14.3 Grease Interceptors, Oil Separators, and Solids Interceptors
Key Takeaways
- IPC 1003.3.2 prohibits a food waste disposer from discharging to a grease interceptor.
- IPC 1003.3.7 determines gravity grease interceptor capacity by multiplying peak drain flow in gallons per minute by a retention time of 30 minutes.
- IPC 1003.3.5.2 requires grease interceptors to be equipped with flow control devices, vented and terminating not less than 6 inches above the flood rim level.
- IPC 1003.4 requires oil separators at repair garages with floor or trench drains, car washing facilities, factories producing oily and flammable liquid wastes, and hydraulic elevator pits.
- IPC 1003.4.2.2 requires an oil separator at a garage or service station to have a capacity of not less than 6 cubic feet for the first 100 square feet drained, plus 1 cubic foot for each additional 100 square feet.
The general requirement — IPC 1003.1
Interceptors and separators shall be provided to prevent the discharge of oil, grease, sand and other substances harmful or hazardous to the public sewer, the private sewage system or the sewage treatment plant or processes.
IPC 1003.2 Approval: size, type and location are designed and installed per the manufacturer's instructions and this section, based on the anticipated conditions of use. Wastes that do not require treatment or separation shall not be discharged into any interceptor or separator — sending clean waste through a grease interceptor dilutes its retention and shortens its service interval.
Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(vv) adds an exception to 1003.1 where special regulations exist by the local wastewater or sanitation district into which the grease trap or interceptor effluent is transported or treated: those regulations may supersede the IPC requirement. In Colorado, always check with the district before sizing.
Grease interceptors — IPC 1003.3
1003.3.1 Where required
A grease interceptor or automatic grease removal device is required to receive drainage from fixtures and equipment with grease-laden waste located in food preparation areas, such as restaurants, hotel kitchens, hospitals, school kitchens, bars, factory cafeterias and clubs. The fixtures and equipment include:
- pot sinks;
- prerinse sinks;
- soup kettles or similar devices;
- wok stations;
- floor drains or sinks into which kettles are drained;
- automatic hood wash units; and
- dishwashers without prerinse sinks.
Interceptors shall receive waste only from fixtures and equipment that allow fats, oils or grease to be discharged. Where space or other constraints prevent installation or replacement, one or more interceptors may be installed on or above the floor and upstream of an existing grease interceptor.
1003.3.4 Where not required
A grease interceptor or an automatic grease removal device shall not be required for individual dwelling units or any private living quarters.
1003.3.2 Food waste disposers
A food waste disposer shall not discharge to a grease interceptor.
Ground food solids overwhelm a grease interceptor's retention volume and are carried through with the effluent.
Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(ww) adds an exception to the food waste disposer restriction "when using a gravity interceptor equal to or greater than 500 gallon capacity."
1003.3.3 Additives
Dispensing systems that dispense interceptor performance additives are prohibited except where they dispense microbes for aerobic bioremediation of grease and other organic material, or for inhibiting growth of pathogenic organisms by anaerobic methods. Such microbial systems are permitted only where the interceptor manufacturer's instructions allow them and the systems conform to ASME A112.14.6. Systems that discharge emulsifiers, chemicals or enzymes to grease interceptors shall be prohibited — an emulsifier simply carries the grease past the interceptor and into the sewer.
Two sizing methods
| Type | Sizing rule | Section |
|---|---|---|
| Hydromechanical grease interceptors, FOG disposal systems and automatic grease removal devices | Sized per ASME A112.14.3, ASME A112.14.4, ASME A112.14.6, CSA B481.3 or PDI G101; grease retention capacity per Table 1003.3.5.1 | 1003.3.5 |
| Gravity grease interceptors | Peak drain flow into the interceptor in gpm x a retention time of 30 minutes; designed and tested per IAPMO/ANSI Z1001 | 1003.3.7 |
Table 1003.3.5.1 Capacity of grease interceptors pairs a flow-through rating with a grease retention capacity, and the relationship is simple: retention capacity in pounds is twice the flow-through rating in gpm.
| Total flow-through rating (gpm) | Grease retention capacity (pounds) |
|---|---|
| 4 | 8 |
| 10 | 20 |
| 15 | 30 |
| 20 | 40 |
| 25 | 50 |
| 35 | 70 |
| 50 | 100 |
| 75 | 150 |
| 100 | 200 |
Footnote a: for flow-through ratings greater than 100 gpm, double the flow-through rating to determine the grease retention capacity.
Worked gravity interceptor sizing
A restaurant's kitchen fixtures produce a peak drain flow of 45 gpm into a gravity grease interceptor.
- Capacity = peak flow x 30 minutes = 45 x 30 = 1,350 gallons.
Compare the hydromechanical route at the same flow: a 50 gpm flow-through unit provides 100 pounds of grease retention capacity under Table 1003.3.5.1 — a far smaller device that must be serviced far more often.
1003.3.5.2 Flow control
Grease interceptors shall be equipped with devices to control the rate of water flow so that the water flow does not exceed the rated flow. The flow-control device shall be vented and terminate not less than 6 inches above the flood rim level, or be installed in accordance with the manufacturer's instructions.
A hydromechanical interceptor separates by residence time. Flow faster than its rating pushes grease straight through. The flow control restricts the rate, and the vent on the flow control prevents the restriction from siphoning the interceptor.
1003.3.6 and 1003.3.8
- Automatic grease removal devices are located downstream of each fixture or multiple fixtures per the manufacturer, sized to pretreat the measured or calculated flows for all connected fixtures, with ready access for inspection and maintenance.
- 1003.3.8 Direct connection: the discharge piping from a grease interceptor shall be directly connected to the sanitary drainage system. Not indirect — directly connected.
Remember the slope rule from IPC 704.1: piping upstream of a grease interceptor slopes not less than 1/4 inch per foot, regardless of size.
Oil separators — IPC 1003.4
At repair garages where floor or trench drains are provided, car washing facilities, factories where oily and flammable liquid wastes are produced and hydraulic elevator pits, oil separators shall be installed into which oil-bearing, grease-bearing or flammable wastes shall be discharged before emptying into the building drainage system or other point of disposal.
Exception: an oil separator is not required in hydraulic elevator pits where an approved alarm system is installed. Such alarm systems shall not terminate the operation of pumps used to maintain emergency operation of the elevator by fire fighters.
Design requirements
| Rule | Requirement |
|---|---|
| 1003.4.1 | A mixture of treated or untreated light and heavy liquids with various specific gravities shall be separated in an approved receptacle |
| 1003.4.2 | Oil separators shall be listed and labeled, or designed per 1003.4.2.1 and 1003.4.2.2 |
| 1003.4.2.1 | Depth not less than 2 feet below the invert of the discharge drain; the outlet opening shall have not less than an 18-inch water seal |
| 1003.4.2.2 | Garages and service stations: capacity not less than 6 cubic feet for the first 100 square feet of area drained, plus 1 cubic foot for each additional 100 square feet |
1003.4.2.2 also carves out two cases: parking garages in which servicing, repairing or washing is not conducted and gasoline is not dispensed do not require a separator, and areas of commercial garages used only for storage of automobiles need not drain through a separator.
Worked oil separator sizing
A repair garage drains 1,400 square feet of floor area through trench drains.
- First 100 square feet: 6 cubic feet.
- Remaining 1,300 square feet: 1,300 / 100 = 13, at 1 cubic foot each = 13 cubic feet.
- Total required capacity: 19 cubic feet.
Recall the companion rule from IPC 301.6: floor drains, sumps and sump pumps at the base of an elevator shaft must be indirectly connected and comply with Section 1003.4 — the oil separator section — because elevator pits collect hydraulic oil.
Other interceptors and separators
| Application | Requirement | Section |
|---|---|---|
| Sand and heavy solids in commercial establishments | Designed and located with ready access for cleaning; water seal not less than 6 inches | 1003.5 |
| Clothes washer discharge | Discharge through an interceptor with a wire basket or similar removable device preventing passage of solids 1/2 inch or larger, string, rags, buttons or similar material. Exceptions: clothes washers in individual dwelling units, and a single dwelling-unit-type washer installed outside a dwelling unit | 1003.6 |
| Bottling establishments | Process wastes discharge into an interceptor separating broken glass or other solids | 1003.7 |
| Slaughterhouses | Slaughtering and dressing room drains equipped with approved separators preventing discharge of feathers, entrails and other clogging materials | 1003.8 |
Venting, access and materials
- 1003.9 Venting: interceptors and separators shall be designed so as not to become air bound and shall be vented in accordance with one of the methods in Chapter 9. Recall the exception in IPC 905.4: the 6-inch vertical rise requirement does not apply to vents for interceptors located outdoors.
- 1003.10 Access and maintenance: access shall be provided to each interceptor and separator, which shall be maintained by periodic removal of accumulated grease, scum, oil, other floating substances and deposited solids.
- 1004.1 Materials: materials and methods comply with Chapter 10 and the applicable provisions of Chapters 4 and 7; fittings shall not have ledges, shoulders or reductions capable of retarding or obstructing flow.
Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(uu) adds an exception to IPC 1002.1 permitting trench and floor drains connected to a sand oil interceptor to go untrapped, provided the drain piping from the trench or floor drains is turned down after entering the interceptor so the discharge point is a minimum of 4 inches below the standing water level of the interceptor.
What is the required capacity of a gravity grease interceptor serving a peak drain flow of 45 gpm?
May a food waste disposer discharge to a grease interceptor under the model IPC?
A repair garage drains 1,400 square feet of floor area. What minimum oil separator capacity does IPC 1003.4.2.2 require?
What water seal does IPC 1003.5 require for a sand interceptor in a commercial establishment?