What is the 25% Rule with Grease Traps?
What is the 25% Rule with Grease Traps?
Ever heard of the 25% rule? If you&#;re scratching your head, you&#;re not alone. Many FOG ordinances, enforced by City Water Authorities throughout the United States, make reference to the 25% rule in the context of grease trap maintenance. But what exactly does this rule mean?
What is the 25% Rule?
A grease trap plays a crucial role in capturing grease from kitchen wastewater during dishwashing and cooking processes. By regulating wastewater flow and allowing sufficient time for separation between grease and water, the trap effectively intercepts Fats, Oils and Grease (FOG). The separated grease, floating to the surface, remains confined in the tank, permitting only the &#;clean&#; water to enter the drains.
As grease separates, it forms three layers within the grease trap: surface grease, water in the middle, and solids at the bottom. While a properly sized grease trap can accommodate waste up to a certain point, it eventually reaches a saturation point where 25% of the contents, comprising surface grease and/or bottom solids, signals a loss of efficiency.
This marks a tipping point, beyond which the tank lacks sufficient volume to handle additional FOG. Consequently, the grease trap requires a complete emptying and refilling with clean water. Unfortunately, many kitchen operators struggle to determine when this critical 25% mark is reached.
How to Identify the 25% Mark in a Grease Trap:
- Calculation: Conduct a bit of detective work to estimate the trapped grease based on the number of covers or meals per day and the grease trap&#;s size. Seek assistance from your supplier for accurate calculations.
- Sludge Judge: Employ a device like the Sludge Judge, which measures grease and solids within the tank by taking a sample using a transparent cylinder.
- Inspection Window (Easiest Way) : Some grease traps, such as the Grease Guardian GGX Manual series, feature &#;globe&#; shaped windows at the 25% mark on the tank&#;s side. When the window displays a grease build-up, it&#;s a clear signal to empty the tank. See image below.
Strategies to Bypass the 25% Rule:
- Automatic Grease Removal Devices: Use Automatic Grease Removal Devices (AGRD), such as the Grease Guardian GGX series, to efficiently eliminate surface grease on a daily basis. These units filter out solid particles using a strainer basket, leading to savings on pumping costs.
- Regular Emptying: Commit to monthly emptying of grease traps to ensure compliance. In cases where the 25% rule cannot be checked, many city authorities mandate monthly emptying.
Being aware of when to empty a grease trap not only ensures compliance but also minimises issues such as odours and overflows associated with neglected grease traps.
How often should I pump out my gravity grease interceptor?
A grease interceptor is a device connected to your plumbing system, which is specifically designed to remove Fats, Oil, and Grease (FOG) from the wastewater before it can enter the sewer system. It works by slowing the flow of water to allow the FOG to float to the top where it is contained within the baffle system.
There are several types and sizes of gravity grease interceptors ranging from large to -gallon in-ground units to smaller under-counter units, known as hydromechanical grease interceptors.
The proper pumping and cleaning frequently are dependent upon many variables, such as the type of food preparation, cooking and cleaning methods, the volume of food or meals prepared, and the size of your gravity grease interceptor. Lake County Special Districts recommend that all gravity grease interceptors are inspected frequently and owners use the "25% Rule" where interceptors are pumped out when the combined thickness of the floating FOG and settleable solids layers exceed 25% of the total liquid depth of the interceptor. All gravity grease interceptors should be pumped out at least once every three months.
To effectively remove FOG, a gravity grease interceptor must retain the water long enough for the FOG and settleable solids to separate within the baffle chamber. Lake County Special Districts suggest that gravity grease interceptors are sized to match the number of Drainage Fixture Units (DFUs) of the kitchen or source as follows:
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Gravity Grease Interceptors Sizing Table
Drainage Fixture Units (DFUs)Gravity Grease Interceptors Volume (Gallons)
Example #1: Typical fast food kitchen = 17 DFUs = 750 gallon GGI
Example #2: Typical larger kitchen = 45 DFUs = gallon GGI
Please note: For a smaller hydro-mechanical unit, use the Hydro-Mechanical Grease Traps Calculation Sheet (PDF).
FOG in the sewer system builds up on the walls of the sewer lines, accumulates in pump station wet wells, creates odors, and clogs pumping and sensing equipment. When FOG builds up on the walls of the sewer line it reduces the system's capacity and can result in complete blockage. This results in sewer backups and overflows, greatly increased man hours and maintenance costs, equipment downtime, and fines.
Provisions were made in the ordinance to allow facilities with no or low levels of grease to be exempt from the requirements. The facility must provide information and sampling data that substantiate the request. Other facilities could request a variance from the sizing requirements and be allowed to install approved types of smaller interior hydromechanical grease interceptors and grease removal devices.
Absolutely. The ground-up solids that go through the disposal will settle to the bottom of the grease interceptor and take up valuable space. The reduced volume will lower the detention time of the device and will reduce its efficiency. The increased loading will also lead to an increase in needed maintenance frequency.
Special Districts Administration can permit the installation of certain types of interior hydromechanical grease interceptors and grease removal devices instead of the exterior in instances of space limitations. However, smaller interior units require substantially increased maintenance and implementation of best management practices to maintain compliance and effective grease removal. Please contact Lake County Special Districts at 707-263- to be considered for interior hydromechanical grease interceptor approval.
Most plumbers and plumbing contractors install gravity grease interceptors and hydromechanical grease interceptors. All installations must comply with California Plumbing Code Requirements.
If you have any questions or would like additional information, please feel free to contact the Lake County Special Districts Administration at 707-263-.
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