Ultraviolet (UV) Disinfection in Water Treatment Samir Kumar Khanal, Ph.D., P.E. Department of...
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Transcript of Ultraviolet (UV) Disinfection in Water Treatment Samir Kumar Khanal, Ph.D., P.E. Department of...
Ultraviolet (UV) DisinfectionUltraviolet (UV) Disinfectionin Water Treatmentin Water TreatmentSamir Kumar Khanal, Ph.DSamir Kumar Khanal, Ph.D., P.E.., P.E.
Department of Civil, Construction and Environmental EngineeringDepartment of Civil, Construction and Environmental Engineering
Iowa State UniversityIowa State UniversityMarch 5, 2004March 5, 2004
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