| 
|
Once, it was pretty simple to make the distinction. Grease traps are inside the food service establishment (FSE); they’re attached to sink drains for grease-collection; and they’re limited in holding capacity to 55 gallons. Grease interceptors are outside, serving as aqueous catch-alls and having a minimum size of 750 gallons.
And, though the naming was simple, the sizing of traps and interceptors had depended on a complicated and ambiguous formula, which often resulted in outdoor tanks of several thousand gallons.
Now, though, brand-new (and likely to be extremely confusing) terminology replaces the old plumbing codes’ standard “traps” and “interceptors.” And a radically revised, much easier (and, to some, controversial) new formula for sizing grease devices will sharply reduce interceptors’ capacities. The question now becomes: What will the impact be on controlling the fats, oils, and greases (FOGs); and will FSEs be sufficiently diligent in adjusting their often inadequate maintenance schedules to the new regimen?
The Grease Device Formerly Known as “Trap”
The most dramatic difference in the code, and probably most problematic for the industry to digest, will be the name changes. As one of the code-writing task group members notes, the well-established conventions on “interceptors” and “traps” will be superseded with two gangly new phrases. First, “gravity grease interceptors” (GGIs) becomes the term for the larger devices that are typically outdoors; and second, “hydromechanical grease interceptors” (HGIs) will serve as the new designation for smaller indoor receptors, i.e., the former “traps.”
 |
| New terminology replaces the old plumbing code's references to "traps" and "interceptors." |
John Shaffer, a member the IAPMO task group that developed these new names and the accompanying FOG-control sizing criteria, observes: “It’s going to be chaotic for a couple of years, because people were just getting comfortable with ‘small devices are traps, larger ones outside are interceptors.’ Now, that’s gray.”
IAPMO (the International Association of Plumbing and Mechanical Officials) overhauls its plumbing codes routinely every three years. Shaffer is president of the Santa Ana, CA-based Environmental Engineering & Contracting Inc., a FOG-control consultancy primarily to cities and sewer districts.
Moreover, he continues, the term hydromechanical “won’t make sense to anybody” until it’s explained. Any discussion of kitchen plumbing will have to digress into clarifying the very specific new terminology.
The same goes with speaking of a “gravity” device to describe what everyone now calls a grease interceptor. Both the hydromechanical and the gravity interceptors employ gravity, of course, and thus to label one as “gravity” and the other as “hydromechanical” may seem a bit counter-intuitive. But the hydromechanical design elements—things like air-injecting flow controls, counter-flow or boundary layer migration blocking baffles—agitate the FOGgy inflow, greatly enhancing the efficiency of separation. Max Weiss, an expert on HGIs and also on IAMPO’s code-writing task group, explains: “They dispel energy of incoming water or dissipate that energy... They change the relative viscosities and densities of the fluids ... and otherwise assist separation and retention. This is not passive, it’s active.”
Understanding the logic in the distinctive new phrases—indicating agitated flow in one, vs. a purely gravity-based device—makes the name-changes perfectly sensible.
As if these novelties in the code aren’t enough, two other similar-sounding FOG-control devices are also defined in the new plumbing code for the first time:
- Grease Removal Devices (GRDs), which are truly mechanical interceptors “that,” as the Code states, “automatically, mechanically remove non-petroleum fats, oils and greases (FOG) from the interceptor, the control of which may be either automatic or manually initiated.”
- FOG Disposal Systems (FDSs), defined as grease interceptors that reduce fats, oils and greases in effluent by separation, and mass, and volume reduction.
GRD technologies, Weiss says, “are mainly applied to hydromechanical interceptors—though nothing would preclude them from being attached to gravity grease interceptors.” As for their functions, GRDs, he adds, “either continually or periodically remove the grease from the separation and retention vessel, into a container,” either for subsequent pump-out or legally prescribed disposal. Rapid and reliable grease removal by means of a GRD is extremely desirable, he notes, due to the negative consequences of it remaining. However, there are limited options for its disposal, and this remains a big problem for the FOG-control field.
By comparison, FOG Disposal Systems, by the newly formalized definition, “separate and retain the material... then reduce its volume and mass” by various means, e.g., thermally, electrically, biochemically, using dissolved air flotation separation, submerged thermo- or electro-coagulation, or other chemical means, “altering the FOG molecules,” says Weiss. Manufacturers of such devices include, among others, EEC, US Filter, Jay R. Smith, and Stuth Corporation. Weiss himself is a co-inventor of a FOG Disposal System known as the Remediator, manufactured by Jay R. Smith. Weiss points out that “None of the [disposal] methods results in materials that are 100% disposed. There’s always some resultant sludge. They’re designed to extend the service interval by minimizing material requiring disposal.”
New Sizing Formula
Three other important plumbing code changes linked to the two main devices, GGIs and HGIs, include:
- The former 55 gallon-per-minute maximum flow rate that had applied to what were “grease traps” is now removed from HGIs;
- The restriction on connecting more than four plumbing fixtures to what were “grease traps” is now lifted from HGIs; and-
- The 750-gallon minimum for the outside interceptor (now GGI) is also removed.
 |
| Once the distinction was simple: Grease traps were located inside the restaurant, while grease interceptors were outside. |
Shaffer notes that, in the past, some FSE owners or their plumbers had believed that a single HGI should service only a single drain and no other drains in the kitchen—a belief and practice which tended to result in some significant grease waste drains being left with no FOG-control. He observes: “I am happy to say that the Uniform Plumbing Code has now pluralized the language, so that we shouldn’t continue to have this problem of people just installing one device on one fixture.” Rather, as a result of the code changes, future kitchen layouts may dictate that one HGI will service three, four or more drains—or, say, two will serve 10 drains, or whatever. The code-writers on UPC’s Grease Task Force agreed that HGIs need to be on all the grease-bearing waste drains in a restaurant.
Moreover, the number and total capacity of HGIs will be more easily determined, again, by counting the drainage fixture units (DFUs) and referring to the table.
Still another revision comes in the sizing criteria of both GGIs and HGIs. Under the old and convoluted formula, the newly named gravity grease interceptor’s capacity was figured by guesstimating the number of meals an FSE served at peak times, and factoring-in other variables such as dishwashers and hours of operation. This imprecise method was difficult to apply consistently and often resulted in very big tanks.
Shaffer illustrates: “Under the old formula a restaurant serving 200 meals per hour, with a dishwasher and a couple of dishwashing-pot sinks and floor drains,” might be sized at a spacious 4,000 gallons.
Now, though, the new code simplifies the sizing by basing it on the number of kitchen sink or floor drain fixtures. Simply count the drains that will be running into the grease device—adjusting for pipe diameters and the fixture’s purpose—and this yields “drainage fixture units” (DFUs).
“The easiest way to define DFUs,” Shaffer continues, “is that it’s based on kitchen size. If you have a lot of floor sinks and drains, you’re going to have a lot of drainage fixture units.... over 40 or 50. And you’ll probably have a 1,250-gallon interceptor.” Conversely, a very small kitchen “with just one three-compartment sink and a floor drain” will have only seven fixture-units and would require a 500-gallon interceptor (eight DFUs or less call for 500 gallons; nine to 21 receive a 750-gallon device). He adds: “It doesn’t matter any more if you’re open 24 hours a day or 8 hours a day, or the number of meals served. It’s the flow rate that’s important.”
For another example, under the new formula the 200-meals-per-hour restaurant that would have been specced for a 4,000-gallon “backyard swimming pool” interceptor would be recalculated to yield about 40 DFUs; by the new table this would call for a GGI of just 1,250 gallons—”still big enough to trap the grease and solids sufficiently,” he says.
Three more examples: A pot sink with three compartments would equal three DFUs. A mop sink with a 2-inch trap would yield three DFUs. A kitchen floor drain would count as two DFUs.
In Shaffer’s view, any experienced plumbing engineer should be able to eyeball a kitchen, do the arithmetic in seconds, and look up the spec on the DFU chart. In fact, when retrofitting kitchens without original plumbing drawings, he says, “You can just estimate, and if you’re off by 10% or 20% it won’t matter. There’s huge room for error in the formula.”
The easier system was devised jointly by EEC and plumbing engineer Tim Allinson.
Using the new sizing criteria, he continues, more than 90% of gravity grease interceptors will wind up being 750-1,250 gallons in size, in contrast to the current range of 1,000 to 2,500 gallons. Typical averages will probably drop to about 1,000 gallons. Very large kitchens that would have seen a 3,000-gallon tank, will be specced for 1,250 gallons.
Why the Downsizing?
Underlying all this there’s a deep concern that long water-retention times occurring in big interceptors result in foul odors, low pH, and, above all, the formation of hydrogen sulfide, with seriously corrosive consequences.
 |
| Interceptors will have to be maintained and pumped more frequently under the new code. |
Reducing tank and sewer-system corrosion is thus supremely important, Shaffer says, because acidic damage is becoming pervasive; it’s a significant cause of system failure these days, and it exposes interceptor and sewer line maintenance workers to dangerous levels of hydrogen sulfide.
However, there’s a major tradeoff suffered with smaller tanks, and, under the new code, there’s something of a gamble: Interceptors will need to be diligently maintained and pumped more frequently—theoretically, twice as often, says Shaffer. “That’s a general rule.” Otherwise, grease and food sediment will accumulate quickly and cause flow-through.
Unfortunately, there’s probably a considerable risk here that, at least in some of the UPC code-areas’ lax jurisdictions, FSEs won’t be pumped frequently enough. In fact, it is already the case that many wastewater department inspectors are not checking the maintenance activity either knowledgeably or with sufficient frequency.
Says Shaffer: “You need to maintain your interceptor as appropriate to avoid passing grease into the sewer.” But he adds: “Those are pretty meaningless words to a restaurant. How does a restaurant decide what is ‘proper frequency?’” The answer is often left to the pumper’s advice and to subjective factors such as odors—or even pumping fees.
Thus, there’s a concern that the smaller-tank standard may possibly backfire if it is not adopted responsibly. Municipalities typically rubber-stamp the new UPC criteria, and may do so this time, without fully appreciating the higher maintenance that’s demanded. Shaffer concedes: “I’ve been telling [local sewering agencies] that, ‘You don’t really want to make this change to your code unless you plan to go out and enforce the proper maintenance of an interceptor.’ Small tanks retain a lot less grease and will reach maximum capacity faster,” he says. As a result, the grease will pass through it sooner if the tank isn’t properly maintained.
All in all, though, a well-maintained smaller gravity grease interceptor is a win-win, because the shorter retention-time greatly reduces hydrogen sulfides and odors. The latter, in fact “will probably be cut by 90%, minimum,” he thinks.
Smaller gravity grease interceptors are also being promoted by CalFOG, a group made up primarily of California sewering agencies; Shaffer is also a member. California sewering agencies, he notes, have recently multiplied their FOG enforcement by adding hundreds of new inspectors. Shaffer’s firm, EEC, has inspected more than 2,500 FSEs and hundreds of interceptors, in the course of doing local agency enforcement, “and so I understand,” he says, “how much grease or solids are generated by different types of restaurants, and how much quicker smaller interceptors fill up.” Nevertheless, EEC has also discovered-based on extensive hydrogen sulfide monitoring—that, “If you store kitchen wastewater too long, you create problems.”
Maintenance Frequencies
The new code does add a statement regarding mandatory maintenance. It requires that, “Interceptors [i.e., both HGIs and GGIs] shall be maintained in efficient operating condition by periodic removal of accumulated grease, scum, oil, or other floating substances and solids deposited in the interceptor.”
 |
| Some communities have devised a kind of ad hoc standard setting a minimum 90-day interval between pumps. |
Moreover, due to past shortcomings in FSE maintenance practices, sewering agencies are now authorized in the new code, as it states, to “mandate a maintenance program or installation of additional equipment or devices.”
In Shaffer’s locality, Orange County, CA, “Agencies don’t want to go around inspecting every gravity grease interceptor every two or three months. That would be cost-prohibitive... And,” he adds, “most corporate chain restaurants have made ‘proactive decisions’ on pumping.” That county and some neighboring communities have thus devised a kind of ad hoc standard, setting a minimum 90-day interval between pumps. This occurs by schedule, says Shaffer, “even though they don’t check their interceptors, and they have no idea how full they are.” The 90-day interval standard is now catching on quickly.
One advantage in taking this strategy, he says, is that it sets a baseline from which future inspection routines can then focus more intently on determining which specific “high FOG” FSEs require more frequent maintenance and regulatory oversight.
Likewise, FSEs that pump at this 90-day frequency and pass the inspection once, and can show the inspector their pumping records, are probably not in need of re-inspection much at all. “You may not have to physically inspect that interceptor more than once every year or two,” he says. “But the ones that were pumped-out two months ago, and their gravity grease interceptors are already 40% or 50% full again—those are the ones where you need to talk to about how often they need to be pumped,” i.e., probably requiring this monthly or so, he says, adding: “That’s really what my guys spend much of their time doing.”
Prioritization and “grading” FSE FOG is becoming sort of standard practice in some of Southern California, which has experienced notorious sewage spills, largely caused by FOG blockages.
For overseeing HGIs, he adds, the sewering agency’s inspection criteria will be more variable and not easily reducible to a set formula. “These devices require more frequent maintenance than GGIs,” he notes, and this chore is usually done by kitchen staff. The frequency of inspection will thus be based on factors like equipment design; manufacturers’ recommended intervals; the volume of FOG being generated; and the facility’s past maintenance track-record.
Taking the Other Side
The UPC’s sizing changes to smaller gravity interceptors isn’t universally applauded, however.
 |
| The contents of interceptors can be disposed of at special process areas, such as the city of Flagstaff, Az's Wildcate Hill Wastewater Treatment Facility. |
One faction on the IAPMO Grease Task Group pushed a wholly different strategy, in fact; Weiss was and is one of its proponents. In Weiss’ view, some practitioners in FOG-control “have equated hydrogen sulfide generation with size of the interceptor,” which is false, he says, except as size is related to absence of dissolved oxygen due to stagnation within the device. Thus, those who advocate smaller GGIs and shorter retention times are perhaps not appreciative of current research on interceptor fluid dynamics. “Substantial studies,” he says, now show that the production of hydrogen sulfides within the tank begins “almost immediately.” Likewise, hydrolysis—resulting from FOG contact with various cleaning chemicals, biochemical activity and contact with the water itself—”suggests [that] separation of glycerols and fatty acids” starts right away. The glycerin doesn’t float, and certain fatty acids can be soluble or semi-soluble.
Hence, a strategy allowing “any long-term storage of separated FOG in contact with flowing water” may not be a sound one, in that, hydrolyzed FOG is potentially, he says, “more obstructive and corrosive to collection and treatment systems than raw FOG,” depending on the drainage chemical environment. Esterified, water-soluble molecules easily can flow downstream. When they contact iron oxides in the sewer lining, hard crusting results.
All in all, then, passive, gravity-based interceptors are actually in a no-win situation in terms of extended storage, Weiss believes. “Storage of organic compounds in any quantities in an anaerobic environment will inevitably result in sulfur-reducing organisms generating hydrogen sulfide,” he says, and in hydrogen sulfide-reducing organisms generating elemental sulfuric acid.
In sum: Shorter water-retention times ultimately won’t protect tanks from corrosion.
There’s an irreconcilable tradeoff, as Shaffer also noted. Smaller interceptors don’t allow sufficient time for FOG separation to occur—”Essentially,” says Weiss, “a small tank is just a wide pipe.” FOG escapes into the sewer line. But larger tanks potentially allow too much anaerobic activity and resulting hydrogen sulfide.
From a purely scientific standpoint, then, GGIs, ubiquitous as they are—especially if they become smaller—may actually be “unsuitable” for FOG pollution attenuation devices, says Weiss, depending on effluent requirements. In support he cites research by the American Petroleum Institute done 50 years ago.
Weiss’ bottom line: The most cost-effective solution is a properly sized, well-maintained HGI, combined with frequent FOG removal. Although HGIs do require frequent care, maintenance is also required with GGIs, if pass-through and hydrogen sulfide generation are to be minimized, he adds.
Sizing criteria of GGIs in the new code also lack scientific validity, he says. “The efficiency of either type of interceptor depends on, first, sizing to accept peak flow and duration of peak flow; and, second, maintenance.” Sizing should thus be “strictly based on the laws of physics rather than for administrative reasons. And maintenance should be performed as frequently as necessary to ensure effluent quality.
“Sizing based on sound engineering and scientific principles has not been successfully completed by the task group...” Weiss foresees that IAPMO’s UPC changes may result in “ineffective separation and retention initially, and maintenance requirements are not within the scope of the code.”
He adds: “Gravity interceptors appear to have certain advantages—there’s no question. The idea that a large tank can capture everything is attractive. It’s not necessarily true, but it’s attractive ...There is no proof of it. But there is proof of downstream plugging.
“FOG separation, and retention, and disposal,” he sums up, “is not as simple as people think. It is very problematic, especially if you’re looking at achieving an effluent quality of 100 mgs. per liter or less.” IAPMO’s new UPC Code is expected to be available for purchase this year at www.IAPMO.org. Comparative changes between the old and new tests are highlighted in the Preprint document included in the Report on Comments.
Writer DAVID ENGLE specializes in construction-related topics.
OW - March/April 2006 |
