Over the past few years, all of the model plumbing codes have changed their requirements regarding grease traps and grease interceptors. Likewise, many states (but not all) have re-addressed requirements for grease.
There have been a number of reasons for the changes in the code requirements. Anyone who has ever been around an open grease trap knows that it stinks to high heaven. Grease also causes problems with stopped up drains. Finally, grease plays havoc with sewage treatment plants.