Steel grease interceptor's costly but last tearout and replacement

Steel grease interceptor's corrode and fail over time.  That's a fact that's generally not in dispute.

How long it can take can vary of course,  but is influenced by restaurant menu, frequency of pumpouts and thoroughness of cleaning.

A corroding steel interceptor feeds FOG deposit formation in collection systems with lots of iron oxide, and when it fails it leaches it's contents and contaminates the surrounding soil.

The average life expectancy for a steel interceptor is roughly five years.

The cost to replace a failed steel interceptor runs in the thousands of dollars, which is why we put together a video; we wanted to show just what it takes to tearout and replace a corroded steel interceptor.

The best long term strategy to prevent the problems associated with failing steel interceptors, of course, is to mandate or approve only interceptors made with non-corrosive materials such as heavy duty thermoplastics or fiberglass. 

Eliminating steel interceptors will benefit all stakeholders including restaurant owners, wastewater authorities and the rest of us.

Check out the video here: https://vimeo.com/130551325

YouTube Video - Grease Production Sizing Method

I realize that I recently blogged about the topic of Schier's Grease Production Sizing Method (here), but as I travel around the country visiting with pretreatment professionals I repeatedly see the need for a better sizing approach for grease interceptors.

Schier created a video to provide another tool to help jurisdictions, specifiers and contractors to not only understand how to size by grease production but also to be able to quickly explain the method to anyone else.

Flow rate or liquid volume based sizing for grease interceptors is inaccurate and inadequate, having led to thousands and thousands of incorrect installations across North America.

Grease Production Sizing is the only method that considers how much grease a restaurant will produce to ensure that the grease interceptor selected has enough capacity for a consistent and affordable pumpout schedule.

Here is a link to the video if you want to check it out:

http://youtu.be/c3HLV3dF89c

The 25% Rule; where did it come from?

Have you heard of the 25% rule?

In case you are unaware or have been off-planet for a while let me explain.

The 25% rule is used primarily by pretreatment authorities to determine when a grease interceptor (or oil separator) is full. A fairly universal definition would be:

"The total depth of the floating grease layer plus the settle-able solids layer cannot exceed 25% of the total liquid depth of the interceptor."

Determination is made by taking a core sample with something like a Sludge Judge or Dipstick Pro (I know of a few jurisdictions that use florescent light covers (clear plastic tubes) from Home Depot or Lowe's, with a rubber stopper).  The device is lowered slowly through the fats, oils and grease layer all the way to the bottom through the solids layer of the interceptor and then capped or plugged and slowly removed and set aside to rest.  This allows the captured FOG to collect at the top of the device while the solids settle at the bottom.

A measurement is taken, typically in inches, from the top of the FOG layer to the bottom of the device, which represents the tanks total water column.  Then the FOG and solids layers are each measured, also typically in inches, and added together.  If the combined FOG and solids layers are equal to or greater than 25% of the total water column then the interceptor is considered full.

For example lets take a typical gravity interceptor in the field like the one pictured here on the left. 

The technician is using a Dipstick Pro which appears to be showing a 48" water column and the technician is showing by the spread of his fingers a FOG depth of about 6" (okay, I'm guessing on that, but I have fairly large hands - not like Wilt Chamberlains, but I wear a large golf glove - and when I spread my fingers like his against a ruler its about 4.5" and adding a bit for the extra FOG above and below his fingers its about 6" or so, give or take).  If the solids layer at the bottom of the device is also 6" that would be a combined 12" of FOG and solids.  When you divide 12 by 48 you get 25%.

This particular interceptor is full, hence the stunned demeanor from the restaurant owner/manager as the technician gives him the bad news.

But wait, there appears to be quite a bit of space left in the interceptor for collecting even more FOG and solids, so how do we know that this interceptor is actually full (a question this restaurant owner/manager probably asked the technician)?

Here's the thing, it's not that the rule is a scientifically based determination of efficiency breakdown, or that the EPA has mandated it, it's more like a generally accepted rule-of-thumb that many jurisdictions have adopted.

Where did it come from?

Good question.

I've been looking for the answer for a while now and no one seems to know.

Seriously.

In 2011, while preparing for a presentation at the Pacific Northwest Grease Summit in Bellevue Washington, I wondered if there was a correlation between the capacities of certified hydromechanical grease interceptors and the 25% rule.

I took all of the major manufacturers certified units (JR Smith, Zurn, Mifab, Watts, Josam, and Wade) and did some very basic math.  For example, if a unit was certified at 20 gpm with 40 lbs grease capacity using lard, I converted the amount of lard in the interceptor, when it was full, into gallons and then divided that by the amount of water the unit could hold.

It didn't matter which manufacturer's unit I checked, the results were very similar and all within a narrow range.  The maximum capacity for storing grease before failure in each unit I checked was between 25% and 35%.

This is further supported by the Plumbing and Drainage Institutes 1998 (R-2010) paper Guide to Grease Interceptors - Eliminating the Mystery, in which they stated that PDI-G101 certified interceptors may need maintenance when as little as 25% of their rated capacity has been reached.

Fast forward to my more recent research in which I have been emailing jurisdictions, googling the internet and searching all available forums for any clue as to the origins of the 25% rule.

Honolulu appears to be one of the early if not earliest users of the rule.  A post on the Yahoo Pretreatment Coordinators forum said that the jurisdiction did the same calculations as far back as 1995 as they were developing their FOG program.  It was stated that the jurisdiction chose 25% to be conservative and it became the rule for grease interceptor maintenance enforcement in their new FOG program.

Many of the jurisdictions in Orange County California use the 25% rule based on a recommendation in the Orange County FOG Control Study which was not based on any science, but rather on a survey of FOG control programs around the US, many of which were using the 25% rule or similar standard such as maximum inches of accumulation of FOG or solids.

The 25% rule appears to be ubiquitous in FOG programs and ordinances, not because of any scientific or technical merit, but rather it seems to have its footing in the idea that 'everyone else is doing it' so it must be right.

The problem now is that the rule is well entrenched in these FOG programs and ordinances making it difficult for jurisdictions to be flexible with newer technologies that hold more grease in comparable foot prints to traditional designs, in some cases matching the storage capacities of much larger gravity style interceptors.

Schier Products Great Basin, Thermaco Trapzilla and other products looming on the horizon are capable of storing grease and solids to well over 50% of their liquid volume, but jurisdictions are challenged to figure out a way to allow an owner to actually benefit from these higher capacities, owing to limitations set on themselves through enacted policy.

Hopefully by understanding how we got where we are, jurisdictions can gain insight into how to either avoid the pitfalls in setting universal capacity limits and/or perhaps, correct any problems that may have been created in enacted policies that inadvertently punish owners who would choose to use newer more efficient higher capacity technologies.

Anyone out there that has more information on the history of the 25% rule please message me and I'll update this post. 

Grease Production Sizing

Although sizing grease interceptors, whether gravity or hydromechanical, has always been based solely on flow rate, this strategy falls short in that it does not consider how much grease a specific food service facility could produce.

There are many times when volume or flow rate sizing would lead to the same size interceptor for a subway sandwich shop as for a Mexican grill, however it is well understood by inspectors that these two types of restaurants produce significantly different amounts of fats, oils and grease (FOG).

Schier recommends using a grease production calculation to determine how much grease a particular restaurant is likely to produce in order to ensure that the specified grease interceptor has sufficient grease storage capacity to allow for a realistic and affordable pump out frequency.


 

We developed the above categories for restaurants based on feedback from jurisdictions and pumper contractors around the country, combined with reports such as the Brown Grease Study (Kennedy Jenks 2011) which gives detailed information about restaurant types and menu's as well as grease and solids production data.

The formula for calculating grease production requires three bits of information:
1. Grease production per meal - you simply have to decide by menu type which category (low, medium or high) that the restaurant falls under and then whether the restaurant uses flatware or disposable (plastic or paper) forks, knives, spoons, plates, cups, etc.

2. Meals or customers per day - if this is a franchise they typically have this information available. Independent start-ups may not know this information up front, in which case you may have to make an educated guess or phone a friend or consult a medium. Most of the time you can get close enough that the calculation makes sense.  Just remember that its better to err on the high side.

3. Days per pump-out cycle - this is simply the maintenance cycle you plan to use for pumping out the interceptor.  Most people will not maintain an interceptor that is sized to be cleaned out more often than once per month and most jurisdictions won't let an interceptor be maintained less often than once every 90 days.  Somewhere in between is the sweet spot for your project.

The formula for calculating grease production is very straight forward. You simply take the amount of grease expected per meal (a,b,c,d,e, or f), times the number of meals expected per day, times the number of days between pump outs to arrive at the grease capacity required for the interceptor.

Lets take a couple of real-world examples:

Example 1
McDonalds (medium grease producer, no flatware - category "c")
400 meals per day X 0.025 lbs per meal = 10 lbs FOG per day, or 300 lbs every 30 days, or 600 lbs every 60 days, or 900 lbs every 90 days.

You can also take a grease interceptors' certified capacity and divide it by the amount of grease production per day, to determine the pump out frequency as follows:

10 lbs per day would require:

Schier GB-75, 75 gpm, 616 lbs = 61 days between pump-outs
Schier GB-250, 100 gpm, 1076 lbs = 108 days between pump-outs
Trapzilla TZ-400, 75 gpm, 400 lbs = 40 days between pump-outs
Trapzilla TZ-600, 75 gpm, 600 lbs = 60 days between pump-outs
Mifab BigMax 750, 75 gpm, 150 lbs* = 15 days between pump-outs
Mifab BigMax 1150, 100 gpm, 200 lbs* = 20 days between pump-outs

*based on grease interceptors' actual third party certification (not based on the manufacturer's claims of performance, which cannot be proven).

Example 2
Buffalo Wild Wings (high grease producer with flatware, category "f")
642 meals per day X 0.455 lbs per meal = 29.2 lbs per day, or 876 lbs every 30 days, or 1,752 lbs every 60 days, or 2,628 lbs every 90 days.

29.2 lbs per day would require:

Schier GB-75, 75 gpm, 616 lbs = 21 days between pump-outs
Schier GB-250, 100 gpm, 1076 lbs = 36 days between pump-outs
Trapzilla TZ-400, 75 gpm, 400 lbs = 14 days between pump-outs
Trapzilla TZ-600, 75 gpm, 600 lbs = 20 days between pump-outs
Mifab BigMax 750, 75 gpm, 150 lbs* = 5 days between pump-outs
Mifab BigMax 1150, 100 gpm, 200 lbs* = 7 days between pump-outs

Of course you can increase capacity by increasing the number of interceptors in order to lengthen the pump-out cycle, i.e:

Schier GB-250 (2), 100 gpm, 2152 lbs = 74 days between pump-outs

Using the grease production sizing method is not limited to any specific manufacturer, you can use it for any interceptor.

The only thing to watch out for is the funny-business some manufacturers' play in making unsubstantiated claims of capacity that they want to be used in determining a pump-out frequency.

Sorry Charlie, that's just not going to work.

When in doubt ask them for their certified test reports to see what their actual/real/genuine/true/factual capacity is, then base the pump-out cycle on that.

What's Wrong with Semi-Automatic Draw-Off?

The contents of a grease interceptor, especially one that has not been cleaned out recently, is nothing short of breathtaking!

By 'breathtaking' of course I mean one whiff makes your eyes water and gives you the kind of nausea common on commercial fishing charters, while you reel backwards in a desperate fight for oxygen...and a gas mask.

I had the same experience one time when I accidentally smelled one of my teenagers dirty socks.

It's the kind of experience you are not likely to forget and if you are a restaurant owner it's one you are not likely to repeat - at least very often.

As the saying goes, "necessity is the mother of invention," and not opening a grease interceptor is considered, at least by some, a necessity.  

Enter the semi-automatic draw-off grease interceptor, which as one manufacturer's literature states, "permits removal of accumulated grease without cover removal."

Yeah baby, the holy grail of indoor grease interceptors, right?!

Not so fast.

Here are two major reasons that semi-automatic draw-off is not the right solution:


1. Typical cleaning instructions:

• Run full stream of hot water (preferably 140 deg F or higher) for at least two minutes
• Turn off hot water for three to five minutes - to allow grease to liquify
• These interceptors come with a shut-off valve connected to the outlet - step three is to close the shut-off valve
• Most units come with a draw-off valve on top connected to a hose or pipe - step four is to open this valve and place a container under the hose or pipe
• Now run hot water through the unit at 1.5 to 2.5 gpm causing the unit to fill, raising the accumulated and now liquified grease into an internal cone and out the draw-off connection
• Continue to run the hot water through the interceptor until clear water appears then shut off the flow
• Close the draw-off valve and open the shut-off valve and the interceptor is now supposedly clean and ready for use again

As an owner you have to do this process each and every time you service the interceptor.  How many full buckets of the interceptor's contents - which, by the way contain the very odor the owner was hoping to avoid in the first place - would it take for the owner to give up ever wanting to service the interceptor again?

Another thing to consider is that some places employ teenagers whom will be tasked with this job.

Teenagers!

I raised three of them myself and I can tell you, based on my experience trying to teach them to make their beds every day, that I have grave concerns about trusting them to properly follow the instructions above...ever.

If you are a teenager reading this post and you feel that my comment does not apply to your bed-making skills then I apologize for lumping you in with my kids, and basically every other teen that has ever been born.


2. How are accumulated solids removed?

It is a well established fact that grease interceptors collect solids, which have to be removed regularly because they decompose inside the interceptor creating all kinds of problems not the least of which is the unforgettable odor I mentioned earlier.

To remove the solids you have to remove the cover, which should cause you to stop and think, "hey, wait a second, why would I want a semi-automatic draw-off if I have to take the cover off the interceptor to clean out the solids anyway?"

Exactly!

So what is the right application for a semi-automatic draw-off?

Let me see, that would have to be a restaurant that does not serve food of any kind and that does not employ teenagers whom would be tasked with the responsibility of maintaining the interceptor and that has an owner that doesn't mind bucket full after bucket full of the interceptors contents stinking up the joint.

So, doing the math, there are approximately 990,000 restaurants in the US according to the National Restaurant Association, and the total number that do not serve any food of any kind would be roughly 0.1% or about 990.  Of those, the number that do not employ teenagers or that have a masochistic owner would be...lets see...divide by...carry the zero...

We're working with very small percentages here, but I think the answer is one.

Whatever the number is, it is too small to justify the existence of the semi-automatic draw-off.

For most restaurants, there is a better way.

A High-efficiency and high-capacity grease interceptor installed outside with all of the kitchen fixtures routed to it, properly sized and properly maintained is the real solution!

ps. teenagers make great restaurant employees, just don't expect them to make their beds every day, or really ever.