Does Your Municipality Have a Fog Problem? - What IS FOG?

FOG is a widely-used acronym for “fats, oil and grease”, the substance that most commercial kitchens produce as a byproduct of cooking and food preparation. Fats, oil and grease typically make their way into the wastewater when dishes are being washed or kitchen equipment is being cleaned.

Grease that accumulates in pipes and plumbing fixtures, in sewer lines and in sewage treatment plants creates numerous, expensive problems. As a result, most wastewater systems in North America and in many countries around the world require fats, oil and grease to be removed from wastewater before that effluent enters the sewer system.

When it’s not properly intercepted and trapped, grease creates significant problems. Vitrified clay pipe, metal and plastic, which are used in most sewer lines, are “oleophilic” which means that grease adheres to those surfaces. That creates problems. Grease can:

  • Accumulate into large masses and clog pipes, causing blockages and back-ups.
    Collect on floats used in sewage lift stations, with fist-sized floats growing to the size of basketballs. When this happens, those lift stations malfunction, which can lead to backups.

  • Clog pumps at lift stations, treatment plants and the like. The pumps then must be repaired.

  • Lead to the creation of hydrogen sulfide, a poisonous gas. Certain kinds of bacteria that feed on fats, oil and grease release hydrogen sulfide, which smells like rotten eggs. This gas is potentially life threatening to people working in enclosed spaces, such as underground chambers built to access sewer lines. Mixed with water, hydrogen sulfide creates sulfuric acid, which causes the infrastructure to corrode and eventually fail.

To avoid FOG problems, OMAG's Risk Management Services department recommends that all municipalities adopt and enforce grease trap ordinances for restaurants and other food service establishments, which require the use and maintenance of grease traps or interceptors.

A grease trap is a receptacle that kitchen wastewater flows through before entering the sanitary sewer lines. This receptacle can range from one with a small capacity that fits under the counter to one with a large capacity that is buried underground. These receptacles can effectively “trap” grease and reduce your municipality’s FOG problem.

Grease, the industry term for animal fats and vegetable oils, is 10 to 15 percent less dense than water. Grease also won’t mix with water. As a result, fats and oils float on top of water. When kitchen wastewater flows through a grease trap, the grease and oils rise to the surface inside the trap and are trapped using a system of baffles. The captured grease and oils fill the trap from the top down, displacing “clean” water out of the bottom of the trap and into the sewer line.

Grease traps accumulate a mat of grease. When the mat of grease gets deep enough, the trap must be cleaned or it will not function properly, allowing too much grease into the system. When the trap does not function properly, it creates problems for wastewater system operators, collection systems and food service establishments due to sewer blockages and overflows.

This makes it important to not only adopt ordinances for restaurants and other food service establishments, but to visually inspect grease traps on a regular basis and review each food service establishment’s records to assure that the removal of grease is being performed by a qualified waste hauler.  

OMAG has sample grease trap ordinances for you to examine and adopt for your municipality. Contact Gary Cauthen at (800) 234-9461 or email for sample ordinances. 

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