LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
14­
1
14.0
Membrane
Filtration
14.1
Introduction
Microfiltration
and
ultrafiltration
(
MF/
UF)
are
membrane
processes
which
remove
microorganisms
and
other
contaminants
by
filtration.
Contaminants
larger
than
the
pore
size
of
the
membrane
are
retained
on
the
membrane
and
removed
from
the
water.
MF/
UF
processes
that
meet
the
requirements
for
membrane
filtration
under
the
LT2ESWTR
will
receive
Cryptosporidium
removal
credit.

EPA
recently
published
the
Membrane
Filtration
Guidance
Manual
for
systems
applying
MF/
UF
for
removal
of
pathogens
from
public
water
supplies.
The
manual
provides
detailed
guidance
on
applying
membrane
filtration
to
comply
with
the
requirements
of
the
LT2ESWTR.
Readers
interested
in
detailed
information
on
membrane
filtration
should
consult
the
Membrane
Filtration
Guidance
Manual.
This
chapter
will
focus
on
the
comparison
of
membrane
filtration
with
other
technologies
for
inactivation
of
Cryptosporidium.

14.2
Log
Inactivation
Requirements
Most
commercially
available
MF/
UF
membranes
designed
for
drinking
water
treatment,
have
been
demonstrated
to
remove
Cryptosporidium
to
detection
limits,
provided
the
membrane
is
intact.
Systems
that
demonstrate
membrane
integrity
through
a
challenge
test
before
installation
and
through
daily
membrane
integrity
testing
during
operation
will
be
eligible
for
2.5
log
additional
credit
for
Cryptosporidium
removal
under
the
LT2ESWTR.

14.3
Toolbox
Selection
Considerations
MF/
UF
is
a
highly
efficient
technology
for
removing
pathogens
and
other
particulates
from
drinking
water.
Its
main
advantages
are
listed
below:

°
Essentially
complete
removal
of
all
particles
larger
than
the
exclusion
characteristic
of
the
membrane
°
Minimal
installation
effort
when
supplied
as
skid­
mounted
package
plants
°
Minimal
operator
attention
and
training
needed
when
supplied
with
fully
automated
controls
°
Forms
no
disinfection
byproducts
because
it
is
a
physical
removal
process
Chapter
14
­
Membrane
Filtration
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
14­
2
MF/
UF
is
an
advanced
technology
and
can
be
more
expensive
than
conventional
technologies.
Its
major
disadvantages
are:

°
Total
cost
may
exceed
that
of
conventional
technologies
°
Membrane
fouling
may
limit
application
in
some
cases
°
Does
not
provide
a
disinfectant
residual
in
the
distribution
system
14.4
Design
Considerations
Membrane
systems
are
usually
supplied
in
skid­
mounted
packages.
The
package
typically
contains
the
membrane
units,
a
pre­
filter
for
removal
of
large
particles,
low
pressure
feed
pumps,
high
pressure
backwash
pumps,
a
chemical
cleaning
system,
a
chlorination
system,
and
a
backwash
residuals
handling
and
disposal
system.

A
major
design
variable
for
membrane
systems
is
the
permeate
flux.
MF/
UF
membranes
are
designed
to
operate
within
a
specific
range
of
pressures
and
fluxes,
and
a
membrane
system
must
be
designed
to
operate
within
these
specifications.
Pilot
studies
are
often
performed
to
find
the
optimal
combination
of
flux,
pressure,
pretreatment,
and
cleaning
interval
for
a
particular
application.
Flux
through
a
membrane
is
highly
temperature
dependent,
so
the
average,
minimum,
and
maximum
temperature
of
the
water
to
be
treated
must
be
considered
when
designing
the
system.
The
flux
and
the
desired
flow
rate
are
used
to
determine
the
size
and
number
of
membrane
units
required.
Water
with
high
turbidity
or
high
TOC
levels
can
foul
membranes,
causing
poor
performance
and
shortening
membrane
life.
If
MF/
UF
is
installed
after
conventional
treatment
in
the
treatment
train,
high
turbidity
levels
should
not
be
a
problem.
TOC,
however,
may
still
be
a
problem,
even
after
conventional
filtration.
If
there
are
high
TOC
levels,
pretreatment
should
be
considered.
If
the
membrane
process
is
being
relied
upon
to
remove
viruses
as
well
as
bacteria
and
protozoa,
UF
membranes
will
be
needed.
Considerations
should
also
be
made
for
treatment
and/
or
disposal
of
backwash
residuals.

14.5
Operational
Considerations
In
operating
a
membrane
system,
there
are
several
factors
that
must
be
balanced.
Operating
at
higher
pressures
will
allow
greater
flow
rates.
It
will
also
result
in
greater
operating
costs
and
increased
cleaning
and
backwash
frequency.
Operating
at
lower
pressures
may
result
in
reduced
cleaning
and
backwash
frequency
but
increased
area
requirements.
To
ensure
the
unit
is
working
properly,
regular
integrity
testing
of
the
membrane
should
be
conducted.
While
indicators
such
as
turbidity
can
be
useful,
the
integrity
of
the
membrane
should
be
directly
tested
at
least
daily.
Even
with
pretreatment,
membranes
will
eventually
foul.
Periodic
cleaning
of
the
membranes
will
improve
membrane
performance
and
life.
The
appropriate
length
of
time
between
cleanings
can
be
determined
by
monitoring
the
long
term
decrease
in
productivity
and
backwash
efficiency.
Chapter
14
­
Membrane
Filtration
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
14­
3
