| (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.
(ii) Coarse bubble air diffusers may be used for mixing
in a pre-anoxic tank.
(B) Scum and Foam Handling. An MBR must control scum
and foam so that scum or foam does not interfere with treatment, and
must prevent unauthorized discharge of scum or foam from a treatment
unit.
(C) Cranes and Hoists. A crane, hoist, or other process
or mechanism approved in writing by the executive director must be
provided for periodic cleaning and maintenance of the membranes.
(11) Disinfection.
(A) An owner may request and the executive director
may approve, in writing, decreased ultraviolet light or chlorine dosing
requirements for MBR effluent.
(B) the design for ultraviolet light disinfection for
MBR effluent that is based on greater than 75% transmissivity must
be justified in the engineering report.
(e) MBR operation.
(1) Membrane cleaning. The following methods may be
used to clean membranes:
(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;
(B) a mixture of air scouring as described in subparagraph
(A) of this paragraph and mixed liquor jet feed;
(C) back-flushing;
(D) relaxation; or
(E) chemical cleaning.
(2) Operational Control Parameters.
(A) In-line continuous turbidity monitoring of filtrate
from each membrane train or cassette must be provided for operational
control and indirect membrane integrity monitoring. An alarm must
be provided to notify the wastewater treatment facility operator of
turbidity greater than or equal to 1.0 nephelometric turbidity units
(NTU).
(B) An owner must follow the manufacturer's recommended
frequency for MBR component inspection, testing, and maintenance.
The manufacturer's recommended inspection, testing, and maintenance
procedures and frequencies must be included in the wastewater treatment
facility's operation and maintenance manual.
(C) An owner must provide a wastewater treatment 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 the operation
and maintenance manual for the wastewater treatment facility.
(3) Control instrumentation. A wastewater treatment
facility must have the ability to operate in full manual mode.
(f) Chemical Use and Disposal.
(1) The chemicals used in treatment and maintenance
must not harm the MBR system or interfere with treatment.
(2) The chemicals used in treatment and maintenance,
including concentrations of the chemicals and chemical disposal methods,
must be identified in the engineering report.
(g) Training.
(1) The individuals trained to operate an MBR system
must be familiar with the sequencing and set points of all operations
and actions typically controlled by automated systems and be able
to identify and respond to irregularities.
(2) The operation and maintenance manual must include
instructions on how to operate the MBR in manual mode.
(h) Warranty and Bonds.
(1) All membranes must have a warranty of at least
five years.
(2) The executive director may require a performance
bond that meets the requirements of §217.7(b)(2)(E) of this title.
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