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Demonstration and evaluation of germicidal UV-LEDs for point-of-use water disinfection


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Ultraviolet (UV) irradiation is a common disinfection option for water treatment in the developed world. There are a few systems installed in developing countries for point-of-use treatment, but the low-pressure mercury lamps currently used as the UV irradiation source have a number of sustainability issues including a fragile envelope, a lifetime of approximately one year, and they contain mercury. UV light emitting diodes (LEDs) may offer solutions to many of the sustainability issues presented by current UV systems. LEDs are small, efficient, have long lifetimes, and do not contain mercury. Germicidal UV LEDs emitting at 265 nm were evaluated for inactivation of E. coli in water and compared to conventional low-pressure UV lamps. Both systems provided an equivalent level of treatment. A UV-LED prototype was developed and evaluated as a proof-of-concept of this technology for a point-of-use disinfection option, and the economics of UV-LEDs were evaluated.
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Demonstration and evaluation of germicidal UV-LEDs for
point-of-use water disinfection
Christie Chatterley and Karl Linden
Christie Chatterley
Karl Linden (corresponding author)
Department of Civil, Environmental, and
Architectural Engineering,
University of Colorado at Boulder,
Boulder, CO 80304,
Tel.: 303-492-4798
Fax: 303-492-7317
Ultraviolet (UV) irradiation is a common disinfection option for water treatment in the developed
world. There are a few systems installed in developing countries for point-of-use treatment, but
the low-pressure mercury lamps currently used as the UV irradiation source have a number of
sustainability issues including a fragile envelope, a short lifetime of approximately one year,
and they contain toxic mercury. UV light emitting diodes (LEDs) may present solutions to many of
the sustainability issues presented by current UV systems. LEDs are small, efficient, have long
lifetimes, and do not contain mercury. Germicidal UV LEDs emitting at 265 nm were evaluated
for inactivation of E. coli in water and compared to conventional low-pressure UV lamps. Both
systems provided an equivalent level of treatment. A UV-LED prototype was developed and
evaluated as a proof-of-concept of this technology for a point-of-use disinfection option, and
the economics of UV-LEDs were evaluated.
Key words
household water treatment, light emitting diodes, ultraviolet light
Diarrheal illnesses are one of the leading causes of
morbidity and mortality in developing countries (Pruss
2002;WHO 2002). In many analyses of interventions to
reduce diarrhea, “improved water quality” is shown to have
a lower effect than other interventions such as sanitation
and hygiene. However, these reviews focus upon source
water quality improvements rather than improvements at
point-of-use (Gundry et al. 2004). Fewtrell & Colford
(2004), showed the increased impact of treating water at
the household level compared to treating at the source. This
information has created an interest in household water
treatment technologies. A number of point-of-use technol-
ogies have been evaluated including boiling, biosand
filtration, chlorination, chlorination plus flocculation,
solar disinfection (SODIS), and ceramic filters (Sobsey
et al. 2008). Disinfection using ultraviolet (UV) radiation in
the UV-C range may be a more favorable option for many
applications. It does not utilize chemicals and disinfects at
much higher rates than SODIS which utilizes temperature
and radiation in the UV-A range.
UV disinfection is a well-established disinfection tech-
nology that has been used in centralized water and
wastewater facilities in developed countries for decades.
UV radiation inactivates bacteria, viruses, and protozoa,
with the benefits of no taste and odor issues, no known
disinfection byproducts (DBPs), no danger of overdosing,
relatively fast treatment rates compared to sand and
ceramic filters, and low-maintenance requirements. Over
the last ten years, small UV systems have become available,
including commercially available household systems and
the low-cost, locally manufactured UV-Tube system that
have become an appropriate treatment option for develop-
ing communities in a number of countries including
Mexico, Sri Lanka, and India (Brownell et al. 2008).
For developing communities, UV disinfection can be
an improvement over other treatment options, such as
doi: 10.2166/wh.2010.124
1QIWA Publishing 2010 Journal of Water and Health
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chemical disinfection, for many applications, but there are
sustainability issues that arise from current low-pressure
lamp systems in use. They use toxic mercury as the UV
radiation source and typically only last for 8,000 10,000
hours, at which time communities are faced with a number
of issues: finding and paying for replacement lamps,
transporting these fragile glass and filament tubes, and
disposing of mercury contained in the used lamp in areas
that do not typically have a toxic waste disposal system
(US EPA 2006).
UV light emitting diodes (LEDs) may provide solutions
to many of the sustainability issues of UV mercury lamps.
They are small (5–9 mm diameter), and do not contain
glass, filament or mercury, aiding their transport and
disposal (Bettles et al. 2007). Warm-up time is not required
for LEDs, saving energy and allowing for intermittent use
and quick recovery from a power failure—important
characteristics for rural applications especially. LEDs are
replacing a number of light sources currently utilized today
including traffic lights and household lights. LEDs have an
excellent track record for lowering system costs through
energy savings, lower maintenance, and longer replacement
intervals. The average electrical-to-germicidal efficiency of
low-pressure UV mercury tube lamps is 35–38% (US EPA
2006). Visible LEDs can operate at 75% efficiency for ten
years (100,000 hours) (Bettles et al. 2007). Currently, the
efficiencies of UV-LEDs are less than 1% with lifetimes of
around 1,000 hours (Bettles et al. 2007;Gaska 2007).
Although research of this technology is still in its infancy,
improvements to UV-LEDs are expected to occur rapidly
following visible LED source trajectories, resulting in a high
efficiency, low power input.
The availability of specific output wavelengths using
UV-LEDs may also increase their inactivation efficacy.
UV-LEDs currently operate in the wavelength range of
247 –365 nm (Gaska 2007). Effective UV sources should
emit high intensities in the peak absorbance wavelengths of
DNA—the germicidal target of UV photons. However,
germicidal effectiveness as a function of wavelength can
vary for different microorganisms and may differ from the
DNA absorbance spectrum. Supplementing peak DNA
wavelengths with other UV emissions may provide a
synergistic disinfection effect, increasing the effectiveness
of UV inactivation of pathogens (Mamane-Gravetz et al.
2005;US EPA 2006;Linden et al. 2007). Low-pressure
lamps are monochromatic (254 nm) and some pathogens,
such as adenovirus, are not most effectively inactivated at
this wavelength. Medium Pressure lamps are polychromatic,
but peak intensities occur at set wavelengths based on the
emission properties of mercury. A distinct advantage over
conventional UV sources is that UV-LED systems can
incorporate an LED array of differing UV wavelengths,
maximizing their combined germicidal effect. This would
allow units to be custom designed based on the specific
pathogens of concern in source waters, or for a broad range
of pathogens under a single system.
Limited research has been conducted on the effective-
ness of UV-LEDs for water disinfection. Most of the data
available are for LEDs that emit light in the UVA range
(320 –400 nm), which is less efficient at disinfection than
light in the germicidal range of UVC (200–280 nm) since it
is poorly absorbed by DNA (Sinha & Ha¨ der 2002; ISO
21348 2007). UVA radiation inactivates microorganisms by
damaging proteins and producing hydroxyl and oxygen
radicals that can destroy cell membranes and other cellular
components (Sinha & Ha¨ der 2002). This process takes more
time than the damage produced by UV-C, which directly
effects the DNA of microorganisms by producing cyclobu-
tane thymine dimers, among other products, inactivating
them without intermediate steps (Grossweiner & Smith
1989). Hamamoto et al. (2007) demonstrated the ability of
UVA-LEDs at 365 nm to inactivate bacteria in water. They
found that E. coli DH5awere reduced by .5 log at a dose
of 315 J/cm
approximately 30,000 times higher dose than
required for UV 254 nm. Sandia National Laboratories
documented inactivation of E. coli with LEDs in the UVC
range at 270 nm (Crawford et al. 2005), and found
comparable inactivation to LP UV. Sensor Electronics
Technologies (SET) has also demonstrated inactivation of
E. coli B using 265 –310 nm UV-LEDs (Gaska 2007),
reporting wavelength dependent inactivation with inacti-
vation decreasing by more than 6 orders of magnitude from
265 nm to 310 nm.
Research objectives
The goal of this research was to evaluate the efficacy of
Ultraviolet Light Emitting Diode (UV-LED) technology for
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the development of point-of-use (POU) water disinfection
systems to improve public health in rural communities in a
sustainable, environmentally responsible manner. There are
a number of POU technologies available, but the appli-
cation of UV-LEDs as a disinfection source will provide an
additional technology to the POU toolbox that will enable
longer-life disinfection systems with low user input and very
low energy cost compared to current low-pressure mercury
lamps. This will improve public health by increasing system
reliability and decreasing maintenance needs.
Specifically, this research evaluated the use of UV-
LEDs at 265 nm for inactivation of E. coli in water through
the following objectives: (1) Compare the inactivation
efficiency of UV-LEDs at 265nm to conventional low-
pressure lamps (254 nm) for inactivation of E. coli, (2)
Evaluate a point-of-use UV-LED flow-through prototype,
and (3) Determine if UV-LEDs are a feasible option for
water treatment based on economics and current state of
the technology.
Microbial methods
E. coli K12 (ATCC #29425) was used as an indicator
organism to compare the efficiency of the LP and UV-LED
systems, and to evaluate the UV-LED prototype. One
colony (to assure genetic homogeneity) was obtained from
a tryptic soy agar (TSA, Difco #236950) plate after 24 hours
of incubation at 378C and added to 10 mL of sterile tryptic
soy broth (TSB, Cellgro #61-412-RO) in a sterile 15 mL vial.
The vial was rapidly vortexed to break up the colony and
then the 10 mL solution was added to 90 mL of TSB in a
sterile 250 mL glass bottle with a sterile magnetic stir bar.
The stock solution was incubated at 378C on a stir-plate to
assure constant mixing and oxygen levels throughout the
stock. This solution was kept at 48C for less than 2 weeks to
inoculate future stock solutions. Purity was verified by
streak plating and visual observation on TSA.
A growth curve was developed based on the optical
density at 600 nm (OD600), measured every 30 minutes,
and cultured colonies to identify the log growth phase. Tests
were conducted at log growth phase. The E. coli were
washed three times in phosphate buffer solution (PBS) by
centrifuging and added to 194 mL of PBS to achieve a
concentration of approximately 10
CFU E. coli per mL for
batch irradiation testing. The ultraviolet absorbance was
adjusted for flow-through tests by varying the E. coli
preparation steps (washing).
After irradiation, each sample was successively vortexed
and serially diluted. E. coli concentrations were measured
using the spot plating method (Gaudy et al. 1962), which is
advantageous because four dilutions of five replicates each
can be read on one 100 mm diameter plate, which would
otherwise require twenty 60 mm diameter plates using the
vacuum filtration method. Once the spots had completely
dried, the plates were placed upside down in a 378C
incubator and incubated for 24 hours before colonies
were counted. Spots with 3 to 30 colonies were recorded
(CFU/0.01 mL). If two dilutions had results that fell into
this range, the lower dilution (more colonies in each spot)
was chosen.
Experimental set-up
Low-pressure (LP) UV lamps were housed in a UV
collimated beam apparatus (Bolton & Linden 2003).
A UV-LED batch irradiation system was designed with an
array of three UV-LEDs using a circuit wire-wrapped with
30 gauge wire, to an electronic Perfboard (a fiberglass board
with holes every 2.5 mm). A 150-ohm resistor was wired in
series with each LED to create 6 volts across each LED at
20 amps with a 9 volt input voltage from a power supply.
These values were within manufacturer specifications for
voltage and current. Socket pins were wire-wrapped to
the Perfboard to hold the LEDs in place for easy removal
and replacement. A flow-through prototype consisting of
a compact row of ten UV-LEDs was created using similar
electronics to the batch system. The LEDs were placed over a
6.5 mm £6.5 mm aluminum channel 1 mm above the water
surface, with a water depth of 7 mm. The 265 nm hemi-
spherical UV LEDs were purchased from Sensor Electronic
Technology, Inc (SET) (Columbia, South Carolina).
Irradiance measurements
Irradiance for the LP and LED light sources was measured
with a radiometer (International Light IL1400A, SEL
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240/TD detector) calibrated at 254 nm. The manufacturer’s
detector response curve was used to adjust the radiometer
reading to the 265 nm peak output wavelength of the LEDs.
The radiometer measurements were checked and corrobo-
rated using an iodide/iodate actinometer (Rahn et al. 2003).
The absolute irradiance and spectral output of each LED
was also evaluated using an Ocean Optics spectrometer
(USB 2000 þ, Dunadin, FL).
UV irradiation
All tests were completed within two hours and irradiated
samples were covered to minimize photoreactivation as
much as possible.
To benchmark the efficiency of LP UV, the collimated
beam apparatus was used to expose 40 mL portions of E.
coli spiked PBS at UV fluences ranging from 0 to 20 mJ/cm
in a sterile 50 mL glass crystallization dish (2.2cm diameter)
stirred with a sterile magnetic stir bar. The UV-LED devices
were evaluated by exposing 7 mL of E. coli spiked PBS in a
10 mL beaker (2.2 cm diameter) stirred with a sterile
magnetic stir bar to UV doses between 0 and 20 mJ/cm
The UV-LED prototype was evaluated by flowing E. coli
spiked PBS and E. coli spiked natural water (collected from
a local pond) through the system. Initial E. coli concen-
tration was tested by running the sample through the
prototype with the LEDs turned off. Log reduction of E. coli
was evaluated for multiple flow rates and multiple UV
absorbance values. The system was disinfected between
tests using a low concentration chlorine solution.
UV dose calculations
The average irradiance in the UV-exposed sample was
calculated according to Bolton and Linden (Bolton &
Linden 2003). A petri factor of 0.98 and 1 were determined
for the LP and LED systems, respectively, and a reflection
factor for water of 0.975 was used. The water factor
accounted for the UV absorbance of the water through
the sample water depth at 254 nm and 266 nm for the LP
and LED systems, respectively (measured with a spectro-
photometer, HACH DR 5000).
Irradiation time was controlled by a manual shutter for
LP tests and by turning on/off the LEDs. The LP lamps and
LEDs were allowed to warm-up for 10 minutes before tests
and the LEDs were turned off for a maximum of 10 seconds
while tests were being set-up, which did not significantly
affect the irradiance upon turning back on.
The E. coli colonies were averaged for the five spots and
converted to CFU/mL by multiplying by the dilution factor.
The log reduction (log N
/N) was calculated for each dose
based on the initial non-irradiated E. coli concentration, N
(CFU/mL) and the concentration of E. coli post-irradiation,
N (CFU/mL).
Irradiance during warm-up time
The irradiance over time (0, 1, 2, 5, 10, and 20 minutes from
start) was measured to determine the warm-up time of both
the low-pressure (LP) lamps and the UV-LEDs. Over the
first 10 minutes after start-up, the irradiance of the UV-
LEDs decreases by about 7% and the irradiance of the LP
lamps increases by about 20%, after which time both
sources level out (Figure 1).
Seven LEDs from SET were tested including four flat
top 265 nm LEDs, one flat top 250 nm LED, one flat top
280 nm LED, and one hemispherical lens 280 nm LED. The
spectral irradiance of each LED was measured with a
spectrometer (Ocean Optics USB 2000 þ) as presented in
Figure 2. The UV-LEDs from SET had a broader bandwidth
than the monochromatic 253.7 nm produced by low-
pressure lamps. The full width at half maximum (FWHM),
measured across the spectral output at 50% of the peak
Figure 1
Warm-up time for UV-LEDs (B) versus Low Pressure Lamps (O).
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irradiance, was 11 nm for the 265 nm LED, slightly lower
than the manufacturer FWHM specification of 12 nm. The
broader emission spectra could have implications for
system designs, paricularly if very specific wavelengths
are desired.
Irradiance from a single 265 nm hemispherical lens
UV-LEDs was measured at distances from the source up to
four cm, to estimate the effect of distance on irradiance
changes, specifically for future modeling and estimating UV
dose for the prototype unit. The irradiance output from the
265 nm LEDs tested varied from 60 to 30 mW/cm
distances of 0.5 to 4 cm as illustrated in Figure 3.
Inactivation of E. coli
Low-pressure versus UV-LEDs
Log reduction of E. coli K12 appears to be slightly improved
for the LED source at low doses and approximately the
same at higher doses, based on twenty three and eighteen
data points in duplicate for the LED and LP sources
respectively, as illustrated in Figure 4.
The relationship of log inactivation versus dose received
was modeled using a logarithmic regression. Based on
results of paired t-tests conducted over the log inactivation
data at each dose (2, 5, 10, 15, and 20 mJ/cm
) for low-
pressure versus LED sources, it can not be concluded that
the low-pressure and LED sources are statistically different
for the inactivation of E. coli K12 at a 95% confidence,
although there is a statistically significant difference at a
90% confidence level.
UV-LED flow-through prototype
The ten-LED prototype was evaluated using biodosimetry
with E. coli K12. The linear trendlines for log reduction with
varying UV absorbance values all have a similar slope
(within one log reduction per one liter per hour) and the
waters with lower UV absorbance values are disinfected to
the same level as waters with higher UV absorbance values
when lower flow rates were used (Figure 5). The inacti-
vation in natural water (UV absorbance of 0.259) was
similar to the PBS samples.
In order to compare the prototype to commercial
systems, the dose provided for a given flow rate in
mL/min and influent water UV transmittance (UVT) are
needed. The log reduction of E. coli for a given UV-LED
dose was calculated based on the logarithmic regression
model (log reduction ¼1.25 £Ln(Dose) 20.3665) on the
Figure 2
Irradiance and spectral emission from 250, 265, and 280 nm UV-LEDs.
Figure 3
Irradiance of one 265 nm LED as a function of distance from the LED.
Figure 4
Log reduction of E. coli K12 by irradiation from low-pressure lamps (254 nm)
and LEDs (265 nm). Data lines represent logarithmic regression and error
bars represent one standard deviation of the mean of quintuplicates.
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E. coli inactivation data presented in Figure 4. For a UVT of
88%, a dose of 10 mJ/cm
can be achieved at a flow rate of
14 mL/min. For a UVT of 74%, the flow rate required for a
dose of 10 mJ/cm
is 11.1 mL/min. Therefore, forty LEDs
(four rows of 10 LEDs in the same geometry as the
prototype) at a flow rate of 11.1 mL/min could provide a
dose of roughly 40 mJ/cm
, a typical dose for commercial
UV disinfection systems. Forty LEDs emitting at 265 nm
have a total rated output of 14.4 mW of power, therefore
1.3 mW are needed per mL/min flow rate to achieve a dose
of 40 mJ/cm
. This value is used to compare LED and LP
systems in Table 1. However, direct comparison is highly
dependent on reactor hydraulics and the comparison
presented is used only as a case study based on the LED
prototype evaluated. The power requirements for UV-LED
systems have the potential to be reduced by optimizing
reactor geometry and water depth. The use of UV-LEDs
may facilitate optimization through creative system design
options based on their small individual size.
Evaluation of current and future UV-LED technology
LEDs that emit light in the germicidal wavelength range are
a relatively new technology and current values for cost,
output power, and lifetime do not at present allow them to
be a viable option for the replacement of low-pressure
lamps used for drinking water disinfection, especially in
developing communities. Based on a household system that
needs to provide twenty liters per person per day for a
family of four (eighty liters per day total), and a dose of
40 mJ/cm
and 75% UVT, a comparison was conducted of
current UV-LEDs with current LP systems such as the
UV-Tube and the Sterilight (R-Can Environmental Inc.,
Guelph, Ontario, Canada) systems. The base case includes
current UV-LED specifications and assumes a constantly
running system. The comparison presented in Table 1
shows the much greater cost of UV-LEDs, both upfront
and over time since the lifetime is much lower than the LP
systems. However, SET and Crystal IS (Green Island, New
York), manufacturers of UV-LEDs, estimate great improve-
ments in the next three to four years. If the projected values
manufacturers are aiming for are met, a UV-LED system
could be a viable and improved option over current LP
systems and fill a gap for low-flow, inexpensive systems in
three to four years (Table 1).
Increasing power output will be necessary for systems to
utilize a reasonable number of LEDs independent of lamp
cost. Each LED requires wiring and other electrical
components such as resistors and heat sinking material.
More LEDs also require a larger system and more materials
that will cost more up front. Maintenance will also be more
difficult with a larger number of LEDs since each device will
need to be monitored to detect failures. This will be
particularly important for systems that require a high flow
rate, where thousands of LEDs may become difficult to
install and maintain. Based on manufacturer expectations,
100 mW (power output) LEDs should be on the market by
2013. Improving the power output based on manufacturer
projections over the next three to four years, shows a large
Figure 5
Dose for given flow rate and UV transmittance for E. coli K12 spiked into
PBS and natural water.
Table 1
Comparison of current and projected future UV-LEDs with LP systems
UV-Tube Sterilight Base case
3– 4 year
MW/Lamp (output) 15,000 10,000 0.36 100
Lifetime (hrs) 9,000 9,000 1,000 10,000
Cost ($/mW)*0.0013 0.0055 664 0.1
Flow rate (mL/min) 6,000 1,890 55.55 55.55
Total mW (output)
72.22 72.22
Number of LEDs 201 1
Upfront lamp cost ($) 20 55 47,943 7
3 year cost 60 165 1,260,063 21
20 year cost 389 1,071 8,400,421 123
$ values in USD. Current LED cost based on purchase price from SET December 2007.
Total power output was calculated by multiplying the flow rate by 1.3 as found in the
prototype testing.
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decrease in the number of LEDs required (from over 200 to
only one LED) for a constantly running household system
that would treat eighty liters per day at 40 mJ/cm
with a
UVT as low as 75%.
One of the most desired features of LEDs for disinfec-
tion systems is their long lifetime, particularly for develop-
ing communities, where replacements can be difficult to
come across. According to SET engineers, UV-LEDs in the
germicidal wavelength range currently have very low life-
times of approximately 1,000 hours before 50% power
reduction is reached. Manufacturer projections for the next
three to four years would offer lifetimes equal to that of LP
lamps (10,000 hours by around 2012). However, since they
do not need to warm-up, they can be effectively run
intermittently on demand, increasing the total lifetime ten
to twenty fold assuming no decay due to frequent on-off
switching. LP lamps can be run intermittently as well, but
due to the required warm-up time, water is not available on
demand without the need for storage, a known hygiene risk.
Because UV LEDs were shown to be as effective for
bacterial inactivation as LP UV lamps, the most influential
factor to improve the adoption of UV-LED disinfection is
cost decrease. Based on manufacturer’s three to four year
projections, the cost will decrease over 1,000 fold to $0.1
per mW in 2013. The large decrease in three-year cost for a
household system brings the total cost to $190 USD, which
is almost as cheap as the three year cost for the Sterilight
system lamps at $165 USD (Table 1).
Combining projected improvements to power output,
lifetime, and cost per mW, results in UV-LEDs being a
feasible option and an improvement over LP systems
around the year 2013 (Table 2). If the projections can be
met, it will be possible to develop a household system that
will treat eighty liters per day at 40 mJ/cm
(if UVT of
water greater than or equal to 75%) for $7 USD of upfront
lamp cost, compared to $20 to $55 USD for lamps in the
UV-Tube and Sterilight systems, respectively. The cost
savings will increase yearly with slightly higher lifetime
values of 10,000 hours for the LEDs, versus 9,000 hours for
the LP lamps, resulting in lower yearly replacement costs.
The long-term cost savings can be increased further
and the maintenance required to replace burned out lights
Table 2
Effect of improving all three parameters; power output, lifetime, and cost
Vary all Base case Case 1 Case 2 Case 3 Case 4 Case 5
MW/lamp 0.36 2 5 10 50 100
Lifetime (hrs) 1,000 2,000 4,000 6,000 8,000 10,000
Cost ($/mW) 664 332 100 10 1 0.1
Total lifetime (days) 42 83 167 250 333 417
Total lifetime (years) 0.11 0.23 0.46 0.68 0.91 1.14
Number of LEDs 201 37 15 8 2 1
Total lamp cost (upfront) USD 47,943 23,975 7,222 722 72 7
Cost for 3 years USD 1,260,063 315,068 47,450 3,163 237 19
Table 3
Effect of increasing flow rate for future UV-LED systems
Vary flow rate Constant Case F1 Case F2 Case F3 Case F4 Case F5
Flow rate (mL/min) 55.55 500 1,000 1,890 5,000 6,000
Hours/day 24.0 2.7 1.3 0.7 0.3 0.2
Total lifetime (days) 417 3,750 7,500 14,175 37,500 45,000
Total lifetime (years) 1.14 10.27 20.55 38.84 102.74 123.29
Total mW 72.22 650 1,300 2,457 6,500 7,800
Number of LEDs 1 7 13 25 65 78
Total lamp cost (upfront) 7 65 130 245.7 650 780
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can be decreased, by increasing the system flow rate and
turning on the LEDs intermittently as water is needed
without the need for storage where recontamination can
easily occur (Table 3).
UV-LEDs are an effective technology to inactivate E. coli in
water, comparable to LP UV mercury vapor lamp technol-
ogy. The efficiency of UV-LEDs at 265 nm was not found to
be statistically different from low-pressure UV sources.
A ten LED prototype served as a proof-of-concept for
flow-through water treatment, but currently UV-LEDs in
the germicidal wavelength range are much too expensive,
low power and have short lifetimes. For UV-LEDs to be a
feasible option for field implementation the cost needs to
decrease and the power output needs to increase substan-
tially. However, according to an analysis of manufacturer
projections, UV-LEDs should be a viable and economic
option within four years, by around 2013. Once UV-LEDs
become a viable option, there are numerous possible
applications for UV-LED technology within the water
sector, including low-pressure lamp replacement in drink-
ing water, wastewater, and gray water treatment systems, in
solar powered or plug-in point-of-use treatment systems in
rural and urban households in developing countries, and in
portable systems.
This work was funded by a fellowship to Ms. Christie
Chatterley from the National Water Research Institute
(NWRI) and a grant from the University of Colorado
Engineering Excellence Fund (EEF). The authors wish to
thank Dr. Kevin McCabe (University of Colorado), Mr. Tim
Bettles (Crystal IS), Tim May (University of Colorado),
Naomi Levine (Boulder, CO), Christina Barstow (University
of Colorado) and David Sparkman (University of Colorado)
for their assistance in the research and data analyses.
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First received 26 August 2009; accepted in revised form 2 January 2010. Available online 9 March 2010
8C. Chatterley and K. Linden
UV-LEDs for water disinfection Journal of Water and Health
Uncorrected Proof
... Besides, due to its low energy efficiency of 15-35%, a high-pressure mercury lamp consumes a significant amount of energy to work. Additionally, due to its short average lifespan, its effect on pathogens weakens and disappears if it is not renewed in time (Chatterley & Linden, 2010;Autin et al., 2013). On the other hand, UV-Led lamps are economical lighting and sterilization lamps made of semiconductor material and available in various wavelengths (Harris, Pagan & Batoni, 2013). ...
The present study was planned with the aim of inactivating the total bacterial load and species in tilapia fish tanks kept in fresh and seawater conditions with high stock density with different UV lamp models. In this context, the UVC+UVA-Led lamp system was compared with the conventional UVC lamp system and the total bacterial load in the tanks and the inactivation effect on the bacterial species were determined. Total bacterial load on the medium and bacteria species were identified in terms of their morphological characteristics using the spread plate method. Bacteria that emerged at different times in the trial sets were identified as Edwardsiella tarda, Salmonella sp., Aeromonas hydrophila, Pantoea sp., Citrobacter youngae, Serratia ficaria and Citrobacter freundii. The total bacterial load in both freshwater and seawater environments in both lamp groups showed a decrease compared to the control group. With this, the conventional lamp model was more effective on the total bacterial load in the samples taken during the trial. Although all bacteria were inactive in both lamp groups, Serratia ficaria bacteria were not eliminated in the seawater environment. The results show that UV LEDs can be a better alternative to traditional UV mercury lamps for water disinfection.
... Conventional UV sources for disinfection systems include low-or medium-pressure mercury lamps able, respectively, to produce a single monochromatic wavelength of 254 nanometers or multiple types of wavelengths ranging from 200 to 400 nanometers [23]. Although still widely used, they present several critical issues as brittleness, toxicity (due to mercury), a relatively short lifetime, and a significant energy demand [24,25]. Nevertheless, in the past few years, with the rapid development and improvement of the semiconductor industry, UV light-emitting diodes (UV-LEDs) have emerged as a new source to generate UV radiation [22]. ...
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Surfaces in highly anthropized environments are frequently contaminated by both harmless and pathogenic bacteria. Accidental contact between these contaminated surfaces and people could contribute to uncontrolled or even dangerous microbial diffusion. Among all possible solutions useful to achieve effective disinfection, ultraviolet irradiations (UV) emerge as one of the most "Green" technologies since they can inactivate microorganisms via the formation of DNA/RNA dimers, avoiding the environmental pollution associated with the use of chemical sanitizers. To date, mainly UV-C irradiation has been used for decontamination purposes, but in this study, we investigated the cytotoxic potential on contaminated surfaces of combined UV radiations spanning the UV-A, UV-B, and UV-C spectrums, obtained with an innovative UV lamp never conceived so far by analyzing its effect on a large panel of collection and environmental strains, further examining any possible adverse effects on eukaryotic cells. We found that this novel device shows a significant efficacy on different planktonic and sessile bacteria, and, in addition, it is compatible with eukaryotic skin cells for short exposure times. The collected data strongly suggest this new lamp as a useful device for fast and routine decontamination of different environments to ensure appropriate sterilization procedures.
... In addition, these lamps are energyconsuming, with low efficiency. And they have a short service life, approximately 10,000 hours [13,14]. ...
... In addition, these lamps are energyconsuming, with low efficiency. And they have a short service life, approximately 10,000 hours [13,14]. ...
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Introduction. Disinfection of sweat water is one of the main factors of the epidemiological well-being of the population. The classic and most common method of water purification is the use of chemicals. But this method has a whole effect on chemicals, in particular, on chemicals that can cause health problems, in particular, when chlorine compounds are used as a negative disinfecting agent. In addition, during military operations or man-made disasters, there is a need for individual means of water disinfection. This method, an alternative to the classical method, is the use of ultraviolet radiation for water disinfection. Today, during infectious industrial disinfection at city water treatment plants, UV radiation is used in combination with chemical and other physical methods of disinfection of drinking water. But today, low-pressure UV lamps work there, which additionally creates a large amount of ozone. For individual use, even in conditions where the power supply is limited or absent, this is unacceptable. Therefore, in the context of compactness and energy saving, it is effective to use LED lamps, which have an undeniable advantage over old UV lamps, especially low-pressure mercury lamps. In our review of the features of the work of LEDs, in particular, the bactericidal effect at different wavelengths, the time of their effective use. At the same time, one of the main factors affecting the use of UV LEDs is the possibility of creating monochrome sources of ultraviolet radiation and very low energy consumption, which allows you to create a compact device specifically for individual use. Thus, it is possible to obtain a program that will be effective for disinfecting sweat water without the use of chemicals or boiling. The aim of the study is to analyze literature data and determine ways to improve the method of using UV radiation for drinking water disinfection. Materials and methods. Analytical review of scientific publications was carried out using scientometric databases SCOPUS, Web of Science, Index Copernicus International Google Scholar CrossRef and others, periodicals and publications. Results and their discussion. The advantages and disadvantages of the main methods of drinking water purification are considered and summarized, depending on their effectiveness, convenience, and the presence of side effects for human health. Modern ultraviolet LEDs have been found to be a promising alternative for water disinfection due to many advantages over traditional means and methods. Their use opens up the possibilities of using various wavelengths, opening angles and innovative designs. The unique characteristics of UV LEDs, including multiple wavelengths and pulsed illumination, can increase disinfection efficiency not only under optimal conditions, but also when used in the field, during combat operations, or in emergency situations where the normal water supply is disrupted.. Conclusions. Today, in the conditions of the Russian war against Ukraine, there is an urgent need to develop a portable device for disinfecting drinking water in the field, during hostilities, or in emergency situations (natural disasters, man-made accidents and disasters, etc.), to provide military personnel or civilians population with drinking water without the risk of infectious diseases transmitted by the fecal-oral route. A promising direction of water disinfection may be the development of methods and devices using portable energy-saving sources of UV radiation based on LED technologies. Keywords: ultraviolet radiation, drinking water disinfection, microorganisms, UV lamps, UV LED monochrome source.
... Several studies have demonstrated the effectiveness of germicidal UV LED irradiation emitted at 255 nm, 265 nm, 269 nm, 275 nm, 280 nm or near relatively narrow bandwidths (total nominal width at half the maximum, FWHM, 10-12 nm) to inactivate the microorganism Escherichia Coli. These studies achieved excellent results, especially at wavelengths of 265nm and 280nm (Chatterley and Linden, 2010, Vilhunen, 2010, Bowker et al., 2011, Oguma et al., 2013, Oguma et al., 2016, Lui et al., 2016. ...
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report on the experimentation of the combination between wavelengths of 265 nm and 280 nm and study of its effects on viral cells • Bilal Cakir-Master of science (biochemistry)-Istanbul Sabahattin Zaim University • Regonesi Giuliano-NOOR Technologies A.S. Ultraviolet (UV) light emitting diodes (LEDs) are an emerging technology for disinfection processes. Deep UV LEDs that emit UV-C radiation have proved to be effective in neutralizing the structures of bacterial, viral, and protozoal pathogens. UV-C LEDs have huge potential as they are smaller, lighter, and less brittle than traditional mercury vapor lamps (Vilhunen, 2010). Furthermore, they do not contain mercury and provide instant switching on and off functionalities. Given their size, smaller than 1mm2, multiple diodes can emit from different angles unlike traditional tubular UV light sources, providing more options for a unique ballast design (Lui et al., 2016; Oguma et al., 2016). Some major studies have examined UV-C LED systems of various wavelengths for inactivating pathogens. Several studies have demonstrated the effectiveness of germicidal UV LED irradiation emitted at 255 nm, 265 nm, 269 nm, 275 nm, 280 nm or near relatively narrow bandwidths (total nominal width at half the maximum, FWHM, 10-12 nm) to inactivate the microorganism Escherichia Coli. These studies achieved excellent results, especially at wavelengths of 265nm and 280nm (Chatterley and Linden, One of the main advantages of UV LEDs is that it is possible to combine different wavelengths to optimize the inactivation of pathogens; and their lower energy consumption and higher efficiency can be achieved at a low energy cost to reach this decommissioning potential. Some disinfection processes have studied the combination of multiple UV LED wavelengths to inactivate pathogens and non-pathogenic microorganisms. Oguma et al. have experimented with combined LEDs that scatter radiation across the germicidal range and they have measured the mass inactivation of E. coli (Oguma et al., 2013). Oguma et al. did not report synergistic effects from the combined wavelengths derived from fluidity-based inactivation data. These conflicting results, as well as industry interest in combining UV LEDs for water disinfection and a general knowledge gap on the effectiveness of combined UV-C wavelengths on bacteria and viruses, created an opportunity. for further synergistic research (Song et al., 2016).
... It has also been reported that UVC-LEDs at 265 nm have higher antibacterial efficacies than LP-UV, but are limited by the higher costs of disinfection temporarily. (Chatterley and Linden, 2010). The majority of UVC disinfection devices are designed as pipeline systems, which allows optical path of UVC can be controlled and ensure the efficiency of disinfection. ...
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Ultraviolet disinfection is an important method for controlling the large-scale outbreaks of diseases in aquaculture. As a novel and promising light source, ultraviolet light-emitting diode (UV-LED) has the advantages of safety, high efficiency and no environmental pollution risks. However, it remains unclear whether UV-LEDs can replace traditional UV light sources for aquaculture water treatment processes. Present study aimed to investigate the efficacy of UVC-LEDs (265 nm) on pathogenic bacteria, specifically Aeromonas salmonicida and Escherichia coli . The effects of UVC-LED dose, light conditions, and temperature on bacterial reactivation were also investigated. The results showed that exposure to UVC-LED effectively inactivated both types of bacteria. To achieve 4.5-log inactivation of A. salmonicida and E. coli , 24 mJ/cm ² and 28 mJ/cm ² UVC-LED irradiation were required, and the inactivation rate increased with increasing UVC-LED fluence. Both A. salmonicida and E. coli were revived after UVC-LED disinfection, and photoreactivation was significantly higher than dark reactivation. Bacterial reactivation rate due to high-dose UVC-LED treatment was significantly lower than that of low-dose. After 72 h of reactivation, photoreactivation and dark reactivation rates were 1 ± 0.4% and 2.2 ± 0.2%for A. salmonicida , and 0.02% and 0% for E. coli , respectively. Besides, the photoreactivation rates for the two bacteria exhibited different correlations with temperature. The highest photoreactivation rate for A. salmonicida was 68.7 ± 4% at 20°C, while the highest photoreactivation rate for E. coli was 53.98 ± 2.9% at 15°C for 48 h. This study reveals the rapid and efficient inactivation of bacteria by UVC-LED, and elucidates the mechanism and influencing factors for inactivation and reactivation by UVC-LED. The study also highlights that adequate UVC-LED irradiation and avoidance of visible light after UVC-LED disinfection can effectively inhibit bacterial reactivation. Our findings form a reference for the design and operation of UV disinfection in aquaculture.
An integrated ultraviolet C light-emitting diode (UV-C LED) water disinfection system activated by microbial fuel cells (MFCs) was developed, and optimized via electric circuit and device voltage profiling. The intensity of the renewable energy operated, self-powered UV-C LED for E. coli inactivation was calculated by bio-dosimetry to be 2.4 × 10-2 μW cm-2 using fluence-based rate constant (k) of ∼1.03 (±0.11) cm2/mJ to obtain the reduction equivalent fluence kinetics value. Finally, the first-order rate constant for E. coli inactivation during the tailored hybrid disinfection system was found to be 0.53 (±0.1) cm2/mJ by multiplying intensity with 1.09 (±0.1) × 10-5 s-1 derived from the linear regression of E. coli inactivation as a function of time. Furthermore, selected model microbial consisting of two bacteria (Salmonella sp. and Listeria sp.) and three viruses (MS2 bacteriophage, influenza A virus, and murine norovirus-1) were treated with UV-C LED irradiation under controlled experimental conditions to validate the disinfection efficiency of the system. Consequently, the required to achieve significant removal (i.e., >3-log; 99.9%) UV fluence and dose time were calculated to be 4-7 cm2/mJ and 54-76 h and 33-53 cm2/mJ and 400-622 h for model bacterial and viral, respectively. This study expands the applicability of microbial electrochemical system (MES) for microbial disinfection and could be utilized in future MFCs implementation studies for predicting and measuring the kinetics of microbial elimination using a tailored hybrid water treatment system.
In many places of the world, the lack of municipal facilities for water sanitation and purification makes self-treatment at a familiar scale, the only realistic solution to ensure continuous access to drinking water. In this context, UV disinfection treatment is a portable and efficient alternative to conventional methods, however, its power need is hindering its implementation in remote off-grid households. This work presents a portable water sterilizer device using UV-C LEDs, conceived for its direct implementation in isolated rural communities. Pulsed radiation operation has been studied as strategy to reduce the device energy demand. Most relevant parameters affecting the device operation and performance, namely voltage, radiation time, frequency and duty cycle; are thoroughly studied using the Design of Experiments methodology to optimize energy consumption and Escherichia coli removal from polluted water. The optimal conditions, found for pulsed radiation, showed a noteworthy reduction of 68 % of the energy consumption while improving the sterilization effectiveness, compared with continuous radiation. Furthermore, the efficiency of sterilization of the optimized prototype was benchmarked against a commercial device using river water samples. The presented prototype achieved higher E. coli disinfection effectiveness using a fraction of the energy consumption. All in all, the presented water sterilization device is an example of a technological improvement which uses energy efficiency as key developing driver while achieving performance requirements. Thus, contributing to the creation of affordable and efficient technological solutions to promote global access to drinking water.
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Ultraviolet (UV) disinfection has been incorporated into both drinking water and wastewater treatment processes for several decades; however, it comes with negative environmental consequences such as high energy demands and the use of mercury. Understanding how to scale and build climate responsive technologies is key in fulfilling the intersection of UN Sustainable Development Goals 6 and 13. One technology that addresses the drawbacks of conventional wastewater UV disinfection systems, while providing a climate responsive solution, is UV light emitting diodes (LEDs). The objective of this study was to compare performance of bench-scale 280 nm UV LEDs to bench-scale low pressure (LP) lamps and full-scale UV treated wastewater samples. Results from the study demonstrated that the UV LED system provides a robust treatment that outperformed LP systems at the bench-scale. A comparison of relative energy consumptions of the UV LED system at 20 mJ cm⁻² and LP system at 30 and 40 mJ cm⁻² was completed. Based on current projections for wall plug efficiencies (WPE) of UV LED it is expected that the energy consumption of LED reactors will be on par or lower compared to the LP systems by 2025. This study determined that, at a WPE of 20%, the equivalent UV LED system would lead to a 24.6% and 43.4% reduction in power consumption for the 30 and 40 mJ cm⁻² scenarios, respectively.
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About this series... This series is produced by the Health, Nutrition, and Population Family (HNP) of the World Bank's Human Development Network. The papers in this series aim to provide a vehicle for publishing preliminary and unpolished results on HNP topics to encourage discussion and debate. The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) and should not be attributed in any manner to the World Bank, to its affiliated organizations or to members of its Board of Executive Directors or the countries they represent. Citation and the use of material presented in this series should take into account this provisional character. For free copies of papers in this series please contact the individual authors whose name appears on the paper. Enquiries about the series and submissions should be made directly to the Editor in Chief Alexander S. Preker ( or HNP Advisory Service (, tel 202 473-2256, fax 202 522-3234). For more information, see also
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We present the results of a one year LDRD program that has focused on evaluating the use of newly developed deep ultraviolet LEDs in water purification. We describe our development efforts that have produced an LED-based water exposure set-up and enumerate the advances that have been made in deep UV LED performance throughout the project. The results of E. coli inactivation with 270-295 nm LEDs are presented along with an assessment of the potential for applying deep ultraviolet LED-based water purification to mobile point-of-use applications as well as to rural and international environments where the benefits of photovoltaic-powered systems can be realized.
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A great deal of progress has been made in the past decade demonstrating that household water treatment and safe storage (HWTS) improve the microbiological quality of water stored in the home and reduce the risk of diarrheal diseases in people using these technologies in developing countries. Several organizations are developing strategies to increase the impact of HWTS by scaling-up programs that promote the proven HWTS options: chlorination, solar disinfection, flocculation/chlorination, biosand filtration, and ceramic filtration (1-3). A recent review estimated that over 18 million people use HWTS, with 12.8 million using chlorination with liquid or tablet, 2.1 million using solar disinfection, 934,000 using flocculation/chlorination, 700,000 using biosand filtra-tion, and 350,000 using ceramic filtration (4). While these numbers appear impressive, they are small compared to the estimated 1.1 billion people worldwide without access to improved water supplies. Sobsey et. al (2) suggest an approach for evaluating and ranking HWTS options and conclude: "Ceramic and biosand household water filters are identified as most effective according to the evaluation criteria applied and as having the greatest potential to become widely used and sustainable for improving household water quality to reduce waterborne disease and death." We believe that this ranking system has several flaws and provides a biased perspective that does not support efforts for worldwide HWTS promotion. The flaws include (1) incomplete and vague definitions of the ranking system criteria, therefore making it subject to bias; (2) scores assigned drawn from insufficient evidence; and (3) omission of key sustainability criteria, including consumer preference, eco-nomic considerations, cultural practices, and local water quality.
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We estimated the disease burden from water, sanitation, and hygiene at the global level taking into account various disease outcomes, principally diarrheal diseases. The disability-adjusted life year (DALY) combines the burden from death and disability in a single index and permits the comparison of the burden from water, sanitation, and hygiene with the burden from other risk factors or diseases. We divided the world's population into typical exposure scenarios for 14 geographical regions. We then matched these scenarios with relative risk information obtained mainly from intervention studies. We estimated the disease burden from water, sanitation, and hygiene to be 4.0% of all deaths and 5.7% of the total disease burden (in DALYs) occurring worldwide, taking into account diarrheal diseases, schistosomiasis, trachoma, ascariasis, trichuriasis, and hookworm disease. Because we based these estimates mainly on intervention studies, this burden is largely preventable. Other water- and sanitation-related diseases remain to be evaluated. This preliminary estimation of the global disease burden caused by water, sanitation, and hygiene provides a basic model that could be further refined for national or regional assessments. This significant and avoidable burden suggests that it should be a priority for public health policy.
Ultraviolet (UV) disinfection is now an accepted technology for inactivation of a variety of waterborne pathogens in wastewater and drinking water. However, the techniques used in much of the previous research aimed at providing information on UV effectiveness have not yet been standardized. Thus in many peer reviewed published literature, it is not clear how the UV irradiations were carried out, nor how the average fluence (or UV dose) given to the microorganisms has been determined. A detailed protocol for the determination of the fluence (UV dose) in a bench scale UV apparatus containing UV lamps emitting either monochromatic or broadband UV light was developed. This protocol includes specifications for the construction of a bench scale UV testing apparatus, methods for determination of the average irradiance in the water, details on UV radiometry, and considerations for microbiological testing. Use of this protocol will aid in standardization of bench scale UV testing and provide increased confidence in data generated during such testing.
We report on the development of AlGaN-based deep UV light emitting diodes (LEDs) with emission wavelengths from 254 to 340 nm, focusing on the improvement of 280 nm LEDs efficiency. Under optimal device structure the UV LEDs efficiency was found to strongly depend on the AlGaN material quality. Milliwatt-power level LEDs were demonstrated for the 254-340 nm spectral range, and for 280 nm LEDs powers reaching 2.5 mW was achieved at 20 mA DC.
Ultraviolet UV disinfection is now an accepted technology for inactivation of a variety of waterborne pathogens in waste-water and drinking water. However, the techniques used in much of the previous research aimed at providing information on UV effectiveness have not yet been standardized. Thus in many peer reviewed published literature, it is not clear how the UV irradiations were carried out, nor how the average fluence or UV dose given to the microorganisms has been determined. A detailed protocol for the determination of the fluence UV dose in a bench scale UV apparatus containing UV lamps emitting either monochromatic or broadband UV light was developed. This protocol includes specifications for the construction of a bench scale UV testing apparatus, methods for determination of the average irradiance in the water, details on UV radiometry, and considerations for microbiological testing. Use of this protocol will aid in standardization of bench scale UV testing and provide increased confidence in data generated during such testing.
The quantum yield (QY) of the iodide–iodate chemical actinometer (0.6 M KI–0.1 M KIO3) was determined for irradiation between 214 and 330 nm. The photoproduct, triiodide, was determined from the increase in absorbance at 352 nm, which together with a concomitant measurement of the UV fluence enabled the QY to be calculated. The QY at 254 nm was determined to be 0.73 ± 0.02 when calibration was carried out against a National Institute of Standards and Technology traceable radiometer or photometric device. At wavelengths below 254 nm the QY increased slightly, leveling off at ∼0.80 ± 0.05, whereas above 254 nm the QY decreases linearly with wavelength, reaching a value of 0.30 at 284 nm. In addition, the QY was measured at different iodide concentrations. There is a slight decrease in QY going from 0.6 to 0.15 M KI, whereas below 0.15 M KI the QY drops off sharply, decreasing to 0.23 by 0.006 M KI. Calibration of the QY was also done using potassium ferrioxalate actinometry to measure the irradiance. These results showed a 20% reduction in QY between 240 and 280 nm as compared with radiometry. This discrepancy suggests that the QY of the ferrioxalate actinometer in this region of the spectrum needs reexamination.
Increases in ultraviolet radiation at the Earth's surface due to the depletion of the stratospheric ozone layer have recently fuelled interest in the mechanisms of various effects it might have on organisms. DNA is certainly one of the key targets for UV-induced damage in a variety of organisms ranging from bacteria to humans. UV radiation induces two of the most abundant mutagenic and cytotoxic DNA lesions such as cyclobutane–pyrimidine dimers (CPDs) and 6–4 photoproducts (6–4PPs) and their Dewar valence isomers. However, cells have developed a number of repair or tolerance mechanisms to counteract the DNA damage caused by UV or any other stressors. Photoreactivation with the help of the enzyme photolyase is one of the most important and frequently occurring repair mechanisms in a variety of organisms. Excision repair, which can be distinguished into base excision repair (BER) and nucleotide excision repair (NER), also plays an important role in DNA repair in several organisms with the help of a number of glycosylases and polymerases, respectively. In addition, mechanisms such as mutagenic repair or dimer bypass, recombinational repair, cell-cycle checkpoints, apoptosis and certain alternative repair pathways are also operative in various organisms. This review deals with UV-induced DNA damage and the associated repair mechanisms as well as methods of detecting DNA damage and its future perspectives.
A statistical study of the spot-plate technique was made for the purpose of establishing an acceptable counting range. The organism used in these studies was Micrococcus lysodeikticus. Standard deviations and coefficients of variation were computed for counts ranging from 20 to 440. The lower and upper limits for acceptable counts, based on coefficients of variation of 10 and 5.8, respectively, were chosen as 100 and 300.