Grease interceptor requirements

By Ron George,CPD,
President, Ron George Design & Consulting Svcs.

I was recently talking with a colleague about an issue he was having with grease interceptors. He does a lot of engineering for several national restaurant chains. He site-adapts standard drawings of various size buildings based on the building’s orientation and utility locations. One of his biggest complaints is that grease interceptor sizing and grease waste requirements change from municipality to municipality, depending on which code or AHJ is involved in the project. We had a long discussion about why there are so many different local code requirements for grease interceptors. The problem stems from the lack of a grease waste system design standard. It seems that every agency has a different but conflicting way of routing the piping and sizing and locating grease interceptors. Food codes and ordinances also have conflicting language.

Sewer department or utility district ordinances regulate the discharge in many areas, with maximum allowable effluent levels and requirements for sampling manholes or monitoring wells on the building drain. When a food waste grinder is installed and bypassed around a grease interceptor it can cause the sanitary waste effluent to exceed the allowable levels in the sewer.

These various ordinances affect the installations my colleague works on, and they are not consistent. He said he wished there was a credible source of information such as a grease interceptor sizing guideline and a standardized design method for the piping installation that everyone agreed upon and that the codes could agree to reference. My experience has been that the codes are very political and easily changed depending on the whims of various interests.

Sizing and grease waste system design is a complicated issue. We need some organization, such as the American Society of Plumbing Engineers (ASPE) to develop a Grease Waste Design Standard and, maybe, a grease interceptor sizing method.

Food waste grinders

Because a food waste grinder could quickly plug up a grease interceptor with solids, many ordinances allow the grinder to bypass the grease interceptor. When grease adheres to food particles it acts like the aggregate or filler in a concrete mix and makes a gooey ball, causing problems with the drains downstream. Some ordinances require only the wash sink of a three-compartment sink to flow through the grease interceptor; they mandate that the other two sinks flow directly to the building drain.

Some ordinances require various handwash sinks in the kitchen and kitchen floor drains to bypass the grease interceptor, while others require every fixture in the kitchen to go through it. There is no code language mandating a greater slope for grease waste lines to get the grease to the interceptor quicker, although slope is mentioned in several engineering resource books.

Pre-wash sinks with a food waste grinder are probably where the most grease enters the waste system, yet these are allowed to bypass the interceptor in a few local ordinances because they do not know how to address the solids and the grease, which seems counter-productive. There seems to be a marketing campaign by food waste disposal manufacturers to dismiss the grease waste from a pre-wash sink as a myth.

Grease interceptor terminology and requirements have flip-flopped in the codes recently. Over the last eight years, there have been many efforts to change or fix terminology problems in the two model plumbing codes with respect to the industry standards for grease interceptors. A recent code change cycle saw several code changes proposals put forth with good technical justifications, but the sheer quantity sometimes seemed to overwhelm the plumbing code committees. A few changes went through, but it was clear more work was needed to standardize the language in the two model codes. The term for “grease trap” in one code meant something completely different in the other code.

For example, in the past in the Uniform Plumbing Code, the term “grease trap” referred to devices that removes grease and were smaller than 750 gallons. The UPC also referred to a “grease interceptor” as a device that removed grease and was 750 gallons or larger. So the UPC terminology changed based on the size of the device. The term “trap” is defined in the codes in relationship to trapping sewer gasses, not trapping grease waste. The proper terminology is “grease interceptor” and “interceptor” is the terminology used in the industry standards for these products. The devices have air vents between the chambers to allow air to move freely from the inlet to the outlet. Because of this airway, it should not be referred to as a trap.

Grease removal devices are hydro-mechanical or gravity-type grease interceptors with either a heater and grease pump or a heater and a skimmer wheel to remove the fats, oils and grease (FOG) that floats at the top of the interceptor and pump it or drain it by gravity to an adjacent container for easy removal.

The American Society of Mechanical Engineers (ASME) standard for grease interceptors, ASME A112.14.3, addresses hydro-mechanical grease interceptors, and the ASME A112.14.6 standard addresses grease removal devices.

Many proposals have dealt with the terminology updates that started the grease interceptor debate. Everyone wanted to change the code to require something unique to their area or to the products they sold. Concrete tank manufacturers supported a code change proposal allowing only large outside grease interceptors. The reason given was that grease interceptors were smelly and objectionable when opened in the kitchen area. Smaller grease interceptor manufacturers supported a code change that allowed only inside grease interceptors. Their reasoning was that grease coagulates in long runs of piping leading to outside grease interceptors and that food decays in large interceptors, causing odors and concrete spalling. Still another code change proposal was that the minimum size of any grease interceptor be at least 1,500 gallons. During the code change discussions on the 1,500-gallon minimum, someone testified that the minimum size should be 2,500 gallons because that was the requirement in their area of the U.S.

The ensuing debate stirred a lot of emotions, including asking that, if the minimum size were 2,500 gallons and the interceptor was located outside, what would happen to Mom and Pop sandwich shops or delis in an urban area or downtown location with only a three-compartment sink and practically no grease waste discharge.

Some codes require a solids interceptor between the food waste grinder and the grease interceptor. The additional cost of a solids separator is significant, so some food waste grinder manufacturers have been lobbying the model code organizations to allow an exception to allow the grease waste to bypass the grease interceptor if there is a food waste grinder on the sink. That logic allows the most grease-laden waste mixed with a high concentration of food particles to be introduced into the building drain and the sewers. Bypassing the grease interceptor with greasy food particles will likely lead to an increase in clogged building drains and sewers. Most drain and sewer cleaning companies would likely welcome this option because it will guarantee increases in their future business.

Grease interceptor facts

1. Cooking and preparing foods results in the production of fats, oils and grease, (FOG), which can congeal or solidify in the sanitary sewer pipes inside a building or downstream from a building as the grease laden wastes cool down. This is harmful to building drains and sewers.

2. The purpose of a grease interceptor is to remove FOG from the waste flow before it gets into the public sewers.

3. The congealing of grease in a building drain or sewer can cause sewage to back up into a building or multiple buildings, or sewage can fill a manhole and flow out of a manhole cover in the street and down the storm drain to the natural waterways.

4. Sanitary sewer overflows near major bodies of water have contributed to many fish kills and to contamination of natural waterways, lakes and oceans.

5. Sewage backups inside a building or in the public sewer are a health hazard and an environmental hazard. For this reason, model plumbing codes require removal of all harmful substances that can be detrimental to the sewers. (Sand interceptors, grease interceptors, oil interceptors, lint interceptors, etc.)

6. The EPA has fined many water and sewer districts for not properly addressing grease waste issues after sanitary sewer overflows contaminated waterways because local codes and grease interceptor ordinances were found to be inadequate and because they did not address the issue after earlier citations.

7. The amount of grease waste production varies depending on the restaurant, the type of foods served and the cooking habits of the staff.

Proposed Grease Waste System Design Standard

I would like to see ASPE develop a Grease Waste System Design standard that covers:

1. Grease waste potential of various restaurant types
2. Calculation of the number of meals served per day, week, month, year.
3. Amount of grease waste developed based on number and type of meals
4. Fixtures likely to produce grease waste
5. Design and layout of grease waste piping system
6. Types of interceptors
7. Size and location of the grease interceptor
8. Maintenance requirements of a grease interceptor
9. Recommended grease interceptor maintenance ordinance
10. Maximum number of days between cleanings based on grease production
11. Recommended grease interceptor cleaning frequency ordinance

I would like to see the ASPE Research Foundation and/or the Plumbing Efficiency Research Coalition (PERC) study some of these grease waste issues. I would also like to see ASPE consider the development of a Standard for the Design of Grease Waste Systems.

Hydro-mechanical grease interceptors utilize a flow control device that limits the flow of waste through the interceptor and through a series of baffles. The baffles cause the waste to start flowing upward on the inlet side of the interceptor. This improves the efficiency of the interceptor, especially when hot water or detergents have broken up the grease into tiny droplets that are more difficult to separate by gravity. The increased velocity of the waste flow through the smaller interceptor can make it difficult for separation without the flow control device, baffles or partitions. The FOG attaches to the debris in the waste stream and can pass through if the flows are excessive. This type of interceptor will plug up in short order if a food waste grinder is connected to the unit without a solids separator.

There can be problems with this type of installation if the flow control device is at a lower level than the grease interceptor. This increases the head pressure on the inlet to the flow control orifice, and the flow rate through the flow control device and interceptor increases proportionally. If the elevation change is significant, the flow can be so high it flushes the grease right through a smaller interceptor. Make sure the flow control device is near the sink. The Standard calls for the flow control device to be about 11 inches below the sink so that the flow will be consistent from each tested device. In the field, it can vary an inch or two without much of a change in flow.

A gravity-type grease interceptor works based on a much larger volume, while it slows the waste flow down through the interceptor to the point that the grease is allowed to rise to the top of the interceptor over a time period of a minimum of 30 minutes.

A flow control device is used to maintain the correct flow rate through the grease interceptor to avoid excessive flow turbulence and velocity, which could allow grease to pass through the interceptor. Flow control devices are typically not installed on the larger outside interceptors, because the pipe size is the flow restrictor. The interceptor is large enough to take care of the flow.

A number of proposals from a variety of sources and members of the ASME committees dealt with grease interceptors and grease removal devices, solids interceptors and food waste grinders. A few code changes were submitted to both model codes in an effort to bring both codes in line with the terminology from the ASME standards. The code changes were intended to have been working for common terminology in the model codes.

IAPMO had a FOG task group that met over a period of several years at the IAPMO headquarters in Ontario, Calif. There was a push to differentiate the types of grease interceptors. It was also pointed out that there was a need for a consensus standard that addresses gravity type or large outdoor concrete grease interceptor performance. Standards for concrete septic tanks and an IAPMO product standard for grease interceptors did not address performance. Both seemed to focus on reinforcing, concrete strength and structural traffic loading for the tops. I am still not sure if IAPMO/ANSI Z1001 addressed lining of the concrete tanks to resist the acidic environment; at last check, they were not addressing the grease removal efficiency of the concrete interceptors. They only were addressing concrete strength and traffic loading. I’m not sure how that turned out.

Ron George is president of Plumb-Tech Design and Consulting Services LLC. He has served as chairman of the International Residential Plumbing & Mechanical Code Committee. Visit www.Plumb-TechLLC.com, e-mail Ron@Plumb-TechLLC.com or phone 734/755-1908.