Simply put, a grease trap is a receptacle that kitchen wastewater flows through before entering the sanitary sewer lines. This receptacle captures or “traps” grease. How? Grease, the industry term for animal fats and vegetable oils, is 10 to 15% less dense or lighter than water. Grease is also immiscible than water, which is to say it does not mix with water. Thus, grease and oils float on water. When kitchen wastewater flows through grease trap, the grease and oils rise to the surface and are trapped inside the receptacle using a system of baffles. The captured grease and oils fill the grease trap from the top down, displacing “clean” water out of the bottom of the trap and into the sanitary sewer line. This is why you see a grease “mat” when observing a grease trap. When a significant layer of grease has accumulated, the trap must be cleaned out.
In the United States, the predominant grease traps found in food service operations are small passive grease traps and large, pre-cast concrete grease traps. Passive grease traps date back to 1885 when the first US patent was issued. Today’s large and small grease traps use the same basic operating design as the 1885 model. While they do a fine job trapping grease, removing grease is a task left to the owner. Whether the trap is a small passive trap or a large passive trap, it must be pumped out by a professional grease trap cleaning company with a vacuum or pump truck.
The single most important aspect to understand is that, as a grease trap fills, its separation efficiency diminishes. When a trap is filled to capacity with retained grease/oils there is no separation occurring and the trap no longer works. Since grease and oils fill grease traps from the top down, it is frequently hard to measure the depth or fullness of the grease trap, making it difficult to know when it needs to be cleaned. Failure to clean the grease trap in time creates a considerable volume of business for pipe cleaners and headaches for sewer systems and septic fields.
Sometimes the owner carries the burden of measuring the grease levels and either hand scoops the grease or pays grease trap cleaning services to pump the trap. When the grease trap is not serviced professionally, materials can cause blockages to the system thus causing back-ups and overflows. A healthy grease trap is professionally serviced and pumped on a regular schedule which will eliminate the need for additional grease trap cleaning service and a possible violation from the city inspectors.