| (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
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