LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
13­
1
13.0
Ultraviolet
Light
13.1
Introduction
The
use
of
ultraviolet
(
UV)
light
for
disinfection
of
drinking
water
is
a
relatively
new
application
in
the
United
States,
although
used
for
many
years
in
the
wastewater
industry.
UV
disinfection
is
the
process
of
irradiating
water
with
UV
light.
The
UV
light
is
absorbed
by
the
genetic
material
of
microorganisms,
damaging
it
and
preventing
the
microorganisms
from
reproducing.
UV
has
been
found
to
be
particularly
effective
against
protozoa
and
bacteria.

In
addition
to
this
guidance
manual,
EPA
developed
the
UV
Disinfection
Guidance
Manual
that
contains
detailed
information
of
the
design
and
operation
of
UV
systems
and
the
validation
testing
that
must
be
conducted
for
compliance
with
the
LT2ESWTR.
This
chapter
summarizes
the
requirements
for
water
systems
using
UV
disinfection
to
achieve
compliance
with
the
LT2ESWTR.

13.2
Log
Inactivation
Requirements
To
receive
credit
for
disinfection
with
UV
light,
the
LT2ESWTR
(
40
CFR
141,
Subpart
W,
Appendix
D)
requires
utilities
to
demonstrate
through
validation
testing
that
the
UV
reactor
can
deliver
the
required
UV
dose.
The
testing
must
determine
a
range
of
operating
conditions
that
can
be
monitored
by
the
system
and
under
which
the
reactor
delivers
the
required
UV
dose.
EPA
developed
UV
dose
requirements
for
Cryptosporidium,
Giardia,
and
virus
that
are
used
during
the
validation
process
(
see
UV
Disinfection
Guidance
Manual
for
dose
requirements
and
application
during
validation).

Validation
testing
is
not
intended
to
be
site­
specific,
rather
product­
specific.
As
a
result,
validation
testing
will
likely
be
conducted
by
the
manufacturer
or
third
party
and
tested
over
a
range
of
water
quality
and
flow
conditions.
As
long
as
the
water
system
operates
within
those
conditions
tested,
they
are
achieving
the
log
inactivation
credit
demonstrated
during
the
validation
testing.

13.2.1
Monitoring
Requirements
In
addition
to
reactor
validation,
the
LT2ESWTR
(
40
CFR
141.729(
d))
requires
utilities
to
monitor
for
parameters
necessary
to
demonstrate
compliance
with
the
operating
conditions
that
were
validated
for
the
required
UV
dose.
At
a
minimum,
utilities
must
monitor
each
reactor
for
flow
rate,
lamp
outage,
UV
intensity
as
measured
by
a
UV
sensor,
and
any
other
parameters
required
by
the
State.
Chapter
13
­
Ultraviolet
Light
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
13­
2
13.2.2
Reporting
Requirements
The
LT2ESWTR
requires
utilities
to
report
the
following
(
40
CFR
141.730):

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

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

13.3
Toolbox
Selection
Considerations
 
Advantages
and
Disadvantages
There
are
several
advantages
to
using
UV
disinfection
over
other
technologies
for
the
inactivation
of
Cryptosporidium.
UV
is
a
relatively
simple
to
use
and
highly
effective
technology
for
inactivating
Cryptosporidium.
Its
main
advantages
include:

°
Ability
to
achieve
up
to
3
log
Cryptosporidium
inactivation
credit
at
relatively
low
operating
costs
°
Low
cost
technology
for
inactivation
of
Cryptosporidium,
relative
to
other
toolbox
options
for
disinfection
°
Produces
no
halogenated
disinfection
byproducts
°
Easy
to
install
and
requires
minimal
operator
attention
or
experience
The
disadvantages
of
UV
disinfection
include:

°
A
higher
dose
is
required
to
inactivate
virus.
If
a
water
system
is
seeking
to
obtain
4
log
virus
inactivation
with
UV
disinfection,
operating
costs
will
be
higher,
possibly
offsetting
the
lower
capital
costs.

°
Does
not
provide
a
residual
disinfectant
to
guard
against
regrowth
or
contamination
in
the
distribution
system.

°
Lamp
start­
up
time
after
a
power
outage
can
be
long,
at
which
time
the
UV
system
is
not
operating
within
validated
conditions
and
thus,
not
achieving
the
given
log
inactivation
credit.
Chapter
13
­
Ultraviolet
Light
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
13­
3
13.4
Design
and
Operational
Considerations
A
UV
disinfection
system
consists
of
the
UV
reactor
and
a
control
panel.
The
reactor
consists
of
UV
lamps,
quartz
sleeves,
UV
intensity
sensors,
quartz
sleeve
wipers,
and
temperature
sensors.
The
quartz
sleeves
serve
to
insulate
and
protect
the
lamps.
Some
reactors
come
with
automatic
cleaning
mechanisms
for
the
quartz
sleeves.
Reactors
are
equipped
with
UV
intensity
monitors,
flow
meters,
and
occasionally
UV
transmittance
meters
to
measure
the
dose
being
delivered.
There
are
two
primary
types
of
lamps
available,
low­
pressure
and
medium­
pressure.
Low­
pressure
lamps
emit
light
at
one
wavelength
(
i.
e.,
monochromatic)
and
operate
with
the
mercury
under
a
vacuum.
Medium­
pressure
lamps
are
polychromatic
and
operate
at
higher
temperatures
with
the
mercury
at
pressures
of
100
to
10,000
Torr.

When
considering
UV
disinfection
as
a
treatment
option
the
following
design
and
operational
issues
should
be
addressed:

°
Source
water
quality
­
Fouling
of
the
lamp
sleeves
and
other
reactor
equipment
will
affect
the
frequency
of
cleaning
required
and
type
of
cleaning
system.
Fouling
is
dependent
on
hardness,
alkalinity,
lamp
temperature,
pH,
and
certain
inorganic
constituents
(
e.
g.,
iron
and
calcium).

°
Power
quality
­
The
lamps
operate
continuously
and
as
long
as
there
is
power
to
the
lamps.
The
quality
of
power
supply
should
be
considered
with
UV
systems.
When
the
lamp
loses
power,
even
on
the
order
of
seconds,
it
requires
several
minutes
to
recharge,
at
which
time
no
disinfection
is
occurring.
An
uninterruptible
power
supply
(
UPS)
is
often
recommended
for
UV
systems
to
supply
backup
power
during
short
power
interruptions.

°
Hydraulic
needs
and
limitations
­
Headloss
through
a
UV
system
is
dependent
on
the
specific
reactor,
piping
configuration,
and
flow
rate.
Typical
headloss
ranges
from
0.5
to
3.0
feet.

°
Maintenance
­
Although
maintenance
requirements
are
low
relative
to
other
treatment
processes,
the
UV
system
will
need
to
be
taken
off­
line
periodically
to
inspect
and
clean
lamps
and
sleeves.
