Grease Trap Design to Remove FOG

# Grease Trap Design to Remove FOG

Grease traps are designed to remove FOG (fats, oils, and grease) from wastewater through gravity separation, allowing lighter FOG to float to the top while heavier solids settle to the bottom. This design prevents FOG from entering municipal sewer systems, where it can cause blockages, backups, and costly maintenance issues.

What it is and why it matters

FOG (fats, oils, and grease) is a common byproduct of commercial kitchen operations, especially in restaurants, cafeterias, and food service facilities. When FOG enters sewer systems, it cools and solidifies, creating blockages that can cause sewage backups, environmental contamination, and expensive municipal repairs.

The EPA Pretreatment Program requires commercial facilities that discharge FOG to install and maintain grease traps or interceptors. These devices use gravity separation to remove FOG before wastewater enters the sewer system, protecting municipal infrastructure and preventing environmental problems.

Proper grease trap installation is essential for restaurants and food service businesses in Miami-Dade County. The Florida Department of Health and Miami-Dade County DERM enforce strict requirements for grease trap design, sizing, and maintenance to ensure effective FOG removal.

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Technical breakdown

Gravity separation mechanism: Grease traps work by slowing down wastewater flow, allowing time for gravity to separate FOG from water. FOG is lighter than water, so it floats to the top of the trap, while heavier solids settle to the bottom. The middle layer of relatively clean water flows out through an outlet pipe positioned below the FOG layer.

Design components: Effective grease traps include an inlet pipe that directs wastewater into the trap, a large holding chamber that provides sufficient retention time for separation, and an outlet pipe positioned at the correct depth to allow only the middle water layer to exit. Baffles or partitions inside the trap help slow flow and improve separation efficiency.

Sizing requirements: Grease trap size is determined by the volume of wastewater and FOG production. The EPA and local regulations specify minimum sizing based on factors like kitchen size, number of meals served, and type of food preparation. Undersized traps cannot effectively remove FOG, while oversized traps may not function properly due to insufficient flow.

Retention time: Effective FOG removal requires sufficient retention time for gravity separation to occur. The University of Florida IFAS Extension explains that properly designed grease traps provide enough time for FOG to rise to the surface and solids to settle, typically requiring a minimum retention time based on flow rate and trap volume.

Temperature considerations: FOG separation works best when wastewater is warm, as FOG solidifies when it cools. Grease traps are typically installed close to the source (under sinks or near dishwashers) to capture FOG while it's still liquid and can be effectively separated from wastewater.

South Florida notes (local relevance)

Miami-Dade County has strict grease trap regulations enforced by DERM to protect municipal sewer systems and prevent FOG-related blockages. All commercial food service facilities must install properly sized grease traps that meet local design requirements for FOG removal.

The county's high volume of restaurants and tourism means FOG management is especially critical. Regular grease trap cleaning is required to maintain effective FOG removal, as accumulated FOG reduces trap capacity and separation efficiency. Miami-Dade DERM requires documentation of regular maintenance to ensure traps continue functioning properly.

Restaurants in Miami-Dade must comply with both state and local requirements for grease trap design and maintenance. Professional grease trap installation services ensure traps are properly sized and installed to meet DERM regulations and effectively remove FOG from wastewater.

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