(a) Applicability.      
        (1) This section contains criteria for low-pressure, vacuum, and gravity ultrafiltration or microfiltration membrane bioreactors (MBRs).       
        (2) Other types of 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).       
      (b) Definitions.      
        (1) Flat plate system--A membrane bioreactor that arranges membranes into rectangular cartridges with a porous backing material that provides structural support between two membranes.       
        (2) Gross flux rate--The volume of water that passes through a membrane, measured in gallons per day  per square-foot of membrane area at a standard temperature of 20 degrees Centigrade.       
        (3) Hollow fiber system--A membrane bioreactor composed of bundles of very fine membrane fibers, approximately 0.5 - 2.0 millimeters in diameter, held in place at the ends with hardened plastic potting material, and supported on stainless steel frames or rack assemblies. The outer surface of each fiber is exposed to the mixed liquor with filtrate flow from outside to inside through membrane pores.       
        (4) Net flux rate--The gross flux rate adjusted for production lost during backwash, cleaning, and relaxation.       
        (5) Transmembrane pressure--The difference between the average pressure on the feed side of a membrane and the  average pressure on the permeate side of a membrane.       
        (6) Tubular system--A system in which sludge is pumped from an aeration basin to a pressure driven membrane system outside of a bioreactor where the suspended solids are retained and recycled back into the bioreactor while the effluent passes through a membrane.       
      (c) Performance Standards.      
        (1) MBR performance standards for conventional pollutants and nutrients are shown in the following table:        
          Attached Graphic         
        (2) The executive director may require an owner to submit a pilot study report or data from a similar wastewater treatment facility if a wastewater treatment facility is designed to achieve  higher quality effluent than the performance standards listed in Table F.7. in Figure: 30 TAC §217.157(c)(1). A similar wastewater treatment facility must have similar characteristics including:                  (A) climate region;                   (B) peak flows;                   (C) customer base, including sources and percent contribution; and                   (D) other characteristics required by the executive director.         
      (d) Wastewater Treatment Facility Design.      
        (1) Pretreatment.                  (A) Each MBR system must have fine screening to prevent damage from abrasive particles or fibrous, stringy material.                      (i) Fine screens must be rotary drum or traveling band  screens with either perforated plates or wire mesh.                       (ii) Fine screens for hollow fiber or tubular systems must have an opening size of 0.5 - 2.0 millimeter (mm).                       (iii) Fine screens for flat plate systems must have an opening size of 2.0 - 3.0 mm.                       (iv) Bypass of a fine screen must be prevented by use of a duplicate fine screen, emergency overflow to a wet well, or an alternative method that has been approved in writing by the executive director.                       (v) A fine screen must be designed to prevent bypass at the peak flow.                       (vi) Coarse screens may be used ahead of fine screens to reduce the complications of fine screening.                     (B) The economic feasibility of primary sedimentation must be evaluated for facilities designed for an average daily flow of 5.0 million gallons per day or more. The economic feasibility evaluation must be included in the engineering report.                   (C) Fat, oil, and grease removal is required if the levels of fat, oil, and grease in the influent may cause damage to the membranes. The specific detrimental concentration must be determined by the equipment manufacturer. Influent concentrations of fat, oil, and grease equal to or more than 100 milligrams per liter (mg/l) must have fat, oil, and grease removal.                   (D) The necessity of grit removal must be evaluated for a wastewater treatment facility that has a collection system with excessive  inflow and infiltration. Excessive grit accumulation is characterized by grit accumulation in any treatment unit following the headworks. An evaluation must be included in the engineering report.         
        (2) Biological Treatment.                  (A) The reactor volume must be determined using rate equations for substrate utilization and biomass growth according to §217.154 of this title (relating to Aeration Basin and Clarifier Sizing--Traditional Design), or another method approved by the executive director in writing.                   (B) The design sludge retention time (SRT) for an MBR must be at least 10 days, but not more than 25 days.                   (C) The design operational range of mixed liquor suspended solids (MLSS)  concentration must be:                      (i) at least 4,000 mg/l but not more than 10,000 mg/l in the bioreactor; and                       (ii) at least 4,000 mg/l but not more than 14,000 mg/l in the membrane tank.                     (D) An MBR system designed for an SRT or MLSS outside the ranges in subparagraph (C) of this paragraph requires a pilot study in compliance with paragraph (8) of this subsection or data from a similar wastewater treatment facility that demonstrates that the design parameters are sustainable and can achieve the expected performance to the executive director's satisfaction.         
        (3) Aeration.                  (A) An aeration system in an MBR must be capable of maintaining dissolved oxygen levels as  listed in subparagraph (C) of this paragraph.                   (B) An aeration system in an MBR must compensate for low oxygen transfer efficiency associated with the maximum MLSS concentrations established in paragraph (2)(C) of this subsection. The alpha value used to determine design oxygen transfer efficiency must be 0.5 or lower.                   (C) The oxygen concentration range used for sizing aeration systems for treatment zones must be:                      (i) not more than 0.5 mg/l for anoxic basins;                       (ii) at least 1.5 mg/l but not more than 3.0 mg/l for aerobic basins; and                       (iii) at least 2.0 mg/l but not more than 8.0 mg/l for membrane basins.                     (D) An MBR must  include dissolved oxygen monitoring and an alarm to notify an operator if dissolved oxygen levels are outside of the design operating range, or if there is a rapid decrease in dissolved oxygen. Alarm systems must comply with §217.161 of this title (relating to Electrical and Instrumentation Systems).         
        (4) Recycle Rates. Facilities without advanced nutrient removal must be designed with recycle rates sufficient to sustain the design mixed liquor concentrations (typically from 200% to 400% of the wastewater treatment facility's influent flow).       
        (5) Nutrient Removal.                  (A) A system designed for advanced nutrient removal must include an isolated tank or baffled zone to separate anoxic, anaerobic, and aerobic  treatment zones.                   (B) The engineer shall submit calculations to support the sizing of the reactor volumes.                   (C) If recycled activated sludge is returned to an anoxic or anaerobic basin, a wastewater treatment facility designed for total nitrogen or advanced nutrient removal must contain a deoxygenation basin, a larger anoxic basin, or another method of decreasing dissolved oxygen concentration approved in writing by the executive director.                   (D) An advanced nutrient removal system must be designed with recycle rates sufficient to sustain the designed mixed liquor concentrations in both the aeration, anoxic, and anaerobic basins (sufficient recycle rates are typically 600% or more of the influent flow).         
        (6) Use of Membranes.                  (A) Use of a membrane system other than a hollow fiber system, tubular system, or a flat plate system is considered an innovative technology and is subject to §217.7(b)(2) of this title.                   (B) The engineering report must provide justification for the use of a membrane material other than one of the following:                      (i) polyethersulfone (PES);                       (ii) polyvinylidene fluoride (PVDF);                       (iii) polypropylene (PP);                       (iv) polyethylene (PE);                       (v) polyvinylpyrrolidone (PVP); or                       (vi) chlorinated polyethylene (CPE).                     (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.                   (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.                   (E) Any chemical used for cleaning must not adversely affect the membrane material.         
        (7) Membrane Design Parameters.                  (A) MBRs must be designed for:                      (i) an average daily net flux rate equal to or less than 15 gallons per day per square-foot of membrane area;                       (ii) a peak daily net flux rate equal to or less than 1.25 times the average daily net flux rate; and                       (iii) a two-hour peak net flux rate equal to or less than 1.5 times the average daily net flux rate.                     (B) The executive director may approve larger net flux rates if the rates are substantiated to the executive director's satisfaction with a pilot study or data from a similar wastewater treatment facility.                   (C) An MBR system with a peak flow rate that is greater than 2.5 times the average daily flow must use an equalization basin, off-line storage, or reserve membrane capacity to accommodate the higher peak flow.                   (D) Hollow Fiber Transmembrane Pressure (TMP).                      (i) The operational TMP of a hollow fiber MBR system must be at least 2.0 pounds per square inch (psi) but not  more than 10.0 psi.                       (ii) The TMP of a hollow fiber MBR system must not exceed 12.0 psi.                     (E) Flat Plate TMP.                      (i) The operational TMP of a flat plate MBR system must be at least 0.3 psi but not more than 3.0 psi.                       (ii) The TMP of a flat plate MBR system must never exceed 4.5 psi.                     (F) Tubular, Out of Basin TMP.                      (i) The operational TMP of a tubular, out of basin MBR system must be at least 0.5 psi but not more than 5.0 psi.                       (ii) The TMP of a tubular, out of basin MBR system must never exceed 10.0 psi.           
        (8) Supporting Data. An owner must provide pilot study reports or data  from a similar wastewater treatment facility for a wastewater treatment facility that is either:                  (A) required to meet stricter standards than in Table F.7. in Figure: 30 TAC §217.157(c)(1); or                   (B) designed to operate outside normal operating parameters defined within this section.                      (i) A pilot study must be conducted for at least 30 days after the initial start-up and acclimation period.                       (ii) A pilot study must be designed to evaluate the membrane performance under actual operational conditions, including flow variations and influent wastewater characteristics.                       (iii) The treatment and pretreatment processes evaluated in a pilot study or similar wastewater  treatment facility must be equivalent to the processes that will be used in the wastewater treatment facility.                       (iv) The results of the pilot study must include the following recommendations:                          (I) net flux rates for design flow and peak flow;                           (II) average and maximum transmembrane pressure;                           (III) cleaning and backwash intervals;                           (IV) expected percent chemical recovery after chemical cleaning;                           (V) dissolved oxygen concentrations for reactors and membrane basins;                           (VI) MLSS concentrations for reactors and membrane basins;                           (VII) SRTs for reactors and membrane basins; and                           (VIII) expected effluent concentrations of conventional pollutants and nutrients, including the pollutants and nutrients that will be limited or monitored in the wastewater treatment facility's wastewater permit.             
        (9) Redundancy.                  (A) A wastewater treatment facility must be able to operate at normal operating parameters and conditions for design flow with the largest MBR unit or train out of service.                   (B) Acceptable methods of providing redundancy are additional treatment trains, additional treatment units, or storage. The engineering report must include calculations that demonstrate adequate redundancy within the wastewater treatment facility.         
        (10) Other Components.                  (A) Mixers.                      (i) Unaerated (deoxygenation, pre/post anoxic, and anaerobic) zones must have a submersible mixing system, or an alternative mixing system that has been approved in writing by the executive director.                      Cont'd...