Summary: Grease traps are a necessary evil for all restaurant operators. City and state laws require grease traps to be installed to prevent grease from being dumped into public sewers.
If you operate a restaurant or any type of food preparation facility you know you are required by regulatory agencies to install and properly maintain a grease trap or grease interceptor.
First, let's define one from the other. The interior above-ground box that traps grease entering from the three-bay sink is commonly called a grease trap. The large, concrete, in-ground tank is most often called a grease interceptor. Both are supposed to do similar work and that is, trap fats, oils and grease.
Neither of the systems is perfect, but I would have to give my vote to the in-ground grease interceptor for doing the better of the two. Size alone is a major factor in the effectiveness of these systems. The in-ground grease tank ranges in size from 500 to 2500 gallons, while the interior grease traps are generally from 40 to 100 gallon tanks.
The purpose of both traps and interceptors is to accumulate grease to prevent it from escaping into the municipal sewer system. To succeed, the grease must cool down, solidify and float to the top of the box or tank. The larger in-ground tank allows this to happen much more efficiently than the smaller above ground boxes.
So, why aren't all food preparation facilities required to install the in-ground tank? Back in the days before strip-centers and shopping malls most restaurants did, in fact, have in-ground grease interceptors. However, with limited space and restaurants only renting a site, mall owners did not want the responsibility of having to maintain abandoned grease tanks when restaurants went out of business. Thus, the development of portable or above-ground grease traps.