Field Characterization of External Grease Abatement Devices Tarek N. Aziz^'*, Leon M. Holt^, Kevin M. Keener^, John W. Groninger"*, Joel J. Ducoste^ ABSTRACT: This study characterized some of the physical and chemical features of large outside field grease abatement devices (GADs). 24-hour measurements of several food service establishments' (FSEs') influent GAD fiowrates indicated highly intermittent conditions with hydraulic retention times (HRTs) that exceeded the common recommen- dation (30 minutes) by two to five times. Investigation into the chemical characteristics of GADs indicated highly variable influent and effluent fat, oil, and grease (FOG) concentrations. Low pH and dissolved oxygen values were measured throughout the GAD, indicating the likely occurrence of anaerobic microbial processes. Detailed spatial and temporal observations of the accumulation of FOG and food solids were also discussed. Though the FOG layer remained relatively constant for all GAD configurations investigated, results indicated that commonly-used GAD configurations with a straight submerged inlet tee or no-inlet tee configuration may result in the transport of food solids into the second compartment. The present research showed increased accumulation of food solids in the first compartment with a retro-fit fiow distributive inlet. This retro-fit displays promise for potentially improving the separation characteristics of existing GADs. Water Environ. Res., 84, 237 (2012). KEYWORDS: collection systems, fat, oil, and grease, grease abate- ment, sanitary sewers, food waste. doi:10.2175/106143012X13347678384161 Introduction The reduction in sewer pipe capacity that results from FOG accumulation is a significant problem for many municipalities. In a 2004 report to Congress, the U.S. EPA attributed 40% of sewer line blockages to FOG accumulation (U.S. EPA, 2004). These FOG accumulations occurred despite the active usage and maintenance of GADs. Further investigation of the performance of GADs is necessary to better understand their FOG removal effectiveness. ' North Carolina State University, Department of Civil, Construction, and Environmental Engineering. 2501 Stinson Drive, Campus Box 7908, Raleigh, N.C. 27695 USA, tnaziz@ncsu.edu, jducoste@ncsu.edu. ^ Town of Cary, N.C, Department of Public Works and Utilities, P.O. Box 8005, Cary, N.C. 27512 USA, holtenvironmental@embarqmail.com. (Retired)" ^ Purdue University, Department of Food Science, 745 Agriculture Mall Drive, West Lafayette, I.N. 47907 USA, kkeener@purdue.edu. * Southern Illinois University Forestry Department, Carbondale, I.L. 62901-4411 USA, groninge@siu.edu. " (Retired) Current Address; Leon M. Holt, 3509 Catlett Farm Rd., Wake Forest, N.C. 27587 USA. * Corresponding Author Many municipalities require FOG-producing FSEs to be equipped with GADs as an on-site pre-treatment step. There are two broad categories of GADs: external or volume-based, and internal or flow-based. External GADs are typically the larger of the two categories and are sized to provide a design hydraulic retention time (typically less than 30 minutes). Flow- based GADs are typically found within FSE kitchens and are commonly rated for FOG-holding capacity (Plumbing and Drainage Instituted, 2010; American Society of Mechanical Engineers, 2001). Flow-based GADs, when flowing at design rate, often experience hydraulic retention times on the order of 1 minute (Gallimore et al., 2011). The present study focuses entirely on the field performance of the larger, external GADs. Currently, limited peer reviewed literature exists regarding the field performance of GADs. Literature that is available for oil separation is primarily for the petroleum industry in the design of oil water separators (Wang et al., 2006; API, 1969). Petroleum oil wastes differ significantly from FOG-laden waste streams of FSEs, as a result of both the diverse nature of influent food constituents beyond FOG and the intermittency of fiow common in commercial food preparation. Literature suggests that an HRT of 30 minutes or greater is necessary to adequately remove FOG (Metcalf and Eddy, 1991). In addition, different methods exist for sizing GADs. U.S. EPA documentation for on-site wastewater treat- ment describes a GAD-sizing equation that includes FSE seating number and a loading factor (U.S. EPA, 1980), whereas some municipalities opt for sizing based on FSE plumbing configura- tion (Town of Cary, 2010). An increasingly common trend has been the sizing of GADs based on a tally of fixtures that enable draining into the GAD (International Association of Plumbing and Mechanical Officials, 2006). Regardless of the method used to predict flow into a GAD, no research has been performed to measure the magnitude or transient nature of flow entering actual GADs. Garza et al. (2005) provided some discussion of the trends observed in waste strength and kitchen practices from a number of FSEs. Garza noted that the waste strength was a function of the following: (1) number of seats, (2) use of self-serve salad bars, and (3) primary cuisine type. In a more recent study, Lesikar et al. (2006) performed the field analysis of GADs for 28 restaurants, ranging in size of the restaurant, fast food vs full fare, and cuisine types. Five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), FOG concentration, and flow (in the form of total gallons accumulated per day) measurements were performed for six consecutive days, around the same time per day. A second set of BOD5, TSS, FOG con- centration, and flow measurements were performed at the same iVlarch 2012 237