1. Ultraviolet (UV) Disinfection in Water Treatment
Hans van Leeuwen.
Department of Civil, Construction and Environmental Engineering
Iowa State University
April 15, 2011

2. History of UV Disinfection
Ancient Hindu source written at least 4000 years ago - raw water
be boiled, exposed to sunlight, filtered, and then cooled in an
earthen vessel.
Germicidal properties of sunlight: 1887
Artificial UV light (Mercury lamp)
developed: 1901
First application in drinking water:
Marseilles, France in 1910
Substantial research on UV in the first half of 20th century
Limited field application: Low cost and maturity of Cl2 disinfection
technology coupled with operation problems associated with early UV
systems

3. Advantage and Disadvantage of UV Disinfection
9. Fouling of UV lamps

4. Increasing Popularity of UV Disinfection
Chlorinated disinfection byproducts (DBPs): THM, HAA etc.
Potential to inactivate protozoan: Cryptosporidium - resistant to Cl2
UV Radiation
Radio IR
Visible
Light UV
X-Rays
UV-A
UV-B
UV-C
Vacuum
400nm
100nm
Germicidal Range
200nm
300nm l
UV light: 100 to 400 nm
UV spectrum – 4 regions
Vacuum UV:100–200 nm
UV – C : 200 – 280 nm
UV – B : 280 – 315 nm
UV – A : 315 – 400 nm

5. Germicidal Range of UV Light
Vacuum UV- most effective – attenuates rapidly in short distance –
not practical
UV-A : less effective – long exposure time – also not practical
UV disinfection – germicidal action mainly from UV- C and
partly from UV - B

6. ULTRAVIOLET RADIATION
Physical Process
Damages Nucleic Acids in Organisms
Stops Reproduction of Organisms by Breaking Apart the DNA Bonds
Wavelengths Between nm

7. Mechanisms of UV Disinfection
Disinfection by UV radiation- physical process- electromagnetic
waves are transferred from a UV source to an organisms cellular
materials (especially genetic materials)
UV light does not necessarily kill the microbial cell
UV light inactivates microorganisms by damaging nucleic acids
(DNA or RNA) thereby interfering with replication of the
microorganisms and therefore incapable of infecting a host
Different microorganisms have
different degree of susceptibility
to UV radiation depending
on DNA content
Viruses are the most resistant
Microbial repair: regain of infectivity

8. UV Lamps UV light can be produced by the following lamps:
Low-pressure (LP) mercury vapor lamps
Low-pressure high-output (LPHO) mercury vapor lamps
Medium-pressure (MP) mercury vapor lamps
Electrode-less mercury vapor lamps
Metal halide lamps
Xenon lamps (pulsed UV)
Eximer lamps
UV lasers
Full-scale drinking water applications : LP, LPHO, or MP lamps

10. Mercury vapor Lamp Comparison

11. UV Lamp and UV Absorbance of DNA

12. LOW AND MEDIUM PRESSURE MERCURY LAMPS
LOW PRESSURE
20-25 Seconds
30% power efficiency
0.3 kW
$2500 per lamp
85% at nm
MEDIUM PRESSURE
2-5 Seconds
20% power efficiency
3.0 kW
$25,000 per lamp
Equals 7-10 low pressure lamps
Wide range wavelength

13. ULTRAVIOLET WAVELENGTHS

14. UV Dose The effectiveness of UV disinfection is based on the UV
dose to which the microorganisms are exposed
UV dose is analogous to Cl2 dose
Cl2 dose = Cl2 conc. x contact time (t) or Cx t
UV dose (D) = I x t or if intensity not constant
Where, D = UV dose, mW.s/cm2 or mJ/cm2
I = UV intensity, mW/cm2
t = exposure time, s
UV dose can be varied by varying either the intensity or the
contact time

15. UV Disinfection Kinetics – Similar to Cl2 Disinfection
dN/dt = Rate of change in the concentration of organisms with time
k = inactivation rate constant, cm2/mW.s
I = average intensity of UV light in bulk solution, mW/cm2
N = number of microorganisms at time t
t = exposure time, s
Residual microorganisms protected in particles

16. UV dose required for a 4log inactivation
of selected waterborne pathogens
Pathogens
UV dose mJ/cm2 4log inactivation (99.99)
Cryptosporidium parvum oocysts
<10
Giardia lamblia cysts
Vibrio cholerae
2.9
Salmonella typhi
8.2
Shigella sonnei
Hepatitis A virus 30
Poliovirus Type 1
Rotavirus SA11 36

17. Components of UV Disinfection System
Components of UV system
1. UV lamps
2. Quartz sleeves: to house and protect lamp
3. supporting structures for lamps and sleeves
4. Ballasts to supply regulated power to UV lamps
5. Power supply
6. Sleeve wiper – to clean the deposit from sleeves
UV Reactors
Open-Channel System
Closed-Channel System

18. Open-Channel Disinfection System
Lamp placement: horizontal and parallel to flow (a)
: vertical and perpendicular to flow (b)
Flows equally divided into number of channels
Each channel - two or more banks of UV lamps in series
Each bank - number of modules (racks of UV lamps)
Each module: number of UV lamps (2, 4, 8, 12 or 16)

19. Closed-Channel Disinfection System
Mostly flow perpendicular to
UV lamp
Mechanical wiping: clean
quartz sleeves
Drinking Water installation, Busselton, Australia

20. Lamp Array

21. Absorption (Bear’s law):
Point Source Summation
a. Intensity Attenuation
Dissipation:
b. Calculation Protocol
Absorption (Bear’s law):
Divide lamp into N sections
Power output of each section
Intensity at a given distance from
a single point source of energy:
Add all point-source contributions:

22. Factors Affecting UV Disinfection
Reactor Hydraulics: reduced activation due to poor reactor
hydraulics resulting short-circuiting
density current – incoming water moving top/bottom of UV lamp
inappropriate entry and exit conditions : uneven velocity profiles
dead zones within reactor
Short circuiting/dead zone reduces the contact time
Remedial measures for
open-channel system
Submerged perforated diffuser
Corner fillets in rectangular
channel with horizontal lamps
Flow deflectors with vertical
lamps
Ideally plug-flow reactor

23. closed-channel system
Remedial measures for
closed-channel system
perforated plate diffuser
Plumb correctly
Presence of Particles:
- reduce the intensity of UV dose
acts as shield to protect the particle-bound pathogens

24. Characteristics of Microorganisms
- Inactivation governed by the DNA/RNA content
Pathogens
UV dose mJ/cm2 4log inactivation (99.99)
Cryptosporidium parvum oocysts
<10
Giardia lamblia cysts
Vibrio cholerae
2.9
Salmonella typhi
8.2
Shigella sonnei
Hepatitis A virus 30
Poliovirus Type 1
Rotavirus SA11 36

25. Effect of Water constituents on UV Disinfection