Sewers and Grease: A Bad Combination

Fats, oil and grease, known as FOG in the wastewater business, can have a negative impact on wastewater collection and treatment systems. Most wastewater collection system blockages can be traced to FOG. Blockages in the wastewater collection system are serious, causing sewage spills, manhole overflows and sewage backups in homes and businesses. 

Two types of FOG pollutants are common to wastewater systems. The first is petroleum-based oil and grease, which occurs at businesses using these products.  This type of FOG can usually be identified and regulated through local limits and industrial pretreatment permit conditions. 

The second type of FOG is animal and vegetable-based oil and grease used for cooking and food preparation. This type is more difficult to regulate due to the large number of residential areas, restaurants and fast-food outlets.

In our District, we are faced mostly with this second type of FOG problem, which is grease from homes and restaurants. But is that type of grease really a problem? In the sewage collection and treatment business, the answer is definitely yes.  Grease is singled out for special attention by many municipalities and sewer agencies because of its poor solubility in water and its tendency to separate from the liquid solution.

Large amounts of oil and grease in the wastewater cause trouble in the collection system pipes. They can decrease pipe capacity that, besides causing blockages, can cause collection systems to have to be cleaned more frequently and be replaced sooner than otherwise expected. The costs associated with increased maintenance can be significant. 

Oil and grease can 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 grease mats on the surface of settling tanks, digesters and the interior of pipes and other surfaces that may cause a shutdown of wastewater treatment units. 

While the District does not treat any of its wastewater, we do pay for the costs associated with such treatment. Residential customers can help to eliminate FOG problems by simply discarding their grease in the trash instead of rinsing it down the sink. Food service establishments have several required methods to eliminate grease in the collection system, including grease traps and interceptors, but the key is maintenance.

Our goal at CVWD is to have zero sanitary sewer overflows, and this goal takes the help of community members like you!