Wis. Admin. Code Department of Natural Resources NR 811.45

Current through September 30, 2024

Section NR 811.45 - Aeration

Aeration treatment devices described in this section may be used for oxidation, separation of gases, or for taste and odor control. Air stripping towers shall meet the requirements of s. NR 811.53 (2), which can be used for the removal or reduction of some volatile organic compounds. The following requirements shall be met:

(1) NATURAL DRAFT AERATION. The design for natural draft aeration shall provide that:

(a) Water is distributed uniformly over the top tray.

(b) Water is discharged through a series of 3 or more trays with separation of trays not less than 6 inches.

(c) Trays are loaded at a rate of one to 5 gallons per minute for each square foot of total tray area.

(d) Trays have slotted, heavy woven wire mesh with 0.5-inch openings or perforated bottoms.

(e) Perforations are 3/16 to 1/2 inches in diameter, spaced one to 3 inches on center, when perforations are used.

(f) Construction is of durable material resistant to the aggressiveness of the water and dissolved gasses.

(g) Contamination from sources such as those listed is sub. (7) is minimized by providing down-turned, louvered or hooded, screened air inlet or outlet openings. Screens shall be constructed of 24-mesh corrosion resistant material.

(h) Exhaust air is discharged directly to the outside atmosphere and in a location that will be protective of public health.

(2) FORCED OR INDUCED DRAFT AERATION. The design for forced or induced draft aeration shall provide that:

(a) Water is distributed uniformly over the top tray.

(b) The blower and blower motor are weatherproof and are installed in a weather-tight, screened enclosure.

(c) There is an adequate countercurrent flow of air through the enclosed aeration column.

(d) Aerator trays are loaded at a rate of one to 5 gallons per minute for each square foot of total tray area.

(e) Water will discharge through a series of 5 or more trays with separation of trays not less than 6 inches or as approved by the department.

(f) Construction is of durable material resistant to the aggressiveness of the water and dissolved gasses.

(g) The aerator is insect-proof, watertight, and light-proof.

(h) The air intake is located above grade and the air introduced into the column is as free as possible from contamination sources such as those listed in sub. (7).

(i) The water outlet is adequately sealed to prevent unwanted loss of air.

(j) Interior and exterior sections of the aerator can be easily reached or removed for maintenance.

(k) The air inlet to the blower and the tower discharge vent shall meet all of the following requirements:

1. Be screened.

2. Be 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.

3. Be constructed of 24-mesh corrosion resistant material and installed at a location least susceptible to vandalism or damage.

4. Contain an air inlet that is provided with a dust filter.

(l) Exhaust air is discharged directly to the outside atmosphere and in a location that will be protective of public health.

(3) PRESSURE AERATION. Pressure aeration installations shall meet the following requirements:

(a) Pressure aeration may be used for oxidation purposes. Pressure aeration will not be approved for removal of dissolved gases.

(b) Filters following pressure aeration shall be provided with adequate exhaust devices for release of air.

(c) Pressure aeration devices shall be designed to cause a thorough mixing of compressed air with the water being treated.

(d) Pressure aeration devices shall provide screened and filtered air that is free of obnoxious fumes, dust, dirt, and other contaminants.

(e) Air compressors supplying pressure aerators shall be oil-less.

(3m) PACKED TOWER AERATION. Packed tower aeration systems shall meet all of the following requirements:

(a) Materials of construction shall meet all of the following requirements:

1. The packing material shall be certified by ANSI/NSF standard 61 dated March 15, 2022, which is incorporated by reference.

Note: A copy of ANSI/NSF standard 61 dated March 15, 2022 is available for inspection at the Legislative Reference Bureau and may be obtained for personal use from NSF International, https://www.nsf.org.

2. The tower shall be constructed of stainless steel, concrete, or aluminum.

(b) Process design shall meet all of the following requirements:

1. Water loading rates shall be in the range from 15 to 30 gallons per minute per square foot. Water loading rates outside of this range may be used if justified to the department by pilot testing under s. NR 811.44.

2. The ratio of the packing height to column 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 study.

3. The minimum volumetric air to water ratio at peak water flow shall be 25:1 and the maximum shall be 80:1. Air to water ratios outside of these ranges may be justified to the department by pilot testing under s. NR 811.44.

(c) The water flow system shall meet all of the following requirements:

1. Water shall be distributed uniformly at the top of the tower using spray nozzles or orifice-type distributer trays that prevent short circuiting.

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. Smooth-end sample faucets shall be provided on the influent and effluent piping.

5. The effluent sump shall have easy access for inspection and cleaning.

6. A pump to waste line shall be provided in the effluent piping to allow for discharge of water and chemicals used to clean the tower.

7. The design shall prevent freezing of the influent riser and effluent piping when the unit is not operating. If piping is buried, it shall be maintained under positive pressure higher than the ground surface.

8. The water flow to each tower shall be metered.

9. Include an overflow line that discharges 12 to 24 inches above a splash pad or drainage inlet. Proper drainage shall be provided to prevent flooding of the area.

10. Butterfly valves may be used in the water effluent line for better flow control and to minimize air entrainment.

11. Include means to prevent flooding of the air blower.

12. The water influent pipe shall be supported separately from the tower's main structural support.

(d) The air flow system shall meet all of the following requirements:

1. The air intake and outlet vent shall be protected with a 24-mesh corrosion resistant screen and cover and be accessible for maintenance and inspection.

2. The air inlet shall be in a location protected from airborne contaminants.

3. An air flow meter or an alternative method to determine air flow shall be provided on the influent air line.

4. A positive air flow sensing device and a pressure gauge shall be installed on the air influent line. The positive air flow sensing device shall be a part of an automatic control system that will turn off the influent water if positive air flow is not detected. The pressure gauge shall serve as an indicator of the fouling buildup. The backup motor for the air blower shall be readily available.

(e) Other design features shall meet all of the following requirements:

1. Include 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. Include a method of cleaning the packing material when fouling may occur.

3. Tower effluent collection and pumping wells shall be constructed to potable reservoir construction standards as required under subch. IX.

4. Include provisions for extending the tower height without major reconstruction.

5. Include disinfection application points both ahead of and after the tower to control biological growth.

6. Include disinfection and adequate contact time after the water has passed through the tower, prior to the distribution system.

7. Include adequate packing support to allow free flow of water and prevent deformation with deep packing heights.

8. Include adequate foundation to support the tower and lateral support to prevent overturning to wind loading.

9. Include protections to prevent vandalism to the tower.

10. Provide access of all components of the tower, including the exhaust port and demister.

11. The operation of the blower and chemical feed pump shall be interlocked with the operation of the appropriate well or service pump.

(4) OTHER METHODS OF AERATION. Other methods of aeration may be approved by the department only if a pilot plant study conducted in accordance with s. NR 811.44 demonstrates the method's effectiveness. Methods include spraying, diffused air, and mechanical aeration. The treatment processes shall be designed to meet the particular needs of the water to be treated.

(5) DISINFECTION. Aerated water other than from pressure aeration shall receive continuous disinfection treatment. A corporation stop shall be provided on the inlet piping to all non-pressure aerators to allow disinfection for emergency or maintenance purposes.

(6) PROTECTION FROM WIND. Aerators that discharge through the atmosphere shall be protected by being placed in a louvered enclosure designed to provide easy access to the interior.

(7) PROTECTION FROM CONTAMINATION. Aerators that are used for oxidation or removal of dissolved gases from waters that will be given no further treatment other than chlorination shall be protected from contamination from insects and birds, obnoxious fumes, all types of precipitation and condensation, and windborne debris or dust.

(8) BYPASS PIPING. Bypass piping and any associated valves or other appurtenances shall be installed to allow water to be bypassed around a non-pressure aerator unless the aerator is necessary to comply with primary maximum contaminant levels or the requirement is waived by the department because the water system has access to other water sources that can provide at least an average day supply of water.

(9) REDUNDANCY. Redundant aeration systems shall be provided for units installed to comply with primary maximum contaminant levels unless the requirement is waived by the department because the water system has access to other water sources that can provide at least an average day supply of water.

(10) WATER QUALITY. A metal smooth-end sampling faucet installed on the aerator outlet piping and test equipment shall be provided to test for appropriate water quality parameters following aeration such as dissolved oxygen, pH, iron, manganese, radon gas, and carbon dioxide when required by the department to insure proper operation of the aeration equipment.

Wis. Admin. Code Department of Natural Resources NR 811.45

CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10.

Amended by, CR 22-074: am. (1) (e), r. and recr. (2) (k), cr. (3m) Register January 2024 No. 817, eff. 2/1/2024