(1) BAG OR
CARTRIDGE FILTERS. Public water 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 criteria
in pars. (a) to (j). To be eligible for this credit, water suppliers for
systems shall report the results of challenge testing that meets the
requirements of pars. (b) to (i) to the department. The filters shall treat the
entire plant flow taken from a surface water or GWUDI source.
(a) The Cryptosporidium treatment credit
awarded to bag or cartridge filters shall be based on the removal efficiency
demonstrated during challenge testing that is conducted according to the
criteria in pars. (b) to (i). 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
shall 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 pars.
(b) to (i).
(b) Challenge testing
shall 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 shall be challenge tested in the same
configuration that the system will use, either as individual filters or as a
series configuration of filters.
(c) Challenge testing shall 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 shall 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.
(d) The maximum feed water concentration that
can be used during a challenge test shall be based on the detection limit of
the challenge particulate in the filtrate, including filtrate detection limit,
and shall be calculated using the following equation:
Maximum Feed Concentration = 1 x 104 x (Filtrate Detection
Limit)
(e) Challenge
testing shall be conducted at the maximum design flow rate for the filter as
specified by the manufacturer.
(f)
Each filter evaluated shall 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.
(g) Removal efficiency of
a filter shall 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 shall be used for the feed and filtrate
concentrations. If the challenge particulate is not detected in the filtrate,
then the term Cp shall be set equal to the detection limit.
(h) Each filter tested shall be challenged
with the challenge particulate during 3 periods over the filtration cycle:
within 2 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 shall
be calculated for each of these challenge periods for each filter tested. The
LRV for the filter (LRV filter) shall be assigned the value of the minimum LRV
observed during the 3 challenge periods for that filter.
(i) If fewer than 20 filters are tested, the
overall removal efficiency for the filter product line shall be set equal to
the lowest LRV filter among the filters tested. If 20 or more filters are
tested, the overall removal efficiency for the filter product line shall be set
equal to the 10th percentile of the set of LRV filter values for the various
filters 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.
(j) 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 shall be conducted and submitted to the department.
(2) MEMBRANE FILTRATION.
(a)
Definitions. In this
subsection:
1. "Flux" means the throughput of
a pressure driven membrane process expressed as flow per unit of membrane
area.
2. "Module" means the
smallest component of a membrane unit in which a specific membrane surface area
is housed in a device with a filtrate outlet structure.
3. "Recovery" means 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
such as backwashing.
(b)
Removal credit. 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
s.
NR 810.02(27) are eligible for this
credit. The level of treatment credit a system receives is equal to the lower
of the values determined under the following:
1. The removal efficiency demonstrated during
challenge testing conducted under the conditions in par. (b).
2. The maximum removal efficiency that can be
verified through direct integrity testing used with the membrane filtration
process under the conditions in par. (c).
(c)
Challenge testing. The
membrane used by the system shall undergo challenge testing to evaluate removal
efficiency, and the water supplier for the system shall report the results of
challenge testing to the department. Challenge testing shall be conducted
according to the criteria in subds. 1 to 7. 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 shall 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.
2. Challenge testing shall 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, shall 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 may be used during a challenge test is based on the
detection limit of the challenge particulate in the filtrate and shall be
determined according to the following equation:
Maximum Feed Concentration = 3.16 x 106 x (Filtrate
Detection Limit)
4.
Challenge testing shall be conducted under representative hydraulic conditions
at the maximum design flux and maximum design process recovery specified by the
manufacturer for the membrane module.
5. Removal efficiency of a membrane module
shall 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
shall 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 shall be
calculated for each membrane module evaluated during the challenge test.
6. The removal efficiency of a
membrane filtration process demonstrated during challenge testing shall 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 shall 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 shall 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 shall be conducted and
submitted to the department.
(d)
Direct integrity
testing. Systems shall 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 requirements
described in subds. 1. to 6. In this subsection, a direct integrity test means
a physical test applied to a membrane unit in order to identify and isolate
integrity breaches, including one or more leaks that could result in
contamination of the filtrate.
1. The direct
integrity test shall 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 shall have a
resolution of 3 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 shall 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 shall be determined using the
approach in either this subd. 3. a. or b. 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 shall 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 shall 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 shall
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 subd. 4., the system shall remove
the membrane unit from service. Systems shall 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 shall conduct direct integrity
testing on each membrane unit at a frequency of not less than 3 times 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.
(e)
Indirect integrity monitoring. Systems shall conduct continuous
indirect integrity monitoring on each membrane unit according to the criteria
in subds. 1. to 5. In this subsection, indirect integrity monitoring means
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 par. (d)
1. to 5. is not subject to the requirements for continuous indirect integrity
monitoring. Water suppliers for systems shall 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 shall
include continuous filtrate turbidity monitoring.
2. Continuous monitoring shall be conducted
at a frequency of no less than once every 15 minutes.
3. Continuous monitoring shall 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, or
2 consecutive 15-minute readings above 0.15 NTU, direct integrity testing shall
immediately be performed on the associated membrane unit as specified in par.
(d) 1. to 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 shall immediately be
performed on the associated membrane units as specified in par. (d) 1. to
5.
(3) SECOND
STAGE FILTRATION. Public water systems receive 0.5 -log Cryptosporidium
treatment credit for a separate second stage of filtration that consists of
sand, dual media, 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 shall be preceded by a coagulation step and both
filtration stages shall 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 shall approve the treatment credit
based on an assessment of the design characteristics of the filtration
process.
(4) SLOW SAND FILTRATION
AS SECONDARY FILTER. Public water 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 shall approve the treatment credit based on an assessment of the
design characteristics of the filtration process. This subsection does not
apply to treatment credit awarded to slow sand filtration used as a primary
filtration process.
