Browsing by Author "George Roberts, Committee Member"

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Analysis of Grease Abatement Devices and the Measurement of Fat, Oil, and Grease in Food Service Establishment Waste Streams
(2010-02-16) Aziz, Tarek N; Kevin Keener, Committee Member; George Roberts, Committee Member; Francis de los Reyes, Committee Member; Joel Ducoste, Committee Chair
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.
Modeling Chloramines Formation in Turbulent Flow
(2004-12-03) Liu, Yanjin; Joel J. Ducoste, Committee Chair; George Roberts, Committee Member; Ranji Ranjithan, Committee Member; Detlef Knappe, Committee Member
A study was performed to investigate the use of Computational Fluid Dynamics (CFD) for the analysis of ammonia injection methods to produce chloramines. Three types of ammonia diffusers were simulated and tested in the present work. In this study, CFD fluid flow and turbulence models were combined with chloramines kinetic models to predict downstream spatial distribution of residual free chlorine. As part of this study, two chemical species transport models, single fluid model (SFM) and multi-fluid model (MFM), were evaluated. In addition, several turbulence models were combined with the MFM approach to investigate the impact of turbulent model selection on the free chlorine residual. The turbulence models examined in this study include the standard k-e, RNG k-e, and k-ω models. All model predictions were compared with experimental measurements of the free chlorine residual at different upstream and downstream locations from the ammonia injection point. The experimental tests include the placement of a perforated baffle to investigate the impact of background turbulence on the overall mixing process. A simple flow visualization experiment using an inert tracer was also performed to qualitatively evaluate the fluid flow pattern in the vicinity of the ammonia injection point. Furthermore, a sensitivity analysis was performed to investigate the impact of several turbulent mixing time scales (eddy-dissipation time scale, Kolmogorov time scale, and Corrsin time scale) on the residual free chlorine concentration. Results showed that the flow field with the standard turbulence model and RNG turbulence model reasonably matched the fluid flow pattern characterized by the flow visualization test. The CFD/MFM modeling approach was found to better predict the free chlorine spatial distribution than the CFD/SFM approach. Moreover, results showed that the CFD chloramines model with the standard or RNG turbulence model was able to predict the downstream chloramines formation for a cone-shape diffuser and a three-bar diffuser. Results also showed that the CFD chloramines model with the EDT or KOLM time scale was able to predict the downstream chloramines formation for the cone-shape diffuser and the three-bar diffuser. However, the CFD chloramines model with different turbulence models consistently over-predicted the residual free chlorine for a T-bar diffuser. This could be explained by the complex turbulent structure, produced by a strong inlet jet, was not properly characterized using these two-equation turbulence models. The CFD/MFM chloramines model was found to improve the prediction of the free chlorine spatial distribution for the T-bar diffuser when the Corrsin time scale was used. In addition, a baffle, placed upstream from the injection point to reduce the strong inlet jet, was found to have significant impact on the mixing and chloramines formation for the T-bar diffuser mixer case. Overall, the CFD/MFM chloramines models of the baffle configuration better predicted residual free chlorine for all three diffuser configurations than the un-baffled reactor cases.
Study of Particle Formation using Supercritical CO2 as an Antisolvent
(2007-04-03) Chang, Alan An-Lei; Michael Dykstra, Committee Member; George Roberts, Committee Member; Ruben G. Carbonell, Committee Chair; Richard Spontak, Committee Member; Robert Kelly, Committee Member
Particle design using supercritical CO2 has been of great interest in the pharmaceutical, microelectronic, catalytic, and related industries over the past 10 years. There have been numerous papers and patents published on the processes studied in this work. The solubility of most drug compounds in carbon dioxide is very low, making it a very attractive antisolvent for particle formation at suitable ranges of temperatures and pressures. This thesis explores the use of different CO2 antisolvent precipitation system designs for the formulation of small crystalline drug particles of a given size, morphology, and uniformity, using the precipitation of acetaminophen from ethanol as an example. In order to understand the precipitation process, the equilibrium concentration of acetaminophen in CO2 and CO2 plus ethanol were measured at a range of temperatures and pressures in a high-pressure extraction system. This information is important in understanding the supersaturation of the drug at various precipitation conditions. Several antisolvent processes were tested in order to determine their effectiveness in controlling the precipitation of acetaminophen from ethanol. The first system involved the use of Solvent Enhanced Dispersion by Supercritical Fluids (SEDS) patented by Hanna and York (WO9501221, 1994). This process uses a coaxial nozzle design where the solvent with the solute of interest is injected in the inner tube and the supercritical CO2 is injected in the outer tube. The two streams mix at nearly constant pressure and temperature in a small volume region of the nozzle before expanding through the nozzle tip into a chamber maintained at a fixed temperature and pressure. The fast mixing process rapidly expands the solvent with CO2 in order to induce phase split of the solid drug particles. The chamber pressure is maintained constant and nearly equal to the pressure in the nozzle. This process was studied because it was claimed that SEDS gave the best control of system parameters. However, the thermodynamic, hydrodynamic and kinetic mechanisms resulting in particle formation are still not well understood. The effects of the nozzle dimensions and vessel dimensions on system performance had not been studies previously. In addition, little work has been published on the effects of variables such as liquid solvent and CO2 flow rates, solute concentration, temperature, and pressure on particle size and morphology. A Design of Experiments (DOE) analysis was used to identify the more important process parameters that control particle size and morphology. DOE is a useful statistical tool to reduce the number of experiments necessary to find the most important variables at an early stage of experimentation. With DOE, a 512 full factorial run was reduced to 32 runs by confounding primary variables with higher order interactions (Example: concentration + temperature). The results of these experiments indicated that the most important factors in determining particle size and morphology are the concentration of acetaminophen in the solvent, the nozzle geometry (length of the mixing zone), pressure and temperature. These parameters were singled out for more detailed experiments aimed at determining the influence of these variables on particle size and morphology. A key feature of the experiments described in this thesis is the use of on-line monitoring of the acetaminophen concentration at the exit to the capture vessel in order to determine how the supersaturation of the solute varied with time during the process. In this way it was possible to determine the nozzle effectiveness in particle precipitation. In addition, the experiment performed in this thesis recognized that the SEDS process is in essence a batch process and it studied the effect of transients in co-solvent concentrations in the particle capture vessel on particle size and morphology. In addition to SEDS, the precipitation of acetaminophen from ethanol was carried out using a Precipitation with Compressed Antisolvent (PCA) process, which is very similar to SEDS without the coaxial configuration. This system is simple to install and has been widely studied. The parameters that were important from the SEDS experiments were studied in the PCA to characterize their effects on particle size and morphology for this system. These results were compared to those obtained using the SEDS process. Both SEDS and PCA yielded equal particle size and morphology if designed properly. The major feature of this work was the emphasis on the design of effective nozzles for the PCA application. Similar to the SEDS results, a good mixing volume along with adequate residence time for micromixing are the best nozzle designs.