Frequently Asked Questions (FOG)

Why is fog a problem?

Large amounts of fats, oils and grease in the wastewater cause trouble in the collection system pipes. It decreases pipe capacity and, therefore, requires that piping systems be cleaned more often and/or some piping to be replaced sooner than otherwise expected. Oil and grease also hamper effective treatment at the wastewater treatment plant. Grease in a warm liquid may not appear harmful. But, as the liquid cools, the grease or fat congeals and causes nauseous mats on the surface of settling tanks, digesters, and the interior of pipes and other surfaces which may cause a shutdown of wastewater treatment units.

What is a FOG INTERCEPTOR and how does it work?

An interceptor is a small reservoir built into the wastewater piping at least 15 feet from the grease producing area. Baffles in the reservoir retain the wastewater long enough for the grease to congeal and rise to the surface. The grease can then be removed and disposed properly.


What is a FOG interceptor?

An interceptor is a vault with a minimum capacity of 1000 gallons that is located on the exterior of the building. The vault contains baffles. It includes a minimum of two compartments, and flow between each compartment is designed for grease retention. The capacity of the interceptor provides adequate residence time so that the wastewater has time to cool, allowing any remaining grease not collected by the interceptors time to congeal and rise to the surface where it accumulates until the interceptor is cleaned. To view a FOG interceptor,


Can you recommend a maintenance schedule?

All FOG interceptors should be cleaned at least four times each year. Some establishments will find it necessary to clean their interceptors more often. If the establishment has to clean it too often, the owner may be required to install a larger interceptor.


Do I have a FOG interceptor?

If the establishment is uncertain whether it has an inside FOG interceptor, or outside FOG interceptor, the owner should contact the DeKalb County Department of Watershed Management FOG program at (404) 687-7150 for assistance.


Do I need a FOG interceptor?

Any establishment that introduces fats, oils, or grease into the drainage and sewage system in quantities large enough to cause line blockages or hinder sewage treatment is required to install a FOG interceptor. Interceptors are required for high volume restaurants and large commercial establishments such as hotels, hospitals, factories, or school kitchens. FOG interceptors are required for small volume (fast food or take-out restaurants with limited menus, minimum dishwashing, and/or minimal seating capacity). Medium volume establishments may be required to install an interceptor depending upon the size of the establishment. To view a FOG interceptor, click here


Is the FOG INTERCEPTOR I have adequate?

Please contact the DeKalb County Department of Watershed Management FOG Program at (404) 687-7150 for proper sizing. Proper sizing will depend on many things, and is unique in nearly every establishment. The size will also depend largely upon the maintenance schedule. If a FOG interceptor is not maintained regularly it will not provide the necessary grease removal.


What if I don’t install a FOG Interceptor?

If the establishment uses fats, oils, or grease in food preparation, it will eventually encounter a maintenance problem with a plugged building sewer line. The blockage can create a sewer backup situation and ultimately a potential health problem in the establishment. Someone will have to pay for removing the blockage. If the problem is in the building sewer line, then the establishment has direct responsibility for paying for the maintenance. If the blockage or restriction is in the public sewer main, and it can be proven that the establishment is the cause of the blockage, then the establishment may have to pay for the public sewer to be maintained. Blocking a sanitary sewer line is also a violation of the federal Clean Water Act.


Who determines if I need a FOG interceptor?

Contact the Compliance Inspector for your area. to determine which Compliance Inspector is available for your area. When the Administrative Authority requires waste pretreatment, an approved FOG interceptor shall be installed. The rules of DeKalb County will assist the establishment in determining if a FOG interceptor is required.


How can I get in compliance?

The establishment should contact the DeKalb County Department of Watershed Management FOG program at (404) 687-7150. This will enable DeKalb County to assist the establishment in the proper sizing of their FOG interceptor, cleaning schedules and advise them on kitchen practices.