Current through Register Vol. 41, No. 3, September 23, 2024
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from being withdrawn with the effluent.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.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
