- What is FOG?
- Is grease a problem?
- What is a grease trap and how does it work?
- What is a grease interceptor?
- Can you recommend a maintenance schedule?
- Do I need a grease trap or interceptor?
- Who determines if I need a grease trap or interceptor?
- What are the criteria for inspecting grease traps?
- What is a FOG Control Plan?
- Why do I need a FOG Control Plan?
- What are BMPs?
FOG is short for fats, oils and grease. FOG is found in lots of foods such as meats, sauces, salad dressings, foods cooked in deep fat fryers, cookies, pastries, cheese, butter and many, many more. FOG is in many places in all kitchens and food services.
In the sewage collection and treatment business, the answer is YES! Grease is singled out for special attention because of its poor solubility in water and its tendency to separate from the water and adhere to other surfaces.
Fats, oils and grease in the sanitary sewer coats the insides of the pipe, causing maintenance problems. The consequences include reduced sewer capacity and pipe blockages leading to sanitary sewer overflows.
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 mats to form on the surface of settling tanks, digesters, and the interior of pipes and other surfaces which may cause a shutdown of wastewater treatment processes.
Problems caused by wastes from restaurants and other grease-producing establishments have served as the basis for this ordinance and other regulations on the discharge of grease materials to the sanitary sewer system. Typically a grease trap or grease interceptor is required to control FOG discharges.
King County Metro requirements for sewer state that FOG discharges are limited to 100 mg/L. This equals one teaspoon per thirteen gallons, a very small amount!
A grease trap is a small reservoir built into the wastewater piping a short distance from the grease producing area (typically the kitchen area). It is designed for the purpose of removing fats, oils, and grease and preventing them from entering the sanitary sewer system. Baffles in the grease trap reservoir hold the wastewater long enough for the grease to congeal and rise to the surface. The grease can then be removed and disposed of properly.
An interceptor is an outdoor, underground vault, typically with a capacity of 500 gallons or more, designed for the purpose of removing fats, oils, and grease and preventing them from entering the sanitary sewer system. The vaults have a two or three compartment system. The wastewater flows between each compartment and is given enough time to cool, allowing any remaining grease to congeal and rise to the surface.
Auburn City Code specifies that grease interceptors must be cleaned at least quarterly and grease traps must be cleaned at intervals of no more than 90 days. It is best to clean grease traps weekly. If the trap or interceptor is routinely at or above 25% combined FOG and solids, then the cleaning frequency needs to be increased.
If you discharge FOG to the sewer system then it is likely that you will be required to install either a grease trap or a grease interceptor.
During new construction or remodel the building department may require you to install a grease trap or grease interceptor in accordance with the current plumbing code. Businesses in existing spaces may be required to install a grease trap or grease interceptor by the sewer utility in order to comply with their FOG Control Plan.
Grease trap and grease interceptor inspections follow the same standard guidelines. The inspector will check that the system is functioning properly. The depth of the sediment and grease layers will be checked. If the combined grease and sediment layers equal or exceed 25% of the trap or interceptor capacity, the device will need to be cleaned. The inspector may also ask to see the maintenance and cleaning records for the trap or interceptor.
The FOG Control Plan is an agreement between the business owner and the city regarding use of Best Management Practices and maintenance and cleaning schedules for grease retention devices. The FOG Control Plan also provides the city with information about the business and potential FOG producing activities.
FOG causes many problems in the sewer system and the FOG Control Plan helps outline strategies to reduce FOG problems. Therefore, FOG Control Plans are required for businesses that have the potential to introduce FOG into the sewer system.
BMP stands for Best Management Practice. BMPs are useful for reducing the amount of FOG that goes down the drain, thereby reducing cleaning frequencies on grease traps and interceptors. Reduced FOG also lowers the risk of clogged pipes and sanitary sewer overflows. An example of a BMP is wiping excess grease out of pots and pans with a paper towel before washing them.