Appendix
A
Formation
and
Control
of
Disinfection
Byproducts
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A.
1
Introduction
The
purpose
of
this
appendix
is
to
identify
the
factors
that
affect
formation
of
disinfection
byproducts
(
DBPs)
in
water
treatment
processes
and
distribution
systems.
It
is
intended
to
serve
as
a
tool
for
systems
in
identifying
potential
strategies
for
reducing
DBP
concentrations.
This
appendix
is
divided
into
two
main
sections.
Section
A.
2
discusses
the
factors
that
affect
DBP
formation.
Section
A.
3
discusses
options
for
controlling
DBP
formation
in
general
terms;
it
is
not
intended
to
provide
guidance
on
implementation
of
DBP
control
strategies.

A.
2
Formation
of
DBPs
Organic
DBPs
(
and
oxidation
byproducts)
are
formed
by
the
reaction
between
organic
substances,
inorganic
compounds
such
as
bromide,
and
oxidizing
agents
that
are
added
to
water
during
treatment.
In
most
water
sources,
natural
organic
matter
(
NOM)
is
the
major
constituent
of
organic
substances
and
DBP
precursors.
Total
organic
carbon
(
TOC)
is
typically
used
as
a
surrogate
measure
for
NOM
levels.
The
two
terms
are
used
interchangeably
in
much
of
the
discussion
presented
here.
The
following
major
factor
affecting
the
type
and
amount
of
DBPs
formed.


Type
of
disinfectant,
dose,
and
residual
concentration

Contact
time
and
mixing
conditions
between
disinfectant
(
oxidant)
and
precursors

Concentration
and
characteristics
of
precursors

Water
temperature

Water
chemistry
(
including
pH,
bromide
ion
concentration,
organic
nitrogen
concentration,
and
presence
of
other
reducing
agents
such
as
iron
and
manganese)

A
summary
of
these
factors
follows.

A.
2.1
Impact
of
Disinfection
Method
on
Organic
DBP
Formation
Organic
DBPs
can
be
subdivided
into
halogenated
and
non­
halogenated
byproducts.
Halogenated
organic
disinfection
byproducts
are
formed
when
organic
and
inorganic
compounds
found
in
water
react
with
free
chlorine,
free
bromine,
or
free
iodine.
The
formation
reactions
may
take
place
in
the
treatment
plant
and
the
distribution
system.
Free
chlorine
can
be
introduced
to
water
directly
as
a
primary
or
secondary
disinfectant,
or
as
a
byproduct
of
the
manufacturing
of
chlorine
dioxide
and
chloramines.
Reactions
between
NOM,
bromide
and
iodide
ions
and
chlorine
lead
to
the
formation
of
a
variety
of
halogenated
DBPs
including
THMs
and
HAAs.
Further,
the
oxidation
of
organic
nitrogen
can
lead
to
the
formation
of
DBPs
containing
nitrogen,
such
as
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haloacetonitriles,
halopicrins,
and
cyanogens
halides
(
Reckhow
et
al.,
1990;
Hoigné
and
Bader,
1988).

Non­
halogenated
DBPs
may
form
when
precursors
react
with
strong
oxidants.
For
example,
the
reaction
of
organics
with
ozone
and
hydrogen
peroxide
results
in
the
formation
of
aldehydes,
aldo­
and
keto­
acids,
and
organic
acids
(
Singer,
1999).
Chlorine
can
also
trigger
the
formation
of
some
non­
halogenated
DBPs
(
Singer
and
Harrington,
1993).
Many
of
the
low
molecular
weight
non­
halogenated
DBPs
are
biodegradable.

Trussell
and
Umphres
(
1978)
reported
that
the
presence
of
bromide
can
affect
both
the
rate
and
the
yield
of
DBPs,
as
well
as
that
as
the
ratio
of
bromide
to
NOM
(
measured
as
total
organic
carbon)
increases,
the
percentage
of
brominated
DBPs
also
increases.
Free
chlorine
and
ozone
oxidize
bromide
ion
to
hypobromite
ion/
hypobromous
acid.
Hypobromous
acid
is
a
more
effective
substituting
agent
than
hypochlorous
acid
(
a
better
oxidant)
and
can
in
turn
react
with
NOM,
forming
brominated
DBPs
such
as
bromoform,
and
mixed
bromo­
chloro
species
(
Krasner,
1999).
Similarly,
the
presence
of
iodide
may
result
in
the
formation
of
mixed
chlorobromoiodomethanes
byproducts
(
Bichsel
and
Von
Gunten,
2000).

Studies
have
documented
that
chloramines
produce
significantly
lower
halogenated
DBP
levels
than
free
chlorine,
and
there
is
no
clear
evidence
that
the
reaction
of
NOM
and
chloramine
leads
to
the
formation
of
THMs
(
Singer
and
Reckhow,
1999;
USEPA,
1999).
Predictions
of
an
empirical
DBP
formation
model
calibrated
using
ICR
data
indicated
that
under
chloraminated
conditions
THMs
and
HAAs
are
formed
in
full­
scale
plants
and
distribution
systems
at
a
fraction
of
the
amount
that
would
be
expected
based
on
observations
of
DBP
formation
under
free
chlorine
conditions.
The
amount
of
formation
with
chloramines
varied
from
5%
to
35%
of
that
calculated
for
free
chlorine,
depending
on
the
individual
DBP
species
(
Swanson
et
al.,
2001).
The
benefits
of
low
DBP
formation
with
chloramines
are
especially
important
for
controlling
formation
at
the
extremities
of
the
distribution
system.

When
chloramination
is
used,
it
is
possible
that
DBPs
might
form
if
chlorine
is
added
before
ammonia.
If
the
mixing
process
is
inefficient,
it
is
also
possible
that
DBPs
might
form
during
the
mixing
of
chlorine
and
ammonia.
In
this
case,
free
chlorine
might
react
with
NOM
before
the
complete
formation
of
chloramines.
In
addition,
monochloramine
slowly
hydrolyzes
to
release
free
chlorine
in
water.
This
free
chlorine
may
contribute
to
the
formation
of
small
amounts
of
additional
DBPs
in
the
distribution
system.

The
application
of
chlorine
dioxide
does
not
produce
significant
amounts
of
organic
halogenated
DBPs
unless
chlorine
is
formed
as
an
impurity
in
the
generation
process.
Only
small
amounts
of
total
organic
halides
(
TOXs,
a
surrogate
measure
for
halogenated
organic
compounds
including
THMs
and
HAAs)
are
formed.
However,
THMs
and
HAAs
will
form
if
excess
chlorine
is
added
to
water
to
ensure
complete
reaction
with
sodium
chlorite
during
the
production
of
chlorine
dioxide.
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To
date,
there
is
no
evidence
to
suggest
that
ultraviolet
irradiation
(
UV)
results
in
the
formation
of
any
disinfection
byproducts;
however,
little
research
has
been
performed
in
this
area.
Most
of
the
research
regarding
application
of
UV
and
DBP
formation
has
focused
on
chlorinated
DBP
formation
as
a
result
of
UV
application
prior
to
the
addition
of
chlorine
or
chloramines
(
Malley
et
al.,
1995).
Malley,
et
al.
conducted
studies
comparing
the
effects
of
UV
light
followed
by
chlorination
versus
chloramination.
Evidence
suggests
UV
does
not
affect
DBP
formation
in
either
of
these
two
cases.

Ozone
does
not
directly
produce
chlorinated
DBPs.
However,
if
chlorine
is
added
before
or
after
ozonation
mixed
bromo­
chloro
DBPs
as
well
as
chlorinated
DBPs
can
form.
Ozone
can
alter
the
reactions
characteristics
of
NOM
and
affect
the
concentration
and
speciation
of
halogenated
DBPs
when
chlorine
is
subsequently
added
downstream.
In
waters
with
sufficient
bromide
concentrations,
ozonation
can
lead
to
the
formation
of
bromate
and
other
brominated
DBPs.
Bromate,
like
TTHMs
and
HAA5,
is
a
regulated
DBP.
Ozonation
of
natural
waters
also
produces
aldehydes,
haloketones,
ketoacids,
carboxylic
acids,
and
other
types
of
biodegradable
organic
material.
The
biodegradable
fraction
of
organic
material
can
serve
as
a
nutrient
source
for
microorganisms,
and
should
be
removed
to
prevent
microbial
regrowth
in
the
distribution
system.

To
date,
many
of
the
byproducts
that
result
from
chlorination
or
from
alternative
disinfectants
are
still
unknown
and
unregulated.
One
explanation
for
this
shortcoming
is
that
these
compounds
are
too
polar
or
too
high
in
molecular
weight
to
be
detected
using
conventional
gas
chromotography
techniques
(
James,
1999).
As
more
refined
analytical
techniques
become
available
additional
classes
of
disinfection
byproducts
may
be
scrutinized.

A.
2.2
Disinfectant
Dose
The
concentration
of
disinfectant
can
affect
the
formation
of
DBPs.
As
the
concentration
of
disinfectant
increases
the
production
of
DBPs
also
increases
and
formation
reactions
continue
as
long
as
precursors
(
NOM)
and
disinfectant
are
present.
In
general,
the
impact
of
disinfectant
concentration
is
greater
during
primary
disinfection
than
during
secondary
disinfection.
The
amount
of
disinfectant
added
during
primary
disinfection
is
usually
less
than
the
long­
term
demand,
therefore,
the
concentration
of
disinfectant
is
often
the
limiting
factor
while
unreacted
precursors
are
available.
On
the
contrary,
during
secondary
disinfection
DBP
formation
reactions
are
often
precursor
limited
since
an
excess
of
disinfectant
is
added
to
the
water
to
maintain
a
residual
concentration
(
Singer
and
Reckhow,
1999).
In
distribution
systems,
DBP
formation
reactions
can
become
disinfectant­
limited
when
the
free
chlorine
residual
drops
to
low
levels.
As
a
rule
of
thumb,
Singer
and
Reckhow
(
1999)
suggested
this
event
takes
place
when
the
chlorine
concentration
drops
below
approximately
0.3
mg/
L.

In
many
systems
booster
disinfection
is
applied
to
raise
disinfectant
residual
concentration,
especially
in
remote
areas
of
the
distribution
system
or
near
storage
tanks
where
water
age
may
be
high
and
disinfectant
residuals
can
be
low.
The
additional
chlorine
dose
applied
to
the
water
at
these
booster
facilities
may
increase
THM
and
HAA
levels.
Further,
booster
chlorination
can
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maintain
high
HAA
concentrations
because
the
increased
disinfection
residuals
can
prevent
the
biodegradation
of
HAAs.
However,
as
discussed
further
in
Section
A.
3.4
booster
chlorination
can
also
be
useful
in
decreasing
DBP
levels
by
reducing
levels
of
secondary
disinfectant
needed
in
the
finished
water
leaving
the
plant.

A.
2.3
Time
Dependency
of
DBP
Formation
In
general,
DBPs
continue
to
form
in
drinking
water
as
long
as
disinfectant
residuals
and
reactive
DBP
precursors
are
present,
and
the
longer
is
the
contact
time
between
disinfectant/
oxidant
and
NOM
present,
the
greater
is
the
amount
of
DBPs
that
can
be
formed.
High
concentrations
of
DBPs
can
accumulate
in
water.
This
is
a
consequence
of
the
chemical
stabilities
of
THMs
and
HAAs,
which
are
generally
quite
high
in
the
disinfected
drinking
water
as
long
as
a
significant
disinfectant
residual
is
still
present
(
Singer
and
Reckhow,
1999).

High
THM
levels
usually
occur
where
the
water
age
is
the
oldest.
Unlike
THMs,
HAAs
cannot
be
consistently
related
to
water
age
because
HAAs
are
known
to
biodegrade
over
time
when
the
disinfectant
residual
is
low.
This
might
result
in
relatively
low
HAAs
concentrations
in
areas
of
the
distribution
system
where
disinfectant
residuals
are
depleted.

In
contrast
to
chlorination
byproducts,
ozonation
byproducts
form
more
rapidly,
but
their
period
of
formation
is
much
shorter
than
that
of
chlorination
byproducts.
This
is
due
to
the
quicker
dissipation
of
the
ozone
residual
compared
to
chlorine
(
Singer
and
Reckhow,
1999).

A.
2.4
Concentration
and
Characteristics
of
Precursors
The
formation
of
halogenated
DBPs
is
related
to
the
concentration
of
NOM
at
the
point
of
chlorination.
In
general
greater
DBP
levels
are
formed
in
waters
with
higher
concentrations
of
precursors.
Studies
conducted
with
different
fractions
of
NOM
have
indicated
the
reaction
between
chlorine
and
NOM
with
high
aromatic
content
tends
to
form
higher
DBP
levels
than
NOM
with
low
aromatic
content.
For
this
reason,
UV
absorption
at
254
nm
[
UV
254],
which
is
generally
linked
to
the
aromatic
and
unsaturated
components
of
NOM,
is
considered
a
good
predictor
of
the
tendency
of
a
source
water
to
form
THMs
and
HAAs
(
Owen
et
al.,
1998;
Singer
and
Reckhow,
1999).
Specific
ultraviolet
light
absorbance
(
SUVA)
is
also
often
used
to
characterize
aromaticity
and
molecular
weight
distribution
of
NOM.
This
parameter
is
defined
as
the
ration
between
UV
254
and
the
dissolved
organic
carbon
(
DOC)
concentration
of
water
(
Letterman
et
al.,
1999).
It
should
be
noted,
that
the
more
highly
aromatic
precursors,
characterized
by
high
UV
254,
in
source
waters
are
more
easily
removed
by
coagulation.
Thus,
it
is
the
UV
254
measurement
immediately
upstream
of
the
point(
s)
of
chlorination
within
a
treatment
plant
that
is
more
directly
related
to
THM
and
HAA
formation
potential.
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A.
2.5
Water
Temperature
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The
rate
of
formation
of
THMs
and
HAAs
increases
with
increasing
temperature.
Consequently,
the
highest
THM
and
HAA
levels
may
occur
in
the
warm
summer
months.
However,
water
demands
are
often
higher
during
these
months,
resulting
in
lower
water
age
within
the
distribution
system
which
helps
to
control
DBP
formation.
Furthermore,
high
temperature
conditions
in
the
distribution
system
promote
the
accelerated
depletion
of
residual
chlorine,
which
can
mitigate
DBP
formation
and
promote
biodegradation
of
HAAs
unless
chlorine
dosages
are
increased
to
maintain
high
residuals
(
Singer
and
Reckhow,
1999).
For
these
reasons,
depending
on
the
specific
system,
the
highest
THM
and
HAA
levels
may
be
observed
during
months
which
are
warm,
but
not
necessarily
the
warmest.

Seasonal
trends
affect
differently
where
high
THM
and
HAA
concentrations
might
be
found.
For
example,
when
water
is
colder,
microbial
activity
is
typically
lower
and
DBP
formation
kinetics
are
slower.
Under
these
conditions,
the
highest
THM
and
HAA
concentrations
might
appear
coincident
with
the
oldest
water
in
the
system.
In
warmer
water,
the
highest
HAA
concentrations
might
appear
in
fresher
water,
which
is
likely
to
contain
higher
disinfectant
residuals
that
can
prevent
the
biodegradation
of
HAAs.

A.
2.6
Water
pH
In
the
presence
of
NOM
and
chlorine,
THM
formation
increases
with
increasing
pH,
whereas
the
formation
of
HAAs
and
other
DBPs
decrease
with
increasing
pH.
The
increased
THM
production
at
high
pH
is
likely
promoted
by
base
hydrolysis
(
favored
at
high
pH).
HAAs
are
not
sensitive
to
base
hydrolysis
but
their
precursors
are.
Consequently,
pH
can
alter
their
formation
pathways
leading
to
decreased
production
with
increasing
pH
(
Singer
and
Reckhow,
1999).

The
major
byproducts
of
ozonation
are
not
affected
by
base
hydrolysis.
However,
pH
can
play
a
role
by
affecting
the
rate
of
decomposition
of
ozone
to
hydroxyl
radical.
The
decomposition
of
ozone
accelerates
as
pH
increases.
This
occurrence
is
thought
to
be
responsible
for
the
decrease
of
some
byproducts
(
e.
g.,
aldeydes)
and
the
increase
of
others
(
e.
g.,
carbonyl
byproduct
and
total
organic
halides;
Singer
and
Reckhow,
1999).
Water
pH
affects
the
balance
of
hypobromite
and
hypobromous
acid
formation
during
the
ozonation
of
waters
containing
significant
concentrations
of
bromides.
At
low
pH,
the
equilibrium
shifts
to
the
less
reactive
hypobromous
acid.
Consequently,
the
overall
formation
of
bromate
decrease
as
pH
decrease
(
Singer
and
Reckhow,
1999).
On
the
other
hand,
Song
et
al.
(
1997)
suggested
that
lower
pHs
favor
the
formation
of
TOX
(
most
likely
TOBr)
during
ozonation.
Singer
and
Reckhow
(
1999)
attributed
this
occurrence
to
the
concurrent
suppressed
decomposition
of
ozone,
changes
in
the
speciation
of
the
oxidized
bromine
and
the
hydrolysis
of
brominated
byproducts.

A.
3
Control
of
DBPs
Alternatives
to
minimize
the
formation
of
DBPs
focus
on
the
removal
of
precursors
during
treatment,
modifications
of
the
oxidation
and
disinfection
processes,
control
of
oxidants
dose
and
Significant
Excursion
Guidance
Manual
Proposal
Draft
July
2003
A­
7
residual,
reduction
of
the
residence
time
in
the
distribution
system,
and
removal
of
DBPs
after
formation.
Because
DBPs
are
difficult
to
remove
after
they
have
formed,
control
strategies
typically
focus
on
the
first
four
methods.

A.
3.1
Improving
Precursors
Removal
The
removal
of
organic
precursors
can
be
improved
by
optimizing
coagulation
practices
or
by
employing
advanced
precursor
removal
processes
such
as
granular
activated
carbon
(
GAC)
adsorption,
membrane
filtration,
or
biofiltration.

The
process
of
improving
the
removal
of
NOM
during
the
coagulation
process
is
defined
as
enhanced
coagulation.
Greater
NOM
removal
can
be
obtained
with
adjustments
in
treatment
practice,
specifically
pH
reduction
and
increased
coagulant
dosage.
The
coagulation
of
NOM
appears
to
be
most
efficient
in
the
5
to
6
pH
range.

A
number
of
sources
have
documented
that
granular
activated
carbon
(
GAC)
and
nanofiltration
(
NF)
can
be
more
effective
DBP
precursor
removal
processes
than
conventional
coagulation
treatment
(
McGuire
et
al.,
1989;
Owen
et
al.,
1998;
Snoeyink
et
al.,
1999;
Jacangelo,
1999;
Taylor
and
Wiesner,
1999;
and
references
therein).
Reverse
osmosis
(
RO)
can
also
be
very
effective
for
removing
precursors.
However,
when
precursor
removal
(
as
opposed
to
demineralization)
is
the
primary
treatment
objective,
NF
is
usually
preferred
to
RO
because
of
its
lower
operating
pressure
and
associated
costs.
Both
NF
and
RO
can
remove
bromide
(
Jacangelo,
1999)
while
GAC
does
not
appear
to
remove
bromide
to
any
significant
extent
(
Snoeyink
et
al.,
1999)

Biofiltration
can
be
used
to
remove
a
portion
of
the
NOM
from
water
by
converting
it
into
inorganic
carbon
(
CO
2)
and
it
is
considered
a
viable
treatment
alternative
for
precursors
removal
(
Hozalski
and
Bouwer,
1999).
In
general,
the
ideal
location
for
a
biofilter
is
in
a
rapid
media
filter
and
its
performance
can
vary
from
one
plant
to
another
depending
on
factors
such
as
NOM
source
and
characteristics,
use
of
ozone
for
preoxidation,
residence
time
in
the
biofilter,
media
type,
and
water
temperature
(
Hozalski
and
Bouwer,
1999).

Watershed
management
practices
as
well
as
timing
and
location
of
withdrawals
can
also
achieve
reductions
of
DBP
precursors
in
the
raw
water.
The
extent
of
the
benefit
of
implementing
this
strategy
is
site
specific.

A.
3.2
Disinfection
and
Oxidation
Methods
and
Disinfectant
Dose
Chlorination
generally
produces
the
highest
THM
and
HAA
levels.
Other
oxidation
alternatives
to
chlorine
(
e.
g.,
use
of
ozone,
chloramines,
chlorine
dioxide,
potassium
permanganate,
and
UV
radiation)
can
be
used
to
minimize
the
formation
of
TTHM
and
HAAs.
Generally,
decreasing
the
disinfectant
dose
and
residual
reduces
DBP
levels
(
see
Section
A.
2).
However,
when
considering
disinfectant
changes
it
is
important
to
consider
disinfection
needs
and
Significant
Excursion
Guidance
Manual
Proposal
Draft
July
2003
A­
8
maintain
the
appropriate
CT
for
disinfection.
Some
alternative
disinfectants
cannot
be
used
for
secondary
disinfection.
A
detailed
discussion
of
alternative
disinfectants
can
be
found
in
the
Alternative
Disinfectants
and
Oxidants
Guidance
Manual
(
USEPA,
1999,
815­
R­
99­
014).

A.
3.3
Shifting
the
Point
of
Disinfectant
Application
Shifting
the
point
of
disinfectant
application
from
upstream
to
downstream
of
the
coagulation/
settling
process
can
significantly
reduce
the
formation
of
DBPs
for
two
main
reasons:
the
amount
of
precursors
is
reduced
prior
to
disinfectant
addition,
and
(
particularly
for
chlorination)
the
contact
time
between
disinfectant
and
NOM
is
reduced.
The
implementation
of
this
strategy
must,
however,
take
into
account
disinfection
needs.
Adequate
contact
time
must
be
always
provided
after
the
application
of
disinfectant
to
achieve
the
desired
inactivation
of
microorganisms.

A.
3.4
Control
of
DBP
Formation
in
the
Distribution
System
For
systems
maintaining
free
chlorine
residual,
significant
DBP
formation
can
occur
in
the
distribution
system.
A
long
detention
time
in
the
distribution
system,
the
presence
of
NOM
in
the
finished
water
and
the
presence
of
free
chlorine
residual
can
promote
this
occurrence.
It
is
not
uncommon
that
water
leaving
a
treatment
plant
with
low
THM
and
HAA
concentrations
is
found
to
have
high
levels
of
these
compounds
in
the
distribution
system.
Generally,
application
of
secondary
disinfectant
(
particularly
chlorine)
to
form
and
maintain
a
residual
in
the
distribution
system
results
in
DBP
formation.
Implementation
of
distribution
system
water
quality
monitoring,
minimization
of
"
dead
ends,"
optimization
of
storage
tank
utilization,
execution
of
effective
planned
system
flushing
and
management
of
water
age
can
minimize
DBP
formation.

In
some
cases,
booster
chlorination
has
also
been
used
to
control
disinfectant
application
and
minimize
DBP
formation.
For
example,
where
the
majority
of
the
distribution
system
is
in
a
confined
area
near
the
plant,
but
a
small
part
is
far
away
from
the
plant
a
large
dose
of
disinfectant
would
be
required
to
maintain
a
residual
in
the
extreme
part
of
the
system.
A
much
higher
residual
concentration
than
is
needed
would
be
present
in
the
majority
of
the
system.
Thus,
booster
disinfection
in
the
extreme
part
of
the
system
could
dramatically
reduce
the
disinfectant
dose
at
the
plant
and
reduce
DBP
formation
through
the
system.
However,
it
must
also
be
noted
that
in
areas
following
booster
disinfection
facilities,
the
residence
time
is
often
long.
If
conditions
favor
formation
(
i.
e.
water
age,
temperature,
NOM
concentration)
the
additional
disinfectant
added
might
lead
to
the
formation
of
high
TTHM
and
HAA
levels.
Increased
disinfectant
residual
can
also
prevent
biodegradation
of
HAA,
further
increasing
distribution
system
levels.
The
use
or
addition
of
booster
disinfection
requires
careful
consideration
in
any
DBP
control
strategy.

A.
3.5
Assessing
DBP
Formation
and
Control
with
the
WTP
Model
Significant
Excursion
Guidance
Manual
Proposal
Draft
July
2003
A­
9
If
a
utility
determines,
based
upon
distribution
system
monitoring,
that
the
DBP
levels
in
their
system
need
to
be
reduced,
they
may
consider
implementing
treatment
changes
in
their
water
treatment
plant.
To
evaluate
the
potential
impact
of
treatment
changes
on
distribution
system
DBP
levels
prior
to
the
implementation
of
these
changes,
a
system
may
consider
using
the
Water
Treatment
Plant
Simulation
Model
(
WTP
Model)
as
a
preliminary
tool.
This
model
was
initially
developed
to
support
the
DBP
rule
making
process
and
was
later
revised
to
improve
the
predictive
accuracy
using
data
collected
under
the
Information
Collection
Rule
(
ICR).
The
WTP
Model
consists
of
empirical
models
developed
from
bench­,
pilot­,
and
full­
scale
treatability
data.
The
majority
of
the
predictive
algorithms
have
been
verified
with
independent
data
sets
(
Solarik
et
al.,
1999),
and
many
key
algorithms
have
been
calibrated
using
ICR
data
from
full­
scale
surface
water
treatment
plants
(
Swanson
et
al.,
2001).
A
description
of
the
original
model
was
presented
by
Harrington,
et
al.
(
1992)
and
is
available
from
the
USEPA's
Technical
Support
Center
in
Cincinnati.
The
WTP
Model
was
developed
as
a
central
tendency
model,
and
was
not
specifically
designed
to
yield
site
specific
predictions.
However,
a
significantly
improved
form
of
the
WTP
Model
(
Version
2.0)
currently
under
review
by
the
agency
will
facilitate
site
specific
calibration
of
the
model.
Extensive
experiments
to
determine
water
quality
characteristics
are
required
to
validate
site
specific
model
use.

In
addition
to
simulating
the
effects
of
traditional
surface
water
treatment
processes,
such
as
coagulation
(
or
lime
softening),
flocculation,
sedimentation,
and
filtration,
the
WTP
Model
supports
many
advanced
disinfection
and
DBP
control
processes,
such
as:


Enhanced
coagulation

GAC
adsorption

Microfiltration/
ultrafiltration

Nanofiltration/
reverse
osmosis

Ozonation

Biological
filtration

Chlorine
dioxide
addition
The
WTP
Model
generates
predictions
of
bromate
formation
during
ozonation,
chlorite
formation
during
chlorine
dioxide
addition,
and
THM,
HAA,
and
TOX
formation
due
to
free
chlorine
and
chloramine
addition.
These
predictions
are
generated
at
the
effluent
of
each
unit
treatment
process
and
within
the
distribution
system
(
detention
times
are
required
as
inputs).
The
WTP
Model
also
calculates
CT
values
achieved
for
the
various
disinfectants
used
during
treatment
and
log
inactivation
values
for
virus,
Giardia,
and
Cryptosporidium.
Thus,
the
Significant
Excursion
Guidance
Manual
Proposal
Draft
July
2003
A­
10
program
can
be
used
to
evaluate
the
relative
effects
of
treatment
modifications
on
disinfection
and
DBP
formation.

References
Bichsel,
Y.,
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Von
Gunten
U.,
2000.
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Z.
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M.
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Hozalski,
R.
M.,
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1999.
Biofiltration
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Jacangelo,
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