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Our sewers are gagging on grease. "Strong waste," in industry parlance—i.e., rendered fats, oils from vegetables or petroleum, and chunky grease—is strangling thousands of miles of drains and culverts. No fewer than three-fourths of the nation's sewers are now suffering impairment, operating at less than 50% capacity due to congealing FOG (fats, oils, and grease), as reported by the Wall Street Journal several years ago.
Or, as environmental scientist Robert Rubin observes, the true impact is really closer to universal. The US has 19,000 permitted wastewater plants, he notes, "and every one of them has a problem with fats, oil and grease—or rather," he states more positively, "an opportunity for improved management."
Fat City
Massive opportunities of a similar kind are also in store for tens of thousands of FOG producers, namely, the restaurants, cafeterias, dining halls, and other food-service establishments (FSEs) that are spewing forth strong wastes at an unprecedented magnitude. Dining out has been on a roll for over a decade now; more kitchens are ladling out meals than ever before, meals necessitating more lard and coagulating oils. Collectively, an estimated 1.5 million tons of FOGs are oozing into US sewers each year, according to figures cited by a commercial supplier of environmental equipment (www.rgf.com) Resulting backups and overflow incidents are hard to enumerate (and probably under-reported), but the same study extrapolates the number at 40,000 per year. Of these, perhaps as many as 5,000 are specifically FOG-related backups caused by an estimated 21,000 restaurants—but again these numbers may be conservative, as the food industry is understandably reluctant to publicize its failings.
A survey by the City of New York, though, done a few years ago, uncovered a 73% rate of "grease trap abuse" and non-compliance among restaurants; the city has now instituted a $1,000-per-day fine for FOG violations by scofflaw FSEs.
In Boston, still more evidence of a disposal crisis came to light when city workers unearthed a ghastly, rancid, serpentine grease blockage measuring 350 feet long putrefying beneath historic Fanueil Hall.
Not to be outdone, the City of Los Angeles (having the nation's largest sewage system), has produced 4,500 sewage spills from multiple causes in the past decade. FOG-clog from LA's 10,000 restaurants was identified as a leading cause of these, according to a study last year by the EPA. As a punitive inducement to make the city fix its spills and sewage odor problems, the agency slapped LA with penalties totaling $1.6 million. The city was ordered to undergo an aggressive new EPA regimen called "Capacity, Management, Operations, and Maintenance" (CMOM) aimed at identifying, repairing, and/or replacing problem sewers before they spill (for CMOM details, visit www.cmom.net )
As for other municipalities, mandatory pumping of grease tanks must occur every 30, 60, or 90 days, depending on local circumstances—but, as an EPA news release concerning the problem points out, such mandates "are not a viable long-term solution," being prohibitively expensive both to carry out and to enforce.
Elsewhere, as Rubin (who is now with the environmental engineering firm of McKim and Creed in Wilmington, NC) points out, "more and more municipal wastewater authorities are combating the problem" by imposing mandatory measures of assorted kinds, including inspections, periodic grease pumping, stiff penalties, and even criminal citations for violators, along with "strong waste" monthly surcharges added to restaurant sewer bills. Surcharges are reportedly ranging from $100 to as high as $700 and more, the fees being deemed necessary to cover the cost of inspections and upgraded infrastructure.
Onsite Septic Failures Epidemic
Meanwhile, restaurants in outlying suburban and rural areas, equipped with septic tanks, aren't faring any better. Although figures aren't compiled (as, again, no one wants to advertise mistakes), anecdotal evidence suggests that costly blunders are commonplace. Eugene C. Bassett, a New Mexico wastewater design and maintenance contractor who serves on the board of the National Onsite Wastewater Recycling Association Inc. (NOWRA), notes, "Where you have cooking oils and grease—and the final destination is the drainfield—you'll often have failure within a few years. It's pretty common," he says. "I've seen a lot of failures."
Moreover, he adds, sewer-connected restaurateurs in Albuquerque and Santa Fe are reportedly being socked with surcharges for high-FOG, aka strong waste, at the high end, in the neighborhood of "$700 to $900 a month." The City of Santa Fe sends inspectors to measure restaurants' oil and grease in milligrams per liter, he notes, but this policy isn't yet being done statewide.
Bassett's clientele include local McDonald's restaurants, which (along with other major chains) have conducted extensive research to measure and evaluate their franchisees' FOG characteristics. The composition and severity actually turn out to vary significantly from site to site. This can stem from a a range of variables, he explains—for example, on the preferred cooking medium for the deep fryers (i.e., either lard or light vegetable oils); on the presence or absence of a dressing-laden salad bar; and on what's specifically popular on the menu. Such diversity therefore necessitates that control efforts be carefully customized. FOG-treatment and septic solutions that might work for one eatery may not suffice for another, and in fact may even backfire. For instance, Bassett says, some ethnic cooking contains preservatives that tend to alter the biological oxygen demand (BOD) to the point that it "can just kill a drainfield." Applying a more typical FOG strategy would only mask the real problem. (Note: the BOD index reflects the amount of O 2 needed by microorganisms to oxidize the organics in a liter of water.)
As destructive as FOGs, high BODs, and other constituents can be, you might expect that the knowledge base for best practices would be well-honed. Unfortunately, the opposite seems to be the case, as the praxis is in considerable flux. In his circle of professional acquaintances within this specialty, Bassett regards only a few persons as fully on top of the game, and only one as deserving of "guru" status, namely, his mentor Bill Stuth. As president of Aqua Test Inc. (Kent, WA), Stuth is a respected consultant on restaurant waste and best known as the inventor of the first and still widely used restaurant grease-reducing technology, the Nibbler, introduced two decades ago. Earlier this year he was asked to give a talk on FOG-cutting and septics for NOWRA, and this fall he'll teach a similar course at the University of Washington. Stuth draws upon more than 40 years of experience.
The difficulty in getting a handle on this surprisingly multi-faceted topic, Stuth says, begins with the fact that it involves so many diverse participants.
First you have multiple levels of public-sector regulatory and standard-setting organizations; for example, grease traps are typically specified by building and/or plumbing code-writers who may incorrectly assume that the facility will connect into a sewer tie—and this, "in an ideal world," he says. As for wastewater treatment regulators, their standards typically specify permissible BOD or TSS (total suspended solids) for systems, he notes, but in many cases "they don't even mention fats, oils, and grease, which are the greater challenge," especially because FOG, BOD, and TSS interact dynamically.
Next, Stuth continues, come the professional sectors, including consultants, engineers, research scientists, and academics; all have their say in these matters. Here and elsewhere, he notes, knowledge about septic systems is overwhelmingly biased towards residential systems, which, again, are "a different animal."
At the bottom rung come restaurant wage employees themselves. Typically they're the ones who must put the prescriptive solutions into practice (or who disregard and/or circumvent them). Challenges in effectively communicating with these high-turnover, low-skilled workers can be daunting.
Last of all, amidt these several viewpoints, there are the FSEs' owners, food-service executives, and kitchen workshift supervisors—some or all of whom, Stuth finds, "are kind of in denial" about the intricacies in restaurant wastewater and the expensive consequences of missteps.
Still another recurring complication in the mix arises from the budding array of onsite technologies being offered to help lower FOGs. Most of them probably do perform, but most are lacking in independent, scientific support for their ambitious claims. Stuth recalls that when he launched the Nibbler in the mid-1980s he also had to introduce his own testing lab service because, he says, "there was nobody doing testing on restaurant wastewater." He has since developed a database on thousands of FSE sites and their FOG conditions and case histories. Nevertheless, he continues, even if additional independent lab verification did exist, vendors would be hard-pressed to guarantee that performance scores would hold up in the field in every circumstance—due to, for example, the very localized character of culinary tastes and resulting FOGs, as noted earlier.
All in all, says Stuth, it's extremely difficult to reduce the FOG-control technologies, disposal options, and reduction strategies "to one simple formula appropriate to all restaurants" in all locales, to be dutifully carried out by all participants.
Thus, in view of these inherent complexities, the following discussion will focus on onsite septics primarily—which, although only a small subset of total restaurant wastewater FOG issues, are probably worth this special attention here, because the cost of septic field failure is so high, and the expertise needed to grapple with it is in relatively short supply. Naturally, much of what follows pertains to both types of restaurant waste disposal.
What Happens When a Drainfield Fails, and Why?
Most basically, Stuth explains, in any septic system a delicate pH balance must be maintained in the BOD content, while FOGs are simultaneously being kept to an absolute minimum. If fats, oils, or grease should inadvertently enter any drainfields, he says, "they will plug up almost all of them in short time." This occurs in part because the FOG has a tendency to lower the pH, "so that the field will go acidic really fast." At this point the effluent turns the soil into a black, pasty muck, "and it simply won't absorb any more water."
Why does this happen?
A very common root-cause is the original drain field design. Again, most contractors "cut their teeth" on residential septic system and BOD levels, and so they replicate these systems— "which haven't even been tested with the addition of fats, oils, and grease"—at every FSE they engineer.
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PHOTO: CITY OF FLAGSTAFF, AZ |
| At a treatment plant, FOG is broken down by bacteria. |
Obviously, then, a good design must reflect some cognizance of potentially manifold restaurant FOG. Bassett points out that soil studies show that a field can handle BOD of around 100, and a system may be designed for that, but, even this rule-of thumb is often inadequate to account for real-world interaction and stress dynamics. A study done at the University of Wisconsin and later cited in the EPA's Small Flows Quarterly (1991) reported that measured restaurant septic BOD effluent ranges quite widely from 100 mg/L up to as high as 900 mg/L—thus suggesting that a system designer should anticipate BODS at the high end, for safety sake, unless there's some compelling reason to do otherwise.
In his own desert Southwest, Bassett offers the opinion that drainfields should incorporate sidewalls,"so the water doesn't go down," adding, "And I do not like, in any way, shape or form, a chamber system drainfield. You definitely want sidewalls."
Also, drainfields ought to be large . "My advice is," he says, "make it as big as possible," i.e. in the thousands of square feet. In most of the Southwest, water will evapotranspirate up; naturally this will differ in rainier climates having different soils.
Often, recycled water will be used to nourish the landscape, but, Bassett says, if this isn't needed, "there's no reason to put that water in the soil." Ideally, the design should be plumbed so that some of the filtered water can be reused in the FSE's toilets. "You don't have to have crystal-clear water to flush a toilet," he notes. But this cutting-edge concept is rarely considered or applied.
As for his take on septic-field failures, Bassett finds a common problem to be the owner's unwillingness to ante up the pricey $40,000 or $50,000-plus needed for an adequately sized, fully BOD-capable system. More typically, a low bidder wins. At root, again, is the fact that septic designers are accustomed to home septics, and there's as yet no agreed-upon minimum design criteria for handling the high-strength-effluent FSEs.
A cheap-to-build but inadequate system will likely fail and prove more costly in the long run, he says. Still worse, because the basic failure to make a distinction still remains, there'll be a tendency to repeat the mistake again in the new replacement patch. Far better, says Bassett, is to learn first how to "de-FOG" a wastewater stream, and lower the BOD in it before the water ever hits the field. If you do this, he says, "there's a chance the field will come back," but in any case it's critical to follow best management practices from faucet to field—otherwise you're throwing good money after bad.
Grease Traps and Interceptors
That said, the primary focus of effective FOG-control—and often the only line of defense—must lie in proper management of the grease trap and/or grease interceptor. Errors here will lower a leach field's lifespan considerably. On the other hand, if these devices are functioning well and correctly maintained, an eatery's chances of getting up to several decades of duty from a field are greatly enhanced.
First, to distinguish between grease traps and interceptors: traps typically reside inside the establishment near a sink; grease interceptors consist of larger tanks (i.e., with a minimum capacity of between 500 and 750 gallons) set outside, below ground, according to A Guide to Restaurant Grease Management: A Regulator's Desk Reference (2004) published by the Interagency Resource for Achieving Cooperation (IRAC), on which some of the following is based.
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PHOTO; AUSTIN WATER UTILITY'S OFFICE OF INDUSTRIAL WASTE |
| As wastewater enters a trap, the water slows and the grease particles— are lighter than water— coalesce and float toward the top of the tank. |
Sizing, selection. An interceptor will usually be necessary for high-volume FSEs serving more than 40 meals per peak hour or so; for smaller-volume fast-food and take-out restaurants with limited menus and having minimal dishwashing and/or seating, a grease trap should be adequate.
The Uniform Plumbing Code (UPC) requires that no grease trap have a capacity less than 20 gallons per minute or more than 55 gpm. Between those limits, specific sizing is largely driven by the number of sink fixtures plumbed to it; local ordinance vary, and some now set minimum sizes for grease traps—or disallow them altogether and require interceptors.
If options are still being permitted, Bassett advises, "I would put in as big a tank as I possibly could," to protect the drainfield from FOGs. However, an over-sized tank increases the risk of odors and possibly corrosive stagnation.
Stuth strongly advises that restaurant grease collectors not be sized based exclusively on aqueous loading (as is now widely done), but on the anticipated poundage of FOGs to be collected.
In most instances, if onsite septics and a drainfield are in view, a large, external (and in-ground), easily accessed grease interceptor will probably be preferred to an interior grease trap, the former being a much more robust anti-FOG safeguard. However, bigness alone isn't an adequate FOG strategy, Stuth says. If a designer specifies a mega-tank, and the drainfield happens to do well, then this one "lucky success" may give the designer a misplaced confidence so that he or she begins specifying cookie-cutter replications elsewhere—leading to misapplications. What's most critical, Bassett says, "is understanding the situation," meaning, doing an in-depth measurement and refined assessment of the total FOGs anticipated, broken-down into their relative proportions.
Operation : Whether trap or interceptor, the working principle is the same. First, hot, greasy wastewater enters the tank, where it sits and cools. As it does, the ingredients slowly stratify; food scraps and debris settle to the bottom, and the fatty-oily-greasy elements float to the surface and congeal. As this slime thickens, it can be skimmed off and appropriately discarded. Meanwhile, below this surface layer the "clarified" water—which hopefully no longer contains food scraps (having settled down) or FOGs (having floated up)—can now exit though an outflow pipe to the drainfield or sewer.
Generally, the longer the wastewater stays in the tank the better the separation—but only to a point. As the surface layer of grease thickens and the heavier sludge accumulates on the bottom, water retention-time decreases, and further cooling is reduced. Also, if the tank remains unattended, the decaying organics at the bottom may enter the outflow pipe, raising the BOD undesirably high. Likewise, the floating FOG can become re-emulsified in the heat, and thus escape. If either passes into the drainfield, potentially irreversible damage can occur.
From this description, it's easy to see how even one misstep might spell disaster. For example,
- a drastic change in the volume of incoming FOGs (due to, say, a change in the restaurant's ownership and cuisine, or employee turnover leading to operational errors or neglect) could ruin the tank environment;
- a change in pH due to detergents or chemicals could spike up the acidity, potentially eating through the tank walls and allowing leaks to escape, or food debris to reach the field;
- hotter inflowing wastewater from a newly installed dishwasher might melt the grease slick, releasing bits of it; or
- clogging of the outflow could result from unusual debris inflow.
The hazards are many. Here, we're being generous in assuming that the tank was well-designed and appropriately sized in the first place, and that no inherent problems existed.
Customizing fat and oil handling. Stuth alluded to this previously in his point about assessing the FOG constituents. "It's really a more complex issue," he says, "because when you say 'fats, oils, and grease,' you have to realize that fat is animal fat, oil is vegetable oil, and grease may be petroleum-based." When being collected in a grease trap or interceptor, all three become lumped together (literally), but still behave and react differently in the wastewater stream. For example, vegetable oil happens to be "much harder to treat than animal fat"—which is rather ironic, considering that our diets now tend to shun lards in favor of unsaturated oils; what's healthier for people turns out to be worse for septics. Generally, animal fats can be more easily trapped and contained by lowering the tank inflow under 85°F or 90°F, notes Stuth. Oils, however, "will still pass thru the system" at these temperatures—clinging to the food scraps—and cause serious problems downstream." Thus, specific remedies aimed at oils are needed.
Heat control and water chemistry. A major hazard to be addressed is FOG emulsification due to excessive heat and/or the use of harsh detergents. Instead of cooling and hardening within the trap or interceptor, the still-hot FOGs remain free and flow downstream.
IRAC suggests that an ideal dishwashing layout is a three-sink system: one for washing, one for rinsing, and a third for sanitizing in a 50 ppm to 100 ppm bleach solution. Water temperatures should remain below 140°F in all three, especially the pre-rinse sink before the automatic dishwasher (which uses hotter water). The UPC prohibits discharging the dishwasher to grease traps, IRAC notes.
Stuth points out rather urgently that soapy chemical emulsifiers—which may work well at dissolving grease when it's heading for a public sewer—would, if used in a drainfield system, spell disaster. Unfortunately, this does happen. An unwitting restaurant supply salesperson might be ignorant of the distinction and sell harsh dishwasher soaps and additives, "which will go in there and do more damage than they'll do good," he says.
Moreover, manual dishwashing raises the risk of FOG-trap "escapes," especially if cleanup supervisors don't know about the importance of moderate water temperature and mild soap chemistry. (And let's face it: how many of the kitchen help are going to be conversant about adipose emulsification surfactants?)
Thus, Stuth advises, many smaller fast-food operations that don't serve food on plates, and that normally do some washing by hand, "are actually better off using a machine dishwasher than a sink program. They'll usually fill it up and do only one load a day," which is more efficient and yields a more chemically consistent and reduced outflow. Conversely, lathering by hand might triple the volume of problematic suds.
Another Wrinkle
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| Imhoff cones. The sample on the left in both images contains a FOG concentration of 120 mg/L. TOP: The sample on the right is aerobic treatment with FOG <20 mg/L. BOTTOM: The sample on the right is aerobic treatment with FOG <10 mg/L. |
Water softeners and even fabric softeners are often hazardous to a drainfield's health, Bassett and Stuth note. More specifically, the regenerated or salty wastewater brine must be collected independently and drained to a separate ditch or flower bed rather than to the field. Some country restaurants also wash table linens or do other laundry on the site; the use of liquid fabric softeners is a no-no, but this, unfortunately, happens anyway. Says Stuth, "The sad thing is, the softener should say on the box 'this shouldn't be used with an onsite septic system,' but they often don't, and an expensive drain field is destroyed."
Of course, caustics, acids, solvents, other emulsifying agents, wax, axle grease, or other oily substances should be properly discarded away from the field.
System misuse, staff ignorance. Even otherwise competent food-service managers can prove to be surprisingly clueless regarding the fine points of restaurant wastewater and, given other competing priorities in their remit, dirty dishwater is rarely accorded its due attention.
At the lower rungs of the operation, Bassett finds that typical workers, realistically, "just don't care" about any of this, thus making for a perilous high-risk-factor indeed, because kitchen staff are arguably the single most effective element—and hence, probably the weakest link—in a FOG-reduction campaign.
Doesn't that mean, then, that better training is called for? Obviously, yes, but unfortunately, he adds, trainability is another likely shortcoming that one will encounter. Another consultant who shares a similar pessimism about staff is Brian T. Rabe, a water treatment specialist with Cascade Earth Sciences in Oregon. "Milk, gravy, soup, soda pop, and other high-strength components go down the drain" routinely in poorly supervised cleanup practice, he says, and, being soluble, "it passes through the primary treatment system with little or no reduction." Rabe's firm does customization of onsite water treatment systems.
Notwithstanding these cavalier staff habits, any time investment made by managers in training and tighter supervision will be probably be time well spent.
Best housekeeping practices begin with dry-wiping pots, pans, and dishware prior to dishwashing; scraping food scraps from plates into garbage cans; dumping grease, oils, and fatty liquids into a grease bucket or other container placed outside the sinks, rather than hosing-off items inside; inserting a catch-basin and screens in sinks ("down to about 1/8-inch mesh," Bassett suggests) to bar food particles; and cleaning out this screen often (however, without making it easily removable—or that's what the staff will want to do permanently). Bassett's business regularly services one fast-food establishment where the screens' proper functions have somehow been defeated by the staff despite every effort—leaving the grease trap studded with latex gloves and French fries.
Two more tips, suggested by IRAC: (1) post "No Grease" signs above sinks and on the front of dishwashers; and (2) blot up FOG spills rather than hosing them down a floor drain.
As for disposal of the saved grease, this too is becoming more problematic, because not all landfills or wastewater facilities want to deal with pounds of gunk anymore. Ask the local landfill about its grease policies. The preferred option, IRAC states, is to place collected grease in a watertight container (e.g. a trash bag) then send it to a rendering/tallow plant for recycling. Other disposal avenues are now being explored quasi-experimentally, including, notes Rubin, burning it as a fuel. The State of Connecticut now requires that all grease be incinerated at the state's coal power plants, he notes, and other locales may someday follow suit.
M aintenance of traps and interceptors. The interval for cleaning and care of traps is often spec'd by manufacturers as "daily," but, in the real world, neglect is more often the norm, Stuth and Bassett have found.
Among increasingly grease-leery municipalities, codes are tending more towards requiring periodic emptying and cleaning of traps and interceptors or, alternatively, gauging the appropriate response interval based on accumulated content. Naturally, jurisdictions vary. Whenever the pumping does occur, IRAC suggests that it's a good idea to observe that it's properly done.
In locales where pumping is still optional, owners are naturally averse to wasting money on pumping deemed to be excessive. (Pumper visits cost perhaps several hundred dollars per month. That expense can be increased considerably if the trap/interceptor happens to be undersized, but if that's the case, pumping is all the more critical.) Conversely, pumping expenses can be lowered nicely if restaurant staff continue doing best housekeeping practices.
As for mucking-out the grease interceptor , This too should be professionally done on an appropriate interval. For decades now, the standard has been determined by the so-called "25% rule" or benchmark, i.e., when the floating grease and bottom sludge combine to displace about one-quarter of the tank's total depth, it's time for pumping.
Measurements can be taken with a dip stick or other sensors. Keep a careful log of results, pump-out servicing, and other maintenance activities. In the event of a spill, mop up with absorbent pads (not loose granular "kitty litter" media) and discard in a dumpster rather than spray-washing to a storm drain.
One regulatory oddity here, to complicate matters a bit more, is that the 1991 federal standard governing the pumping of domestic biosolids (40 CFR part 503) curiously enough excludes handling grease trap waste. "So," as Rubin points out, "we've got all of these people pumping septic tanks and portable toilets. but this other stuff [i.e., grease] is regulated under a different program," thereby causing agencies to back off from efficiently integrated waste management "because they're afraid of violating some rule."
Summing Up
Prudent FOG management will pay handsome cost-avoidance dividends by negating the "bite" from high-strength sewer surcharges, potential fines, and possibly even business interruption caused by a spill or chronic odors.
For FSEs served by septic fields, a peak-performing wastewater system will prove a valuable property asset. As Bassett noted, recycled water can be re-used even for toilet bowls. Rubin points out that it can irrigate the landscape, thereby "maintaining the proper carbon, nitrogen, and phosphorous ratios." Treated wastewater, he says "is a great food source for microorganisms. If you apply this stuff at the proper rate in the field, it helps the soil. Unfortunately," Rubin says, on a note indicative of the learning curve that still lies ahead, "most probably don't apply it at the proper rate."
La Mesa, CA–based writer DAVID ENGLE, is a frequent contributor
to Forester publications.
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- September/October 2005
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