[HISTORY: Prepared by NIRA Consulting Engineers, Inc. April
2009. Amendments noted where applicable.]
A.
Restaurants and other food service businesses generate literally
tons of fats, oils and grease (FOG) waste every day. If this waste
is not managed properly, it can cause major environmental problems.
Some of the FOG waste generated by these businesses is in solid form
and can be properly disposed of in the trash.
B.
However, when improperly discharged to the municipal sewer system,
liquid waste containing FOG will build up inside sewer lines and cause
wastewater overflows to occur inside the restaurant or elsewhere in
the sewer system. This can cause a major disruption in the operation
of a business, be a significant public health hazard, and be very
expensive to clean up.
C.
Businesses that generate greasy wastewater can reduce the likelihood
of a sewer backup by adopting good housekeeping practices and minimizing
the amount of FOG waste that goes down their drains by installing
and properly maintaining a grease removal system. Currently, several
types of grease removal systems are available. Typical installations
utilize a grease trap and/or a grease interceptor.
Properly sized grease removal systems create sufficient detention
time for the oil-laden waste contained within the unit to separate
by means of gravity. A flow-control device at the front end of the
unit slows down the flow and minimizes the turbulence to allow the
separation of the FOG and water. Once this separation occurs, the
clarified water exits the collection chamber and flows to the sewer
system, leaving behind the FOG and food solids to be removed later.
Most grease removal systems function in this manner. Consequently,
bigger is usually better because of increased detention time and less
frequent cleanings. However, grossly oversizing a grease removal system
is not recommended. Extended time periods between cleanings can result
in septic conditions which allow the formation of corrosive hydrogen
sulfide gas and foul odors.
A.
A grease trap is typically a smaller grease removal system installed
inside the building and frequently under a sink. Its purpose is to
remove FOG from the wastewater flow stream of one or more (up to four)
smaller grease-emitting fixtures. Where inside-the-building grease
traps exist, food disposals and other "solids" producing equipment,
such as potato peelers, must be connected to a solids interceptor
first, then be routed to the building's sanitary sewer, bypassing
the grease trap. Additionally, automatic dishwashers typically create
a soapy, high-temperature waste flow stream that will inundate a grease
trap, emulsifying the FOG already collected and washing it downstream.
Consequently, facilities with only an inside-the-building grease trap,
automatic dishwashers, must be connected directly to the sanitary
sewer.
B.
Allegheny County Health Department Plumbing Division regulations
require that inside-the-building grease traps that are located in
the same room where food is prepared, cooked, handled, or stored must
be the semiautomatic draw-off type.
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"Inside the Building" Grease Trap Installations (Typical)
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A
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Flow from 4 or fewer kitchen fixtures enters the grease trap.
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B
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An approved flow-control device is installed to restrict the
flow to the grease trap to the rated capacity of the trap. Required
by the Collier Township Municipal Authority ("Authority").
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C
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An air intake valve allows air into the open space of the grease
trap to prevent siphonage and back-pressure.
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D
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The baffles help to retain grease toward the upstream end of
the grease trap, since grease floats and will generally not go under
the baffle. This helps to prevent grease from leaving the grease trap
and moving further downstream where it can cause blockage problems.
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E
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Solids in the wastewater that do not float will be deposited
on the bottom of the grease trap and will need to be removed during
trap cleaning.
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F
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Oil and grease floats on the water surface and accumulates behind
the baffles. The oil and grease will be removed during routine grease
trap cleaning.
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G
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Air relief is provided to maintain proper air circulation within
the grease trap.
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H
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Some grease traps have a sample point at the outlet end of the
trap to sample the quality of the grease trap effluent flow. Required
by the Authority.
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I
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A cleanout is provided at the outlet or just downstream of the
outlet to provide access into the pipe to remove any blockages.
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J
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The water exits the grease trap through the outlet pipe and
continues on to the grease interceptor or to the sanitary sewer system.
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A grease interceptor is a larger grease removal system installed
outside and underground, frequently collecting the waste from all
grease-bearing equipment within an establishment. Some installations,
however, utilize both an inside-the-building grease trap and an outside
grease interceptor. This arrangement works well in that equipment
that emits higher concentrations of FOG, such as the prerinse sink
and wok ovens, are connected to the grease trap and the dishwasher,
disposal, floor drains and mop sinks are connected to the grease interceptor.
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"Outside the Building" Grease Interceptor Installation
(Typical)
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A
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Flow from under-sink grease traps or directly from plumbing
fixtures enters the grease interceptor. The Authority requires that
all flow entering the interceptor must enter through the inlet pipe.
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B
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An approved flow-control or -restricting device is installed
to restrict the flow to the grease interceptor to the rated capacity
of the interceptor.
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C
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An air intake valve allows air into the open space of the grease
interceptor to prevent siphonage and back-pressure.
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D
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Oil and grease floats on the water surface and accumulates behind
the grease-retaining fittings and the wall separating the compartments.
The oil and grease will be removed during routine grease interceptor
cleaning.
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E
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Solids in the wastewater that do not float will be deposited
on the bottom of the grease interceptor and will need to be removed
during routine grease interceptor cleaning.
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F
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Grease-retaining fittings extend down into the water to within
12 inches of the bottom of the grease interceptor. Because grease
floats, it generally does not enter the fitting and is not carried
into the next compartment. The fittings also extend above the water
surface to provide air relief.
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G
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Some grease interceptors have a sample box so that inspectors
or employees of the establishment can periodically take effluent samples.
Having a sample box is required in all new installations by the Authority.
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H
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Flow exits the grease interceptor through the outlet pipe to
the sanitary sewer system.
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A solids interceptor is a passive device installed very close
to food disposals or other equipment that produces a waste stream
contaminated with solids. Smaller units typically serve one fixture
and have low inlets and high outlets and are located where a fixture's
p-trap is positioned. Larger units can collect the waste from multiple
fixtures and are either built into the floor or are mounted on the
floor. All types of solids interceptors are equipped with easily removable
strainer baskets that serve to retain the filtered solids, while allowing
the water to pass through. Solids interceptors greatly improve the
operation and efficiency of semiautomatic draw-off type grease traps,
greatly reducing the conditions that result in foul odors. Consequently,
the Authority requires that solids interceptors be installed when
"solids" producing equipment is present and only an inside-the-building
grease trap is used.
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The following requirements apply to inside-the-building grease
traps:
A.
Semiautomatic draw-off-type grease traps: minimum 30 gallons per
minute flow rate if located in the same room in which food is present.
B.
Hot-water-only prerinse dish and pot washing procedure: maximum temperature
of 140° F.
C.
An applicant must provide grease trap sizing calculations to the
Authority prior to approval and installation.
D.
Use of appropriately sized solids interceptors at disposal.
E.
Automatic dishwashers are not permitted to be connected to interior
grease traps under any circumstances.
The following requirements apply to outside-the-building grease
traps:
A.
New installations, as well as remedial improvements to malfunctioning
existing systems, generally will require an exterior in-ground two-chamber
grease interceptor (1,000 gallons or larger) that is sized to provide
a minimum of 24 minutes of retention during peak hydraulic load conditions.
B.
Grease removal systems must be equipped with a sampling box and access
cover at the effluent discharge end of the grease interceptor.
C.
Each installation must provide all ancillary equipment recommended
by the manufacturer, including, but not limited to, the following:
flow control fixtures, air intake vents, removable baffles, thirty-inch-diameter
manway access covers for systems located outside.
D.
An applicant must provide a grease interceptor sizing calculation
to the Authority prior to approval and installation.
E.
Dishwasher and disposal waste can be discharged to an outside-the-building
grease interceptor, but not to an inside-the-building grease trap.
A.
The Authority requires that all grease removal systems be cleaned
when the grease and solids accumulation reaches 50% of the unit's
capacity or every 45 days, whichever occurs first.
B.
The Authority requires that grease removal system operators (restaurant
and kitchen managers) conduct twice-monthly inspections of the system
and record the depth of collected grease in the trap, as well as confirm
the system is functioning properly.
C.
The Authority requires that grease removal system operators (restaurant
and kitchen managers) maintain a log of system cleanings and inspections.
For cleaning and disposal, the following information shall be recorded:
date of the cleaning and disposal, amount of solids and grease removed,
method/place of disposal, hauler's name (company), hauler's/driver's
signature, and manager's signature. For system inspections, the following
information shall be recorded: date of inspection, capacity percentage
or depth/amount of grease in unit, verification of proper system function,
and manager's signature. These maintenance/inspection logs must be
made available to the Authority upon request for the previous three
years of operation.
D.
The Authority prohibits the use of all enzymes, bacterias and chemicals
for the intended use of grease digestion, removal or abatement. These
products only transfer the grease downstream in the sewer system.
Currently, no industry-wide sizing standard has been adopted
for inside-the-building grease traps. Various manufacturers approach
sizing differently. This information illustrates one particular manufacturer's
recommended sizing calculations.
A.
Sizing
for single fixture.
(1)
Grease traps are sized according to the rate of incoming flow,
in gallons per minute (GPM). Associated with the incoming flow rate
is the grease trap capacity. The rated capacity, in pounds, is listed
at twice the flow rate in GPM. For example, a ten-gallons-per-minute
grease trap has a rated capacity of 20 pounds. Interior grease traps
do not include "detention time" in their sizing calculations.
(2)
General procedure.
(a)
To determine the flow rate of each sink:
[1]
Calculate the capacity of the sink in cubic inches:
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_____ (Length) x _____ (Width) x _____ (Depth) = ____ Cu. In.
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[2]
Convert the capacity from cubic inches to gallons per minute
(GPM):
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_____ Cu. In. x 231 Cu. In./Gal. = _____ GPM
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[3]
Adjust for displacement:
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_____ GPM x 0.75 = _____ GPM
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[4]
The result is the flow rate required to drain the sink in one
minute.
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Example:
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Three-compartment pot sink, with each compartment 12" x 12"
x 15"
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1.
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12" x 12" x 15" = 2,160 Cu. In. x 3 Comp. = 6,480 Cu. In.
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2.
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6,480 Cu. In. ÷ 231 Cu. In./Gal. = 28 GPM
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3.
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28 GPM x 0.75 = 21 GPM
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A 20 GPM grease trap would permit the sink to drain in slightly
more than one minute.
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*Discharge from spray hoods is determined by the flow rate of
the hood.
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(b)
Grease traps shall not exceed a flow rate of 35 GPM. Grease
interceptors shall be used when the flow rate exceeds 35 GPM.
B.
Sizing
for multiple fixtures.
(1)
Determine the flow rate for each fixture to be serviced by the
grease trap.
(2)
Add together 100% of the largest flow rate, 50% of the second
largest, and 25% of all others.
(3)
The result is the recommended flow rate of the grease trap.
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Example:
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1.
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Fixture A: 35 GPM flow rate
Fixture B: 26 GPM flow rate
Fixture C: 18 GPM flow rate
Fixture D: 12 GPM flow rate
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2.
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35 GPM (A) x 100% = 35 GPM
26 GPM (B) x 50% = 13 GPM
30 GPM (C + D) x 25% = 7.5 GPM
Total Flow Rate = 55.5 GPM
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In this case, a 50 GPM outside grease interceptor is recommended
for this installation.
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C.
Typical
configurations.
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*
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The Authority requires a minimum 22.5 GPM interior grease trap.
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+
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Automatic dishwashers must bypass interior grease traps.
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++
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Food waste grinders, disposals and potato peelers must be connected
to a solids interceptor then go to the sanitary sewer in this type
of installation.
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A.
Example No. 1.
(1)
Use this chart to size exterior grease interceptors that will
serve multiple fixtures. Use the sizing calculation to select the
grease interceptor when the interceptor is not more than four feet
(vertically) below the fixtures being served. Use the next size larger
(grease interceptor) than the calculation indicates when the interceptor
is more than four feet below the equipment being served. Never install
a grease interceptor smaller than the calculation indicates.
(2)
Description of installation: a grease interceptor installed
to receive wastes from multiple fixtures, including: one dish washing
machine (floor sink), a grease-extracting ventilation hood, one tilt
kettle floor trough, one mop sink, a three-compartment pot sink, one
prerinse sink with garbage disposal, and four floor drains. No solids
interceptor is required. Use a twenty-four-minute retention time period.
The following examples are based on two different manufacturer's requirements.
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Manufacture #1
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Step 1 — Determine the Hydraulic Loading of Each Fixture,
in Fixture Units (FU)
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1.
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Dishwasher receptor (floor sink) with 4" trap and trap arm =
8 FU
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2.
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Grease-extracting ventilation hood receptor (2" floor sink)
= 3 FU
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3.
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Tilt kettle trough (minimum 2" trap and trap arm) = 4 FU. Mop
sink = 3 FU
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4.
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Three-compartment (commercial) sink = 3 FU
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5.
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Prerinse sink with garbage disposal (2" trap and trap arm) =
4 FU
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6.
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Four floor drains x 2 FU each = 8 FU
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Step 2 — Establish the Total Hydraulic Loading on the
Interceptor in Fixture Units
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8FU + 3FU + 4FU + 3FU + 4 FU + 8FU = 30 Fixture Units
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Step 3 — Determine the Minimum Size Interceptor Required
in Gallons
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The twenty-four-minute retention time applies to all fixtures
even though all fixtures may not discharge simultaneously.
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30 (FU) x 3 (GPM) x 24 (Minutes) Retention Time = 2,160 Gallons
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Solution: Choose the next larger available size three-compartment
interceptor (i.e., 2,500- or 3,000-gallon capacity)
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Manufacture #2
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Kind of Fixture
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Trap and Arm Size
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Fixture Units
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3-Compartment Sink
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1 1/2", 2"
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3, 4
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2-Compartment Sink
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1 1/2"
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2
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Dishwasher
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2"
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4
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Garbage Grinder
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1 1/2"
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2
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Wok Stove
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2"
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4
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Hand Sink
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—
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0
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Mop Sink
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—
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0
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Floor Drains (2", 3", 4")
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2", 3", 4"
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2, 3, 4
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Floor Sinks (3", 4")
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3", 4"
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3, 4
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Notes: Hand sinks and mop sinks are not required to be plumbed
to the grease trap. For indirect waste systems where hub drains and
floor sinks are used as receptors for dishwashers, 2- and 3-compartment
sinks, etc., the fixture unit count shall be twice (2x) the floor
sink or hub drain fixture unit count. In such cases, the fixture count
of the indirect waste is not counted.
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B.
Example No. 2.
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The Uniform Plumbing Code Formula
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Follow these six simple steps to determine grease interceptor
size.
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Enter Calculations Here
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No. of Meals Per Peak Hours
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Waste Flow Rate
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Retention Time
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Storage Factor
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Calculated Interceptor Size
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Grease Interceptor
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_____ x
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_____ x
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_____ x
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_____ =
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_____
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_____
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Step 1
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Step 2
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Step 3
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Step 4
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Step 5
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Step 6
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Number of Meals per Peak Hour (Recommended Formula):
Seating Capacity x Meal Factor = Meals per Peak Hour
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Notes:
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1
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Establishment Type:
Fast Food (45 min.)
Restaurant (60 min.)
Leisure Dining (90 min.)
Dinner Club (120 min.)
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Meal Factor
1.33
1.00
0.67
0.50
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Waste Flow Rate:
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2
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Condition
With a Dishwashing Machine
Without a Dishwashing Machine
Single-Service Kitchen
Food Waste Disposer Only
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Flow Rate
6 Gallons
5 Gallons
2 Gallons
1 Gallon
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Notes:
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Retention Time
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3
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Commercial Kitchen Waste
Dishwasher
Single-Service Kitchen
Single Serving
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2.5 Hours
1.5 Hours
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Notes:
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Storage Factor
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4
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Kitchen Type — Commercial
Hours of Operation
8 Hours
12 Hours
16 Hours
24 Hours
Single-Service Kitchen
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Storage Factor
1.00
1.50
2.00
3.00
1.50
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Notes:
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5
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Calculate Liquid Capacity
Multiply the values obtained from Steps 1, 2, 3 and 4. The result
is the approximate grease interceptor size for this application.
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Notes:
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6
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Select Grease Interceptor
Using the approximate required liquid capacity from Step 5,
select an appropriate size as recommended by the manufacturer.
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Notes:
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The Authority encourages those commercial foods establishments
that are served by the Authority sewage collection system to institute
a program of best management practices.
A.
Train kitchen staff about how they can help ensure that BMPs are
consistently maintained.
B.
Post "No Grease" signs at sinks and dishwashers.
C.
Reduce hot water temperatures at all sinks, but especially at the
prerinse sink, before the dishwasher to 140° F. Grease emulsifies
at temperatures above 140° F.
D.
Utilize a three-sink dish-washing system: wash, rinse and sanitize
in a 75 ppm to 100 ppm chlorine bleach solution, in lieu of using
a mechanical dishwasher, which operates at temperatures well above
140° F.
E.
Recycle waste cooking oil.
F.
"Dry wipe" pots, pans and dishware prior to washing with disposable
towels. Discard used towels to trash.
G.
Dispose of food waste directly to the trash bin.
H.
Inspect grease removal traps and/or interceptors every two weeks.
Record findings in a maintenance log. Keep logs available for review
by the Authority for three years.
I.
Clean exhaust system filters only in areas where the runoff will
be conveyed to a grease removal device. Do not clean filters where
the runoff will be collected in a storm sewer.
J.
Use absorbent pads to clean up grease or oil spills. Do not use granular
materials such as kitty litter or oil dry for these purposes.
K.
Locate grease and oil receptacles away from stormwater inlets, catch
basins and drains. Protect grease and oil receptacles from weather
and vandalism. Provide secure lids for all receptacles.
