Pretreatment devices shall be designed and installed in accordance with the sizing criteria found in this section. A sampling port/box/T, which will accommodate the collection of a valid oil and grease sample, shall be included on all pretreatment device installations.
A. Hydromechanical grease interceptors (HGI), which are generally installed inside, may be used when there are four or fewer fixtures. The minimum size HGI installed shall be rated no less than twenty-five gallon per minute with a fifty pound grease retention capacity. A flow control device shall be installed so that the flow through the device shall at no time be greater than the rated flow. If a dishwasher or food waste disposal unit is used in the facility, an HGI cannot be used and an appropriately sized GGI or alternative pretreatment device capable of accepting these wastes must be installed.
Hydromechanical grease interceptors must be cleaned at least monthly. An HGI located indoors should be cleaned during non-business hours to prevent objectionable odors/germs from being released into the facility.
B. A gravity grease interceptor (GGI) is typically installed outside and in the ground when a FSF has greater than four fixtures, or when dishwasher or food waste disposal units are used in the facility. The minimum sized GGI to be installed shall be three hundred gallons. Gravity grease interceptors shall be installed such that they are easily accessible for inspection, cleaning and the removal of FOG and solid material. A GGI shall meet the following minimum criteria: no obstruction to prevent the proper access and cleaning of the GGI; access covers located such that the influent and effluent sanitary "T" and compartment transition points (if applicable) are accessible for proper cleaning and inspection; and an access cover for each chamber and constructed with the appropriate traffic rating.
The GGI must be pumped-in-full at least every six months or when the total accumulation of surface FOG (including floating solids) and settled solids reaches twenty-five percent of the GGI's overall depth.
C. Gravity grease interceptor sizing criteria:
V(min) = F x R x S
Where:
V(min)= Minimum gravity grease interceptor operating volume, gallons
F = Flow rate (maximum), gallons per minute
R = Retention time = 30 minutes
S = Storage factor = 25 percent
Thus: V (min) = F x 30 x 1.25
To calculate flow rate (F), use Drainage Fixture Units (DFU) values found in the tables below.
The flow rate shall be determined based on the total flow rate from all equipment and plumbing fixtures connected to the gravity grease interceptor using one of the following equations:
1. Drainage fixture units less than or equal to forty:
F = (0.8 x DFU)
2. Drainage fixture units greater than forty:
F = (0.3 x DFU) + 20
Where:
DFU = Drainage fixture units, defined by the tables below.
The below fixture counts are for determining the size of a gravity grease interceptor.
Drainage Fixture Units for Food Service Facilities. | |
Fixture Type | Drainage Fixture Unit (DFU) Value |
Drainage Fixture Units for Food Service Facilities. | |
Fixture Type | Drainage Fixture Unit (DFU) Value |
2-Compartment Sink | 2 |
3-Compartment Sink | 3 |
Automatic Dishwasher greater than 2 inch Drain | 6 |
Automatic Dishwasher less than 2 inch Drain | 3 |
Food Prep Sink | 2 |
Food Waste Grinder | 4 |
Hand Sink | 1 |
Mop Sink/Mop Basin | 2 |
Pre-Rinse Sink | 3 |
Pre-Rinse Sink w/Food Waste | 4 |
Rotisserie w/Drain | 3 |
Tilt Soup Kettle | 3 |
Wok Stove | 4 |
For Fixtures not listed above use Table 709.2 below of the 2012 International Plumbing Code. | |
Drainage Fixture Units for Fixture Drains or Traps. | |
Fixture Drain or Trap Size (inches) | Drainage Fixture Unit (DFU) Value |
Drainage Fixture Units for Fixture Drains or Traps. | |
Fixture Drain or Trap Size (inches) | Drainage Fixture Unit (DFU) Value |
1½ inches | 1 |
1½ Inches | 2 |
2 inches | 3 |
2½ inches | 4 |
3 inches | 5 |
4 inches | 6 |
GGI sizing is summarized below: | |
Gravity Grease Interceptor Sizing | Minimum Size (gallons) |
GGI sizing is summarized below: | |
Gravity Grease Interceptor Sizing | Minimum Size (gallons) |
Up to 10 DFUs | 300 |
11—16 DFUs | 500 |
17—25 DFUs | 750 |
26—33 DFUs | 1,000 |
34—44 DFUs | 1,250 |
45—66 DFUs | 1,500 |
67—111 DFUs | 2,000 |
Greater than 112 DFUs Contact IWC. | |
Retention Time:
The minimum retention time of thirty minutes is based on Wastewater Engineering, Treatment, Disposal and Reuse, Third Edition, Metcalf and Eddy, Inc., McGraw-Hill, Inc., page 1028.
Storage Factor:
A minimum of twenty-five percent storage is required for fats, oils, grease and settled solids for gravity grease interceptors.
Providing additional interceptor capacity may reduce an interceptor's maintenance frequency. However, solids accumulation and low flows in an interceptor may, over an extended period of time, produce a corrosive environment which can damage the structural integrity of the interceptor. An oversized interceptor can also generate odor problems.
D. If an alternative pretreatment device is used instead of an HGI or GGI, the design must be submitted to the director for prior approval. The information submitted to the director must include, but not be limited to, the number of DFUs the device is going to service, and the manufacturer's recommended sizing criteria.
E. The introduction of emulsifying agents such as chemicals, solvents or enzymes, either directly or indirectly into the pretreatment device, other than what is considered typical business operational practices such as dishwashing or sanitation, is strictly prohibited.
Products which reduce FOG, such as bacteria, may be used in the pretreatment device, in addition to the regular maintenance program, but shall not be a consideration in determining sizing or maintenance frequency.
(Ord. 2013-32 (part), 2013)