La. Admin. Code tit. 51 § XII-185

Current through Register Vol. 50, No. 11, November 20, 2024

Section XII-185 - Aeration

A. Aeration processes generally are used in two types of treatment applications. One is the transfer of a gas to water (e.g., adding oxygen to assist in iron and/or manganese removal) and is called gas absorption, or aeration. The second is the removal of gas from water (reduce or remove objectionable amounts of carbon dioxide, hydrogen sulfide, etc. or reduce the concentration of taste and odor-causing substances or removal of volatile organic compounds) and is classified as desorption or air stripping. The materials used in the construction of the aerator(s) shall meet NSF/ANSI 61 or be approved by the state health officer.

1. Natural Draft Aeration. Design shall provide:

a. perforations in the distribution pan 3/16 to 1/2 inches in diameter, spaced 1 to 3 inches on centers to maintain a six inch water depth;

b. for distribution of water uniformly over the top tray;

c. discharge through a series of three or more trays with separation of trays not less than 12 inches;

d. loading at a rate of 1 to 5 gallons per minute for each square foot of total tray area (2.5 - 12.5 m/hr);

e. trays with slotted, heavy wire (1/2 inch openings) mesh or perforated bottoms;

f. construction of durable material resistant to aggressiveness of the water and dissolved gases; and

g. protection from insects by 24-mesh screen when used in applications where the water will not be subject to open vessels in downstream treatment processes.

2. Forced or Induced Draft Aeration. Devices shall be designed to:

a. insure adequate counter current of air through the enclosed aerator column;

b. exhaust air directly to the outside atmosphere;

c. include a down-turned air outlet and inlet. Protection from insects by 24-mesh screen when used in applications where the water will not be subject to open vessels in downstream treatment processes;

d. be such that air introduced in the column shall be as free from obnoxious fumes, dust, and dirt as possible;

e. be such that sections of the aerator can be easily reached or removed for maintenance of the interior or installed in a separate aerator room;

f. provide loading at a rate of 1 to 5 gallons per minute for each square foot of total tray area (2.5 - 12.5 m/hr);

g. insure that the water outlet is adequately sealed to prevent unwarranted loss of air;

h. when trays are used, discharge through a series of five or more trays with separation of trays not less than six inches or as approved by the state health officer;

i. provide distribution of water uniformly over the top tray; and

j. be of durable material resistant to the aggressiveness of the water and dissolved gases.

3. Spray Aeration. Design shall provide:

a. a hydraulic head of between 5 - 25 feet;

b. nozzles, with the size, number, and spacing of the nozzles being dependent on the flowrate, space, and the amount of head available;

c. nozzle diameters in the range of 1 to 1.5 inches to minimize clogging; and

d. an enclosed basin to contain the spray. Any openings for ventilation, etc. shall be protected from insects by 24-mesh screen when used in applications where the water will not be subject to open vessels in downstream treatment processes.

4. Pressure Aeration. Pressure aeration shall be used for oxidation and biological filtration purposes only. Filters following pressure aeration must have adequate exhaust devices for release of air. Pressure aeration devices shall be designed to:

a. give thorough mixing of compressed air with water being treated; and

b. provide screened and filtered air, free of obnoxious fumes, dust, dirt and other contaminants.

5. Packed Tower Aeration. Packed tower aeration (PTA) which is also known as air stripping involves passing water down through a column of packing material while pumping air counter-currently up through the packing. PTA is used for the removal of volatile organic chemicals, trihalomethanes, carbon dioxide, and radon.

a. Process design for PTA includes the following.

i. The tower shall be designed to reduce contaminants to below the maximum contaminant level (MCL).

ii. The ratio of the packing height to column diameter should 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 work.

iii. The minimum volumetric air to water ratio at peak water flow should be 25:1 and the maximum should be 80:1. Air to water ratios outside these ranges should not be used without prior approval from the state health officer.

iv. The design shall consider potential fouling problems from calcium carbonate and iron precipitation and from bacterial growth

b. Materials of Construction. The tower shall be constructed of a material that is suitable for contact with the water being treated. Packing materials shall be resistant to the aggressiveness of the water, dissolved gases and cleaning materials and shall be suitable for contact with potable water.

c. Water Flow System. Design of the water flow system includes the following.

i. Water should be distributed uniformly at the top of the tower using spray nozzles or orifice-type distributor trays that prevent short circuiting.

ii. A mist eliminator shall be provided above the water distributor system.

iii. 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.

iv. Sample taps shall be provided in the influent and effluent piping.

v. The effluent sump, if provided, shall have easy access for cleaning purposes and be equipped with a drain valve. The drain shall not be connected directly to any storm or sanitary sewer.

vi. A blow-off line should be provided in the effluent piping to allow for discharge of water/chemicals used to clean the tower.

vii. A means of measuring the water flow to each tower shall be provided.

viii. An overflow line shall be provided which discharges 12 to 14 inches above a splash pad or drainage inlet. Proper drainage shall be provided to prevent flooding of the area.

ix. Means shall be provided to prevent flooding of the air blower.

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

d. Air Flow System. Design of the air flow system includes the following.

i. The air inlet to the blower and the tower discharge vent shall be downturned and protected with a non-corrodible 24-mesh screen to prevent contamination from extraneous matter.

ii. The air inlet shall be in a protected location.

iii. A means of ensuring that air is being provided when water is being delivered to the air strippers shall be provided.

e. The following features shall be provided.

i. 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.

ii. A method of cleaning the packing material when fouling may occur.

iii. An acceptable alternative treatment shall be available during periods of maintenance and operation interruptions when used for treatment of a primary contaminant. No bypass shall be provided unless specifically approved by the state health officer.

iv. Disinfection application points ahead of the tower to control biological growth.

v. Adequate packing support to allow free flow of water and to prevent deformation with deep packing heights.

6. Other Methods of Aeration. Other methods of aeration may be used if applicable to the treatment needs. Such methods include but are not restricted to spraying, diffused air, cascades and mechanical aeration. The treatment processes shall be designed to meet the particular needs of the water to be treated and are subject to the approval of the state health officer.

7. Protection of Aerators. All aerators except those discharging to lime softening or clarification plants shall be protected from contamination by birds, insects, wind borne debris, rainfall and water draining off the exterior of the aerator.

8. Bypass. A bypass should be provided for all aeration units except those installed to comply with maximum contaminant levels.

9. Redundancy. Redundant equipment shall be provided for units installed to comply with the Safe Drinking Water Act primary contaminants, unless otherwise approved by the state health officer.

La. Admin. Code tit. 51, § XII-185

Promulgated by the Department of Health, Office of Public Health, LR 44324 (2/1/2018), effective 8/1/2018.

AUTHORITY NOTE: Promulgated in accordance with the provisions of R.S. 40:4.A.(8), 40:4.13.D.(1)(2) and 40:5.A.(2)(3)(5)(6)(7)(17).