Cooking ends up generating a lot of dirt and waste, especially liquid waste. This buildup of waste, if left unchecked, not only becomes gross but can also be a serious and expensive process to undo.
For example, it can create issues at local water treatment facilities and clog sewer system in the neighborhood. As such, it’s a really bad idea and unnecessary to pour fats, oils, and grease (FOG) down the drain and affect everyone’s sewer system.
While it’s a simple process to get rid of FOG at homes by just pouring it into a can or jar that’s empty, it becomes a rather daunting task for larger-scale establishments. This is where grease traps/grease inceptors come in handy.
Inspection Chambers are not large enough for man-entry but allow the drain to be reached from ground level. Amendments to Part H of the Building Regulations that came into force April 2002 brought it in line with Table NB.2 of the British Standard for Drains and Sewers Systems Outside Buildings BS EN 752-3. ■Hynds Inspection Chamber risers are manufactured using high strength concrete and fabricated circular steel reinforcement to achieve a “standard” strength inspection chamber suitable for standard installations. ■The chamber includes nominal internal riser diameters from 300 to 900 mm. ■Refer to Table 3 for a range of standard sizes.
What is a Grease Trap?
Grease traps have been in use since Victorian times, with the first patent for a modern-day grease trap issued to Nathaniel Whiting in the late 1800s.
Grease traps vary in size, with smaller variations designed to connect individual sinks and larger ones installed to service larger facilities.
The definition of a grease trap is “a trap in a drain or waste pipe to prevent grease from passing into a sewer system.”
A grease trap is in simple terms a plumbing fixture that contains decomposing food waste, bettering the sewer system.
What is The Purpose of a Grease Trap?
The wastes in food solids, even oil and grease (FOG), generated by large establishments such as schools, cafeterias, and restaurants is significantly more in both frequency and volume. If left unchecked, the food solids could end up accumulating in sewer pipes and create sewer system problems such as:
-Foul Odors
-Blocked drainpipes and sewers
-Restricted flow rate of wastewater
To prevent these problems from arising it becomes necessary to install specialized devices. The device in question is called a grease interceptor or a grease trap (these terms are used interchangeably).
Health inspectors typically ensure that large establishments have grease traps (or grease inceptors) installed on their premises.
How Does A Grease Trap Work?
In the most fundamental term, a grease trap or grease inceptor functions by cooling warm or hot greasy water. By allowing the fats, oils and grease (FOG) to cool, a grease trap is able to separate the different layers of wastes with water.
Fats, oils and grease are lighter in density and float at the surface of the tanks, and the cooled water – minus the FOG – continues draining to the sewer system.
The fats, oils and grease float to the top of the water are then trapped by the grease trap. For its use to be effective, the grease trap/grease inceptor should be emptied when the sludge level reaches 25% of the tank level.
The larger “gravity” or “passive” traps rely more on gravity and time to separate FOG. Standpipes, internal baffling, and larger tank sizes allow the magic of gravity to work by increasing the “retention time” on these passive grease traps. The services of a professional should often be sought at intervals.
For smaller, indoor types a hydro-mechanical grease interceptor should be used instead. The traps used in the interceptor utilize internal baffles that provide more space and time for separation by lengthening the flow path and maximizing the flow rate.
In order to maximize separation of FOG from effluents, the wastewater making its way inside the grease trap should be regulated by control devices that at this stage also allow mixing of air.
Grease Trap or Interceptor Sizing
The size of a grease trap is, needless to say, the most important thing for an establishment to consider. This is tied to the rating that hydro-mechanical interceptors have in terms of the allowable maximum drainage in gallons per minute (GPM). Naturally, hydro-mechanical receptors have a 100gpm handling capacity, and anything beyond this should be left to the gravity receptor.
Things that influence the grease trap/interceptor sizing are:
-Sizing as per Values of Drain Fixture Unit (DFU)
-Sizing as per the volume of total flowing fixtures
-Sizing based on waste pipe’s diameter
To this end, it becomes necessary to have a manufacturer that provides charts with GPM flow listing based on the diameter of the pipe.
Provided you know the waste pipe’s size and type of the grease trap/grease interceptor, this method becomes very simple. Similarly, using DFU values for sizing is straightforward because one only has to sum up the DFU values for the waste flowing into the grease trap.
Some basic math is required when calculating the grease interceptors’ size based on the flow and capacity of the actual waste.
First, you’ll need to determine the fixture’s dimensions, which will, in turn, determine the fixture’s volume in cubic inches.
Secondly, that figure would need to be converted to gallons. To better illustrate this, divide the volume aforementioned (cubic inches) by 231 to find the number of gallons of waste.
Thirdly, multiply the figure resulting from above by 75%. This is because it is very unlikely that the fixture will fill to the brim even on busy occasions.
Finally, calculate the flow/drain rate.
So how is a flow rate calculated?
You’d need to fill the fixture with water to 75% capacity, which is 3/4 of the total fixture. Next, time the length of the period it takes for the fixture to drain completely.
Lastly, take the result you had in the third step above and divide it by the time it takes for the fixture to come out. The result you get is now the rate in GPM.
At this stage, it would be advisable to seek the guidance of a professional or a manufacturer. Also, depending on the local laws, you may need to consult the local health and hygiene department to be sure that the grease trap you have fits your needs as, let’s say, with owning commercial kitchens.
If grease traps are too large, and you run the risk of damaging things downstream as sulfuric acid may be created within the tank.
If grease traps are too small, and the unit will not do its purpose of preventing FOG from passing through freely unless it’s periodically cleaned.
Furthermore, the Code of Uniform Plumbing that acts as a guideline in this space prescribes that unless specifically required by the jurisdiction’s authority, dishwashers are not to be attached to a grease trap.
This is because chemicals and other detergents used can emulsify the FOG rendering the grease traps/grease inceptors unusable.
Again, the Code only permits garbage disposals to flow unhampered into drainage systems, affecting plumbing. It goes without saying that it is imperative to check with the local authority before purchasing or getting down with the sizing process of grease traps.
What Could Possibly Go Wrong With Grease Traps?
If the trapped FOG is not pumped out when needed, it becomes thick and may begin to escape via the outlet tee.
Also, when blocking occurs in the downstream pipes, the grease traps and drains containing the wastewater could flood out.
This could consequently lead to your kitchen being shut down by local sanitary officials for wastewater plumbing system damage. Grease traps are a way to prevent this.
How Often Should You Pump Your Grease Interceptor?
For the correct functioning of grease traps/grease inceptors, a deep layer of water is needed. To this end, it’s recommended that a grease trap be drained as soon as the food layers and grease occupy 25% of the trap’s space.
Pumping is dependent on:
1) Cleaning practices
To reduce the amount of FOG going down the drain, it’s necessary that dishes be scraped before being washed. As a result, less food and grease (FOG) will make its way down the drain. Again, as a standard practice, high-fat liquids and fryer oil should never be allowed to flow down the drains, even with water, or else the need for grease recovery increases.
2) The type of food
The more grease in the waste, the more often it needs to be pumped. Waste in the form of frostings, sauces, meats, salad dressing, and butter oil means a higher frequency.
3) The amount of food
Busy establishments lead to more waste products being washed down the drains. For this reason, busy seasons mean a higher pumping frequency. Needless to say, busy season isn’t a convenient time for having your kitchen flooded.
4) The trap or interceptor sizing
It goes without saying that the smaller the grease traps/grease inceptors are, the more often it will need to be pumped.
Besides The Pumping, Is Anything Else Needed for an Effective Grease Trap?
If the grease interceptor is not drained often enough, the inlet and outlet often become clogged with fats, oils and grease. For this reason, the drainage should be cleaned at a higher frequency.
Furthermore, other drain lines in your establishment also require some maintenance in terms of periodical cleaning. The frequency depends on the amount of “fall” in the lines, on usage, and other conditions. For best practice, have the sewer lines cleaned at least once a year, and more often if the need arises.
Common Guidelines for Commercial Kitchens
To mitigate issues associated with foul odors from blocked drains and sewer system issues, officials from the local health and hygiene department recommend the following tips:
-Using quick breaking biological additives and detergents for boosting the operation of the system
-Using grease traps/grease inceptors service providers for periodical grease trap washing (if you’re located in North Carolina, we can help you with that!)
-Minimizing the amount of grease, oils, and solids entering the grease traps/grease inceptors
-Minimizing wastewater temperature to enhance the functionality of grease traps. The lower the temperatures of the waste, the better.
-Ensuring that wastewater volumes and flow rates correspond to the grease trap’s design capacity
-Installing sufficient pre-treatment devices that reduce the contaminant levels in wastewater from sculleries, kitchens, etc.
-Avoiding the use of running water for thawing frozen food
-By ensuring that dishwaters are only used in cases where there’s a full load
-Reducing wastage by turning off taps when not in use/when water isn’t needed
-Setting waste cooking oil aside for recycling rather than disposing of it
Inspection Chamber Grease Trap
-Scraping food from plates and dishes before washing them
-Identifying and understanding the input sources to the wastewater stream
A well-maintained grease trap/grease inceptor will give you years of service. Even more importantly, it’ll also prevent health and hygiene-related issues, especially when the inspectors from the local jurisdiction come calling.
Properly maintaining your grease trap is essential. Now that you know how a grease trap works, make sure you contact a local grease trap cleaning provider to set up a regular maintenance schedule.
by Nick Gromicko, CMI®
Commercial property inspectors, especially those who inspect food-handling establishments, can assist their clients in understanding the operation of grease traps so that their maintenance is not neglected. An inoperable or clogged grease trap can cause serious problems not only for the inspected establishment, but also for neighbors and even the entire local community.
Grease traps are plumbing devices designed to intercept fats, oils and grease -- collectively known as FOG -- before they enter a wastewater disposal system. FOG originates from the cleaning process of pots, pans, plates and silverware that contain food products such as deep-fried foods, meats, sauces, gravy, dressings, baked goods, cheese and butter.
The terms “grease traps” and “grease interceptors” are often used interchangeably, but they are distinctly different technologies. While they both remove grease from water and operate by similar principles, here are some of their differences:
- Grease traps have a small capacity and are installed indoors and near the location where the grease is generated. They can be monitored and cleaned by restaurant employees and require no special equipment to clean.
- Grease interceptors are large, underground units (some having a capacity of several thousand gallons) that typically serve high-flow applications, such as larger restaurants, factories and grocery stores. To install a grease interceptor, a large trench must first be excavated and a cement footing built for support. The interceptor is placed into the trench where gravel is then poured to fill the space between the interceptor and the earth. An extension collar connects the buried interceptor with a manhole cover at ground level, approximately 30 inches above. Grease interceptors must be cleaned by licensed grease haulers who use specialized pumps and hoses.
Grease Traps vs. Removal or Converter Units
Most grease traps are passive, which means that they operate without any moving or mechanical parts. Greasy wastewater entering the trap passes through a vented flow control that regulates the flow of the wastewater. The wastewater passes over a series of baffles that separate the grease and oil from the water by slowing the flow to allow enough detention time for lighter fats, oils and greases to rise. The clean water rests at the bottom, where it may leave the unit through an exit valve, retaining the FOG within the trap until it is cleaned out.
Without these devices, grease will enter sanitary sewer systems to create economic, safety and environmental hazards by clogging and damaging pipes and interfering with water-treatment plant operations. The U.S. Environmental Protection Agency estimates that nearly half of all the 400,000 sewer blockages that occur annually are caused by grease, and many of these contribute to the 40,000 annual sewer overflows. Even accumulated FOG that does not lead to an overflow or blockage may increase public maintenance and costs. Homeowners, business owners and municipalities are burdened by cleanup costs that can exceed $100,000 per incident. People may be responsible for overflows that are not their fault, as was the case in 2007 when the city of Fort Worth, Texas, declared immunity to severe damage caused to three residences when effluent from the public sewer system flooded their homes.
Restaurants are the most common source of FOG that causes backups, and they're particularly vulnerable to the resulting damage, often in the form of lost business during temporary closure, spoiled food, and injured reputation. The use of adequately sized and regularly inspected grease traps is thus mandated by local jurisdictions in restaurants, along with hotels, food-processing establishments, supermarkets, factories, and other places that routinely generate significant amounts of grease that would otherwise wind up in public sewers.
Inspection Checklist
InterNACHI commercial inspectors and business operators can use the following checklist for inspecting grease traps:
- proper capacity. If the traps are too small, they will not be able to prevent some of the FOG from entering the sewer system. If they are too large, they can promote the creation of hydrogen sulfide gas, which may be converted into hydrochloric acid, which can damage metal and concrete structures downstream. Traps are sized based on the combined flow rate of the connected fixtures, including the sink, dishwasher and mop drain. As a rough guide, the city of Newton, Massachusetts, requires that grease traps have a retention capacity of at least 2 pounds of grease for each gallon-per- minute of water flow. The type of food served may also be a factor in sizing, as especially greasy or fried foods will require a larger grease trap;
- the presence of a flow-control valve. These T-shaped metal fittings control the rate of flow of wastewater into the trap and protect against sudden surges from the sink or other fixtures from overloading the system. They should be placed beyond the last connection from the fixtures and as close as possible to the underside of the lowest fixture. When two or more sinks or fixtures are combined and served by one trap, a single flow-control fitting can be used;
- the presence of an air intake for the flow-control valve. The flow-control device must be properly vented to permit air to mix with the fluid entering the interceptor to maintain adequate pressure. A vent will prevent a vacuum from forming within the trap, which can force water to enter the trap too quickly;
- proper clearance. Traps should be accessible for cleaning and inspection, whether located inside the kitchen, outside the building, or above or below ground;
- adequate distance from fixtures. Sources disagree over the proper distance that a grease trap should be installed from the fixtures being served. Some experts say that high temperatures may cause FOG to dissolve and exit the trap only to re-congeal once it cools in the sewer system, so traps should be installed some distance from dishwashers and other hot-water fixtures to allow time for the water to cool. Other sources, however, warn that placing the trap too far from fixtures will expose the building’s piping to grease buildup. Inspectors and restaurant owners can consult their authority having jurisdiction (AHJ) for local ordinances concerning appropriate water temperature and distance from fixtures of the grease trap;
- intact construction of the trap. It should be free of cracks in any part of the trap, including the baffles;
- whether the garbage disposal empties into the grease trap, which is not desirable. Ground food scraps will overload the trap and reduce its efficiency. Solid food scraps will also decay in the trap, creating unpleasant odors and unsanitary conditions;
- watertightness. Underground interceptors must be watertight to prevent the infiltration of groundwater or the escape of grease into groundwater or public sewers. Cracks should not be visible and the lid should be tight-fitting; and
- whether the grease trap has been re-purposed to serve multiple functions. Grease traps should never serve toilets or other sanitary systems.
Cleaning the Grease Trap
It is important to understand that the grease trap’s efficiency diminishes as the trap fills with FOG, and when it is filled to capacity, it will no longer separate any FOG from water. The operator may not realize that the trap is full, however, as it will continue to accept water even after it fills, sending the unfiltered FOG directly into the sewer system. And because grease fills the trap from the top down (combined with variations in grease load), it can be difficult to know when the trap needs to be cleaned. And, unfortunately, cleaning grease traps, especially large units, is an unpleasant undertaking that may require restaurant operations to temporarily cease, so this important maintenance task is often neglected. Sometimes, too, amidst the hustle and bustle of a restaurant environment, the chore of cleaning the grease trap is simply forgotten.
The plumbing industry standard states that grease traps should be cleaned when 25% of the volume is occupied by grease (and 75% by water). Traps may need to be cleaned before hitting this threshold, however, so the operator will need to monitor the trap, particularly grease accumulation on the outlet baffle, to determine an appropriate cleaning schedule for the commercial enterprise.
After disassembling the trap, the layer of FOG should be placed into a watertight bag or container and placed in the trash. Unlike “yellow grease” collected from deep-fat fryers that can be used in the production of biodiesel, soap and rubber, FOG is not recyclable and it must be placed in the trash. The interior sides, baffles and lid should then be scraped of FOG and cleaned. Rubber gloves should be worn and soap and antibacterial substances should be avoided during the cleaning process. When the trap is re-assembled, care should be taken to align the parts properly as, once flow is resumed, misaligned parts may allow overflowing and contamination of grease into the restaurant. While cleaning grease interceptors, care should be taken to avoid pinch points created by heavy manhole covers and to avoid damaging the rubber lining that prevents odors from escaping above ground. Any large items found at the bottom of the interceptor tank should be removed. One company reported having discovered a tricycle in their tank.
Inspection Chamber Sealing Grease
To reduce the need for cleaning the grease trap, unfinished food, fats, cooking oil and grease remaining in pots and pans should be dry-wiped or scraped out and into the trash prior to wet-washing. This measure can substantially reduce FOG discharged into the grease trap and prevent the release of foul sulfur gases into the commercial establishment.
In summary, grease traps and grease interceptors are plumbing devices required in food service facilities that prevent fats, oils and grease from entering the public sewer system. InterNACHI inspectors and business operators should learn how these devices work and how they are cleaned, maintained and inspected.
Inspecting Commercial Kitchen Exhaust
