Wisconsin Administrative Code › Department of Natural Resources › NR 800 - Environmental Protection - Water Supply › Chapter NR 811 - Requirements For The Operation And Design Of Community Water Systems › Subchapter VII - Treatment › Section NR 811.53 - Organics removal

Current through June 24, 2024
(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.