Current through Register Vol. 56, No. 24, December 18, 2024
(a) The
Department does not examine plans covering fire and explosive hazards, heat
controlling equipment or safety devices and such safeguards are the
responsibility of the design engineer.
(b) Supernatant liquor from sludge digestion
tanks shall be returned downstream of the influent monitoring points to the raw
sewage except that at activated sludge plants, or other plants utilizing air as
a method of biological treatment, provisions may be made for disposal in
aeration or reaeration tanks. The wastewater treatment facility shall be
designed to treat the increased pollutant concentration and hydraulic loading
of the supernatant or means shall be provided for separate treatment.
(c) The minimum diameter of all sludge pipes
shall be eight inches for gravity flow and six inches for sludge
pumping.
(d) A fresh-water hydrant
near the sludge digestion tanks is recommended, and, if present, shall be
provided with a suitable backflow-prevention device.
(e) Provisions shall be made for the
introduction of chemicals into all sludge storage or digestion tanks.
(f) Digesters which are proposed to be
utilized to satisfy stabilization requirements shall be designed to meet the
requirements for pathogen reduction and vector attraction reduction in
accordance with N.J.A.C. 7:14A-20.
(g) Sludge digestion tanks shall be in
conformance with the following:
1. Two or
more separate units shall be provided, a single digestion tank may be approved
if the plan and report show all emergency provisions and the proposed use is
for small installations (design capacity of less than 150,000 gpd) where
alternate sludge storage is available for emergency use without creating a
local nuisance, and where pumps and piping are available for such
emergency.
2. Suitable equipment to
insure mixing or circulation of the tank contents shall be provided for primary
digesters.
3. The proportion of
tank depth to area shall be such as to permit the formation of a reasonable
depth of supernatant liquor.
4.
Tank bottoms shall slope toward the withdrawal pipe not less than three inches
per foot. Flat bottom tanks will not be approved.
5. At least two access manholes of adequate
size shall be provided in the top of the digester in addition to the gas dome.
An access manhole in the side wall of the tank is recommended.
6. In the case of multiple tanks, a provision
shall be made to direct the raw sludge to any tank. In circular tanks the raw
sludge inlet shall be at a point that is removed from the overflow or
supernatant draw-offs by a distance at least equal to the radius of the tank.
In rectangular tanks the raw sludge inlet shall be at the opposite end from the
overflow and digested sludge draw-off lines.
7. An emergency overflow shall be provided.
Provisions shall be made for sampling and removal of supernatant from several
levels.
8. Means shall be provided
for sampling of digested sludge in accordance with
N.J.A.C.
7:14A-23.14. Digested sludge withdrawal
piping shall extend from the center and bottom of circular tanks. Means shall
be provided for backflushing digested sludge withdrawal piping. Adequate
transfer piping shall be provided.
9. Unheated primary anaerobic digestion tanks
will not be approved.
10. The
mixing of the contents of anaerobic digesters by air is prohibited.
(h) Separate sludge digestion
capacity shall be in conformance with the following:
1. Separate sludge digestion capacity shall
be as follows, unless acceptable justification is submitted for an alternate
design:
| Type of Plant | Minimum Cubic Feet per |
| Capita |
| Primary | 2 to 3 |
| Primary plus standard filter | 2.5 to 3 |
| Primary plus high rate filter | 3 to 4 |
| Chemical coagulation | 4 to 6 |
| Activated sludge | 4 to 6 |
2.
Larger volumes of sludge digestion capacity shall be provided for smaller
plants.
3. The sludge digestion
capacity shall be increased when industrial wastes and/or garbage solids are
present, and may be reduced if the sludge is thickened. Volumes shall be
computed on the basis of the bottom sloping up 30 degrees from the horizontal
unless mechanical sludge collection is employed.
(i) Anaerobic digestor gas collection shall
meet the following general requirements:
1.
Waste gas burners shall be provided for excess gas.
i. Burners shall be placed at least 25 feet
away from structures if placed at ground level, or may be located on roofs of
buildings provided they are remote from digestion tanks.
ii. Burners shall be equipped with pilot
lights and means for igniting manually, and shall be equipped with flame
traps.
2. All enclosures
containing gas piping or apparatus shall be equipped with forced draft
ventilation either of the wind-driven or motor-operated type. If of the motor
type, the design shall be such that the motor does not come in contact with
gases; or spark-proof motors shall be used.
3. A gas meter shall be provided and a bypass
installed.
4. Boilers utilizing gas
shall be located in a separate enclosure having adequate means of ventilation
and preferably located at ground level.
5. All gas lines shall have suitable flame
traps and other safety equipment.
(j) Anaerobic digestor heating shall meet the
following general requirements:
1. Preference
shall be given to means of external heating by means of a heat exchanger.
Heating capacity shall be adequate to maintain sludge at 85 to 95 degrees
Fahrenheit at all times. Suitable controls shall be provided for automatic
operation.
2. Thermometers shall be
provided to show temperatures of sludge in the digester, and the sludge going
to and from the heat exchanger. Thermometers shall also be provided to show the
temperature of the water going to and from the heating coils or heat
exchanger.
3. An auxiliary fuel
shall be provided, such as oil or commercial gas.
