What is a Precast Concrete Grease Interceptor?
Precast grease interceptors are large basins with strategically designed chambers which separate fats, oils, and grease (FOG) and solid sediment from free flowing water.
Grease interceptors differ from grease traps, which are much smaller and are typically located under kitchen sinks. Grease interceptors are designed to handle much larger volumes of water and are typically buried underground near the affected building to prevent foul smells from affecting the indoor environment.
There are two distinct grease interceptor designs: Baffle and Stand Pipe. Baffle designs are simpler and work well for naturally slow-flowing water. Stand Pipe systems utilize a crossover pipe to slow the flow of water and adequately increase retention times to meet municipal standards.
Precast grease interceptors can handle anywhere from 500 to 15,000 gallons of moving water. FOGs rise to the top and are blocked from flowing through the interceptor by barriers which descend from the top of the basin, whereas solid sediment falls to the floor and is blocked by barriers rising from the bottom.
The best solution results from a size and design that accommodates relatively slow rate of flow. It is important to refer to state and municipal guidelines for sizing and collection specifics.
- Shape and design to collect and remove waste in accordance with state and municipal standards
- Concrete strength and design that withstands the pressure of vehicular traffic if located beneath a roadway
- Concrete that can handle applicable thermal effects
- Easy access for waste removal and maintenance
Precast Concrete Advantages – For Designers
- Unmatched durability and strength
- High quality concrete mix designs
- Documented QA/QC programs
- Easily customizable to meet project needs
Precast Grease Interceptor Sizing
Proper grease interceptor sizing should be determined based on the anticipated volume of wastewater that must flow through the system.
Below is some helpful information regarding sizing methodology.
U.S. EPA Sizing Method
(D) x (GL) x (ST) x (LF)x(HR/2) Grease Interceptor Liquid Capacity =
D = Number of seats in dining area
GL = Gallons of wastewater per meal, normally 5 gallons
ST = Storage capacity factor – minimum of 1.7, onsite disposal, 2.5
HR = Number of hours open
LF = Loading factor
a) 1.25 interstate freeways
b) 1.0 other freeways
c) 1.0 recreation areas
d) 0.8 main highways
e) 0.5 other highways
Reprinted from the EPA Design Manual, Onsite Wastewater Treatment and Disposal Systems.
State, City and Municipality Requirements
Each state Department of Transportation, city and even municipality may have different requirements and regulations that govern grease interceptors. It is important to work with a producer that is familiar with these requirements and can supply a product that meets all local standards.
ASTM C1613 Standard Specification for Precast Concrete Grease Interceptor Tanks
This specification covers design requirements, manufacturing practices, and performance requirements for monolithic or sectional precast concrete grease interceptor tanks.