1. (a) Applicability.

   1. (1) This section contains criteria for low-pressure, vacuum, and gravity ultrafiltration or microfiltration membrane bioreactors.
   2. (2) Other types of membrane bioreactors (MBRs) are considered innovative technology and are subject to the requirements of §217.7(b)(2) of this title (relating to Types of Plans and Specifications Approvals).

2. (b) Performance Standards.

   1. (1) MBR performance standards for conventional pollutants and nutrients are shown in the following table:
      Attached Graphic
      
   2. (2) An owner may be required to submit a pilot study report or data from a similar facility if a proposed facility is designed to achieve higher quality effluent than the performance standards listed in the table in paragraph (1) of this subsection.

3. (c) Facility Design.

   1. (1) Pretreatment.

      1. (A) Each MBR system must have fine screening to prevent damage from abrasive particles or fibrous, stringy material.

         1. (i) Fine screens must be rotary drum or traveling band screen with either perforated plate or wire mesh with an opening size of 0.5 - 2.0 millimeter (mm) for hollow fiber systems and tubular systems and 2.0 - 3.0 mm for flat plate systems.
         2. (ii) Bypass of a fine screen must be prevented with either a duplicate fine screen, overflow to a wet well, or an alternative that has been approved by the executive director.
         3. (iii) A fine screen must be designed to prevent overflow at the peak flow.
         4. (iv) Coarse screens followed by fine screens may be used in larger facilities to minimize the complications of fine screening.
      2. (B) The economic feasibility of primary clarification must be evaluated for facilities designed for an average daily flow of 5.0 million gallons per day (mgd) or more. The evaluation must be included in the report.
      3. (C) Oil and grease removal is required if the oil and grease levels in the influent may cause damage to the membranes. The specific detrimental concentration must be determined by the equipment manufacturer. However, influent concentrations of oil and grease equal to or more than 100 milligram per liter (mg/l) must have oil and grease removal.
      4. (D) The necessity of grit removal must be evaluated for a facility that has a collection system with excessive inflow and infiltration. An evaluation must be included in the report.

   2. (2) Biological treatment.

      1. (A) The reactor volume for any biological treatment zone must be determined using rate equations for substrate utilization and biomass growth in a manner similar to determining basin sizes for conventional activated sludge processes.
      2. (B) The design sludge retention time (SRT) for an MBR must be at least 10 days but no more than 25 days.

      3. (C) The design operational range of mixed liquor suspended solids concentration (MLSS) must be:

         1. (i) at least 4,000 mg/l but not more than 10,000 mg/l in the bioreactor; and
         2. (ii) at least 4,000 mg/l but not more than 14,000 mg/l in the membrane tank.
      4. (D) A system designed for an SRT or MLSS outside theses ranges requires a pilot study in compliance with paragraph (8) of this subsection, or data from a similar facility that demonstrates that the design parameters are sustainable and can achieve the expected performance.

   3. (3) Aeration.

      1. (A) An aeration system in a bioreactor must be capable of maintaining dissolved oxygen levels as listed in subparagraph (C) of this paragraph.
      2. (B) A bioreactor aeration system must compensate for a low oxygen transfer efficiency due to the higher MLSS concentrations with a justified alpha value of 0.5 or lower.

      3. (C) The design oxygen concentration range used for sizing aeration systems for treatment zones must be:

         1. (i) Anoxic: not more than 0.5 mg/l;
         2. (ii) Aerobic: at least 1.5 mg/l but not more than 3.0 mg/l; and
         3. (iii) Membranes: at least 2.0 mg/l but not more than 8.0 mg/l.
      4. (D) A design must include oxygen monitoring and an alarm to notify an operator of potential or actual oxygen depravation.
   4. (4) Recycle Rates. Facilities without advanced treatment must be designed with recycle rates sufficient to sustain the design mixed liquor concentrations; typically from 200% to 400% of the facility's influent flow.

   5. (5) Nutrient removal.

      1. (A) A system designed for enhanced nutrient removal must include an isolated tank or baffled zone for anoxic treatment, anaerobic treatment, or both.

      2. (B) Calculations for sizing the reactor volumes must be based on one of these models for nutrient removal:

         1. (i) Bardenpho;
         2. (ii) modified Ludzak-Etinger;
         3. (iii) University of Capetown; or
         4. (iv) an alternative approved by the executive director.
      3. (C) A facility designed for nitrogen or biological nutrient removal must contain a deoxygenation basin, a larger anoxic basin, or another method approved by the executive director of decreasing dissolved oxygen concentration, if the recycled activated sludge is returned to an anoxic or anaerobic basin.
      4. (D) An advanced nutrient removal system must be designed with recycle rates sufficient to sustain the designed mixed liquor concentrations in both the aeration and anoxic basins; typically totaling 600% or more of the influent flow.

   6. (6) Use of Membranes.

      1. (A) Use of a membrane system other than a hollow fiber system, tubular system, or a flat plate system must be considered innovative treatment technology and is subject to §217.7(b)(2) of this title.

      2. (B) Use of a membrane material other than one of the following must be justified in the report:

         1. (i) polyethersulfone (PES);
         2. (ii) polyvinylidene fluoride (PVDF);
         3. (iii) polypropylene (PP);
         4. (iv) polyethylene (PE);
         5. (v) polyvinylpyrrolidone (PVP); or
         6. (vi) chlorinated polyethylene (CPE).
      3. (C) The nominal pore size used in an MBR for microfiltration membranes must be at least 0.10 micrometers (microns) but not more than 0.4 microns.
      4. (D) The nominal pore size used in an MBR for ultrafiltration must be at least 0.02 microns but not more than 0.10 microns.
      5. (E) Any chemical used for cleaning must not adversely affect the membrane material.

   7. (7) Membrane design parameters.

      1. (A) MBRs must be designed for:

         1. (i) An average daily net flux rate of not more than 15 gallons per day per square-foot of membrane area (gfd);
         2. (ii) A peak daily net flux rate equal to or less than 1.25 times the average daily net flux rate; and
         3. (iii) A two-hour peak net flux rate equal to or less than 1.5 times the average daily net flux rate.
      2. (B) The executive director may approve larger net flux rates if the rates are substantiated with a pilot study or data from a similar facility that substantiate the proposed duration, frequency, and recovery time from peak flow.
      3. (C) A system with a peak flow rate that is greater than 2.5 times the average daily flow must use equalization volume, off-line storage, or reserve membrane capacity to accommodate the higher peak flow.

      4. (D) Hollow fiber transmembrane pressure (TMP).

         1. (i) The operational pressure range must be at least 2.0 pounds per square inch (psi) but not more than 10.0 psi.
         2. (ii) The maximum pressure must not exceed 12.0 psi.

      5. (E) Flat plate TMP.

         1. (i) The operational pressure range must be at least 0.3 psi but not more than 3.0 psi.
         2. (ii) The maximum pressure must not exceed 4.5 psi.

      6. (F) Tubular, Out of Basin TMP.

         1. (i) The operational pressure range must be at least 0.5 psi but not more than 5.0 psi.
         2. (ii) The maximum pressure must not exceed 10.0 psi.

   8. (8) Supporting Data. Pilot study reports or data from similar facilities must be provided if a facility is designed to achieve better than the performance standards in Table F.7 in subsection (b)(1) of this section, or outside normal operating parameters defined within this section.

      1. (A) A pilot study must be operated at least 30 days after the initial start-up and acclimation period.
      2. (B) A pilot study must be designed to evaluate the membrane performance during actual operational conditions including flow variations and influent wastewater characteristics.
      3. (C) The treatment and pretreatment processes in a pilot study or similar facility must be equivalent to the proposed facility.

      4. (D) The results of the pilot study must include the following recommendations:

         1. (i) average, peak day, and peak two-hour design net flux rates;
         2. (ii) average and maximum TMP;
         3. (iii) cleaning and backwash intervals;
         4. (iv) expected percent recovery after chemical cleaning;
         5. (v) dissolved oxygen concentrations for reactors and membrane basins;
         6. (vi) MLSS concentrations for reactors and membrane basins;
         7. (vii) SRTs for reactors and membrane basins; and
         8. (viii) expected effluent concentrations of conventional pollutants and nutrients, including the pollutants and nutrients that will be limited or monitored in the facility's wastewater permit.

   9. (9) Redundancy.

      1. (A) A facility must be able to operate at normal operating parameters and conditions for daily average flow with one MBR unit or train out of service.
      2. (B) Acceptable methods of providing redundancy are additional treatment trains, additional treatment units, or storage. Calculations must be included in the report to demonstrate adequate redundancy.

   10. (10) Other components.

       1. (A) Mixers.

          1. (i) Unaerated (deoxygenation, pre/post anoxic, and anaerobic) zones must have submersible mixers or an alternative mixer that has been approved by the executive director.
          2. (ii) Coarse bubble air diffusers may be used for mixing in a pre-anoxic tank.

       2. (B) Scum and Foam Handling.

          1. (i) Scum and foam must not interfere with treatment or overflow a treatment unit.
          2. (ii) Surface wasting of excess mixed liquor or skimmers may be used to control scum and foam.
          3. (iii) Surface wasting may be performed in a aerated basin, a membrane basin, or both.
       3. (C) Cranes and Hoists. A crane, hoist or some other process or mechanism must be provided for periodic cleaning and maintenance.

   11. (11) Disinfection.

       1. (A) An owner may request and the executive director may grant decreased ultraviolet light or chlorine dosing requirements for MBR effluent.
       2. (B) Design for ultraviolet light disinfection for MBR effluent that is based on greater than 75% transmissivity must be justified in the report.

4. (d) MBR operation.

   1. (1) Membrane cleaning. The following methods may be used:

      1. (A) Air scouring of at least 0.01 standard cubic feet per minute of air per square foot of membrane area but not more than 0.04 standard cubic feet per minute of air per square foot of membrane area;
      2. (B) A mixture of air scouring with mixed liquor jet feed;
      3. (C) Back-flushing;
      4. (D) Relaxation, which is short periods of air scouring without filtration; or
      5. (E) Chemical cleaning.

   2. (2) Operational control parameters.

      1. (A) In-line continuous turbidity monitoring of filtrate from each membrane train or cassette or an equivalent must be provided for operational control and indirect membrane integrity monitoring. If turbidity is used for indirect integrity monitoring, the value that indicates problems must be less than or equal to 1.0 nephelometric turbidity units (NTU).
      2. (B) An owner must follow the manufacturer's recommended frequency for MBR component inspection, testing, and maintenance. The inspection, testing, and maintenance procedures and frequencies must be included in the facility's operation and maintenance manual.
      3. (C) An owner must provide a facility operator access to any specialized tool necessary for the operation or maintenance of an MBR system. A description of all specialized tools and instructions for their use must be included in a operation and maintenance manual for the facility.

   3. (3) Control instrumentation.

      1. (A) A facility must have the ability to run in full manual mode in case of an automatic control failure; or
      2. (B) An operational backup programmable logic control center (PLC) is required if manual control is not possible.

5. (e) Chemical Use and Disposal.

   1. (1) The chemicals used in treatment and maintenance must not harm the MBR system or interfere with treatment.
   2. (2) The chemicals, including concentrations and disposal methods, must be identified in the report.

6. (f) Training.

   1. (1) Key staff must be trained to operate the particular MBR at a facility. They must be familiar with the sequencing and set points of all operations and actions typically controlled by automated systems in order to identify and respond to irregularities.
   2. (2) Proposals for staff training must be included in the report.

7. (g) Warranty and Bonds.

   1. (1) The membranes must have a warranty of at least five years.
   2. (2) The executive director may require a performance bond that meets the requirements of §217.7(b)(2)(E) of this title.

Source Note:The provisions of this §217.157 adopted to be effective August 28, 2008, 33 TexReg 6843.