2012 Progress Report: An Integrated Approach to Understanding and Reducing Fat, Oil, and Grease (FOG) Deposit Formation for Sustainable Sewer Collection Systems

EPA Grant Number: R834264
Title: An Integrated Approach to Understanding and Reducing Fat, Oil, and Grease (FOG) Deposit Formation for Sustainable Sewer Collection Systems
Investigators: Ducoste, Joel
Institution: North Carolina State University
EPA Project Officer: Page, Angela
Project Period: August 1, 2009 through July 31, 2012 (Extended to July 31, 2014)
Project Period Covered by this Report: July 29, 2011 through July 29,2012
Project Amount: $569,568
RFA: Innovative and Integrative Approaches for Advancing Public Health Protection Through Water Infrastructure Sustainability (2008) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , Sustainability , Water

Objective:

The objectives of this study are as follows: 1) perform bench-scale experiments that attempt to recreate FOG deposits and determine parameters that significantly influence their formation rate, 2) develop a numerical model that describes FOG deposit formation kinetics, 3) perform bench-scale tests to explore enhanced treatment methods to improve the removal of FOG deposit chemical precursors with grease interceptors, 4) perform pilot-scale experiments on a continuous flow sewer collection system to explore spatial variations in FOG deposit formation, and 5) develop a modified EPA storm water management model (SWMM) to predict FOG deposit formation in sewer collection systems.

Progress Summary:

Significant progress has been made in the research project.
 
The fate and transport of FOG deposit reactant constituents and the complex interactions during the FOG deposit formation process are still largely unknown. Batch tests were performed to elucidate the mechanisms of FOG deposit formation that lead to sanitary sewer overflows (SSOs). Tests showed that calcium, the dominant metal in FOG deposits, was released from concrete under low pH conditions. We report the first formation of FOG deposits on a concrete surface in the laboratory. We show that small amounts of oil to grease interceptor effluent play the role of carrier of free fatty acids (FFAs) and facilitate surface reactions between FFAs and calcium to produce surface FOG deposits. Tests of different fatty acids revealed that more viscous FOG deposit solids were formed on concrete surfaces, and concrete corrosion was accelerated, in the presence of unsaturated FFAs versus saturated FFAs. Based on all the data, we propose a comprehensive model of the mechanisms of FOG deposit formation in sewer systems.
 
While a model has been proposed, we also wanted to quantify the factors that may affect the formation of FOG deposits and their chemical and rheological properties. These factors included the types of fats used in FSEs, environmental conditions in sewer systems (i.e., pH and temperature), and the source of calcium in sewer systems. The results of this study showed that properties of calcium-based fatty acid salts depend upon the solubility of the calcium source, which is related to pH and temperature of the system. The fatty acid profile of the calcium-based fatty acid salts produced under alkali driven hydrolysis were identical to the profile of the fat source and did not match the profile of field FOG deposits, which displayed a high fraction of palmitic, a long chain saturated fatty acid. The results suggest that selective microbial metabolism of fats and/or biologically induced hydrogenation may contribute to the FOG deposit makeup in sewer systems. These results suggest the critical importance for the selective removal of palmitic in pretreatment processes prior to the discharge of FSE wastes into the sewer collection system.
 
The results of model predictions show that the Cotte, et al. (2006) saponification model could reasonably represent the experimental saponification data prepared under sewer environmental conditions. The Cotte, et al. model was able to predict the kinetic data reasonably well with optimized adjustments of all three empirical constants. However, it is important to mention that Cotte, et al. were unable to predict the initial instantaneous saponification, particularly under conditions that produced low soap formation. Foubert, et al., the empirical crystallization model, did not predict the experimental data as well as Cotte, et al. Although the empirical Cotte, et al. (2006) saponification models could reasonably represent the experimental data, the behavior of the model fitting parameters was difficult to determine. In addition, triglyceride hydrolysis in Cotte, et al.’s saponification model was not sensitive to changes in pH and temperature without making modifications to the empirical constants. An alternative mechanistic model was developed that involved stepwise hydrolysis and saponification kinetics. The step-wise alkali hydrolysis model displayed improved model prediction of the saponification data. However, the model in its current form was still unable to predict the initial soap formation that may be due to the possible presence of a fraction of FFA in the fats introduced. An advanced search algorithm was employed to find the optimized values of the parameters involved.
 
The EPA developed the standard measurement method (Method 1664) to measure FOG. However, ongoing research has found that Method 1664 may be ill equipped to determine the FOG concentration when analyzing samples from food service establishment’s (FSE) waste streams that contain a significant amount of protein. A new FOG measurement procedure was developed that provided improved FOG recovery, especially in the presence of protein. Results of the new method showed that when the protein was either 150 mg/L or 350 mg/L, Method 1664 either failed or yielded a significantly low and unacceptable recovery rate while the proposed method always yielded a higher recovery rate.
 
During this third year, we quantified the spatial variation in FOG deposit formation and accumulation in a pilot-scale sewer collection system. The pilot system contained straight pipes, manholes, root intrusions, and a pipe sag. Calcium and oil were injected into the system and operated at alkaline (pH = 10) and neutral (pH = 7) pH conditions. Preliminary results showed that solid accumulations were higher at a higher pH. FOG solids were found to preferentially accumulate on root surface, in manhole surfaces, and in the pipe sag region. FTIR analysis on the solids samples confirmed that the solids were indeed calcium-based fatty acid salts. However, the fatty acid profiles of the solids deviated from the profile found from FOG deposits from field sewer systems, which were primarily saturated fatty acids. These results confirm the work done previously in bench-scale kinetics experiments and suggest an alternative fate of unsaturated fatty acids that does not lead to their incorporation in FOG deposits in full-scale sewer systems.
 
We have begun analyzing two additional full-scale collection systems and we plan to develop a numerical sewer collection system model. These systems were analyzed during year 3 to assess patterns of FOG deposit cleanup maintenance relative to nearby location of FSE discharge. Flow data have been collected to input into the numerical model developed during year 2. We are in the process of constructing the model for these two collection systems and will compare the model prediction of the rate of FOG deposit formation with site locations that have been reported as frequent removal of FOG accumulation.


Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 22 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Dominic CCS, Szakasits M, Dean LO, Ducoste JJ. Understanding the spatial formation and accumulation of fats, oils and grease deposits in the sewer collection system. Water Science & Technology 2013;68(8):1830-1836. R834264 (2012)
R834264 (2013)
R834264 (Final)
  • Abstract from PubMed
  • Full-text: ResearchGate-Full Text PDF
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  • Abstract: IWA Publishing
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  • Journal Article He X, Iasmin M, Dean LO, Lappi SE, Ducoste JJ, de los Reyes III FL. Evidence for fat, oil, and grease (FOG) deposit formation mechanisms in sewer lines. Environmental Science & Technology 2011;45(10):4385-4391. R834264 (2012)
    R834264 (2013)
    R834264 (Final)
  • Abstract from PubMed
  • Full-text: ES&T-Full Text PDF
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  • Abstract: ES&T-Abstract
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  • Other: ResearchGate-Full Text PDF
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  • Journal Article He X, de los Reyes III FL, Leming ML, Dean LO, Lappi SE, Ducoste JJ. Mechanisms of fat, oil and grease (FOG) deposit formation in sewer lines. Water Research 2013;47(13):4451-4459. R834264 (2012)
    R834264 (2013)
    R834264 (Final)
  • Abstract from PubMed
  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDirect-Abstract
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  • Other: ScienceDirect-Full Text PDF
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  • Journal Article Iasmin M, Dean LO, Lappi SE, Ducoste JJ. Factors that influence properties of FOG deposits and their formation in sewer collection systems. Water Research 2014;49:92-102. R834264 (2012)
    R834264 (2013)
    R834264 (Final)
  • Abstract from PubMed
  • Full-text: ScienceDirect-Full Text HTML
    Exit
  • Abstract: ScienceDirect-Abstract
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  • Other: ScienceDirect-Full Text PDF
    Exit
  • Supplemental Keywords:

    chemical transport, chemicals, pollution prevention, treatment, engineering, modeling, sewer collection system, SSO, FOG, separation, storm water management

    Progress and Final Reports:

    Original Abstract
  • 2010 Progress Report
  • 2011 Progress Report
  • 2013 Progress Report
  • Final Report