What is the 25% Rule with Grease Traps?

Have you heard of the 25% rule? If you’re unsure, you're not alone. Many Fats, Oils, and Grease (FOG) ordinances, enforced by City Water Authorities across the United States, reference this rule when discussing grease trap maintenance. But what does this rule really entail?

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What is the 25% Rule?

A grease trap is essential for capturing grease from kitchen wastewater, especially during dishwashing and cooking. It regulates wastewater flow and allows sufficient time for the separation of grease and water, effectively intercepting FOG. The grease that separates floats to the surface and remains contained in the tank, allowing only 'clean' water to pass into the drains.

As grease separates, it creates three distinct layers within the grease trap: surface grease, water in the middle, and solids at the bottom. While a properly sized grease trap can manage waste to a certain extent, it will eventually reach a saturation point. When 25% of the trap's contents comprise surface grease and/or bottom solids, it indicates a loss of efficiency.

This point marks a critical threshold, beyond which the grease trap cannot effectively handle additional FOG. As a result, the trap necessitates a complete emptying and refilling with clean water. Unfortunately, many kitchen operators find it challenging to determine when this vital 25% mark is reached.

How to Identify the 25% Mark in a Grease Trap:

1. Calculation: Gather data to estimate the trapped grease based on the number of covers or meals prepared daily, along with the grease trap’s size. Consult your supplier for precise calculations.
2. Sludge Judge: Use a device such as the Sludge Judge, which measures grease and solids within the tank by collecting a sample with a transparent cylinder.
3. Inspection Window (Easiest Way): Some grease traps, like the Grease Guardian GGX Manual series, feature 'globe' shaped windows positioned at the 25% mark on the tank's side. When the window indicates grease build-up, it's a clear reminder to empty the tank.

Strategies to Bypass the 25% Rule:

• Automatic Grease Removal Devices: Implement Automatic Grease Removal Devices (AGRD), such as the Grease Guardian GGX series, to effectively remove surface grease routinely. These devices filter out solid particles using a strainer basket, resulting in significant savings on pumping costs.

• Regular Emptying: Commit to emptying grease traps at least monthly to ensure compliance. In situations where it’s difficult to check the 25% rule, many city authorities require monthly emptying.

Understanding when to empty a grease trap not only ensures compliance but also reduces issues like odors and overflows related to poorly maintained grease traps.