N.J. Admin. Code § 7:14A-23.21

Current through Register Vol. 56, No. 21, November 4, 2024

Section 7:14A-23.21 - Activated sludge

(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 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.

N.J. Admin. Code § 7:14A-23.21