9 Va. Admin. Code § 25-790-710 - Sequencing batch reactors (SBR)
A.
Usage. In accordance with the requirements of this chapter and standards
contained in this chapter, batch operation modifications of the activated
sludge process will be considered as conventional secondary treatment
processes. Adequate performance data and information from a full scale
treatment works of similar design, including the levels of influent wastewater
characteristics that produce hydraulic and organic loading rates within 25% of
values used in the proposed design, shall be provided if an SBR design is to
accomplish an effluent quality more advanced than a secondary level.
B. Design. The design shall meet the
applicable loading requirements. The operating cycle normally consists of FILL,
REACT, SETTLE, DRAW, and IDLE sequences with alternating sequences of mixing
and aeration on and off.
1. A minimum of two
basins shall be provided for design flows in excess of 0.1 mgd. The minimum
total basin volume shall be equal to the design daily influent flow volume and
either upstream in-line or off-line storage is necessary to minimize influent
flow during settling and decanting. Effective scum collection and removal
equipment shall be provided.
2. The
design basis for meeting oxygen requirements shall consider the variation in
liquid level depth and the aeration sequence time.
3. The basin depth shall be sufficient to
provide optimum separation of the settled biomass and the point of effluent
withdrawal.
4. Adequate mixing
shall be provided to resuspend settled solids at the start of the FILL sequence
and maintain solids in suspension over the design liquid volume
range.
5. A high liquid level
overflow shall be provided between basins. The overflow shall be located as far
as possible from the outlet device and in no case be closer than 10 feet from
the outlet device.
6. Inlets to
each basin shall be located as far as possible from the outlet and in no case
be closer than 10 feet from the outlet.
7. Scum baffles or other suitable
arrangements shall be provided to prevent scum from being withdrawn with the
effluent.
8. Outlet facilities
shall be designed to prevent resuspension of the settled solids in the basins.
An adjustable flow rate control device shall be provided on each basin
outlet.
9. Waste sludge control
facilities shall have a rate per day equal to 50% of the total basin
volume.
10. The FILL and DRAW
sequences for an individual basin shall not overlap.
C. Features. Automatic control valves and
switches shall be provided for controlling the operating sequences of each
basin. Automatic control valves shall be capable of manual operation. Control
sequences shall be adjustable to allow flexibility in operating time periods
for each sequence. The control system shall provide automatic operation of the
inlet valve and outlet valve to each basin, the air supply valve to each basin
and the blowers or mechanical aerators.
1. The
control system shall provide for automatic operation of downstream units or
equipment as necessary. The control system should also provide automatic
control of the waste sludge removal system. A spare automatic control unit
shall be provided.
2. A monitoring
system shall be provided that will indicate control system status and actual
valve position of each automatically operated valve. Also, the control system
status and the actual operational status of both the air supply system (blowers
or mechanical aerators) and sludge removal system shall be monitored, when
equipped for automatic operation. The monitoring system shall include an alarm
to indicate a malfunction of the control system.
3. Dual hydraulic pumps and air compressors
shall be provided when such facilities are utilized in conjunction with valve
operators. Electrically operated valves shall be designed so as to fail only in
the open position.
4. A high liquid
level alarm for each basin shall be provided to signal an alarm condition prior
to reaching the overflow pipe or port.
5. Influent flow and effluent flow
measurement for the treatment facility shall be provided. The extent of the
flow measurement equipment shall be in accordance with this chapter.
6. Disinfection and other downstream
treatment units shall be sized based on the maximum design DRAW sequence flow
rate.
Notes
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
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