| (a) System Sizing and Reliability.
(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) An SBR must have a minimum decantable volume that
is sufficient to pass the design flow, and must be capable of meeting
permitted effluent limits, with the largest basin out of service.
(3) A two-basin wastewater treatment facility without
removable aeration devices is required to have aerated storage of
mixed liquor separate from the SBR tank(s).
(4) An SBR with a fixed level decanter must have more
than two basins and additional decantable storage volume.
(5) An equalization basin is required if an SBR has
fixed decant equipment and decant volumes that do not accommodate
the peak flow.
(6) Organic loadings must conform to the values in
Table F.1. in Figure: 30 TAC §217.154(b)(2) of this title (relating
to Aeration Basin and Clarifier Sizing--Traditional Design). Organic
loadings must be below 35 pounds of five-day biochemical oxygen demand
per 1,000 cubic feet of tank volume.
(7) The reactor mixed liquor suspended solids (MLSS)
level at the normal operating level must range from at least 3,000
milligrams per liter (mg/l) to not more than 5,000 mg/l.
(8) The minimum depth of the MLSS during a react phase
is 9.0 feet.
(9) The minimum side water depth of an SBR tank is
12 feet.
(10) An SBR must include sludge digestion pursuant
to the requirements in Subchapter J of this chapter (relating to Sludge
Processing).
(b) Decanter Design.
(1) A decanter 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) The entrance velocity to a decanter must not exceed
1.0 foot per second.
(3) A decanter must draw effluent from below the water
surface and include a device that excludes scum.
(4) A decanter must maintain a zone of separation between
the settled sludge and the decanter of no less than 12 inches.
(5) A decanter must prevent solids from entering the
decanter during a react cycle by using one the following methods:
(A) recycling treated effluent to wash out solids trapped
in a decanter;
(B) mechanically closing a decanter when it is not
in use; or
(C) filling a decanter with air except during a decant
period.
(6) The performance of a decanter and related pipes
and valves must not be affected by ambient temperatures below 32 degrees
Fahrenheit.
(7) A fixed decanter is prohibited in a basin where
simultaneous fill and decant may occur.
(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) An SBR system utilizing more than two basins must
allow the decanting of at least two tanks simultaneously.
(10) If units downstream of an SBR are not capable
of accepting the peak flow rate of the decanting cycle, flow equalization
must be provided between the decanter and the downstream units.
(c) SBR Tank Details.
(1) An SBR requires multiple tanks.
(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) An elongated tank must be used for an SBR system
if influent baffling is required.
(4) An SBR tank must have a minimum freeboard of 18
inches at the maximum liquid level.
(5) An SBR tank must not be buoyant when empty.
(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) Each SBR wall must be watertight.
(8) A sump must be provided in any basin with a flat
bottom.
(9) An SBR system must have a dedicated means of transferring
sludge between aeration basins.
(10) An SBR system must include a means of scum removal
in each aeration basin.
(11) Each SBR tank must include a dewatering system
and an emergency overflow to another aeration tank or a storage tank.
(12) At a wastewater treatment facility that is not
staffed 24-hours per day, a manually operated SBR tank must include
a high-level alarm that notifies wastewater treatment facility staff
in accordance with §217.161 of this title (relating to Electrical
and Instrumentation Systems).
(13) A design must specify the means and frequency
for removal of grit and other debris from the SBR tanks.
(14) All equipment must be accessible for inspection,
maintenance, and operation. Walkways shall be provided to allow inspection,
maintenance, and process control sampling and to allow access to instrumentation,
mechanical equipment, and electrical equipment.
(15) An SBR may use fine screens pursuant to §217.122
of this title (relating to Fine Screens).
(16) An SBR preceded by a primary clarifier may use
a comminutor.
(17) An SBR must have a sufficient number of tanks
to operate at design flow with the largest tank out of service.
(d) Aeration and Mixing Equipment.
(1) In addition to the requirements of §217.155
of this title, aeration equipment must handle the cyclical operation
in an SBR.
(2) The aeration and mixing equipment must not interfere
with settling.
(3) A dissolved oxygen concentration of 2.0 mg/l must
be maintained in a tank during the fill cycle.
(4) The design must specify the blower discharge pressure
at the maximum water depth.
(5) An 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) The design of an SBR must allow for the removal
of air diffusers or mechanical aeration devices without dewatering
the tank.
(e) Control Systems.
(1) The motor control center must include programmable
logic controllers (PLC) that are able to operate with limited operator
adjustment and be programmed to meet the effluent limitations in the
wastewater permit at the design loadings. An SBR must have the ability
to run in full manual mode.
(2) A hard-wired backup means of operating the SBR
is required.
(3) The PLC must include battery backup. A duplicate
set of all circuit boards must be kept at the wastewater treatment
facility.
(4) Adequate controls for the separate operation of
each tank must be provided.
(5) A tank level system must include floats or pressure
transducers.
(A) A float system must be protected from prevailing
winds and freezing.
(B) A bubbler system in a tank level system is prohibited.
(6) The control panel switches must include the following
switches:
(A) pumps - hand/off/automatic;
(B) valves - open/closed/automatic;
(C) blowers or aerators - hand/off/automatic; and
(D) selector switch for tank(s) - in operation/standby.
(7) The control panel visual displays must include:
(A) a mimic diagram of the process that shows the status
and position of all pumps, valves, blowers, aerators, and mixers;
(B) process cycle and time remaining;
(C) instantaneous and totalized influent flow to the
wastewater treatment facility and effluent flow of the final discharge;
(D) tank level gauges or levels;
(E) sludge pumping rate and duration; and
(F) airflow rate and totalizer.
(8) The annunciator panel must include the following
alarm condition indicators:
(A) high and low water levels in each tank;
(B) failure of all automatically operated valves;
(C) decanter failure;
(D) blowers, if used - low pressure, high temperature,
and failure;
(E) mechanical aerator, if used - high temperature
and failure;
(F) pump - high pressure and failure; and
(G) mixers, if used - failure.
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