Environmental Science and Engineering

Assessment of Grease Interceptor Performance

Publication Date: October 2008
Cooperating Institution: North Carolina State University
Principal Investigator: Joel J. Ducoste, Ph.D.
Project Budget: $276,000
Project Identifier: 03-CTS-16T


Fat, oil, and grease (FOG) is generated everyday by food preparation and cleaning activities conducted at commercial establishments and, on a smaller scale, by residential sewer usage. FOG accumulations in the sanitary sewer collection system result in reduced capacity that may lead to sanitary sewer overflows (SSO) if not periodically removed. As the accumulation commences, the effect of slowed wastewater flow exacerbates the rate of accumulation and deposit of FOG materials onto the pipe walls, thereby reducing capacity. The primary means of controlling FOG blockages is to capture and retain FOG materials before discharge into sewer systems through the use of passive grease interception devices.

Limited scientific studies have evaluated the performance of these devices. Many claims of enhanced performance made by manufacturers of grease and oil interception devices need to be verified by objective and unbiased research protocols. The final report, Assessment of Grease Interceptor Performance, presents the evaluation of field grease interceptors through their separation and cleaning cycles. In addition, researchers performed controlled laboratory scale grease interceptor tests and numerical simulations to assess removal efficiency by grease interceptors (GI) at different residence times and under different geometric configurations. Numerical simulations included a 3-D multi-phase flow model of a grease interceptor to evaluate design changes, and operation and maintenance conditions on the removal of FOG from foodservice waste streams. The results from experimental tests performed on lab-scale grease interceptors were used to validate the model results.

A second report, the Fog Interceptor Design and Operations (FOGIDO) Guidance Manual, outlines the recommendation for the sizing and configuration of grease interceptors using research information from the companion final report. The manual provides a design methodology suitable to submit to the International Association of Plumbing& Mechanical Officials (IAMPO) for consideration for inclusion into the Uniform Plumbing Code. In addition, a Microsoft Excel® spreadsheet GI size calculator has been developed to compute flows and FOG loading to size the GI for a specific food service establishment.