(1) GENERAL REQUIREMENTS. Organic compounds
may be removed by a variety of processes. All process designs shall be based on
information from a pilot study conducted in accordance with s.
NR 811.44 with the compounds to be removed unless the
pilot study is waived by the department. Unless the department approves other
requirements, the processes shall be designed to remove a minimum of 99% of the
contaminant in question.
(2) PACKED
TOWER AERATION. Packed tower aeration units shall meet the following
requirements:
(a)
General.
Packed tower aeration, which is also known as air stripping, may be used for
the removal of volatile organic chemicals, trihalomethanes, carbon dioxide, and
radon.
(b)
Process
design. The process design shall include determination of the Henry's
Constant for each contaminant, the mass transfer coefficient, air pressure
drop, and stripping factor. Justification shall be provided for the selected
design parameters including the height and other dimensions of the unit, air to
water ratio, packing specifications, packing depth, and surface loading rate.
1. Pilot testing considerations:
a. The pilot study shall evaluate a variety
of loading rates and air to water ratios at the peak contaminant concentration.
Special consideration shall be given to removal efficiencies when multiple
contaminants occur.
b. If there is
adequate past performance data on the contaminant to be treated, including at
the peak contaminant concentration, the department may approve the process
design based on the appropriate calculations without pilot testing.
2. The installation shall be
designed to reduce contaminants to below the maximum contaminant level and to
the lowest practical level.
3. The
packing material shall be NSF/ANSI Standard 61 approved for use in potable
water in accordance with s.
NR 810.09 (5). The packing material shall be resistant
to the aggressiveness of the water, dissolved gasses, any chemicals added to
the water supply, and any cleaning materials.
4. The packing tower shall be constructed of
materials compatible with potable water including stainless steel, reinforced
concrete, aluminum, reinforced fiberglass, or plastic. The tower construction
materials shall be resistant to the aggressiveness of the water, dissolved
gasses, any chemicals added to the water supply, and any cleaning materials.
Towers constructed of light weight materials shall be provided with adequate
support to prevent damage from wind.
5. The ratio of the column diameter to the
packing diameter shall be at least 7:1 for the pilot unit and at least 10:1 for
the full scale tower. The type and size of the packing used in the full scale
unit shall be the same as that used in the pilot unit.
6. The blower shall be adequately sized to
provide sufficient air to achieve the desired removal rates. The minimum
volumetric air to water ratio at the maximum water flow rate shall be 25:1. The
maximum air to water ratio shall not exceed 80:1.
7. The design shall give consideration to
potential fouling problems from calcium carbonate, iron and manganese
precipitation, and from bacterial growth. Pretreatment shall be provided where
necessary to prevent significant fouling. Disinfection capability shall be
provided immediately before and after packed tower aeration.
8. The effects of temperature shall be
considered in the process design as a drop in water temperature can result in a
drop in contaminant removal efficiency.
(c)
Water flow system.
1. Water shall be distributed uniformly at
the top of the tower using spray nozzles or orifice-type distributor trays that
prevent short circuiting. For multi-point injection, a minimum of one injection
point for every 30 square inches of tower cross-sectional area shall be
installed.
2. A mist eliminator
shall be provided above the water distributor system.
3. A side wiper redistribution ring shall be
provided at least every 10 feet in order to prevent water channeling along the
tower wall and short circuiting.
4.
Sample faucets shall be provided on the tower inlet and outlet
piping.
5. An outlet sump, if
provided, shall be accessible for cleaning purposes and be equipped with a
drain valve. The drain shall not be directly connected to a storm or sanitary
sewer.
6. A drain fitting shall be
installed in the outlet piping to allow for the discharge of water and any
chemicals used to clean the tower. The drain shall not be directly connected to
a storm or sanitary sewer.
7. The
design shall prevent freezing of the inlet riser, tower, and the outlet piping
when the unit is not operating.
8.
All buried piping shall be maintained under a positive pressure greater than
the elevation of the ground surface.
9. The water flow to each tower shall be
metered.
10. Consideration shall be
given to installing a butterfly valve in the inlet piping to control the water
flow rate and to minimize air entrainment.
11. A means shall be provided to prevent
flooding of the air blower.
12. The
inlet piping shall be supported separately from the tower's main structural
support.
(d)
Air
flow system.1. The air inlet shall
be installed in a protected location.
2. The air inlet to the blower and the tower
discharge vent shall be screened and provided with a downturned, hooded or
mushroom cap that protects the screen from the entrance of extraneous matter
including insects and birds, obnoxious fumes, all types of precipitation and
condensation, and windborne debris or dust. The screens shall be constructed of
24-mesh corrosion resistant material and installed at a location least
susceptible to vandalism or damage. The air inlet shall also be provided with a
dust filter.
Note: It is recommended that a 4-mesh
corrosion resistant screen be installed in front of the 24-mesh screen on the
air inlet system.
3. The
blower shall be provided with a weather-proof motor, a tight housing, and an
adequate foundation.
4. An air flow
meter or department approved alternative method for determining the air flow
shall be installed on the air inlet piping.
5. A positive air flow sensing device and a
pressure gauge shall be installed on the air inlet line to the tower. If
positive air flow is not detected, the device shall automatically shut down the
water flow.
6. A backup motor for
the blower shall be readily available where the tower is used to maintain
primary drinking water standards.
(e)
Other requirements.
1. The tower shall be provided with a
sufficient number of access ports with a minimum diameter of 24 inches to
facilitate inspection, media replacement, media cleaning, and maintenance of
the interior.
2. A means shall be
provided for cleaning the packing material should it become fouled.
3. Any clearwell or reservoir constructed to
receive water from a tower shall be constructed to meet the potable water
reservoir requirements of s.
NR 811.64.
4.
The tower shall be designed and constructed so that it can be extended without
major reconstruction.
5. A means of
bypassing the tower shall be provided unless the requirement is waived by the
department because the water system has access to other water sources that can
provide an average day supply of water at minimum.
6. Disinfection application points shall be
provided on the tower inlet and outlet piping.
7. Any water passed through the tower shall
be continuously disinfected. If raw water has bacteriological issues, the
department may require a minimum of 4-log inactivation of viruses as determined
by the department on a case-by-case basis.
8. The water supply pump or pumps, blower
motor, disinfection equipment, and the positive air flow sensing device shall
be electrically interconnected to operate in series.
9. Adequate packing support shall be provided
to allow the free flow of water and to prevent packing deformation.
10. Adequate auxiliary power shall be
provided to operate the air blower and disinfection equipment during power
failures unless the requirement is waived by the department because the water
system has access to other water sources that can provide an average day supply
of water at minimum or operation of the tower is not mandatory to meet primary
drinking water standards.
11. The
tower shall be provided with an adequate foundation and lateral support to
prevent overturning due to wind loading.
12. The equipment shall be located within a
secure building or within a locked security fence to prevent
vandalism.
13. An access ladder
with safety cage shall be provided to allow access and inspection of all areas
of the tower.
14. Exhaust air shall
be discharged directly to the outside atmosphere and in a location that will be
protective of public health. Air emissions controls shall be provided if
necessary to meet air quality standards.
15. Noise control equipment shall be provided
where systems are located in residential areas.
(3) GRANULAR ACTIVATED CARBON FILTERS.
Granular activated carbon filter installations shall meet the following
requirements:
(a) The maximum filtration rate
for pressure filters shall be 6 gallons per minute per square foot of filter
area. The maximum filtration rate for gravity filters shall be 3 gallons per
minute per square foot of filter area. Higher rates may be justified based on
pilot studies for removal of the contaminant in question.
(b) The water from the carbon filter shall be
continuously disinfected.
(c) The
filter design shall provide for:
1. Loss of
head gauges on the inlet and outlet pipes of each filter.
2. A meter or flow indicator.
3. Adequate freeboard for backwashing based
on the specific gravity of the media.
4. An underdrain system to effectively
collect the filtered water and distribute the backwash water.
5. Backwash and air relief valves having
discharges that terminate in a free air break at least 24 inches above the
floor.
6. Smooth-end sampling
faucets on the inlet and outlet pipes of each filter.
7. The ability to conveniently inspect,
replace, or regenerate the media.
(d) The carbon used shall be virgin
carbon.
(e) Information supporting
selection of the carbon for removal of the contaminants in question shall be
provided to the department.
(f) A
plan for the disposal of the spent carbon shall be included in the
specifications. Disposal of spent granular activated carbon shall comply with
s.
NR 811.859.
(g) An assessment of the impacts of radon and
its decay products on operation, operator safety, and waste disposal shall be
provided to the department.