Bruce Arey - Academia.edu (original) (raw)

Papers by Bruce Arey

Journal of Nuclear Materials, 2016

Mitigation of hazardous and radioactive waste can be improved through conversion of existing wast... more Mitigation of hazardous and radioactive waste can be improved through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. However, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granular samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.

The U.S. Department of Energy (DOE) Office of River Protection prime contractor, Washington River... more The U.S. Department of Energy (DOE) Office of River Protection prime contractor, Washington River Protection Solutions, LLC (WRPS), is responsible for the storage, retrieval, and disposal of Hanford Site tank waste. As part of this effort, WRPS contracted with Pacific Northwest National Laboratory to conduct testing for selected key contaminants present in residual waste remaining in the single-shell tank 241-C-108 (C-108). Release model data will be used to support tank closure performance assessments that will be performed by WRPS. This report presents the results from laboratory characterization, testing, and analysis of a tank C-108 post modified sluicing residual waste composite sample (designated 20578). The tank C-108 residual waste sample was taken following an assessment that determined through material balance data the modified retrieval sluicing system deployed at the tank could no longer efficiently retrieve waste (met the limit of the technology). These studies were completed to characterize concentration and form of contaminant of interest in the residual waste; assess the leachability of contaminants from the solids; and develop release models for contaminants of interest. It is expected that additional retrieval processing will take place. As a result, the sample analyzed here is not expected to represent final retrieval sample. Total elemental analysis using the U.S. Environmental Protection Agency (EPA) acid digestion method, indicates that tank C-108 partial retrieval residual waste (sample 20578) is composed of the following major elements Na at 15.5%, Al at 12.3%, P at 4.0%, Fe at 1.6%, Ni at 0.22%, U at 0.18%, and Mn at 0.13%. Concentrations of 99 Tc and 238 U were determined to be 0.636 µg/g waste (0.0108 µCi/g) and 1870 µg/g waste (6.27 × 10-4 µCi/g). Average concentrations of 237 Np, 239 Pu, and 241 Am were determined to be 1.24 × 10-4 µCi/g (237 Np), 2.90 × 10-2 µCi/g (239 Pu), and not detected (241 Am). The concentrations of 137 Cs and 90 Sr were found at significant concentrations in tank C-108 residual waste, with averages of 1.69 × 10 4 µCi/g (137 Cs) and 1.22 × 10 5 µCi/g (90 Sr). The results determined from the fusion dissolution procedure were generally very similar to those determined with the EPA acid digestion method. Solid phase characterization by x-ray diffraction (XRD) indicated the presence of the following phases in the as-received tank C-108 composite sample: gibbsite [Al(OH) 3 ], natrophosphate [Na 7 (PO 4) 2 F•19H 2 O], sodium fluoride phosphate hydrate [Na 7 F(PO 4) 2 •19H 2 O], sodium phosphate (Na 3 PO 4), nickel oxide hydroxide (NiOOH), and nitratine (NaNO 3). Solid phase characterization by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) analyses indicated the majority of the particles in the as-received tank C-108 composite sample are composed of Al-Na-O-P-F, Al-Na-O-P, Na-O-P-F, Na-O-P, Al-Na-O, and Na-O, all in variable proportions. Note that all phases could also potentially contain H and C, which cannot be quantified by EDS. Combining the XRD with the SEM/EDS results, the following conclusions can be made regarding the presence of solid phases in the tank C-108 residual waste composite sample: • Gibbsite was the major phase present and appears to be coated and mixed with variable amounts of phases such as natrophosphate, sodium fluoride phosphate hydrate, sodium phosphate, sodium carbonate, sodium hydroxide, and sodium nitrate • Fe-oxides occurred as a minor phase. Its particles were coated and mixed with variable amounts of other solid phases such as natrophosphate, sodium fluoride phosphate hydrate, sodium phosphate, sodium carbonate, sodium hydroxide, and sodium nitrate • Minor amounts of Ni and traces of other metals such as Pb, Zn, and Cu, were associated with the Fe-oxides

This report describes the results of testing sludge samples from Hanford tanks 241-AY-102 (AY-102... more This report describes the results of testing sludge samples from Hanford tanks 241-AY-102 (AY-102) and 241-BX-101 (BX-101). These tests were conducted to characterize the sludge and assess the water leachability of contaminants from the solids. A key finding of these tests is that technetium-99 is not completely water leachable and mobile from some of the tank sludges. In the case of tank AY-102, only 25% of the technetium-99 is water leachable, whereas for tank BX-101 all of it is water leachable. This work is being conducted to support the tank closure risk assessments being performed by CH2M HILL Hanford Group, Inc. for the U.S. Department of Energy. This is the first report of testing of BX-101 sludge and the second report of testing of AY-102. Lindberg and Deutsch (2003) described the first phase of testing on AY-102 material. Initial (Tier 1) testing of BX-101 sludge consisted of acid digestion to determine the composition of the sludge and water leaching to estimate the soluble portion of the sludge. Subsequent analyses of samples from both BX-101 and AY-102 consisted of X-ray diffraction (XRD) to identify crystalline solids, scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS) to view and measure the composition of the solids, and oxidation and reduction capacity measurements to evaluate the redox condition of the sludge. In addition to these tests, the composition of the sludge from AY-102 was measured by fusion analysis and the water leachability of the sludge was evaluated using periodic replenishment and selective extraction tests. The drainable liquid from tank AY-102 was tested using the X-ray absorption near edge structure (XANES) technique to determine redox state of the dissolved technetium. The acid digestion and analysis of BX-101 showed that the predominant metals are aluminum, sodium, uranium-238, iron, manganese, and chromium. The predominant anions are carbonate/ bicarbonate, nitrate, nitrite, sulfate, phosphate, and oxalate. In comparison with sludge from tank BX-101, AY-102 (previously analyzed) has higher concentrations of iron(8x), manganese(4x), nickel(20x), and sodium(2x), and lower concentrations of aluminum(1.7x) and uranium-238(31x). Uranium-238 and technetium-99 are two of the primary tank waste contaminants of concern because of their long-half lives and relatively high mobility in the environment. The water leachabilities of these two radionuclides from the tank sludges were very different. Leach tests on BX-101 sludge showed that all of the technetium-99 but less than 10% of the uranium-238 was water leachable compared to leachabilities of only 20% of the technetium-99 and greater than 60% of the uranium-238 in sludge from AY-102. These results show the heterogeneities in tank compositions and the variabilities that exist in contaminant leaching.

As directed by Congress, the U.S. Department of Energy (DOE) established the Office of River Prot... more As directed by Congress, the U.S. Department of Energy (DOE) established the Office of River Protection in 1998 to manage DOE's largest, most complex environmental cleanup project-retrieval of radioactive waste from Hanford Site tanks for treatment and eventual disposal. Sixty percent by volume of the nation's high-level radioactive waste is stored at the Hanford Site in aging, deteriorating tanks. If not cleaned up, this waste is a threat to the nearby Columbia River and the Pacific Northwest. CH2M HILL Hanford Group, Inc. is the DOE Office of River Protection's prime contractor responsible for the storage, retrieval, and disposal of Hanford Site tank waste. As part of this effort, CH2M HILL Hanford Group, Inc. contracted with Pacific Northwest National Laboratory (PNNL) to conduct testing for selected key contaminants present in residual waste remaining in the single-shell tank 241-S-112 (S-112). This report presents the results of laboratory characterization, testing, and analysis of two samples (designated 20406 and 20407) of residual waste collected from tank S-112 after final waste retrieval. These studies were completed to characterize the residual waste and assess the leachability of contaminants from the solids. This is the first report from this PNNL project to describe the composition and leach test data for residual waste from a salt cake tank. All previous PNNL reports describing contaminant release models, and characterization and testing results for residual waste in single-shell tanks were based on samples from sludge tanks. 1,2 gibbsite particles are likely coated with an Al-Na-O(±H±C) solid. The phase composition of this encrustation could not be established with certainty but appears to have a composition of 29 wt% Na, 18 wt% Al, and 52 wt% O. Results of geochemical modeling indicate dawsonite [NaAlCO 3 (OH) 2 ] was near equilibrium with 1-month double-deionized water extracts, which suggests this phase may be an X-ray diffraction (XRD) results for sample 20407 indicate that the primary crystalline phase in the residual waste is gibbsite [Al(OH) 3 ] and comprises more than ~90 wt% of the solid material. Scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) results are consistent with the XRD results, indicating the primary solid phase is Al-O(±H±C) with a composition that is 39 wt% Al and 60 wt% O (consistent with the composition of gibbsite). The SEM/EDS results also indicate that the Chromium was the most concentrated contaminant of concern in the tank S-112 residual waste samples, occurring at 1,690 to 1,750 μg/g-dry waste. The other important contaminants, 99 Tc and 238 U, were measured in the residual waste at concentrations that ranged from 0.46 to 0.48 μg/g and 17 to 36 μg/g, respectively. Some solution analyses were conducted on supernatant from as-received sample 20406 and on leachates from sample 20407 extracted by a 1-month single-contact leach test with double deionized water at a water-to-waste ratio of 100:1. The percentages of 99 Tc, 238 U, and Cr that were extractable in the 1-month single-contact leachates were 17%, 0.65%, and 10.7%, respectively, relative to the measured concentrations in the unleached bulk solid. Significant percentages of other metals in the extract leachates include Al (9.3%), Ca (81%), and Na (87%) relative to the bulk waste composition. Concentrations of all major anions determined by ion chromatography were below the detection limit, indicating that hydroxide and carbonate were the major anions in the water leachates. Calculations were made to estimate a hypothetical pore water composition that would occur if all the dissolved components measured in the sample 20407 1-month single-contact leach tests were initially dissolved in the entrained pore water. These concentrations were compared with concentrations measured for the supernatant solution present in sample 20406. These results indicate the majority of the 99 Tc, Al, and Na in the 1-month double-deionized water extracts come from dilution of residual supernatant in the waste sample. In the case of 238 U, it appears dilution of pore fluid results in precipitation of most of the 238 U. This may have occurred as a result of diminished hydrolysis and carbonate complexation upon 3

International Journal of Greenhouse Gas Control, 2013

Long-term geologic storage of carbon dioxide (CO2) is considered an integral part to moderating C... more Long-term geologic storage of carbon dioxide (CO2) is considered an integral part to moderating CO2 concentrations in the atmosphere and subsequently minimizing effects of global climate change. Although subsurface injection of CO2 is common place in certain industries, deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability.

Environmental Science & Technology, 2006

Bulk X-ray diffraction (XRD), synchrotron X-ray microdiffraction (µXRD), and scanning electron mi... more Bulk X-ray diffraction (XRD), synchrotron X-ray microdiffraction (µXRD), and scanning electron microscopy/ energy-dispersive X-ray spectroscopy (SEM/EDS) were used to characterize solids in residual sludge from singleshell underground waste tanks C-203 and C-204 at the U.S. Department of Energy's Hanford Site in southeastern Washington state. Č ejkaite [Na 4 (UO 2)(CO 3) 3 ] was the dominant crystalline phase in the C-203 and C-204 sludges. This is one of the few occurrences of čejkaite reported in the literature and may be the first documented occurrence of this phase in radioactive wastes from DOE sites. Characterization of residual solids from water leach and selective extraction tests indicates that čejkaite has a high solubility and a rapid rate of dissolution in water at ambient temperature and that these sludges may also contain poorly crystalline Na 2 U 2 O 7 [or clarkeite Na[(UO 2)O(OH)](H 2 O) 0-1 ] as well as nitratine (soda niter, NaNO 3), goethite [R-FeO(OH)], and maghemite (γ-Fe 2 O 3). Results of the SEM/EDS analyses indicate that the C-204 sludge also contains a solid that lacks crystalline form and is composed of Na, Al, P, O, and possibly C. Other identified solids include Fe oxides that often also contain Cr and Ni and occur as individual particles, coatings on particles, and botryoidal aggregates; a porous-looking material (or an aggregate of submicrometer particles) that typically contain Al, Cr, Fe, Na, Ni, Si, U, P, O, and C; Si oxide (probably quartz); and Na-Al silicate(s). The latter two solids probably represent minerals from the Hanford sediment, which were introduced into the tank during prior sampling campaigns or other tank operation activities. The surfaces of some Fe-oxide particles in residual solids from the water leach and selective extraction tests appear to have preferential dissolution cavities. If these Fe oxides contain contaminants of concern, then the release of these contaminants into infiltrating water would be limited by the dissolution rates of these Fe oxides, which in general have low to very low solubilities and slow dissolution rates at near neutral to basic pH values under oxic conditions.

Applied Geochemistry, 2014

Subsurface regions of alluvial sediments characterized by an abundance of refractory or lignitic ... more Subsurface regions of alluvial sediments characterized by an abundance of refractory or lignitic organic carbon compounds and reduced Fe and S bearing minerals, which are referred to as naturally reduced zones (NRZ), are present at the Integrated Field Research Challenge site in Rifle, CO (a former U mill site), and other contaminated subsurface sites. A study was conducted to demonstrate that the NRZ contains a variety of contaminants and unique minerals and potential contaminant hosts, investigate micron-scale spatial association of U with other co-contaminants, and determine solid phase-bounded U valence state and phase identity. The NRZ sediment had significant solid phase concentrations of U and other co-contaminants suggesting competing sorption reactions and complex temporal variations in dissolved contaminant concentrations in response to transient redox conditions, compared to single contaminant systems. The NRZ sediment had a remarkable assortment of potential contaminant hosts, such as Fe oxides, siderite, Fe(II) bearing clays, rare solids such as ZnS framboids and CuSe, and, potentially, chemically complex sulfides. Micron-scale inspections of the solid phase showed that U was spatially associated with other co-contaminants. High concentration, multi-contaminant, micron size (ca. 5-30 lm) areas of mainly U(IV) (53-100%) which occurred as biogenic UO 2 (82%), or biomass-bound monomeric U(IV) (18%), were discovered within the sediment matrix confirming that biotically induced reduction and subsequent sequestration of contaminant U(VI) via natural attenuation occurred in this NRZ. A combination of assorted solid phase species and an abundance of redox-sensitive constituents may slow U(IV) oxidation rates, effectively enhancing the stability of U(IV) sequestered via natural attenuation, impeding rapid U flushing, and turning NRZs into sinks and long-term, slow-release sources of U contamination to groundwater.

Applied Geochemistry, 2007

This article was published in an Elsevier journal. The attached copy is furnished to the author f... more This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author's institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Investigations of contaminant release from Hanford Site tank residual waste have indicated that i... more Investigations of contaminant release from Hanford Site tank residual waste have indicated that in some cases certain contaminants of interest (Tc and Cr) exhibit inhibited release. The percentage of Tc that dissolved from residual waste from tanks 241-C-103, 241-C-106, 241-C-202, and 241-C-203 ranged from approximately 6% to 10%. The percent leachable Cr from residual waste from tanks C-103, C 202, and C-203 ranged from approximately 1.1% to 44%. Solid phase characterization results indicate that the recalcitrant forms of these contaminants are associated with iron oxides. X-ray absorption near edge structure analysis of Tc and Cr in residual waste indicates that these contaminants occur in Fe oxide particles as their lower, less soluble oxidation states [Tc(IV) and Cr(III)]. The form of these contaminants is likely as oxides or hydroxides incorporated within the structure of the Fe oxide. Leaching behavior of U from tank residual waste was studied using deionized water, and CaCO3 and Ca(OH)2 saturated solutions as leachants. The release behavior of U from tank residual waste is complex. Initial U concentrations in water and CaCO3 leachants are high due to residual amounts of the highly soluble U mineral cejkaite. As leaching and dilution occur NaUO2PO4 · xH2O, Na2U2O7(am) and schoepite (or a similar phase) become the solubility controlling phases for U. In the case of the Ca(OH)2 leachant, U release from tank residual waste is dramatically reduced. Thermodynamic modeling indicates that the solubility of CaUO4(c) controls release of U from residual waste in the Ca(OH)2 leachants. It is assumed the solubility controlling phase is actually a hydrated version of CaUO4 with a variable water content ranging from CaUO4 to CaUO4 · (H2O). The critically reviewed value for CaUO4(c) (log KSP0 = 15.94) produced good agreement with our experimental data for the Ca(OH)2 leachates.

MRS Proceedings, 2006

Solid phase physical and chemical characterization methods have been used in an ongoing study of ... more Solid phase physical and chemical characterization methods have been used in an ongoing study of residual wastes from several single-shell underground waste tanks at the U.S. Department of Energy's Hanford Site in southeastern Washington State. Because these wastes are highly-radioactive dispersible powders and are chemically-complex assemblages of crystalline and amorphous solids that contain contaminants as discrete phases and/or co-precipitated within oxide phases, their detailed characterization offers an extraordinary technical challenge. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) are the two principal methods used, along with a limited series of analyses by synchrotron-based methods, to characterize solid phases and their contaminant associations in these wastes. Depending on the specific tank, numerous solids (e.g., èejkaite; Na2U2O7; clarkeite; gibbsite; böhmite; dawsonite; cancrinite; Fe oxides such as hematit...

npj Materials Degradation, 2021

Glass alteration in the presence of microorganisms has been a topic of research for over 150 year... more Glass alteration in the presence of microorganisms has been a topic of research for over 150 years. Researchers from a variety of disciplines, including material science, biology, chemistry, geology, physics, and cultural heritage materials preservation have conducted experiments in this area to try and understand when, how, and why microorganism may interact and subsequently influence the alteration of glass. The breadth and depth of these studies are the topic of this review. This review presents a detailed history and a comprehensive overview of this field of research, while maintaining focus on the terrestrial alteration of anthropogenic silicate glasses. Within this manuscript is a schema for bio-interaction with silicate glasses and an outline of an evidence-based hypothesis on how these interactions may influence glass alteration processes. Topics discussed include microbial colonization of glass, development, and interactions of biofilms with glass surface, abiotic vs. bioti...

Microscopy and Microanalysis, 2018

Surface and Interface Analysis, 2019

This work presents in situ imaging of synthesized boehmite (γ-AlOOH) particles ranging from 20 to... more This work presents in situ imaging of synthesized boehmite (γ-AlOOH) particles ranging from 20 to 100 nm, suspended in liquid, in a vacuum compatible microfluidic sample holder using a scanning electron microscopy (SEM) under the high vacuum mode and highlights the advantage of in situ liquid imaging of colloids. Nanometersized boehmite particles in high-level radioactive wastes at the Hanford site are known to be difficult to dissolve and cause rheological problems for processing in the nuclear waste treatment plant. Therefore, it is important to characterize boehmite particles and understand how they form aggregates in the liquid state. Several technical advancements are made to optimize in situ liquid SEM chemical imaging resulting in the improved ability to obtain secondary electron (SE), backscattered electron (BSE) images, and energy dispersive X-ray spectroscopy (EDX) spectra. Moreover, our results show mixed particles could be studied and identified based on the particle shape and elemental composition using in situ SEM imaging and EDX. Thus, we provide a new and improved approach to observe the evolution of particle dispersion and stability in liquid under conditions similar to those in the waste tank.

Microscopy and Microanalysis, 2017

Environmental science & technology, Jan 13, 2017

Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as importan... more Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important source of electron equivalents limiting the transport of redox active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced clays in field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) concentration, but FeTOTAL remains constant demonstrating no Fe loss during redox cycling. At its native pH of 8.6, the anoxic fraction despite its significant Fe(II) (~23% of FeTOTAL), exhibits minimal reactivity with TcO4- and CrO42- and much slower reaction kinetics than that measured in studies with biologically/chemically ...

Microscopy and Microanalysis, 2016

Science of The Total Environment, 2016

Wetlands mitigate the migration of groundwater contaminants through a series of biogeochemical gr... more Wetlands mitigate the migration of groundwater contaminants through a series of biogeochemical gradients that enhance multiple contaminant-binding processes. The hypothesis of this study was that wetland plant roots contribute organic carbon and release O 2 within the rhizosphere (plant-impact soil zone) that promote the formation of Fe(III)-(oxyhydr)oxides. In turn, these Fe(III)-(oxyhydr)oxides stabilize organic matter that together contribute to contaminant immobilization. Mineralogy and U binding environments of the rhizosphere were evaluated in samples collected from contaminated and non-contaminated areas of a wetland on the Savannah River Site in South Carolina. Based on Mössbauer spectroscopy, rhizosphere soil was greatly enriched with nanogoethite, ferrihydrite-like nanoparticulates, and hematite, with negligible Fe(II) present. X-ray computed tomography and various microscopy techniques showed that root plaques were tens-of-microns thick and consisted of highly oriented Fenanoparticles, suggesting that the roots were involved in creating the biogeochemical conditions conducive to the nanoparticle formation. XAS showed that a majority of the U in the bulk wetland soil was in the +6 oxidation state and was not well correlated spatially to Fe concentrations. SEM/EDS confirm that U was enriched on root plaques, where it was always found in association with P. Together these findings support our hypothesis and suggest that plants can alter mineralogical conditions that may be conducive to contaminant immobilization in wetlands.

Nature communications, Jan 2, 2015

Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Br... more Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al-Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.

PloS one, 2015

Yarrowia lipolytica is an oleaginous ascomycete yeast that accumulates large amounts of lipids an... more Yarrowia lipolytica is an oleaginous ascomycete yeast that accumulates large amounts of lipids and has potential as a biofuel producing organism. Despite a growing scientific literature focused on lipid production by Y. lipolytica, there remain significant knowledge gaps regarding the key biological processes involved. We applied a combination of metabolomic and lipidomic profiling approaches as well as microscopic techniques to identify and characterize the key pathways involved in de novo lipid accumulation from glucose in batch cultured, wild-type Y. lipolytica. We found that lipids accumulated rapidly and peaked at 48 hours during the five day experiment, concurrent with a shift in amino acid metabolism. We also report that exhaustion of extracellular sugars coincided with thickening of the cell wall, suggesting that genes involved in cell wall biogenesis may be a useful target for improving the efficiency of lipid producing yeast strains.