Document ID: EPA-HQ-OW-2002-0039-0031
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-07-09T04:00Z

ULTRAVIOLET
DISINFECTION
GUIDANCE
MANUAL
United
States
Environmental
Protection
Agency
Office
of
Water
(
4601)
EPA
68­
C­
02­
026
June
2003
Draft
Note
on
the
Ultraviolet
Disinfection
Guidance
Manual,
June
2003
Draft
Purpose:
The
purpose
of
this
guidance
manual,
when
finalized,
is
solely
to
provide
technical
information
on
the
application
of
ultraviolet
light
for
the
disinfection
of
drinking
water
by
public
water
systems.
EPA
is
developing
this
manual
to
support
two
upcoming
drinking
water
regulations:
the
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule,
which
would
require
certain
systems
to
provide
additional
treatment
for
Cryptosporidium,
and
the
Stage
2
Disinfection
Byproducts
Rule,
which
would
place
more
stringent
limits
on
certain
disinfection
byproducts.
Chapter
1
of
this
manual
contains
additional
information
about
these
regulations.

This
guidance
is
not
a
substitute
for
applicable
legal
requirements,
nor
is
it
a
regulation
itself.
Thus,
it
does
not
impose
legally­
binding
requirements
on
any
party,
including
EPA,
states,
or
the
regulated
community.
Interested
parties
are
free
to
raise
questions
and
objections
to
the
guidance
and
the
appropriateness
of
using
it
in
a
particular
situation.
Although
this
manual
covers
many
aspects
of
implementing
a
UV
system,
it
is
not
comprehensive
in
terms
of
all
types
of
UV
systems,
design
alternatives,
and
validation
protocols
that
may
provide
satisfactory
performance.
The
mention
of
trade
names
or
commercial
products
does
not
constitute
endorsement
or
recommendation
for
use.

Authorship:
This
manual
was
developed
under
the
direction
of
EPA's
Office
of
Water,
and
was
prepared
by
Malcolm
Pirnie,
Inc.,
Carollo
Engineers,
P.
C.,
and
The
Cadmus
Group,
Inc.
Questions
concerning
this
document
should
be
addressed
to:

Dan
Schmelling
U.
S.
Environmental
Protection
Agency
Mail
Code
4607M
1200
Pennsylvania
Avenue
NW
Washington,
DC
20460­
0001
Tel:
(
202)
564­
5281
Fax:
(
202)
564­
3767
Email:
schmelling.
dan@
epa.
gov
Request
for
comments:
EPA
is
releasing
this
manual
in
draft
form
in
order
to
solicit
public
review
and
comment.
The
Agency
would
appreciate
comments
on
the
content
and
organization
of
technical
information
presented
in
this
manual.
A
list
of
topics
for
comment
pertaining
to
specific
chapters
and
appendices
is
provided
later
in
this
manual.
Please
submit
any
comments
no
later
than
90
days
after
publication
of
the
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule
proposal
in
the
Federal
Register.
Detailed
procedures
for
submitting
comments
are
stated
below.
Acknowledgements:
The
following
provided
valuable
technical
information
to
assist
in
the
development
of
this
manual:

American
Water
Works
Association
Dave
Battigelli
(
Clancy
Environmental
Consultants)
William
Bellamy
(
CH2M
Hill)
Jim
Bolton
(
Executive
Director,
International
Ultraviolet
Association)
Calgon
Carbon
Corporation
Tom
Hargy
(
Clancy
Environmental
Consultants)
Oluf
Hoyer
(
DVGW)
Richard
Hubel
(
American
Water)
Chris
McMeen
(
then
with
Washington
Department
of
Health)
Alexander
Mofidi
(
Metropolitan
Water
District
of
Southern
California)
Ondeo
Degremont
Richard
Sakaji
(
California
Department
of
Health
Services)
Severn
Trent
Services
Regina
Sommer
(
University
of
Vienna)
Paul
Swaim
(
CH2M
Hill)
Trojan
Technologies
Wedeco­
Ideal
Horizons
John
Young
(
American
Water)

Procedures
for
submitting
comments:
Comments
on
this
draft
guidance
manual
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EPA's
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Docket.
You
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2002­
0039.

 
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20460,
Attention
Docket
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No.
OW­
2002­
0039.

 
To
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Center,
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1301
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Ave.,
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Washington,
DC,
Attention
Docket
ID
No.
OW­
2002­
0039.
Please
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ROM.

For
public
commenters,
please
note
that
EPA's
policy
is
that
public
comments,
whether
submitted
electronically
or
in
paper,
will
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made
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public
viewing
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public
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statute.
Table
of
Contents
Table
of
Contents.............................................................................................................................
i
List
of
Figures
................................................................................................................................
vi
List
of
Tables
................................................................................................................................
vii
Glossary
.......................................................................................................................................
viii
Acronyms
and
Abbreviations
......................................................................................................
xiii
1.0
Introduction....................................................................................................................
1­
1
1.1
Guidance
Manual
Objectives...............................................................................
1­
1
1.2
Organization.........................................................................................................
1­
2
1.3
Regulations
Summary..........................................................................................
1­
3
1.3.1
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule..........................
1­
4
1.3.1.1
Filtered
Systems.....................................................................
1­
5
1.3.1.2
Unfiltered
Systems.................................................................
1­
6
1.3.1.3
UV
Requirements
For
Filtered
And
Unfiltered
Systems.......
1­
7
1.3.2
Stage
2
DBPR
..........................................................................................
1­
9
1.4
Alternative
Approaches
for
Disinfecting
with
UV
Light
....................................
1­
9
2.0
Overview
of
UV
Disinfection.........................................................................................
2­
1
2.1
History
of
UV
Light
for
Drinking
Water
Disinfection
........................................
2­
1
2.2
Fundamental
Aspects
of
UV
Light
......................................................................
2­
2
2.2.1
Nature
of
UV
Light..................................................................................
2­
2
2.2.2
Propagation
of
UV
Light
.........................................................................
2­
3
2.3
Microbial
Response
to
UV
Light.........................................................................
2­
6
2.3.1
Mechanisms
of
Microbial
Inactivation
by
UV
Light...............................
2­
6
2.3.2
Microbial
Repair
......................................................................................
2­
7
2.3.3
UV
Dose
and
Dose
Distribution
............................................................
2­
10
2.3.4
Microbial
Response
(
UV
Dose­
Response)
............................................
2­
11
2.3.5
Microbial
Spectral
Response
.................................................................
2­
11
2.4
UV
Reactors.......................................................................................................
2­
12
2.4.1
Reactor
Configuration............................................................................
2­
13
2.4.2
UV
Lamps..............................................................................................
2­
14
2.4.3
Lamp
Power
Supply
and
Ballasts
..........................................................
2­
17
2.4.4
Lamp
Sleeves
.........................................................................................
2­
17
2.4.5
Cleaning
Systems...................................................................................
2­
18
2.4.6
UV
Intensity
Sensors
.............................................................................
2­
19
2.4.7
UV
Transmittance
Monitors
..................................................................
2­
20
2.4.8
Temperature
Sensors..............................................................................
2­
21
2.4.9
Monitoring
UV
Disinfection
Performance
............................................
2­
21
UV
Disinfection
Guidance
Manual
i
June
2003
Proposal
Draft
Table
of
Contents
(
Continued)

UV
Disinfection
Guidance
Manual
ii
June
2003
2.5
Water
Quality
Impacts
and
Byproduct
Formation.............................................
2­
22
2.5.1
Water
Quality
Impacts
...........................................................................
2­
22
2.5.2
Byproducts
from
UV
Disinfection.........................................................
2­
25
3.0
Planning
and
Design
Aspects
for
UV
Installations
.....................................................
3­
1
3.1
UV
Installations
Planning
....................................................................................
3­
4
3.1.1
Defining
UV
Disinfection
Goals
.............................................................
3­
4
3.1.2
Identifying
Potential
Locations
For
UV
Installations..............................
3­
5
3.1.2.1
Combined
Filter
Effluent
Installation
....................................
3­
6
3.1.2.2
Individual
Filter
Effluent
Piping
Installation.........................
3­
6
3.1.2.3
UV
Disinfection
Downstream
of
The
Clearwell
...................
3­
8
3.1.3
Defining
Design
Parameters
....................................................................
3­
9
3.1.3.1
Assessing
Water
Quality......................................................
3­
10
3.1.3.2
Determining
Design
Flow
Rate
...........................................
3­
17
3.1.3.3
Assessing
Electrical
Power
..................................................
3­
17
3.1.4
Evaluating
Potential
UV
Reactors
.........................................................
3­
20
3.1.4.1
UV
Reactors.........................................................................
3­
20
3.1.4.2
UV
Reactor
Control
Strategies
............................................
3­
22
3.1.4.3
Equipment
Validation
Issues
...............................................
3­
22
3.1.5
Evaluating
Operational
Strategies..........................................................
3­
24
3.1.6
Evaluating
Hydraulics
and
Process
Footprint........................................
3­
25
3.1.6.1
Hydraulic
Considerations.....................................................
3­
25
3.1.6.2
Process
Footprint
.................................................................
3­
27
3.1.7
Preparing
Preliminary
Costs
and
Selecting
the
UV
Installation
Option
3­
28
3.2
Equipment
Procurement
Options.......................................................................
3­
29
3.3
UV
Installation
Design
Elements.......................................................................
3­
30
3.3.1
UV
Installation
Hydraulics
....................................................................
3­
30
3.3.1.1
Inlet
and
Outlet
Piping
Configuration..................................
3­
31
3.3.1.2
Flow
Distribution,
Control,
and
Measurement
....................
3­
31
3.3.1.3
Level
Control
.......................................................................
3­
36
3.3.1.4
Air
Relief
and
Pressure
Control
Valves...............................
3­
36
3.3.1.5
Flow
Control
and
Isolation
Valves
......................................
3­
37
3.3.1.6
Intermediate
Booster
Pumps
................................................
3­
37
3.3.2
Operational
Strategy
Determination
......................................................
3­
38
3.3.3
Instrumentation
and
Control
..................................................................
3­
38
3.3.3.1
UV
Reactor
Start­
Up............................................................
3­
39
3.3.3.2
UV
Reactor
Automation
......................................................
3­
39
3.3.3.3
UV
Intensity
and
Calculated
Dose
(
If
Applicable)..............
3­
39
3.3.3.4
UV
Transmittance................................................................
3­
40
3.3.3.5
Flow
Measurement...............................................................
3­
40
3.3.3.6
Lamp
Age.............................................................................
3­
40
3.3.3.7
Lamp
and
Reactor
Status
.....................................................
3­
41
3.3.3.8
Alarms
and
Control
Systems
Interlocks
..............................
3­
41
Proposal
Draft
Table
of
Contents
(
Continued)

UV
Disinfection
Guidance
Manual
iii
June
2003
3.3.4
Electrical
Power
Configuration..............................................................
3­
42
3.3.4.1
Power
Requirements
............................................................
3­
43
3.3.4.2
Backup
Power
Supply..........................................................
3­
43
3.3.4.3
Ground
Fault
Interrupt
and
Electrical
Lockout....................
3­
44
3.3.5
UV
Installation
Layouts.........................................................................
3­
45
3.3.5.1
Site
Layout...........................................................................
3­
45
3.3.5.2
UV
Installation
Layout
........................................................
3­
45
3.3.6
Elements
Of
UV
Reactor
Specifications................................................
3­
47
3.3.6.1
Information
Provided
by
Manufacturer
in
UV
Reactor
Bid
..........................................................................
3­
49
3.3.7
Final
UV
Installation
Design
.................................................................
3­
51
3.3.7.1
Design
Drawings..................................................................
3­
51
3.3.7.2
Specifications.......................................................................
3­
52
3.4
Reporting
to
the
State.........................................................................................
3­
52
3.4.1
Planning
.................................................................................................
3­
52
3.4.2
Equipment
Procurement.........................................................................
3­
53
3.4.3
Drawings
and
Specifications..................................................................
3­
53
3.4.4
Validation
Report/
Start­
up
Confirmation
..............................................
3­
53
4.0
Overview
of
Validation
Testing
....................................................................................
4­
1
4.1
LT2ESWTR
UV
Disinfection
Requirements
......................................................
4­
1
4.2
Overview
of
Validation
Process
..........................................................................
4­
2
4.2.1
Relating
the
Experimental
RED
to
Log
Inactivation
Credit....................
4­
4
4.2.1.1
Tier
1
and
Tier
2
Approaches
for
Establishing
Inactivation
Credit......................................................................................
4­
5
4.2.2
Location
and
Application
of
Validation
Testing
.....................................
4­
5
4.2.3
Third­
Party
Oversight
..............................................................................
4­
6
4.3
Considerations
for
Validation
Testing
.................................................................
4­
6
4.3.1
Inlet
and
Outlet
Hydraulics......................................................................
4­
7
4.3.2
UV
Equipment
.........................................................................................
4­
7
4.3.2.1
UV
Reactor
Documentation...................................................
4­
7
4.3.2.2
Control
Strategies...................................................................
4­
7
4.3.2.3
UV
Intensity
Sensor...............................................................
4­
8
4.3.2.4
Lamp
Aging
...........................................................................
4­
8
4.3.3
Additives
Used
in
Validation
Testing......................................................
4­
8
4.3.3.1
Challenge
Microorganism......................................................
4­
8
4.3.3.2
UV­
Absorbing
Material
.........................................................
4­
9
4.4
Validation
Testing
................................................................................................
4­
9
4.4.1
Microorganism
Preparation
.....................................................................
4­
9
4.4.2
Collimated
Beam
Testing
........................................................................
4­
9
4.4.3
Biodosimetry
of
Full­
Scale
Reactors.....................................................
4­
10
Proposal
Draft
Table
of
Contents
(
Continued)

UV
Disinfection
Guidance
Manual
iv
June
2003
4.5
Data
Analysis
.....................................................................................................
4­
11
4.5.1
Developing
Challenge
Microorganisms
Dose­
Response
Curve............
4­
12
4.5.1.1
Calculate
Dose­
Response
Data
From
Collimated
Beam
Testing..................................................................................
4­
12
4.5.1.2
Fitting
Dose­
Response
Data
to
a
Curve
..............................
4­
13
4.5.2
Determining
Log
Inactivation
from
Biodosimetry
Testing
...................
4­
13
4.5.3
Determining
the
RED
............................................................................
4­
14
4.5.3.1
Calculating
the
RED
Values
................................................
4­
14
4.5.3.2
Selecting
the
Appropriate
RED
for
Log
Inactivation
Credit
Determination
...........................................................
4­
14
4.5.3.3
Interpolating
RED
as
a
Function
of
Test
Conditions...........
4­
15
4.5.4
Determining
Inactivation
Credit
............................................................
4­
15
4.6
Tier
1
Criteria.....................................................................................................
4­
17
4.6.1
UV
Intensity
Sensors
.............................................................................
4­
17
4.6.2
UV
Lamp
Output
...................................................................................
4­
19
4.6.3
Flow
Measurements
...............................................................................
4­
19
4.6.4
Collimated
Beam
Apparatus..................................................................
4­
19
4.6.5
Challenge
Microorganism
Dose­
Response............................................
4­
19
4.6.6
Medium
Pressure
Lamps........................................................................
4­
20
4.6.7
Biodosimetry
Sampling
.........................................................................
4­
21
5.0
Start­
Up
and
Operation
of
UV
Installations
...............................................................
5­
1
5.1
Start­
up
of
UV
Installation...................................................................................
5­
3
5.1.1
Final
Inspection........................................................................................
5­
3
5.1.2
Functional
Testing
...................................................................................
5­
3
5.1.2.1
Verification
of
Mechanical
Operation
...................................
5­
4
5.1.2.2
Verification
of
Monitoring
Equipment
..................................
5­
4
5.1.2.3
Verification
of
Instrumentation
and
Control
Systems
...........
5­
5
5.1.2.4
Verification
of
Flow
Distribution
and
Headloss....................
5­
6
5.1.3
Performance
Testing
................................................................................
5­
7
5.1.4
Operations
and
Maintenance
Manual
......................................................
5­
9
5.2
Operation
of
UV
Installations............................................................................
5­
10
5.2.1
Operational
Requirements
.....................................................................
5­
11
5.2.2
Recommended
Operational
Tasks
.........................................................
5­
11
5.2.3
Start­
up
and
Shutdown
of
UV
Reactors.................................................
5­
12
5.2.3.1
Routine
Start­
up
...................................................................
5­
12
5.2.3.2
Routine
Shutdown................................................................
5­
13
5.2.3.3
Winterization........................................................................
5­
13
5.3
Maintenance
of
UV
Reactors.............................................................................
5­
13
5.3.1
Summary
of
Recommended
Maintenance
Tasks...................................
5­
14
5.3.2
General
Guidelines
for
UV
Reactor
Maintenance
.................................
5­
15
5.3.2.1
UV
Lamp
Characteristics.....................................................
5­
15
5.3.2.2
UV
Intensity
Sensors
...........................................................
5­
16
5.3.2.3
Lamp
Sleeves
.......................................................................
5­
18
5.3.2.4
Fouling
.................................................................................
5­
18
Proposal
Draft
Table
of
Contents
(
Continued)

UV
Disinfection
Guidance
Manual
v
June
2003
5.3.2.5
On­
line
UVT
Monitor
Calibration
........................................
5­
20
5.3.2.6
Flowmeter
Calibration
..........................................................
5­
20
5.3.2.7
UV
Reactor
Temperature......................................................
5­
20
5.3.2.8
Electrical
Concerns
...............................................................
5­
21
5.3.3
Spare
Parts
.............................................................................................
5­
22
5.4
Monitoring,
Recording,
and
Reporting
of
UV
Installation
Operation...............
5­
24
5.4.1
Monitoring
and
Recording
Frequency
for
Compliance
Parameters
......
5­
24
5.4.2
Monitoring
and
Recording
for
Other
Operational
Parameters
..............
5­
25
5.4.3
Reporting
to
the
State.............................................................................
5­
26
5.5
Determination
of
Validated
Operational
Parameters.........................................
5­
27
5.6
Operational
Challenges......................................................................................
5­
32
5.6.1
Low
UV
Intensity
or
Low
Calculated
UV
Dose....................................
5­
32
5.6.2
Low
UV
Transmittance..........................................................................
5­
34
5.6.3
Rapid
Flow
Increase
or
High
Flow........................................................
5­
36
5.6.4
Unreliable
UV
Intensity
Sensor
Readings
.............................................
5­
36
5.6.5
Power
Quality
Problems
........................................................................
5­
37
5.7
Staffing
Issues....................................................................................................
5­
37
5.7.1
Staffing
Levels.......................................................................................
5­
38
5.7.2
Training..................................................................................................
5­
38
5.7.3
Safety
Issues...........................................................................................
5­
39
6.0
References.......................................................................................................................
6­
1
Appendices
Appendix
A
Fundamentals
of
UV
Disinfection
..........................................................
A­
1
Appendix
B
Derivation
of
UV
Dose­
Response
Requirements
...................................
B­
1
Appendix
C
Validation
of
UV
Reactors
......................................................................
C­
1
Appendix
D
Microbiological
Methods
.......................................................................
D­
1
Appendix
E
Measuring
Challenge
Microorganism
UV
Dose­
Response
....................
E­
1
Appendix
F
Background
to
the
UV
Reactor
Validation
Protocol
..............................
F­
1
Appendix
G
Issues
for
Unfiltered
Systems
................................................................
G­
1
Appendix
H
Issues
for
Ground
Water
Systems
..........................................................
H­
1
Appendix
I
Issues
for
Small
Systems
.........................................................................
I­
1
Appendix
J
Pilot­
Scale
and
Demonstration­
Scale
Testing
.........................................
J­
1
Appendix
K
Preliminary
Engineering
Report
............................................................
K­
1
Appendix
L
Regulatory
Timeline
...............................................................................
L­
1
Appendix
M
Compliance
Forms
.................................................................................
M­
1
Appendix
N
UV
Lamp
Breakage
Issues
.....................................................................
N­
1
Appendix
O
Case
Studies
[
This
appendix
will
be
included
in
the
final
draft
when
more
information
being
available.]
......................................
O­
1
Appendix
P
Validation
Protocol
Calculator
Tool
.......................................................
P­
1
Proposal
Draft
List
of
Figures
Figure
2.1
UV
Light
in
the
Electromagnetic
Spectrum.........................................................
2­
3
Figure
2.2
Refraction
of
Light...............................................................................................
2­
4
Figure
2.3
Reflection
of
Light...............................................................................................
2­
4
Figure
2.4
Scattering
of
Light
...............................................................................................
2­
5
Figure
2.5
Structure
of
DNA
and
Nucleotide
Sequences
Within
DNA................................
2­
6
Figure
2.6
UV
Absorbance
of
Nucleotides
and
Nucleic
Acid
at
pH
7
................................
2­
7
Figure
2.7
Hypothetical
Dose
Distributions
for
Two
Reactors
with
Differing
Hydraulics............................................................................................................
2­
9
Figure
2.8
Shapes
of
UV
Dose­
Response
Curves...............................................................
2­
11
Figure
2.9
Comparison
of
Microbial
UV
Action
and
DNA
UV
Absorbance.....................
2­
12
Figure
2.10
UV
Disinfection
System
Schematic...................................................................
2­
13
Figure
2.11
Example
of
Closed
and
Open
Channel
Reactors
...............................................
2­
14
Figure
2.12
UV
Output
of
LP
and
MP
Mercury
Vapor
Lamps
............................................
2­
16
Figure
2.13
UV
Lamp
Output
and
its
Relation
to
the
UV
Absorbance
of
DNA
..................
2­
17
Figure
2.14
UV
Transmittance
of
Quartz
that
is
1
mm
Thick
at
a
Zero
Degree
Incidence
Angle
.................................................................................................
2­
18
Figure
2.15
Mechanical
Wiper
System
and
Physical­
Chemical
Wiper
System
...................
2­
19
Figure
2.16
UV
Intensity
Sensor
Viewing
Lamps
within
a
UV
Reactor
..............................
2­
20
Figure
2.17
UV
Transmittance
Monitor
Design
...................................................................
2­
21
Figure
3.1
Flowchart
for
Planning,
Design,
and
Construction
of
UV
Facilities...................
3­
3
Figure
3.2
Schematic
for
UV
Installation
(
Upstream
of
Clearwell)
.....................................
3­
6
Figure
3.3
Schematic
of
Individual
Filter
Effluent
Piping
Installation
in
Filter
Gallery
......
3­
7
Figure
3.4
UV
Disinfection
Downstream
of
High
Service
Pumps
.......................................
3­
8
Figure
3.5
Example
CF
Diagram
for
Three
Filtered
Waters...............................................
3­
12
Figure
3.6
Example
Flow
and
UV
Absorbance
(
at
254)
Data
............................................
3­
13
Figure
3.7
Example
Effect
of
Pre­
ozonation
on
UV
Absorbance
if
Ozone
is
Quenched
Prior
to
UV
Disinfection...................................................................
3­
16
Figure
3.8
Open­
Channel
Flow
Distribution
Options
.........................................................
3­
33
Figure
3.9
Flow
Measurement
and
Control
Options...........................................................
3­
36
Figure
4.1
Steps
of
a
Validation
Process...............................................................................
4­
3
Figure
4.2
Collimated
Beam
Test
Apparatus
......................................................................
4­
10
Figure
4.3
Biodosimetry
Test
Components.........................................................................
4­
11
Figure
4.4
Examples
of
UV
Intensity
Sensor
Spectral
Response
Ranges...........................
4­
18
Figure
4.5
Dose­
Response
with
a
Shoulder
........................................................................
4­
20
Figure
4.6
Criteria
for
the
Minimum
UVT
of
MP
UV
Systems
Under
Tier
1....................
4­
21
Figure
5.1
Start­
Up
and
Operation
Flowchart.......................................................................
5­
2
Figure
5.2
Example
2­
Interpoloation
of
Validation
Data
to
Determine
UV
Intensity
Setpoints.............................................................................................................
5­
29
Figure
5.3
Interpolation
of
Validation
Data
to
Determine
UV
Intensity
Setpoints
at
Different
Flows
and
Cryptosporidium
Inactivation...........................................
5­
30
Figure
5.4
Low
UV
Intensity
of
Low
Calculated
UV
Dose
Decision
Chart.......................
5­
33
Figure
5.5
High
UV
Absorbance
Decision
Chart................................................................
5­
35
UV
Disinfection
Guidance
Manual
vi
June
2003
Proposal
Draft
List
of
Tables
Table
1.1
Summary
of
Microbial
and
Disinfection
Byproduct
Rules
.................................
1­
4
Table
1.2
Bin
Requirements
for
Filtered
Systems
...............................................................
1­
6
Table
1.3
Bin
Requirements
for
Unfiltered
Systems
...........................................................
1­
7
Table
1.4
UV
Dose
Requirements
Used
During
Validation
Testing...................................
1­
7
Table
2.1
Mercury
Vapor
Lamp
Characteristics................................................................
2­
15
Table
2.2
Mercury
Vapor
Lamp
Comparison....................................................................
2­
15
Table
2.3
Water
Quality
Data
and
Fouling
Observed
for
UV
Disinfection
Pilot
and
Demonstration
Studies.......................................................................................
2­
24
Table
3.1
Potential
Method
to
Determine
Design
Flow
....................................................
3­
17
Table
3.2
Start
and
Restart
Times
for
LPHO
and
MP
Lamps
...........................................
3­
18
Table
3.3
UV
Reactor
Control
Strategies
..........................................................................
3­
22
Table
3.4
Summary
of
Recommended
Hydraulic
Configurations
for
Validation
and
Installation.................................................................................
3­
23
Table
3.5
Potential
Operational
Strategies.........................................................................
3­
25
Table
3.6
Potential
UV
Reactor
Procurement
Options
......................................................
3­
30
Table
3.7
Comparison
of
Techniques
for
UV
Installation
Flow
Measurement.................
3­
35
Table
3.8
Typical
Alarm
Conditions
for
UV
Systems.......................................................
3­
42
Table
3.9
Recommended
Content
for
UV
Reactor
Specifications
....................................
3­
48
Table
3.10
Recommended
Information
to
be
Provided
by
UV
Manufacturer/
Vendor
.......
3­
50
Table
4.1
Tier
1
RED
Targets
for
UV
System
with
LP
of
LPHO
Lamps
.........................
4­
16
Table
4.2
Tier
1
RED
Targets
for
UV
System
with
MP
Lamps........................................
4­
16
Table
5.1
Example
Monitoring
During
a
Four
Week
Performance
Test.............................
5­
9
Table
5.2
Recommended
Operational
Tasks
for
the
UV
Reactor......................................
5­
11
Table
5.3
Recommended
Maintenance
Tasks....................................................................
5­
14
Table
5.4
Design
and
Guaranteed
Lives
of
Major
UV
Components.................................
5­
23
Table
5.5
Off­
Specification
Operations
for
Each
Control
Strategy...................................
5­
24
Table
5.6
Monitoring
Parameters
and
Recording
Frequency
............................................
5­
25
Table
5.7
Recommended
Monitoring
Parameters
and
Recording
Frequency
...................
5­
26
Table
5.8
UV
Reactor
Control
Strategies
..........................................................................
5­
27
Table
5.9
Example
Validation
Data
for
Variable
Setpoint
Operation
...............................
5­
28
Table
5.10
UV
Intensity
Setpoint
for
Different
Flow
Ranges
.............................................
5­
28
Table
5.11
Example
Validation
Data
for
Variable
Setpoint
Operation
...............................
5­
29
Table
5.12
UV
Intensity
Setpoint
for
Different
Flow
Ranges
.............................................
5­
30
Table
5.13
Dose
Setpoints
for
Various
Log
Inactivation
of
Cryptosporidium....................
5­
31
Table
5.14
Factors
Impacting
Staffing
Needs......................................................................
5­
38
UV
Disinfection
Guidance
Manual
vii
June
2003
Proposal
Draft
Glossary
The
following
definitions
were
derived
from
existing
UV
literature,
standard
physics
textbooks,
and/
or
industry
standards
and
conventions.
Some
concepts
have
more
than
one
acceptable
term
or
definition,
but
for
consistency
within
the
document,
only
one
term
is
used.

Absorption
 
the
transformation
of
UV
light
to
other
forms
of
energy
as
it
passes
through
a
substance.

Action
Spectrum
 
the
relative
efficiency
of
UV
energy
at
different
wavelengths
in
inactivating
microorganisms.
Each
microorganism
has
a
unique
action
spectrum.

Ballast
 
provides
the
proper
voltage
and
current
required
to
initiate
and
maintain
the
gas
discharge
within
the
UV
lamp.

Bioassay
 
a
procedure
used
to
determine
the
response
of
a
specific
microorganism
after
exposure
to
UV
light,
usually
in
UV
reactors.
Bioassay
is
a
term
typically
utilized
in
toxicology,
describing
the
testing
of
the
bio­
toxicity
of
a
contaminant.
Bioassay
has
been
used
in
the
UV
disinfection
literature
in
the
same
context
as
"
biodosimetry"
(
see
biodosimetry).

Biodosimeter
 
the
challenge
microorganism
used
to
measure
UV
inactivation
and
ultimately
calculate
the
reduction
equivalent
dose
(
RED;
see
UV
dose)
in
a
UV
reactor.

Biodosimetry
 
a
procedure
used
to
determine
the
reduction
equivalent
dose
(
RED)
of
a
UV
reactor.
Biodosimetry
involves
measuring
the
inactivation
of
a
challenge
microorganism
after
exposure
to
UV
light
in
a
UV
reactor
and
comparing
the
results
to
the
known
UV
dose­
response
curve
of
the
challenge
microorganism
(
determined
using
collimated
beam
testing)
to
determine
the
RED
(
see
UV
Dose).

Challenge
Organism
 
a
microorganism
used
in
UV
reactor
biodosimetry
testing.

Collimated
Beam
Test
 
a
carefully
controlled
bench­
scale
test
that
is
used
to
determine
the
UV
dose­
response
of
a
microorganism.
Both
time
and
UV
light
intensity
are
accurately
measured,
resulting
in
a
specific
calculation
of
delivered
UV
dose
for
the
microorganism
being
tested.
Collimated
beam
tests
are
described
in
detail
in
Appendix
C.

Dark
Repair
 
an
enzyme­
mediated
microbial
process
that
removes
and
regenerates
a
damaged
section
of
deoxyribonucleic
acid
(
DNA),
using
an
existing
complimentary
strand
of
DNA.
Dark
repair
refers
to
all
microbial
repair
processes
not
requiring
reactivating
light.

Delivered
UV
Dose
 
see
UV
Dose
Dose
Control
Strategy
 
the
technique
used
by
a
UV
system
to
control
the
delivered
dose
that
typically
involves
adjusting
the
lamp
power
or
turning
"
on"
or
"
off"
banks
of
UV
lamps
to
respond
to
changes
in
UV
absorbance,
lamp
intensity,
and
flow.
Typically,
the
dose
control
strategy
is
different
for
LP/
LPHO
and
MP
systems.

UV
Disinfection
Guidance
Manual
viii
June
2003
Proposal
Draft
Glossary
(
Continued)

UV
Disinfection
Guidance
Manual
ix
June
2003
Dose
Distribution
 
see
UV
Dose,
Delivered
UV
Dose
Distribution.

Emission
Spectrum
 
the
relative
light
power
emitted
by
a
lamp
as
a
function
of
wavelength.

Fluence
 
see
UV
Dose
Fluence
Rate
 
see
UV
Intensity
Gas
Discharge
 
a
mixture
of
non­
excited
atoms,
excited
atoms,
cations,
and
free
electrons
formed
when
a
sufficiently
high
voltage
is
applied
across
a
volume
of
gas.
Most
commercial
UV
lamps
use
mercury
gas
discharges
to
generate
UV
light.

Germicidal
Effectiveness
 
the
relative
inactivation
efficiency
of
each
UV
wavelength
in
a
polychromatic
emission
spectrum.
This
value
is
usually
approximated
by
the
relative
absorbance
of
DNA
at
each
wavelength,
although
individual
microorganisms
may
respond
differently.
By
convention,
germicidal
effectiveness
of
the
254
nm
emission
line
by
LP
UV
lamps
is
considered
to
be
unity.
The
germicidal
effectiveness
is
typically
used
to
weight
a
polychromatic,
MP
UV
lamp
output
to
reflect
the
germicidal
energy
of
that
specific
source.

Germicidal
Range
 
the
range
of
UV
wavelengths
responsible
for
microbial
inactivation
in
water
(
200
to
300
nm).

Lamp
Envelope
 
the
exterior
surface
of
the
UV
lamp,
which
is
typically
made
of
quartz.

Lamp
Sleeve
 
the
quartz
tube
that
surrounds
and
protects
the
UV
lamp.
The
exterior
is
in
direct
contact
with
the
water
being
treated.
There
is
typically
an
air
gap
(
approximately
1
cm)
between
the
lamp
envelope
and
the
quartz
sleeve.

Light
Pipe
 
a
quartz
cylinder
that
transmits
light
from
the
interior
of
the
UV
reactor
to
the
photodetector
of
a
UV
intensity
sensor.

Lignin
Sulfonate
 
a
commercially
available
reagent
grade
chemical
that
can
simulate
the
UV
absorbance
spectrum
of
natural
waters
and
be
used
to
adjust
UV
transmittance
during
validation
testing.

Low
Pressure
(
LP)
Lamp
 
a
mercury
vapor
lamp
that
operates
at
an
internal
pressure
of
0.001
to
0.01
torr
(
2
x
10­
5
to
2
x
10­
4
psi)
and
electrical
input
of
0.5
watts
per
centimeter.
This
results
in
essentially
monochromatic
light
output
at
254
nanometers.

Low
Pressure
High
Output
(
LPHO)
Lamp
 
a
low
pressure
mercury
vapor
lamp
that
operates
under
increased
electrical
input
(
1.5
to
10
W/
cm),
resulting
in
a
higher
UV
intensity
than
LP
lamps.
It
also
has
essentially
monochromatic
light
output
at
254
nanometers.

Medium
Pressure
(
MP)
Lamp
 
a
mercury
vapor
lamp
that
operates
at
an
internal
pressure
of
100
to
10,000
torr
(
2
to
200
psi)
and
electrical
input
of
50
to
150
W/
cm.
This
results
in
a
polychromatic
(
or
broad
spectrum)
output
of
UV
and
visible
light
at
multiple
wavelengths,
including
the
germicidal
range.

Proposal
Draft
Glossary
(
Continued)

UV
Disinfection
Guidance
Manual
x
June
2003
Monochromatic
 
light
output
at
only
one
wavelength.
For
example,
because
low
pressure
and
low
pressure
high
output
lamps
only
significantly
emit
light
at
254
nanometers,
they
are
considered
monochromatic
UV
light
sources.

Monitoring
Window
 
a
quartz
disc
that
transmits
light
from
the
interior
of
the
UV
reactor
to
the
photodetector
of
a
UV
intensity
sensor.

Offline
Chemical
Clean
(
OCC)
 
a
process
to
clean
lamp
sleeves
where
the
UV
reactor
is
taken
off­
line
and
a
cleaning
solution
(
typically
an
acid)
is
manually
pumped
into
the
reactor.
After
the
foulant
has
dissolved,
the
reactor
is
drained,
rinsed,
and
returned
to
service.
Also
called
flush­
and­
rinse
systems.

Online
Mechanical
Clean
(
OMC)
 
a
process
to
clean
lamp
sleeves
where
an
automatic
mechanical
wiper
(
e.
g.,
O­
ring,
brush)
wipes
the
surface
of
the
lamp
sleeve
at
a
prescribed
frequency.

Petri
Factor
 
a
ratio
used
in
collimated
beam
testing
that
is
equal
to
the
average
intensity
measured
across
the
surface
of
a
suspension
in
a
petri
dish
divided
by
the
intensity
at
the
center
of
a
petri
dish.
The
petri
factor
is
used
to
help
calculate
delivered
UV
dose
as
described
in
Appendix
C.

Photodetector
 
a
device
that
produces
an
electrical
current
proportional
to
the
UV
light
intensity
at
the
detector's
surface.

Photoreactivation
 
a
microbial
repair
process
where
enzymes
activated
by
light
in
the
near
UV
and
visible
range
(
310
to
490
nm)
split
pyrimidine
dimers,
thereby
repairing
UV
induced
damage.
Photoreactivation
requires
the
presence
of
light.

Polychromatic
 
light
energy
output
at
several
wavelengths
such
as
with
MP
lamps.

Quartz
Sleeve
 
see
lamp
sleeve
Radiometer
 
an
instrument
used
to
measure
UV
irradiance
Reduction
Equivalent
Dose
(
RED)
 
see
UV
Dose,
RED.

Reflection
 
the
change
in
direction
of
light
propagation
when
deflected
by
an
interface
or
surface.

Refraction
 
the
change
in
direction
of
light
propagation
as
it
passes
through
one
medium
to
another.

Scattering
 
the
change
in
direction
of
light
propagation
caused
by
interaction
with
a
particle.

Spectral
UV
Absorbance
 
the
determination
of
UV
Absorbance
(
A)
over
a
range
of
wavelengths
(
e.
g.
200
to
400
nm)

Proposal
Draft
Glossary
(
Continued)

UV
Disinfection
Guidance
Manual
xi
June
2003
State
 
the
agency
of
the
state,
tribal,
or
federal
government
that
has
jurisdiction
over
public
water
systems.

UV
absorbance
(
A)
 
a
measure
of
the
amount
of
UV
light
that
is
absorbed
by
a
substance
(
e.
g.,
water,
microbial
DNA,
lamp
envelope,
quartz
sleeve)
at
a
specific
wavelength
(
e.
g.,
254
nm).
This
measurement
accounts
for
absorption
and
scattering
in
the
medium
(
e.
g.,
water).
Typically
the
absorbance
is
measured
on
a
per
centimeter
(
cm)
basis
in
a
1
cm
quartz
cuvette.
Standard
Method
5910B
details
this
measurement
method.
However,
for
UV
disinfection
applications,
the
sample
should
not
be
filtered
or
adjusted
for
pH
as
described
in
Standard
Methods.

UV
Dose
 
the
energy
per
unit
area
incident
on
a
surface,
typically
in
units
of
mJ/
cm2
or
J/
m2
(
older
literature
also
used
the
units
mW­
s/
cm2
where
1
mW­
s/
cm2
=
1
mJ/
cm2).
The
UV
dose
received
by
a
waterborne
microorganism
in
a
reactor
vessel
accounts
for
the
effects
on
UV
intensity
of
the
absorbance
of
the
water,
absorbance
of
the
quartz
sleeves,
reflection
and
refraction
of
light
from
the
water
surface
and
reactor
walls,
and
the
germicidal
effectiveness
of
the
UV
wavelengths.
This
guidance
also
uses
the
following
terms
related
to
UV
dose:

 
Delivered
UV
dose
distribution
 
the
probability
distribution
of
delivered
UV
doses
that
microorganisms
receive
in
a
flow­
through
UV
reactor;
typically
shown
as
a
histogram.
An
example
is
shown
in
Figure
2­
7.

 
Reduction
Equivalent
Dose
(
RED)
 
a
calculated
dose
for
a
flow
through
UV
reactor
that
is
based
on
biodosimetry
(
i.
e.,
measuring
the
level
of
inactivation
of
a
challenge
microorganism
with
a
known
UV
dose­
response).
The
RED
is
set
equal
to
the
UV
dose
in
a
collimated
beam
test
that
achieves
the
same
level
of
inactivation
of
the
challenge
microorganism
as
measured
for
the
flow­
through
UV
reactor
during
biodosimetry
testing.

UV
Dose­
Response
 
the
relationship
indicating
the
level
of
inactivation
of
a
microbe
as
a
function
of
UV
dose.
Inactivation
is
often
plotted
as
log10(
N0/
N)
where
N0
is
the
number
of
microbes
present
prior
to
UV
light
exposure
and
N
is
the
number
of
microbes
present
after
UV
light
exposure.
Examples
are
shown
in
Figure
2­
8.

UV
Installation
 
all
of
the
components
of
the
UV
disinfection
process,
including
(
but
not
limited
to)
UV
reactors,
control
systems,
piping,
valves,
and
building
or
enclosure.

UV
Intensity
 
the
power
per
unit
area
passing
through
an
area
perpendicular
to
the
direction
of
propagation.
UV
intensity
is
used
in
this
guidance
manual
to
describe
the
magnitude
of
UV
light
in
a
UV
reactor
and
in
bench­
scale
UV
experiments.

UV
Intensity
Sensor
 
a
photosensitive
detector
used
to
measure
the
UV
intensity
at
a
point
within
the
UV
reactor.

UV
Irradiance
 
the
power
per
unit
area
incident
to
the
direction
of
light
propagation
at
all
angles,
including
normal.

UV
Light
 
electromagnetic
radiation
with
wavelengths
from
200
to
400
nm.

Proposal
Draft
Glossary
(
Continued)

UV
Disinfection
Guidance
Manual
xii
June
2003
UV
Reactor
 
the
vessel
or
chamber
where
exposure
to
UV
light
takes
place,
consisting
of
UV
lamps,
quartz
sleeves,
UV
intensity
sensors,
quartz
sleeve
cleaning
systems,
and
baffles
or
other
hydraulic
controls.
The
UV
reactor
also
includes
additional
hardware
for
controlling
UV
dose;
typically
comprised
of
(
but
not
limited
to):
UV
intensity
sensors,
UV
transmittance
monitors,
ballasts,
and
control
panels.

UV
Reactor
Validation
 
a
process
by
which
a
UV
reactor's
disinfection
performance
is
determined
relative
to
operating
parameters
that
can
be
monitored.
Reactors
are
validated
to
indicate
that
they
achieve
a
certain
delivered
UV
dose
for
a
range
of
flow,
UV
intensity,
and
water
quality
conditions
(
e.
g.,
UV
transmittance).
Appendix
C
details
the
protocol
for
validating
UV
reactors.

UV
Transmittance
(
UVT)
 
a
measure
of
the
fraction
of
incident
light
transmitted
through
the
water
column.
The
UV
transmittance
is
the
ratio
of
the
light
entering
the
water
to
that
exiting
the
water.
The
UVT
is
usually
reported
for
a
pathlength
of
1
cm.
In
an
alternate
pathlength
is
used,
it
should
be
specified.
UVT
is
often
represented
as
a
percentage
and
is
related
to
the
UV
absorbance
by
the
following
equation:
%
UVT
=
100
x
10­
A.
As
the
UV
absorbance
increases,
the
UV
transmittance
decreases.

Proposal
Draft
List
of
Acronyms
and
Abbreviations
A254
ultraviolet
absorbance
at
254
nanometers
AC
alternating
current
ACGIH
American
Conference
of
Governmental
Industrial
Hygienists
ACS
Automatic
cleaning
system
ANSI
American
National
Standards
Institute
AOC
assimilable
organic
carbon
APHA
American
Public
Health
Association
ATCC
American
Type
Culture
Collection
atm
atmospheres
AWWA
American
Water
Works
Association
AwwaRF
American
Water
Works
Association
Research
Foundation
BDL
below
detectable
limits
BDOC
biodegradable
dissolved
organic
carbon
°
C
degrees
Centigrade
CCPP
calcium
carbonate
precipitation
potential
CF
cumulative
frequency
CFD
computational
fluid
dynamics
CFR
Code
of
Federal
Regulations
cfu
colony
forming
unit
CIP
clean­
in­
place
cm
centimeter
CPEL
ceiling
level
permissible
exposure
limit
CSI
Construction
Specifications
Institute
CT
residual
disinfectant
concentration
(
mg/
L)
x
time
(
min)
CWS
community
water
system
DBP
disinfection
byproduct
DBPR
disinfection
byproduct
rule
DC
direct
current
D/
DBP
disinfectants/
disinfection
by­
product
DNA
deoxyribonucleic
acid
DOC
dissolved
organic
carbon
DVGW
Deutsche
Vereinigung
des
Gas­
und
Wasserfaches
(
German
Association
for
Gas
and
Water)

e
exponent
of
the
base
of
the
natural
logarithm
EPA
United
States
Environmental
Protection
Agency
°
F
degrees
Fahrenheit
ft
feet
g
gram
GAC
granular
activated
carbon
UV
Disinfection
Guidance
Manual
xiii
June
2003
Proposal
Draft
List
of
Acronyms
and
Abbreviations
(
Continued)

UV
Disinfection
Guidance
Manual
xiv
June
2003
gal
gallon
GFI
ground
fault
interrupt
gpm
gallons
per
minute
GWR
ground
water
rule
GWUDI
ground
water
under
the
direct
influence
[
of
surface
water]

h
hour
HAA
haloacetic
acid
HDPE
high­
density
polyethylene
HGL
hydraulic
grade
line
hp
horsepower
HPC
heterotrophic
plate
count
HSP
high
service
pump
Hz
hertz
I
UV
intensity
IDLH
Immediately
Dangerous
to
Life
or
Health
IDSE
initial
distribution
system
evaluation
IESWTR
Interim
Enhanced
Surface
Water
Treatment
Rule
IT
UV
intensity
x
time
J
joule
kW
kilowatt
kW­
hr
kilowatt­
hour
ln
natural
logarithm
LP
low
pressure
LPHO
low
pressure
high
output
LRAA
locational
running
annual
average
LSI
Langlier
Saturation
Index
LT1ESWTR
Long
Term
1
Enhanced
Surface
Water
Treatment
Rule
LT2ESWTR
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule
 
wavelength
m
meter
mA
milliamp
MCL
maximum
contaminant
level
mg
milligram
mgd
million
gallons
per
day
min
minutes
mJ
millijoule
mL
milliliter
mm
millimeter
MP
medium
pressure
MS2
male
specific­
2
bacteriophage
µ
g
microgram
µ
m
micrometer,
micron
Proposal
Draft
List
of
Acronyms
and
Abbreviations
(
Continued)

UV
Disinfection
Guidance
Manual
xv
June
2003
NEL
National
Electric
Code
nm
nanometer
NIOSH
National
Institute
for
Occupational
Safety
and
Health
NIST
National
Institute
of
Standards
and
Technology
NOM
natural
organic
matter
NSF
National
Science
Foundation
NTNCWS
non­
transient
non­
community
water
system
NTU
nephelometric
turbidity
units
NWRI
National
Water
Research
Institute
O&
M
operation
and
maintenance
OCC
offline
chemical
clean
OMC
online
mechanical
clean
ÖNORM
Österreichisches
Normungsinstitut
(
Austrian
Standards
Institute)
OSHA
Occupational
Safety
and
Health
Administration
PAC
powdered
activated
carbon
PEL
permissible
exposure
limit
%
percent
PER
preliminary
engineering
report
pfu
plaque
forming
unit
pH
negative
logarithm
of
the
effective
hydrogen
ion
concentration
PHA
process
hazard
analysis
PLC
programmable
logic
controller
POE
point
of
entry
psi
pounds
per
square
inch
psig
pounds
per
square
inch
gauge
PVC
polyvinyl
chloride
QA/
QC
quality
assurance/
quality
control
r
radial
distance
from
center
r2
correlation
coefficient
RAA
running
annual
average
RCRA
Resource
Conservation
and
Recovery
Act
RED
reduction
equivalent
dose
RMS
root­
mean­
square
RNA
ribonucleic
acid
rpm
revolutions
per
minute
RPZ
reduced
pressure
zone
s
second
SARA
Superfund
Amendments
and
Reauthorization
Act
SCADA
supervisory
control
and
data
acquisition
SDWA
Safe
Drinking
Water
Act
SMCL
secondary
maximum
contaminant
level
SMP
standard
monitoring
program
Proposal
Draft
List
of
Acronyms
and
Abbreviations
(
Continued)

UV
Disinfection
Guidance
Manual
xvi
June
2003
SOP
standard
operating
procedure
SSS
system­
specific
study
SUVA
specific
ultraviolet
absorbance
SWTR
Surface
Water
Treatment
Rule
T10
time
at
which
ten
percent
of
water
has
passed
through
the
reactor
TCLP
toxic
characteristic
leaching
procedure
TCR
total
coliform
rule
TDH
total
dynamic
head
TDS
total
dissolved
solids
THM
trihalo
methane
TLV
threshold
limit
values
TNTC
too
numerous
to
count
TOC
total
organic
carbon
TOX
total
organic
halides
TSA
tryptic
soy
agar
TSB
tryptic
soy
broth
TSS
total
suspended
solids
TTHM
total
trihalomethane
UPS
uninterruptible
power
supply
UV
ultraviolet
UVT
ultraviolet
transmittance
VFD
variable
frequency
drive
W
watt
WTP
water
treatment
plant
Proposal
Draft
Requested
Feedback
on
the
UV
Disinfection
Guidance
Manual
Chapter
or
Appendix
Title
Specific
Issues
for
Comment
Glossary
1.
Are
there
additional
terms
that
should
be
defined?
2.
Is
each
definition
accurate
and
clearly
presented?

1.
Introduction
1.
Does
this
chapter
provide
the
appropriate
amount
of
information
on
the
relevant
regulations?

2.
Overview
Of
UV
Disinfection
1.
Is
the
level
of
detail
appropriate?
2.
Is
there
additional
information
that
should
be
provided?

3.
Planning
And
Design
Aspects
For
UV
Installations
1.
Is
the
overall
UV
installation
design
flowchart
realistic?
Is
the
chapter
organization
reader­
friendly?
2.
Is
the
issue
of
off­
specification
operation
and
its
implications
on
the
UV
installation
design
clearly
described?
3.
Are
the
recommendations
on
developing
design
criteria
helpful?
Are
there
other
approaches
that
should
be
discussed?
4.
Is
the
power
quality
information
clear?
Is
more
information
needed?
5.
Are
there
additional
planning
or
design
issues
that
should
be
discussed?

4.
Overview
of
Validation
1.
Are
the
elements
of
validation
clearly
presented?
2.
Is
there
other
information
from
the
detailed
validation
protocol
(
Appendix
C)
that
should
be
described
here?

5.
Start­
Up
And
Operation
Of
UV
Installations
1.
Are
there
other
elements
of
the
UV
installation
start­
up
that
should
be
discussed?
2.
Are
the
organization
of
the
chapter
and
presentation
of
information
appropriate?
3.
Are
the
operational
requirements
examples
clearly
described?
4.
Are
there
other
operation
and
maintenance
issues
that
should
be
discussed?
5.
Are
the
operational
challenges
described
realistic,
and
are
the
solutions
helpful?

6.
References
1.
Are
there
any
references
that
were
overlooked
that
should
be
added
to
help
clarify
any
points
made
in
the
UVDGM?

UV
Disinfection
Guidance
Manual
xvii
June
2003
Proposal
Draft
Requested
Feedback
on
the
UV
Disinfection
Guidance
Manual
UV
Disinfection
Guidance
Manual
xviii
June
2003
A.
Fundamentals
of
UV
Disinfection
1.
Is
the
level
of
detail
appropriate?
2.
Is
there
additional
information
that
should
be
provided?

B.
Derivation
of
UV
Dose­
Response
Requirements
1.
Are
there
published
or
unpublished
data
available
that
are
not
included
in
this
analysis?

C.
UV
Validation
Protocol
Testing
1.
Is
the
description
of
the
testing
methods
clear?
2.
Are
the
distinctions
between
Tier
1
and
2
clearly
described?
3.
To
provide
a
better
assessment
of
the
RED
bias,
please
provide
dose
distributions
for
UV
reactors
you
have
modeled
at
UVTs
of
95,
90,
85,
and
80%.
4.
Are
the
Tier
1
criteria
acceptable?
If
not,
please
provide
data
and
rational
to
support
alternative
criteria.
5.
During
validation,
the
uncertainty
of
some
measurements
will
not
be
random.
In
particular,
errors
associated
with
measurements
made
by
the
radiometer
will
likely
be
a
systematic
error
(
i.
e.,
the
radiometer
will
always
read
high
or
read
low
for
the
duration
of
the
validation
testing).
Other
such
errors
could
occur
with
the
intensity
sensors
or
the
reference
sensor
used
to
calibrate
the
duty
sensors.
Currently,
the
UVGM
combines
these
sources
of
uncertainty
with
other
random
sources
of
uncertainty
to
define
an
expanded
uncertainty.
Because
these
sources
of
error
are
not
random
during
a
given
validation,
should
the
following
approach
be
used:

If
the
error
of
a
measurement
during
validation
is
constant
and
systematic,
should
the
uncertainty
of
the
measurement
be
used
to
define
a
bias
error
that
is
applied
to
the
validation
results?
Under
the
current
approach,
this
would
apply
to
the
uncertainty
of
the
radiometer
and
move
it
from
the
expanded
uncertainty
to
its
own
bias
error.
For
example,
if
the
uncertainty
of
the
radiometer
is
8
%,
a
safety
factor
of
1.08
is
added
to
the
RED
bias,
polychromatic
bias,
and
expanded
uncertainty.
This
will
increase
RED
targets
for
Tier
1
and
2.

6.
The
expanded
uncertainty
is
calculated
for
an
80
percent
confidence
interval
to
ensure
at
least
nine
out
of
ten
cases
of
UV
system
operation
meet
target
dose
values.
Should
the
expanded
uncertainty
calculation
be
based
on
a
90
or
95
percent
confidence
interval
to
ensure
a
higher
percentage
of
UV
systems
meet
requirements?

D.
Validation
Microbial
Methods
1.
The
bounds
provided
for
the
MS2
and
B.
subtilis
data
come
from
an
analysis
of
data
published
in
the
literature.
Should
these
bounds
be
used?
If
not,
please
provide
data
to
support
using
alternative
bounds?
Should
any
of
the
literature
data
used
to
develop
these
bounds
not
be
included?
If
yes,
please
provide
a
rational
for
not
including
that
data.
2.
Are
the
methods
for
analyzing
the
collimated
beam
data
and
subsequent
UV
doseresponse
curve
clearly
stated
and
appropriate?
Are
there
other
options
that
should
be
considered?

Proposal
Draft
Requested
Feedback
on
the
UV
Disinfection
Guidance
Manual
UV
Disinfection
Guidance
Manual
xix
June
2003
E.
Collimated
Beam
Apparatus
 
Measuring
Challenge
Microbe
UV
Dose­
Response
1.
Is
the
collimated
beam
testing
description
clear?

F.
Validation
Background
1.
The
following
is
an
alternate
approach
for
monitoring
dose
delivery
that
is
not
included
in
the
manual
because
it
has
not
been
applied
or
referenced.

Calculate
the
percent
UV
output
from
the
lamp
to
the
water
based
on
the
sensor
readings
using
the
formula:

100
)
(
'
 
=
UVT
S
S
P
L
where
PL
=
UV
output
from
the
lamp
to
the
water
(%)
S
=
Sensor
reading
S'(
UVT)
=
Sensor
reading
expected
with
a
new
lamp
operating
with
unfouled
sleeves
at
a
given
UVT
UVT
=
UVT
of
the
water
at
254
nm
The
calculated
lamp
power
and
measured
UVT
should
be
above
setpoint
values
established
during
validation.
The
relation
S'(
UVT)
is
measured
during
validation
as
opposed
to
being
calculated.

This
approach
has
the
following
potential
benefits:

 
No
requirement
on
sensor
position
 
Could
measure
S'(
UVT)
with
NOM
and
compare
with
LSA
or
coffee
as
an
experimental
approach
for
reducing
the
Polychromatic
Bias
to
one.

Should
this
approach
be
discussed
in
the
manual?

G.
Issues
for
Unfiltered
Systems
1.
Is
the
level
of
detail
appropriate?
2.
Is
there
additional
water
quality
related
design
or
operational
concerns
for
unfiltered
systems
that
should
be
addressed?

H.
Issues
for
Ground
Water
Systems
1.
Are
there
design
or
operational
issues
with
UV
disinfection
of
groundwater
that
are
not
addressed?

I.
Issues
for
Small
Systems
1.
Is
the
level
of
detail
appropriate?
2.
Are
the
design
concerns
facing
small
systems
adequately
addressed?
3.
Design
information
is
presented
in
Chapter
3,
and
this
appendix
only
includes
areas
where
small
system
design
differs
from
the
design
issues
discussed
in
Chapter
3.
Is
this
approach
effective?

Proposal
Draft
Requested
Feedback
on
the
UV
Disinfection
Guidance
Manual
UV
Disinfection
Guidance
Manual
xx
June
2003
J.
Pilot­
Scale
and
Demonstration­
Scale
Testing
1.
Is
the
level
of
detail
appropriate?
2.
Were
all
of
the
recommended
testing
methods
clearly
explained?
3.
Are
there
any
other
example
testing
protocols
that
should
be
included
in
this
appendix?

K.
Preliminary
Engineering
Report
1.
Are
there
any
elements
of
this
report
that
would
benefit
from
more
detail?
2.
Is
there
any
information
missing
from
this
report
that
you
would
like
to
see
included
in
a
standard
template
(
i.
e.,
in
this
example
Design
Engineering
Report)?

L.
Regulatory
Timeline
1.
Is
this
appendix
helpful
for
UV
installation
planning?
2.
Are
the
time
allocations
for
the
tasks
listed
in
the
timeline
appropriate?

M.
Compliance
Forms
1.
Are
the
example
compliance
forms
well
organized
and
easy
to
complete?
2.
Are
there
other
forms
that
would
be
helpful
to
the
utility
or
the
State?

N.
UV
Lamp
Breakage
Issues
1.
Considering
available
information,
are
the
major
issues
surrounding
lamp
breakage
adequately
presented
in
this
appendix?
Are
there
additional
issues
or
sources
of
information
to
be
discussed?
2.
Are
there
additional
methods
for
the
prevention
or
mitigation
of
on­
line
lamp
breaks
that
should
be
presented?

O.
Case
Studies
There
are
no
questions
related
to
this
appendix
because
it
is
not
included
in
this
draft.

P.
Validation
Protocol
Calculator
Tool
There
are
no
questions
related
to
this
appendix.

Proposal
Draft
1
Throughou
t
this
document,
the
terms
"
State"
or
"
States"
are
used
to
refer
to
all
types
of
primacy
agenc
ies,
including
U.
S.
Territories,
Indian
Tribes,
and
EP
A
Regions.

UV
Disinfection
Guidance
Manual
1­
1
June
2003
Propo
sal
Draft
1.
Introduction
There
is
growing
interest
among
public
water
systems
in
using
ultraviolet
(
UV)
light
to
disinfect
drinking
water,
based
on
its
ability
to
inactivate
certain
microorganisms
without
forming
harmful
disinfection
byproducts
(
DBPs).
Some
pathogens,
such
as
Cryptosporidium,
are
resistant
to
commonly
used
disinfectants,
whereas
UV
light
has
proven
effective
against
these
microorganisms.

The
United
States
Environmental
Protection
Agency
(
EPA)
is
developing
the
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule
(
LT2ESWTR)
to
further
control
microbial
contamination
of
drinking
water.
The
rule
requires
additional
treatment
for
some
systems
based
on
their
source
water
Cryptosporidium
concentrations.
UV
disinfection
is
one
of
the
options
utilities
have
to
comply
with
the
treatment
requirements.

UV
light
has
been
widely
used
to
disinfect
effluent
from
wastewater
treatment
facilities,
particularly
those
that
reuse
effluent
for
irrigation.
Until
recently,
the
use
of
UV
treatment
for
drinking
water
applications
was
primarily
limited
to
small
ground
water
systems,
due
to
the
belief
that
it
was
not
effective
for
inactivating
protozoa
and
was
not
cost­
effective
for
large
systems.
In
1998,
however,
research
demonstrated
that
UV
light
could
effectively
inactivate
Cryptosporidium
at
low
dosages
(
Buhkari
et
al.
1998),
prompting
more
research
to
better
understand
its
potential
for
widespread
application.

UV
disinfection
design,
operation,
and
maintenance
needs
differ
from
those
of
traditional
chemical
disinfectants
used
in
drinking
water
applications.
EPA
is
therefore
developing
this
guidance
manual
to
familiarize
States1
and
utilities
with
these
important
issues
as
well
as
regulatory
requirements.
Areas
of
particular
design
and
operational
importance
include
hydraulic
control,
reliability,
redundancy,
lamp
cleaning
and
replacement,
and
lamp
breakage.
Regulatory
requirements
are
addressed
through
UV
reactor
validation,
monitoring,
and
reporting.

1.1
Guidance
Manual
Objectives
This
manual
provides
guidance
to
utilities,
States,
manufacturers,
and
other
interested
parties
on
the
disinfection
of
drinking
water
with
UV
light,
including
the
regulatory
requirements
associated
with
UV
disinfection.
The
LT2ESWTR
requirements
do
not
cover
all
aspects
of
the
disinfection
process.
In
the
areas
not
directly
addressed
by
the
rule,
the
manual
provides
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
2
June
2003
Propo
sal
Draft
recommendations
to
assist
utilities
and
regulatory
agencies
in
assessing
the
disinfection
capability
and
performance
of
UV
installations.
The
manual's
objectives
are
as
follows:

°
Provide
public
water
systems
and
designers
with
technical
information
and
guidance
on
the
selection,
design,
and
operation
of
UV
installations
and
the
UV­
related
requirements
for
compliance
with
the
LT2ESWTR.

°
Provide
States
with
guidance
and
the
necessary
tools
to
assess
UV
installations
at
the
design,
start­
up,
and
routine
operation
phases.

°
Provide
manufacturers
with
testing
and
performance
standards
for
UV
components
and
systems
for
treating
drinking
water.

1.2
Organization
This
manual
consists
of
six
chapters
and
appendices:

°
Chapter
1
 
Introduction.
The
remainder
of
this
chapter
summarizes
the
LT2ESWTR
and
Stage
2
DBPR
and
discusses
regulatory
requirements
for
disinfection
of
drinking
water
with
UV
light.

°
Chapter
2
 
Overview
of
UV
Disinfection.
This
chapter
describes
the
principles
of
disinfection
with
UV
light
including
inactivation
mechanisms,
dose­
response
relationships,
water
quality
impacts,
and
UV
reactors.

°
Chapter
3
 
Planning
and
Design
Aspects
for
UV
Installations.
This
chapter
discusses
the
key
design
features
for
UV
disinfection
facilities
and
presents
some
common
approaches
to
facility
design.
Key
design
features
include
treatment
goals,
existing
infrastructure,
water
quality,
hydraulics,
and
operation
and
control
strategies.

°
Chapter
4
 
Overview
of
UV
Reactor
Validation.
This
chapter
describes
the
LT2ESWTR
requirements
for
validating
UV
reactors
and
provides
an
overview
of
validation
protocol
presented
in
Appendix
C.

°
Chapter
5
 
Start­
up
and
Operation
of
UV
Installations.
This
chapter
discusses
start­
up
and
operation
issues
of
UV
disinfection
facilities
as
well
as
required
monitoring
for
regulatory
compliance.

°
Chapter
6
 
References.
This
chapter
lists
the
full
references
from
Chapters
1­
5.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
3
June
2003
Propo
sal
Draft
°
The
appendices
and
their
titles
follow:

Appendix
A.
Fundamentals
of
UV
Disinfection
Appendix
B.
Derivation
of
UV
Dose­
Response
Requirements
Appendix
C.
Validation
of
UV
Reactors
Appendix
D.
Microbiological
Methods
Appendix
E.
Collimated
Beam
Apparatus:
Measuring
Challenge
Microorganism
UV
Dose­
Response
Appendix
F.
Background
to
the
UV
Reactor
Validation
Protocol
Appendix
G.
Issues
for
Unfiltered
Systems
Appendix
H.
Issues
for
Ground
Water
Systems
Appendix
I.
Issues
for
Small
Systems
Appendix
J.
Pilot­
Scale
and
Demonstration
Scale
Testing
Appendix
K.
Preliminary
Engineering
Report
Appendix
L.
Regulatory
Time
Line
Appendix
M.
Compliance
Forms
Appendix
N.
UV
Lamp
Breakage
Issues
Appendix
O.
Case
Studies
[
This
appendix
will
be
included
in
the
final
draft
at
which
time
EPA
anticipates
more
information
being
available.]
Appendix
P.
Validation
Protocol
Calculator
Tool
1.3
Regulations
Summary
This
section
summarizes
the
drinking
water
regulations
for
microbial
and
DBP
control.
The
Stage
2
Disinfectants
and
Disinfection
Byproduct
Rule
(
DBPR)
aims
to
reduce
peak
DBP
concentrations
in
the
distribution
system
by
modifying
the
Stage
1
DBPR
monitoring
requirements
and
procedures
for
compliance
determination.
The
LT2ESWTR
and
Stage
2
DBPR
are
to
be
promulgated
together
to
address
the
risk­
risk
trade
off
between
microbial
disinfection
and
the
byproducts
formed
by
commonly
used
disinfectants.
Consequently,
when
a
utility
assesses
its
disinfection
strategy,
not
only
the
disinfection
of
target
pathogens
is
important,
but
also
the
DBP
formation
from
each
disinfectant.
Table
1.1
summarizes
the
microbial
treatment
requirements
and
DBP
maximum
contaminant
levels
(
MCLs)
from
the
Surface
Water
Treatment
Rule
(
SWTR),
Interim
Enhanced
Surface
Water
Treatment
Rule
(
IESWTR),
Long
Term
1
Enhanced
Surface
Water
Treatment
Rule
(
LT1ESWTR),
LT2ESWTR,
Stage
1
DBPR,
and
Stage
2
DBPR.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
4
June
2003
Propo
sal
Draft
Table
1.1
Summary
of
Microbial
and
Disinfection
Byproduct
Rules
Surface
W
ater
Treatmen
t
Rules
­
Minim
um
Trea
tment
Req
uirements
Regulation
Giard
ia
Virus
Cryptosporidium
SWTR
3
log
removal
and
inactivation
4
log
removal
and
inactivation
Not
addressed
IESWTR
and
LT1ESWTR
No
change
from
SWTR
2
log
removal
LT2ESWTR
No
change
from
SWTR
0­
2.5
log
additional
treatment1
2­
3
log
treatment2
Disinfection
Byproduct
Rules
­
MCLs
Based
on
Run
ning
Annual
Averages
(
RAAs)

Regulation
Trihalomethanes
(
TTHM)
(
µ
g/
L)
Haloacetic
Acids
(
HAA5)
(
µ
g/
L)
Bromate
(
µ
g/
L)
Chlorite
(
µ
g/
L)

Stage
1
DBPR
80
as
RAA
60
as
RAA
10
1000
Stage
2A
DBPR3
120
as
LRAA
100
as
LRAA
No
change
from
Stage
1
Stage
2B
DBPR4
80
as
LRAA
60
as
LRAA
No
change
from
Stage
1
1Requirement
for
filtered
systems
is
in
addition
to
removal
achieved
by
conventional
treatment
complying
with
the
IESWTR
and
LT1ESWTR.
Specific
requirements
for
each
plant
depend
on
source
water
monitoring
results
(
40
CFR
141.720).
2Unfiltered
systems
must
provide
2­
3
log
inactivation;
specific
requirements
for
each
plant
depend
on
source
water
monitoring
results
(
40
CFR
141.721(
b)).
3Stage
2A
bases
compliance
on
a
locational
running
annual
average
(
LRAA)
at
the
Stage
1
monitoring
locations.
Stage
1
RAAs
must
still
be
met
during
this
time.
Stage
2A
begins
[
3
years
after
rule
promulgation]
for
all
systems.
4Stage
2B
bases
compliance
on
an
LRAAs
at
revised
monitoring
locations
identified
during
the
Initial
Distribution
System
Evaluation.
Stage
2B
begins
[
6
years
after
rule
promulgation]
for
large
systems
and
[
7.5­
8.5
years
after
rule
promulgation]
for
small
systems
dependent
on
their
LT2ESWTR
requirements.

1.3.1
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule
The
LT2ESWTR
applies
to
all
public
water
systems
that
use
surface
water
or
ground
water
under
the
direct
influence
of
surface
water
(
GWUDI),
except
those
that
purchase
all
their
surface
and
GWUDI
water.
It
builds
on
the
SWTR,
IESWTR,
and
the
LT1ESWTR
by
improving
control
of
microbial
pathogens,
specifically
the
contaminant
Cryptosporidium.
Unlike
the
previous
rules,
the
LT2ESWTR
bases
treatment
requirements
on
a
system's
source
water
Cryptosporidium
concentration
and
type
of
treatment
provided.
This
section
describes
the
rule
requirements
for
filtered
and
unfiltered
systems.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
5
June
2003
Propo
sal
Draft
1.3.1.1
Filtered
Systems
The
LT2ESWTR
requires
systems
that
use
a
surface
water
or
GWUDI
source
(
referred
to
collectively
in
this
manual
as
surface
water
systems)
to
conduct
source
water
monitoring
to
determine
average
Cryptosporidium
concentrations,
unless
they
have
historical
Cryptosporidium
data
equivalent
to
what
is
required
under
the
LT2ESWTR
(
40
CFR
141.701(
a)).
Based
on
its
average
source
water
Cryptosporidium
concentration,
filtered
systems
will
be
classified
in
one
of
four
possible
bins.
A
system's
bin
assignment
determines
the
extent
of
any
additional
Cryptosporidium
treatment
requirements.
The
rule
requires
systems
to
comply
with
additional
treatment
requirements
by
using
one
or
more
management
or
treatment
techniques
from
a
toolbox
of
options
(
40
CFR
141.720(
b)).
The
process
is
described
in
more
detail
below;
the
full
monitoring
requirements
are
described
in
the
Source
Water
Monitoring
Guidance
Manual
for
Public
Water
Systems
for
the
Long
Term
2
Enhanced
Surface
Water
Treatment
Rule
(
USEPA
2003).

Bin
Classification
Table
1.2
presents
the
bin
classifications
and
their
corresponding
additional
treatment
requirements
for
all
filtered
systems
(
40
CFR
141.709
and
40
CFR
141.720).
Systems
with
average
Cryptosporidium
concentrations
of
less
than
0.075
oocysts
per
liter
are
placed
in
Bin
1,
for
which
no
additional
treatment
is
required.
For
concentrations
of
0.075
or
more,
additional
treatment
is
required
on
top
of
that
required
by
existing
rules.
The
additional
treatment
required
for
each
bin,
specified
in
terms
of
log
removal,
depends
on
the
type
of
treatment
already
in
place
by
the
system.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
6
June
2003
Propo
sal
Draft
Table
1.2
Bin
Requirements
for
Filtered
Systems1
If
your
Cryptosporidium
concentration
(
oocy
sts/
L)
is...
Your
bin
classification
is...
And
if
yo
u
use
the
follo
wing
filtration
tre
atment
in
full
compliance
w
ith
existing
re
gulations
,
then
you
r
additional
treatm
ent
req
uirem
ents
ar
e...

Conventional
Filtration
Treatment
(
includes
softening)
Direct
Filtration
Slow
Sand
or
Diatomaceous
Earth
Filtration
Alternative
Filtration
Technologies
<
0.075
1
No
additional
treatment
No
additional
treatment
No
additional
treatment
No
additional
treatment
>
0.075
an
d
<
1.0
2
1
log
treatment2
1.5
log
treatment2
1
log
treatment2
As
determined
by
the
State
2,4
>
1.0
and
<
3.0
3
2
log
treatment3
2.5
log
treatment3
2
log
treatment3
As
determined
by
the
State
3,5
>
3.0
4
2.5
log
treatment3
3
log
treatment3
2.5
log
treatment3
As
determined
by
the
State
3,6
1
(
40
CFR
141.709
and
40
CFR
141.720)
2
Systems
may
use
any
technology
or
combination
of
technologies
from
the
microbial
toolbox.

3
Systems
must
achieve
at
least
1
log
of
the
required
treatment
using
ozone,
chlorine
dioxide,
UV
disinfection,
membranes,
bag/
cartridge
filters,
or
bank
filtration.
4
Total
Cryptosporidium
treatment
must
be
at
least
4.0
log.
5
Total
Cryptosporidium
treatment
must
be
at
least
5.0
log.
6
Total
Cryptosporidium
treatment
must
be
at
least
5.5
log.

1.3.1.2
Unfiltered
Systems
All
existing
requirements
for
unfiltered
systems
under
the
SWTR
(
40
CFR
141.71
and
141.72(
a))
remain
in
effect.
This
includes
disinfection
to
achieve
at
least
3
log
inactivation
of
Giardia
and
4
log
inactivation
of
viruses
and
to
maintain
a
disinfectant
residual
in
the
distribution
system
(
e.
g.,
free
chlorine
or
chloramines).
The
IESWTR
and
LT1ESWTR
did
not
change
the
disinfection
requirements
for
unfiltered
systems.
The
LT2ESWTR
requires
2
log
or
3
log
inactivation
of
Cryptosporidium,
depending
on
the
source
water
concentration
of
Cryptosporidium
(
40
CFR
141.721(
b)).

The
arithmetic
mean
concentration
of
all
Cryptosporidium
samples
taken
is
used
to
determine
the
amount
of
treatment
required,
as
shown
in
Table
1.3
(
40
CFR
141.721(
a)).
If
the
mean
concentration
is
less
than
or
equal
to
0.01
oocysts/
L,
the
system
must
provide
2
log
inactivation
of
Cryptosporidium
(
40
CFR
141.721(
b)).
If
the
mean
concentration
of
Cryptosporidium
exceeds
0.01
oocysts/
L,
the
system
must
provide
at
least
3
log
inactivation
of
Cryptosporidium
(
40
CFR
141.721(
b)).
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
7
June
2003
Propo
sal
Draft
Table
1.3
Bin
Requirements
for
Unfiltered
Systems
Bin
Number
Average
Cryptosporidium
Concentration
(
oocysts/
liter)
Additional
Cryptosporidium
inactivation
requirements
1
<
0.01
2
log1
2
>
0.01
3
log1
1
Overall
disinfection
requirements
must
be
met
with
a
minimum
of
two
disinfectants
(
40
CFR
141.721(
d)).

1.3.1.3
UV
Disinfection
Requirements
for
Filtered
and
Unfiltered
Systems
To
receive
disinfection
credit
for
a
UV
reactor,
the
LT2ESWTR
requires
utilities
to
demonstrate
through
validation
testing
that
the
reactor
can
deliver
the
required
UV
dose
(
40
CFR
141,
Subpart
W,
Appendix
D).
EPA
developed
dose
requirements
for
Cryptosporidium,
Giardia,
and
virus
as
presented
in
Table
1.4
and
described
in
Appendix
B
of
this
guidance
manual.
These
dose
requirements
account
for
uncertainty
associated
with
the
dose­
response
of
the
microorganisms
in
controlled
experimental
conditions.
In
practical
application,
other
sources
of
uncertainty
are
introduced
due
to
the
hydraulic
effects
of
the
UV
installation,
UV
reactor
equipment,
and
monitoring
approach
(
e.
g.,
UV
intensity
sensors).
Therefore,
the
validation
protocol
(
described
in
Chapter
4
and
Appendix
C
of
this
guidance
manual)
applies
a
safety
factor
to
the
Table
1.4
dose
requirements
to
account
for
these
areas
of
uncertainty
and
variability.

Table
1.4
UV
Dose
Requirements
Used
During
Validation
Testing1
Log
Inactivation
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Cryptosporidium
1.6
2.5
3.9
5.8
8.5
12
­
­

Giard
ia
1.5
2.1
3.0
5.2
7.7
11
­
­

Virus
39
58
79
100
121
143
163
186
1
40
CFR
141.729(
d)

The
LT2ESWTR
(
40
CFR
141,
Subpart
W,
Appendix
D)
specifies
the
following
with
respect
to
reactor
validation:

C
Validation
testing
must
determine
a
range
of
operating
conditions
that
can
be
monitored
by
the
system
and
under
which
the
reactor
delivers
the
required
UV
dose.

C
Operating
conditions
must
include
flowrate,
UV
intensity,
and
lamp
status,
at
a
minimum.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
8
June
2003
Propo
sal
Draft
C
Validated
conditions
determined
by
testing
must
account
for
UV
absorbance
of
the
water,
lamp
fouling
and
aging,
measurement
uncertainty
of
on­
line
UV
intensity
sensors,
UV
dose
distributions
arising
from
the
velocity
profiles
through
the
reactor,
failure
of
UV
lamps
or
other
critical
installation
components,
and
inlet
and
outlet
piping
or
channel
configurations
of
the
UV
reactor.

Using
the
above
requirements
as
a
basis,
Appendix
C
provides
guidance
for
several
possible
approaches
to
reactor
validation.
States
may
approve
modifications
to
these
approaches
or
alternative
approaches
at
their
discretion.

Monitoring
Requirements
(
40
CFR
141.729(
d))

The
LT2ESWTR
requires
utilities
to
monitor
their
reactors
to
demonstrate
that
they
are
operating
within
the
range
of
conditions
that
were
validated
for
the
required
UV
dose.
At
a
minimum,
utilities
must
monitor
each
reactor
for
flowrate,
lamp
outage,
UV
intensity
as
measured
by
a
UV
intensity
sensor,
and
any
other
parameters
required
by
the
State.
UV
absorbance
should
also
be
measured
where
it
used
in
a
dose
control
strategy.
Systems
must
check
the
calibration
of
UV
intensity
sensors
and
must
recalibrate
sensors
in
accordance
with
a
protocol
approved
by
the
State.
The
LT2ESWTR
does
not
specify
monitoring
frequency
(
section
5.4
of
this
guidance
describes
the
monitoring
requirements
with
recommended
frequencies).

Reporting
Requirements
(
40
CFR
141.730)

The
LT2ESWTR
requires
utilities
to
report
the
following
items:

°
Initial
reporting
­
Validation
test
results
demonstrating
operating
conditions
that
achieve
the
UV
dose
required
for
the
inactivation
credit
desired
for
compliance
with
the
LT2ESWTR.

°
Routine
reporting
­
Volume
of
water
entering
the
distribution
system
that
was
not
treated
by
the
UV
reactors
operating
under
validated
conditions
on
a
monthly
basis.

For
the
purposes
of
this
guidance
manual,
when
a
UV
reactor
is
operating
outside
of
its
validated
limits,
it
is
considered
"
off­
specification."

Additional
Requirement
for
Unfiltered
Systems
(
40
CFR
141.721(
c)(
2))

For
unfiltered
systems
using
UV
disinfection
to
meet
the
LT2ESWTR
requirements,
the
required
Cryptosporidium
log
inactivation
by
UV
disinfection
must
be
achieved
in
at
least
95
percent
of
the
water
delivered
to
the
public
during
each
calendar
month.
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
9
June
2003
Propo
sal
Draft
1.3.2
Stage
2
DBPR
The
requirements
of
the
Stage
2
DBPR
will
apply
to
all
community
water
systems
(
CWSs)
and
nontransient
noncommunity
water
systems
(
NTNCWSs)
 
both
ground
and
surface
water
systems
 
that
add
a
disinfectant
other
than
UV
light,
or
that
deliver
water
that
has
been
treated
with
a
disinfectant
other
than
UV
light.

Initial
Distribution
System
Evaluations
The
Stage
2
DBPR
is
designed
to
reduce
DBP
occurrence
peaks
in
the
distribution
system
by
changing
compliance
monitoring
requirements.
Compliance
monitoring
will
be
preceded
by
an
initial
distribution
system
evaluation
(
IDSE)
to
identify
compliance
monitoring
locations
that
represent
high
TTHM
and
HAA5
levels.
The
IDSE
consists
of
either
a
standard
monitoring
program
(
SMP)
or
a
system­
specific
study
(
SSS).
NTNCWSs
serving
fewer
than
10,000
people
are
not
required
to
perform
an
IDSE,
and
other
systems
may
receive
waivers
from
the
IDSE
requirement.

Compliance
Determination
and
Schedule
The
Stage
2
DBPR
changes
the
way
sampling
results
are
averaged
to
determine
compliance.
The
determination
for
the
Stage
2
DBPR
is
based
on
a
LRAA
(
i.
e.,
compliance
must
be
met
at
each
monitoring
location)
instead
of
the
system­
wide
RAA
used
under
the
Stage
1
DBPR.

The
Stage
2
DBPR
will
be
implemented
in
two
phases,
Stage
2A
and
Stage
2B.
Under
Stage
2A,
all
systems
must
comply
with
TTHM/
HAA5
MCLs
of
120/
100
µ
g/
L
measured
as
LRAAs
at
each
Stage
1
DBPR
monitoring
site,
while
continuing
to
comply
with
the
Stage
1
DBPR
MCLs
of
80/
60
µ
g/
L
measured
as
RAAs.
Under
Stage
2B,
systems
must
comply
with
TTHM/
HAA5
MCLs
of
80/
60
µ
g/
L
at
locations
identified
under
the
IDSE.

Significant
Excursion
Evaluations
Because
Stage
2
DBPR
MCL
compliance
is
based
on
an
annual
average
of
DBP
measurements,
a
system
could
from
time
to
time
have
DBP
levels
significantly
higher
than
the
MCL
(
referred
to
as
a
significant
excursion)
while
still
being
in
compliance.
This
is
because
the
high
concentration
could
be
averaged
with
lower
concentrations
at
a
given
location.
If
a
significant
excursion
occurs,
a
system
must
conduct
a
significant
excursion
evaluation
and
discuss
the
evaluation
with
the
State
no
later
than
the
next
sanitary
survey.

1.4
Alternative
Approaches
for
Disinfecting
with
UV
Light
This
manual
provides
technical
information
about
using
UV
disinfection
for
drinking
water
treatment.
Although
it
covers
many
aspects
of
implementing
a
UV
installation,
from
design
and
validation
to
operation,
it
is
not
comprehensive
in
terms
of
all
types
of
UV
installations,
design
alternatives,
and
validation
protocols
that
may
provide
satisfactory
1.
Introduction
UV
Disinfection
Guidance
Manual
1­
10
June
2003
Propo
sal
Draft
performance.
For
example,
pulsed
UV
and
eximer
lamps
are
two
types
of
UV
technologies
not
included
in
this
manual,
but
they
may
provide
effective
disinfection.
Currently,
a
significant
level
of
research
is
being
conducted
surrounding
UV
disinfection
and
its
applications
in
various
industries.
As
more
information
becomes
available,
other
UV
equipment
or
methods
of
operation,
design,
and
validation
will
evolve.
States
may
recognize
alternatives
in
UV
installation
design,
operation,
and
validation
that
are
not
described
in
this
manual.
2.
Overview
of
UV
Disinfection
Chapter
2
provides
an
overview
of
UV
disinfection.
The
material
ranges
from
an
explanation
of
the
process
in
terms
of
basic
chemical
and
physical
principles
to
a
description
of
the
components
of
a
UV
installation
and
performance
monitoring.
Appendix
A,
Fundamentals
of
UV
Disinfection,
serves
as
a
companion
to
this
chapter
by
providing
more
detailed
information
on
each
of
the
topics
discussed.
The
corresponding
appendix
sections
are
noted
throughout
the
text.
The
organization
of
this
chapter
is
presented
below,
including
the
key
question
each
section
addresses.

 
What
are
the
fundamental
characteristics
of
UV
light,
and
what
happens
to
UV
light
as
it
propagates
through
water?
..................................
Section
2.2
 
How
does
UV
light
inactivate
microorganisms?
.......................................
Section
2.3.1
 
Can
microorganisms
undergo
repair
and
become
infectious
after
inactivation
by
UV
light?
..................................................................
Section
2.3.2
 
How
are
UV
dose
and
microbial
response
determined?
..............................................................................
Sections
2.3.3
and
2.3.4
 
How
does
UV
dose
vary
in
a
UV
reactor?
.................................................
Section
2.3.3
 
What
affects
a
microorganism's
response
to
UV
light?
..................................................................................
Sections
2.3.4
and
2.3.5
 
What
do
UV
reactors
look
like
and
how
do
the
key
components
function?
..................................................................................
Section
2.4
 
What
are
the
differences
between
low
pressure
and
medium
pressure
lamps?...........................................................................................
Section
2.4.2
 
How
do
the
utility
and
the
State
know
the
UV
reactor
is
delivering
the
required
UV
dose?
...............................................................
Section
2.4.9
 
How
does
water
quality
affect
UV
reactor
performance?
..........................
Section
2.5.1
 
Do
any
disinfection
byproducts
form
as
a
result
of
UV
disinfection?................................................................................................
Section
2.5.2
2.1
History
of
UV
Light
for
Drinking
Water
Disinfection
UV
disinfection
is
an
established
technology
supported
by
decades
of
fundamental
and
applied
research
and
practice
in
North
America
and
Europe.
Downes
and
Blunt
(
1887)
discovered
the
germicidal
properties
of
sunlight.
The
development
of
mercury
lamps
as
artificial
UV
light
sources
in
1901
and
the
use
of
quartz
as
a
UV
transmitting
material
in
1906
was
soon
UV
Disinfection
Guidance
Manual
2­
1
June
2003
Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
2
June
2003
followed
by
the
first
drinking
water
disinfection
application
in
Marseilles,
France
in
1910.
In
1929,
Gates
identified
a
link
between
UV
disinfection
and
absorption
of
UV
light
by
nucleic
acid.
The
development
of
the
fluorescent
lamp
in
the
1930s
led
to
the
production
of
germicidal
tubular
lamps.
Considerable
research
on
the
mechanisms
of
UV
disinfection
and
the
inactivation
of
microorganisms
occurred
during
the
1950s
(
Dulbecco
1950;
Kelner
1950;
Powell
1959;
Brandt
and
Giese
1956).

While
there
was
substantial
research
on
UV
disinfection
during
the
first
half
of
the
20th
century,
the
low
cost
of
chlorine
and
operational
problems
with
early
UV
disinfection
systems
limited
the
growth
of
UV
disinfection
as
a
drinking
water
treatment
technology.
The
first
reliable
applications
of
UV
light
for
disinfecting
municipal
drinking
water
occurred
in
Switzerland
and
Austria
in
1955
(
Kruithof
and
van
der
Leer
1990).
By
1985,
the
number
of
installations
in
these
countries
had
risen
to
approximately
500
and
600,
respectively.
With
the
discovery
of
chlorinated
disinfection
byproducts
(
DBPs),
UV
disinfection
became
popular
in
Norway
and
the
Netherlands
with
the
first
installations
occurring
in
1975
and
1980,
respectively.

As
of
1996,
there
were
over
2000
UV
disinfection
systems
treating
drinking
water
in
Europe
(
USEPA
1996),
primarily
treating
flows
less
than
1
million
gallons
per
day
(
MGD).
A
survey
conducted
in
2000
found
that
UV
disinfection
is
currently
being
used
to
treat
larger
flows,
including
two
installations
treating
a
combined
flow
of
76
MGD
in
Helsinki,
Finland
(
Toivanen
2000),
and
that
the
number
of
installations
is
increasing
(
USEPA
2000).
Several
large
installations
across
the
United
States
are
currently
under
design.
Because
of
the
susceptibility
of
Cryptosporidium
to
UV
disinfection
and
the
emphasis
in
recent
regulations
on
controlling
Cryptosporidium,
the
number
of
utilities
using
UV
disinfection
is
expected
to
increase
significantly
over
the
next
decade.

2.2
Fundamental
Aspects
of
UV
Light
The
use
of
UV
light
to
disinfect
drinking
water
involves
(
1)
the
generation
of
UV
light
with
the
desired
germicidal
properties
and
(
2)
the
delivery
(
or
transmission)
of
that
light
to
pathogens.
This
section
provides
a
basic
description
of
how
UV
light
is
generated
and
the
environmental
conditions
that
affect
its
delivery
to
pathogens.

2.2.1
Nature
of
UV
Light
UV
light
is
the
region
of
the
electromagnetic
spectrum
that
lies
between
x­
rays
and
visible
light
(
Figure
2.1).
The
UV
spectrum
is
divided
into
four
regions
as
shown
in
Figure
2.1:
vacuum
UV
(
100
to
200
nm),
UV­
C
(
200
to
280
nm),
UV­
B
(
280
to
315
nm),
and
UV­
A
(
315
to
400
nm)
(
Meulemans
1986).
UV
disinfection
occurs
due
to
the
germicidal
action
of
UV­
B
and
UV­
C
with
microorganisms.
The
germicidal
action
of
UV­
A
is
small
relative
to
UV­
B
and
UV­
C
and
therefore
needs
very
long
exposure
times
to
be
effective
as
a
disinfectant.
Light
in
the
vacuum
UV
range
is
very
effective
in
disinfecting
microorganisms
(
Munakata
et
al.
1991).
However,
it
is
impractical
for
water
disinfection
applications
because
it
rapidly
attenuates
over
very
short
distances
in
water.
For
the
purposes
of
this
manual,
the
practical
germicidal
wavelength
for
UV
light
ranges
between
200
and
300
nm.

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Figure
2.1
UV
Light
in
the
Electromagnetic
Spectrum
254
nm
100
nm
400
nm
100
nm
200
nm
300
nm
400
nm
315
nm
280
nm
X­
ray
Gamma
Rays
UV
Visible
Infrared
Vacuum
UV
UV­
C
UV­
B
UV­
A
Typically,
UV
light
is
generated
by
applying
a
voltage
across
a
gas
mixture,
resulting
in
a
discharge
of
photons.
The
specific
wavelengths
of
light
emitted
from
photon
discharge
depend
on
the
elemental
composition
of
the
gas
and
the
power
level
of
the
lamp
(
section
A.
1.1).
Nearly
all
UV
lamps
designed
for
water
treatment
use
a
gas
mixture
containing
mercury
vapor.
Mercury
is
an
advantageous
gas
for
UV
disinfection
applications
because
it
emits
light
in
the
germicidal
wavelength
range,
as
discussed
in
section
2.3.5.
The
light
output
depends
on
the
concentration
of
mercury
atoms,
which
is
directly
related
to
the
mercury
vapor
pressure.
Mercury
at
low
vapor
pressure
(
near
vacuum;
0.001
to
0.01
torr,
2
x
10­
5
to
2
x
10­
3
psi)
and
moderate
temperature
(
40
º
C)
produces
essentially
monochromatic
UV
light
at
253.7
nm.
At
higher
vapor
pressures
(
100
to
10,000
torr,
2
to
200
psi)
and
higher
operating
temperatures
(
600
to
900
º
C),
the
frequency
of
collisions
between
mercury
atoms
increases,
producing
UV
light
over
a
broad
spectrum
(
polychromatic)
with
an
overall
higher
intensity.
Mercury
vapor
pressure
between
0.01
and
100
torr
does
not
efficiently
produce
UV
light.

2.2.2
Propagation
of
UV
Light
As
UV
light
propagates
from
its
source,
it
interacts
with
the
materials
it
encounters
through
absorption,
reflection,
refraction,
and
scattering.
In
disinfection
applications,
these
phenomena
result
from
interactions
between
the
emitted
UV
light
and
UV
reactor
components
(
i.
e.,
lamp
envelopes,
lamp
sleeves,
and
reactor
walls)
and
also
the
water
being
treated.
When
assessing
water
quality,
UV
absorbance
or
UV
transmittance
is
the
parameter
that
incorporates
the
impact
of
absorption
and
scattering.
This
section
briefly
describes
both
the
phenomena
that
influence
light
propagation
and
measurement
techniques
to
quantify
UV
light
propagation.
More
detailed
information
is
provided
in
sections
A.
1.2.1
through
A.
1.2.5.

Absorption
is
the
transformation
of
light
to
other
forms
of
energy
as
it
passes
through
a
substance.
UV
absorption
of
a
substance
will
vary
with
the
wavelength
of
the
light.
The
components
of
the
reactor
and
the
water
passing
through
the
reactor
all
absorb
UV
light
to
varying
degrees,
depending
on
their
material
composition.
When
UV
light
is
absorbed,
it
is
no
longer
available
to
disinfect
microorganisms.

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Unlike
absorption,
the
phenomena
of
refraction,
reflection,
and
scattering
change
the
direction
of
UV
light,
but
the
UV
light
is
still
available
to
disinfect
microorganisms.

Refraction
(
Figure
2.2)
is
the
change
in
the
direction
of
light
propagation
as
it
passes
from
one
medium
to
another.
In
UV
reactors,
refraction
occurs
when
light
passes
from
the
UV
lamp
through
an
air
gap,
through
the
lamp
sleeve,
and
through
the
water.
These
changes
alter
the
angle
that
UV
light
strikes
target
pathogens.

Figure
2.2
Refraction
of
Light
Incident
Light
from
UV
Lamp
Air
Gap
Quartz
Sleeve
Water
Refracted
Light
 A
 Q
 W
 A
>
 W
>
 Q
Reflection
is
the
change
in
direction
of
light
propagation
when
it
is
deflected
by
a
surface
(
Figure
2.3).
Reflection
may
be
classified
as
specular
or
diffuse.
Specular
reflection
occurs
from
smooth
polished
surfaces
and
follows
the
Law
of
Reflection
(
the
angle
of
incidence
is
equal
to
the
angle
of
reflection).
Diffuse
reflection
occurs
from
rough
surfaces
and
scatters
light
in
all
directions
with
little
dependence
on
the
incident
angle.
In
UV
reactors,
reflection
will
take
place
at
interfaces
that
do
not
transmit
UV
light
(
e.
g.,
the
reactor
wall)
and
also
at
UV
transmitting
interfaces
(
e.
g.,
the
inside
of
a
lamp
sleeve).
The
type
of
reflection
observed
and
intensity
of
light
reflected
from
a
surface
depends
on
the
material
of
the
surface.

Figure
2.3
Reflection
of
Light
Specular
Reflection
Reflected
Light
Incident
Light
Diffuse
Reflection
Incident
Light
 1
 1
Reflected
Light
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Scattering
of
light
is
the
change
in
direction
of
light
propagation
caused
by
interaction
with
a
particle
(
Figure
2.4).
Particles
can
cause
scattering
in
all
directions,
including
towards
the
incident
light
source
(
back­
scattering).
Scattering
of
light
caused
by
particles
smaller
than
the
wavelength
of
the
light
is
called
Rayleigh
scattering
(
section
A.
1.2.4).
Particles
larger
than
the
wavelength
of
light
scatter
more
light
in
the
forward
direction
but
also
cause
some
backscattering.
Rayleigh
scattering
depends
inversely
on
wavelength
to
the
fourth
power
(
1/
 4)
and
thus
is
more
prominent
at
shorter
wavelengths.
Scattering
by
particles
larger
that
the
wavelength
of
the
light
is
relatively
independent
of
wavelength.

Figure
2.4
Scattering
of
Light
Incident
Light
Target
Pathogens
Forward
Scattered
Light
90
°
Scattered
Light
Back
Scattered
Light
Incident
Light
Target
Pathogens
Forward
Scattered
Light
90
°
Scattered
Light
Back
Scattered
Light
UV
absorbance
(
A254)
is
a
commonly
used
water
quality
parameter
that
characterizes
the
decrease
in
the
amount
of
incident
light
as
it
passes
through
a
water
sample
over
a
specified
distance
or
pathlength.
Various
procedures
call
for
filtering
the
sample
through
a
0.45
µ
m
membrane
before
measuring
the
absorbance.
If
the
measurement
is
made
according
to
a
modified
version
of
Standard
Method
5910B
(
APHA
et
al.
1998),
the
water
sample
is
not
pH
adjusted
or
filtered.
Since
most
particles
in
drinking
water
are
strong
absorbers
of
UV
light,
it
is
recommended
that
absorbance
measurements
be
made
without
filtering
the
sample.
Therefore,
the
modified
measurement
accounts
for
scattering
and
some
absorption
from
particles
in
the
water
sample
that
may
interfere
with
UV
disinfection.
Although
Standard
Methods
identifies
this
measurement
as
UV
absorption,
this
manual
will
refer
to
it
as
absorbance
since
the
latter
term
is
widely
used
in
the
water
treatment
industry.

The
term
UV
transmittance
(
UVT)
has
also
been
used
extensively
in
the
literature
when
describing
the
behavior
of
UV
light.
UVT
is
the
percentage
of
light
passing
through
a
water
sample
over
a
specified
distance
and
is
related
to
UV
absorbance
by
Equation
2.1:

254
10
100
%
A
UVT
 
 
=
Equation
2.1
where
UVT
=
UV
transmittance
at
specified
wavelength
(
e.
g.,
254
nm)
and
pathlength
(
e.
g.,
1
cm)
A254
=
UV
absorbance
at
specified
wavelength,
based
on
1
cm
pathlength
(
unitless;
UV
absorption
as
measured
by
Standard
Method
5910B)

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2.3
Microbial
Response
to
UV
Light
The
mechanism
of
disinfection
by
UV
light
differs
considerably
from
chemical
disinfectants
such
as
chlorine
and
ozone.
Chemical
disinfectants
inactivate
microorganisms
by
destroying
or
damaging
cellular
structures,
interfering
with
metabolism,
and
hindering
biosynthesis
and
growth
(
Snowball
and
Hornsey
1988).
UV
light
inactivates
microorganisms
by
damaging
their
nucleic
acid,
thereby
preventing
the
microorganism
from
replicating.
A
microorganism
that
cannot
replicate
cannot
infect
a
host.

When
studying
UV
disinfection
effectiveness,
it
is
important
to
use
microbial
assays
that
measure
infectivity,
not
viability.
Until
recently,
viability
assays
such
as
excystation
and
vital
dyes
were
used
to
determine
inactivation.
However,
these
assays
do
not
evaluate
changes
in
the
ability
of
a
microorganism
to
reproduce
and
infest
a
host.
The
importance
of
using
assays
that
measure
inactivation
is
highlighted
by
the
history
of
UV
disinfection
for
Cryptosporidium.
It
was
believed
that
UV
disinfection
was
not
effective
for
Cryptosporidium
inactivation
because
results
of
early
Cryptosporidium
inactivation
studies
were
based
on
viability
assays.
The
ability
of
UV
light
to
inactivate
Cryptosporidium
at
low
doses
was
revealed
when
infectivity
was
assessed
by
inoculating
mice
with
UV
treated
water,
which
showed
greater
than
4­
log
inactivation
of
Cryptosporidium
at
doses
less
than
20
mJ/
cm2
(
Bukhari
et
al.
1999).

This
section
discusses
the
damage
that
causes
microbial
inactivation,
the
ability
of
microorganisms
to
repair
the
damage,
methods
for
determining
microbial
inactivation,
and
how
wavelength
of
UV
light
affects
inactivation.

2.3.1
Mechanisms
of
Microbial
Inactivation
by
UV
Light
UV
light
inactivates
microorganisms
by
damaging
deoxyribonucleic
acid
(
DNA)
or
ribonucleic
acid
(
RNA),
thereby
interfering
with
replication
of
the
microorganism
(
section
A.
2.2).
In
normal
DNA
replication,
the
double
helix
strand
separates
allowing
the
single
strands
to
serve
as
a
template
for
reconstructing
the
opposite
strand
of
nucleotides:
adenine
bonds
to
thymine
and
guanine
bonds
to
cytosine
(
Figure
2.5).

Figure
2.5
Structure
of
DNA
and
Nucleotide
Sequences
Within
DNA
DNA
STRUCTURE
Sugar­
Phosphate
Backbone
DNA
SEQUENCE
A
=
Adenine
C
=
Cytosine
T
=
Thymine
G
=
Guanine
 
A
 
T
 
G
 
C
 
G
 
A
 
T
 
C
 
 
T
 
A
 
C
 
G
 
C
 
T
 
A
 
G
 
Hydrogen
Bonded
Nitrogenous
Base
Pairs
(
A,
T,
G,
C)

Purines
Pyrimidines
|
|
|
|
|
|
|
|

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Light
that
is
absorbed
by
a
system
can
induce
a
chemical
reaction.
As
shown
in
Figure
2.6,
each
of
the
nucleotides
absorbs
UV
light
from
200
to
300
nm
(
section
A.
2.2).
The
UV
absorption
of
DNA
results
from
the
combination
of
nucleotides
and
has
a
peak
near
260
nm
and
a
local
minimum
near
230
nm.
DNA
absorbs
light
in
the
wavelength
range
emitted
by
UV
lamps,
enabling
photobiological
effects
that
lead
to
nucleic
acid
damage.

Figure
2.6
UV
Absorbance
of
Nucleotides
(
left)
and
Nucleic
Acid
(
right)
at
pH
7
(
adapted
from
Jagger
1967)

200
260
300
Wavelength
(
nm)
UV
absorbance
(
Relative
Scale)

Adenine
Guanine
Thymine
Cytosine
220
240
280
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
DNA
200
260
300
Wavelength
(
nm)
220
240
280
UV
absorbance
(
Relative
Scale)

Damage
to
nucleic
acid
does
not
prevent
the
cell
from
undergoing
metabolism
and
other
cell
functions.
Although
the
microbial
cell
is
alive
after
exposure
to
UV
light,
it
cannot
reproduce,
and
therefore
it
is
incapable
of
infecting
a
host.
To
kill
the
microbial
cell,
the
UV
dose
would
need
to
be
increased
by
orders
of
magnitude
as
compared
to
the
UV
dose
needed
to
prevent
replication.

Variations
in
DNA
content
cause
microorganisms
to
absorb
UV
light
differently,
thereby
contributing
to
the
differences
in
microorganism
susceptibility
to
UV
disinfection.
There
can
be
significant
disparity
in
the
susceptibility
of
different
strains
of
bacteria
and
viruses
to
UV
disinfection
(
section
A.
2.7).
Among
the
pathogens
of
interest
in
drinking
water,
viruses
are
most
resistant
to
UV
disinfection
followed
by
bacteria
and
Cryptosporidium
oocysts
and
Giardia
cysts.
Appendix
B
provides
statistical
evaluations
for
dose­
response
data
of
Giardia
cysts,
Cryptosporidium
oocysts,
and
viruses,
and
Chapter
1
contains
the
regulatory
requirements
for
inactivating
these
pathogens.

2.3.2
Microbial
Repair
Because
microorganisms
that
have
been
exposed
to
UV
light
still
retain
metabolic
functions,
some
are
able
to
repair
the
damage
done
by
UV
light
to
a
limited
degree
as
described
in
section
A.
2.3.
In
some
cases,
the
microorganism
regains
infectivity.
These
microorganisms
have
evolved
enzyme­
mediated
mechanisms
for
reversing
UV
damage.
Repair
of
UV
lightinduced
DNA
damage
includes
photoreactivation
and
dark
repair
(
Knudson
1985).
In
photoreactivation
(
or
photorepair),
enzymes
energized
by
exposure
to
light
between
310
and
490
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nm
(
near
and
in
the
visible
range)
repair
damaged
sections
of
DNA.
Photoreactivation
needs
the
presence
of
reactivating
light.
Dark
repair
is
defined
as
when
a
repair
process
does
not
need
reactivating
light.
The
term
is
somewhat
misleading
because
dark
repair
can
occur
in
the
presence
of
light,
and
therefore
does
not
need
dark
conditions.
Excision
repair,
a
form
of
dark
repair,
is
an
enzyme­
mediated
process
where
the
damaged
section
of
DNA
is
removed
and
regenerated
using
the
existing
complimentary
strand
of
DNA.

Knudson
(
1985)
found
that
bacteria
are
able
to
repair
in
light
and
dark
conditions,
suggesting
that
bacteria
may
have
the
enzymes
necessary
for
photorepair
and
dark
repair.
Viral
DNA
lacks
the
necessary
enzymes
for
repair,
but
can
repair
using
the
enzymes
of
a
host
cell
(
Rauth
1965).
Linden
et
al.
(
2002a)
did
not
observe
photoreactivation
or
dark
repair
of
Giardia
at
UV
doses
typical
for
UV
disinfection
applications
(
16
and
40
mJ/
cm2).
However,
unpublished
data
from
the
same
study
show
Giardia
reactivation
in
light
and
dark
conditions
at
very
low
UV
doses
(
0.5
mJ/
cm2;
Linden
2002).
Shin
et
al.
(
2001)
reported
Cryptosporidium
does
not
regain
infectivity
after
inactivation
by
UV
light.
One
study
has
shown
that
Cryptosporidium
contains
the
capability
to
undergo
some
DNA
repair
(
Oguma
et
al.
2001).
However,
even
though
the
DNA
is
repaired,
infectivity
is
not
restored.

Knudson
(
1985)
demonstrated
that
photorepair
can
be
overcome
by
increasing
the
damage
to
the
DNA
through
higher
UV
doses.
However,
it
is
unknown
if
higher
UV
doses
can
reduce
dark
repair
because
it
is
more
difficult
to
study
experimentally.
Research
is
continuing
to
evaluate
this
phenomenon.
At
the
doses
typically
used
in
UV
disinfection,
microbial
repair
can
be
controlled
and
accounted
for
as
discussed
in
section
3.1.1.

2.3.3
UV
Dose
and
Dose
Distribution
UV
dose
is
a
measurement
of
the
energy
per
unit
area
that
is
incident
on
a
surface.
UV
dose
is
the
product
of
the
average
intensity
acting
on
a
microorganism
from
all
directions
and
the
exposure
time.
Units
commonly
used
for
UV
dose
are
J/
m2,
mJ/
cm2,
and
mWs/
cm2
(
10
J/
m2
=
1
mJ/
cm2
=
1
mWs/
cm2)
with
mJ/
cm2
being
the
most
common
units
in
North
America
and
J/
m2
being
the
most
common
in
Europe.

In
a
batch
system
such
as
a
bench
scale
collimated
beam
test
(
described
in
Appendix
E),
the
average
intensity
is
determined
mathematically.
For
collimated
beam
tests
using
a
lowpressure
lamp,
the
UV
intensity
measured
by
a
radiometer,
the
UV
absorbance
of
the
water,
the
thickness
of
the
water
layer,
the
distribution
of
light
across
the
water
surface,
and
the
reflection
and
refraction
of
light
from
the
water
surface
all
are
considered
in
calculating
the
average
intensity.
The
UV
dose
can
be
determined
in
a
batch
system
by
multiplying
the
calculated
average
intensity
by
the
specific
exposure
time.

When
using
polychromatic
light
sources
(
e.
g.,
medium­
pressure
lamps),
UV
dose
calculations
in
batch,
bench
scale
experiments
also
incorporate
the
same
parameters
as
a
lowpressure
lamp
collimated
beam
test.
In
addition,
the
intensity
at
each
wavelength
in
the
germicidal
range
and
the
germicidal
effectiveness
at
the
associated
UV
wavelengths
are
also
considered
because
microorganisms
absorb
different
amounts
of
UV
light
at
different
wavelengths.
The
UV
dose­
response
measured
with
polychromatic
lamps
will
match
the
UV
Proposal
Draft
2.
Overview
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UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
9
June
2003
dose­
response
of
monochromatic
lamps
when
the
UV
dose
delivered
by
the
polychromatic
source
is
properly
calculated
(
Cabaj
et
al.
2001;
section
A.
2.4.1).

Dose
delivery
in
a
continuous­
flow
UV
reactor
is
subject
to
hydrodynamic
irregularities
and
a
variable
UV
intensity
distribution
and
is
a
function
of
the
UV
absorbance
of
the
water,
the
flowrate
through
the
reactor,
the
UV
output
from
the
lamps,
and
the
hydraulic
characteristics
within
the
reactor.
As
such,
it
is
difficult
to
calculate
directly
UV
dose
within
a
UV
reactor.
If
the
reactor
has
plug
flow
with
complete
mixing
perpendicular
to
that
flow,
all
microorganisms
leaving
the
reactor
receive
the
same
dose,
and
the
reactor
would
be
termed
an
"
ideal"
reactor.
However,
these
ideal
conditions
do
not
generally
do
not
exist
in
continuous­
flow
UV
reactors.
As
such,
microorganisms
passing
through
a
UV
reactor
are
exposed
to
different
doses.
The
difference
in
UV
doses
experienced
by
microorganisms
in
a
flowing
reactor
is
best
characterized
by
a
dose
distribution.

A
dose
distribution
is
the
probability
distribution
of
UV
doses
that
microorganisms
receive
in
a
flow­
through
UV
reactor;
typically
shown
as
a
histogram
(
Figure
2.7).
Some
microorganisms
travel
close
to
the
UV
lamps
and
experience
a
higher
dose
while
others
that
travel
close
to
the
reactor
walls
may
experience
a
lower
dose.
Some
microorganisms
move
through
the
reactor
quickly
while
others
travel
a
more
circuitous
path.
A
narrow
dose
distribution
(
Figure
2.7a)
indicates
more
ideal
hydrodynamic
conditions.
A
wider
distribution
(
Figure
2.7b)
indicates
less
efficient
reactor
performance
and
results
in
a
greater
degree
of
"
overdosing"
to
ensure
that
the
minimum
desired
dose
is
achieved
for
the
microorganisms
at
the
lower
end
of
the
dose
distribution.

Figure
2.7
Hypothetical
Dose
Distributions
for
Two
Reactors
with
Differing
Hydraulics
0.1
0.2
0.3
0.4
0.5
0.6
UV
Dose
(
mJ/
cm2)
Occurrence
Probability
a.
Narrow
Dose
Distribution
(
Better
Hydraulic
Conditions)

0
15
30
45
75
90
0.0
Occurrence
Probability
b.
Wide
Dose
Distribution
(
Worse
Hydraulic
Conditions)

0.1
0.2
0.3
0.4
0.5
0.6
0.0
UV
Dose
(
mJ/
cm2)
0
15
30
45
75
90
There
are
currently
no
methods
to
measure
directly
the
dose
distribution
in
a
continuous
flow
UV
reactor,
but
mathematical
models
can
help
to
characterize
dose
distribution.
Therefore,
the
UV
dose
in
a
UV
reactor
is
estimated
as
the
reduction
equivalent
dose
(
RED).
The
RED
is
a
calculated
dose
for
a
flow
through
UV
reactor
that
is
based
on
biodosimetry
(
i.
e.,
measuring
the
level
of
inactivation
of
a
challenge
microorganism
with
a
known
UV
dose­
response).
The
RED
is
set
equal
to
the
UV
dose
in
a
collimated
beam
test
that
achieves
the
same
level
of
inactivation
Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
10
June
2003
of
the
challenge
microorganism
as
measured
for
the
flow­
through
UV
reactor
during
biodosimetry
testing.
Methods
for
collimated
beam
testing
and
biodosimetry
are
in
Appendix
E
section
4.2,
respectively.

2.3.4
Microbial
Response
(
UV
Dose­
Response)

The
response
of
microorganisms
to
UV
light
is
calculated
by
determining
the
concentration
of
infectious
microorganisms
before
and
after
exposure
to
a
measured
UV
dose
and
applying
Equation
2.2.

N
N
on
Inactivati
Log
0
10
log
=
Equation
2.2
Where
N0
=
Concentration
of
infectious
microorganisms
before
exposure
to
UV
light
N
=
Concentration
of
infectious
microorganisms
after
exposure
to
UV
light
UV
dose­
response
relationships
can
be
expressed
as
either
the
proportion
of
microorganisms
inactivated
(
log
inactivation,
results
in
a
dose­
response
curve
with
a
positive
slope)
or
the
proportion
of
microorganisms
remaining
(
log
survival,
results
in
a
dose­
response
curve
with
a
negative
slope)
as
a
function
of
UV
dose.
The
proportion
of
microorganisms
remaining
and
the
log
inactivation
are
typically
shown
on
a
logarithmic
(
base
10)
scale,
while
the
UV
dose
is
typically
shown
on
a
linear
scale.
This
manual
will
present
microbial
response
as
log
inactivation
since
the
terminology
is
widely
accepted
in
the
industry.
Therefore,
all
doseresponse
curves
presented
will
have
a
positive
slope.

Although
several
approaches
may
be
used
to
measure
microbial
dose­
response,
the
bench­
scale
collimated
beam
test
has
evolved
as
the
customary
method
because
it
has
carefully
controlled
conditions,
allowing
for
accurate
and
repeatable
determination
of
UV
dose.
Accurate
determination
of
UV
dose
is
beneficial
for
developing
meaningful
relationships
between
UV
dose
and
microbial
response.

Figure
2.8
presents
examples
of
UV
dose­
response
curves.
In
general,
the
UV
doseresponse
of
disperse
microorganisms
follows
first
order
inactivation
(
Figure
2.8,
E.
coli
curve;
section
A.
2.5.1).
However,
some
microorganisms
are
slower
to
respond,
producing
a
shoulder
at
low
UV
doses
followed
by
near­
linear
inactivation
(
Figure
2.8,
B.
subtilis
curve;
section
A.
2.5.2).
UV
dose­
response
is
generally
independent
of
how
the
germicidal
UV
light
is
produced
(
i.
e.,
low­
pressure
or
medium­
pressure
UV
light),
UV
absorbance,
temperature,
and
pH.

Proposal
Draft
2.
Overview
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UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
11
June
2003
Figure
2.8
Shapes
of
UV
Dose­
Response
Curves
(
adapted
from
Chang
et
al.
1985)

0
1
2
3
4
5
6
0
20
40
60
80
100
UV
Dose
(
mJ/
cm2)
Log
Inactivation
E.
coli
B.
subtilis
spores
Total
coliform­
wastewater
Rotavirus
UV
dose­
response
is
affected
by
particle­
association
and
clumping
of
microorganisms.
Solids
present
in
wastewater
samples
can
cause
a
tailing
or
flattening
of
the
dose­
response
curve
at
higher
inactivation
levels
(
Figure
2.8,
total
coliform
curve;
section
A.
2.5.3)
because
clumping
or
particle
association
shields
a
fraction
of
the
microorganisms
from
UV
light.
In
these
wastewater
experiments,
the
microorganisms
are
present
in
the
treated
water
at
very
high
concentrations
so
that
any
particle
association
with
turbidity
reflects
the
impact
of
upstream
treatment
processes.

Research
by
Linden
et
al.
(
2002b)
indicated
that
the
UV
dose­
response
of
microorganisms
added
to
filtered
drinking
waters
is
not
altered
by
variation
in
turbidity
that
meets
regulatory
requirements
(
40
CFR
141.73).
For
unfiltered
waters,
Passantino
and
Malley
(
2001)
found
that
source
water
turbidity
up
to
10
NTU
does
not
impact
the
UV
dose­
response
of
separately
added
(
seeded)
microorganisms.
In
these
experiments,
however,
microorganisms
were
added
to
waters
containing
various
levels
of
treated
or
natural
turbidity.
Therefore,
it
was
not
possible
to
examine
microorganisms
associated
directly
with
particles
in
their
natural
or
treated
states.
Consequently,
these
drinking
water
studies
can
only
suggest
the
impact
of
turbidity
on
dose­
response
as
it
relates
to
the
impact
of
UV
light
scattering
by
particles,
rather
than
particle­
association
or
clumping
of
microorganisms.

2.3.5
Microbial
Spectral
Response
The
action
spectrum
(
also
called
UV
action)
of
a
microorganism
is
a
measure
of
inactivation
effectiveness
as
a
function
of
wavelength.
Figure
2.9
illustrates
the
UV
action
for
three
microbial
species
and
also
the
UV
absorbance
of
DNA
as
a
function
of
wavelength.
Because
of
the
similarity
between
UV
action
and
DNA
absorbance,
and
because
DNA
absorbance
is
easier
to
measure
than
UV
action,
the
DNA
absorbance
spectrum
of
a
microorganism
is
often
used
as
a
surrogate
for
its
UV
action
spectrum.
The
scale
of
the
y­
axis
Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
12
June
2003
represents
the
ratio
of
inactivation
effectiveness
at
a
given
wavelength
to
the
inactivation
effectiveness
at
254
nm.
For
most
microorganisms,
the
UV
action
peaks
at
or
near
260
nm,
has
a
local
minimum
near
230
nm,
and
drops
to
zero
near
300
nm.
Although
the
sensitivity
of
the
organism
often
increases
below
230
nm,
the
strong
absorption
of
UV
light
by
components
in
natural
water
at
these
wavelengths
offsets
the
increased
organism
sensitivity
in
this
region.
Nevertheless,
an
operating
definition
of
the
effective
germicidal
range
for
UV
light
in
water
includes
wavelengths
from
200
to
300
nm.

Figure
2.9
Comparison
of
Microbial
UV
Action
and
DNA
UV
Absorbance
(
adapted
from
Rauth
1965
and
Linden
et
al.
2001)

0.0
0.5
1.0
1.5
2.0
200
300
Wavelength
(
nm)
UV
Action
or
DNA
Absorbance
Relative
to
254
nm
DNA
Cryptosporidium
MS2
Herpes
simplex
virus
220
240
260
280
2.4
UV
Reactors
The
goal
in
designing
UV
reactors
for
drinking
water
disinfection
is
to
deliver
efficiently
the
necessary
dose
to
inactivate
pathogenic
microorganisms.
An
example
UV
reactor
is
shown
in
Figure
2.10.
Commercial
UV
reactors
consist
of
open
or
closed­
channel
vessels
containing
UV
lamps,
lamp
sleeves,
UV
intensity
sensors,
lamp
sleeve
wipers,
and
temperature
sensors.
UV
lamps
are
housed
within
the
lamp
sleeves,
which
protect
and
insulate
the
lamps.
Some
reactors
include
automatic
cleaning
mechanisms
to
keep
the
lamp
sleeves
free
of
deposits
that
may
form
due
to
contact
with
the
water.
UV
intensity
sensors,
flow
meters,
and
in
some
cases,
UVT
monitors
are
used
to
monitor
dose
delivery
by
the
reactor.
This
section
briefly
describes
UV
reactor
components.
A
more
detailed
discussion
of
these
components
is
provided
in
section
A.
3.

Proposal
Draft
2.
Overview
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UV
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Guidance
Manual
2­
13
June
2003
Figure
2.10
UV
Disinfection
System
Schematic
(
courtesy
of
Severn
Trent
Services)

Influent
Pipe
UV
Transmittance
Monitor
Control
Panel
UV
Lamp
Housed
in
Quartz
Sleeve
UV
Intensity
Sensor
UV
Intensity
Sensor
Reactor
Casing
Temperature
Sensor
Electrical
Connection
to
Lamp
Effluent
Pipe
Quartz
Sleeve
Wiper
Wiper
Motor
2.4.1
Reactor
Configuration
UV
reactors
are
typically
classified
as
either
open
or
closed
channel.
Water
flows
under
pressure
(
i.
e.,
no
free
surface)
in
closed
channel
reactors
(
Figure
2.11a).
Drinking
water
UV
applications
have
used
only
closed
reactors
to­
date.
Open
channel
reactors
(
Figure
2.11b)
are
open
basins
with
channels
containing
racks
of
UV
lamps.
Open
channel
reactors
are
most
commonly
used
in
wastewater
applications.

Proposal
Draft
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UV
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Disinfection
Guidance
Manual
2­
14
June
2003
Figure
2.11
Example
of
Closed
(
a)
and
Open
(
b)
Channel
Reactors
(
courtesy
of
Trojan
Technologies)

a.
Closed­
Channel
Reactor
b.
Open­
Channel
Reactor
Reactors
are
designed
to
optimize
dose
delivery,
and
the
reactor
hydrodynamics
play
an
important
role
in
design.
Lamp
placement,
inlet
and
outlet
conditions,
and
baffles
all
affect
mixing
within
a
reactor.
Improvements
to
the
hydraulic
behavior
of
a
reactor
are
often
obtained
at
the
expense
of
headloss.
Individual
reactor
designs
employ
various
methods
to
optimize
dose
delivery
(
e.
g.,
higher
lamp
output
versus
lower
lamp
output
and
improved
hydrodynamics
through
increased
headloss).

2.4.2
UV
Lamps
UV
light
can
be
produced
by
the
following
variety
of
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
generally
use
LP,
LPHO,
or
MP
lamps.
As
such,
the
subsequent
discussions
in
this
manual
are
limited
to
these
UV
lamp
technologies.
Table
2.1
Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
15
June
2003
lists
characteristics
associated
with
these
lamps,
and
Table
2.2
lists
operational
advantages
and
disadvantages
of
the
lamp
types.

Table
2.1
Mercury
Vapor
Lamp
Characteristics
Parameter
Low­
pressure
Low­
pressure
high­
output
Medium­
pressure
Germicidal
UV
light
Monochromatic
at
254
nm
Monochromatic
at
254
nm
Polychromatic,
including
germicidal
range
(
200
to
300
nm)

Mercury
Vapor
Pressure
(
torr)
Optimal
at
0.007
0.76
300
 
30,000
Operating
Temperature
(
°
C)
Optimal
at
40
130
 
200
600
 
900
Electrical
Input
(
W/
cm)
0.5
1.5
 
10
50
 
250
Germicidal
UV
Output
(
W/
cm)
0.2
0.5
 
3.5
5
 
30
Electrical
to
Germicidal
UV
Conversion
Efficiency
(%)
35
 
38
30
 
40
10
 
20
Arc
length
(
cm)
10
 
150
10
 
150
5
 
120
Relative
Number
of
Lamps
Needed
for
a
Given
Dose
High
Intermediate
Low
Lifetime
(
hrs)
8,000
 
10,000
8,000
 
12,000
4,000
 
8,000
Table
2.2
Mercury
Vapor
Lamp
Comparison
Low­
pressure
Medium­
pressure
Comparative
Advantages
 
Higher
germicidal
efficiency;
nearly
all
output
at
254
nm
 
Smaller
power
draw
per
lamp
(
less
reduction
in
dose
if
lamp
fails)
 
Longer
lamp
life
 
Higher
power
output
 
Fewer
lamps
for
a
given
application
 
Smaller
reactors
 
Smaller
footprint
Comparative
Disadvantages
 
More
lamps
needed
for
a
given
application
 
Larger
footprint
 
Higher
operating
temperature
can
accelerate
fouling
(
section
2.5.1)
 
Shorter
lamp
life
 
Lower
electrical
to
germicidal
UV
conversion
efficiency
The
light
emitted
by
LP
and
LPHO
lamps
is
essentially
monochromatic
at
253.7
nm
(
Figure
2.12a)
and
is
near
the
maximum
of
the
microbial
action
spectrum.
MP
lamps
emit
at
a
wide
range
of
wavelengths
across
the
action
spectra
(
Figure
2.12b).
Therefore,
LPHO
lamps
convert
power
to
germicidal
light
more
efficiently.
In
either
lamp
type,
power
not
converted
to
light
is
primarily
lost
as
heat.

Proposal
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Disinfection
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Manual
2­
16
June
2003
Figure
2.12
UV
Output
of
LP
(
a)
and
MP
(
b)
Mercury
Vapor
Lamps
(
Sharpless
and
Linden
2001)

0.0
0.2
0.4
0.6
0.8
1.0
1.2
200
250
300
350
400
Wavelength
(
nm)
Relative
Lamp
Output
Lamp
Output
Relative
to
Maximum
Output
in
Range
b.
Medium
Pressure
Lamp
0.0
0.2
0.4
0.6
0.8
1.0
1.2
200
250
300
350
400
Wavelength
(
nm)
Relative
Lamp
Output
Lamp
Output
Relative
to
Maximum
Output
in
Range
a.
Low
Pressure
Lamp
Figure
2.13
shows
the
output
of
LP
and
MP
lamps
superimposed
with
the
DNA
absorption
spectrum.
In
Figure
2.13,
the
DNA
absorbance
is
plotted
relative
to
the
maximum
absorbance
in
the
range
(
260
nm).
The
lamp
outputs
are
also
presented
on
a
relative
scale.
However,
in
absolute
terms,
there
is
a
significant
difference
in
the
intensity
and
power
of
LP
and
MP
lamps
(
see
Table
2.1
for
more
information
on
lamp
operating
characteristics).

Proposal
Draft
2.
Overview
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UV
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UV
Disinfection
Guidance
Manual
2­
17
June
2003
Figure
2.13
UV
Lamp
Output
and
its
Relation
to
the
UV
Absorbance
of
DNA
(
courtesy
of
Bolton
Photosciences,
Inc.)

200
250
300
Wavelength
(
nm)
Lamp
Output
Relative
to
Maximum
Output
in
Range
DNA
Absorbance
MP
Output

LP
Output

DNA
Absorbance
Relative
to
Maximum
Absorbance
in
Range
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
UV
lamps
may
be
oriented
parallel,
perpendicular,
or
diagonal
to
flow
or
ground.
Orienting
MP
lamps
horizontally
relative
to
the
ground
prevents
differential
heating
of
the
lamps
and
reduces
the
potential
for
lamp
breakage.
Lamp
breakage
is
discussed
further
in
Appendix
N.

UV
lamps
degrade
as
they
age
resulting
in
a
reduction
in
output
(
section
A.
3.1.6).
MP
lamps
may
have
a
shift
in
spectral
output
as
well.
Lamp
degradation
will
impact
dose
delivery
over
time.

2.4.3
Lamp
Power
Supply
And
Ballasts
Ballasts
supply
the
UV
lamps
with
the
appropriate
power
to
energize
and
operate
the
UV
lamps.
Ballasts
use
inductance
(
coil
or
transformer),
capacitance,
and
a
starting
circuit.
Power
supplies
and
ballasts
are
available
in
many
different
configurations
and
are
tailored
to
a
unique
lamp
type
and
application.
UV
reactors
may
use
electronic
ballasts,
magnetic
ballasts,
or
transformers.
The
various
ballast
types
and
their
differences
are
detailed
in
section
A.
3.2.

2.4.4
Lamp
Sleeves
UV
lamps
are
housed
within
lamp
sleeves
to
help
keep
the
lamp
at
optimal
operating
temperature
and
to
protect
the
lamp
from
breaking.
Lamp
sleeves
are
tubes
of
quartz
(
or
vitreous
silica).
The
sleeve
length
is
sufficient
to
include
the
lamp
and
associated
electrical
connections.
The
sleeve
diameter
is
typically
2.5
cm
for
LP
lamps
and
5
to
10
cm
for
MP
lamps.
The
distance
between
the
exterior
of
the
lamp
and
interior
of
the
lamp
sleeve
is
approximately
1
cm.
Sleeve
walls
are
typically
2
to
3
mm
thick
and
absorb
some
UV
light
(
Figure
2.14).
UV
lamps
are
usually
centered
radially
within
lamp
sleeves
using
spacers.

Proposal
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UV
Disinfection
Guidance
Manual
2­
18
June
2003
Figure
2.14
UV
Transmittance
of
Quartz
that
is
1
mm
Thick
at
a
Zero
Degree
Incidence
Angle
(
GE
Quartz
2001)

50
60
70
80
90
100
200
220
240
260
280
300
320
340
360
380
400
Wavelength
(
nm)
UV
Transmittance
(%)

Lamp
sleeves
can
fracture
and
foul,
and
their
transmittance
will
decrease
as
they
age.
Fractures
can
occur
from
internal
stress
and
external
mechanical
forces
such
as
wiper
jams,
water
hammer,
resonant
vibration,
and
impact
by
objects.
Microscopic
fractures
may
also
occur
if
lamp
sleeves
are
not
handled
properly
when
removed
for
manual
cleaning.
If
the
sleeve
fractures
while
in
service,
water
can
enter
the
sleeve,
making
the
lamp
vulnerable
to
breakage
as
a
result
of
temperature
differences
between
the
lamp
and
the
water.
Lamp
breakage
is
undesirable
due
to
potential
for
mercury
release.
Appendix
N
discusses
the
potential
effects
of
lamp
breakage
and
possible
response
plans.

Fouling
on
the
internal
lamp
sleeve
surface
arises
from
the
deposition
of
material
from
components
within
the
lamp
or
sleeve
due
to
temperature
and
exposure
to
UV
light.
The
UV
reactor
manufacturer
can
control
internal
lamp
sleeve
fouling
through
appropriate
material
selection.
Fouling
on
external
surfaces
is
caused
by
the
reaction
of
compounds
in
the
water
with
the
lamp
sleeve
surface.
Compounds
that
contribute
to
fouling
are
discussed
in
section
2.5.1.
External
fouling
must
be
removed
by
cleaning.
In
addition,
exposure
of
quartz
contaminated
with
metal
cations
can
cause
solarization
as
lamp
sleeves
age.
Both
fouling
and
solarization
can
decrease
the
UV
transmittance
of
the
sleeve.

2.4.5
Cleaning
Systems
UV
reactor
manufacturers
have
developed
different
approaches
for
cleaning
lamp
sleeves,
depending
on
the
application.
These
approaches
include
both
off­
line
chemical
cleaning
(
OCC)
and
on­
line
mechanical
cleaning
(
OMC)
methods.

In
OCC
systems,
the
reactor
is
shut
down,
drained,
and
flushed
with
a
cleaning
solution.
Solutions
used
to
clean
lamp
sleeves
include
citric
acid,
phosphoric
acid,
or
a
food
grade
Proposal
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Disinfection
UV
Disinfection
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Manual
2­
19
June
2003
proprietary
solution
provided
by
the
UV
reactor
manufacturer.
The
reactor
is
rinsed
and
returned
to
operation
after
sufficient
time
to
dissolve
the
substances
fouling
the
sleeves
is
allowed.
LPHO
systems
typically
use
OCC
systems.

OMC
systems
are
built­
in
UV
reactor
components
that
consist
of
wipers
that
are
driven
by
either
screws
attached
to
electric
motors
or
pneumatic
pistons.
There
are
two
types
of
wipers
used
in
OMC
systems:
mechanical
wipers
and
physical­
chemical
wipers.
Mechanical
wipers
may
consist
of
stainless
steel
brush
collars
or
Teflon
®
rings
that
move
along
the
lamp
sleeve
(
Figure
2.15a).
Physical­
chemical
wipers
have
a
collar
filled
with
cleaning
solution
that
moves
along
the
lamp
sleeve
(
Figure
2.15b).
The
wiper
physically
removes
fouling
on
the
lamp
sleeve
surface
while
the
cleaning
solution
within
the
collar
dissolves
fouling
materials.
The
use
of
mechanical
and
physical­
chemical
wipers
does
not
necessitate
that
the
UV
reactor
be
drained.
Therefore,
the
reactor
can
remain
on­
line
while
the
lamp
sleeves
are
cleaned.
MP
systems
typically
use
OMC
systems
because
the
higher
lamp
temperatures
can
accelerate
fouling
under
certain
water
qualities.

Figure
2.15
(
a)
Mechanical
Wiper
System
(
courtesy
of
Calgon
Carbon
Corporation),
(
b)
Physical­
Chemical
Wiper
System
(
courtesy
of
Trojan
Technologies)

a
b
2.4.6
UV
Intensity
Sensors
UV
intensity
sensors
are
photosensitive
detectors
that
measure
the
UV
intensity
at
a
point
within
the
UV
reactor
(
Figure
2.16).
Sensors
are
used
to
indicate
dose
delivery
by
providing
information
related
to
UV
intensity
at
different
points
in
the
reactor.
The
measurement
responds
to
changes
in
lamp
output
due
to
lamp
power
setting,
lamp
aging,
lamp
sleeve
aging,
and
lamp
sleeve
fouling.
Depending
on
sensor
position,
UV
intensity
sensors
may
also
respond
to
changes
in
UV
absorbance
of
the
water
being
treated
(
section
A.
3.8.2).
UV
intensity
sensors
are
composed
of
optical
components,
a
photodetector,
an
amplifier,
a
housing,
and
an
electrical
connector.
The
optical
components
may
include
monitoring
windows,
light
pipes,
diffusers,
apertures,
and
filters.
Monitoring
windows
and
light
pipes
are
designed
to
deliver
light
to
the
Proposal
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Manual
2­
20
June
2003
photodetector.
Diffusers
and
apertures
are
designed
to
reduce
the
amount
of
UV
light
reaching
the
photodetector,
thereby
reducing
sensor
degradation
that
is
caused
by
UV
energy.
Optical
filters
are
used
to
modify
the
spectral
response
such
that
the
sensor
only
responds
to
germicidal
wavelengths
(
i.
e.,
200
to
300
nm).
At
the
time
of
publication,
sensors
are
specific
to
each
manufacturer
and
are
subject
to
validation
as
described
in
sections
4.3.2.3
and
C.
4.7.

Figure
2.16
UV
Intensity
Sensor
Viewing
Lamps
within
a
UV
Reactor
(
courtesy
of
Severn
Trent
Services)

UV
intensity
sensors
can
be
classified
as
wet
or
dry.
Dry
sensors
monitor
UV
light
through
a
monitoring
window,
whereas
wet
UV
intensity
sensors
are
in
direct
contact
with
the
water
flowing
through
the
reactor.
Monitoring
windows
and
the
wetted
ends
of
wet
sensors
can
foul
over
time
and
need
cleaning
similar
to
lamp
sleeves.

2.4.7
UV
Transmittance
Monitors
As
stated
previously,
UVT
is
an
important
parameter
in
determining
the
efficiency
of
UV
disinfection.
Therefore,
monitoring
UV
transmittance
(
or
UV
absorbance
to
calculate
UVT)
is
critical
to
ensure
the
success
of
a
UV
disinfection
application.
UVT
can
be
determined
either
through
grab
samples
with
a
laboratory
instrument
or
on­
line.
Several
commercial
UV
reactors
use
the
measurement
of
UVT
to
help
monitor
and
control
the
calculated
UV
dose
in
the
reactor.

In
general,
commercial
on­
line
UVT
monitors
calculate
UVT
by
measuring
the
UV
intensity
at
various
distances
from
a
lamp.
One
such
monitor
is
schematically
displayed
in
Figure
2.17.
In
this
monitor,
a
stream
of
water
passes
through
a
cavity
containing
a
LP
lamp
with
three
UV
intensity
sensors
located
at
various
distances
from
the
lamp.
The
difference
in
sensor
readings
is
used
to
calculate
UVT.

Proposal
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UV
Disinfection
Guidance
Manual
2­
21
June
2003
Figure
2.17
UV
Transmittance
Monitor
Design
(
courtesy
of
Severn
Trent
Services)

UV
Lamp
UV
Intensity
Sensor
Inlet
Outlet
A
B
C
UV
Lamp
UV
Intensity
Sensor
Inlet
Outlet
A
B
C
UV
Lamp
UV
Intensity
Sensor
Inlet
Outlet
A
B
C
2.4.8
Temperature
Sensors
Energy
input
per
unit
volume
is
relatively
high
for
a
UV
reactor.
The
water
flowing
through
a
reactor
efficiently
absorbs
the
wasted
heat
and
maintains
operating
temperatures
within
a
desirable
range.
Nevertheless,
temperatures
can
become
elevated
under
the
following
circumstances:

 
Water
level
in
the
reactor
drops
and
lamps
are
exposed
to
air.

 
Water
stops
flowing
in
the
reactor.

UV
reactors
are
equipped
with
temperature
sensors
that
monitor
the
water
temperature
within
the
reactor.
If
the
temperature
is
above
the
recommended
operating
temperature
range,
the
reactor
will
shut
off
to
minimize
the
potential
for
the
lamps
overheating.

2.4.9
Monitoring
UV
Disinfection
Performance
The
performance
of
an
operating
UV
disinfection
system
must
be
monitored
to
demonstrate
that
adequate
disinfection
is
being
achieved
(
40
CFR
141,
Subpart
W,
Appendix
D).
Because
the
concentration
of
pathogenic
organisms
cannot
be
measured
continuously
in
the
UVtreated
water
and
the
dose
distribution
cannot
be
measured
directly
in
real
time,
various
strategies
have
been
developed
to
monitor
dose
delivery.
Any
dose
monitoring
method
must
be
evaluated
during
reactor
validation
(
as
described
in
section
4.3.2.2),
and
the
outputs
measured
during
validation
will
be
part
of
the
monitoring
requirements
described
in
section
5.4.1
(
40
CFR
141.729(
d)).

Proposal
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Disinfection
Guidance
Manual
2­
22
June
2003
Currently,
there
are
three
fundamental
approaches
to
monitor
UV
disinfection
performance
in
a
UV
reactor:

1.
UV
Intensity
Setpoint
Approach.
In
this
approach,
measurements
made
by
the
UV
intensity
sensor
are
used
to
control
the
UV
reactor.
The
UV
intensity
sensor
is
located
in
a
position
that
allows
it
to
properly
respond
to
both
changes
in
UV
intensity
output
of
the
lamps
and
also
UVT
of
the
water.
The
UV
intensity
sensor
output
and
the
flowrate
are
used
to
monitor
dose
delivery.
The
setpoint
value
for
UV
intensity
over
a
range
of
flowrates
is
determined
during
validation.

2.
UV
Intensity
and
UVT
Setpoint
Approach.
This
approach
is
similar
to
the
UV
intensity
sensor
setpoint
approach,
except
that
the
UV
sensor
is
placed
close
to
the
lamp
such
that
it
only
responds
to
changes
in
UV
lamp
output.
UVT
is
monitored
separately.
For
a
specific
flowrate,
the
UV
intensity
and
UVT
measurements
are
used
to
monitor
dose
delivery.
The
setpoints
for
UV
intensity
and
UVT
over
a
range
of
flowrates
are
determined
during
validation.

3.
Calculated
UV
Dose
Approach.
In
this
approach,
the
UV
intensity
sensor
is
placed
close
to
the
lamp,
which
is
similar
to
the
UV
intensity
and
UVT
setpoint
approach.
Flowrate,
UVT,
and
UV
intensity
are
all
monitored,
and
the
outputs
are
used
to
calculate
UV
dose
via
a
validated
computational
algorithm
developed
by
the
UV
reactor
manufacturer.

The
strategy
for
dose
monitoring
depends
on
the
manufacturer
and
may
be
proprietary.
Dose
monitoring
recommendations
are
discussed
in
section
5.4.2.

2.5
Water
Quality
Impacts
and
Byproduct
Formation
Constituents
in
the
water
subjected
to
treatment
affect
the
performance
of
UV
disinfection.
In
addition,
all
disinfectants
can
form
byproducts,
and
the
goal
of
the
overall
disinfection
process
is
to
maximize
disinfection
while
minimizing
byproduct
formation.
This
section
discusses
water
quality
characteristics
impacting
UV
disinfection
performance
and
finishes
with
a
discussion
of
byproducts
formed
during
the
UV
disinfection
process.

2.5.1
Water
Quality
Impacts
UVT,
particle
content,
and
constituents
that
foul
lamp
sleeves
and
other
wetted
components
are
the
most
significant
water
quality
factors
impacting
UV
disinfection
effectiveness.
In
spite
of
these
effects,
the
impact
of
water
quality
on
dose
delivery
can
be
adequately
addressed
in
virtually
all
drinking
water
applications
if
carefully
considered
during
the
design
of
the
UV
disinfection
system,
as
discussed
in
section
3.1.3.1.

The
most
important
water
quality
parameter
affecting
reactor
performance
is
UVT.
As
UVT
decreases,
the
intensity
throughout
the
reactor
decreases
for
a
given
lamp
configuration.
This
results
in
a
reduction
in
UV
dose
delivered
to
the
microorganism
and
the
measured
UV
Proposal
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2­
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June
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intensity
for
a
given
lamp
output.
Section
3.1.3.1
discusses
how
to
incorporate
the
impact
of
UVT
into
UV
disinfection
system
design.

Several
chemicals
used
in
water
treatment
processes
can
decrease
the
UVT
of
water
(
e.
g.,
Fe+
3
and
ozone).
However,
some
oxidants
(
including
ozone)
can
increase
the
UVT
(
APHA
et
al.
1998)
by
degrading
natural
organic
matter.
Water
treatment
processes
upstream
of
the
UV
reactors
can
be
operated
to
control
UVT,
thereby
optimizing
the
design
and
costs
of
the
UV
reactor
(
section
A.
4.1.3
and
section
3.1.3.1).

Particle
content
can
also
impact
UV
disinfection
performance.
Particles
may
scatter
light
and
reduce
the
UV
intensity
delivered
to
the
microorganisms.
Particles
may
also
shield
microorganisms
from
UV
light,
effectively
reducing
disinfection
performance.

Compounds
in
the
water
can
cause
fouling
in
a
UV
reactor
on
the
external
surfaces
of
the
lamp
sleeves
and
other
wetted
components
(
e.
g.,
monitoring
windows
of
UV
intensity
sensors).
Fouling
on
the
lamp
sleeves
reduces
the
transmittance
of
UV
light
through
the
sleeve
into
the
water,
thereby
reducing
power
efficiency.
Fouling
on
the
monitoring
windows
impacts
UV
intensity
and
dose
monitoring.
Hardness,
alkalinity,
temperature,
iron
concentration,
and
pH
all
influence
the
rate
of
fouling
and,
subsequently,
the
frequency
of
sleeve
cleaning.
The
following
compounds
can
cause
fouling:

 
Compounds
whose
solubility
decreases
as
temperature
increases
will
precipitate
(
e.
g.,
CaCO3,
CaSO4,
MgCO3,
MgSO4,
FePO4,
FeCO3,
Al2(
SO4)
3).
These
compounds
will
foul
MP
lamps
faster
than
LP
lamps
due
to
differences
in
operating
temperature.

 
Compounds
with
low
solubility
will
precipitate
(
e.
g.,
Fe(
OH)
3,
Al(
OH)
3).

 
Particles
will
deposit
on
the
lamp
sleeve
surface
due
to
gravity
settling
and
turbulence­
induced
collisions
(
Lin
et
al.
1999a).

Fouling
rate
kinetics
have
been
reported
as
first
order
over
time
following
a
short
induction
period
(
Lin
et
al.
1999b).
Depending
on
the
water
quality
and
UV
lamp
type,
significant
fouling
may
occur
in
hours
or
take
up
to
several
months.
Although
there
is
currently
not
sufficient
information
to
predict
fouling
based
on
water
quality,
a
facility
can
use
the
Langelier
Saturation
Index
(
LSI)
or
the
Calcium
Carbonate
Precipitation
Potential
(
CCPP)
as
a
tool
to
determine
if
precipitation
is
likely
to
occur
(
section
A.
4.1.4).
Data
have
been
generated
from
pilot­
scale
testing
on
waters
of
low
to
moderate
hardness
and
iron
content
(
Mackey
et
al.
2001
and
Mackey
et
al.
2003).
At
total
and
calcium
hardness
levels
less
than
140
mg/
L
and
iron
less
than
0.1
mg/
L,
standard
cleaning
protocols
and
wiper
frequencies
(
one
sweep
every
15
minutes
to
an
hour)
were
sufficient
to
overcome
the
impact
of
sleeve
fouling
at
all
sites
tested.
At
sites
with
high
hardness
or
iron
in
the
feed
water,
it
may
be
advantageous
to
evaluate
fouling
rates
as
described
in
section
J.
5.1
on
a
site­
specific
or
worst
case
basis
via
pilot­
scale
or
demonstration­
scale
testing
to
identify
how
best
to
keep
the
lamp
sleeves
clean.

Table
2.3
is
a
summary
of
water
quality
data
and
the
fouling
observed
for
various
pilot
and
full­
scale
UV
reactors.
All
of
the
MP
systems
shown
had
mechanical
cleaning
(
except
at
Boxalls
Lane),
and
the
LPHO
systems
used
manual
chemical
cleaning.
The
fouling
observed
at
individual
sources
is
reported
as
shown
in
the
following
list:

Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
24
June
2003
 
Not
Significant
 
no
significant
drop
in
UV
intensity
(
based
on
UV
intensity
sensor
readings)

 
Moderate
 
slight
decrease
in
UV
intensity
and
slight
scale
observed
on
sleeves
 
Significant
 
large
decrease
in
UV
intensity
and
significant
deposits
observed
on
sleeves
Table
2.3
Water
Quality
Data
and
Fouling
Observed
for
UV
Disinfection
Pilot
and
Demonstration
Studies
Name
of
Plant
Boxalls
Lane1
Atlanta2
Ulrich
Water
Treatment
Plant2
Central
Utah2
Neenah
Water
Utility2
Cudahy
Water
Utility2
Location
Hampshire,
UK
Atlanta,
GA
Austin,
TX
Orem,
UT
Neenah,
WI
Cudahy,
WI
Lamp
Type
MP
MP/
LPHO
MP/
LPHO
MP/
LPHO
MP/
LPHO/
LP
MP/
LPHO/
LP
A254
(
cm­
1)
NA
0.01­
0.04
0.03­
0.08
0.01­
0.04
0.03­
0.10
0.00­
0.03
LSI
NA
NA
NA
0.5
0.7
­
0.1
Iron
(
mg/
L)
NA
<
0.04
0.01
<
0.02
0.02
0.01
Manganese
(
mg/
L)
NA
<
0.015
<
0.001
<
5.03
0.003
0.012
Calcium
Hardness
(
mg/
L
as
CaCO3)
NA
NA
40
162
54
80
Hardness
(
mg/
L
as
CaCO3)
325­
370
21.5
101
180
87
138
Alkalinity
(
mg/
L
as
CaCO3)
260­
280
13.7
60
159
52
125
pH
7.1­
7.2
6.6
9.6
7.8
9
7.7
Fouling
Observed
not
significant
not
significant4
moderate5
not
significant
moderate6
not
significant
not
significant
1
Bourgine
et
al.
1995
2
Mackey
et
al.
2001
3
Detection
Limit
4
Cleaning
wipers
on
(
MP
system)
5
Cleaning
wipers
off
(
MP
system)
6
After
8
months
of
operation
(
LPHO
system)
NA
=
Not
available
None
of
the
systems
studied
and
listed
in
Table
2.3
exhibited
"
significant"
fouling,
and
in
all
cases,
the
observed
fouling
was
controllable
by
regular
system
maintenance
and
cleaning.

Lastly,
algae
may
grow
upstream
or
downstream
of
UV
reactors.
Visible
light
emitted
from
the
lamps
is
transmitted
through
water
at
further
distances
than
germicidal
wavelengths.

Proposal
Draft
2.
Overview
of
UV
Disinfection
UV
Disinfection
Guidance
Manual
2­
25
June
2003
Depending
on
the
concentration
of
nutrients
in
the
water
and
the
amount
of
visible
light
transmitted
beyond
the
reactor,
algae
growth
may
need
to
be
controlled
through
periodic
maintenance.

2.5.2
Byproducts
from
UV
Disinfection
UV
DBPs
arise
either
directly
through
photochemical
reactions
or
indirectly
through
reactions
with
products
of
photochemical
reactions
(
section
A.
4.2).
Photochemical
reactions
will
only
take
place
if
a
chemical
species
absorbs
UV
light,
and
the
resulting
excited
state
reacts
to
form
a
new
species.
The
resulting
concentration
of
new
species
will
depend
on
the
concentration
of
the
reactants
and
the
UV
dose.

In
drinking
water,
research
has
focused
on
the
impact
of
UV
light
on
the
formation
of
halogenated
DBPs
after
subsequent
chlorination
and
the
transformation
of
organic
material
to
more
degradable
components.
For
ground
water
and
filtered
drinking
water,
UV
disinfection
at
typical
doses
has
been
shown
not
to
impact
the
formation
of
trihalomethanes
or
haloacetic
acids,
two
categories
of
DBPs
currently
regulated
by
the
United
States
Environmental
Protection
Agency
(
EPA)
(
Malley
et
al.
1995;
Kashinkunti
et
al.
2003).

Several
studies
have
shown
low­
level
formation
of
non­
regulated
DBPs
(
e.
g.,
aldehydes)
as
a
result
of
applying
UV
light
to
wastewater
and
raw
drinking
water
sources.
However,
a
study
performed
with
filtered
drinking
water
indicates
no
significant
change
in
aldehydes,
carboxylic
acids,
or
total
organic
halides
(
TOX)
(
Kashinkunti
et
al.
2003).
The
difference
in
results
can
be
attributed
to
the
difference
in
water
quality,
most
notably
the
higher
concentration
of
organic
material
in
raw
waters
and
wastewaters.

Finally,
the
conversion
of
nitrate
to
nitrite
is
possible
with
MP
lamps
that
emit
at
low
wavelengths
(
von
Sonntag
and
Schuchman
1992).
However,
due
to
the
low
conversion
rate
(
about
1
percent;
Sharpless
and
Linden
2001),
this
is
of
minimal
concern
in
drinking
water
applications.

Proposal
Draft