Texas Administrative Code
Title 30 - ENVIRONMENTAL QUALITY
Part 1 - TEXAS COMMISSION ON ENVIRONMENTAL QUALITY
Chapter 217 - DESIGN CRITERIA FOR DOMESTIC WASTEWATER SYSTEMS
Subchapter F - ACTIVATED SLUDGE SYSTEMS
Section 217.155 - Aeration Equipment Sizing
Universal Citation: 30 TX Admin Code § 217.155
Current through Reg. 49, No. 52; December 27, 2024
(a) Oxygen Requirements (O2R) of Wastewater.
(1) An aeration system must be designed to
provide a minimum dissolved oxygen concentration in the aeration basin of 2.0
milligrams per liter (mg/l).
(2)
Mechanical and diffused aeration systems must supply the
O2R calculated by Equation F.2. in Figure: 30 TAC
§217.155(a)(3), or use the recommended values presented in Table F.3. in
Figure: 30 TAC §217.155(a)(3), whichever is greater.
(3) The O2R values in
Table F.3. in Figure: 30 TAC §217.155(a)(3) use concentrations of 200 mg/l
five-day biochemical oxygen demand (BOD 5) and 45 mg/l
ammonia-nitrogen (NH3-N) in Equation F.2. in Figure: 30 TAC §217.155(a)(3):
(b) Diffused Aeration System. An airflow design must be based on either paragraph (1) or (2) of this subsection.
(1) Design Airflow Requirements -
Default Values. A diffused aeration system may use Table F.4. in Figure: 30 TAC
§217.155(b)(1) to determine the airflow for sizing aeration system components:
(2) Design Airflow Requirements -
Equipment and Site Specific Values. A diffused aeration system may be based on
calculations of the airflow requirements for the diffused aeration equipment in
accordance with subparagraphs (A) - (D) of this paragraph.
(A) Determine Clean Water Oxygen Transfer
Efficiency.
(i) A diffused aeration system
design may be based on a clean water oxygen transfer efficiency greater than
4%, only if the clean water oxygen transfer efficiency is supported by full
scale diffuser performance data. Full scale performance data must be developed
by an accredited testing laboratory or a licensed professional engineer. Data
developed by a professional engineer must be sealed by the engineer.
(ii) A testing laboratory or licensed
engineer shall use the oxygen transfer testing methodology described in the
most current version of the American Society of Civil Engineers (ASCE)
publication, A Standard for the Measurement of Oxygen Transfer in Clean
Water.
(iii) A diffused
aeration system with a clean water transfer efficiency greater than 18% for a
coarse bubble system or greater than 26% for a fine bubble system is considered
an innovative technology and is subject to §
217.7(b)(2)
of this title (relating to Types of Plans and Specifications
Approvals).
(iv) A design for clean
water transfer efficiencies obtained at temperatures other than 20 degrees
Celsius must be adjusted for a diffused aeration system to reflect the
approximate transfer efficiencies and air requirements under field conditions
by using the following equation:
(B) Determining Wastewater Oxygen Transfer
Efficiency (WOTE).
(i) The WOTE must be
determined from clean water test data by multiplying the clean water transfer
efficiency by 0.65 for a coarse bubble diffuser or by multiplying the clean
water transfer efficiency by 0.45 for a fine bubble diffuser.
(ii) The executive director may require
additional testing and data to justify actual WOTE for a wastewater treatment
facility treating wastewater containing greater than 10% industrial
wastes.
(C) Determining
Required Airflow (RAF). The RAF must be calculated using the following equation
to determine the size needed for a diffuser submergence of 12.0 feet. If the
diffuser submergence is other than 12.0 feet, a diffused aeration system must
correct the RAF, as detailed in subparagraph (D) of this paragraph.
(D) Corrections to RAF based on
varying diffuser submergence depths. The engineer shall provide the
manufacturer's laboratory testing data if the diffuser submergence depth in the
design is the same as the diffuser submergence depth in the manufacturer's
testing. The engineer shall apply a correction factor from Table F.5. in
Figure: 30 TAC §217.155(b)(2)(D) to the required airflow rate calculated using
Equation F.4. in Figure: 30 TAC §217.155(b)(2)(C) if the manufacturer's
laboratory testing data is not available for the design diffuser submergence
depth. Linear interpolation is allowed for diffuser submergence depths not
shown in Table F.5. in Figure: 30 TAC §217.155(b)(2)(D).
(3) Mixing Requirements for Diffused Air. The
air requirements for mixing must be calculated using an airflow rate:
(A) from Design of Municipal
Wastewater Treatment Plants, Fifth Edition, Chapter 11, a joint
publication of the ASCE and the Water Environment Federation, for mixing
requirements; or
(B) greater than
or equal to 20 standard cubic feet per minute (scfm) per 1,000 cubic feet for a
coarse bubble diffuser and greater than or equal to 0.12 scfm per square foot
for a fine bubble diffuser.
(4) Blowers and Air Compressors.
(A) A blower and an air compressor system
must provide the required design airflow rate for biological treatment and
mixing, based on paragraphs (1) - (3) of this subsection, and the air
requirements of all other supplemental units where air must be
supplied.
(B) The engineering
report must include blower and air compressor calculations that show the
maximum air requirements for the temperature range where the wastewater
treatment facility is located, including both summer and winter conditions, and
the impact of elevation on the air supply.
(C) A diffused aeration system must have
multiple compressors arranged to provide an adjustable air supply to meet the
variable organic load on the wastewater treatment facility.
(D) The air compressors must be capable of
handling the maximum design air requirements with the largest single air
compressor out of service.
(E) A
blower unit and a compressor unit must restart automatically after a power
outage, or have a telemetry system or an auto-dialer with battery backup to
notify an operator of any outage.
(F) The design of a blower and air compressor
system must specify blowers and air compressors with sufficient capacity to
handle air intake temperatures that may exceed 100 degrees Fahrenheit (38
degrees Celsius), and pressures that may be less than standard (14.7 pounds per
square inch absolute).
(G) The
design of a blower and air compressor system must specify the capacity of the
motor drive necessary to handle air intake temperatures that may be 20 degrees
Fahrenheit (-7 degrees Celsius) or less.
(H) A blower must include a governor or other
means to regulate airflow.
(5) Diffuser Systems - Additional
Requirements.
(A) Diffuser Submergence.
(i) For a new wastewater treatment facility,
the submergence depth for any diffuser must meet the minimum depths in the
following table:
(ii) For
an alteration or expansion of an existing wastewater treatment facility, the
diffuser submergence depth may vary from the values in Table F.6. in Figure: 30
TAC §217.155(b)(5)(A)(i) to match existing air pressure, delivery rate, and
hydraulic requirements.
(iii) The
submerged depth for a diffuser must be at least 7.0 feet. A wastewater
treatment facility with a design flow of less than 5,000 gallons per day may
have a diffuser submergence depth of less than 7.0 feet, but only if justified
by the engineer and approved in writing by the executive director.
(B) Grit Removal. A wastewater
treatment facility that uses diffusers and has wastewater with concentrations
of grit that would interfere with the operation of a diffuser must either
include a grit removal unit upstream of an aeration process, or include
multiple aeration basins so that one basin may be taken out of service to allow
for grit removal.
(C) Aeration
System Pipes.
(i) Each diffuser header must
include an open/close or throttling type control valve that can withstand the
heat of compressed air.
(ii) A
diffuser header must be able to withstand temperatures up to 250 degrees
Fahrenheit.
(iii) The capacity of
an air diffuser system, including pipes and diffusers, must equal 150% of
design air requirements.
(iv) The
design of an aeration system must minimize head loss. The engineering report
must include a hydraulic analysis of the entire air pipe system that quantifies
head loss through the pipe system and details the distribution of air from the
blowers to the diffusers.
(v) An
aeration system may use non-metallic pipes only in the aeration basin, but the
pipes must be a minimum of 4.0 feet below the average water surface elevation
in the aeration basin.
(c) Mechanical Aeration Systems.
(1) Required Airflow - Equipment and Site
Specific Values. The airflow requirements for a mechanical aeration system must
be calculated in accordance with subparagraphs (A) and (B) of this paragraph.
(A) Clean Water Oxygen Transfer Efficiency.
(i) The engineering report must include the
clean water oxygen transfer efficiency rate for the mechanical
equipment.
(ii) The clean water
oxygen transfer efficiency must not exceed 2.0 pounds of oxygen per
horsepower-hour unless justified by full scale performance data. Full scale
performance data must be developed by an accredited testing laboratory or a
licensed professional engineer. Data developed by a professional engineer must
be sealed by the engineer. Full scale performance tests must follow the oxygen
transfer testing methodology described in the most current version of the ASCE
publication, A Standard for the Measurement of Oxygen Transfer in Clean
Water.
(iii) A technology
with a proposed clean water oxygen transfer efficiency in excess of 2.0 pounds
of oxygen per horsepower-hour is innovative technology and subject to the
requirements of §
217.7(b)(2)
of this title (relating to Types of Plans and Specifications
Approvals).
(B)
Wastewater Oxygen Transfer Efficiency.
(i)
The engineering report must include the actual wastewater oxygen transfer
efficiency and data to justify the actual wastewater oxygen transfer
efficiency.
(ii) If a wastewater
treatment facility will receive more than 10% industrial wastewater by volume,
all mechanical aeration equipment must be sized based on a wastewater oxygen
transfer efficiency of no more than 0.65 times the clean water oxygen transfer
efficiency.
(2) Mixing Requirements.
(A) A mechanical aeration device must provide
mixing to prevent mixed liquor suspended solids (MLSS) deposits under any flow
condition.
(B) A mechanical
aeration device must be capable of re-suspending the MLSS after a shutdown
period.
(C) Mechanical aeration
devices with a channel or basin layout must have a minimum of 100 horsepower
per million gallons of aeration basin volume or 0.75 horsepower per thousand
cubic feet of aeration basin volume.
(3) Mechanical Components.
(A) Process Reliability.
(i) Each aeration basin must include a
minimum of two mechanical aeration devices.
(ii) A mechanical aeration device must meet
the maximum design requirements for oxygen transfer with the largest single
unit out of service.
(iii) A
mechanical aeration device must either automatically restart after a power
outage, or have a telemetry system or an auto-dialer with battery backup to
notify an operator of any outage.
(B) Operation and maintenance.
(i) A mechanical aeration device must have
two-speed or variable-speed drive units, unless another means of varying the
output is provided.
(ii) To vary
the output, a mechanical aeration device may use single-speed drive units with
timer-controlled operation if the device also includes an independent means of
mixing.
(iii) A wastewater
treatment facility must be designed such that an operator is able to perform
routine maintenance on the aeration equipment without coming into contact with
wastewater.
(iv) Each bearing,
drive motor, or gear reducer must be accessible to an operator for maintenance
and must be equipped with a splash prevention device. A splash prevention
device must be designed to protect the operator from contact with wastewater
and to prevent wastewater from escaping the basin.
(v) Each gear reducer must have a drainage
system to prevent operator contact with mixed liquor.
Disclaimer: These regulations may not be the most recent version. Texas 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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