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Basics of UV Disinfection Systems and Validation Methods Ernest (Chip) R. Blatchley III, Ph.D., P.E., BCEE
Ernest (Chip) R. Blatchley III is a Professor in the School of Civil Engineering and in the Division of Environmental & Ecological Engineering at Purdue University. Professor Blatchley teaches and conducts research in the area of Physico/Chemical Processes of Environmental Engineering, with particular emphasis on disinfection systems. Research within the Blatchley group has focused on UV-based systems, and has been important in the development of fundamental photochemical reactor theory. The Blatchley group and collaborators have developed numerical and experimental methods for measurement of the behavior of UV systems. The Blatchley group has been active in the area of swimming pool chemistry for roughly five years. The focus of work in this area has been on defining the basic chemistry of DBP formation and control in swimming pools. Recent and ongoing research in the Blatchley group addresses the effects of UV-based treatment on water and air chemistry in chlorinated, indoor pools. Abstract UV photoreactors are used in aquatics facilities to promote disinfection and to improve water chemistry. However, the design of UV systems for these applications is often based on empiricism, rather than science. The basic characteristics of UV reactors are reviewed, including fundamental principles of photochemistry and reactor theory. These basic principles also form the basis reactor design protocols. At present, three general methods of reactor characterization and validation are available for UV systems: Biodosimetry, Lagrangian Actinometry, and Computational Fluid Dynamics-Intensity Field (CFD-I) models. The basic characteristics of these three methods of reactor analysis are presented, along with a discussion of the strengths and weaknesses of each method. Some recommendations regarding UV system design and validation are also presented.
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 1
Basics of UV Disinfection Systems
and Validation Methods
Ernest R. Blatchley III, Ph.D., P.E., BCEE
Purdue University
School of Civil Engineering
Division of Environmental & Ecological Engineering
Purdue Water Community
World Aquatic Health Conference
Seattle, WA
13 October 2011
UV Myths (or at least unproven
hypotheses) from the Internet
• “UV reduces risk of cancer”
• “Depending on the type of chloramine, different wavelengths are required for the photolysis process such as:
– Monochloramine - 245 nm
– Dichloramine - 297 nm
– Trichloramine - 260 & 340 nm”
• “UV disinfection is a purely physical process; organisms can not become resistant to it as they have to chemicals like chlorine.”
Outline
• Introduction/Definitions
• Laws of Photochemistry
• Photochemical Kinetics: UV Dose = Master Variable
• Effects of UV in Chlorinated Pools
• UV System Types
• Reactor Analysis and Validation
• Uncertainty in UV Design for Pools
• Chlorination + UV
• Future Work
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 2
Electromagnetic Spectrum
http://blog.widen.com/blog/the-color-space/call-me-mr-biv-v1
UV Spectrum
UV Range Wavelengths (nm) Applications
UVA 315-400 Sunburn,
“Blacklight”
UVB 280-315 Sunburn,
Germicidal
UVC 200-280 Germicidal,
Photochemistry
Vacuum UV 100-200 High-Energy
Applications
Photochemistry Basics
• Laws of Photochemistry:
– First Law (Grotthus-Draper): Target Molecule Must Absorb Radiation
– Second Law (Stark-Einstein): Absorbed Radiation Must Have Sufficient Photon Energy to Break or Form a Chemical Bond
• Photon Energy Depends on Wavelength
– Shorter wavelengths have higher energy
• Bond Energy Often Similar to Photon Energy Within Ultraviolet (UV) Spectrum
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 3
Laws of Photochemistry:
Implications
• Photochemical Reactions Favored by:
– Strong absorbance by target molecule
– High intensity
• Absorbed UV Radiation Can Promote
Reactions
• Photochemical Reactions Demonstrate
Wavelength Dependence
Wavelength (nm)
200 220 240 260 280 300
ε =
Mol
ar A
bsor
ptiv
ity (
M-1
cm-1
)
0
2000
4000
6000
8000
10000
12000
14000
MonochloramineDichloramine Trichloramine
UV Absorbance Spectra:
Inorganic Combined Chlorine
(NH2Cl, NHCl2, NCl3)
Wavelength (nm)
200 220 240 260 280 300
ε =
Mol
ar A
bsor
ptiv
ity (
M-1
cm-1
)
0
100
200
300
400
NaOCl HOCl Free Chlorine pH = 7
UV Absorbance Spectra:
Free Chlorine (HOCl + OCl-)
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 4
NH2Cl
UV Dose (mJ/cm2)
0 100 200 300 400
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
λ = 282 nmλ = 254 nmλ = 222 nm
UV Photodegradation of Monochloramine
(pH = 7.5)
Li, J. and Blatchley III, E.R. (2009) “UV Photodegradation of Inorganic Chloramines,”
Environmental Science & Technology, 43, 60-65.
NHCl2
UV Dose (mJ/cm2)
0 100 200 300 400
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
Dark Experiment Time (min)0 20 40 60 80 100
λ = 282 nmλ = 254 nmλ = 222 nmdark control
UV Photodegradation of Dichloramine
(pH = 7.5)
Li, J. and Blatchley III, E.R. (2009) “UV Photodegradation of Inorganic Chloramines,”
Environmental Science & Technology, 43, 60-65.
NCl3
UV Dose (mJ/cm2)0 100 200 300 400
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
λ = 282 nmλ = 254 nmλ = 222 nm
UV Photodegradation of Trichloramine
(pH = 7.5)
Li, J. and Blatchley III, E.R. (2009) “UV Photodegradation of Inorganic Chloramines,”
Environmental Science & Technology, 43, 60-65.
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 5
Photochemical Kinetics
AI0,λ
V l
Dose = I∙t
UV Photodegradation
of Inorganic
Chloramines
(pH = 7.5)
NH2Cl
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
NHCl2
C/C
0
0.0
0.2
0.4
0.6
0.8
Dark Experiment Time (min)0 20 40 60 80 100
λ = 282 nmλ = 254 nmλ = 222 nmdark control
NCl3
UV Dose (mJ/cm2)0 100 200 300 400
C/C
0
0.0
0.2
0.4
0.6
0.8
Li, J. and Blatchley III, E.R. (2009) “UV
Photodegradation of Inorganic
Chloramines,” Environmental Science &
Technology, 43, 60-65.
UV Dose (mJ/cm2)
0 100 200 300 400
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
λ = 282 nm (ε = 562 M-1cm-1)λ = 254 nm (ε = 211 M-1cm-1)λ = 222 nm (ε = 1662 M-1cm-1)
CH3NCl2 Photodecay; pH = 7.5
Alkalinity = 120 mg/L as CaCO3
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 6
UV Systems in Pools: Photochemistry +
Chlorination (Disinfection)UV Disinfection
• Damage to DNA, Proteins
• Broad-Spectrum
Antimicrobial Agent
• Effective Against Bacteria,
Protozoa
• Limited Effectiveness
Against (Some) Viruses
Chlorine Disinfection
• Damage to Cell Membranes,
Enzymes, etc.
• Broad-Spectrum
Antimicrobial Agent
• Effective Against Bacteria,
Viruses
• Minimal Effectiveness
Against Protozoa (e.g.,
Crypto)
In properly designed UV systems in pools, disinfection is
unlikely to control. Overall system design and
performance will be limited by photochemical changes.
UV Systems in Pools: Photochemistry +
Chlorination (Chemistry)
UV System
• Photolysis of Susceptible
Bonds
– NCl
– NO
• Chemistry is Not Completely
Defined
Chlorination
• Common Reaction Types:
– Chlorine Substitution
– Oxidation
– Hydrolysis
• Chemistry is Not Completely
Defined
UV and Chlorine Work Together
to Alter Pool Chemistry
• LP Lamps
– Monochromatic (λ=254 nm)
– Low output power
• MP
– Polychromatic (200 < λ < 400 nm)
– High output power
From: Koutchma (2010) Proceedings of SPIE-The
International Society for Optical Engineering, Volume
7789, DOI: 10.1117/12.860259.
UV Sources: LP and MP Hg Lamps
From: Lakretz et al. (2011) Biofouling, 27, 3, 295-307.
Short Wavelength UV Can Open
Up Some Reaction Pathways
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 7
UV254 Dose (mJ/cm2)
0 100 200 300 400
C/C
0
0
1
2
20
40
60 FreeCHCl3
NCl3
CNCl CNCHCl2
UV254 Irradiation of Pool WaterC
/C0
0
1
2
10
20
30
40
50
60
FreeCHCl
3
NCl3
CNCl CNCHCl
2
UV222 Dose (mJ/cm2)
0 50 100 150 200 250 300 350
NO
2- co
nce
ntra
tion
(µg
/L)
0
100
200
300
400
500
NO
3- C
onc
entr
atio
n (
mg/
L)
0
10
20
30
40
50
60
NO2
-
NO3
-
UV222 Irradiation of Pool Water
Dose = Master Variable(Particle-Specific Basis)
• Exposure Time
• Intensity Field
• Intensity History
• Particle Trajectory
∫=τ
0
)( dttIDose
All UV Reactors Deliver a Distribution of Doses. The Dose
Distribution Governs Reactor Performance. Reactor Validation
Methods Focus on Measurement of Delivered Dose.
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 8
• Measure Dose-Response Behavior with Collimated-Beam
• Measure Inactivation on Flow-Through System
• Equate Inactivation to “Reduction Equivalent Dose” by Comparison with Collimated-Beam Data
Flow Rate (m3/hr)
0 5 10 15 20 25 30
Log 1
0 (N
/N0)
-4
-3
-2
-1
0
UV Dose (mJ/cm2)
0 20 40 60 80 100Lo
g 10
(N/N
0)
-4
-3
-2
-1
0
Conventional Method: Biodosimetry“Reduction Equivalent Dose” (RED)
RED = 48 mJ/cm2
Flow Field Simulation:
Computational Fluid Dynamics (CFD)
Dose Distribution CalculationCFD-I, Lagrangian Approach
ΔtLamp
∑=
∆=n
iiitrajectory tzRID
1
),(
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 9
http://www.hazenandsawyer.com/work/projects/
catskill-delaware-uv-disinfection-facility/
Dyed Microspheres: Lagrangian ActinometryBlatchley et al. (2006) “Dyed Microspheres for Quantification of UV Dose Distributions:
Photochemical Reactor Characterization by Lagrangian Actinometry,”J. Environmental Engineering, ASCE, 132, 11, 1390-1403.
• Particle mimics microorganism
size, specific gravity, ∴trajectory
• Linked UV-sensitive
chromophore (S)
• Becomes fluorescent under UV
irradiation (P)
• Bead fluorescence intensity (FI)
is correlated to UV dose
received.
• FI measured by flow cytometry
WaterborneMicroorganism
Microbial Mimetic
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 10
UV Reactor Validation: Approach
• Identify Target Contaminants
– Microbial Pathogens
– Chemicals
• Identify Limiting Factor (Chemistry)
• Define Dose Requirement (40, 60, 80 mJ/cm2 ???)
• Apply Validation Method(s)
UV Validation: Methods
(Details in Next Presentation)
Biodosimetry
• Long History of
Use
• Familiarity
• Widely Applied
• Difficulty with
Translation from
Challenge
Organism to
other Targets
Lagrangian
Actinometry
• Measurement
of Dose
Distribution
• Results
Translate to All
Photochemical
Targets
• Standardized
Method
Available
CFD-I
• Simulation of
Dose
Distribution
• Results
Translate to All
Photochemical
Targets
• Mathematical
Complexity
Uncertainty in UV Design for Pools
• Current Designs Based on Empiricism
• Design Dose = 40, 60, 80 mJ/cm2 ???
• Effects of UV Systems on Water (and Air)
Chemistry are Incompletely Defined
• Lack of Industry-Wide Treatment Standards
• Effects of Lamp Type
– LP
– MP
•Design Dose?
•Which?
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 11
Effects of UV and Chlorine in Combination
• Continuous recirculation
• Chlorination and UV on each pass
• Volatile compounds escape to gas phase
• Both processes affect water and air chemistryCl2
UV
Gas-Liquid
Transfer
Pool
Sample
Post-UV
Sample
Inorganic Chloramines
Date
Mon 31 Mon 07 Mon 14 Mon 21 Mon 28
Con
cent
ratio
n (m
g/L
as C
l 2)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
NH2Cl
NHCl2NCl3
Before and After Inclusion of UV (1)
Before and After Inclusion of UV (2)CHCl3
Date
Mon 31 Mon 07 Mon 14 Mon 21 Mon 28
Con
cent
ratio
n (m
g/L)
0.0
0.1
0.2
0.3
0.4
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 12
Before and After Inclusion of UV (3)CH3NCl2
Date
Mon 31 Mon 07 Mon 14 Mon 21 Mon 28
Con
cent
ratio
n (m
g/L)
0.00
0.01
0.02
0.03
0.04
Inorganic Chloramines: Pool Water and Post-UV
Day 1
NH2Cl NHCl2 NCl3
Con
cen
trat
ion
(mg/
L as
Cl 2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
8 AM Pool8 AM Post-UV 10 AM Pool10 AM Post-UV
Day 2
NH2Cl NHCl2 NCl30.0
0.1
0.2
0.3
0.4
0.5
0.6
Effects of Rechlorination (1)
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 13
Effects of Rechlorination (2)
Effects of UV-Based Treatment on Water and
Air Chemistry in Chlorinated, Indoor Pools (1)
• Project Period = 2011-2014
• Field Experiments
– Year 1: Control (no UV)
– Year 2: LP UV
– Year 3: MP UV
– Measure Water and Air Chemistry
• AP Chemistry Students at Local High School(s)
Effects of UV-Based Treatment on Water and
Air Chemistry in Chlorinated, Indoor Pools (2)
• Laboratory Experiments
• UV/Chlorination of Model Compounds
– Amino Acids
– Creatinine
• Kinetics and Mechanisms of Relevant
Reactions
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 14
Effects of UV-Based Treatment on Water and
Air Chemistry in Chlorinated, Indoor Pools (3)
• Effects of UV on Disinfection Byproducts (DBPs) in Pools
• Target Compounds– Free and Combined Chlorine
– NO3-/NO2
- (MP UV Systems)
– Chlorinated Nitriles• UV Enhances Production
• Chlorine Needed for Formation and Decay
– Nitrosamines• Known to be formed efficiently in pools
• UV is known to be effective for control
• Effects in pools essentially undefined
• Results to Serve as Basis for UV System Design in Pools
Data from WLHS Study
National Swimming Pool Foundation ∙ 4775 Granby Circle ∙ Colorado Springs, CO 80919 ∙ (719)540-9119 ∙ www.nspf.org 15