Section NR 811.53 - Organics removal(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.Wis. Admin. Code Department of Natural Resources NR 811.53
CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10.Amended by, CR 22-074: am. (2) (e) 7. Register January 2024 No. 817, eff. 2/1/2024