Analysis of Grease Abatement Devices and the Measurement of Fat (Paperback)

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 who are responsible for maintaining these collection systems have little guidance as there is a substantial lack of scientifically-based information 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 that are designed for adequate hydraulic retention time (HRT) to provide separation of light FOG material from influent wastewater. Common designs for GAD utilize dual compartments and are sized for approximately 30 min HRT. However, results of this research indicated highly intermittent systems with the vast majority experiencing 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 commonly used configurations. Implementation of a distributive inlet displayed an elimination of this channeling effect and significant reduction in second compartment food solid accumulation.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.Preliminary analysis of FOG concentration form independent commercial laboratories indicated high variability and under-recovery of known concentrations. For this reasons, an investigation into the n-hexane liquid-liquid extraction of FOG from water was undertaken. Observation of edible-FOG recovery in the presence of 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 o