater. Water Engineering &
Management, vol. 137. no. 12. pp. 15-18.
Hanzon, B.D. and Vigilia, R. 1999. UV
Disinfection. Wastewater Technology
Showcase, vol. 2. no. 3. pp. 24-28.
Hrentstein, B, Dean, T., Anderson, D., and
Ellgas, W. October 1993. Dechlorination
at EBMUD: Innovative and Efficient and
Reliable. Proceeding of the Water
Environment Federation Sixty-sixth Annual
Conference and Exposition. Anaheim,
California.
Kwan, A.; J. Archer; F. Soroushian; A.
Mohammed; and G. Tchobanoglous. March
17-20, 1996. "Factors for Selection of a
High-Intensity UV Disinfection System for
a Large-Scale Application." Proceedings
from the Water Environment Federation
(WEF) Speciality Conference: Disinfecting
Wastewater for Discharge and Reuse. WEF.
Portland, Oregon.
Metcalf & Eddy, Inc. 1991. Wastewater
Engineering: Treatment, Disposal, and
Reuse. 3ded. The McGraw-Hill Companies.
New York, New York.
Task Force on Wastewater Disinfection.
1986. Wastewater Disinfection. Manual of
Practice No. FD-10. Water Pollution
Control Federation. Alexandria, Virginia.
10. U.S. Environmental Protection Agency
(EPA). 1986a. Design Manual: Municipal
Wastewater Disinfection. EPA Office of
Research and Development. Cincinnati,
Ohio. EPA/625/1-86/021.
11. U.S. EPA. 1986b. Disinfection with
Ultraviolet Light—Design, Construct, and
Operate for Success. Cincinnati, Ohio.
12. U.S. EPA. 1988. Ultra Violet Disinfection:
Special Evaluation Project. EPA Region 5.
Chicago, Illinois.
ADDITIONAL INFORMATION
Brown and Caldwell
Raymond Matasci
P.O. Box 8045
Walnut Creek, CA 94596
Roy F. Weston Inc.
Peter J. Lau
1515 Market Street, Suite 1515
Philadelphia, PA 19102-1956
Salcor Engineering
Dr. James E. Cruver
P.O. Box 1090
Fallbrook, CA 92088-1090
Tacoma-Pierce County, WA
Steve Marek
Water Resources Section
3629 South D. Street
Tacoma, WA 98408-6897
Trojan Technologies, Inc.
David Tomowich
3020 Gore Road
London, Ontario N5 V 4T7
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U.S. Environmental Protection
Agency.
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The technical content of this fact sheet was provided by the National Small Flows
Clearinghouse and is gratefully acknowledged.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
IMTB
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MUNICIPAL TECHNOLOGY BRANCH
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