Engineering Bulletin

PURPOSE
For nearly a hundred years, grease interceptors have been used in plumbing wastewater systems to permit free flow of drainage
from sinks and similar equipment. They have played an important role in preventing grease accumulations from clogging waste
pipes and sewer lines. They also help to improve operations at wastewater treatment facilities and prevent environmental problems
caused by grease.
Engineered GREASE INTERCEPTORS
INSTALLATION
Installation Considerations
Install the interceptor as close as practical to the fixture(s) being
served. The interceptor may be placed on the floor, partially
recessed in the floor, recessed with top flush with the floor,
or fully recessed below the floor, in order to accommodate
piping and structural conditions.
Anticipate sufficient clearance for removal of the interceptor
cover and baffle for cleaning. Also, take into consideration the
possibility of pipelines becoming clogged with congealed
grease that may collect before reaching the grease interceptor.
Do not install the grease interceptor in a waste line from
a garbage grinder. Garbage grinder waste must bypass the
interceptor because rapid accumulation of solid matter will
greatly reduce the grease interceptor efficiency, preventing
operation in compliance with its rated capacity. Solid material
should not be permitted to enter the grease interceptor. In an
application where solids are present, a solids interceptor
should be used.
A separate grease interceptor is recommended for each
commercial dishwasher. The size of the interceptor is
determined by the discharge rate of the dishwasher as
specified by the manufacturer.
Placement of the interceptor in a high traffic area is an
important concern. If the interceptor is to be installed flush
with the floor, it is necessary to determine whether or not the
interceptor will experience heavy-duty load traffic. The standard
grease interceptor is designed for foot and light traffic only.
If a greater load rating is required, the interceptor must be
constructed accordingly to accept the higher load.
Caution: Z1171 installations using indirect piping to unit
could result in standing water in floor sink or flooding if
line blockage occurs.
Flow Control
The use of a flow control device (Z1108), furnished with all
grease interceptors, is an important factor in the operation of
the interceptor. The flow control device should be installed in
the waste line upstream of the grease interceptor. It should be
placed beyond the last connection from the fixture(s) and as
close as possible to the underside of the lowest fixture. When
two or more sinks or fixtures are combined and served by one
interceptor, a single flow control fitting can be used.
The flow control device must be properly vented to permit air
to mix with the fluid entering the interceptor. Air facilitates
separation and, more importantly, is necessary to maintain
the proper pressure, thus, the proper operating level within
the separation chamber.
Air intake for the flow control device may terminate under the
sink drain board, as high as possible, to prevent overflow or
terminate in a return bend at the same height outside of the
building. When a fixture is individually trapped and back-vented,
air intake may intersect the vent stack. All installation recom-
mendations are subject to approval of code authority.
Venting
Grease interceptors must have a vented waste, sized in
accordance with code requirements for venting traps,
to retain a water seal and to prevent siphoning.
Multiple Fixture Installation
One interceptor to serve multiple fixtures is recommended only
where fixtures are located close together. In such installations,
each fixture should be individually trapped and back-vented.
MAINTENANCE
General Considerations
Design and installation are key factors to the operation of a
grease interceptor. However, without disciplined maintenance,
most performances are lost. For a manual interceptor to perform
as designed, a strict maintenance schedule must be adhered
to. If adequate maintenance is not performed, excessive grease
buildup will occur until water ladened with grease passes
directly through the unit. Therefore, no matter how efficient
the design or how proper the installation, grease interceptors
perform only as well as the maintenance routine allows.
Cleaning
All grease interceptors must be cleaned regularly. The frequency
of grease removal is dependent upon the capacity of the inter-
ceptor and the quantity of grease in the wastewater. Grease
removal intervals may therefore vary from once a week to once
in several weeks. When the grease removal interval has been
determined for a specific installation, regular cleaning at that
interval is necessary to maintain the rated efficiency of the
interceptor. After the accumulated grease and waste material
has been removed, the interceptor should be thoroughly checked
to make certain the inlet, outlet, and air relief ports are clear
of obstructions.