(a) Oxygen Requirements (O             2            R) 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 O                 2                R 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 O                 2                R 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):        
          Attached Graphic         
      (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:        
          Attached Graphic         
        (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:            
              Attached Graphic             
          (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.          
            Attached Graphic                     (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).          
            Attached Graphic           
        (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:            
              Attached Graphic             
            (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.           
     Source Note:        The provisions of this §217.155 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254