1. (a) System Sizing and Reliability.

   1. (1) A sequencing batch reactor (SBR) must meet the reliability requirements in §217.155(b) and (c)(3) of this title (relating to Aeration Equipment Sizing), and power source reliability requirements in §217.36 of this title (relating to Emergency Power Requirements).
   2. (2) A SBR must have a minimum decantable volume that is sufficient to pass the design flow without changing cycle times with the largest basin out of service.
   3. (3) A two-basin treatment facility without removable aeration devices is required to have aerated storage of mixed liquor separate from the SBR tank(s).
   4. (4) An SBR with a fixed level decanter must have more than two basins and additional decantable storage volume because of the added settling time before a discharge may occur.
   5. (5) An SBR with fixed decant equipment and decant volumes that do not accommodate the design flow requires an equalization basin.
   6. (6) Organic space loadings must conform to the values in Figure: 30 TAC §217.154(b)(2), Table F.1 of this title (relating to Aeration Basin and Clarifier Sizing--Traditional Design). Maximum space loadings must be below 35 pounds of five-day biochemical oxygen demand (CBOD₅) per 1,000 cubic feet of tank volume.
   7. (7) The reactor mixed liquor suspended solids (MLSS) level at the normal operating level must range be at least 3,000 milligrams per liter (mg/l) but not more than 5,000 mg/l.
   8. (8) The minimum depth MLSS during a react phase is 9.0 feet.
   9. (9) The minimum side water depth of a tank is 12 feet.
   10. (10) An SBR must include sludge digestion pursuant to the requirements in Subchapter J of this chapter (relating to Sludge Treatment Units).

2. (b) Decanter Design.

   1. (1) A decanter design must control the velocity at an inlet port or at the edge of submerged weirs to prevent vortexing, disturbance of the settled sludge, and entry of floating materials.
   2. (2) The entrance velocity to a decanter must not exceed 1.0 foot per second.
   3. (3) A decanter must draw effluent from below the water surface and include a device that excludes scum.
   4. (4) A decanter must maintain a zone of separation between the settled sludge and the decanter of no less than 12 inches.

   5. (5) A decanter must prevent solids from entering the decanter during a react cycle by one the following methods:

      1. (A) Recycle treated effluent to wash out solids trapped in a decanter;
      2. (B) Mechanically close a decanter when it is not in use; or
      3. (C) Fill a decanter with air except during a decant period.
   6. (6) The design of a decanter and related pipes and valves must include freeze protection, if located in a location subject to freezing.
   7. (7) A fixed decanter is prohibited in a basin where simultaneous fill and decant may occur.
   8. (8) For any system of tanks that is fed sequentially, the size of the decant system must accommodate the design flow with a constant cycle time with the largest tank out of service.
   9. (9) An SBR system utilizing more than two basins must allow the decanting of at least two tanks simultaneously.
   10. (10) If units downstream of an SBR are not capable of accepting the peak flowrate of the decanting cycle, flow equalization must be provided between the decanter and the downstream units.

3. (c) SBR Tank Details.

   1. (1) An SBR requires multiple tanks.
   2. (2) An SBR with two tanks or an SBR system operating with a continuous feed during settling and decanting phases must include influent baffling and physical separation from the decanter.
   3. (3) An elongated tank must be used for an SBR system if influent baffling is required.
   4. (4) An SBR tank must have a minimum freeboard of 18 inches at the maximum liquid level.
   5. (5) An SBR tank must resist buoyant uplift when empty.
   6. (6) Structures using a common wall must be designed to accommodate the stresses generated when one basin is full and an adjacent basin is empty.
   7. (7) Each SBR wall must be watertight.
   8. (8) A sump must be provided in any basin with a flat bottom.
   9. (9) An SBR system must have a dedicated means of transferring sludge between aeration basins.
   10. (10) An SBR system must include a means of scum removal in each aeration basin.
   11. (11) Each SBR tank must include a dewatering system and an overflow to another aeration tank(s) or a storage tank.
   12. (12) At a facility that is not staffed 24-hours each day, a manually operated SBR tank must include a high-level alarm that notifies facility staff, in accordance with §217.161 of this title (relating to Electrical and Instrumentation Systems).
   13. (13) A design must specify the means and frequency for removal of grit and other debris from the basins.
   14. (14) All equipment must be accessible for inspection, maintenance, and operation.
   15. (15) An SBR may use fine screens pursuant to §217.122 of this title (relating to Fine Screening Devices).
   16. (16) An SBR preceded by a primary clarifier may use a comminutor.
   17. (17) An SBR must have a sufficient number of tanks to operate at design flow with one tank out of service.

4. (d) Aeration and Mixing Equipment.

   1. (1) In addition to the requirements of §217.155 of this title aeration equipment must handle the cyclical operation in an SBR.
   2. (2) The aeration and mixing equipment must not interfere with settling.
   3. (3) The oxygen transfer rate for the aerators at average water depth during a fill cycle must provide a residual of 2.0 mg/l dissolved oxygen in the basin.
   4. (4) A design must specify the blower discharge pressure at the maximum water depth.
   5. (5) A SBR used for biological nutrient removal or reduction must meet the design requirements of §217.163 of this title (relating to Advanced Nutrient Removal).
   6. (6) The design of an SBR must allow for the removal of air diffusers or mechanical aeration devices without dewatering the tank.

5. (e) Control Systems.

   1. (1) The motor control center must include programmable logic controllers (PLC) with able to operate with limited operator adjustment and be programmed to meet the required effluent limitations for the design loadings.
   2. (2) A hard-wired backup means of operating the SBR is required.
   3. (3) The PLC must include battery backup. A duplicate set of all circuit boards must be kept at the facility.
   4. (4) Adequate controls for the separate operation of each reactor tank must be provided.

   5. (5) A tank level system must include floats or pressure transducers.

      1. (A) A float system must be protected from prevailing winds and freezing.
      2. (B) A bubbler system in a tank level system is prohibited.

   6. (6) The control panel switches must include at least:

      1. (A) Pumps - hand/off/automatic;
      2. (B) Valves - open/closed/automatic;
      3. (C) Blowers or aerators - hand/off/automatic; and
      4. (D) Selector switch for tank(s) - in operation/standby.

   7. (7) The control panel visual displays must include:

      1. (A) Mimic diagram of the process that shows the status and position of any pumps, valves, blowers or aerators, and mixers;
      2. (B) Process cycle and time remaining;
      3. (C) Instantaneous and totalized flow to the facility and of the final discharge;
      4. (D) Tank level gauges or levels;
      5. (E) Sludge pumping rate and duration; and
      6. (F) Airflow rate and totalizer.

   8. (8) The required alarm condition indicators for an annunciator panel must include:

      1. (A) High and low water levels in each tank;
      2. (B) Failure of all automatically operated valves;
      3. (C) Decanter failure;
      4. (D) Blowers, if used - low pressure, high temperature, and failure;
      5. (E) Mechanical aerator, if used - high temperature and failure;
      6. (F) Pump - high pressure and failure; and
      7. (G) Mixers, if used - failure.

Source Note:The provisions of this §217.156 adopted to be effective August 28, 2008, 33 TexReg 6843.