LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
8­
1
8.0
Bag
and
Cartridge
Filters
8.1
Introduction
Under
the
LT2ESWTR,
bag
and
cartridge
filters
are
defined
as
pressure
driven
separation
processes
that
remove
particles
larger
than
1

m
using
an
engineered
porous
filtration
medium
(
generally
a
fabric
material)
through
either
surface
or
depth
filtration
(
40
CFR
141.2).
Typically,
small
systems
use
bag
and
cartridge
filters
for
protozoa
or
other
particle
removal.
The
pore
sizes
in
the
filter
bags
and
cartridges
designed
for
protozoa
removal
are
small
enough
to
remove
protozoan
cysts
and
oocysts
but
generally
large
enough
that
viruses,
bacteria,
and
fine
colloidal
clays
could
pass
through.

The
distinction
between
bag
filters
and
cartridge
filters
is
based
on
the
type
of
filtration
media
used
and
the
manner
in
which
the
devices
are
constructed.
Bag
filters
are
typically
constructed
of
a
non­
rigid,
fabric
filtration
media
housed
in
a
pressure
vessel
in
which
the
direction
of
flow
is
from
the
inside
of
the
bag
to
the
outside.
Cartridge
filters
are
typically
constructed
as
rigid
or
semi­
rigid,
self­
supporting
filter
elements
housed
in
pressure
vessels
in
which
flow
is
from
the
outside
of
the
cartridge
to
the
inside.
A
pressure
vessel
may
contain
either
single
or
multiple
filters
in
a
series
or
in
parallel.

As
the
water
flows
through
a
bag
or
cartridge
filter,
particles
collect
on
the
filter
and
the
difference
in
pressure
from
the
inlet
to
the
outlet,
termed
"
pressure
drop,"
increases.
Once
a
"
terminal
pressure
drop"
is
reached,
the
bag
or
cartridge
filter
must
be
replaced.
Bag
and
cartridge
filters
are
disposable
and
designed
to
be
easily
replaced;
however,
a
few
cartridge
filter
devices
are
reportedly
designed
to
be
cleaned
and
operated
through
multiple
filtration
cycles.

This
chapter
provides
background
information
on
the
treatment
performance,
design,
and
operation
of
bag
and
cartridge
filters,
with
emphasis
on
those
issues
that
a
system
should
consider
for
integrating
bag
or
cartridge
filters
into
its
treatment
process
to
comply
with
the
LT2ESWTR.
This
chapter
is
organized
as
follows:

8.2
LT2ESWTR
Compliance
Requirements
­
describes
criteria
and
reporting
requirements
that
systems
must
meet
to
receive
Cryptosporidium
treatment
credit.
8.3
Toolbox
Selection
Considerations
­
describes
the
advantages
and
disadvantages
of
integrating
a
bag
and
cartridge
filtration
process
for
compliance
with
the
LT2ESWTR.

8.4
Challenge
Testing
­
describes
the
challenge
testing
that
a
bag
or
cartridge
filter
must
pass
to
be
awarded
Cryptosporidium
treatment
credit
for
the
LT2ESWTR.

8.5
Design
Considerations
­
discusses
influent
water
quality,
size
of
filter
system
and
redundancy,
layout
features,
filter
cycling,
pressure
monitoring,
valves
and
appurtenances,
air
entrapment,
and
NSF
certification.
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
8­
2
8.6
Operational
Issues
­
discusses
pressure
drop
across
the
filter,
and
monitoring
to
assess
performance
and
indicate
possible
process
upsets
with
the
bag
or
cartridge
filter
or
other
upstream
processes.

8.2
LT2ESWTR
Compliance
Requirements
8.2.1
Credits
Bag
and
cartridge
filtration
processes
that
meet
the
EPA
definition
and
demonstrate
Cryptosporidium
removal
through
challenge
testing
may
receive
the
following
Cryptosporidium
removal
credit
for
the
LT2ESWTR
(
40
CFR
141.728(
a)):

°
1
log
removal
for
bag
filtration
showing
a
minimum
of
2
log
removal
in
challenge
testing
°
2
log
removal
for
cartridge
filtration
showing
a
minimum
of
3
log
removal
in
challenge
testing
A
1
log
factor
of
safety
is
applied
to
the
allowable
removal
credit
over
that
demonstrated
by
challenge
testing
because
bag
and
cartridge
filters
cannot
have
their
integrity
directly
tested;
hence,
there
are
no
means
of
verifying
their
removal
efficiency
during
routine
use.

Recently,
some
cartridge
filtration
devices
have
been
developed
for
drinking
water
treatment
using
membrane
media,
which
can
be
direct
integrity
tested.
These
membrane
cartridge
filters
(
MCFs)
could
be
considered
a
membrane
filtration
process
for
the
purpose
of
compliance
with
the
LT2ESWTR
treatment
requirements
for
Cryptosporidium
(
i.
e.,
the
MCF
process
would
be
eligible
for
the
same
credit,
and
subject
to
the
same
requirements,
as
a
membrane
filtration
process).
A
direct
integrity
test
is
a
physical
test
applied
to
a
membrane
unit
to
identify
and
isolate
integrity
breaches
(
i.
e.,
one
or
more
leaks
that
could
result
in
contamination
of
the
filtrate).
Manufacturers
can
provide
information
on
direct
integrity
testing
and
whether
it
is
feasible
with
their
products.
Refer
to
the
EPA
Membrane
Filtration
Guidance
Manual
for
direct
integrity
testing
and
other
membrane
filtration
requirements.

States
may
choose
to
award
removal
credits
in
excess
of
1
and
2
log
for
bag
and
cartridge
filtration,
respectively,
if
challenge
testing
demonstrates
that
the
process
can
reliably
achieve
a
greater
removal
efficiency.

8.2.2
Reporting
Requirements
All
reporting
requirements
for
the
Surface
Water
Treatment
Rule
(
SWTR),
Interim
Chapter
8
­
Bag
and
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Filters
LT2ESWTR
Toolbox
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8­
3
Enhanced
Surface
Water
Treatment
Rule
(
IESWTR),
and
Long
Term
1
Enhanced
Surface
Water
Treatment
Rule
(
LT1ESWTR)
are
still
applicable;
the
LT2ESWTR
does
not
modify
or
replace
any
previous
rule
requirements.
The
location
of
filter
effluent
turbidity
monitoring
for
compliance
with
the
IESWTR
and
LT1ESWTR
does
not
change
with
the
installation
of
a
bag
or
cartridge
filter
as
a
secondary
filtration
process.
That
is,
a
system
would
still
monitor
filter
effluent
turbidity
after
the
primary
filters
for
compliance
with
the
IESWTR
and
LT1ESWTR.

The
LT2ESWTR
requires
an
initial
report
be
submitted
by
[
72
months
after
rule
promulgation]
for
large
systems
and
[
102
months
after
rule
promulgation]
for
small
systems
that
demonstrates
the
following
(
40
CFR
141.730):

°
Process
meets
the
definition
of
a
bag
or
cartridge
filter
°
Removal
efficiency
from
challenge
testing
(
described
in
section
8.4)
that
must
show
at
least
2
log
removal
for
bag
filters
and
3
log
removal
for
cartridge
filters
For
routine
compliance
reporting,
the
rule
requires
verification
that
all
flow
was
treated
by
the
bag
or
cartridge
filter
(
40
CFR
141.730).
One
possible
approach
States
may
elect
to
use
for
flow
verification
is
to
have
operators
certify
each
month
that
all
flow
was
treated
by
the
filter.
States
may
require
additional
reporting
at
their
discretion.
Section
8.6
provides
recommendations
for
filter
effluent
and
process
monitoring.

8.2.3
Integration
Into
a
Treatment
Process
Train
To
achieve
compliance
with
the
IESWTR
and
LT1ESWTR,
all
plants
(
except
those
meeting
the
filter
avoidance
criteria
in
40
CFR
141.71)
must
have
a
filtration
process
approved
by
the
State.
Approved
processes
receive
2
log
Cryptosporidium
removal
credit
under
the
IESWTR
and
LT1ESWTR.
For
compliance
with
additional
treatment
requirements
for
the
LT2ESWTR,
bag
and
cartridge
filters
should
be
added
as
an
additional
filtration
process
following
the
existing
primary
filtration
(
see
Figures
8.1
and
8.2).
The
bag
and
cartridge
filters
provide
additional
removal
of
the
smaller
contaminants
and
any
contaminants
that
break
through
the
granular
media
filters
during
the
end
of
a
run
cycle
or
process
upsets.
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
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June
2003
8­
4
Raw
water
Coagulation
Flocculation
Sedimentation
Granular
Filters
Service
pump
(
if
needed)
Bag
or
Cartridge
Filter
Clearwell
High
service
pump
Distribution
System
Raw
water
Primary
Bag
or
Cartridge
Filter(
s)
Clearwell
High
service
pump
Distribution
System
Secondary
Bag
or
Cartridge
Filter(
s)
Figure
8.1
Schematic
of
Treatment
Process
with
Bag/
Cartridge
Filters
For
those
systems
using
a
bag
or
cartridge
filter
process
to
meet
LT1ESWTR
requirements,
thus
serving
as
the
primary
filtration
process,
it
may
be
possible
to
configure
the
bag
or
cartridge
filters
in
a
series
(
see
Figure
8.2).

Figure
8.2
Bag/
Cartridge
Filters
in
Series
Another
possible
configuration
is
a
bag
or
cartridge
filter
followed
by
a
UV
system
(
see
Figure
8.3).
This
configuration
would
allow
removal
of
particles
and
microbial
pathogens
as
well
as
inactivation
of
Cryptosporidium,
Giardia,
and
viruses.
In
this
case,
the
bag
or
cartridge
filter
would
serve
as
the
primary
filter
and
thus,
be
subject
to
SWTR,
IESWTR,
and
LT1ESWTR
requirements,
while
the
UV
system
would
be
subject
to
the
LT2ESWTR
requirements.
Refer
to
EPA's
UV
Disinfection
Guidance
Manual
for
information
regarding
UV
systems
and
associated
requirements
with
LT2ESWTR.
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
8­
5
Raw
water
Bag
or
Cartridge
Filter(
s)
Clearwell
High
service
pump
Distribution
System
UV
System
Figure
8.3
Bag/
Cartridge
Filter
with
UV
System
Other
factors
that
should
be
considered
when
developing
a
treatment
process
scheme
include
available
space,
hydraulic
profile,
and
point
of
disinfection.
Space
requirements
are
small
for
bag
and
cartridge
filter
systems,
but
extra
space
for
maintenance
activities
should
be
accounted
for
in
the
planning
process.
Because
a
significant
head
loss
is
associated
with
an
additional
filtration
process,
a
utility
should
consider
its
hydraulic
profile
when
integrating
new
filters
into
an
existing
process
sequence.
Although
the
addition
of
a
new
bag
filtration
process
does
not
necessarily
require
that
the
point
of
primary
disinfection
be
changed,
some
bag
filtration
applications
chlorinate
prior
to
the
bag
filtration
process
to
minimize
biofilm
growth
on
the
bags.
However,
if
considering
a
process
train
with
a
bag
or
cartridge
filter
as
the
primary
filter,
as
in
Figure
8.3,
chlorinating
prior
to
filtration
will
likely
cause
higher
disinfection
byproduct
formation
compared
to
post­
filter
chlorination
since
the
filtration
process
will
remove
some
organic
material.

8.3
Toolbox
Selection
Considerations
This
section
describes
the
advantages
and
disadvantages
of
integrating
a
bag
and
cartridge
filtration
process
for
compliance
with
the
LT2ESWTR.

8.3.1
Advantages
The
advantages
of
bag
and
cartridge
filtration
processes
include
low
maintenance
requirements,
relatively
low
capital
cost,
minimal
operator
skill
and
attention
required,
and
low
space
requirements.
The
only
routine
maintenance
required
is
filter
replacement
when
a
defined
terminal
pressure
drop
or
other
operating
parameter,
such
as
filter
age
or
volume
treated,
is
reached.
The
operation
of
these
systems
is
straightforward
and
requires
little
technical
skill.
In
addition,
the
filter
materials
are
relatively
inexpensive
and
the
housing
system
is
not
complex,
resulting
in
relatively
low
capital
costs.
Chapter
8
­
Bag
and
Cartridge
Filters
1
Specific
sections
of
the
EPA/
NSF
ETV
Protocol
that
provide
guidance
for
developing
and
conducting
a
challenge
test
for
LT2ESWTR
include:
section
10.4,
Pre­
Filter
Water
Quality
Analysis;
section
11.0,
Operating
Conditions;
section
12.3,
Workplan;
section
13.0,
Data
Management;
and
section
14.0,
QA/
QC.

LT2ESWTR
Toolbox
Guidance
Manual
Proposal
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June
2003
8­
6
8.3.2
Disadvantages
A
disadvantage
of
bag
and
cartridge
filtration
processes
is
most
filters
must
be
replaced
instead
of
regenerated.
For
larger
flows,
or
water
with
higher
particle
loads,
frequent
filter
replacement
increases
operation
and
maintenance
costs.
Additional
pumps
may
be
required
to
provide
needed
pressure.
Also,
redundancy
should
be
built
into
the
process
design,
increasing
costs.

8.4
Challenge
Testing
Manufacturers
commonly
rate
fabric
filters
by
pore
size
or
pore
distribution.
However,
there
is
no
industry
standard
for
measuring
or
reporting
these
characteristics.
This
lack
of
standardization
causes
problems
for
establishing
design
criteria
to
ensure
that
a
given
bag
or
cartridge
filter
will
effectively
remove
a
given
percentage
of
Cryptosporidium.
Furthermore,
an
oocyst
has
different
structural
characteristics
than
the
markers
used
to
determine
pore
size;
thus,
the
rate
of
rejection
may
differ
for
an
oocyst
versus
the
test
markers
used
to
determine
pore
size
or
molecular
weight
cutoff.
To
compensate
for
these
factors
of
uncertainty
for
Cryptosporidium
removal,
the
LT2ESWTR
requires
bag
or
cartridge
filters
to
be
challenge
tested
 
a
process
in
which
a
known
quantity
of
Cryptosporidium
oocysts
(
or
an
acceptable
surrogate)
is
added
to
the
filter
influent
and
the
effluent
concentration
is
measured
to
determine
the
removal
capabilities
of
the
filter
(
40
CFR
141.728(
a)).
This
testing
is
product­
specific,
not
site­
specific,
meaning
it
does
not
have
to
be
tested
at
every
water
system
seeking
removal
credit.
Instead,
a
manufacturer
(
or
independent
third
party)
would
challenge
test
each
of
its
products
in
order
to
obtain
a
1
or
2
log
Cryptosporidium
removal
rating.

For
compliance
with
the
LT2ESWTR,
EPA
defined
a
set
of
test
conditions
that
must
be
met
for
an
acceptable
challenge
test.
These
conditions
provide
only
a
framework
for
the
challenge
test
and
States
may
develop
additional
testing
requirements.
The
EPA
Membrane
Filtration
Guidance
Manual
contains
detailed
guidance
on
developing
challenge
test
protocol
and
conducting
the
test
for
membrane
processes
that
relate
to
these
requirements.
Additionally,
NSF
International,
in
cooperation
with
EPA,
developed
the
Protocol
for
Equipment
Verification
Testing
for
Physical
Removal
of
Microbiological
and
Particulate
Contaminants
with
a
chapter
for
testing
bag
and
cartridge
filters.
Although
the
protocol
was
developed
for
compliance
with
the
SWTR,
some1
testing
principles
still
apply.

Section
8.4.1
describes
the
test
conditions
required
by
the
LT2ESWTR
(
40
CFR
141,
Subpart
W,
Appendix
B).
Section
8.4.2
shows
how
to
calculate
the
log
removal
value
for
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
8­
7
challenge
testing
results.
Section
8.4.3
discusses
modifications
to
the
filter
unit
(
e.
g.,
change
in
filter
media)
occurring
after
challenge
testing
that
may
require
additional
challenge
testing.

8.4.1
Testing
Conditions
(
141,
Subpart
W,
Appendix
B)

8.4.1.1
Full
Scale
Filter
Element
Challenge
testing
must
be
conducted
on
a
full­
scale
filter
element
identical
in
material
and
construction
to
the
filter
elements
proposed
for
use
in
full­
scale
treatment
facilities.
For
this
challenge
testing,
a
filter
element
consists
of
the
filter
media,
filter
housing,
and
inlet
and
outlet
piping.

8.4.1.2
Challenge
Particulate
Challenge
testing
must
be
conducted
using
Cryptosporidium
oocysts
or
a
surrogate
which
is
removed
no
more
efficiently
than
Cryptosporidium
oocysts.
The
organism
or
surrogate
used
during
challenge
testing
is
referred
to
as
the
"
challenge
particulate."
The
concentration
of
the
challenge
particulate
must
be
determined
using
a
method
capable
of
discreetly
quantifying
the
specific
organism
or
surrogate
used
in
the
test,
and
gross
measurements
such
as
turbidity
cannot
be
used.
Key
physical
characteristics
to
be
considered
for
identifying
an
acceptable
surrogate
include
size,
shape,
surface
charge,
and
mono­
dispersion
(
i.
e.,
particles
remain
discrete
in
solution
and
do
not
aggregate).

Chapter
3
of
EPA's
Membrane
Filtration
Guidance
Manual
describes
the
characteristics
of
acceptable
surrogates
and
lists
potential
and
inert
surrogates
for
Cryptosporidium.
Examples
of
possible
microbial
surrogates
are
P.
dimunita
and
Serratia
marcessans.

8.4.1.3
Feed
Concentration
In
order
to
demonstrate
a
removal
efficiency
of
at
least
2
or
3
log
for
bag
or
cartridge
filters,
respectively,
it
may
be
necessary
to
seed
the
challenge
particulate
into
the
test
solution.
A
criticism
of
this
approach
is
that
the
seeded
levels
are
orders
of
magnitude
higher
than
those
encountered
in
natural
waters,
which
could
lead
to
artificially
high
estimates
of
removal
efficiency.
To
address
this
issue,
EPA
set
a
limit
on
the
maximum
feed
concentration
applied
to
a
filter
during
the
challenge
study.
The
limit
is
based
on
the
detection
limit
of
the
challenge
particulate:

Cartridge
filters:
Maximum
Feed
Concentration
=
3.16
×
104
×
Filtrate
Detection
Limit
Bag
filters:
Maximum
Feed
Concentration
=
3.16
×
103
×
Filtrate
Detection
Limit
Chapter
8
­
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and
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Filters
LT2ESWTR
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2003
8­
8
These
concentrations
allow
the
demonstration
of
up
to
3.5
log
removal
for
bag
filters
and
4.5
log
removal
for
cartridge
filters
during
challenge
testing,
if
the
challenge
particulate
is
removed
to
the
detection
limit.

8.4.1.4
Time
Periods
of
Challenge
Testing
The
challenge
test
must
run
until
"
terminal
pressure
drop"
is
reached.
Terminal
pressure
drop
is
a
parameter
specified
by
the
manufacturer
which
establishes
the
end
of
the
useful
life
of
the
filter.
However,
continuous
challenge
particulate
feed
is
not
required
(
i.
e.,
intermittent
seeding
is
permitted).
At
a
minimum,
removal
efficiency
must
be
determined
during
three
periods
over
the
filtration
cycle:

1)
Within
2
hours
of
start­
up
after
a
new
bag
or
cartridge
filter
has
been
installed.

2)
When
the
pressure
drop
is
between
45
and
55
percent
of
the
terminal
pressure
drop.

3)
At
the
end
of
the
run
after
the
pressure
drop
has
reached
100
percent
of
the
terminal
pressure
drop.

The
rule
does
not
specify
the
number
of
samples
that
must
be
collected
during
each
of
the
three
periods.
Because
the
effluent
concentration
is
often
very
low
and
near
the
detection
limit,
it
may
be
beneficial
to
collect
more
effluent
than
influent
samples
to
obtain
a
more
accurate
removal
efficiency.
If
one
sample
has
an
uncharacteristically
high
concentration
this
can
result
in
a
low
log
removal
value
(
LRV)
that
is
not
necessarily
representative
of
the
filter's
removal
efficiency.

8.4.1.5
Water
Quality
of
Challenge
Test
Solution
Water
quality
can
have
a
significant
impact
on
the
removal
of
particulate
contaminants,
such
as
Cryptosporidium.
In
general,
bag
and
cartridge
filters
in
water
treatment
do
not
experience
influent
turbidity
concentrations
much
greater
than
10
NTU;
and
for
the
application
of
the
LT2ESWTR,
will
receive
filtered
water
and
thus,
very
low
turbidity.

A
clean­
water
challenge
test
will
generally
provide
the
most
conservative
estimate
of
removal
efficiency.
However,
since
the
challenge
test
must
run
until
terminal
head
loss
is
reached,
the
challenge
test
solution
will
need
to
contain
some
solids
to
cause
the
head
loss
build­
up
across
the
filter,
but
not
an
excessive
amount
that
will
cause
a
rapid
build­
up.
Particulate
foulants
that
may
be
appropriate
to
add
to
the
test
solution
include
clay
particles
(
such
as
bentonite
or
kaolin)
or
carbon
powder,
as
long
as
they
are
not
excessively
fine­
sized.
Chapter
8
­
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and
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Filters
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8­
9
The
following
are
recommended
for
the
challenge
test
solution:


High
quality
water
with
a
low
to
moderate
concentration
of
suspended
solids
should
be
used
as
the
challenge
solution.
Suspended
solids
concentration
should
be
high
enough
to
achieve
a
reasonable
rate
of
headloss
buildup,
but
not
so
high
that
the
headloss
builds
up
too
rapidly
to
conduct
the
challenges
at
the
various
headloss
levels.


No
oxidants,
disinfectants,
or
other
pretreatment
chemicals
should
be
added
to
the
test
solution.


Characterized
with
respect
to
basic
water
quality
parameters,
such
as
pH,
turbidity,
temperature,
and
total
dissolved
solids.

For
the
initial
sampling
conducted
at
zero
percent
headloss
(
see
section
8.4.1.8),
no
particulate
foulant
needs
to
be
added
to
the
test
solution.
This
can
be
accomplished
if
the
foulant
is
injected
into
the
feed
stream,
rather
than
fed
in
batch.
In
this
case
the
foulant
feed
pump
would
not
be
turned
on
until
the
zero
percent
challenge
is
completed.
If
the
particulate
foulant
is
added
in
batch,
then
the
zero
percent
headloss
challenge
must
be
completed
before
five
percent
of
the
terminal
headloss
is
reached.

8.4.1.6
Maximum
Design
Flow
Rate
The
challenge
test
must
be
conducted
at
the
maximum
design
flow
rate
specified
by
the
manufacturer.

8.4.1.7
Challenge
Particulate
Seeding
Method
There
are
two
basic
approaches
to
seeding:
batch
seeding
and
in­
line
injection.
In
batch
seeding,
all
of
the
challenge
particulates
are
introduced
into
the
entire
volume
of
test
solution
and
mixed
to
uniformity.
In­
line
injection
allows
for
the
continuous
or
intermittent
introduction
of
challenge
particulates
into
the
feed
stream
entering
the
bag
or
cartridge
system.
While
both
methods
are
acceptable,
intermittent,
in­
line
injection
may
the
most
practical
seeding
method
for
the
testing.

Batch
seeding
requires
the
entire
test
solution
to
be
contained
in
a
reservoir
and
for
the
reservoir
to
be
well
mixed
to
ensure
a
uniform
concentration
of
the
seeded
particles.
Generally,
batch
seeding
is
used
for
small
scale
systems
that
only
require
relatively
small
amounts
of
feed
solution
for
testing.

While,
in­
line
injection
of
the
challenge
particle
can
be
either
continuous
or
intermittent,
the
intermittent
feed
may
be
more
practical
to
conduct
the
challenge
test
at
the
required
periods
(
i.
e.,
a
minimum
of
beginning,
middle,
and
end­
of­
run;
see
section
8.4.1.4).
It
is
vital
that
Chapter
8
­
Bag
and
Cartridge
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LT2ESWTR
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2003
8­
10
equilibrium
is
achieved
during
each
seeding
event
prior
to
the
collection
of
feed
and
filtrate
samples.

In­
line
injection
delivers
the
challenge
particles
from
a
concentrated
stock
solution
with
a
known
feed
concentration
(
C
stock).
The
concentration
of
the
stock
solution
should
be
50
to
200
times
the
desired
concentration
in
the
test
feed
solution
(
C
feed).
The
stock
solution
delivery
rate
(
SSDR)
for
in­
line
injection
is
calculated
using
the
equation
below:

SSDR
=
(
C
feed
x
Q
feed
)
/
C
stock
Equation
8­
1
Where:
SSDR
=
stock
solution
deliver
rate
(
gpm)
C
feed
=
feed
solution
concentration
(#
or
mass
/
volume)
Q
feed
=
feed
flow
(
gpm)
C
stock
=
stock
solution
concentration
(#
or
mass
/
volume)

The
stock
solution
should
be
continuously
mixed
to
ensure
a
uniform
concentration
of
particles
are
injected
into
the
feed
stream.

In­
line
injection
requires
additional
equipment,
such
as
chemical
feed
pumps,
injection
ports
and
in­
line
mixers.
A
more
detailed
description
of
in­
line
injection
is
available
in
the
Membrane
Filtration
Guidance
Manual
(
USEPA,
2003).

8.4.1.8
Challenge
Test
Solution
Volume
The
total
volume
of
test
solution
required
for
the
challenge
should
be
the
same
for
the
different
challenge
particle
seeding
methods.
However,
the
seeded
test
solution
volume
can
differ
for
the
different
methods.

In
general,
the
volume
of
the
test
solution
depends
on
filtrate
flow
rate,
test
duration,
and
hold­
up
volume
of
the
test
system
and
can
be
calculated
by
the
following
equation.

V
test
=
(
Q
f
x
T
+
V
sys
)
x
SF
Equation
8­
2
Where:
V
test
=
Volume
of
test
solution
(
gallons)
Q
f
=
Filtrate
flow
rate
(
gallons
per
minute)
T
=
Duration
of
test
(
minutes)
V
sys
=
Volume
of
solution
contained
within
the
filter
unit(
gallons)
SF
=
Safety
factor
(
dimensionless)

To
calculate
the
total
volume
of
test
solution,
the
T
value
in
the
above
equation
is
the
time
between
the
initiation
of
flow
to
the
filter
unit
to
the
time
the
last
sample
is
drawn
when
terminal
Chapter
8
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headloss
is
reached.
For
batch
seeding
and
continuous
in­
line
injection
tests,
the
seeded
test
solution
volume
(
V
seeded)
is
the
same
as
the
total
test
solution
volume.

For
intermittent,
in­
line
injection,
the
seeded
test
solution
volume
can
be
considerably
less
than
that
required
for
batch
seeding.
To
calculate
this
smaller
volume,
the
equation
above
can
be
modified
as
follows:

V
seeded
=
(
Q
f
x
T
seed
+
V
sys
+
V
eq)
x
SF
Equation
8­
3
Where:
V
seeded
=
seeded
test
solution
volume
(
gallons)
V
eq
=
volume
required
to
reach
feed
equilibrium
(
gallons)
T
seed
=
Duration
of
sampling
(
minutes)

The
equilibrium
volume
(
V
eq)
is
the
quantity
of
seeded
test
solution
needed
to
pass
through
the
filter
to
reach
a
stable
feed
concentration
of
the
challenge
particle.
In
general,
filtrate
sampling
cannot
begin
until
this
volume
has
passed
through
the
system.
A
common
assumption
is
that
a
minimum
of
three
to
five
system
volumes
are
needed
to
reach
equilibrium
(
i.
e.,
V
eq

3V
sys).
The
duration
of
the
test,
T,
does
not
include
time
needed
to
reach
equilibrium,
as
this
is
accounted
for
by
V
eq.
Thus,
T
represents
the
time
necessary
to
conduct
the
actual
sampling
as
discussed
in
section
8.4.1.9).
Section
3.10.5
of
the
Membrane
Filtration
Guidance
Manual
(
USEPA,
2003)
contains
a
detailed
example
of
challenge
test
solution
design.

For
in­
line
injection
of
the
challenge
particles
the
volume
of
stock
solution
needed
can
be
calculated
from
the
seeded
test
volume
as
follows:

V
stock
=
(
V
seeded
x
C
feed)
/
(
C
stock)
Equation
8­
4
Where:
V
stock
=
volume
of
stock
solution
(
gallons)
V
seeded
=
seeded
test
solution
volume
(
gallons)
C
feed
=
feed
solution
concentration
(#
or
mass
/
volume)
C
stock
=
stock
solution
concentration
(#
or
mass
/
volume)

8.4.1.9
Sampling
An
effective
sampling
program
depends
on
a
detailed
sampling
plan
and
the
use
of
appropriate
sampling
methods,
locations,
and
QA/
QC
measures.

Samples
can
be
collected
using
either
grab
or
composite
sampling
methods.
Grab
samples
consist
of
pre­
determined
amounts
of
water
taken
from
the
feed
or
filtrate
streams,
while
composite
samples
are
of
the
entire
process
stream.
It
is
likely
that
grab
sampling
methods
will
be
used
in
the
challenge
test.
Good
sampling
practices
include
flushing
samples
taps,
using
clean
Chapter
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8­
12
sample
containers
and
preventing
cross
contamination
of
samples.
QA/
QC
measures
include
clearly
identifying
samples,
collecting
duplicates
and
using
blanks.
The
time
of
filtrate
sampling
should
be
based
on
the
initiation
of
seeding
for
a
given
sampling
period
and
flow
rate.
The
influent
should
be
sampled
just
prior
to
entering
the
filter
(
but
at
least
10
pipe
diameters
downstream
of
the
particle
injection
point
and
in­
line
mixers).
Sampling
of
the
filtrate
should
occur
immediately
following
the
filter,
but
after
any
filtrate
side
instrumentation
that
may
be
affected
by
the
sampling.

Sample
port
design
is
an
important
consideration
and
should
ensure
that
a
representative
sample
is
obtained.
Poorly
designed
ports
contain
large
volumes
where
stagnation
may
occur
(
e.
g.,
large
valves
and
long
sample
tubes)
and
pull
the
sample
from
the
edge
of
the
pipe.
A
well
designed
port
has
a
sample
quill
that
extends
into
the
center
of
the
pipe
to
draw
a
more
representative
sample.

Chapter
3
of
the
Membrane
Filtration
Guidance
Manual
(
USEPA,
2003)
contains
additional
information
on
developing
sampling
plans
and
provides
schematics
of
typical
sampling
apparatuses.

8.4.2
Calculation
of
Log
Removal
To
determine
the
maximum
feed
concentration,
use
Equation
8­
5.
To
determine
the
log
removal
efficiency
of
the
filter
process
tested,
calculate
the
log
removal
using
Equation
8­
6.

Maximum
Feed
Concentration
=
3.16
x
106
x
(
Filtrate
Detection
Limit)
Equation
8­
5
LRV
=
Log
10(
Feed
Concentration)
­
Log
10(
Filtrate
Concentration)
Equation
8­
6
The
feed
and
filtrate
concentrations
must
be
expressed
in
the
same
units
(
number
of
challenge
particulate
per
unit
volume).
If
the
challenge
particulate
is
not
detected
in
the
filtrate,
then
the
filtrate
concentration
is
set
equal
to
the
detection
limit.

Example
1
­
Determining
maximum
allowable
filtrate
concentration
If
the
detection
limit
of
the
surrogate
test
is
2
units/
L
then
the
maximum
feed
concentration
is
3.16
x
106
x
(
2)
=
6.32
x
106
Chapter
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13
Example
2
­
Calculating
the
LRV
Feed
Concentration
20,000
units/
L
Filtrate
Concentration
3
units/
L
LRV
=
Log(
20,000)
­
Log(
3)
LRV
=
4.30
­
0.48
=
3.82
The
LT2ESWTR
does
not
specify
how
the
feed
and
effluent
concentration
must
be
determined.
One
possible
approach
is
to
use
the
average
of
all
the
feed
samples
and
average
of
all
the
filtrate
samples.
A
more
conservative
approach
would
be
to
use
the
lowest
feed
concentration
and
highest
filtrate
concentration
from
each
filter
run.

A
challenge
test
will
likely
evaluate
multiple
filters.
An
LRV
must
be
calculated
for
each
filter
tested.
The
final
log
removal
efficiency
assigned
to
the
filter
process
tested
depends
on
the
number
of
filters
tested:

$
If
fewer
than
20
filters
were
tested
during
a
challenge
study,
then
the
lowest
LRV
observed
would
be
the
removal
efficiency
assigned
to
the
process.

$
If
20
filters
were
tested
during
challenge
testing,
then
the
removal
efficiency
assigned
for
the
process
is
the
10th
percentile
of
the
LRVs
observed
during
the
challenge
study.
(
The
percentile
is
defined
by
[
i/(
n+
1)]
where
i
is
the
rank
of
n
individual
data
points
ordered
lowest
to
highest.
If
necessary
the
system
may
calculate
the
10th
percentile
using
linear
interpolation.)

8.4.3
Modifications
to
Filtration
Unit
after
Challenge
Test
If
any
significant
modifications
to
the
filter
unit
are
made
after
challenge
testing,
additional
challenge
testing
is
required
to
demonstrate
removal
efficiency
of
the
modified
unit.
Significant
modifications
specified
by
the
rule
are,
but
not
limited
to:

$
Changes
to
the
filtration
media
(
e.
g.,
different
fabric,
change
in
the
filter
manufacturing
process)

$
Changes
to
the
configuration
of
the
filtration
media
$
Modifications
to
the
sealing
system
Chapter
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14
8.5
Design
Considerations
Bag
and
cartridge
filter
systems
may
contain
anywhere
from
one
to
over
twenty
filter
units.
There
is
no
maximum
number
of
filters
a
system
can
include;
however,
membrane
or
other
filtration
processes
become
more
practical
for
larger
flows
since
bag
and
cartridge
filters
are
generally
replaced
instead
of
backwashed
or
regenerated.
A
single
filter
unit
is
comprised
of
the
filter
media
(
bag
or
cartridge),
housing,
and
associated
piping
and
valves.
Figure
8.4
shows
a
typical
single
filter
vessel
(
housing).

Figure
8.4
Single
Filter
Vessel
Source:
U.
F.
Strainrite
Systems
with
multiple
filters
may
be
designed
as
a
manifold
with
connective
piping
between
the
individual
filters
in
separate
housing
or
alternatively
as
multiple
filters
in
a
single
housing.
Figures
8.5
and
8.6
show
the
manifold
design
and
multiple
filter
vessel
design,
respectively.
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Figure
8.5
Manifold
Bag
Filter
Design
Chapter
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Figure
8.6
Multiple
Filter
Vessel
Source:
U.
F.
Strainrite
The
designs
of
bag
and
cartridge
filters
are
not
complex,
however,
there
are
a
couple
of
key
issues
that
should
be
taken
into
consideration.
First,
the
filter
units
must
be
designed
integrally
with
their
respective
housing
systems.
Poor
fittings
can
cause
leaks
and
premature
failure.
Manufacturers
can
provide
individual
filter
units
that
can
be
retrofitted
into
the
existing
process
or
complete
filter
houses
that
are
skid
mounted.
It
is
important
to
adhere
to
the
manufacturer's
instructions
on
filter
installation.

Second,
the
overall
water
treatment
process
design
should
minimize
sudden
changes
in
pressures
applied
to
the
bag
or
cartridge
filters.
Each
time
the
flow
to
the
filter
is
interrupted
and
then
restarted,
a
sudden
increase
in
pressure
can
occur
across
the
filter
unit
unless
steps
are
taken
to
allow
for
gradual
pressure
ramp­
up.
The
particle
load
in
the
filter
effluent
often
increases
when
the
filter
cycle
begins.
A
study
by
McMeen
(
2001)
reported
that
the
increase
in
particle
load
could
be
occurring
due
to
the
seal
at
the
top
of
the
filter
failing
when
the
pressure
suddenly
increases.
Bag
filters
are
especially
susceptible
to
cycling
because
these
pressure
fluctuations
also
increase
wear
on
the
fabric
and
seams,
causing
premature
failure.
Section
8.5.4
provides
recommendations
for
reducing
filter
cycling.
Chapter
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Bag
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8.5.1
Water
Quality
As
previously
described,
systems
seeking
compliance
with
the
LT2ESWTR
will
most
likely
integrate
a
bag
or
cartridge
filter
process
after
the
primary
filtration
process.
As
a
result,
influent
water
quality,
with
respect
to
high
particulate
levels,
should
not
be
an
issue.
However,
for
systems
with
existing
processes
that
use
coagulants,
the
presence
of
residual
coagulant
in
the
primary
filter
effluent
may
clog
the
pores
of
a
bag
or
cartridge
filter.
Although
this
will
not
impair
removal
efficiency
for
Cryptosporidium,
it
will
shorten
the
time
until
the
terminal
pressure
drop
is
reached,
thus
reducing
filter
life.

Another
water
quality
issue
is
the
potential
for
biofilm
growth
on
the
bag
or
cartridge
filter
media.
Systems
can
add
a
disinfectant
prior
to
the
bag
or
cartridge
filters
to
prevent
biofilm
growth.
(
The
filters
must
be
compatible
with
the
disinfectant.)

8.5.2
Size
of
Filter
System
and
Redundancy
Systems
should
be
adequately
designed
to
handle
maximum
day
or
maximum
instantaneous
flow,
depending
on
the
existing
treatment
process
design.
Prolonged
operation
at
maximum
flow
velocity
wears
the
filter
media
at
a
higher
rate
than
operating
at
lower
flow
velocities.
The
total
volume
throughput
is
greater
when
operating
at
a
flow
velocity
lower
than
maximum
flow
velocity
rated
for
the
filter.

A
minimum
of
two
bag
or
cartridge
filter
housings
should
be
provided
to
ensure
continuous
water
treatment
in
the
event
of
failure
in
the
filter
operation.
For
water
systems
that
do
not
require
continuous
operation,
a
State
may
approve
a
single
filter
housing
operation.
Redundancy
in
pumps
is
also
recommended
to
ensure
continuous
operation.

8.5.3
Design
Layout
Design
layout
features
that
should
be
considered
for
most
designs
are
as
follows:

$
Piping
should
be
designed
to
allow
isolation
of
the
individual
filter
units
or
vessels
for
maintenance
and
filter
replacement
$
Common
inlet
and
outlet
headers
for
the
filter
units
$
Sufficient
available
head
to
meet
the
terminal
pressure
drop
and
system
demand
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8.5.4
Filter
Cycling
Filter
cycling
refers
to
the
starting
and
stopping
of
the
pump
or
filter
operation.
This
can
be
problematic
with
bag
filter
processes
(
cartridge
filters
are
not
known
to
have
this
problem)
in
which
water
is
pumped
directly
from
the
source
to
the
filter,
and
then
out
to
the
distribution
system.
In
these
situations,
the
filters
operate
on
demand,
similar
to
wells
for
small
systems,
and
the
sudden
increase
in
pressure
across
the
filter
causes
premature
wear
and
filter
failure.
For
LT2ESWTR
compliance,
systems
with
bag
filters
in
a
series
or
followed
by
UV
disinfection
should
consider
the
following
recommendations
for
controlling
the
flow
into
the
filter
process
to
minimize
filter
cycling.

$
Lengthen
the
filter
runs
by
reducing
the
flow
as
much
as
possible
through
the
filter.

$
Install
or
divert
the
flow
to
a
storage
facility
(
e.
g.,
pressure
tank,
clearwell)
after
the
bag
filtration
process.
The
stored
water
can
supply
the
frequent
surges
in
demand
and
thus
reduce
the
bag
or
cartridge
filter
cycling.

During
filter
start­
up
and
other
hydraulic
surges,
bag
and
cartridge
filters
often
experience
an
increase
in
filter
effluent
turbidity.
Systems
should
consider
the
following
options
to
improve
filtered
water
quality:

$
Design
for
filter
to
waste
capability.
EPA
strongly
recommends
filtering
to
waste
for
the
first
five
minutes
of
the
filter
cycle.

$
Install
a
slow
opening
and
closing
valve
ahead
of
the
filter
to
reduce
flow
surges.

8.5.5
Pressure
Monitoring,
Valves,
and
Appurtenances
As
previously
mentioned,
once
the
terminal
pressure
drop
has
been
reached,
the
filter
should
be
replaced.
At
a
minimum,
pressure
gauges
should
be
located
before
and
after
the
bag
or
cartridge
filter
system
and
should
be
monitored
at
least
daily.
A
valve
or
flow
restricter
should
be
installed
on
the
inlet
header
pipe
of
the
filters
to
maintain
flows
below
the
maximum
operating
flow
for
the
filters.

8.5.6
Air
Entrapment
An
automatic
air
release
valve
should
be
installed
on
the
top
of
the
filter
housing
to
release
any
air
trapped
in
the
filter.
These
valves
should
be
checked
routinely
and
properly
maintained.
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8.5.8
NSF
Certification
All
components
used
in
the
drinking
water
treatment
process
should
be
evaluated
for
contaminant
leaching
and
certified
under
ANSI/
NSF
Standard
61.

8.6
Operational
Issues
8.6.1
Pressure
Drop
(
Inlet/
Outlet
Pressures)

The
pressure
drop
across
the
filter
directly
relates
to
the
amount
of
particle
build­
up
on
the
filter
material
and
to
the
time
when
the
filter
should
be
replaced.
Typical
pressure
drops
across
a
clean
filter
are
1
to
2
psig
(
pounds
per
square
inch­
gauge)
and
can
increase
to
a
differential
of
20
to
30
psig
when
the
terminal
pressure
drop
is
achieved.
The
pressure
differential
does
not
increase
linearly
with
run
time;
the
differential
pressure
increases
at
a
faster
rate
with
the
duration
of
the
run
or
as
more
material
accumulates
on
the
filter.
The
time
between
filter
replacement
is
primarily
dependent
on
flow
rate,
but
also
on
influent
water
quality
and
filter
material
(
i.
e.,
size
of
pores).

The
differential
pressure
between
the
inlet
and
outlet
header
should
be
monitored
to
determine
when
the
filter
needs
replacement.
An
alarm
could
also
be
linked
to
the
pressure
gauge
to
ensure
the
operator
is
alerted.

8.6.2
Monitoring
In
addition
to
monitoring
the
pressure
drop
across
the
filter,
the
influent
and
effluent
turbidity
or
particle
count
should
be
monitored
to
assess
performance
and
indicate
possible
process
upsets
with
the
bag
or
cartridge
filter
or
other
upstream
processes.
The
recommended
monitoring
frequency
depends
on
the
influent
water
quality
and
its
variability.
At
a
minimum,
the
pressure
differential
and
effluent
turbidity
should
be
checked
daily.
During
the
initial
start­
up
phase
of
a
newly
integrated
bag
or
cartridge
filtration
system,
monitoring
should
be
more
frequent
and
then
can
be
reduced
once
the
operator
becomes
familiar
with
the
system.
If
continuous
monitoring
of
turbidity
and/
or
pressure
differential
is
employed,
the
output
from
the
sensors
should
be
sent
to
an
alarm
to
warn
operators
of
sudden
changes
in
operation,
or
if
the
filter
element
needs
replacing.

EPA
recognizes
turbidity
has
limitations
as
an
indicator
of
filter
failure
or
pathogen
breakthrough.
However,
in
the
absence
of
a
better
indicator,
monitoring
both
influent
and
effluent
turbidity
over
a
full
run
(
i.
e.,
from
start
to
end
of
the
filter
life)
can
provide
a
performance
baseline.
The
baseline
can
then
be
used
to
indicate
process
upsets.
This
method
may
not
be
applicable
to
all
systems;
since
the
bag
or
cartridge
filter
influent
will
be
filtered
water,
the
difference
between
influent
and
effluent
turbidity
may
be
too
low
to
provide
meaningful
data.
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
Manual
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June
2003
8­
20
Particle
counters
can
be
another
valuable
monitoring
tool.
If
available,
periodic
checks
of
influent
and
effluent
particle
counts
are
also
recommended
to
ensure
the
filter
is
removing
particles
in
the
appropriate
size
range
(
i.
e.,
4­
6
microns).
Chapter
8
­
Bag
and
Cartridge
Filters
LT2ESWTR
Toolbox
Guidance
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Proposal
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2003
8­
21
References
McMeen
(
2001).
Alternate
Filtration:
Placing
New
Technology
in
an
Old
Regulatory
Box.
American
Water
Works
Association,
Membrane
Conference
Proceedings.

NSF
International.
(
2000).
Protocol
for
Equipment
Verification
Testing
for
Physical
Removal
of
Microbiological
and
Particulate
Contaminants.
40CFR35.6450.

USEPA
(
2002).
Draft
Membrane
Filtration
Guidance
Manual,
April
2002
draft.
