MIL-HDBK-1138
Section 4: GREASE TRAPS
4.
4.1
Description. Food-service operations typically
use grease traps to prevent excessive discharge of grease and oil
into the wastewater collection and treatment system. If grease
traps are not properly maintained, slug loads of grease will
interfere with the performance of both the collection and
treatment system. Grease traps are usually located outside the
food-service establishment in an underground tank with ground-
level access. Sometimes under-sink systems are also used for
grease traps; however, these are not recommended because they
generally do not provide adequate grease removal. Where under-
sink models are used, proper maintenance is especially critical
because of the higher potential for release of slug loads of
grease into the wastewater system.
4.1.1
Configuration. Grease traps usually consist of an
underground, watertight concrete tank with inlet and outlet
piping. The outlet pipe has a tee that allows the internal
discharge to be located within 12 inches (0.3 m) of the tank
bottom. The size of the grease trap depends on the anticipated
flow rate, water temperature, and grease concentration. In
general, grease traps range from a minimum capacity of
750 gallons (2.8 m3) to a maximum capacity of 1,250 gallons 3
(4.7 m3). Where a capacity of more than 1,250 gallons (4.7 m ) is
required, two or more grease traps may be placed in a series.
Access to the tank is typically through one or two manhole rings
and covers.
4.1.2
Location. Grease traps should be
located outside
food-service buildings in an accessible location
for inspection
and maintenance. The traps are installed in the
waste line
between the sink drains and kitchen fixtures and
the wastewater
collection system.
Discharges to Grease Traps. Grease traps do not
4.1.3
perform effectively if they receive discharges with elevated
temperatures or high solids concentrations. Grease traps should
not receive discharges from garbage grinders or produce-
preparation sinks. Discharges from mechanical dishwashers are
also not recommended. However, the preflush/prescraping sinks
that serve mechanical dishwashers may be connected to the grease
trap, provided no garbage grinders are used at these sinks.
4.2
Maintenance Procedures. The critical maintenance
procedure for all grease traps is periodic removal of accumulated
waste. If the responsibility and procedures for cleaning grease
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