Trapping and Venting for Grease Interceptors

From time to time I will get an email that contains a schematic of a grease interceptor installation with the question, "does this look right?"

Usually the email-sender wants to know if the trapping and venting is shown correctly.

The answer requires a knowledge of both the applicable plumbing code and the installation requirements of the specific grease interceptor.

Model plumbing codes require each fixture discharging into a grease interceptor be individually trapped and vented, and require the installation of a vent downstream of the grease interceptor.

Standards also come into play when it comes to determining the type and location of vents upstream of a grease interceptor.

PDI G101 mandates the installation of an vented external flow control. The vent on the flow control is an air intake.  As the waste stream flows through the orifice in the flow control device negative pressure is created, drawing in air from the air intake which is intended to mix with the waste water as it enters the grease interceptor aiding in separation efficiency.

ASME A112.14.3 allows four types of ratings as follows:
  Type A - units with external flow control, with air intake (vent): directly connected
  Type B - units with external flow control, without air intake (vent): directly connected
  Type C - units without an external flow control: directly connected
  Type D - units without an external flow control: indirectly connected

Manufacturer's are required to identify which Type their interceptor is rated to when certifying to the ASME standard. 

PDI G101 and ASME A112.14.3 Type A certified interceptors are required to have a vented external flow control installed upstream of the interceptor.

Okay, so lets take a look at some drawings and see what works and what doesn't.

What's wrong with this installation?

It depends on which model plumbing code applies to the installation.

The International Plumbing Code (IPC) 1002.1 (exception 3) allows a grease interceptor to serve as a fixture trap - where it is intended by the manufacturer to serve as a trap - for a single fixture or a combination sink of not more than three compartments so long as the vertical distance from the outlet of the fixture to the inlet of the interceptor is not more than 30 inches and the developed length of the waste pipe from the most upstream fixture outlet to the inlet of the interceptor does not exceed 60 inches.

This drawing for a PDI G101/ASME Type A grease interceptor appears to be compliant with the IPC.  Assuming the interceptor is intended to serve as a fixture trap, there is no requirement to install an additional trap and vent between the fixture and the interceptor. 

The Uniform Plumbing Code (UPC) does not permit a grease interceptor to serve as a fixture trap and also prohibits the installation of a vent between the air intake on the flow control and the grease interceptor. The above diagram would not be compliant with the UPC. There needs to be a trap and vent between the fixture and the vented flow control fitting.

What's wrong with this installation?

Actually, nothing!

The drawing shows a PDI G101/ASME Type A grease interceptor connected to a the three compartment sink that is trapped and vented, an external flow control with air intake and a vent on the downstream side of the grease interceptor.

This installation would be compliant with both the IPC and the UPC.

What's wrong with this installation?

The drawing shows a PDI G101/ASME Type A grease interceptor with an external flow control with air intake, however it also shows a trap on the fixture but no vent for the trap.

This is not compliant with the IPC since the code does not allow double trapped fixtures. The code does allow the interceptor to serve as a trap - assuming that this interceptor is intended to serve as a fixture trap - thus adding a trap to the fixture upstream of the interceptor creates a double trapped fixture installation. Either adding a vent to the trap or removing the trap on the fixture altogether would solve the problem.

The only solution for compliance with the UPC is to add a vent for the trap on the fixture upstream of the vented flow control fitting.

What's wrong with this installation?

This drawing shows a semi-automatic draw-off type grease interceptor but without a vented external flow control.

Since all semi-automatic draw-off grease interceptors are certified to either PDI G101 or ASME A112.14.3 Type A (that I am aware of) an external vented flow control must be shown for compliance with the IPC.

For compliance with the UPC this drawing would have to show both a vented external flow control and a trap and vent for the fixture.

What's wrong with this installation?

Again, there is nothing wrong with this installation, though it may not be immediately obvious as to why.

The unit shown is certified to ASME A112.14.3 Type C (without external flow control) with a built-in or integral flow control and does not require an air intake.

That being the case the interceptor does not require a vented external flow control - jurisdictions unfamiliar with this type of interceptor often question drawings like this and understandably so.

This installation is compliant with both the IPC and the UPC since it shows a trapped and vented fixture discharging through an approved interceptor without external vented flow control with a vent installed downstream.

Air Admittance Valves (AAV)

The UPC does not include provisions for AAVs except as a part of an "Engineered Vent System" under section 912.0, much to the chagrin of engineers around the country. Many states that adopt or adapt the UPC have added an allowance for AAVs so you will have to check with your state to see if they are approved.

The IPC approves the use of and installation requirements for AAVs under section 918.0.

What's important to remember about AAVs is that they only allow for the relief of negative pressure in the drainage system. Therefore, when using an AAV to vent a grease interceptor, it's important that the drainage system has provision for the relief of positive pressure to ensure proper flow.

Boilerplate drawings can be trouble

To be honest, much of the confusion over whether a drawing shows a code compliant installation of a grease interceptor or not, can be the result of boilerplate drawings provided by manufacturers in submittals or installation instructions. Manufacturer's want to provide guidance for a broad range of installations without providing detailed drawings for every single installation variable that can exist. 

When it comes to traps and vents for grease interceptors and the fixtures discharging to them, it's incumbent upon an engineer or contractor to identify and comply with local code requirements regardless what a manufacturer's drawing shows. 

Hopefully after reading this post you will find it easier to identify a drawing that is right for your installation or one that needs to be corrected. 

Regulatory compliance manager; fancy title or job description?

Recent activities I have been involved in have made me think that people really don't understand what it is that I do for a living.

There's no secret that I work for a grease interceptor manufacturer, But, what do I do for Schier?

Am I in sales?  No.

Wait, let me correct that.  I believe everyone is a sales person in one way or another.  For example, my wife would say that she is absolutely not cut out to be in sales.  But when she really wants something, she seems to have no problem presenting me with all of the features and benefits that would justify her request - which usually boil down to me having a happy and contented wife.

Hey, who doesn't want a happy and contented wife?

I generally find that preferable to just about anything else in the entire universe as it tends to provide a much "safer" environment at home.

My kids are some of the best sales people I know, with their mom and dad anyway.  They can be very creative in their justifications for why we should do this thing, or buy that thing, or go to such and such a place, all the while hammering home the features of this or that and the benefits that either they specifically would enjoy or that we all would collectively enjoy together.

Sales is really just the art of persuasion.  Some are naturally more gifted at it than others', and they typically end up selling for a living, but everyone has sold someone something at some point in their life.

Okay, so in the sense of doing "sales" for a living, no, I don't do that anymore. In other words, Schier does not pay me to sell anything.  I can't even tell you what our sales look like anymore because I am very much out of that loop.

So what do I do?

You might say that I am an advocate.

Merriam-Webster's dictionary defines advocate as, "one that defends or maintains a cause or proposal", or "one that supports or promotes the interests of another."

Who or what do I advocate for?

I am an advocate for fats, oils and grease (FOG) abatement in wastewater collection systems to reduce or eliminate sanitary sewer overflows (SSO) and their resultant risks to human health and safety.

That is my job description.  It has taken a while for it to come into clear focus, even for me.

What it means is that, while I am paid to do what I do by Schier Products, I am not paid to promote or sell for Schier Products.

I am in fact paid by Schier Products to advocate for what I think is right for FOG abatement in wastewater collection systems.

The advocacy I do is both internal and external to Schier.

When working with Schier I may advocate for some specific product improvements to make field inspections by pretreatment personnel easier or I might advocate for a new product to solve problems I am seeing in the field.

When working with pretreatment programs I may advocate for improving the requirements in an ordinance, or to remove some restrictive language that will hurt enforcement efforts, or to stop mandating products that are untested for performance.

When working with plumbing codes I may advocate for improved less-confusing-language regarding which fixtures should be routed to an interceptor, or I might take a stand against proposed changes that might lead to conflicts with pretreatment requirements or would loosen restrictions that would, in my opinion, be harmful to wastewater collection systems.

When working with standards such as ASME A112.14.3, I might advocate for more accountability in the standard and less prescriptive design requirements that shackle manufacturers and stifle innovation - something very much needed in grease interceptor design and operation, in my opinion.

I think it's important to understand that I see what I do, not as a job, but as a calling.

I believe in the "cause" of FOG abatement.

When you passionately believe in something you are willing to fight for it. You are willing to take actions that you believe in your heart will make a difference for your cause.

I guess that means that you might ruffle a few feathers. You might not "go along" to get along - if getting along means compromising what you believe in.

That being said, I love engaging with the pretreatment community and others who are equally interested in the issues surrounding FOG deposit formation and the exploration of solutions that might mitigate its deleterious effects.

My job title sure can be confusing, but I take my role in the cause seriously and I welcome the challenges, debates, and struggles that are necessary to make a real difference for us all.

Grease interceptors are not called traps anymore

Every now and again the question of whether a grease interceptor is still considered a trap comes up. 

Grease interceptor...grease trap...you say tomayto, I say tomahto - does it really matter?

The distinction is important enough that you should be on the lookout for a fearsome predator known as a lawyer.  These anal-retentive-jot-and-tittle-semantics-fanatics have already picked up the scent of blood in the water on this subject.

Disclaimer: the sharks in suits pictured here are not intended to represent any particular lawyer or lawyers; any similarity to actual individuals is purely coincidental.

Anyways...

It's interesting to see how the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC) have evolved on this issue over time.

UPC
Through the year 1997, the UPC mandated that grease traps have a 2" water seal (the minimum required for a fixture trap), allowed a maximum connection of four fixtures and allowed the grease trap to be used as a fixture trap for a single fixture provided that the distance between the fixture outlet and the grease trap did not exceed 4 feet and the vertical tailpipe or drain did not exceed 2-1/2 feet. 

In 1994 the UPC added or clarified a restriction by stating that, "no fixture shall be double trapped," which created a conundrum. Since the code prohibited double trapping fixtures, and since a grease trap was allowed to serve up to 4 fixtures, if the grease trap is considered a "trap" owing to its 2" water seal, and it can serve as a fixture trap for a single fixture, and it can receive the discharge of up to 4 fixtures, and each of those fixtures must be individually trapped, and each of those fixtures is then routed to a grease trap, then all 4 fixtures are double trapped, which is a violation of the code.

The 2000 UPC eliminated some confusion by removing the language that allowed a grease trap to serve as a fixture trap as had been previously approved and eliminated the requirement for a minimum 2" water seal. Yet this really only added confusion since a grease trap would no longer be required to have a water or trap seal but it was still called a trap.

The 2006 UPC eliminated the term grease trap and introduced a new term, hydromechanical grease interceptor (HGI), to define passive grease interceptors. By eliminating the term grease trap and all references to it, and by not allowing a HGI to serve as a fixture trap for even a single fixture, the UPC eliminated the confusion that had existed over whether a grease trap was a trap.

It's not.

IPC
Prior to 2006 the IPC defined grease interceptors and grease traps, which were distinguished from each other only in that a grease trap had a rated flow of 50 gpm or less while a grease interceptor had a rated flow exceeding 50 gpm. A grease trap intended to serve as a fixture trap in accordance with the manufacturer's installation instructions was permitted to serve as the trap for a single fixture or a combination sink of not more than three compartments so long as the vertical distance from the fixture outlet to the inlet of the interceptor did not exceed 30 inches and the developed length of the waste pipe from the furthest compartment outlet to the inlet of the interceptor did not exceed 60 inches (1002.1 Exception 3).

In 2006 the IPC removed the definition for grease trap and changed the definition of grease interceptor, removing any reference to rated flow, making it the term for a passive grease interceptor.  The code language under 1002.1 Exception 3 from previous codes was not amended, retaining the term grease trap, a term which was no longer defined in the code.

The 2009 IPC removed all references to the term grease trap. The code language under 1002.1 Exception 3 was amended, changing the term grease trap to grease interceptor.

The 2012 IPC introduced a new definition of grease interceptor adding two new terms; hydromechanical and gravity.  The term hydromechanical grease interceptor (HGI) was introduced as the new term for a passive grease interceptor while the term gravity introduced a liquid volume-retention time based type of interceptor.  Beyond simply defining the term, the code made no further reference to gravity grease interceptors.  Section 1002.1 Exception 3 remained unchanged.

The 2015 IPC added another subcategory for grease interceptors called fats, oils and grease (FOG) disposal systems and added section 1003.3.6 governing gravity grease interceptors and the new FOG disposal systems. Section 1002.1 Exception 3 remains unchanged. 

The problem I see with the IPC is in the misapplication of a HGI because the section doesn't require the interceptor to have a 2" water seal.  Instead it relies on the manufacturer to stipulate that the interceptor is intended to be used as a fixture trap in compliance with the language of the section. 

That's dangerous to me. 

By dangerous of course I mean like wearing tuna-laced swim trunks and swimming in shark infested waters.

The IPC could eliminate the confusion by simply requiring a 2" water seal for any interceptor approved for installation under section 1002.1 Exception 3.

Time for someone to submit a code change proposal for the next code cycle...anyone?

Plumbing Codes and Pretreatment Ordinances

One of the biggest challenges in the evolving world of grease interceptors is understanding the roles of plumbing codes and pretreatment ordinances.

The plumbing code and its inspectors are the watchman over the plumbing systems in commercial and residential building construction.

The pretreatment ordinance and its inspectors are the watchman over the wastewater collection
system.

In the vast majority of jurisdictions in the US the pretreatment ordinance supersedes the plumbing code in authority where a conflict between the two exists.

When it comes to grease interceptors the plumbing code has been mandating their use and governing their approvals since 1946, whereas pretreatment authorities have only more recently gotten involved with them.


This has created an interesting dilemma; pretreatment ordinances are concerned with the quality of the wastewater entering the collection system while plumbing codes are concerned with setting a minimum standard for the construction of a plumbing system.

Are these issues at odds with each other?

Yes, in a way.

Amendments to the 2011 Oregon Plumbing Specialty Code (OPSC) (effective January 1, 2013) illustrate the disconnect between the plumbing code and pretreatment ordinances.

Lets say you are a municipality in Oregon operating under an NPDES permit issued by the EPA mandating you to implement a program to reduce sanitary and combined sewer overflows in your jurisdiction. 

Lets say you go out into your community and begin inspecting restaurants to see what they are doing to mitigate the discharge of fats, oils and grease to your collection system.

Lets say you discover they have a lot of grease build-up in the laterals leading to your collection system.

Lets say you discover that a significant number of these facilities either have no grease interceptor or have an undersized interceptor serving their multi-compartment sink and they are not maintaining it very well or very often.

Lets say you also discover a significant amount of grease discharging through fixtures that are not even connected to the grease interceptor.

Lets say you talk to the plumbing plans review and permitting department and they tell you that they just, "follow the state plumbing code."

Lets say that you read the state plumbing code and discover the following language, "Where it is determined by the Authority Having Jurisdiction (you, in this story) that waste pretreatment is required, an approved type of grease interceptor(s) complying with the provisions of this section shall be correctly sized and properly installed in grease waste line(s) leading from sinks and drains...where grease is introduced into the drainage or sewage system in quantities that can effect line stoppage or hinder sewage treatment..."

Lets say you tell the plans reviewer and permit issuer that you want them to require all fixtures in a commercial kitchen be routed to a grease interceptor and lets say they don't agree with you (because they haven't investigated the discharge of fats, oils and grease from these kinds of facilities and aren't aware of the problem you are trying to address).

This would be the point at which you learn that, in Oregon, you don't have the authority to make such a requirement because of this little clause in ORS Chapter 455 Building Code, Section 455.040, "The state building code shall be applicable and uniform throughout this state and in all municipalities, and no municipality shall enact or enforce any ordinance, rule or regulation relating to the same matters encompassed by the state building code but which provides different requirements unless authorized by the Director of the Department of Consumer and Business Services."

This is very much what happened in Oregon.

Fortunately, stakeholders were able to sit down and discuss the problem which ultimately led to an amendment to the state plumbing code that now reads, "Waste pretreatment is required in all Food Service Establishments...The following plumbing fixtures and drains shall be connected to the grease interceptor(s): All plumbing fixtures, garbage disposals, dish-washers, floor drains, and cooking equipment, with drain connections in food and / or beverage preparation areas of all Food Service Establishments."

This amendment was only possible because plumbing code officials were open to the idea that the plumbing code should support pretreatment program compliance requirements.


Of course ultimately this needs to be done nationally which will require amending plumbing codes such as the Uniform Plumbing Code, the International Plumbing Code as well as the various state plumbing codes to make them more effective and supportive of pretreatment programs.

Effective FOG abatement requires a team effort that includes comprehensive pretreatment ordinances supported by effective plumbing codes.

Oregon provides a case-in-point regarding the disconnect that often exists between plumbing codes and pretreatment program compliance requirements, but also a model for resolution that benefits everyone.

Series versus Parallel Installations

When you need more capacity in a grease interceptor than is available for a given size, you have to make a decision; move up to a larger size interceptor or add another (or more than) one of the same size.

When working with multiple interceptors the question is, how do you connect them together, series or parallel?

What's the difference you may ask?

You may not have actually asked that question, but somebody else must have, because why would I be writing a post to answer a question that nobody has ever asked?

No, I can't share the name of the person who did ask for legal reason's.  Very binding, rigid and inflexible legal reason's that I don't have time to go into here.

Suffice it to say that someone out there, someone you don't know, did indeed ask me the question; you'll just have to take my word for it.

Anyways...

Let me illustrate the differences and then discuss the advantages and disadvantages of series and parallel systems so you know and are comfortable with the proper application of either type.

Series 

Series installations connect the outlet of the first interceptor to the inlet of the second, and the outlet of the second to the inlet of the third, and so on.

This system forces the entering wastewater to pass through each interceptor in the series providing two significant benefits; better efficiency and more capacity.

The limitation of series installations is, the maximum flow rate of the first unit in the series (what it is certified to) becomes the maximum flow rate of the system.

When the flow rate of the system is 100 gpm or less, series is the most effective setup for both
hydromechanical and gravity style interceptors.

The systems in the graphic here are both series layouts.  So long as the flow moves from the first unit through the second, through the third, and so on, the system is set up correctly.

Parallel

In a parallel system the interceptors are set up to each receive a portion of the flow from the facility; the incoming flow is intended to be distributed to each interceptor evenly.

This system is necessary when flow rate requirements exceed 100 gpm, because there are no interceptors currently on the market that are certified to a flow rate over 100 gpm.

Parallel setup's in gravity drainage systems are persnickety. 

By persnickety, of course, I mean that getting the flow to distribute evenly is like getting your daughter to date the guy you like...it's probably not going to happen.

Having raised two daughters and having endured countless "boyfriends", I can confidently tell you that I have liked...lets see...divide by...carry the zero...

Well, I'm not sure I got the math exactly right, but I think the answer is less than or equal to one.

Anyways...getting a parallel system to flow evenly is similar. 

The challenge in a gravity drainage system is that water follows the path of least resistance. Trying to force the water to divide evenly into two or more paths with a fitting is next to impossible especially at low flow rates.

Our own in-house testing of parallel systems revealed that the minimum flow rate needed for an even distribution to multiple tanks (using a fitting) is 50 gpm.  When you consider that the average flow from a restaurant is closer to 5 gpm, you can begin to see the problem. 

The secret to a balanced parallel system is found in what Schier calls the Flow Splitter, which utilizes a static water line to evenly distribute flow across multiple tanks.

Problem solved.

Flow control devices

With hydromechanical grease interceptors, one question that comes up from time to time is whether a flow control device is required for each interceptor in series or parallel installations.

In series installations the flow control on the first interceptor acts as the flow control for the whole system. Therefore in series installations you would only install a flow control on the first interceptor in the series.  This is code compliant with both UPC and IPC.

The point in using a parallel system is that you need to meet a requirement for higher flow rates (over 100 gpm) and as such a flow control device would be required on each interceptor.

Now that you understand series and parallel systems and how they should be utilized, unlike candidates for your daughters boyfriend, you should find these installations to your liking.

Bernoulli's Principle Revisited

One of the most popular posts I have written deals with the question of whether Bernoulli's Principle is behind the operation of hydromechanical grease interceptors, as some have argued.

The specific point I was making in that post (Is Bernoulli's Principle Behind Grease Interceptor Performance?) is that there is no evidence that deliberately adding baffles to the interior of an interceptor (to create regions of higher and lower pressure) enhances grease separation.

Gravity differential separation works best in a laminar low-velocity flow environment.

Attempting to enhance the natural separation of liquids with differing specific gravities by incorporating regions of higher and lower pressure by means of internal baffles, doesn't even make sense.

It would be like hooking your car up to a team of horses to add some "horsepower."

I guess technically the horses add horsepower, but do you really think the car is going to go faster!

So why am I writing about Bernoulli's principle again?

Because, there is a proper application of Bernoulli's Principle in grease interceptor design.

Lets begin with a couple of basic concepts in fluid hydraulics.

Liquids are generally non-compressible, which means you cannot change the volume of a liquid by adding pressure. 

The 'conservation of mass' principle requires every bit of mass (volume of liquid) to be accounted for during a process.

Think of a water hose with a spray nozzle attached.  As you close the nozzle the stream tightens up and goes farther.

The tighter the stream the higher the velocity (the speed at which the liquid is moving).

Since neither the mass nor the volume can change under steady-flow conditions, the velocity must change to allow the mass and volume of liquid to move from the larger area in the hose through the smaller area in the nozzle.

When I was a boy, my brothers and I discovered the awesome power of the tight stream from a hose nozzle which could clean dirt and mud from almost anything.

We often tried to clean each others faces off with this same technique - which invariably led to an opportunity to sit quietly for a while to contemplate our "actions".

I took contemplate to mean ponder all the ways to blame my brothers for the trouble we were in, while plotting appropriate avenues of revenge. 

Anyway, what does this have to do with grease interceptors?

The same is true in reverse!

Think of the nozzle as being the waste piping connecting to a grease interceptor.  The volume and mass of liquid is constant but the velocity changes as the liquid moves from the pipe through the interceptor.

Good interceptor designs will take the mass and volume of water and distribute it throughout the cross-sectional area of the interceptor to reduce the velocity - the speed at which the volume is moving through the interceptor - allowing for gravity differential separation (The real difference between Gravity and Hydromechanical grease interceptors).

Now it may be easier to understand why adding baffles inside the interceptor would not make sense.

The baffles add an obstacle inside of the interceptor that the liquid must flow around.  Velocity increases as the liquid moves around the edges of the baffles and while there is an associated pressure drop, the increase in speed and turbulence more than compensate for the pressure drop making it more difficult for gravity differential separation to occur.

Proof?

If you promise not to get mad, I'll demonstrate the point by comparing several PDI certified 20 gpm units to Schier's GB-20:

Yes, the Schier GB-20 holds more water than the other units.  That's why we are looking at lbs per gallon to compare each interceptor's efficiency in capturing and storing grease.  It simply illustrates that the baffles in these PDI certified units do not enhance the interceptors performance.

The Schier unit has no internal baffles - it's wide open. It does a better job of distributing the volume of liquid throughout the units cross-sectional area which reduces velocity and enhances separation.

So now you can rest easy - feel free to even snore a bit - knowing that Bernoulli's principle does figure into good grease interceptor design - just not the way you might have thought.

Understanding Rated Grease Capacity versus Maximum Grease Capacity

The grease interceptor revolution is about challenging the status quo.

It's about asking tough questions and thinking radically different about the answers.

It's about listening to the people who are affected by the products we make.

The revolution is about making High-capacity grease interceptors because contractors, engineers, restaurant owners and jurisdictions are demanding superior performance.

As more manufacturers see the light and join the revolution it's important that you understand what to look for to make sure that an interceptor that claims to be high-capacity really is high-capacity.

The journey to enlightenment begins with an understanding of the testing and rating requirements of both nationally (US) recognized and plumbing code approved standards and ends with an understanding of some of the tricks of the trade used to disguise an interceptors performance to make it appear to be something that it is not.

Testing and rating requirements

In most jurisdictions across the US, hydromechanical grease interceptor's must be tested and rated to either PDI G-101 and ASME A112.14.3.

Both standards are similar in most respects including the same testing and rating protocol, however there is a key difference between them; PDI allows for either Rated Grease Capacity (RGC) or Maximum Grease Capacity (MGC), while ASME currently only allows for MGC.

What's the difference between RGC and MGC?

An interceptor certified to MGC has actually been tested all the way to its breakdown point while an interceptor tested to RGC has not.

Let me quote from PDI G-101 so you can see the difference between the two ratings:

7.6.2 Determination of Test Breakdown Point (Maximum Grease Capacity)

The test failure, or breakdown point of the interceptor, shall be established at the increment preceding two (2) successive increments in which either the average efficiency is less than ninety (90) percent or the incremental efficiency is less than eighty (80) percent.

7.7 Efficiency Determinations (Rated Grease Capacity)

The grease shall be removed from the skimming tank and the efficiency of the interceptor shall be computed at the (13) thirteenth increment. This provides at least a twelve and one-half (12.5) percent safety factor on the ratio of the rated grease retention capacity to flow rate as indicated in Table 1:



To put the difference between RGC and MGC into perspective lets review the actual test data from NSF for Schier Product's GB-250:




You can see at the 13th increment the GB-250 had an average efficiency of 95.2% and had separated 247.46, which under PDI would allow it to be certified at 200 lbs grease storage capacity according to Table 1.

Under ASME A112.14.3 (which this unit is certified to) there isn't an option for RGC so you have to test to failure (prior to 2007 this wasn't an option under PDI either).

As you can see the GB-250 suffered two successive increments (59 and 60) with incremental efficiencies below 80%. The test breakdown point (the increment that is to be used for certification of the interceptor) is increment 58 at which the GB-250 had an average efficiency of 92.8% and separated 1076 lbs of grease at 100 gpm.

The revolution is gaining momentum

As I said earlier, other manufacturers are apparently starting to see the light.

As new products emerge to compete in the arena of high-capacity grease interceptors though, it's important not only to know how grease interceptors are rated, but also how a manufacturer reports their ratings.

Tricks of the trade

How do you know if the grease capacity shown on a specification or submittal sheet is the interceptor's actual certified capacity or an unsubstantiated claim?

To be honest it can be difficult.

One manufacturer uses the term Grease Design Capacity to confuse or imply that this is the interceptors actual certified capacity. An investigation into the testing and rating of the interceptor revealed that it was certified as RGC, which means the interceptor wasn't tested to failure and therefore their posted 'design' capacity is uncertified and unsubstantiated.

One manufacturer uses the term Greasy-Sludge Capacity. What does that mean? I'm not sure. The amount listed is more than their certified grease storage capacity. The number appears to be a combination of grease and solids capacities combined. But since neither PDI nor ASME test for solids there is no way this number can be substantiated.

Another manufacturer doesn't use pounds at all, instead opting to show their grease capacity in gallons. When you take the gallons and convert it into pounds, you end up with a lot more claimed grease capacity than their apparent certification.

When in doubt ask for the test report.

At the end of the day there is really only one way to know what the actual grease storage capacity of an interceptor is and that is to ask the manufacturer for the test reports.

In case you were wondering, testing agencies are not obligated to share the certification reports for any of their manufacturer's (I was informed of this in a very lawyer-like manner when I asked). That means you have to ask the manufacturer themselves.

Both PDI and ASME require interceptor tests to be documented on Test Form #1, which records each and every test increment along with incremental and accumulated efficiencies. The test report will tell you whether the interceptor was tested only to 13 test increments and is therefore rated at RGC or if the interceptor was tested to failure and you can see for yourself the interceptors MGC.

Schier Products believes wholeheartedly in the interceptor revolution and as such is working on posting the NSF test reports for each certified unit on its website here : http://www.schierproducts.com/Grease%20Interceptors%20Great%20Basin.html. In the mean time, if you would like to see a test report for any of Schier's certified units, just send me an email and I'll get them to you right away.

Competition is a good thing and manufacturers who want to join the revolution are welcome, but now you know what to look for to be sure that the interceptor that claims to be high-capacity really is high-capacity.

The Grease Interceptor Revolution

They say that imitation is the sincerest form of flattery, which sounds good to me, although I'm not sure who 'they' is.

If it's true, then the Schier team should be blushing, based on whats been happening in the world of grease interceptors recently.

Let me explain (or as Ricky Ricardo used to say, "esplain").

Schier Products is leading a grease interceptor revolution!

Prior to 2006, when Schier launched the Great Basin series, there had been little change in the way grease 'traps' were manufactured and certified. 

Prior to the year 2000, the only standard governing these devices was PDI G-101, which was originally published in 1949 and was based on research conducted at the Iowa Institute of Hydraulic Research (IIHR) in the early 1940s.

Even before the PDI standard was launched, the IIHR had been conducting testing on grease interceptors and had developed a rating system.  Any type of grease interceptor, before it could be installed in an army camp kitchen, had to have a rating certificate from IIHR.  

The image to the left is a schematic of the IIHR test apparatus.  

What was significant about the testing and rating that had been developed at the IIHR was the initial focus on army camp kitchen installations.

It was the army which had requested a standard that could be incorporated into its specification for grease interceptors, MIL-T-18361 (cancelled in 1982), because in the absence of a standard, ratings were determined by each manufacturer for their own interceptors.

IIHR Certified interceptors were required to meet the following minimum performance standards under the test parameters:

• Must have a minimum 90% average efficiency
• Must separate and store 2 lbs of grease for each gpm of flow at the minimum average efficiency.

Since the focus of the research was grease interceptor sizing and rating for army camp kitchens, the researchers created Table B (at right) listing the type of fixtures and recommended minimum rate of flow capacity for any interceptor that would be connected to those fixtures.

This created a problem.

It placed emphasis on how much flow an interceptor could receive while meeting the minimum efficiency and storage capacity requirements.

At left is a typical laboratory test data report for a commercial grease interceptor tested by IIHR.

Notice that the interceptor was tested to failure at multiple different flow rates!  

Why is that?

The goal was to test the interceptor to find the maximum flow rate that the interceptor could be certified to, while meeting the minimum requirements for efficiency and grease storage capacity.

How is that any different than today?

As I said earlier, when it comes to grease interceptor technology, until more recently things were operating pretty much exactly the same.

In 2000 ASME published an alternative standard for grease interceptors, ASME A112.14.3, but unlike the PDI version, this new ASME standard was consensus based and much more flexible with innovative technologies while still requiring the same performance testing as PDI G-101.

The advantage of the ASME standard is that, unlike PDI, a manufacturer does not have to use a vented external flow control and air entrainment as mandated by PDI. Instead, ASME allows for non-vented external flow control, integral (or built-in) flow control, or even an indirect connection.  

At last, an industry recognized and approved standard that lets manufacturer's innovate their interceptor designs to create better performing technology.

Prior to the launch of the new Great Basin series, Schier's R&D team took a radically different view of grease interceptor design based on the flexibility offered under ASME A112.14.3:

• Why create an interceptor that merely meets the minimum performance requirements in the standards?  
• Why not create a design that has a higher average efficiency than 90%?  
• Why not create a design that can hold five or 10 lbs of grease for each gpm of flow rate?  
• What happens to lemmings?

This thinking led Schier to designs that had substantially higher efficiencies and storage capacities than traditional PDI G-101 certified interceptors.  

Schier has certainly not been alone in the revolution!  

Thermaco's Trapzilla grease interceptors have been available for several years and also dramatically outperform traditional PDI G-101 certified interceptors.

Whats finally happening now is that other manufacturer's have 'seen the light' and are introducing certified interceptors intended to compete with Schier's higher effiencies and storage capacities.

While competition is good for the industry, not all competition is the same. 

What is 'design capacity'?  Why do some manufacturer's list different grease storage capacities on the same specification sheet?  Why do some manufacturers use their own terminology instead of recognized industry terms for grease and solids capacities? How do you know how a grease interceptor actually performed during testing?

I will address these questions and more in my next post on grease interceptor testing and ratings - Understanding Rated Grease Capacity versus Maximum Grease Capacity. 

When you know and understand the testing and rating systems in approved standards and what to look for in a certification you'll be better informed when specifying or approving a grease interceptor.

The Standards that govern Grease Interceptors (all types) in North America

UPDATED (June 2014)

When it comes to grease interceptors there are a variety of recognized standards that have been developed over the years that govern performance requirements, construction requirements or both. This post will explore all of the available standards for North America and the types of interceptors they govern.

PDI-G101
This standard governs passive hydromechanical grease interceptors.

PDI stands for the Plumbing and Drainage Institute which is an association of manufacturers of plumbing and drainage products. In the early 1940's PDI was called the Plumbing and Drainage Manufacturers Association and members of the group joined with representatives of the Quartermaster General, Surgeon General, Army Corp of Engineers and researchers from the Iowa Institute of Hydraulic Research to develop a testing program to establish flow rates and grease holding capacities for uniform rating of grease interceptors.

Using the guidelines established in Iowa, the Research Committee continued the testing program at The United States Testing Company, Inc., which culminated with the first issue of this Standard in 1949 and certification of applicable grease interceptors.

Test apparatus used by PDI and ASME

Interceptors are tested and rated for efficiency and grease storage capacity. Approved interceptors will have a minimum average grease removal efficiency of 90% and will retain not less than 2-1/4 lbs of grease for each one gpm of certified flow rate at either the interceptors Rated Grease Capacity per Table 1 below (with a 12.5% safety factor) or at the interceptors Maximum Grease Capacity by determining the break down point.

Certification to a Rated Grease Capacity allows a manufacturer to test their unit through 13 cycles and whether "full" of grease or not, so long as the interceptor meets the requirements for efficiency and the minimum grease capacity per Table 1, it will be certified at the Rated Grease Capacity per Table 1.

The standard also allows a manufacturer to have an interceptor tested to break down to determine its Maximum Grease Capacity. It must meet the same efficiency requirements and minimum grease capacity as an interceptor with a Rated Grease Capacity and so long as it does, it will be certified.

Interceptors that are certified to a Rated Grease Capacity and those certified to a Maximum Grease Capacity are required to label their interceptors the same according to Table 1 above. This essentially discourages manufacturers from continuing to test an interceptor beyond 13 cycles to determine the interceptors break down point because the interceptor will still be certified and listed to the same performance as a Rated interceptor. This makes it difficult to determine if an interceptor certified to PDI-G101 actually exceeds the minimum requirements.

This standard also mandates the use of an external flow control with integral air vent (which provides air entrainment to aid grease in separating from the entering waste stream) and internal baffles or barriers. Currently the standard does not allow for any alternative design elements, which discourages innovation.
Lastly, the standard provides language that would imply that a manufacturer could have an interceptor tested and rated to flow rates in excess of 100 gpm. Unfortunately PDI does not have the ability to actually perform the testing at this time. Currently the maximum flow rate of any interceptor certified to this standard is 100 gpm.

This is the most widely used, recognized and approved standard in North America.

According to PDI's website (www.pdionline.com) there are 24 manufacturer's with grease interceptors certified to this standard.

PDI G-102
This standard sets requirements for how grease interceptor sensing and alarm devices perform to signal that the interceptor is approaching its rated capacity.

ASME A112.14.3
This standard governs passive hydromechanical grease interceptors.

According to the foreword, “In 1994, the Plumbing and Drainage Institute agreed to work with the American Society of Mechanical Engineers for the development of this Standard. This Standard includes criteria for testing and rating of grease interceptors; general requirements for these appurtenances; and an appendix of valuable sizing, installation, and maintenance data.”

Regarding the scope of the Standard the foreword states, “…this Standard is limited to units of 100 gallons per minute (gpm) or less in rated capacity.”

One of the significant differences between PDI G-101 and this Standard is that while PDI G-101 interceptors are restricted to design requirements that include a vented external flow control and internal baffles, this standard classifies interceptors with these design elements as Type “A” Rated.

Type A – Units with external flow control, with air intake (vent), directly connected
Type B – Units with external flow control, without air intake (vent), directly connected
Type C – units without an external flow control, directly connected
Type D – units without an external flow control, indirectly connected

I am not aware of any manufacturer who has certified an interceptor to Type B at this time.

Schier Products Great Basin series and Thermaco's Trapzilla series are the only grease interceptors currently certified to Type C. Canplas' new Endura XL series, which they are advertizing as available this fall, also utilize built-in flow control conforming to Type C.

I am not aware of any manufacturer who has certified an interceptor to Type D at this time.

While the testing under ASME A112.14.3 is identical to that under PDI G-101, there are a couple of differences in performance and rating requirements:

PDI G-101 requires an interceptor to hold 2-1/4 lbs of grease for each one gpm, while the ASME standard only requires 2 lbs for each one gpm.

PDI G-101 allows for either Rated Grease Capacity or Maximum Grease Capacity, while ASME only allows for Maximum Grease Capacity.

ASME A112.14.3 is listed and approved by the Uniform Plumbing Code (UPC), the International Plumbing Code (IPC) as well as the National Standard Plumbing Code (NSPC) and most independent state plumbing codes.

ASME A112.14.4
This standard was first published in 2001 and is the only recognized standard in North America governing automatic grease removal devices (GRD).

The devices required to meet this standard must automatically remove fats, oils and grease from the separation chamber to a point outside of the GRD in a container capable of holding 150% of the interceptors rated capacity. The removal process is supposed to ensure that the removed FOG is 95% free of water, by volume.

The standard mandates that GRDs first be tested and rated according to ASME A112.14.3 to establish that the interceptor's separation chamber can hold 2 lbs of grease for each one gpm of flow rate. Then the standard employs an additional test to ensure that the GRD's collected grease can meet the required percent of water content, not to exceed 5%.

ASME A112.14.6
This standard was developed to address a growing category of interceptors that not only separate and retain FOG, but internally dispose of retained FOG by means of mass and volume reduction through thermal, chemical, electrical and biological processes.

The standard allows for the use of hydromechanical grease interceptors meeting either PDI G-101/ASME A112.14.3 or gravity grease interceptors meeting IAPMO/ANSI Z1001.

Acceptable performance, under the test parameters of this standard, is an effluent concentration limit of 100 mg/L (PPM) as determined using USEPA Method 1664.

CSA B481
This is a consensus standard published by the Canadian Standards Association in 2007 governing hydromechanical grease interceptors. It is a more comprehensive standard that governs material requirements, construction requirements, test methods and performance requirements, marking requirements and sizing guidelines.

CSA both publishes Standards and offers testing and certification services to those standards for a fee.  They also allow other certified/approved agencies to test and certify to their standards.  Testing agencies have their own identifying mark as follows:

This mark identifies an interceptor that has been tested and rated by CSA Group to CSA B481.

This mark identifies an interceptor that has been tested and rated by IAPMO to
CSA B481.

 

This standard offers two different types of ratings; B481.1 and B481.2.

CSA B481.1 Testing and rating of grease interceptors using lard
This certification specifically requires testing to ASME A112.14.3 for the interceptors flow rate and rated capacity and requires the interceptor to be marked with its removal efficiency, flow rating, and maximum grease containment capacity.

CSA B481.2 Testing and rating of grease interceptors using oil
This certification uses effluent concentration sampling for testing the interceptor. The test requires the interceptor to be filled with water first, then have crushed granite added up to the interceptors maximum solids capacity (unless the interceptor is not designed to capture and contain solids), then fill the interceptor with sunflower oil to the point at which 5 test cycles of 12,000 mg/L will fill the interceptor to its rated capacity.

Then the interceptor is tested 5 cycles with the oil mixture in the prescribed concentration and the interceptor’s effluent is sampled multiple times during the cycle. Whatever the average is of the concentration of oil in the effluent grab samples is recorded as the average efficiency for the interceptor in mg/L.

For demonstration purposes let’s say an interceptor’s first cycle has an average effluent concentration of 100 mg/L, 2nd cycle its 120 mg/L, 3rd cycle its 130 mg/L, 4th cycle its 175 mg/L, and 5th cycle its 225 mg/L. The interceptors overall average efficiency would be 100 + 120 + 130 + 175 + 225 = 750 divided by 5 for an average of 150 mg/L. The manufacturer would then be required to post the interceptors Effluent Grease Concentration as 150 mg/L on its label.

There is no predetermined concentration limit that triggers a pass or fail. The test simply requires the manufacturer to list the grease concentration limit as an average of the recorded test results.

There are no certified grease interceptors that meet this standard today.

ASTM C 1613
This is a standard specification for Precast Concrete Grease Interceptor Tanks. It governs the type of cement, method of manufacturing as well as structural and physical design and construction requirements including: the shape and capacity of the tank, number of compartments, location of baffles, minimum and maximum liquid height, volume of free airspace, size and location of manhole covers, and so on.

The only testing requirement contained in the standard is for water-tightness. There is no performance test requirement.

This is not an approved standard in either the Uniform Plumbing Code nor the International Plumbing code.

IAPMO/ANSI Z1001
This is the primary standard governing gravity grease interceptors (GGI), recognized by national model plumbing codes and most independent state plumbing codes. It governs design requirements such as a minimum of two compartments, minimum liquid volume of 300 gallons, minimum free airspace, size and location of manholes covers, and so on. It also governs construction material requirements including concrete, fiberglass, polyethylene and coated steel.

The major drawback to the standard is that it does not require a performance test for certified units, but rather only mandates leakage testing.

Future work on this standard should focus on developing a test protocol to justify detention time based sizing methodologies.

Now you know all of the standards that govern grease interceptors today, the types of interceptors or technologies that are covered and the basic requirements contained in each standard.