021.01 Bag and
Cartridge Filters
Systems receive Cryptosporidium treatment
credit of up to 2.0-log for individual bag or cartridge filters and up to
2.5-log for bag or cartridge filters operated in series by meeting the
following criteria. To be eligible for this credit, systems must report the
results of challenge testing that meets the requirements of 179 NAC 25-021.01
items 2 through 9 to the Department. The filters must treat the entire plant
flow taken from a surface water or ground water under the direct influence of
surface water source.
1. The
Cryptosporidium treatment credit awarded to bag or cartridge
filters must be based on the removal efficiency demonstrated during challenge
testing that is conducted according to the criteria in 179 NAC 25-021.01 items
2 through 9. A factor of safety equal to 1-log for individual bag or cartridge
filters and 0.5-log for bag or cartridge filters in series must be applied to
challenge testing results to determine removal credit. Systems may use results
from challenge testing conducted prior to January 5, 2006 if the prior testing
was consistent with the criteria specified in 179 NAC 25-021.01 items 2 through
9.
2. Challenge testing must be
performed on full-scale bag or cartridge filters, and the associated filter
housing or pressure vessel, that are identical in material and construction to
the filters and housings the system will use for removal of
Cryptosporidium. Bag or cartridge filters must be challenge
tested in the same configuration that the system will use, either as individual
filters or as a series configuration of filters.
3. Challenge testing must be conducted using
Cryptosporidium or a surrogate that is removed no more
efficiently than Cryptosporidium. The microorganism 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 microorganism or
surrogate used in the test; gross measurements such as turbidity may not be
used.
4. The maximum feed water
concentration that can be used during a challenge test must be based on the
detection limit of the challenge particulate in the filtrate (i.e., filtrate
detection limit) and must be calculated using the following equation:
Maximum Feed Concentration = 1 x
104 x (Filtrate Detection Limit)
5. Challenge testing must be conducted at the
maximum design flow rate for the filter as specified by the
manufacturer.
6. Each filter
evaluated must be tested for a duration sufficient to reach 100% of the
terminal pressure drop, which establishes the maximum pressure drop under which
the filter may be used to comply with the requirements of this
chapter.
7. Removal efficiency of a
filter must be determined from the results of the challenge test and expressed
in terms of log removal values using the following equation:
LRV = LOG10(Cf)
- LOG10(Cp)
Where:
LRV = log removal value demonstrated during challenge
testing; Cf = the feed concentration measured during the
challenge test; and Cp = the filtrate concentration
measured during the challenge test. In applying this equation, the same units
must be used for the feed and filtrate concentrations. If the challenge
particulate is not detected in the filtrate, then the term
Cp must be set equal to the detection limit.
8. Each filter tested must be
challenged with the challenge particulate during three periods over the
filtration cycle: within two hours of start-up of a new filter; when the
pressure drop is between 45% and 55% of the terminal pressure drop; and at the
end of the cycle after the pressure drop has reached 100% of the terminal
pressure drop. An LRV must be calculated for each of these challenge periods
for each filter tested. The LRV for the filter
(LRVfilter) must be assigned the value of the minimum
LRV observed during the three challenge periods for that filter.
9. If fewer than 20 filters are tested, the
overall removal efficiency for the filter product line must be set equal to the
lowest LRVfilter among the filters tested. If 20 or more
filters are tested, the overall removal efficiency for the filter product line
must be set equal to the 10th percentile of the set
of LRVfilter values for the various filters tested. The
percentile is defined by [i/(n+1)] where i is the rank of n individiual data
points ordered lowest to highest. If necessary, the
10th percentile may be calculated using linear
interpolation.
10. If a previously
tested filter is modified in a manner that could change the removal efficiency
of the filter product line, challenge testing to demonstrate the removal
efficiency of the modified filter must be conducted and submitted to the
Department.
021.02
Membrane Filtration
25-021.02A Systems
receive
Cryptosporidium treatment credit for membrane
filtration that meets the criteria of this paragraph. Membrane cartridge
filters that meet the definition of membrane filtration in 179 NAC
25-002 are eligible for this credit.
The level of treatment credit a system receives is equal to the lower of the
values determined under item 1 or 2 below:
1.
The removal efficiency demonstrated during challenge testing conducted under
the conditions in 179 NAC
25-021.02B.
2. The maximum removal efficiency that can be
verified through direct integrity testing used with the membrane filtration
process under the conditions in 179 NAC
25-021.02C.
25-021.02B
Challenge
Testing: The membrane used by the system must undergo challenge
testing to evaluate removal efficiency, and the system must report the results
of challenge testing to the Department. Challenge testing must be conducted
according to the following criteria. Systems may use data from challenge
testing conducted prior to January 5, 2006 if the prior testing was consistent
with the following criteria.
1. Challenge
testing must be conducted on either a full-scale membrane module, identical in
material and construction to the membrane modules used in the system's
treatment facility, or a smaller-scale membrane module, identical in material
and similar in construction to the full-scale module. A module is defined as
the smallest component of a membrane unit in which a specific membrane surface
area is housed in a device with a filtrate outlet structure.
2. Challenge testing must be conducted using
Cryptosporidium oocysts or a surrogate that 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, in both the feed
and filtrate water, must be determined using a method capable of discretely
quantifying the specific challenge particulate used in the test; gross
measurements such as turbidity may not be used.
3. The maximum feed water concentration that
can be used during a challenge test is based on the detection limit of the
challenge particulate in the filtrate and must be determined according to the
following equation:
Maximum Feed Concentration = 3.16 x
106 x (Filtrate Detection Limit)
4. Challenge testing must be conducted under
representative hydraulic conditions at the maximum design flux and maximum
design process recovery specified by the manufacturer for the membrane module.
Flux is defined as the throughput of a pressure driven membrane process
expressed as flow per unit of membrane area. Recovery is defined as the
volumetric percent of feed water that is converted to filtrate over the course
of an operating cycle uninterrupted by events such as chemical cleaning or a
solids removal process (i.e., backwashing).
5. Removal efficiency of a membrane module
must be calculated from the challenge test results and expressed as a log
removal value according to the following equation:
LRV = LOG10(Cf)
- LOG10(Cp)
Where:
LRV = log removal value demonstrated during the challenge
test; Cf = the feed concentration measured during the
challenge test; and Cp = the filtrate concentration
measured during the challenge test. Equivalent units must be used for the feed
and filtrate concentrations. If the challenge particulate is not detected in
the filtrate, the term Cp is set equal to the detection
limit for the purpose of calculating the LRV. An LRV must be calculated for
each membrane module evaluated during the challenge test.
6. The removal efficiency of a membrane
filtration process demonstrated during challenge testing must be expressed as a
log removal value (LRVC-Test). If fewer than 20 modules
are tested, then LRVC-Test is equal to the lowest of the
representative LRVs among the modules tested. If 20 or more modules are tested,
then LRVC-Test is equal to the 10th
percentile of the representative LRVs among the modules tested.
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
10th percentile may be calculated using linear
interpolation.
7. The challenge
test must establish a quality control release value (QCRV) for a
non-destructive performance test that demonstrates the Cryptosporidium
removal capability of the membrane filtration module. This performance
test must be applied to each production membrane module used by the system that
was not directly challenge tested in order to verify Cryptosporidium
removal capability. Production modules that do not meet the
established QCRV are not eligible for the treatment credit demonstrated during
the challenge test.
8. If a
previously tested membrane is modified in a manner that could change the
removal efficiency of the membrane or the applicability of the non-destructive
performance test and associated QCRV, additional challenge testing to
demonstrate the removal efficiency of, and determine a new QCRV for, the
modified membrane must be conducted and submitted to the Department.
25-021.02C
Direct
Integrity Testing: Systems must conduct direct integrity testing
in a manner that demonstrates a removal efficiency equal to or greater than the
removal credit awarded to the membrane filtration process and meets the
following requirements. A direct integrity test is defined as a physical test
applied to a membrane unit in order to identify and isolate integrity breaches
(i.e., one or more leaks that could result in contamination of the filtrate).
1. The direct integrity test must be
independently applied to each membrane unit in service. A membrane unit is
defined as a group of membrane modules that share common valving that allows
the unit to be isolated from the rest of the system for the purpose of
integrity testing or other maintenance.
2. The direct integrity method must have a
resolution of three micrometers or less, where resolution is defined as the
size of the smallest integrity breach that contributes to a response from the
direct integrity test.
3. The
direct integrity test must have a sensitivity sufficient to verify the log
treatment credit awarded to the membrane filtration process by the Department,
where sensitivity is defined as the maximum log removal value that can be
reliably verified by a direct integrity test. Sensitivity must be determined
using the approach in either a. or b. below as applicable to the type of direct
integrity test the system uses.
a. For direct
integrity tests that use an applied pressure or vacuum, the direct integrity
test sensitivity must be calculated according to the following equation:
LRVDIT = LOG10
[Qp/(VCF x Qbreach)]
Where:
LRVDIT = the sensitivity of the direct
integrity test; Qp = total design filtrate flow from the
membrane unit; Qbreach = flow of water from an integrity
breach associated with the smallest integrity test response that can be
reliably measured, and VCF = volumetric concentration factor. The volumetric
concentration factor is the ratio of the suspended solids concentration on the
high pressure side of the membrane relative to that in the feed water.
b. For direct integrity tests that
use a particulate or molecular marker, the direct integrity test sensitivity
must be calculated according to the following equation:
LRVDIT =
LOG10(Cf) -
LOG10(Cp)
Where
LRVDIT = the sensitivity of the direct
integrity test; Cf = the typical feed concentration of
the marker used in the test; and Cp = the filtrate
concentration of the marker from an integral membrane unit.
4. Systems must establish a
control limit within the sensitivity limits of the direct integrity test that
is indicative of an integral membrane unit capable of meeting the removal
credit awarded by the Department.
5. If the result of a direct integrity test
exceeds the control limit established under 179 NAC
25-021.02C item
4, the system must remove the membrane unit from service. Systems must conduct
a direct integrity test to verify any repairs, and may return the membrane unit
to service only if the direct integrity test is within the established control
limit.
6. Systems must conduct
direct integrity testing on each membrane unit at a frequency of not less than
once each day that the membrane unit is in
operation. The Department may approve less frequent testing,
based on demonstrated process reliability, the use of multiple barriers
effective for Cryptosporidium or reliable process
safeguards.
25-021.02D
Indirect Integrity
Monitoring: Systems must conduct continuous indirect integrity
monitoring on each membrane unit according to the following criteria. Indirect
integrity monitoring is defined as monitoring some aspect of filtrate water
quality that is indicative of the removal of particulate matter. A system that
implements continuous direct integrity testing of membrane units in accordance
with the criteria in 179 NAC
25-021.02C items
1 through 5 is not subject to the requirements for continuous indirect
integrity monitoring. Systems must submit a monthly report to the Department
summarizing all continuous indirect integrity monitoring results triggering
direct integrity testing and the corrective action that was taken in each case.
1. Unless the Department approves an
alternative parameter, continuous indirect integrity monitoring must include
continuous filtrate turbidity monitoring.
2. Continuous monitoring must be conducted at
a frequency of no less than once every 15 minutes.
3. Continuous monitoring must be separately
conducted on each membrane unit.
4.
If indirect integrity monitoring includes turbidity and if the filtrate
turbidity readings are above 0.15 NTU for a period greater than 15 minutes
(i.e., two consecutive 15-minute readings above 0.15 NTU) direct integrity
testing must immediately be performed on the associated membrane unit as
specified in 179 NAC
25-021.02C items
1 through 5.
5. If indirect
integrity monitoring includes a Department-approved alternative parameter and
if the alternative parameter exceeds a Department-approved control limit for a
period greater than 15 minutes, direct integrity testing must immediately be
performed on the associated membrane units as specified in 179 NAC
25-021.02C items
1 through 5.
021.03 Second Stage Filtration
Systems receive 0.5-log Cryptosporidium
treatment credit for a separate second stage of filtration that
consists of sand, dual media, granular activated carbon (GAC), or other fine
grain media following granular media filtration if the Department approves. To
be eligible for this credit, the first stage of filtration must be preceded by
a coagulation step and both filtration stages must treat the entire plant flow
taken from a surface water or GWUDI source. A cap, such as GAC, on a single
stage of filtration is not eligible for this credit. The Department must
approve the treatment credit based on an assessment of the design
characteristics of the filtration process.
021.04 Slow Sand Filtration (as secondary
filter)
Systems are eligible to receive 2.5-log
Cryptosporidium treatment credit for a slow sand filtration
process that follows a separate stage of filtration if both filtration stages
treat entire plant flow taken from a surface water or GWUDI source and no
disinfectant residual is present in the influent water to the slow sand
filtration process. The Department must approve the treatment credit based on
an assessment of the design characteristics of the filtration process. This
paragraph does not apply to treatment credit awarded to slow sand filtration
used as a primary filtration process.
