(a) Pumping.
(i) Design requirements. Sludge pumps shall
be provided with a positive suction pressure at the pump impeller, rotor or
plunger at dynamic conditions. Discharge pressure shall include static pressure
difference and system friction losses based on the higher viscosity of the
sludge than water.
(ii) Piping and
valves.
(A) Minimum size. Sludge piping and
valves shall at least four (4) inches (10.2 cm) in diameter for pressure piping
and six inches (15.2 cm) in diameter for gravity pipe. Pump suction and
discharge shall not be less than three (3) inches (7.6 cm) in
diameter.
(B) Minimum velocity. For
sludge pipes larger than four (4) inches (10.2 cm) in diameter, the minimum
velocity shall be one fps (0.3 m/sec).
(b) Thickening.
(i) Types.
(A) Gravity. Gravity thickening shall only be
used for primary sludge, digested primary sludge, lime sludge, or combinations
of lime sludge, trickling filter humus and primary sludge.
(B) Dissolved air flotation. Dissolved air
flotation shall only be used for combination of primary and biological sludges,
waste biological sludges, and aluminum and iron salt sludges.
(ii) Design parameters.
(A) Influent solids concentration. The design
for influent solids concentrations to gravity or flotation thickeners shall be
5,000 mg/L or less, except tertiary lime sludge.
(B) Operating schedule. Sludge thickening
facilities shall have the capacity to treat the maximum amount of solids
produced. Where intermittent operation is provided, sludge holding tanks ahead
of and after the thickening process shall be provided.
(C) Solids loading. Solids loadings (solids
applied to the thickener) on thickening devices shall be limited to the
following maximum values.
Sludge Type |
Solids Loading lb/sq ft/day
Gravity |
Dissolved Air Flotation |
kg/m2/d Gravity |
Dissolved Air Flotation
|
Primary |
24 |
NA |
117.2
|
|
Digested |
20 |
NA |
97.6
|
|
primary |
|
|
|
|
Waste |
|
|
|
|
activated, |
|
|
|
|
without |
NA |
12 |
|
58.6 |
polymer with polymer |
|
48
|
|
234.3 |
Primary and |
15 |
-- |
73.2
|
|
trickling filter
|
|
|
|
|
Anaerobically |
NA |
NA
|
|
|
digested |
|
|
|
|
primary and
|
|
|
|
|
activated |
|
|
|
|
Primary and |
20 |
NA |
97.6
|
|
lime Tertiary lime |
60 |
NA
|
292.9 |
|
Alum |
NA |
12 |
|
58.6 |
*NA - Not allow |
ed.
|
|
|
|
(D)
Hydraulic loading. Gravity thickeners shall be designed for 400-800 gpd/ sq ft
(16.3 m3/m²/d to 32.5
m3/m2/d) of surface
area.
(iii) Number of
units. Unless sludge storage capacity for three (3) days is provided, there
shall be at least two (2) units of equal capacity provided for sludge
thickening.
(iv) Controls. Controls
for gravity and flotation sludge thickening operations shall include provision
for influent flow rate control. Centrifuge thickening shall include adjustable
manual controls for differential scroll speed, pool depth, and influent flow
rate. Where chemical conditioning is required, chemical dosage rate shall have
adjustable manual controls.
(v)
Side stream waste characteristics. The flow, organic load, and solids load in
the thickener return flow to the plant shall be included in the plant design
loadings.
(vi) Odor control.
Provisions shall be made for the continuous chlorination of gravity thickener
influent. Any thickening installation for anaerobically digested sludge shall
make provisions for enclosing zones where the sludge or decant is exposed to
atmosphere, exhausting the zone at an adequate rate to prevent escape of gas,
and treating the exhaust air for removal of odor causing agents.
(c) Aerobic digestion.
(i) Solids retention time. Solids shall be
retained in the aerobic digester for thirty (30) days for primary sludge and
twenty (20) days for waste sludge from conventional activated sludge systems.
Waste activated sludge from extended aeration systems shall be retained for a
minimum of ten (10) days.
(ii)
Mixing and aeration requirements. Aeration requirements shall include the
oxygen requirements for BOD stabilization, nitrification of ammonia nitrogen in
the sludge, and nitrification of organic nitrogen in raw sewage solids and
biological solids. A minimum dissolved oxygen of 2 mg/l shall be maintained.
Minimum aeration requirements shall be:
Sludge |
CFM/1,000 lb solids/day |
m3/min/1,000 kg/d |
Extended Aeration |
300 |
18.7 |
Conventional Activated Sludge |
800
|
50.0 |
Primary Sludge |
2,100 |
131.0 |
The aerobic digester aeration shall be provided with
nonclog diffused aeration. Mechanical surface aerators shall not be allowed.
Aeration provisions shall be a minimum of 30 cfm/1,000 cu ft (30
m3/min/1,000 m3) of
volume.
(iii) Number of
digesters. Where aerobic digesters are used, two (2) or more shall be provided
for treatment plants having an average design capacity of 100,000 gpd or more.
Multiple aerobic digesters shall be arranged to permit either parallel or
series operation.
(iv) Supernatant
removal and disposal. Supernatant shall be returned prior to the influent of
the biological treatment process.
(d) Anaerobic digestion.
(i) Sludge characteristics. The minimum
sludge concentration for feed to anaerobic digesters is four percent.
(ii) Number of digesters. Two or more
digesters shall be provided for treatment plants having an average design
capacity of 100,000 gpd (378.54 m3/d) or
more.
(iii) Design requirements.
(A) Temperature. Primary anaerobic digesters
shall be heated to provide a minimum temperature of 95°F (35°C).
Controls shall maintain the digester temperature within ±5°F
(±2° C).
(B) Mixing
equipment. Digester mixing shall, as a minimum, provide control of scum
accumulation at the gas/liquid interface. Mixing that is designed for
increasing the effectiveness of the digester and thereby reducing detention
time shall mix the entire tank contents. Mixing devices and their application
rate that will be considered to provide high-rate digestion are:
Volume |
Per 1,000 cf
|
Per 1,000 m3 |
Slow speed turbine mixers |
0.25 hp
|
6.7 kw |
Draft tube mechanical mixers |
0.40 hp
|
10.5 kw |
External pumps and jet nozzles |
500 gpm
|
66.7 m3/m |
Gas mixing applied at bottom of digester |
10 cfm |
10 m3/m |
Less mixing may be provided; however, longer solids
retention times than described below shall be required.
(C) Solids retention time. The minimum solids
retention time for heated, primary digesters are:
Unmixed
|
Completely mixed
|
30 days |
10 days |
Solids retention time shall be the same as liquid retention
time in the primary digester where waste activated sludge is an aerobically
digested.
(D) Volatile
solids loading. As an alternative design basis to solids retention time, heated
primary digesters may be designed for the following maximum volatile solids
loading:
Unmixed
0.1 lb/ft3/day (1.6
kg/m3/d)
Completely mixed
0.3 lb ft3/day (4.8
kg/m3/d)
(iv) Sludge piping.
(A) Inlet. Except in completely mixed
digesters, multiple inlets shall be provided. The piping shall provide the
opportunity to heat undigested sludge prior to entering the digester.
(B) Sludge withdrawal. Except in completely
mixed digesters, multiple withdrawal pipes shall be provided. One or more
withdrawal pipes shall be from the digester floor.
(C) Supernatant withdrawal. The design basis
for facilities using digesters for waste activated sludge shall assume no
supernatant withdrawal. Piping for supernatant withdrawal may be provided. A
minimum of three (3) supernatant withdrawal levels shall be provided
otherwise.
(v) Gas
system. All portions of the gas system, including the space above the tank
liquor, storage facilities, and piping shall be designed to be under greater
than atmospheric pressure at all times.
(A)
Piping. Gas piping shall be 2.5 inches (6.4 cm) diameter or greater. Piping
from the digester shall be provided with a flame trap. Piping shall slope to
condensate traps. Float controlled condensate traps are not
permitted.
(B) Safety equipment.
All necessary safety equipment shall be included. Pressure and vacuum relief
valves, flame traps and other safety equipment shall be provided. Gas safety
equipment and gas compressors shall be housed in a separate room with an
exterior entrance.
(C) Metering. A
gas meter with bypass shall be provided for measurement of total gas
production.
(vi) Heating
equipment. Sludge and digester contents shall be heated with an external heat
exchanger. Where sludge is heated using digester gas, an auxiliary fuel supply
shall be provided. Boilers using digester gas shall be designed to minimize
corrosion and to facilitate burner replacement. All digester gas that is not
beneficially used shall be incinerated in a waste gas burner.
(vii) Access. The roof of the digester and
the top sidewall shall be provided with sealed access hatches.
(viii) Sampling. One and one-half inches (3.8
cm) or larger sampling ports shall be provided for inlet sludge, effluent
sludge, supernatant and digester contents.
(ix) Supernatant disposal. Supernatant from
secondary digesters or from subsequent thickening or dewatering facilities for
digested sludge shall be treated independently or returned immediately
preceding the biological process. Supernatant shall not be returned to the
primary clarifier.
(e)
Dewatering.
(i) Mechanical dewatering. Where
provided, mechanical dewatering facilities shall include storage tanks for
liquid sludge and shall provide for reliable use.
(ii) Drying beds.
(A) Gravity. Drying beds may be strictly
evaporation or evaporation -percolation. Evaporation-percolation beds shall be
provided with graded gravel and sand beds over perforated underdrain pipe.
Evaporation beds shall be designed for the application of 1.5 feet (0.46 m) of
sludge per year. Evaporation - percolation beds shall be designed for the
application of four feet (1.2 m) of sludge per year. Storage of sludge in the
beds or in separate basins shall provide 180 days of capacity. Percolate shall
be returned to the plant ahead of the biological treatment process.
(B) Vacuum. The bed area for vacuum assisted
open drying beds shall be based on the application of no more than forty (40)
feet (12.2 m) of liquid per year. If the beds are housed, the bed area shall be
based on the application of eighty (80) feet (24.4 m) per year. Where beds are
not housed, sludge storage shall be provided for 180 days of capacity. Polymer
conditioning, chemical feed, chemical storage and facilities for mixing the
polymer with the sludge shall be provided. Vacuum pumps, sump pumps, chemical
feed equipment and motor control equipment shall be housed.
(iii) Filtrate disposal. Filtrate,
centrate or underdrain liquid shall be returned to a point upstream of the
biological treatment process. Centrate or filtrate shall not be returned
upstream of the primary clarifier.
(f) Disposal.
(i) Degree of stabilization.
(A) Land application. Sludges shall be
stabilized. Sludges that are to be used on public lands that are accessed by
the public (parks, golf courses, cemeteries) or sludges that are to be made
available to the public shall be composted or stabilized and stored for a
period of at least one (1) year. Sludges that are to be incorporated into the
land shall be stabilized.
"Stabilized sludge" shall have reduced organic content and
reduced pathogenic content. Stabilized sludge shall have less than 60 lb of
BOD5 per 1,000 lb (60 kg/1,000 kg) of dry weight sludge
solids.
(B) Landfill.
Sludge processed for incorporation into a landfill shall be (1) a solid or
semisolid material that will not release water upon standing, and (2) has been
subjected to anaerobic or aerobic digestion, or chemically treated with lime to
a pH of 12.0 or chemically treated with chlorine to a free chlorine residual.
Waiver of this requirement must be obtained from the Solid Waste Management
Section of the Department of Environmental Quality.
(ii) Storage. Sludge storage shall be
provided in lined earthen lagoons or structural tanks. The lagoon lining shall
be designed to protect the groundwater pursuant to the requirements of Chapter
8 of the Water Quality Divisions rules and regulations. Sludge storage volume
shall be sufficiently large to provide for independent operation of the sludge
dewatering or disposal facilities from preceding liquid or sludge
processes.