Food Service Operations

A grease trap is a device that separates grease and solids from wastewater before it enters the sanitary sewer. Grease traps are installed as part of the plumbing at food service facilities such as restaurants and cafeterias.

Types

There are two types of grease traps:

• Small grease traps (50 gallons or less) are much smaller and are often located indoors under the three-compartment sink.
• Large grease traps (more than 50 gallons) are usually located outside and typically have manhole type lids.

They both operate essentially the same way. Dirty, greasy water from kitchen sinks, dishwashers, etc. goes into the grease trap along with any food scraps that get washed down the drain. The mixture separates into three layers as it cools. Food scraps and solids sink to the bottom, grease floats to the top, and water ends up in the middle. As the grease layer and solids layer build-up, the water goes through a series of baffles and eventually to the outlet of the trap.

Diagram

Some facilities also have a holding tank to recycle used frying oil, but this is not a grease trap since it’s not connected to the sewer system.

In order for a grease trap to function properly, it must be cleaned regularly. When the grease layer inside the trap gets too thick, grease will start to leave the trap with the water since there's no more room for it to remain in the trap. When the grease leaves the trap, it coats the pipes and eventually forms a clog, which will lead to a backup or overflow of sewage. 

Likewise, if the solids are not cleaned out regularly, they will also contribute to potential problems. Food scraps and other solids will eventually begin to decompose and give off a gas called hydrogen sulfide or H2S. The H2S forms sulfuric acid when it mixes with the water. Eventually, the acid will eat a hole in the pipes or even the grease trap itself. Keeping the trap clean can prevent overflow and costly repairs.

Maintaining your restaurant's grease trap or grease interceptor is a must for proper operation, and is required by the City of Abilene fats, oils and grease (FOG) Ordinance.

Cleaning

Cleaning a grease trap involves vacuuming all the contents, scraping built-up grease on the walls, and sucking up the remainder while rinsing with a pressure washer. This cleaning process should be done on large grease traps every 90 days or more frequently if needed. 

Small grease traps should be cleaned every 30 days or when the grease layer reaches 2 inches thick. Trip tickets - which verify who generated the grease, when the trap was cleaned, who cleaned it, how much was pumped out, when and where the grease was disposed of from each cleanout - must be maintained on-site for five years.

Pump Out Frequency

The pump-out frequency is how often the grease trap needs to be cleaned so that it functions effectively. This will vary depending on the size of the grease trap, the number of meals served, grease content of food, etc.

When to Clean

According to the FOG Ordinance:

• Large grease traps must be cleaned at least every 90 days by a licensed transporter
• Small grease traps must be cleaned at least every 30 days, also by a licensed transporter.
• Some facilities may need to clean more often.

Your grease trap needs to be cleaned when the depth of the grease layer plus the depth of the solids layer is 25% of the depth of all three layers. The depth of the solids layer can be difficult to determine without a sampling tube, so it may be easier to check the depth of the grease layer with a rod or stick. 

Generally, when the grease layer is 5 to 6 inches thick in a large grease trap (2 inches for under-sink traps), the 25% rule has been met. If this amount of grease is accumulating long before the next scheduled pump out, then the trap needs to be cleaned more often.

Extensions to the Pumping Frequency

If your food facility hasn't met the 25% rule for two cycles at the minimum frequency, then you can request an extension to the pumping frequency. Requests will be reviewed and granted on a case by case basis. You will be required to provide documentation that the 25% rule has not been met for each of the two cleaning cycles. 

This is generally done by photographing the depth of the grease layer with a ruler or other appropriate scale in the photograph. Download the Request for Extension to Cleaning Frequency Form (PDF) and be sure to include your documentation so that it may be handled without delay.

Alternate Cleaning Schedules for Seasonal Facilities

For seasonal facilities or irregular usage such as concession stands, event venues, church kitchens, etc, an alternate schedule may be developed that will be appropriate for that facility. To request an alternate schedule, complete and return the Alternate Cleaning Schedule Request Form (PDF), which will be handled on a case by case basis.

Other Maintenance Tips

• Recycle used fry oil. Considered a valuable commodity, some renderers may even pay you for it.
• Wipe the grease off of pans with a dry paper towel before running them underwater. And, the prewashing station and dishwasher must drain into a grease trap.
• Scrape excess food off of pots, pans, and plates and throw it away. Don't use the garbage disposal in the sink. When food scraps decompose in the grease trap, they release acids that eat through the walls of the grease trap, drastically reducing its lifespan.

Choosing a Grease Trap

Replacing an old grease trap for your restaurant? Or will you be one of the many new additions to the City of Abilene? A grease trap is about much more than just price. When choosing the best grease trap for your foodservice operations, you also have to consider available space, who will perform maintenance - at what cost - and many other factors.

Without a Grease Trap

Without a well-maintained grease trap, greasy water goes into your building's sewer line and out into the city sewer, coating the pipes with grease along the way. Over time, that grease hardens to form a clog - especially in places where the pipe turns or is dented - which causes the sewer to back up. That could be inside your restaurant or your neighbor's flower shop down the street.

Types of Grease Traps

Small grease traps

50 Gallons or less

• These are typically attached to the drain beneath the three-compartment sink and must be cleaned by a licensed transporter at least every 30 days.
• Pros: These traps are affordable, don’t take up much space, and are easy to install.
• Cons: The downside of small grease traps is that they are usually located inside, which means the smell is also inside if it’s not cleaned regularly. Let the maintenance slide, and you’ve not only got a smelly mess, but you’ve also got a grease trap that is no longer doing its job, resulting in costly plumbing problems.
• To work efficiently, these units must have a flow control device, which gives the hot greasy water time to cool and separate. This can cause slow drainage during high-volume times, which can slow down your kitchen during peak hours.
• Small grease traps are often favored because they have little upfront cost and take up less room than the large grease traps. In some situations, this may be the only option. However, many facilities are simply looking at the initial cost and don’t realize that a smaller grease trap is going to require more time and maintenance in order for it to function efficiently. Small grease traps are usually less effective than large traps for one or more of the following reasons:
  • The flow control device is not present.  This device restricts the flow of water leaving the trap so that the grease has time to cool and separate. However, by restricting the flow, the drain time from the sink is also slowed down, which is inconvenient in a busy restaurant. Without a flow control device, the grease is simply flushed through the trap along with the water.
  • It is not cleaned often enough. A smaller grease trap fills up faster than a larger one and will, therefore, need to be cleaned more frequently. Odor also becomes a problem since most small grease traps are located indoors.
  • It is too small to remove the grease generated by the facility. While a small grease trap may work well for a small, quiet coffee shop, it may be completely overloaded by a busy greasy food place. The greasy food place would have to spend quite a bit of time and effort to keep a small grease trap working efficiently.
  • Because of these issues, many cities are phasing out small grease traps.

Large Grease Traps

More than 50 Gallons

• These are usually located outside and have manhole type lids. They must be cleaned by a licensed transporter at least every 90 days.
• Pros: Large grease traps don’t usually need to be cleaned as often as small grease traps. They have a longer hold time, which allows for more efficient separation of grease and water. Plus, most of them are typically located outside, so odors stay outside where they belong and your guests smell only one thing - your delicious food!
• Cons: Large grease traps require more space and must be accessible by a transporter and their truck. They cost more up-front than a small trap and installation is a bit more involved, as one would expect.

Falling Behind on Maintenance

Falling behind on trap maintenance allows food scraps at the bottom of the grease trap to begin to decompose, giving off a gas called hydrogen sulfide. When that gas mixes with water, you've got sulfuric acid, a strong corrosive that destroys pipes and concrete. When that happens, you're looking at a hefty price tag for a new grease trap, as well as repairs to pipes and infrastructure. It's important to consider all of the pros and cons of large and small grease trap options before choosing the best grease trap for you and your business.

Before choosing a small grease trap for your foodservice facility, it is important to understand the cons and how they may affect your kitchen's efficiency.

Under the Sink

Small grease traps that reside under the sink are often favored because they have little upfront cost and take up less room than the larger outdoor grease traps. In some cases, they may be the only option due to space availability. However, many don't realize that a smaller grease trap requires more time and maintenance for it to function efficiently. It is important to understand that these small grease traps can be less effective than a large trap for at least one of the following reasons:

• Issues with the flow control device. This device restricts the flow of water leaving the trap, to allow the grease time to cool and separate. However, this results in slower drain time, which can be very inconvenient for a busy restaurant. If the flow control device is removed, the grease simply flushes through the trap with the water and enters the sewer system.
• It is not cleaned often enough. A smaller grease trap fills up faster and will need to be cleaned more frequently than a larger grease trap. Small grease traps must be cleaned every 30 days or more often if necessary. If the grease layer is 2 inches thick before the 30 days is up, then the trap needs to be cleaned more often. Unfortunately, due to the odor when opening and cleaning the grease trap, it will be necessary to do it after hours or early enough for the smell to dissipate.
• It is too small to remove the grease generated by the facility. While a small grease trap may work well for a small, quiet coffee shop, it may be completely overloaded by a busy greasy bacon place, which would have to spend quite a bit of time and money to keep the trap clean.

For Help

If you are still undecided whether a small or large grease trap would be best for your business for the long-term, contact the City of Abilene Fats, Oils, and Grease (FOG) Program by calling (325) 437-4505.