LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
1
The
Surface
Water
Treatment
Rule
Guidance
Manual
and
Alternative
Disinfectants
and
Oxidants
Guidance
Manual
are
available
on
EPA's
website:

http://
www.
epa.
gov/
safewater/
mdbp/
implement.
html.
11.0
Ozone
11.1
Introduction
Ozone
is
commonly
used
in
drinking
water
treatment
for
disinfection
and
taste
and
odor
control.
Ozone
is
a
strong
oxidant
that
can
inactivate
microorganisms,
including
Cryptosporidium,
and
also
oxidize
and
break
down
natural
organic
matter.
It
exists
as
a
gas
at
room
temperature
and
must
be
generated
on­
site.
Ozone
reacts
rapidly
with
organic
and
inorganic
compounds
and
does
not
maintain
a
residual
over
the
time
scales
associated
with
secondary
disinfection.

The
Surface
Water
Treatment
Rule
(
SWTR)
and
subsequent
Stage
1
Disinfectants
and
Disinfection
Byproducts
Rule
(
DBPR)
and
Interim
Enhanced
SWTR
(
IESWTR)
all
recognize
the
capability
of
ozone
to
inactivate
pathogens.
As
a
result,
there
is
much
information
and
guidance
available
on
the
application
of
ozone
for
disinfection,
particularly
in
the
following
two
guidance
manuals:

°
Guidance
Manual
for
Compliance
with
the
Filtration
and
Disinfection
Requirements
for
Public
Water
Systems
Using
Surface
Water
Sources
(
USEPA
1991)
(
commonly
referred
to
as
the
Surface
Water
Treatment
Rule
Guidance
Manual).

 
Describes
how
to
calculate
the
CT
value
for
ozone
(
CT
is
described
in
the
next
section),
including
methodologies
for
determining
the
residual
concentration
(
C)
and
contact
time
(
T).

 
Includes
ozone
CT
values
for
log­
inactivation
of
Giardia
and
viruses.

°
Alternative
Disinfectants
and
Oxidants
Guidance
Manual
(
USEPA,
1999).

 
Provides
full
descriptions
of:


ozone
chemistry

on­
site
generation

primary
uses
and
points
of
application

byproduct
production

analytical
methods

operational
considerations
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
2
The
purpose
of
this
chapter
is
to
(
1)
describe
what
systems
need
to
do
to
receive
Cryptosporidium
treatment
credit
for
disinfecting
with
ozone,
(
2)
discuss
design
and
operational
considerations
that
will
assist
water
systems
in
deciding
whether
this
toolbox
option
is
a
practical
option
for
their
system,
and
(
3)
discuss
key
issues
associated
with
using
ozone
as
a
disinfectant.
This
chapter
is
organized
as
follows:

11.2
Credits
­
discusses
Cryptosporidium
inactivation
credit
systems
can
receive
with
the
addition
of
ozone,
and
relates
CT
to
Cryptosporidium
inactivation
credit.

11.3
CT
Determination
­
summarizes
how
CT
is
used
to
determine
log
inactivation
credit
for
the
SWTR
and
highlights
the
changes
in
CT
calculation
methodologies
from
the
SWTR
to
the
LT2ESWTR.

11.4
Monitoring
Requirements
­
discusses
monitoring
requirements
of
both
LT2ESWTR
and
Stage
1
DBPR.

11.5
Unfiltered
Systems
LT2ESWTR
Requirements
­
discusses
Cryptosporidium
inactivation
requirements
that
unfiltered
systems
must
meet.

11.6
Toolbox
Selection
­
discusses
the
potential
advantages
and
disadvantages
of
ozone
processes.

11.7
Disinfection
with
Ozone
­
describes
reaction
pathways
of
ozone
in
water,
and
inorganic
and
organic
byproduct
formation.

11.8
Design
­
discusses
similarities
and
differences
of
different
types
of
ozone
generators
and
contactors,
general
considerations
in
determining
the
locations
of
ozone
addition,
and
filter
media
and
operating
conditions
of
biologically
active
filters.

11.9
Safety
Considerations
in
Design
­
discusses
various
safety
considerations
that
should
be
taken
into
account
in
the
design
of
ozone
generators.

11.10
Operational
Issues
­
discusses
how
ozone
disinfection
and
CT
calculation
are
affected
by
ozone
demand,
pH,
temperature,
and
residual
disinfectant
in
the
distribution
system.

11.2
Credits
Systems
can
receive
between
a
0.5
to
3.0
log
Cryptosporidium
inactivation
credit
with
the
addition
of
ozone,
depending
on
the
ozone
dose
applied.
The
value
of
the
Cryptosporidium
inactivation
credit
that
a
system
receives
is
determined
by
the
CT
or
inactivation
provided
in
the
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
3
treatment
process.
CT
values
are
established
to
provide
a
conservative
characterization
of
the
dose
of
ozone
necessary
to
achieve
a
specified
inactivation
of
Cryptosporidium.
CT
is
defined
as
the
product
of
the
disinfectant
concentration
and
disinfectant
contact
time:

CT
=
Disinfectant
(
mg/
L)
x
Contact
Time
(
minutes)

°
"
T"
is
the
time
it
takes
the
water
to
move
from
the
point
where
the
initial
disinfectant
residual
concentration
is
measured
to
the
point
where
the
final
disinfectant
residual
concentration
is
measured
in
a
specified
disinfectant
segment
°
"
C"
is
the
measured
concentration
of
dissolved
ozone
in
mg/
L
The
concept
of
regulating
surface
water
treatment
disinfection
through
CT
was
first
introduced
in
the
SWTR.
Tables
relating
Giardia
and
virus
log
inactivations
with
associated
CT
values,
commonly
referred
to
as
CT
tables,
were
presented
in
the
SWTR
Guidance
Manual.
For
the
LT2ESWTR,
EPA
developed
CT
values
for
Cryptosporidium
inactivation
by
ozone
(
Table
11.1).

Table
11.1
CT
Values
for
Cryptosporidium
Inactivation
by
Ozone
(
40
CFR
141.730)

Log
credit
Water
Temperature,

C1
<=
0.5
1
2
3
5
7
10
15
20
25
0.5
12
12
10
9.5
7.9
6.5
4.9
3.1
2.0
1.2
1.0
24
23
21
19
16
13
9.9
6.2
3.9
2.5
1.5
36
35
31
29
24
20
15
9.3
5.9
3.7
2.0
48
46
42
38
32
26
20
12
7.8
4.9
2.5
60
58
52
48
40
33
25
16
9.8
6.2
3.0
72
69
63
57
47
39
30
19
12
7.4
1CT
values
between
the
indicated
temperatures
may
be
determined
by
interpolation.

If
a
utility
believes
that
the
CT
values
presented
in
Table
11.1
do
not
accurately
represent
the
conditions
needed
to
achieve
the
desired
level
of
inactivation
in
their
system,
they
have
the
option
of
conducting
a
site
specific
study
to
generate
a
set
of
CT
tables
for
their
facility.
The
study
would
involve
measuring
actual
Cryptosporidium
inactivation
performance
under
site
conditions.
If
accepted
by
the
State,
the
CT
tables
generated
by
the
site
study
would
replace
the
tables
given
in
this
guidance
for
the
site
at
which
the
study
was
performed.
Guidance
on
site
specific
studies
of
Cryptosporidium
inactivation
is
presented
in
Appendix
A.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
4
11.3
CT
Determination
The
recommended
methodologies
and
calculations
for
determining
CT
have
two
modifications
from
the
SWTR
to
the
LT2ESWTR.

°
For
Cryptosporidium,
EPA
recommends
that
no
inactivation
credit
be
granted
for
the
first
dissolution
chamber
due
to
the
higher
CT
requirements
of
Cryptosporidium
compared
to
Giardia
and
virus.
(
This
differs
from
the
SWTR
guidance
manual,
where
EPA
recommends
granting
inactivation
Giardia
and
virus
credit
for
first
chamber
of
an
ozone
contactor,
provided
that
the
residual
ozone
concentration
measured
at
the
outlet
from
the
first
contact
chamber
met
minimum
concentration
levels.)
The
relatively
small
CT
values
normally
achieved
due
to
oxidant
demand
in
the
first
dissolution
chamber
and
the
resources
required
for
routine
ozone
monitoring
would
likely
offset
the
benefit
from
the
small
Cryptosporidium
credit
achieved.

°
If
no
tracer
study
data
are
available
for
determining
T,
EPA
recommends
using
the
continuous
stirred
tank
reactor
(
CSTR)
approach
(
described
below)
or
the
Extended­
CSTR
approach
(
described
in
Appendix
B).
The
T
10/
T
ratios
based
on
baffling
characteristics
presented
in
Table
C­
5
of
the
SWTR
Guidance
Manual
are
based
on
hydraulic
studies
of
clearwells
and
basins.
At
this
time,
EPA
is
not
aware
of
similar
studies
for
ozone
contactors
that
could
be
used
to
develop
comparable
recommendations.

This
guidance
manual
presents
three
methods
for
calculating
CT:

°
T
10
°
Continuous
stirred
tank
reactor
(
CSTR)
°
Extended­
CSTR
These
methods
differ
in
the
level
of
effort
associated
with
them
and,
in
general,
the
ozone
dose
required
to
achieve
a
given
level
of
inactivation.
Selecting
the
appropriate
method(
s)
to
use
depends
on
the
configuration
of
the
ozone
contactor
and
amount
of
process
evaluation
and
monitoring
that
a
system
wishes
to
undertake.
Combinations
of
two
or
more
methods
may
also
be
used.
For
example,
contactors
with
multiple
segments
may
have
one
or
two
segments
with
their
CT
calculated
using
either
the
T
10
or
CSTR
methods,
while
the
CT
for
the
remaining
segment
is
calculated
using
the
Extended­
CSTR
approach.
The
T
10
and
CSTR
are
the
simplest
methods
and
are
described
in
this
chapter.
Appendix
B
provides
more
information
for
choosing
the
appropriate
method
and
detailed
guidance
for
the
Extended­
CSTR
method.
A
fourth
method,
the
Segmented
Flow
Analysis
approach,
is
under
consideration
by
EPA,
but
the
details
of
the
approach
are
not
final.
EPA
is
requesting
comment
on
the
approach
and
any
appropriate
safety
factors
to
ensure
the
inactivation
credit
calculated
using
the
method
is
actually
achieved
(
see
section
11.11
for
comment
requests).
Table
11.2
summarizes
the
current
methods,
including
describing
the
situations
when
their
use
is
appropriate.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
5
Table
11.2
Applicable
Methods
and
Terminology
for
Calculating
the
Log­
Inactivation
Credit
Section
Description
Terminology
Method
for
Calculating
Log­
Inactivation
Restrictions
No
Tracer
Data
Chambers
where
ozone
is
added
First
chamber
First
Dissolution
Chamber
No
log­
inactivation
credit
is
recommended
None
Other
chambers
Co­
Current
or
Counter­
Current
Dissolution
Chambers
CSTR
Method
in
each
chamber
with
a
measured
effluent
ozone
residual
concentration
No
credit
is
given
to
a
dissolution
chamber
unless
a
detectable
ozone
residual
has
been
measured
upstream
of
this
chamber
Reactive
Chambers

3
consecutive
chambers
Extended­
CSTR
Zone
Extended­
CSTR
Method
in
each
chamber
Detectable
ozone
residual
should
be
present
in
at
least
3
chambers
in
this
zone,
measured
via
in­
situ
sample
ports.
Otherwise,
the
CSTR
method
should
be
applied
individually
to
each
chamber
having
a
measured
ozone
residual
<
3
consecutive
chambers
CSTR
Reactive
Chamber(
s)
CSTR
Method
in
each
chamber
None
No
Tracer
Data
Chambers
where
ozone
is
added
First
chamber
First
Dissolution
Chamber
No
log­
inactivation
is
credited
to
this
section
Not
applicable
Other
chambers
Co­
Current
or
Counter­
Current
Dissolution
Chambers
T
10
or
CSTR
Method
in
each
chamber
with
a
measured
effluent
ozone
residual
concentration
No
credit
will
be
given
to
a
dissolution
chamber
unless
a
detectable
ozone
residual
has
been
measured
upstream
of
this
chamber
Reactive
Chambers

3
consecutive
chambers
Extended­
CSTR
Zone
Extended­
CSTR
Method
in
each
chamber
Detectable
ozone
residual
should
be
present
in
at
least
3
chambers
in
this
zone,
measured
via
in­
situ
sample
ports.
Otherwise,
the
T10
or
CSTR
method
should
be
applied
to
each
chamber
having
a
measured
ozone
residual
<
3
consecutive
chambers
T
1o
or
CSTR
Reactive
Chamber(
s)
T
10
or
CSTR
Method
in
each
chamber
None
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
6
The
remainder
of
this
section
describes
how
to
calculate
C
for
the
T
10
and
CSTR
methods
and
then
describes
the
T
10
and
CSTR
methodologies.

11.3.1
Measuring
C
for
T
10
and
CSTR
Methods
The
methods
for
determining
C
have
not
been
modified
from
those
presented
in
the
SWTR
Guidance
Manual.
The
two
methods
for
determining
C
are:

4)
Direct
measure
of
the
concentration
profile
of
dissolved
ozone
in
each
contact
chamber
(
described
in
section
O.
3.2
of
the
SWTR
Guidance
Manual)

5)
Indirect
prediction
of
the
average
C
based
on
dissolved
ozone
measurements
at
the
contact
chamber
outlet
(
described
in
section
O.
3.3
of
the
SWTR
Guidance
Manual)

For
the
second
method,
predicting
the
average
C
based
on
outlet
measurements,
the
correlations
presented
in
Table
11.3
are
to
be
used
for
estimating
C
based
on
C
in
and
C
out
measurements,
based
on
the
flow
configuration
within
the
contact
chamber.
To
be
granted
inactivation
credit
for
a
chamber,
its
final
ozone
concentration
should
be
above
the
detection
limit
(
i.
e.,
have
a
positive
C
out
value).

Table
11.3
Correlations
to
Predict
C*
Based
on
Outlet
Concentration
Turbine
Co­
Current
Flow
Counter­
Current
Flow
Reactive
Flow
C
out
C
out
or
(
C
in+
C
out)/
2
C
out/
2
C
out
*
C
­
Characteristic
concentration,
used
for
CT
calculation
C
out
­
Ozone
residual
concentration
at
the
outlet
from
the
chamber
C
in
­
Ozone
residual
concentration
at
the
inlet
to
the
chamber
11.3.2
T
10
Method
The
T
10
method
is
appropriate
for
contactors
with
hydraulic
conditions
resembling
plug
flow.
Using
the
T
10
approach,
the
contact
time
(
T)
is
the
time
at
which
90
percent
of
the
water
in
the
contactor
or
segment
has
passed
through
the
contactor.
EPA
recommends
that
tracer
studies
be
used
to
determine
the
T
10
for
ozone
contactors.
The
SWTR
Guidance
Manual
describes
how
to
conduct
a
tracer
test.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
7
Chamber
1
Counter­
Current
Chamber
3
Counter­
Current
Chamber
2
Co­
Current
Chamber
4
Reactive
Flow
C
1out
=
1.2
mg/
L
=
C
2in
C
2out
=
0.8
mg/
L
C
3out
=
0.9
mg/
L
=
C
4in
C
4out
=
0.0
mg/
L
CT
can
be
calculated
for
an
entire
treatment
process
(
e.
g.,
an
entire
ozone
contactor)
or
broken
into
segments
(
e.
g.,
individual
contact
chambers)
and
summed
for
a
total
CT
value
for
all
segments.
C
is
measured
either
at
the
end
of
a
given
segment
or
both
the
beginning
and
end
of
the
segment.

The
following
steps
describe
the
CT
calculation
from
measured
C
and
T
values
for
a
segment
or
the
entire
treatment
process:

4)
Calculate
CT
calc
by
multiplying
the
measured
C
and
T
values.

2)
From
the
CT
table
(
Table
11.1),
find
the
CT
value
for
the
log
inactivation
credit
desired,
this
is
CT
table.

3)
Calculate
the
ratio
of
CT
calc/
CT
table
for
each
segment.

4)
If
a
system
has
multiple
segments,
sum
the
CT
calc/
CT
table
ratios
for
a
total
inactivation
ratio.

5)
If
the
ratio
of
CT
calc/
CT
table
is
at
least
1,
then
the
treatment
process
provides
the
level
of
log
inactivation
that
CT
table
represents
(
log
inactivation
credit
desired
from
step
#
2).

Example
CT
Calculation
and
Log
Credit
Determination
using
the
T
10
Method
A
water
system
employs
a
4
chamber
ozone
contactor
to
achieve
a
0.5­
log
Cryptosporidium
inactivation
credit.
The
contactor
is
designed
and
operated
as
shown
in
the
following
diagram.

The
water
temperature
is
5
degrees
Celsius.
Each
chamber
has
a
volume
of
1,000
gallons.
Results
from
a
tracer
test
showed
the
T
10
for
the
entire
contactor
(
i.
e.
through
all
4
chambers)
was
24
minutes.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
8
The
first
step
is
to
determine
the
ozone
concentration
for
each
chamber
(
segment).
EPA
recommends
that
inactivation
credit
not
be
granted
for
the
first
chamber,
therefore
concentrations
are
only
calculated
for
Chambers
2,
3,
and
4.
Using
Table
11.2,
C
can
be
determined
with
the
following
equations:

Chamber
2
C
=
(
C
in
+
C
out)
/
2
or
C
=
C
out
Chamber
3
C
=
C
out/
2
Chamber
4
C
=
C
out
Therefore
for:

Chamber
2:
C
=
(
1.2
+
0.8)
/
2
=
1.0
mg/
L
(
this
equation
gives
the
higher
C
value)
Chamber
3:
C
=
0.9
/
2
=
0.45
mg/
L
Chamber
4:
C
=
0.0
mg/
l
2)
Calculate
the
T
for
each
chamber.

The
T
10
of
all
four
chambers
is
divided
proportionally
by
volume
among
the
four
chambers.
This
method
cannot
be
used
if
the
chambers
with
final
concentrations
of
zero
(
nondetectable
are
50
percent
or
greater
than
the
entire
volume
of
the
chambers.
Only
the
last
chamber
had
a
non­
detectable
final
concentration
and
that
chamber
is
25
percent
the
volume
of
all
the
chambers.
Therefore
the
T
10
can
be
extrapolated
among
the
chambers
to
estimate
individual
T
10
values.

T
10
of
each
chamber
=
T
10(
V
1­
4/
V
T)
=
24(
1,000
gallons/
4,000
gallons)
=
6
min.
(
In
this
example,
the
volume
of
each
chamber
is
same
therefore
the
T
10
of
each
chamber
is
simply
one­
fourth
of
the
total
T
10.)

3)
Calculate
the
CT
for
each
chamber
Chamber
1:
not
calculated
Chamber
2:
CT
=
1.0
mg/
L
×
6
min
=
6.0
mg­
min/
L
Chamber
3:
CT
=
0.45
mg/
L
×
6
min
=
2.7
mg­
min/
L
Chamber
4:
CT
=
0
mg/
L
×
6
min
=
0
mg­
min/
L
Chapter
11
­
Ozone
1k10
is
calculated
from
the
CT
table
with
the
following
equation:
Log
inactivation
=
k10
x
CT
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
9
4)
Identify
the
CT
table
for
the
log
inactivation
credit
desired
for
each
chamber.
Calculate
the
ratio
of
CT
calc
to
CT
table,
and
sum
the
ratios
to
get
a
total
log
inactivation
ratio.

CT
calc
CT
table
for
0.5­
log
Ratio
of
CT
calc
/
CT
table
Chamber
2
6.0
7.9
0.76
Chamber
3
2.7
7.9
0.34
Chamber
4
0
7.9
­

Total
Log
Inactivation
Ratio
1.10
The
log
inactivation
ratio
is
at
least
1,
therefore
this
system
achieves
0.5
log
Cryptosporidium
inactivation
credit.

11.3.3
CSTR
Method
The
CSTR
method
is
recommended
for
contactors
that
experience
significant
back
mixing
or
when
no
tracer
data
is
available.
This
method
uses
the
hydraulic
detention
time
of
the
ozone
contactor,
as
described
below,
for
estimating
the
contact
time.
The
CSTR
method
should
be
applied
to
the
individual
chambers
in
the
contactor.

For
the
CSTR
approach,
the
CT
table
is
not
directly
used
and
instead
log
inactivation
is
calculated
with
the
following
equation:

­
Log
(
I/
I
0)
=
Log
(
1
+
2.303k
10
x
C
x
HDT)
Equation
11­
1
where:
­
Log
(
I/
I
0)
=
the
log
inactivation
k
10
=
log
base
ten
inactivation
coefficient
(
L/
mg­
min)
1
C
=
Concentration
from
Table
11­
2
(
mg/
L)
HDT
=
Hydraulic
detention
time
(
minutes)

Table
11.4
presents
the
k
10
values
for
Cryptosporidium
(
k
10
values
are
calculated
from
the
CT
table).
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
10
Table
11.4
Inactivation
Coefficients
for
Cryptosporidium,
Log
base
10
(
L/
mg­
min)

Water
Temperature,

C
<=
0.5
1
2
3
5
7
10
15
20
25
k
10
0.0417
0.0430
0.0482
0.0524
0.0629
0.0764
0.101
0.161
0.254
0.407
To
interpolate
between
the
temperatures
in
the
table,
the
following
equation
can
be
used:

k
10
=
0.0397
x
(
1.09757)
T
Equation
11­
2
In
order
to
apply
Equation
11­
1,
both
C
and
HDT
must
be
known.
These
two
parameters
can
be
determined
for
individual
chambers
or
for
zones
consisting
of
multiple,
adjacent
chambers.
In
general,
if
the
concentration
is
measured
at
3
or
more
points
in
the
contactor
the
Extended­
CSTR
method
will
be
used,
so
the
CSTR
method
likely
will
not
be
applied
when
3
or
more
zones
(
excluding
the
first
dissolution
chamber)
are
defined.

EPA
recognizes
that,
for
many
situations,
either
the
CSTR
and
T
10
method
can
be
used
to
calculate
inactivation
credit,
and
that
they
may
generate
two
different
estimates
of
log
inactivation.
EPA
recommends
that
systems
use,
and
States
accept,
the
higher
estimate
of
the
log
inactivation
credit.
However,
systems
should
select
one
method
to
be
used
and
use
that
method
consistently.

Example
­
CT
Calculation
and
Log
Credit
Determination
using
the
CSTR
Method
with
the
concentration
measured
for
each
chamber
A
system
employs
a
three
chamber
ozone
contactor,
with
ozone
addition
in
the
first
two
chambers.
The
second
chamber
is
a
counter­
current
flow
dissolution
chamber
with
influent
and
effluent
ozone
concentrations
of
C
in
=
0.3
mg/
L
and
C
out
=
0.3
mg/
L.
The
effluent
ozone
concentration
in
the
third,
reactive
chamber
is
C
out
=
0.2
mg/
L.
At
10

C,
k
10
=
0.1005
L/
mg­
min.
The
HDT
for
each
chamber
=
20
minutes.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
11
Chamber
1
Counter­
Current
Chamber
2
Counter­
Current
Chamber
3
Reactive
Flow
C1out
=
0.3
mg/
L
=
C2in
C2out
=
0.3
mg/
L
C3out
=
0.2
mg/
L
1)
Determine
the
C
values
for
each
chamber
Chamber
1
No
inactivation
credit
recommended
Chamber
2
C
=
C
out/
2
=
0.3
/
2
=
0.15
mg/
L
Chamber
3
C
=
C
out
=
0.2
mg/
L
2)
Calculate
the
log
inactivation
for
each
chamber
using
Equation
11­
1
Chamber
2
Log
inactivation
=
Log(
1
+
2.303
×
0.1005
×
0.15
×
20)
=
0.23
Chamber
3
Log
inactivation
=
Log(
1
+
2.303
×
0.1005
×
0.20
×
20)
=
0.28
3)
Sum
the
log
inactivations
to
determine
the
log
credit
achieved.

The
total
log­
inactivation
across
the
contactor
is
0.23
+
0.28
=
0.51
log
inactivation,
therefore
0.5
log
credit
achieved.

Example
­
CT
Calculation
and
Log
Credit
Determination
using
the
CSTR
Method
with
the
concentration
not
measured
for
each
chamber
A
system
employs
a
four
chamber
ozone
contactor,
with
ozone
addition
in
the
first
two
chambers.
The
second
chamber
is
a
counter­
current
flow
dissolution
chamber
with
influent
and
effluent
ozone
concentrations
of
C
in
=
0.3
mg/
L
and
C
out
=
0.3
mg/
L.
The
effluent
ozone
concentration
in
the
third,
reactive
chamber
is
unknown,
and
in
the
fourth,
reactive
chamber
is
0.1
mg/
L.
At
10

C,
k
10
=
0.1005
L/
mg­
min.
The
HDT
for
each
chamber
=
20
minutes.
Chambers
3
and
4
are
considered
one
zone,
and
the
effluent
concentration
of
Chamber
3
is
assumed
to
be
equal
to
that
of
Chamber
4.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
12
Chamber
1
Counter­
current
Chamber
4
Reactive
Flow
Chamber
3
Reactive
Flow
Chamber
2
Counter­
current
C1
out
=
0.3
mg/
L
=
C2
in
C2
out
=
0.3
mg/
L
C4
out
=
0.1
mg/
L
1)
Determine
the
C
values
for
each
chamber
Chamber
1
No
inactivation
credit
recommended
Chamber
2
C
=
C
2
out/
2
=
0.3
/
2
=
0.15
mg/
L
Chamber
3
C
=
C
4
out
=
0.1
mg/
L
Chamber
4
C
=
C
4
out
=
0.1
mg/
L
2)
Calculate
the
log
inactivation
for
each
chamber
using
Equation
11­
1
Chamber
2
Log
inactivation
=
Log(
1
+
2.303
×
0.1005
×
0.15
×
20)
=
0.23
Chamber
3
Log
inactivation
=
Log(
1
+
2.303
×
0.1005
×
0.1
×
20)
=
0.17
Chamber
4
Log
inactivation
=
Log(
1
+
2.303
×
0.1005
×
0.1
×
20)
=
0.17
3)
Sum
the
log
inactivations
to
determine
the
log
credit
achieved.

The
total
log­
inactivation
across
the
contactor
is
0.23
+
0.17
+
0.17
=
0.57
log
inactivation,
therefore
0.5
log
credit
achieved.

11.3.4
Extended
CSTR
Approach
The
Extended
CSTR
approach
requires
the
measurement
of
the
ozone
concentration
at
a
minimum
of
three
points
within
the
contactor
These
data
are
used
to
develop
a
predicted
ozone
concentration
profile
through
the
contactor.
The
Extended
CSTR
approach
generally
results
in
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
13
lower
doses
of
ozone
resulting
in
the
same
level
of
inactivation,
when
compared
to
the
CSTR
method.
Appendix
B
provides
a
complete
description
of
the
Extended
CSTR
approach.
11.4
Monitoring
Requirements
11.4.1
LT2ESWTR
The
LT2ESWTR
(
40
CFR
141.730)
requires
daily
CT
monitoring
conducted
during
peak
hourly
flow
(
40
CFR
141.729(
a)).
Since
systems
may
not
know
when
the
peak
hour
flow
will
occur,
EPA
recommends
monitoring
on
an
hourly
basis.
Contact
time
does
not
have
to
be
determined
on
a
daily
basis,
only
concentration.
Systems
should
reevaluate
contact
time
whenever
they
modify
a
process
and
the
hydraulics
are
affected
(
e.
g.,
add
a
pump
for
increased
flow,
reconfigure
piping).

The
concentration
of
ozone
must
be
measured
with
the
indigo
colorimetric
method,
Standard
Method
4500­
O
3
B
(
40
CFR
141.729(
a)).
Details
on
these
methods
can
be
found
in
Standard
Methods
for
the
Examination
of
Water
and
Wastewater,
19th
edition,
American
Public
Health
Association,
1995.
Appendix
C
provides
information
on
sample
collection,
preparation
and
stability
of
reagent,
and
calibration
and
maintenance
of
online
monitors.

11.4.2
Stage
1
DBPR
The
Stage
1
DBPR
requires
all
systems
using
ozone
for
disinfection
or
oxidation
to
take
at
least
one
bromate
sample
per
month
for
each
treatment
plant
using
ozone
(
See
the
Stage
1
DBPR,
40
CFR
141.132(
b)
for
further
information).
Samples
must
be
taken
at
the
distribution
system
entry
point
when
the
ozone
system
is
operating
under
normal
conditions.
Systems
may
reduce
monitoring
from
monthly
to
quarterly
if
the
system
demonstrates
that
the
annual
average
raw
water
bromide
concentration
is
less
than
0.05
mg/
l,
based
on
monthly
measurements
for
one
year.
The
MCL
for
bromate
if
10

g/
l
based
on
a
running
annual
average.

11.5
Unfiltered
System
LT2ESWTR
Requirements
The
LT2ESWTR
requires
unfiltered
systems
to
meet
the
following
requirements
(
40
CFR
141.721(
b)
and
(
c)):

°
Provide
at
least
2.0
log
Cryptosporidium
inactivation
°
If
their
source
water
Cryptosporidium
concentration
is
greater
than
0.01
oocyst/
liter
then
the
system
must
provide
3.0
log
Cryptosporidium
inactivation
°
Use
a
minimum
of
two
disinfectants
to
meet
overall
disinfection
requirements
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
14
The
requirements
of
the
previous
SWTR
regulations
still
apply
 
achieve
3
log
inactivation
of
Giardia
and
4
log
inactivation
of
viruses,
and
maintain
a
disinfectant
residual
in
the
distribution
system
(
e.
g.,
free
chlorine
or
chloramines).

The
monitoring
requirements
described
in
section
11.4
apply
to
unfiltered
systems.
Additionally,
unfiltered
systems
must
meet
the
Cryptosporidium
log­
inactivation
requirements
every
day
the
system
serves
water
to
the
public,
except
one
day
per
calendar
month
(
40
CFR
141.721(
c)).
Therefore,
if
an
unfiltered
system
fails
to
meet
Cryptosporidium
log­
inactivation
two
days
in
a
month,
it
is
in
violation
of
the
treatment
technique
requirement.

11.6
Toolbox
Selection
Selecting
ozone
disinfection
to
receive
Cryptosporidium
inactivation
credit
for
compliance
with
the
LT2ESWTR
has
cost,
operational,
and
upstream
and
downstream
process
implications.
The
ozone
CT
requirements
for
Cryptosporidium
inactivation
are
significantly
higher
than
for
Giardia
and
virus,
and
capital
requirements
could
be
substantial
for
a
system
seeking
higher
than
0.5
credit.
As
a
result,
ozone
is
likely
a
better
option
for
systems
that
will
benefit
from
its
other
treatment
effects.
This
section
discusses
the
potential
advantages
and
disadvantages
of
ozone
processes.

11.6.1
Advantages
Ozonation
reduces
many
other
contaminants
and
improves
process
performance,
both
directly
and
indirectly.
The
indirect
benefits
are
those
where
other
aspects
of
the
treatment
process
can
be
improved
or
changed,
resulting
in
a
higher
finished
water
quality.
The
advantages
of
ozone
use
include:

$
Total
organic
carbon
(
TOC)
reduction
$
Iron,
manganese,
and
sulfide
oxidation
$
Taste,
odor,
and
color
control
$
Trihalomethane
(
THM)
and
haloacetic
acid
(
HAA)
reduction
with
reduction
in
chlorine
use
$
Biological
stability
with
biological
filtration
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
15
11.6.2
Disadvantages
Considering
only
benefits
from
Cryptosporidium
inactivation
credit,
the
capital,
operational,
and
maintenance
costs
are
relatively
high
compared
to
other
toolbox
options
for
similar
credit,
especially
for
systems
treating
colder
water.
Other
disadvantages
include:

$
Higher
level
of
maintenance
and
operator
skill
required.

$
Additional
safety
and
containment
issues
with
ozone
contactors.

$
Possible
need
for
three­
phase
power
which
may
not
be
compatible
with
some
water
systems.

$
Bromate
formation
(
bromate
is
a
regulated
DBP).

$
Upstream
processes
can
cause
fluctuations
in
ozone
demand,
thus
affecting
ozone
residual
control.

$
Assimilable
organic
carbon
(
AOC)
production,
which
can
contribute
to
biofilm
growth
in
the
distribution
system
if
not
removed.

$
High
capital
requirements
to
achieve
CT
requirements
with
low
water
temperatures
(
below
10
oC).

11.7
Disinfection
With
Ozone
11.7.1
Chemistry
Ozone
decomposes
spontaneously
during
water
treatment
by
a
complex
mechanism
that
involves
the
generation
of
hydroxyl
free
radicals
(
Hoigné
and
Bader
1983a
and
1983b;
Glaze
et
al.
1987).
The
hydroxyl
free
radicals
are
among
the
most
reactive
oxidizing
agents
in
water,
with
reaction
rates
on
the
order
of
1010
­
1013
M­
1
s­
1
(
Hoigné
and
Bader
1976).
The
half­
life
of
hydroxyl
free
radicals
is
on
the
order
of
microseconds.
Concentrations
of
hydroxyl
free
radicals
can
never
reach
levels
above
10­
12
M
(
Glaze
and
Kang
1988).

When
ozone
is
added
to
water,
it
reacts
through
two
possible
pathways
(
see
Figure
11.1):

$
Direct
oxidation
of
compounds
by
molecular
ozone
in
the
aqueous
phase.

$
Oxidation
of
compounds
by
hydroxyl
free
radicals
produced
during
the
decomposition
of
ozone.
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
16
O
3
(
aqueous)
Direct
Pathway
Oxidation
of
Substrate
and
Microbial
Inactivation
Byproducts
OH

Indirect
Pathway
Slower
Selective
Fast
Non­
Selective
Byproducts
Fast
CO
3
­
2
and
HCO
3
CO
3
­

and
HCO
3

Byproducts
Oxidation
of
Substrate
and
Microbial
Inactivation
As
indicated
in
Figure
11.1,
the
direct
reaction
with
molecular
ozone
is
relatively
slow
compared
to
the
hydroxyl
reaction.
However,
the
reaction
with
many
aqueous
species
is
still
very
rapid
compared
to
other
disinfectants.
The
reaction
mechanisms
for
microbial
inactivation
are
poorly
understood,
and
there
is
conflicting
research
regarding
the
pathway
more
responsible
for
disinfection.

Park
et
al.
(
2001)
researched
the
ozone
reaction
mechanisms
using
natural
waters.
The
authors
described
the
ozone
consumption
rate
with
two
steps:
an
initial
rapid
consumption
step
(
ozone
consumed
after
a
few
seconds)
followed
by
a
slower
ozone
decay
step.
Results
showed
the
ozone
consumption
in
the
initial
rapid
reactions
increased
with
increasing
ozone
dose
(
for
raw
water
only;
sand
filtered
water
showed
no
change)
and
increasing
TOC
levels.
However,
the
slower
decay
reaction
rates
decreased
with
increasing
ozone
dose.
Consequently,
the
decay
reaction
was
slower
at
higher
applied
ozone
doses.
This
is
of
importance
for
considerations
to
ozone
dose
requirements
and
residual
maintenance.

Figure
11.1
Reaction
Pathways
of
Ozone
in
Water
Direct
oxidation
is
the
dominant
pathway
at
neutral
pH
and
lower.
While
the
direct
pathway
is
minor
in
the
initial
reaction,
it
becomes
more
dominant
in
the
slower
decay
stages.
At
higher
pH
levels,
the
formation
of
the
hydroxyl
radical
is
favored.
Advanced
oxidation
processes
induce
conditions
that
favor
the
hydroxyl
radical
formation
and
increase
the
rate
of
ozone
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
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Manual
Proposal
Draft
June
2003
11­
17
decomposition.
(
See
Chapter
7
of
the
Alternative
Disinfectants
Guidance
Manual
for
information
on
advanced
oxidation
processes).

11.7.2
Byproduct
Formation
Reactions
between
ozone
and
natural
organic
matter
(
NOM)
can
form
a
variety
of
organic
byproducts
including
aldehydes,
ketones,
and
acids.
Inorganic
byproducts
are
also
formed.
Bromide
reacts
with
ozone
and
hydroxyl
radicals
to
form
bromate,
a
regulated
drinking
water
contaminant
with
an
MCL
of
10

g/
l.
Brominated
organic
compounds
can
also
be
formed,
such
as
bromoform
and
dibromoacetic
acid,
which
are
also
regulated
through
the
total
trihalomethanes
(
TTHMs)
and
haloacetic
acids
(
HAA5)
MCLs
under
the
Stage
2
DBPR.

11.7.2.1
Bromate
and
Brominated
Organic
Compounds
Bromate
and
brominated
organic
compound
formation
is
dependent
on
water
quality
and
treatment
conditions,
and
only
occurs
in
waters
with
bromide
ion
present.
Bromate
concentration
increases
with
increasing
pH,
carbonate
alkalinity,
bromide
concentration,
ozone
dose,
and
temperature.
However,
attempts
at
reducing
bromate
formation
by
lowering
pH
may
increase
the
formation
of
brominated
organic
byproducts.
The
source
water
bromide
concentration
is
an
important
factor
when
considering
adding
ozone
to
a
treatment
process.

11.7.2.2
Non­
Brominated
Organic
Compounds
Ozone
reacts
with
NOM
and
breaks
larger
organic
molecules
down
into
simpler,
more
biodegradable
compounds
such
as
aldehydes,
ketones,
and
acids.
These
biodegradable
organic
molecules
are
a
food
source
for
microorganisms
and
can
affect
biological
growth
in
the
distribution
system.
Escobar
and
Randall
(
2001)
conducted
a
case
study
at
a
ground
water
treatment
plant
that
was
adding
ozone
to
improve
the
aesthetic
quality
of
the
water.
They
found
that
the
assimilable
organic
carbon
(
AOC;
the
fraction
of
total
organic
carbon
that
is
most
readily
utilized
by
bacteria)
concentrations
significantly
increased
in
the
distribution
system,
however,
with
diligent
maintenance
of
chlorine
residual
biological
growth
was
suppressed.
Biofilters
can
be
used
to
reduce
the
AOC
entering
the
distribution
system.
(
Section
11.9.3
describes
biofilters
and
their
operation.)

11.8
Design
11.8.1
Generators
and
Contactors
There
are
several
types
of
ozone
generators
and
contactors.
All
generators
use
oxygen
as
a
raw
material
and
convert
it
to
ozone
using
electrochemical
reactions.
They
differ
from
each
other
in
the
source
of
oxygen
used
and
the
configuration
of
generator
elements.
Generators
can
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
18
use
either
air
or
pure
oxygen
as
an
oxygen
source.
The
Alternative
Disinfectants
and
Oxidants
Guidance
Manual
describes
the
type
of
generators
and
contactors
in
detail.

11.8.2
Point
of
Addition
Raw
water
quality,
turbidity,
and
ozone
demand
are
commonly
used
to
assess
the
possible
locations
for
adding
ozone.
The
Alternative
Disinfectants
and
Oxidants
Guidance
Manual
describes
the
water
quality
characteristics,
advantages,
and
disadvantages
of
feed
points
at
a
raw
water
location,
after
sedimentation,
and
after
first­
stage
filtration
of
a
two­
stage
process.
The
general
considerations
are:

$
Placing
the
ozone
addition
point
further
downstream
ozone,
particularly
after
physical
removal
processes,
generally
reduces
both
the
ozone
demand
and
byproduct
formation.

$
Adding
ozone
ahead
of
filtration
allows
any
biodegradable
organics,
formed
from
the
ozonation
of
more
recalcitrant
TOC,
to
be
removed
by
subsequent
biological
activity
in
the
filters.
Also,
solid­
phase
manganese
and
iron
formed
through
oxidation
by
ozone
can
also
be
removed
by
the
filters.

In
general,
applying
ozone
prior
to
coagulation
can
enhance
clarification.
Applying
prior
to
filtration
can
also
improve
filtration
performance;
however
these
effects
are
site­
specific
and
are
likely
to
depend
on
ozone
dose.

Detrimental
impacts
on
filtration
operation
have
also
been
reported.
Bishop
et
al.
(
2001)
investigated
the
effects
of
ozone
on
filtration
with
a
raw
water
of
moderate
turbidity,
TOC,
iron,
and
manganese
concentrations.
With
ozone
doses
of
0.5
to
1.0
mg/
L,
turbidity
increased
in
the
contactors
with
visible
floc
formation.
At
lower
ozone
doses,
0.16
to
0.35
mg/
L,
the
turbidity
still
increased,
but
not
as
much
as
the
higher
ozone
dose.
Because
of
the
higher
filter
loadings,
the
duration
of
filter
cycles
decreased.
The
authors
believed
the
increased
turbidity
was
partially
due
to
solid­
phase
manganese
formation,
and
also
likely
due
to
the
organic
matter
and
residual
metals.

11.8.3
Biologically
Active
Filters
When
ozone
oxidizes
organic
matter,
the
AOC
in
the
water
typically
increases.
Some
systems
use
biologically
active
filters
to
remove
the
AOC
prior
to
chlorination
and
entry
to
the
distribution
system.
Microbes
present
in
the
upper
portion
of
the
filters
consume
the
AOC,
mineralizing
them
to
carbon
dioxide
and
water,
and
reducing
the
amount
available
to
microorganisms
in
the
distribution
system
(
e.
g.
microorganisms
in
pipeline
biofilm)
and
for
DBP
formation.
Chapter
11
­
Ozone
LT2ESWTR
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Manual
Proposal
Draft
June
2003
11­
19
11.8.3.1
Media
for
Biologically
Active
Filters
Any
filter
media
which
has
sufficient
surface
area
for
microbes
to
attach
to
can
be
used
for
biological
filtration.
Slow
sand,
rapid
sand,
and
GAC
filters
have
all
been
successfully
used
for
biologically
active
filtration.
Research
indicates
that
both
sand/
anthracite
and
sand/
GAC
filters
can
support
the
total
amount
of
biomass
to
sufficiently
remove
organic
components
(
LeChevallier
et
al.
1992;
Krasner
et
al.
1993;
Coffey
et
al.
1995).
Wang
and
Summers
(
1996)
and
Zhang
and
Huck
(
1996)
have
shown
that
the
contact
time
with
the
biofilm
is
more
important
than
the
mass
of
biofilm
above
a
minimum
level
of
biomass.
Generally,
the
longer
the
contact
time
the
greater
the
removal
of
AOC.
However,
the
increase
in
removal
is
not
a
linear­
relationship;
the
removal
rate
decreases
at
extended
contact
times
(
Zhang
&
Huck
1996).
DBP
precursors
most
often
take
longer
to
biodegrade
making
extended
contact
times
necessary
if
this
is
the
process
goal.
This
can
be
achieved
with
deep
anthracite
filter
beds
or
GAC
filters
(
Prevost
et
al.
1990).
The
adsorption
capacity
of
GAC
provides
a
longer
time
for
the
organic
compounds
to
be
consumed
by
the
biomass
as
the
particles
are
adsorbed
by
the
GAC
(
LeChevallier
et
al.
1992).

11.8.3.2
Operating
Biologically
Active
Filters
It
is
not
necessary
to
seed
a
biological
filter
in
order
to
obtain
the
necessary
biological
growth.
The
organisms
naturally
present
in
the
system
are
sufficient
to
obtain
the
needed
growth.
The
only
additional
requirement
is
to
provide
the
conditions
for
biological
growth.
These
conditions
include
necessary
food
sources,
sufficient
dissolved
oxygen,
nutrients,
proper
pH
and
temperature.
The
products
from
ozone
and
NOM
reactions
will
provide
the
needed
food
for
the
microorganisms
to
grow.
The
reaction
of
ozone
also
produces
oxygen
as
one
of
its
products,
so
the
dissolved
oxygen
concentration
should
be
sufficiently
high.
Generally
the
pH
and
nutrient
levels
in
most
waters
will
also
be
sufficient
to
allow
the
necessary
growth.
Organic
removal
will
generally
be
higher
at
higher
temperatures.
Several
studies
have
found
significantly
decreased
removal
at
temperatures
below
15
degrees
Celsius
(
Krasner
et
al.
1993;
Coffey
et
al.
1995;
Daniel
and
Teefy
1995).

In
order
to
maintain
biological
growth,
a
disinfectant
other
than
ozone
cannot
be
added
prior
to
the
filters.
GAC
filters
can
reduce
small
disinfectant
residuals
through
reaction
with
the
carbon,
however,
this
can
lead
to
physical
breakdown
of
the
GAC
and
more
frequent
media
replacement.
Using
chlorinated
or
chloraminated
backwash
water
can
also
be
a
concern.
Studies
have
shown
mixed
results
with
chlorinated
backwash
water,
with
some
showing
no
effect
and
others
showing
significantly
reduced
removal
(
Miltner
et
al.
1996;
Miltner
et
al.
1995;
Hacker
et
al.
1994;
Reckhow
et
al.
1992;
McGuire
et
al.
1991).
Short
vigorous
backwashes
with
a
relatively
low
chlorine
dose
may
be
more
effective
in
maintaining
biological
filtration
than
less
vigorous
backwashes
at
longer
times
with
higher
chlorine
doses
(
Urfer
et
al.
1997).
Chapter
11
­
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LT2ESWTR
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June
2003
11­
20
11.9
Safety
Considerations
in
Design
Ozone
is
a
corrosive
gas
and
according
to
Occupational
Safety
and
Health
Administration
(
OSHA)
Standards,
exposure
to
airborne
concentrations
should
not
exceed
0.1
mg/
L
(
by
volume)
averaged
over
an
eight­
hour
work
shift.

Ozone
generators
should
be
housed
indoors
for
protection
from
the
environment,
and
to
protect
personnel
from
leaking
ozone
in
the
case
of
a
malfunction.
Ventilation
should
be
provided
to
prevent
excess
temperature
rise
in
the
generator
room,
and
to
exhaust
the
room
in
the
case
of
a
leak.
Adequate
space
should
be
provided
to
remove
the
tubes
from
the
generator
shell
and
to
service
the
generator
power
supplies.
Off­
gas
destruct
units
can
be
located
outside
if
the
climate
is
not
too
extreme.
If
placed
inside,
an
ambient
ozone
detector
should
be
provided
in
the
enclosure.
All
rooms
should
be
properly
ventilated,
heated,
and
cooled
to
match
the
equipment­
operating
environment.

11.10
Operational
Issues
When
using
ozone
for
disinfection,
it
is
important
to
evaluate
all
the
factors
that
could
affect
the
CT
achieved.
For
example,
if
raw
water
quality
fluctuates
and
ozone
demand
increases,
without
adjusting
the
ozone
dose,
the
residual
concentrations
will
decrease.
The
system
is
now
at
risk
of
not
achieving
the
required
level
of
CT.
The
ozone
demand,
pH,
and
temperature
of
the
raw
water,
under
worst­
case
to
best­
case
conditions,
should
be
evaluated
to
determine
their
effect
on
ozone
disinfection.
Systems
should
develop
standard
operating
procedures
(
SOPs)
for
addressing
changes
in
raw
water
quality.
The
remainder
of
this
section
discusses
the
how
these
factors
affect
ozone
disinfection
and
the
CT
calculation.

11.10.1
Ozone
Demand
The
following
water
quality
constituents
contribute
to
ozone
demand:

$
Natural
organic
matter
(
NOM)
COzone
will
oxidize
organic
matter,
which
includes
compounds
causing
taste
and
odor.
As
discussed
in
section
11.8.2
organic
byproducts
are
also
produced.

$
Synthetic
organic
compounds
(
SOCs)
CSome
SOCs
can
be
oxidized
and
mineralized
under
favorable
conditions.

$
BromideCOzone
will
oxidize
bromide
forming,
hypobromous
acid,
hypobromite
ion,
bromate
ion,
brominated
organics,
and
bromamines.
Chapter
11
­
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LT2ESWTR
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June
2003
11­
21
$
Bicarbonate
or
carbonate
ionsCThe
hydroxyl
radical
reacts
with
bicarbonate
and
carbonate
ions
and
form
carbonate
radicals.

Ozone
demand
is
particularly
important
to
the
CT
calculation
since
it
directly
affects
the
residual
ozone
used
in
the
CT
calculation.
Ozone
concentrations
in
water
are
generally
monitored
continuously
using
an
aqueous
ozone
residual
monitor,
and
confirmed
periodically
using
the
batch
indigo
method.
As
the
ozone
demand
changes,
the
amount
of
ozone
applied
can
be
adjusted
to
maintain
the
desired
CT.

11.10.2
pH
The
pH
of
water
does
not
have
a
significant
effect
on
ozone
disinfection
capabilities.
However,
there
is
strong
impact
of
pH
on
ozone
demand
and
decay
rate.
As
pH
increases,
the
hydroxyl
radical
decomposition
pathway
is
favored
and
the
initial
demand
and
rate
of
decay
increase
substantially.

11.10.3
Temperature
The
CT
requirements
are
based
on
temperature;
as
temperature
decreases,
the
CT
required
to
achieve
a
given
level
of
inactivation
increases.
Conversely,
the
rate
of
ozone
decay
decreases
as
temperature
decreases,
generally
resulting
in
a
higher
CT
for
a
given
ozone
dose.
The
ozone
process
should
be
designed
to
provide
the
necessary
log
inactivation
under
all
conditions.
Standard
operating
procedures
(
SOPs)
should
also
describe
process
adjustments
required
to
operate
at
the
lowest
water
temperatures
experienced
by
the
system
in
the
past
10
years.

11.10.4
Maintaining
Residual
Disinfectant
in
the
Distribution
System
It
is
necessary
to
maintain
a
residual
in
the
distribution
system
to
prevent
microbial
regrowth.
Because
of
the
reactive
nature
of
ozone,
its
residual
tends
to
dissipate
within
minutes
and
cannot
be
relied
upon
to
maintain
a
disinfectant
throughout
the
distribution
system.
Therefore,
a
secondary
disinfectant
must
be
used,
usually
either
chlorine
or
chloramines.

11.11
Request
for
Comment
on
Segregated
Flow
Analysis
As
mentioned
in
section
11.3,
EPA
is
evaluating
the
segregated
flow
analysis
(
SFA)
to
estimate
CT
for
ozone
disinfection.
The
SFA
approach
is
based
on
an
assumption
that
the
residence
time
distribution
(
RTD)
of
an
ozone
contactor
is
sufficient
to
completely
describe
the
hydrodynamics
within
the
contactor
(
i.
e.,
zero
micro­
mixing
occurs).
If
micro­
mixing
does
occur,
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
22
then
the
SFA
approach
may
overestimate
the
inactivation
of
microorganisms.
The
degree
to
which
inactivation
may
be
overestimated
depends
on
several
factors
including
the
predicted
ozone
decay,
the
predicted
inactivation,
and
the
extent
that
the
hydrodynamics
within
the
contactor
deviate
from
ideal
plug­
flow
conditions
(
as
indicated
by
the
RTD).

Incorporating
micro­
mixing
calculations
into
the
SFA
is
quite
complicated,
and
likely
impractical
for
many
systems.
EPA
requests
comments
on
the
SFA
approach
and
the
following
questions:

1.
Should
the
impact
of
micro­
mixing
be
considered?

2.
Can
a
worst
case
scenario,
incorporating
reactor
configuration,
reaction
kinetics
and
complete
micro­
mixing
be
developed?

3.
Can
appropriate
safety
factors
be
established
to
ensure
the
SFA
approach
does
not
overestimate
inactivation?
Chapter
11
­
Ozone
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
11­
23
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