Ultraviolet (UV) DisinfectionUltraviolet (UV) Disinfectionin Water Treatmentin Water Treatment

Hans van LeeuwenHans van Leeuwen..

Department of Civil, Construction and Environmental EngineeringDepartment of Civil, Construction and Environmental Engineering

Iowa State UniversityIowa State UniversityApril 15, 2011April 15, 2011

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

History of UV DisinfectionHistory of UV Disinfection

Limited field application: Low cost and maturity of Cl2 disinfection technology coupled with operation problems associated with early UV systems

Advantage and Disadvantage of UV DisinfectionAdvantage and Disadvantage of UV Disinfection

9. Fouling of UV lamps

Chlorinated disinfection byproducts (DBPs): THM, HAA etc.

Potential to inactivate protozoan: Cryptosporidium - resistant to Cl2

Increasing Popularity of UV Disinfection Increasing Popularity of UV Disinfection

UV Radiation UV Radiation

UV light: 100 to 400 nm

UV spectrum – 4 regions

o Vacuum UV:100–200 nm

o UV – C : 200 – 280 nm

o UV – B : 280 – 315 nm

o UV – A : 315 – 400 nm

UV light: 100 to 400 nm

UV spectrum – 4 regions

o Vacuum UV:100–200 nm

o UV – C : 200 – 280 nm

o UV – B : 280 – 315 nm

o UV – A : 315 – 400 nm

Radio IR Visible Light

UV X-Rays

UV-A UV-B UV-CVacuumUV

400nm 100nm

Germicidal Range

200nm300nm

Germicidal Range of UV Light 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

ULTRAVIOLET RADIATIONULTRAVIOLET RADIATION

Physical ProcessPhysical Process Damages Nucleic Acids in OrganismsDamages Nucleic Acids in Organisms Stops Reproduction of Organisms by Breaking Stops Reproduction of Organisms by Breaking

Apart the DNA BondsApart the DNA Bonds Wavelengths Between 100-400 nmWavelengths Between 100-400 nm

Mechanisms of UV Disinfection 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

UV LampsUV Lamps

UV light can be produced by the following lamps:UV light can be produced by the following lamps:

Low-pressure (LP) mercury vapor lampsLow-pressure (LP) mercury vapor lamps

Low-pressure high-output (LPHO) mercury vapor lampsLow-pressure high-output (LPHO) mercury vapor lamps

Medium-pressure (MP) mercury vapor lampsMedium-pressure (MP) mercury vapor lamps

Electrode-less mercury vapor lampsElectrode-less mercury vapor lamps

Metal halide lampsMetal halide lamps

Xenon lamps (pulsed UV)Xenon lamps (pulsed UV)

Eximer lampsEximer lamps

UV lasersUV lasers

Full-scale drinking water applications : LP, LPHO, or MP lampsFull-scale drinking water applications : LP, LPHO, or MP lamps

Mercury vapor Lamp ComparisonMercury vapor Lamp Comparison

UV Lamp and UV Absorbance of DNAUV Lamp and UV Absorbance of DNA

LOW AND MEDIUM PRESSURE LOW AND MEDIUM PRESSURE MERCURY LAMPSMERCURY LAMPS

LOW PRESSURELOW PRESSURE 20-25 Seconds20-25 Seconds 30% power efficiency30% power efficiency 0.3 kW0.3 kW $2500 per lamp$2500 per lamp 85% at 253.7 nm85% at 253.7 nm

MEDIUM PRESSUREMEDIUM PRESSURE 2-5 Seconds2-5 Seconds 20% power efficiency20% power efficiency 3.0 kW3.0 kW $25,000 per lamp$25,000 per lamp Equals 7-10 low Equals 7-10 low

pressure lampspressure lamps Wide range Wide range

wavelengthwavelength

ULTRAVIOLET WAVELENGTHSULTRAVIOLET WAVELENGTHS

UV Dose UV Dose

The effectiveness of UV disinfection is based on the UV The effectiveness of UV disinfection is based on the UV dose to which the microorganisms are exposed dose to which the microorganisms are exposed

UV dose is analogous to ClUV dose is analogous to Cl22 dose dose

ClCl22 dose = Cl dose = Cl22 conc. x contact time (t) or Cx t conc. x contact time (t) or Cx t

UV dose (D) = I x t or UV dose (D) = I x t or if intensity not constant if intensity not constant

Where, D = UV dose, mW.s/cmWhere, D = UV dose, mW.s/cm22 or mJ/cm or mJ/cm22

I = UV intensity, mW/cmI = UV intensity, mW/cm22

t = exposure time, st = exposure time, s

UV dose can be varied by varying either the intensity or the UV dose can be varied by varying either the intensity or the contact timecontact time

dtIt

0

.

UV Disinfection Kinetics – Similar to Cl2 Disinfection

kINdt

dN

doseUV)( tIeN

N kIt

o

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

pkIt NeNN

0

Residual microorganisms protected in particles

UV dose required for a 4log inactivation of selected waterborne pathogens

PathogensUV dose mJ/cm2

4log inactivation (99.99)

Cryptosporidium parvum oocysts <10

Giardia lamblia cysts <10

Vibrio cholerae 2.9

Salmonella typhi 8.2

Shigella sonnei 8.2

Hepatitis A virus 30

Poliovirus Type 1 30

Rotavirus SA11 36http://www.trojanuvmax.com/institutions/disinfection_article2.html

Components of UV Disinfection System

Components of UV system Components of UV system 1. UV lamps1. UV lamps2. Quartz sleeves: to house and protect lamp2. Quartz sleeves: to house and protect lamp3. supporting structures for lamps and sleeves3. supporting structures for lamps and sleeves4. Ballasts to supply regulated power to UV lamps4. Ballasts to supply regulated power to UV lamps5. Power supply5. Power supply6. Sleeve wiper – to clean the deposit from sleeves6. Sleeve wiper – to clean the deposit from sleeves

UV Reactors Open-Channel SystemOpen-Channel System

Closed-Channel SystemClosed-Channel System

Open-Channel Disinfection System Lamp placementLamp placement: horizontal and parallel to flow (a): horizontal and parallel to flow (a)

: vertical and perpendicular to flow (b): vertical and perpendicular to flow (b)

Flows equally divided into number of channelsFlows equally divided into number of channels

Each channel - two or more banks of UV lamps in seriesEach channel - two or more banks of UV lamps in series

Each bank - number of modules (racks of UV lamps)Each bank - number of modules (racks of UV lamps)

Each module: number of UV lamps (2, 4, 8, 12 or 16)Each module: number of UV lamps (2, 4, 8, 12 or 16)

Closed-Channel Disinfection System

Drinking Water installation, Busselton, Australia

Mostly flow perpendicular to Mostly flow perpendicular to UV lampUV lamp

Mechanical wiping: clean Mechanical wiping: clean quartz sleevesquartz sleeves

Lamp Array

)4/( 2RPI

Point Source Summationa. Intensity Attenuation

Dissipation:

Absorption (Bear’s law):

Divide lamp into N sections

Power output of each section NSP

• Intensity at a given distance from a single point source of energy:

)exp(4

/2

RR

NSI

Add all point-source contributions:

b. Calculation Protocol

Factors Affecting UV DisinfectionFactors Affecting UV Disinfection Reactor Hydraulics:Reactor Hydraulics: reduced activation due to poor reactor reduced activation due to poor reactor hydraulics resulting hydraulics resulting short-circuitingshort-circuiting

density currentdensity current – incoming water moving top/bottom of UV lamp – incoming water moving top/bottom of UV lampinappropriate entry and exit conditions : uneven velocity profilesinappropriate entry and exit conditions : uneven velocity profilesdead zones within reactordead zones within reactor

Short circuiting/dead zone reduces the contact timeShort circuiting/dead zone reduces the contact time

Remedial measures for Remedial measures for open-channel systemopen-channel system

• Submerged perforated diffuserSubmerged perforated diffuser

• Corner fillets in rectangular Corner fillets in rectangular channel with horizontal lampschannel with horizontal lamps

• Flow deflectors with vertical Flow deflectors with vertical lampslamps

• Ideally plug-flow reactor Ideally plug-flow reactor

Remedial measures for Remedial measures for closed-channel systemclosed-channel system

• perforated plate diffuserperforated plate diffuser

• Plumb correctlyPlumb correctly

Presence of Particles:Presence of Particles:

- reduce the intensity of UV dose- reduce the intensity of UV dose- acts as shield to protect the particle-bound pathogensacts as shield to protect the particle-bound pathogens

Characteristics of MicroorganismsCharacteristics of Microorganisms- Inactivation governed by the DNA/RNA content- Inactivation governed by the DNA/RNA content

PathogensUV dose mJ/cm2

4log inactivation (99.99)

Cryptosporidium parvum oocysts <10

Giardia lamblia cysts <10

Vibrio cholerae 2.9

Salmonella typhi 8.2

Shigella sonnei 8.2

Hepatitis A virus 30

Poliovirus Type 1 30

Rotavirus SA11 36

http://www.trojanuvmax.com/institutions/disinfection_article2.html

Effect of Water constituents on UV Disinfection Effect of Water constituents on UV Disinfection