Current through Register Vol. 56, No. 24, December 18, 2024
(a) The
activated sludge process may be used when wastewater is amenable to biological
treatment.
(b) The design data
outlined in this section are presumed to achieve a removal of 90 percent or
more of the B.O.D. and suspended solids susceptible to treatment from sewage of
normal characteristics and may not be appropriate where only partial removals
are intended.
(c) Provisions for
pre-chlorination of the raw sewage shall be made depending on the condition of
the influent.
(d) The design of
plants which may receive abnormally strong concentrations of wastewater, or
require an unusual aeration period or special equipment, may be considered for
approval as an activated sludge process upon presentation of appropriate
supporting data obtained from existing installations that demonstrate the
efficiency of the process.
(e)
Settling tanks for the activated sludge process shall be designed in
conformance with the following:
1. A skimming
tank, or equivalent, shall be provided for wastewater which contains greater
than 100 milligrams per liter (mg/l) of oil or grease;
2. Except in small sewage treatment plants
with a design capacity of less than 150,000 gallons per day, a minimum of two
preliminary settling tanks shall be provided with a total capacity that
provides a detention period of 90 to 150 minutes and a maximum surface settling
rate of 1,000 gallons/square foot/day based upon design flow;
3. For plants having a design capacity of 2.0
M.G.D. or less, final settling tanks shall have a minimum eight foot side water
depth and a maximum surface settling rate of 800 gallons per square foot per
day. For plants with a design capacity of more than 2.0 M.G.D. final settling
tanks shall have a minimum 10 foot side water depth and a maximum surface
settling rate of 1,000 gallons per square foot per day;
4. Final settling tanks shall be provided in
multiple units except in small installations;
5. Mechanical means shall be provided for the
collection and removal of sludge from all settling tanks; and
6. The use of upward flow settling tanks may
be considered when accompanied by supporting data on their hydraulic
characteristics and results of operations in actual plants.
(f) If the incoming wastewater to
an activated sludge system contains less than 2.0 parts per million dissolved
oxygen, pre-aeration of the pre-settled wastewater is required before the
admixture of returned sludge.
(g)
Aeration tanks for the activated sludge process shall be designed in
conformance with the following:
1. Multiple
units, capable of independent operation, shall be provided for all
installations;
2. Total required
detention period of aeration tanks, based upon 125 percent of design flow,
shall not be less than six hours. If provisions are made for the re-aeration of
the returned sludge before admixture with the pre-settled sewage, a lesser
detention period in the aeration tanks can be considered (the greater the
return sludge aeration period, the less the required mixed liquor detention
period);
3. Applied loading shall
not exceed 38 pounds of B.O.D., exclusive of return sludge, per 1,000 cubic
feet of tank volume;
4. Liquid
depths of not less than 10 feet, nor more than 15 feet, shall be provided;
and
5. Means to minimize foaming in
aeration tanks shall be provided.
(h) All inlets and outlets shall be equipped
with suitable devices for controlling the flow to each tank unit and to
withdraw any unit from service. Velocity between bays or around baffles shall
not exceed 0.5 feet per second.
1. Channels
and pipes shall be designed to provide self-cleaning velocities, or shall be
equipped with mechanical devices for maintaining solids in continuous
suspension.
(i) Devices
shall be provided for indicating rates of flow of pre-settled effluent, return
sludge, air to each tank unit, and total volume of wasted sludge. These devices
shall also totalize and record as well as indicate flows.
(j) Requirements for air supply are as
follows:
1. Air requirements at all times
shall be sufficient to:
i. Maintain at least
two parts per million of dissolved oxygen in all parts of the aeration
tank;
ii. Maintain sufficient
turbulence to maintain intimate contact of sludge particles with sewage;
and
iii. Prevent deposition of
solids in any part of aeration unit.
2. Aeration capacity at standard temperature
and pressure shall be at least 1.5 cubic feet per gallon of incoming raw sewage
plus the capacity required for reaeration of returned sludge.
3. Blowers shall be in multiple units and of
such capacity that full operation requirements can be met with the largest unit
out of service.
4. Blower capacity
required to deliver air to channels, sludge pumps, foam-control pumps, or
similar demands shall be in addition to that required for tank aeration as
specified in 1 above.
5. The air
diffuser system shall be capable of delivering 150 percent of normal
requirements. Normal requirements are considered to be 1,000 cubic feet per
pound of B.O.D. to be removed from the sewage entering aeration
tanks.
6. Air filters shall be
capable of supplying a continuous air supply having a dust content of not more
than 0.5 milligrams per 1,000 cubic feet.
7. Each blower shall be equipped with a
silencer.
8. Aeration plates, tubes
or jets shall be designed to permit removal for inspection or cleaning, and for
maintaining an even distribution of air throughout the aeration
tanks.
9. Individual assembly units
of diffusers shall have a substantially uniform pressure loss and shall be
equipped with control valves with indicator markings.
(k) Return activated sludge pumps or air
lifts shall have variable combined capacity, capable of pumping at least 25
percent of the projected flow with the largest single unit out of service.
Normal return sludge capacity shall be at least 50 percent of the average
dry-weather sewage flow.
1. In addition to
capacity required for return sludge pumping, waste sludge pumping facilities
shall be provided with a minimum capacity not less than 0.5 percent of design
flow, or 10 gallons per minute, whichever is larger.
2. The means for the further treatment and
management of waste activated sludge shall be specified.
(l) Extended aeration systems shall be
designed in accordance with the following:
1.
Screening equipment consisting of a comminuting device with a bar screen in
parallel is required.
2. Aeration
tanks shall provide a detention period of at least 24 hours based upon design
flow without recirculation. At least two tanks shall be provided in plants with
design capacities of 100,000 gallons per day or more.
3. Air blower equipment shall be at least in
duplicate and shall have capacity with the largest unit out of service to
provide either at least three cubic feet per minute per foot length of aeration
tank or at least 2,100 cubic feet of air per pound B.O.D. of raw sewage,
whichever is greater. Equipment shall provide for variation in the volume of
air to be delivered in at least three steps. Additional air capacity shall be
provided if required for air lifts or other needs.
4. Provisions shall be made for the future
installation of froth-breaking spray equipment, if necessary.
5. Final settling tanks shall provide at
least a 3.5 hour detention period based upon design flow without recirculation.
i. Two or more tanks shall be provided on
installations having capacities of 100,000 gallons per day or more.
ii. For tanks with hopper bottoms, the upper
third of depth of hopper may be considered as effective settling
capacity.
6. Return
sludge capacity of at least 100 percent of design sewage flow shall be
provided.
7. Appropriate means,
such as a V-notch weir, shall be provided for measurement of sewage flow. For
installations having capacities of 100,000 gallons per day or more,
indicating-recording-totalizing equipment is required.
8. Waste sludge holding tanks with a capacity
of at least one cubic foot per capita shall be provided.
(m) Contact stabilization systems shall be
designed in accordance with the following:
1.
Screening equipment consisting of a comminuting device with a bar screen in
parallel is required.
2. Combined
volumes of the contact aeration and sludge reaeration tanks shall provide a
detention period of at least nine hours based on design flow without
recirculation.
i. Aerobic digester tanks
shall provide a capacity of at least three cubic feet per capita.
ii. At a minimum, duplicate tanks shall be
provided in sewage treatment plants with design capacities of 100,000 gallons
per day or more.
iii. When
anaerobic digestion is employed, the design of the drying beds must be in
conformance with
N.J.A.C.
7:14A-23.28.
3. Air blower equipment shall be at least in
duplicate, and shall have capacity with the largest unit out of service to
provide at least 1,600 cubic feet of air per pound B.O.D. of raw sewage for
contact aeration sludge reaeration and aerobic digester requirements.
i. The proposed equipment shall provide for
variation in the volume of air to be delivered in at least three
steps.
ii. Additional air capacity
shall be provided if required for air lifts or other needs. The air supply
requirements stated in (j)1 through 9 above also apply to contact
stabilization.
