Page 152 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SOLID-LIQUID SEPARATION AND INTERCEPTORS

3.20 CHAPTER THREE

DESIGN CONSIDERATIONS

The size and shape of the interceptor must be based on the nature of the waste (either
lighter or heavier than water), the amount of material to be retained, rate and volume of
total discharge into the interceptor, and the corrosion potential of the effluent (acid, caustic,
or abrasive).

STRUCTURAL CONSIDERATIONS

In many cases, the interceptor may be installed either on top of or under the slab, with the
cover or grate extending up to the finished floor above. Many interceptors are very heavy,
and when filled with water they require special support. If the entire cover extends through
the slab, additional strengthening of the slab may be required because of the size of the
required penetration.

LOCATION

The interceptor must be located so that it is easily accessible for cleaning, servicing, and
maintenance. The use of ladders or the need to clear away stored articles in order to remove
the intercepted material is a violation of many codes. In addition, if it is easy to clean out
the interceptor, it will get done regularly.
Most interceptors require manual removal of trapped substances, and so they must be
located in areas where ongoing access will not interfere with normal operations. This must
be balanced with the need to locate these interceptors as close as possible to the source of
the substances that are being removed.

SPECIFIC SUBSTANCES

Food Related Grease Traps and Interceptors
Grease is most commonly discharged from establishments where food is prepared and/or
consumed, such as restaurants, butcher shops, supermarkets, and specialty stores. The hazard
created is mechanical, because the grease that enters a drainage pipe suspended in hot
water will harden as the water cools and accumulates to form a blockage. To be effective,
enough retention time through the unit must be allowed in order for grease to float to the
top. For smaller units, a flow control device on the inlet is required to reduce the flow to that
required to meet unit design requirements. For larger units, the length is usually sufficient
to avoid a flow control device.
For purposes of this handbook, a grease trap shall be a unit capable of retaining up to
approximately 100 lb (45 kg) grease holding capacity and is intended to be placed inside
a facility adjacent to the fixture or equipment discharging grease. A grease interceptor
shall be a larger unit retaining more than 100 lb (45 kg) intended to be installed outside the
facility on the site.

Grease Traps. Grease traps are divided into four categories based on the method used to
remove grease from the unit. First is the manual type, in which the unit’s cover must be
taken off in order to remove the grease by hand. This is the type used most often for smaller

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