Analysis of Grease Abatement Devices and the Measurement of Fat, Oil, and Grease in Food Service Establishment Waste Streams

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Title: Analysis of Grease Abatement Devices and the Measurement of Fat, Oil, and Grease in Food Service Establishment Waste Streams
Author: Aziz, Tarek N
Advisors: Kevin Keener, Committee Member
George Roberts, Committee Member
Francis de los Reyes, Committee Member
Joel Ducoste, Committee Chair
Abstract: The release of fat, oil, and grease (FOG) into collection systems ultimately results in the blockage of pipes and subsequent sanitary sewer overflows (SSOs). SSOs are a risk to public health and the environment as they release untreated sewage laden with high nutrient and pathogen loading. Currently, municipalities whose function it is to maintain these collection systems are at a loss as there is a substantial lack of scientifically-based guidance regarding the effective abatement and measurement of FOG. This research aims to examine the performance of grease abatement devices and to investigate the measurement of FOG in food-laden waste streams. Grease abatement devices (GAD) are commonly large, below ground tanks which act to provide adequate hydraulic retention time (HRT) for the separation of light FOG material from influent wastewater. Common designs for GAD require the use of dual compartments and sizing for an approximate 30 min HRT. 24 hour monitoring of 24 field GADs indicated highly intermittent systems with the vast majority experience HRTs far greater than design. Average HRT for most GADs was greater than 2 hrs with peak discharges 3-7 times the average flow rate. Chemical characterization of GADs indicated the presence of anaerobic microbial activity. Spatial and temporal observation of FOG and food solids profiles in a field GAD indicated what appeared to be the channeling of food solids into the second compartment for a straight pipe and no-inlet configured GAD. Observation of a distributive inlet showed an elimination of this channeling effect and significant reduction in second compartment food solid accumulation. As a result of this improved solids sedimentation, it was hypothesized that distributive configurations may also provide improvements in separation of FOG materials by making more efficient use of the GAD cross-sectional area. Lab-scale and computational fluid dynamics (CFD) modeling of GADs was performed to evaluate a commonly observed submerged inlet pipe configurations and develop design improvements to enhance FOG removal efficiency. Lab-scale results indicated that enhanced FOG removal performance was obtained by tripling the HRT from 20 minutes to 1 hr, however, performance values close to the performance of the 1 hr HRT were obtained with a 20 minute HRT by modifying the internal configuration. As hypothesized from observations of the field GADs, it is believed that the use of distributive inlet configurations may act to reduce short-circuiting effects in GADs. Results indicated lab-scale GAD improvement through the use of distributive configurations. The removal of the baffle wall was also explored in the present study. When the wall was removed with a shortened submerged pipe, GAD performance improved from the standard configuration. When an inverted-inlet tee was used without compartmentalization, however, lab-scale results indicated a poorer performance than the standard configuration. Investigation into CFD simulations of GAD configurations followed performance trends established in the lab-scale experiments except in conditions featuring the inverted tee inlet. It is hypothesized that the exclusion of droplet coalescence and breakup in the CFD simulation resulted in these discrepancies. Investigation into the LLE of edible- FOG in synthetic food-laden waste streams indicated substantial interference in the presence of wheat flour and whey proteins. Other comparisons with sucrose, corn starch, and a surrogate fiber indicated no interference with FOG recovery. LLE of various free-fatty acids and FOG types of varying levels of saturation indicated no significant difference in recovery performance. Investigation of an EPA defined standard material (hexadecane) indicated that the volatile nature of the compound lead to its substantially poorer recovery than food-based standards which indicated no volatilization during testing. All sample recovery was slightly low indicating the persistent adhesion of samples to lab-ware.
Date: 2010-02-16
Degree: PhD
Discipline: Civil Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/4395


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