Aeration

Aeration. 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. 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.