1. ULTRAVIOLET (UV) RADIATION DISINFECTION

2. UV Radiation

3. UV Disinfection
Physical process (inducing photobiochemical changes within microorganisms)
Two conditions must be met:
Radiation of sufficent energy to alter chemical bonds must be available
Such radiation must be absorbed by the target molecule or microorganism
Eʎ = (h*Cv*AN)/ʎ
Eʎ = Radiant energy associated with given wl(kcal/einstein)
h = Planck’s constant, * kcal.s
Cv = Speed of electromagnetic radiation in a vacuum, 3 * 1017 nm/s
ʎ = Wl of electromagnetic radiation, nm
AN = Avogadro’s number, 6.023*1023 photons/einstein

4. Eʎ = 112.8 kcal/einstein ʎ = 253.7 nm
Bond
Bond Dissociation Energy
(kcal/mole)
O – H
110 – 111
C – H
96 – 99
N – H 93
C – N
69 – 75
C – C
83 – 85
Eʎ = kcal/einstein ʎ = nm

5. Two conditions must be met:
DNA and RNA are the two most common forms of nucleid acid, that consists of single or double stranded polymers comprising building blocks called nucleotides. Purines: Adenine, Guanine Pyrimidines: Thymine, Cytosine (DNA), Uracil, Cytosine (RNA) Strong absorbers of UV light.
Physical process (inducing photobiochemical changes within microorganisms)
Two conditions must be met:
Radiation of sufficent energy to alter chemical bonds must be available
Such radiation must be absorbed by the target molecule or microorganism

8. Source of UV Radiation Low-Pressure Low-intensity UV Lamps :
Produce essentially monochromatic UV light at nm. UV light is produced by mercury at low vapor pressure.
Low-Pressure High-Intensity UV Lamps :
Mercury-indium amalgam is used. Allows 2-4 times greater UV-C output. 25% greater lamp life.
Medium-Pressure High-Intensity UV Lamps :
Mercury vapor emission is carried out at higher lamp pressures and temperatures. Produce polychromatic UV light.

11. UV Reactor Configuration
Open – Channel Disinfection Systems
Lamp placement can be
Horizontal
Vertical
Closed – Channel Disinfection Systems
In most design configurations, the direction of flow is perpendicular to the placement of the lamps

18. UV Intensity and UV Dose
UV Intensity is a measure of radiative power per unit of exposed area. The total UV intensity at a point in space is the sum of the intensity of UV light from all directions.
UV Dose is the integral of UV intensity during exposure period.

19. UV Dose
D = I x t D = UV dose, mWs / cm2 I = UV intensity, mW / cm2 t = Exposure time, s

20. UV Disinfection Kinetics
The measured concentration of microorganisms before and after exposure provides the response, or log reduction of microorganisms from exposure to UV light.
Log Reduction = log (N0 / N), where,
N0 is the concentration of infectious microorganisms before exposure to UV light
N is the concentration of infectious microorganisms after exposure to UV light.
UV dose – response relationships can be expressed as either the proportion of microorganisms inactivated (log reduction) or the proportion of microorganisms remaining (log survival) as a function of UV dose.

21. Factors Affecting UV Disinfection
Flow Rate
UVT
Suspended Solids
Water Quality
Iron
Hardness
D = I x t

22. UVT
UVT is the percantage of light passing through material over a specified distance.

23. Suspended Solids Shadowing Microbes within particles
Potential for microbes to pass through system without seeing UV light

24. Water Quality
Iron and Hardness
Deposition of minerals on the sleeve

25. Water Quality
Iron is a strong absorber of UV light

26. Advantages of UV Disinfection
Effective disinfectant
More effective than chlorine in inactivating most viruses, spores, cysts
No chemical addition required
No formation of disinfection byproducts
Water retains its natural flavour and smell
Microorganism inactivation achieved within seconds
Max operational safety
Minimal operating costs