History of the Grease Trap

While plumbing devices designed to intercept grease and solids may have existed before the 1800s, there is little documentation on them until the Victorian Era. Prior to this there was little effort to stop grease and solid waste entering the sewer system, and indeed there was only a perfunctory system in most places. With the advent of the Industrial Revolution, not just industry was revolutionized, and changes were implemented across the whole of society.

With the need to keep sewers moving effectively, without blockages that could cause back-ups and line breaks, innovations were required from inventors. Californian resident Nathaniel T Whiting submitted his design for the first modern Grease Trap to the Patent Office in 1883, and this patent was issued in October 1884. The design of current grease traps does not vary much from his original ideas, but simply take advantage of modern technology in their construction.

Types, Usage and Evolution

The modern standards for the Grease Trap evolved from a 1940 US Army requirement for Grease Traps to be installed in Army posts. This requirement was found to be inadequate, and over the next few years representatives from several army facilities and the Plumbing and Drainage Manufacturer's Association (now the PDI – Plumbing and Draining Institute) worked to determine the best methods of determining flow rates and grease capacity, which allowed a uniform rating system for Grease Traps. This rating meant the traps and interceptors would now have to work more efficiently than Nathaniel T Whiting's original design (at least 85% grease collection), improvements that were made possible by minor changes to design and materials.

The basic Grease Trap falls into two categories, small (Hydro Mechanical Grease Interceptors) and large (Gravity Grease Interceptors), and both work in similar ways. The key differences are size (and thus capacity) and speed of grease separation.

The HMGI is typically located inside a building (image here), and uses the difference between the specific gravity of fats, oils and grease (FOG) and water, as well as a hydraulic flow action and air entrapment. This process works quickly (about 60 seconds), but the system has a low capacity and is only suitable for smaller installations.

The GGI works more slowly, and has to be much larger than the HMGI. They are usually located outside (and underground), and only use the difference between the specific gravity of FOG and water in there operations. However, they are more suited to large volumes of water and waste (normally over 100 gallons per minute), which explains part of their size. The other factor that influences size is the separation speed, which can take up to 30 minutes.

There has been an innovation which works like a Grease Trap, which is the Grease Recovery Device, also known as Automatic Grease Removal Devices (AGRD). These use mechanical skimmers that collect the floating grease from the surface of the water. They have the advantage that they constantly clean the water, removing grease more efficiently, reducing the chances of blockages.

Standards and Regulations for use

There are no national regulations for the usage and implementation of Grease Traps and Interceptors. This is dealt with at a local level, and the standards vary from one jurisdiction to another.

However, there are standards for the construction and capabilities of Grease Traps and Interceptors, and the most commonly followed are those from the American Society of Mechanical Engineers. The full details of the ASME Standards for Grease Interceptors (ASME A112.14.3) are available from the ASME. Another similar and invaluable guide for both large (GGI) and small (HMGI) Grease Traps is the PDI-G101, which although developed in the 1940's has been regularly updated to keep pace with technological changes.