Idaho Administrative Code
Title IDAPA 58 - Environmental Quality, Department of
Rule 58.01.16 - WASTEWATER RULES
Section 58.01.16.490 - FACILITY AND DESIGN STANDARDS FOR MUNICIPAL WASTEWATER TREATMENT OR DISPOSAL FACILITIES: BIOLOGICAL TREATMENT
Universal Citation: ID Admin Code 58.01.16.490
Current through August 31, 2023
If biological treatment is used, the process shall be determined in the preliminary engineering report. The choice shall be based on influent characteristics and effluent requirements. (3-31-22)
01. Trickling Filters. (3-31-22)
a. General. Trickling filters shall be
preceded by effective settling tanks equipped with scum and grease collecting
devices or other suitable pretreatment facilities. (3-31-22)
b. Hydraulics. The flow will be uniformly
distributed across the surface of the media. The piping system, including
dosing equipment and distributor, shall be designed to provide capacity for the
design peak hour flow, including recirculation. (3-31-22)
c. Media. (3-31-22)
i. Quality. The media shall be appropriate
for the wastewater and shall be of sufficient strength to support itself under
design loading and build up of biomass. (3-31-22)
ii. Depth. Trickling filter media shall have
a minimum depth of six (6) feet above the underdrains.
(3-31-22)
d.
Underdrainage System. (3-31-22)
i.
Arrangement. Underdrains shall be provided and the underdrainage system shall
cover the entire floor of the filter. Inlet openings into the underdrains shall
have an unsubmerged gross combined area equal to at least fifteen (15) percent
of the surface area of the filter. (3-31-22)
ii. Ventilation. The underdrainage system,
effluent channels, and effluent pipe shall be designed to permit free passage
of air. (3-31-22)
e.
Special Features. (3-31-22)
i. Maintenance.
All distribution devices, underdrains, channels, and pipes shall be installed
so that they may be properly maintained, flushed or drained.
(3-31-22)
ii. Winter Protection.
Covers shall be provided to maintain operation and treatment efficiencies when
climatic conditions are expected to result in problems due to cold
temperatures. (3-31-22)
iii.
Recirculation. The piping system shall be designed for recirculation as
required to achieve the design efficiency. The recirculation rate shall be
variable and subject to plant operator control at the range of 0.5:1 up to 4:1
(ratio of recirculation rate versus design average flow). A minimum of two (2)
recirculation pumps shall be provided. (3-31-22)
f. Rotary Distributor Seals. Mercury seals
shall not be permitted. (3-31-22)
g. Unit Sizing. Required volumes of filter
media shall be based upon pilot testing with the particular wastewater or any
of the various empirical design equations that have been verified through
actual full scale experience. Such calculations must be submitted to the
Department if pilot testing is not utilized. Trickling filter sizing design
shall consider peak organic load conditions including the oxygen demands due to
solids and process recycle flows. (3-31-22)
02. Activated Sludge. (3-31-22)
a. Aeration. (3-31-22)
i. Capacities and Permissible Loadings. The
size of the aeration tank for any particular adaptation of the process shall be
determined by full scale experience, pilot plant studies, or rational
calculations based mainly on solids retention time, food to microorganism
ratio, and mixed liquor suspended solids levels. Other factors, such as size of
treatment plant, diurnal load variations, and degree of treatment required,
shall also be considered. In addition, temperature, alkalinity, pH, and reactor
dissolved oxygen shall be considered when designing for nitrification.
Calculations shall be submitted to the Department in the preliminary
engineering report to justify the basis for design of aeration tank capacity.
(3-31-22)
ii. Arrangement of
Aeration Tanks. (3-31-22)
(1) Dimensions. The
dimensions of each aeration tank or return sludge reaeration tank shall be such
as to maintain effective mixing and utilization of air. An exception is that
horizontally mixed aeration tanks shall have a depth of not less than five
point five (5.5) feet. (3-31-22)
(2) Number of Units. Total aeration tank
volume plus redundancy requirements shall be divided among two (2) or more
equal units, capable of independent operation. (3-31-22)
(3) Inlets and Outlets. (3-31-22)
(a) Controls. Inlets and outlets for each
aeration tank unit shall be designed to control flow to any unit with
reasonable accuracy and to maintain reasonably constant liquid level. The
properties of the system shall permit the design peak day flow to be treated
with any single aeration tank unit out of service. The properties of the system
shall permit the design peak hour hydraulic flow to be carried with any single
aeration tank unit out of service. (3-31-22)
(b) Conduits. Channels and pipes carrying
liquids with solids in suspension shall be designed to be self-cleansing.
(3-31-22)
(c) Scum and Foam
Control. Aeration tanks shall be designed to include adequate control or
removal of scum and foam. (3-31-22)
(4) Freeboard. All aeration tanks should have
a freeboard of not less than eighteen (18) inches.
(3-31-22)
iii. Aeration
Equipment. (3-31-22)
(1) General. Oxygen
requirements generally depend on maximum diurnal organic loading, degree of
treatment, and level of suspended solids concentration to be maintained in the
aeration tank mixed liquor. Aeration equipment shall be capable of maintaining
a minimum of two point zero (2.0) mg/L of dissolved oxygen in the mixed liquor
at all times and provide thorough mixing of the mixed liquor (for a
horizontally mixed aeration tank system, an average velocity of one (1) foot
per second must be maintained). In the absence of experimentally determined
values, the design oxygen requirements for all activated sludge processes shall
be 1.1 lb 02 per lb of design peak hour BOD5
applied to the aeration tanks, with the exception of the extended
aeration process, for which the value shall be one point five (1.5) to include
endogenous respiration requirements. (3-31-22)
(a) Where nitrification is required or will
occur, the oxygen requirement for oxidizing ammonia must be added to the above
requirement for carbonaceous BOD5 removal and endogenous
respiration requirements. The nitrogenous oxygen demand (NOD) shall be taken as
four point six (4.6) times the diurnal peak hour total Kjeldahl nitrogen
content of the aeration tank influent. In addition, the oxygen demands due to
recycle flows must be considered due to the high concentrations of
BOD5 and total Kjeldahl nitrogen associated with such
flows. (3-31-22)
(b) Meet maximum
oxygen demand and maintain process performance with the largest unit out of
service. Provide for varying the amount of oxygen transferred in proportion to
the load demand on the plant. (3-31-22)
(2) Diffused Air Systems. Air requirements
including, but not limited to, process air, channel aeration, aerobic
digestion, and miscellaneous plant air shall be submitted to the Department in
the preliminary engineering report. Blowers shall be provided in multiple
units, so arranged and in such capacities as to meet the maximum air demand
with the single largest unit out of service. The design shall also provide for
varying the volume of air delivered in proportion to the load demand of the
plant. Aeration equipment shall be easily adjustable in increments and shall
maintain solids suspension within these limits. (3-31-22)
(3) Mechanical Aeration Systems. (3-31-22)
(a) Oxygen Transfer Performance. The
mechanism and drive unit shall be designed for the expected conditions in the
aeration tank in terms of the power performance. Certified testing shall be
provided to verify mechanical aerator performance. Refer to applicable
provisions of Subsection
490.02. In the absence of
specific design information, the oxygen requirements shall be calculated for
mechanical aeration systems using a transfer rate not to exceed two (2) pounds
of oxygen per horsepower per hour in clean water under standard test
conditions. Design transfer efficiencies shall be included in the
specifications. (3-31-22)
(b)
Design Requirements. Motors, gear housing, bearings, grease fittings, etc.,
shall be easily accessible and protected from inundation and spray as necessary
for proper functioning of the unit. (3-31-22)
(c) Winter Protection. Where extended cold
weather conditions occur, the aerator mechanism and associated structure shall
be protected from freezing due to splashing. Due to high heat loss, subsequent
treatment units shall be protected from freezing.
(3-31-22)
b. Non-Aerated Tanks or Zones. Non-aerated
tanks or zones within aeration tanks shall have mixing equipment adequate to
fully mix the contents. Provide calculations in the preliminary engineering
report for sizing of this equipment. (3-31-22)
c. Return Sludge Equipment. (3-31-22)
i. Return Sludge Rate. The return sludge rate
of withdrawal from the final settling tank is a function of the concentration
of suspended solids in the mixed liquor entering it, the sludge volume index of
these solids, and the length of time these solids are retained in the settling
tank. The rate of sludge return shall be varied by means of adjustable weirs,
variable speed pumps, or timers (small plants) to pump sludge.
(3-31-22)
ii. Return Sludge Pumps.
If a consolidated return sludge pump facility is used, the maximum return
sludge capacity shall be obtained with the largest pump out of service. If
individual sludge pumps are used at each settling basin, the pumps shall be
designed to facilitate their rapid removal and replacement with a standby unit
stored at the treatment plant site. If air lifts are used for returning sludge
from each settling tank hopper, no standby unit will be required provided the
design of the air lifts facilitate their rapid and easy cleaning and provided
other suitable standby measures are made available. Air lifts should be at
least three (3) inches in diameter. (3-31-22)
iii. Return Sludge Piping. Discharge piping
should be at least four (4) inches in diameter and shall be designed to
maintain a velocity of not less than two (2) feet per second when return sludge
facilities are operating at normal return sludge rates. Suitable devices for
observing, sampling, and controlling return activated sludge flow from each
settling tank hopper shall be provided. (3-31-22)
iv. Waste Sludge Facilities. Means for
observing, measuring, sampling, and controlling waste activated sludge flow
shall be provided. (3-31-22)
d. Sequencing Batch Reactors. The fill and
draw mode of the activated sludge process commonly termed the Sequencing Batch
Reactor may be used in Idaho. The design must be based on experience at other
facilities and shall meet the applicable requirements under Sections
450,
470 and
490, except as modified in
Subsection 490.02.d.i. through
490.02.d.xi. Continuity and reliability of treatment equal to that of the
continuous flow through modes of the activated sludge process shall be
provided. (3-31-22)
i. At least two (2) tanks
shall be provided. (3-31-22)
ii.
The decantable volume and decanter capacity of the sequencing batch reactor
system with the largest basin out of service shall be sized to pass at least
seventy-five (75) percent of the design maximum day flow without changing cycle
times. A decantable volume of at least four (4) hours with the largest basin
out of service based on one hundred (100) percent of the design maximum day
flow is permissible. (3-31-22)
iii.
System reliability with any single tank unit out of service and the
instantaneous delivery of flow shall be evaluated in the design of decanter
weirs and approach velocities. (3-31-22)
iv. Reactor design shall provide for scum
removal and prevent overflow of settled solids. (3-31-22)
v. An adequate zone of separation between the
sludge blanket and the decanter(s) shall be maintained throughout the decant
phase. Decanters which draw the treated effluent from near the water surface
throughout the decant phase are recommended. (3-31-22)
vi. Solids management to accommodate basin
dewatering shall be considered. (3-31-22)
vii. The blowers shall be provided in
multiple units, so arranged and in such capacities as to meet the maximum air
demand in the oxic portions of the fill/react and react phases of the cycle
with the single largest unit out of service. See Subsection
490.02. (3-31-22)
viii. Mechanical mixing independent of
aeration shall be provided for all systems where biological phosphorus removal
or denitrification is required. (3-31-22)
ix. Flow paced composite sampling equipment
and continuous turbidity metering for separately monitoring the effluent
quality from each basin may be required by the regulatory agency. All
twenty-four (24) hour effluent quality composite samples for compliance
reporting or monitoring plant operations shall be flow-paced and include
samples collected at the beginning and end of each decant phase.
(3-31-22)
x. A programmable logic
controller (PLC) shall be provided. Multiple PLCs shall be provided as
necessary to assure rapid process recovery or minimize the deterioration of
effluent quality from the failure of a single controller. An uninterruptible
power supply with electrical surge protection shall be provided for each PLC to
retain program memory (i.e., process control program, last-known set points and
measured process/equipment status, etc.) through a power loss. A hard-wired
backup for manual override shall be provided in addition to automatic process
control. Both automatic and manual controls shall allow independent operation
of each tank. In addition, a fail-safe control allowing at least twenty (20)
minutes of settling between the react and decant phases shall be provided. The
fail-safe control shall not be adjusted by the operator. (3-31-22)
xi. A sufficient quantity of spare parts
shall be on hand. Consideration shall be given to parts with a low mean time
between failure such as electrical relays and solid state electronics.
(3-31-22)
03. Other Biological Systems. (3-31-22)
a. General. Biological treatment processes
not included in these rules shall be considered in accordance with Subsection
450.03. (3-31-22)
b. Membrane Bioreactors. Details for Membrane
Bioreactor (MBR) plants shall be submitted and approved in the preliminary
engineering report. In addition to the requirements of Section
411, details shall include plant
layout, calculations for hydraulic capacity and air required, membrane
technology considered and membrane type and model selected, results from
similar type MBR plants already in operation, and anticipated sludge
production. (3-31-22)
Disclaimer: These regulations may not be the most recent version. Idaho may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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