Public water systems that install aeration treatment are
subject to the Rules of the Department of Environmental Quality, IDAPA
58.01.01, "Rules for the Control of Air Pollution in Idaho." The system owner
or the design engineer shall 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
DEQ website http://www.deq.idaho.gov.
(3-24-22)
01.
Natural Draft
Aeration. Design shall provide: (3-24-22)
a. Perforations in the distribution pan three
sixteenths to one-half (3/16 - ½) inches in diameter, spaced one to
three (1-3) inches on centers to maintain a six (6) inch water depth.
(3-24-22)
b. For distribution of
water uniformly over the top tray. (3-24-22)
c. Discharge through a series of three (3) or
more trays with separation of trays not less than twelve (12) inches.
(3-24-22)
d. Loading at a rate of
one to five (1-5) gallons per minute for each square foot of total tray area.
(3-24-22)
e. Trays with slotted,
heavy wire (1/2 inch openings) mesh or perforated bottoms. (3-24-22)
f. Construction of durable material resistant
to aggressiveness of the water and dissolved gases. (3-24-22)
g. Protection from insects by twenty-four
(24) mesh or similar non-corrodible screen. (3-24-22)
02.
Forced or Induced Draft
Aeration. Devices shall be designed to: (3-24-22)
a. Include a blower with a weatherproof motor
in a tight housing and screened enclosure. (3-24-22)
b. Ensure adequate counter current of air
through the enclosed aerator column. (3-24-22)
c. Exhaust air directly to the outside
atmosphere. (3-24-22)
d. Include a
down-turned and twenty-four (24) mesh or similar non-corrodible screened air
outlet and inlet. (3-24-22)
e. Be
such that air introduced in the column shall be as free from obnoxious fumes,
dust, and dirt as possible. (3-24-22)
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. (3-24-22)
g.
Provide loading at a rate of one to five (1-5) gallons per minute for each
square foot of total tray area. (3-24-22)
h. Ensure that the water outlet is adequately
sealed to prevent unwarranted loss of air. (3-24-22)
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. (3-24-22)
j.
Provide distribution of water uniformly over the top tray. (3-24-22)
k. Be of durable material resistant to the
aggressiveness of the water and dissolved gases. (3-24-22)
03.
Spray Aeration. Design shall
provide: (3-24-22)
a. A hydraulic head of
between five (5) and twenty-five (25) feet. (3-24-22)
b. Nozzles, with the size, number, and
spacing of the nozzles being dependent on the flowrate, space, and the amount
of head available. (3-24-22)
c.
Nozzle diameters in the range of one (1) to one and one-half (1.5) inches to
minimize clogging. (3-24-22)
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.
(3-24-22)
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. See Subsection
501.19 for general information
on conducting pilot studies. Filters following pressure aeration must have
adequate exhaust devices for release of air. Pressure aeration devices shall 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.
(3-24-22)
05.
Packed Tower
Aeration. Packed tower aeration may be used for the removal of volatile
organic chemicals, trihalomethanes, carbon dioxide, and radon. Final design
shall be based on the results of pilot studies and be approved by the
Department. (3-24-22)
a. Process design
criteria. (3-24-22)
i. Justification for the
design parameters selected (i.e., height and diameter of unit, air to water
ratio, packing depth, surface loading rate, etc.) shall be provided to the
Department for review. 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
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. (3-24-22)
ii. The tower shall be designed to reduce
contaminants to below the maximum contaminant level and to the lowest practical
level. (3-24-22)
iii. The type and
size of the packing used in the full scale unit shall be the same as that used
in the pilot study. (3-24-22)
iv.
The maximum air to water ratio for which credit will be given is 80:1.
(3-24-22)
v. The design shall
consider potential fouling problems from calcium carbonate and iron
precipitation and from bacterial growth. It may be necessary to provide
pretreatment. Disinfection capability shall be provided prior to and after
packed tower aeration. (3-24-22)
vi. The effects of temperature shall be
considered. (3-24-22)
vii.
Redundant packed tower aeration capacity at the design flowrate shall be
provided. (3-24-22)
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 shall be provided with adequate support to prevent
damage from wind. 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. (3-24-22)
c. Water flow system. (3-24-22)
i. Water shall be distributed uniformly at
the top of the tower using spray nozzles or orifice-type distributor trays that
prevent short circuiting. (3-24-22)
ii. A mist eliminator shall be provided above
the water distributor system. (3-24-22)
iii. A side wiper redistribution ring shall
be provided at least every ten (10) feet in order to prevent water channeling
along the tower wall and short circuiting. (3-24-22)
iv. Sample taps shall be provided in the
influent and effluent piping. The sample taps shall satisfy the requirements of
Subsection 501.09. (3-24-22)
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.
(3-24-22)
vi. The design shall
prevent freezing of the influent riser and effluent piping when the unit is not
operating. (3-24-22)
vii. The water
flow to each tower shall be metered. (3-24-22)
viii. An overflow line shall be provided
which discharges twelve (12) to fourteen (14) inches above a splash pad or
drainage inlet. Proper drainage shall be provided to prevent flooding of the
area. (3-24-22)
ix. Means shall be
provided to prevent flooding of the air blower. (3-24-22)
d. Air flow system. (3-24-22)
i. The air inlet to the blower and the tower
discharge vent shall be down-turned and protected with a non-corrodible
twenty-four (24) mesh screen to prevent contamination from extraneous matter.
(3-24-22)
ii. The air inlet shall
be in a protected location. (3-24-22)
iii. An air flow meter shall be provided on
the influent air line or an alternative method to determine the air flow shall
be provided. (3-24-22)
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. (3-24-22)
v. A backup
motor for the air blower must be readily available.
(3-24-22)
e. Other
features that shall be provided: (3-24-22)
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. (3-24-22)
ii. A method of cleaning the packing material
when iron, manganese, or calcium carbonate fouling may occur.
(3-24-22)
iii. Tower effluent
collection and pumping wells constructed to clearwell standards.
(3-24-22)
iv. Provisions for
extending the tower height without major reconstruction. (3-24-22)
v. No bypass shall be provided unless
specifically approved by the Department. (3-24-22)
vi. Disinfection and adequate contact time
after the water has passed through the tower and prior to the distribution
system. (3-24-22)
vii. Adequate
packing support to allow free flow of water and to prevent deformation with
deep packing heights. (3-24-22)
viii. Operation of the blower and
disinfectant feeder equipment during power failures. (3-24-22)
ix. Adequate foundation to support the tower
and lateral support to prevent overturning due to wind loading.
(3-24-22)
x. Fencing and locking
gate to prevent vandalism. (3-24-22)
xi. An access ladder with safety cage for
inspection of the aerator including the exhaust port and demister.
(3-24-22)
xii. Electrical
interconnection between blower, disinfectant feeder and supply pump.
(3-24-22)
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.
(3-24-22)
07.
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.
(3-24-22)
08.
Disinfection. Ground water supplies exposed to the atmosphere by
aeration must receive disinfection as described in Section
530 as the minimum additional
treatment. (3-24-22)
