Idaho Admin. Code r. 58.01.08.534

Current through September 2, 2024

Section 58.01.08.534 - AERATION PROCESSES

PWS owners that install aeration treatment are subject to IDAPA 58.01.01, "Rules for the Control of Air Pollution in Idaho." The PWS owner or the design engineer must contact one of the Department's regional offices for information on obtaining a permit or an exemption for the emissions resulting from the aeration process. General information may be found on the Department website http://www.deq.idaho.gov.

01.Natural Draft Aeration. Design must provide:

a. Perforations in the distribution pan three sixteenths to one-half (3/16 - ¹/₂) inches in diameter, spaced one to three (1-3) inches on centers to maintain a six (6) inch water depth.

b. Distribution of water uniformly over the top tray.

c. Discharge through a series of three (3) or more trays with separation of trays not less than twelve (12) inches.

d. Loading at a rate of one to five (1-5) gallons per minute for each square foot of total tray area.

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.

g. Protection from insects by twenty-four (24) mesh or similar non-corrodible screen.

02.Forced or Induced Draft Aeration. Design must provide:

a. Include a blower with a weatherproof motor in a tight housing and screened enclosure.

b. Ensure adequate counter current of air through the enclosed aerator column.

c. Exhaust air directly to the outside atmosphere.

d. Include a down-turned and twenty-four (24) mesh or similar non-corrodible screened air outlet and inlet.

e. Be such that air introduced in the column will be as free from obnoxious fumes, dust, and dirt as possible.

f. 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.

g. Provide loading at a rate of one to five (1-5) gallons per minute for each square foot of total tray area.

h. Ensure that the water outlet is adequately sealed to prevent unwarranted loss of air.

i. Discharge through a series of five (5) or more trays with separation of trays not less than six (6) inches or as approved by the Department.

j. Provide distribution of water uniformly over the top tray.

k. Be of durable material resistant to the aggressiveness of the water and dissolved gases.

03.Spray Aeration. Design must provide:

a. A hydraulic head of between five (5) and twenty-five (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 one (1) to one and one-half (1.5) inches to minimize clogging.

d. An enclosed basin to contain the spray. Any openings for ventilation must be protected with a twenty-four (24) mesh or similar non-corrodible screen.

04.Pressure Aeration. Pressure aeration may be used for oxidation purposes only if the pilot plant study indicates the method is applicable; it is not acceptable for removal of dissolved gases. Filters following pressure aeration must have adequate exhaust devices for release of air. Pressure aeration devices must be designed to give thorough mixing of compressed air with water being treated and provide twenty-four (24) mesh or similar non-corrodible screened and filtered air, free of obnoxious fumes, dust, dirt and other contaminants.

05.Packed Tower Aeration. Packed tower aeration may be used for the removal of volatile organic chemicals, trihalomethanes, carbon dioxide, and radon. Final design must be based on the results of pilot studies and be approved by the Department.

a. Process design criteria.

i. Justification for the design parameters selected (i.e., height and diameter of unit, air to water ratio, packing depth, surface loading rate, etc.) must be provided to the Department for review. The pilot study must evaluate a variety of loading rates and air to water ratios at the peak contaminant concentration. Special consideration will be given to removal efficiencies when multiple contaminations occur. Where there is considerable past performance data on the contaminant to be treated and there is a concentration level similar to previous projects, the Department may approve the process design based on use of appropriate calculations without a pilot study.

ii. The tower must be designed to reduce contaminants to below the maximum contaminant level and to the lowest practical level.

iii. The type and size of the packing used in the full scale unit must be the same as that used in the pilot study.

iv. The maximum air to water ratio for which credit will be given is 80:1.

v. The design must consider potential fouling problems from calcium carbonate and iron precipitation and from bacterial growth. It may be necessary to provide pretreatment. Disinfection capability will be provided prior to and after packed tower aeration.

vi. The effects of temperature must be considered.

vii. Redundant packed tower aeration capacity at the design flowrate will be provided.

b. The tower may be constructed of stainless steel, concrete, aluminum, fiberglass or plastic. Uncoated carbon steel is not allowed. Towers constructed of light-weight materials must be provided with adequate support to prevent damage from wind. Packing materials must be resistant to the aggressiveness of the water, dissolved gases and cleaning materials and must be suitable for contact with potable water.

c. Water flow system.

i. Water must 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 must be provided above the water distributor system.

iii. A side wiper redistribution ring must be provided at least every ten (10) feet in order to prevent water channeling along the tower wall and short circuiting.

iv. Sample taps must be provided in the influent and effluent piping. The sample taps must satisfy the requirements of Subsection 501.09.

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

vi. The design must prevent freezing of the influent riser and effluent piping when the unit is not operating.

vii. The water flow to each tower must be metered.

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

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

d. Air flow system.

i. The air inlet to the blower and the tower discharge vent must be down-turned and protected with a non-corrodible twenty-four (24) mesh screen to prevent contamination from extraneous matter.

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

iii. An air flow meter must be provided on the influent air line or an alternative method to determine the air flow will be provided.

iv. A positive air flow sensing device and a pressure gauge must be installed on the air influent line. The positive air flow sensing device must be a part of an automatic control system which will turn off the influent water if positive air flow is not detected. The pressure gauge will serve as an indicator of fouling buildup.

v. A backup motor for the air blower must be readily available.

e. Other features that must be provided:

i. A sufficient number of access ports with a minimum diameter of twenty-four (24) inches to facilitate inspection, media replacement, media cleaning and maintenance of the interior.

ii. A method of cleaning the packing material when iron, manganese, or calcium carbonate fouling may occur.

iii. Tower effluent collection and pumping wells constructed to clearwell standards.

iv. Provisions for extending the tower height without major reconstruction.

v. No bypass may be provided unless specifically approved by the Department.

vi. Disinfection and adequate contact time after the water has passed through the tower and prior to the distribution system.

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

viii. Operation of the blower and disinfectant feeder equipment during power failures.

ix. Adequate foundation to support the tower and lateral support to prevent overturning due to wind loading.

x. Fencing and locking gate to prevent vandalism.

xi. An access ladder with safety cage for inspection of the aerator including the exhaust port and de-mister.

xii. Electrical interconnection between blower, disinfectant feeder and supply pump.

06.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 are subject to the approval of the Department.

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

08.Disinfection. Groundwater supplies exposed to the atmosphere by aeration must receive disinfection as described in Section 530 as the minimum additional treatment.

Idaho Admin. Code r. 58.01.08.534

Effective July 1, 2024