Codes
The two Nationally recognized codes of IPC and UPC as well as local amendments greatly differ from each other.
IPC 2006 addresses the Grease Interceptors in section 1003.3. It is relatively short and lacks to totality required to meet the variations in restaurants, and many circumstances that engineer will face. This confusion will lead into many interpretations across the board between jurisdictions, building owners, restaurant operators, the builders, and engineers.
The fixtures that must be on grease collection system are pot sinks, pre-rinse sinks, soup kettles or similar, wok stations, floor drains or floor sinks serving the kettles, automatic hood wash unit, dishwashers without pre-rinse sinks. Only equipments with fat and oil content will be allowed into the system. Equipment with solid content (i.e. food grinders) shall have additional solid interceptor prior to grease interceptor and emulsifiers, chemicals, enzymes, and bacteria shall not discharge into food grinders.
Grease interceptor devices must meet PDI G101, ASME A112.14.3 or A112.14.4. Their capacity is based on total flow rate through in gpm versus the grease retention capacity in pounds. Technically the equation is :
Grease retention capacity (lbs) = 2 x Total flo-through rating (gpm)
To insure the rating for a designed grease interceptor, flow control restrictions must be provided with venting to terminate minimum 6” avove the flood rim level.
Automatic grease removal devices are allowed for one or multiple fixtures with proper access and to meet the guidelines of the manufacturer.
UPC 2006 has extensively modified their code from earlier versions. For years, the grease interceptors have been addressed in appendix of the code. An appendix to the code is only code when the jurisdiction adopts the appendix. In 2006, UPC transferred the section to the body of code and clearly addressed many of the concerns. These concerns were from many directions, from the end users, from an old code equation that many times did not meet the reality of the establishment, from environmentalists, and from jurisdictions.
The new code has seriously resolved many of the old issues concerning the sizes of the grease interceptors. With certain restrictions by the local authorities, only these types are allowed in those jurisdictions. For a small pretzel shop, the minimum of 750 gallons was very large. The lack of production of waste grease into the interceptor would cause secondary heath concerns, bacteria growth, fungi, and erosion of the inner liner of the concrete structure.
In short, many diverse groups saw a major overhaul is necessary. Initially group of engineers and later were joined by many manufacturers’ representative to address the issue of Fat, Oil, Grease (FOG). At the end of all discussion, the following provides the brief review of the code.
In addition, the entire equation was based on meal counts which were extremely susceptible to any interpretations available on the actual meal. The number of meals was based on seat count which did not include the catering or carryout business. In addition, the meal was not defined in pretzel shops or in a bakery. Now with the advent of the new code, the flow rate of each fixture is the primary gage for the sizing of the interceptor. The new code sizing charts are great improvement.
Many health departments do not allow the installations of any type of grease removal system within food preparation areas and must prove the cleaning and maintenance is readily accessible. Like IPC similar kitchen equipment must use the grease piping system: scullery sinks, pots and pan sinks, soup kettles, and floor drains with grease containing exposure. It is believed that the presence of the dishwasher in this section (1014.3.2.1) must be erroneous since it conflicts with section 1014.1.3.
The operators are on notice that a period maintenance is part of the code enforcement, the jurisdiction will use legal means to insure the maintenance. (best management practice- BMP). Unlike IPC, no food waste disposal, commercial food waste disposers, or dishwasher is allowed within the interceptor systems,
Like IPC, hydromechanical grease interceptors (HGI) are now permitted in this code. A non-adjustable flow controller tpo meet the designed flow rate will be installed with a vented interceptor and vent (downstream of unit) shall terminate to roof.
Based on full open channel flow the sizing chart is based on Demabd Flow Unit and HGI flow rate in GPM: The rates are shown in (2% slope pipe) DFU: HGI (GPM).
8:20; 10:25; 13:35; 20:50; 35:75; 172:100; 216:150; 342:200; 428:250; 576:350; 720:500
The total capacity in gallons of the HGI must not exceed 2.5x gpm flow rate or maximum total capacity of 50 gpm flow rate shall be 125 gallons.
The foundation of the gravity grease interceptors (GGI) was based on basic open channel flow and retention/filtration laws. Use the fixture demand units for water consumption as main axes of calculations. The FDU then provides the gpm flow and hence pipe sizing. Based on ½ full circular flow(Mohinder Nayyar Piping Handbook, 3rd Edition, 1992), and FDU units, the input to the grease interceptors was identified. Based on Metcalf & Eddy, Inc. Small and Decentralized Wastewater Management Systems, 3rd Ed. 1998), the most efficient retention time was determined to be 30 minimum. The retention time based on the flow determines the volume, depth, and length of the interceptor. The separation of the grease interceptor is primary based on variations in density. The semi-solid particles settle in bottom of tank, the grease remains in the initial compartment and the water with heavier density escapes in the bottom of the baffle.
The final GGI sizing was simple and substantially less than the previouse code
(DFU:Volume (gallons)) 2% slope pipe
8:500; 21:750; 35:1000; 90:1250; 172:1500;
216:2000; 307:2500; 342:3000; 428:4000;
576:5000; 720:7500; 2112:10,000; 2640:15,000
Not in code: Full extended UPC Table
FDU Flow Pipe Slope Volume
Gpm Inch gallons
8 10 2” 2% 500 gal
21 – – – 750 gal
35 29 3” 2% 1,000 gal
90 – – – 1,250 gal
172 44 4” 1% 1,500 gal
216 62 4” 2% 2,000 gal
307 2,500 gal
342 80 5” 1% 3,000 gal
428 120 5” 2% 4,000 gal
The wrong interceptor sizing works in two directions: both the under sizing as well as over sizing. In the case of under sizing the flow of the mixed fluid is high and does not allow the segregation and isolation time required, and thus, the grease is still mixed and will escape the chamber. In the case of over sizing, the grease gets collected and the call for cleaning increment is prolonged. As the time of retention increases, the organic compound invite bacteria and enzymes, and with the natural sulfides within the water system, the sulfites and created and further transformation to sulfuric acid which transforms the grease interceptor into a chemical reactor. The by products of these event simply corrode and reduce the life expectancy of the interceptor and efficiency. In addition, the grease removal truck have only certain definite volume, and there are no assurance that during the operations proper number of trucks at right time interval clean the interceptor, and in many cases the solid residues are always present and will never be removed.
Types of Grease Interceptors
There are two types of retentions based on their size.
• Large units or grease interceptors that collect the grease globally and work on basic gravity and retention process.
• This multi baffled chamber uses the density gradient of the grease and non-grease fluid, and separates the grease.
• This is based on the fixture count and their loading rate.
• These units are from 250 gallons to 15,000 gallons.
• Their materials can be fiber glass, concrete with lining, and stainless steel. Concrete units are far more fabricated and sold in the country.
• The inner liner provides corrosion barrier to all concrete in contact with the fluids.
• These units are buried underground. The fiber glass or stainless steel can be both underground or above ground. (Proset unit)
• The fiber glass or the stainless steel above ground units are favorite of the high rises or the parking garages below the restaurant within malls.
• In one instance, in a hill side situation, the soil and structure could not be placed underground. (Getty Center)
• The unit was to disturb the existing sloped hill side. The light weight of the fiberglass units in shallow water tables may cause floatation and buoyancy issues. It is recommended to provide additional weight to the unit (“dead-Man’s weight”) to insure proper installation. In many historic and tourist towns, the placement of these units is problematic.
• Extremely small backyards or zero lot line prohibits the use of these units underground outside. (San Francisco, Newport Beach, etc.)
• In addition, there are many circumstances that the substructure pipe work or power/low voltage work has created a cluster that is impossible to burry such mass and volume.
• Smaller size of these units is a size of small compact car and it elongates towards a bus (3000 gallons).
• Once again, these units cannot be too far from the restaurant and for colder climate, the electrical heating jacket is recommended. These units need venting and in many times, pre or post inspection boxes maybe required.
In addition, the entire equation was based on meal counts which were extremely susceptible to any interpretations available on the actual meal. The number of meals was based on seat count which did not include the catering or carryout business. In addition, the meal was not defined in pretzel shops or in a bakery. Now with the advent of the new code, the flow rate of each fixture is the primary gage for the sizing of the interceptor. The new code sizing charts are great improvement.
The smaller grease retention units are called traps. The traps either work passively in the same manner as the interceptors or they “hydro mechanically” extract grease. The unit sizing is very critical. Improper sizing will cause the grease to bypass the original intended mechanical extraction. Based on their small volume, they are limited in number of fixtures. There are health departments that will not allow these units, and if they accept, they must not be in the food prep or cooking area. The physics and science of all hydro mechanical devices are based on the higher surface tension and viscosity of the grease. Different cooking oil has different surface tensions and given the viscosity dependency on the indoor temperature, a calibration of the hydro mechanical system is due.
Restaurants are either operated from small family owned business to franchisee owner to the main corporate headquarter owning the restaurant. In all three there are variations in standard practices (operations and Practices manual). The lack of training, frequent replacement of employees, the disgrental employees, and lack of finances within the store causes the frequent cleaning of the traps to be delayed or forgotten, therefore creating major health issues. The more sophisticated the unit is, the higher cost of maintenance, reduced grease extraction, and less cleaning of the unit in time. This becomes very true in small family operated restaurants.
Placement of these units is also a major challenge. If this unit collects multiple fixtures, the unit must be underground. However, the floor of the restaurants is not conducive for burial of the grease trap. If it is allowed, the superintendent of the construction site must be aware of all issues. In some cases, the floor below is a parking garage. Therefore it is very difficult to install. If the units are for Point-of-Use and serve a single fixture, then the challenge is identifying proper placement of the unit. Generally under the three compartment sink, these units fit only if the sink bowl is shallow and the legs are higher than normal (6”). Even then, there are challenges in placing the pipes without intruding to other space. The study and experience of all engineers concentrated in the restaurant design is needed to evaluate the new hydro-mechanical grease extraction devices. Unfortunately, most engineers are only exposed to sales brochures and the sales skills of the manufacturer’s representative.
For a new shopping center it is best to place the future grease sewer piping for future grease interceptor location till the perspective restaurant tenant moves in. The nominal size not to be greater than 1500 gallons. One does not want to have large interceptors with small unit restaurants.
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