1,720,963 research outputs found
Interactions between Cd and Cu, and Zn influence particulate phytochelatin concentrations in marine phytoplankton: Laboratory results and preliminary field data
No full textThe effect of metal interactions on phytochelatin production by marine phytoplankton has received little attention but yet is critical to understanding the biochemical production of this potentially important metal-binding ligand in the field. Cd, Cu, and Zn additions were made singly and in combination to three species of laboratory cultures and to a natural algal assemblage from pristine coastal seawater. In the laboratory cultures intracellular phytochelatin varied with metal exposure and demonstrated metal- and concentration-dependent synergisms and antagonisms. Most notably, the addition of all three metals together greatly suppressed phytochelatin production in all cultures. Particulate phytochelatin was also measured at two field sites. In the field, phytochelatin production is related to ambient Cd, Cu, and Zn levels, and the deviations from the dose-response relationship are potentially explained by metal interactions similar to those observed in the laboratory cultures. Though particulate glutathione concentrations were very low in some field samples, it did not appear to limit phytochelatin production. Particulate phytochelatin concentrations in samples from both field sites were very similar to those measured in the laboratory cultures when exposed to all three metals together, and thus phytochelatin levels in the field may be regulated by the interaction of Cd, Cu, and Zn
Metal Complexation By Phytochelatins And Microcystins: A Molecular Dynamics Study
Full text linkA better understanding of the metal-peptide complexes formed by phytochelatins and microcystins is necessary to understand the role of these peptides in algal cells and cyanobacteria, respectively. As there are limited structural and thermodynamic data on these metal-peptide complexes, molecular simulations may provide useful insights by providing structural insights in concert with thermodynamic stability predictions. I conducted molecular dynamics simulations of complexes of phytochelatin (n=2), microcystin-LR, and microcystin-RR with Ca2+, Mg2+, Fe2+, Zn2+, and Cu2+. Structural characteristics of the resulting complexes agreed with results from other metal-peptide complexes. The simulation results also indicate that all three peptides bind Cu and Zn preferentially, supporting the peptides' roles in metal regulation. Peptide conformational changes after metal complexation shed light on the hypothesized transporters of the complexes from the cell, as well as on the environmental chemodynamics of the complexes and peptides in surface waters. ii
Processing Of Microalgae: Acoustic Cavitation And Hydrothermal Conversion
Full text linkThe production of energy dense fuels from renewable algal biomass feedstocks - if sustainably developed at a sufficiently large scale - may reduce the consumption of petroleum from fossil fuels and provide many environmental benefits. Achieving economic feasibility has several technical engineering challenges that arise from dilute concentration of growing algae in aqueous media, small cell sizes, and durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation and conversion of the cellular contents is necessary. Research was carried out to address two processing options for efficient microalgae biofuel production: 1. Ultrasonic cavitation for cell disruption and 2. Hydrothermal conversion of a model algal triglyceride. 1. Ultrasonic cell disruption, which relies on cavitating bubbles in the suspension to produce damaging shock waves, was investigated experimentally over a range of concentrations and species types. A few seconds of high intensity sonication at fixed frequency yielded significant cell disruption, even for the more durable cells. At longer exposure times, effectiveness was seen to decline and was attributed, using acoustic measurements, to ultrasonic power attenuation in the ensuing cloud of cavitating bubbles. Processing at higher cell concentrations slowed cell disintegration marginally, but increased the effectiveness of dissipating ultrasonic energy. A theoretical study effectively predicted optimal conditions for a variety of parameters that were inaccessible in this experimental investigation. In that study, single bubble collapse was modeled to identify operating conditions that would increase cavitation, and thus cell disruption. Simulations were conducted by varying frequency and pressure amplitude of the ultrasound wave, and initial bubble size. The simulation results indicated that low frequency, high sound wave amplitudes, and small initial bubble size generate the highest shock wave pressures. 2. Hydrolysis of a pure model triglyceride compound was experimentally examined for the first time at hydrothermal conditions - from 225 to 300°C. Lipid product composition assessed by GC-FID was compared to previous studies with mixed vegetable oils and used to develop a kinetic model for this oil phase reaction
Formation Of Iron Complexes In Soil Organic Matter And Their Influence On Mobility And Bioavailability Of Antimony
Full text linkAntimony (Sb) is a metalloid belonging to group 15 of the periodic table. Chemical similarities between arsenic (As) and Sb produce concerns about potential health effects of Sb and enrichment in the Environment. Sb is found in the environment as an oxyanionic species, antimonate (Sb(OH)6-). As a result of its net negative charge, antimonate was not initially predicted to have strong interactions with natural organic matter. It has been suggested that oxyanionic species could bind the negatively charged organic matter via a ternary complexation mechanism, in which cationic metals mediate the strong association between organic matter functional groups and oxyanions. The structure of these complexes remains poorly characterized. XANES spectroscopy was performed on organic soils amended with increasing iron levels in order to elucidate the structure of organically complexed iron. Humic acid complexes of iron were also synthesized and examined using XANES and Mossbauer spectroscopy. Two distinct iron sites were found in organic materials. A monomeric iron site and an oligomeric site consisting of small clusters of iron at sub-oxide levels. Phosphate exchangeable Sb was predicted to represent the majority of soil bound Sb. However, phosphate extractable Sb from soils is lower than anticipated. The affect to phosphate on Sb retention in organic soils was examined. Phosphate addition significantly reduced Sb retention in organic soils treated with Fe. The influence of organically complexed Fe on the mobility of Sb was assessed. Increasing Fe amendments resulted in an increase in Sb retention in organic soils. Further examination of the bioavailability of Sb to maize seedlings as a function of organically complexed Fe was examined using a greenhouse study. An unexpected increase in plant tissue Sb was observed as organically complexed Fe increased, which was not predicted by extractions commonly used to assess bioavailable Sb. Extraction of soils with organic acids common to the maize rhizosphere suggested that organic acid exudation can readily mobilize Sb bound by organic iron complexes. Overall, iron complexes in soil organic materials were found to have significant implications on mobility and bioavailability of Sb. Additionally, methods used to assess bioavailable Sb underestimate Sb mobility in organic soils
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
MICROBIAL CONTROLS ON NITROGEN POLLUTION MITIGATION WITHIN STORMWATER BASINS
No full textSupplemental file(s) description: AppendixA_EFFECTS OF BLACK CARBON ON CU AVAILABILITY, MICROBIAL UPTAKE AND DENITRIFICATIONWhen considering sustainable urban development, trade-offs between water quality and greenhouse gas emissions exist. Therefore, this study examined the nitrogen (N) cycling dynamics, water quality treatment, and greenhouse gas emissions from stormwater basins located on Cornell University’s campus. Stormwater basins that were often saturated ("Wet Basins") had a greater abundance of denitrification genes, and denitrified a greater proportion of incoming N. However, overall N treatment (measured as the difference between incoming N and N leaving the basin underdrains) was greater in quick draining "Dry Basins" likely due to the large volume of infiltrated stormwater. Rain events did not create hot-moment emissions of N2O or CH4 from these basins. Using EPA calculations, stormwater sent to a WWTP would produce 7X more CO2-eq per L than if it were sent to a Dry Basin. Conversely, stormwater sent to a Wet Basin instead of the WWTP would lead to an approximately 8X increase in CO2. These results suggest that stormwater basins with saturated conditions are likely doing a better job of completely removing N via denitrification, but are also emitting greater quantities of GHGs. Thus, the tradeoff between better N water quality treatment and greater GHG emissions must be considered when designing stormwater basins. In an effort to understand how increased urbanization will influence the soil microbial community, we examined the soil microbiome in stormwater basins after 2-months and 2-years of exposure. Overall, the microbial communities did not shift dramatically within the stormwater sites. Microbial sub-pathways of methanogenesis and V-ATPase were increased within the Wet Basin treatment, likely due to excess Na and soil moisture. While denitrification is also an anaerobic process like methanogenesis, the denitrification genes did not increase within the often saturated Wet Basin treatment. This indicates that denitrification may take longer than 2-years to adjust to new environments, and practices like stormwater basins that rely on denitrification to remove nitrogen and improve water quality may be initially limited. In addition to these field studies, a lab-scale mesocolumn study done in collaboration with Monash University examined the plant-microbe interactions and their impact on N treatment within stormwater basins. We conducted N water quality, N partitioning, soil metagenomics and 16S profiling across 7 unique plant species and 1 soil control over the 2-year experiment. Plant species with greater root volume, plant and microbial assimilation, and NOx removal, had lower denitrification genes and rates. Our hypothesis that greater denitrification would lead to better NOx removal was not supported by these data, because plant species with high NOx removal depressed denitrification genes and rates, but led to a better ‘treatment’ rate as a larger proportion of incoming N was assimilated and did not directly exit the column drainage. This aligns with the other projects where increased denitrification did not necessarily lead to higher N treatment, unless the ultimate fate of N is considered, and then the amount denitrified is more critical. Overall, anaerobic conditions in stormwater basins promoted denitrification and complete removal of N from downstream waters. However, because of excess greenhouse gas emissions, designers should consider the tradeoffs when installing these stormwater treatment technologies
The Influence Of Thiols On Copper Bioavailability To Marine Algae
Full text linkCopper is an essential element for primary productivity in the ocean. However, at concentrations observed surface seawater, copper likely would be toxic to most microbiota if not buffered by a pool of mostly unidentified ligands. These compounds of presumed biological origin can reduce toxicity either by being directly exuded to chelate extracellular bioavailable copper, or by mitigating the toxic effect of copper inside the cell via complexation and subsequent export. This dissertation examines the role of thiols, a presumed component of this pool of ligands, in maintaining copper homeostasis in marine algae. Stability constants of Cu(I) complexes with cysteine, glutathione, Arg-Cys, and Gln-Cys were measured using a new analytical method that employs fluorescent ion indicators and minimized oxidation of Cu(I). Computational methods were used to support reported constants. Speciation models predict that while thiolate ligands can significantly buffer intracellular copper, at concentrations typically observed in surface seawater, their effect on lowering copper is negligible. Uptake experiments in the presence of thiols confirmed speciation predictions. Thiols were only partially effective in reducing Cu(I) uptake, while the Cu(II) ligands EDTA and GSSG were able to effectively block uptake. However, cysteine enhances copper uptake in copper-limited Emiliania huxleyi cells and can increase the bioavailability of copper bound to EDTA. The use of stable isotopes to measure direct uptake of copper in the absence of a ligand, revealed a constitutive copper efflux mechanism in the coccolithophore E. huxleyi. This mechanism allows E. huxleyi to maintain relatively low cellular levels under exposure to a wide range of high copper concentrations, while the diatom Thalassiosira pseudonana only appears to employ export at higher concentrations. Cu-limitation minimizes efflux. These results suggest that E. huxleyi maintains low levels of cellular copper through an intracellular buffering and efflux mechanism. Such a mechanism would give E. huxleyi an ecological advantage in water prone to high copper, such as coastal and those experiencing an upwelling event. Results from a survey of marine algae and estuarine field measurements also demonstrate that the thiols Arg-Cys and Gln-Cys may be biologically and geographically widespread
Dielectric Measurement Of Algal Lipid Content For Biodiesel Production
No full textAlgae are a promising feedstock for biodiesel production. Real-time monitoring of algal lipid content will enable increased productivity of algal biofuel feedstocks. Dielectric spectroscopy is well-suited to automated industrial monitoring and is sensitive to cellular properties, making it a promising method for algal lipid monitoring. In the first portion of this dissertation, I developed a method to measure the dielectric properties of algae cell suspensions and verified dielectric sensitivity to lipid accumulation via calibration with Nile red fluorometry. In order to develop an improved calibration method for my dielectric characterization, I then characterized intact algae cells via flow cytometry and quantitative 1 H NMR for development of an NMR-traceable flow cytometry protocol for algal lipid measurement. Flow cytometry provides information on the distribution of lipid content within algae populations, whereas 1 H NMR provides direct, rapid quantification of lipids in living cell suspensions without the need for cellular disruption and lipid extraction. In the final part of this dissertation, I used microfluidic single-cell impedance cytometry to simultaneously measure the impedance and fluorescence of individual algae cells with a range of lipid contents for development of an industrial algal lipid measurement system. This work has demonstrated the potential of dielectric spectroscopy for automated algal lipid monitoring, which will facilitate reliable harvest of algal biofuel feedstocks with high lipid content
Optimal Production Planning and Hedging for Bio-energy Industry
Full text linkRenewable energy has become a viable alternative to fossil fuel due to its environmental benefits, sustainability, and potential social welfare. Bioethanol, as one of the dominant renewable energy sources, have become a short and medium term solution to reduce our dependency on fossil fuel. A biorefinery is a process that embraces a wide range of technology to convert biomass to value added products such as ethanol, hydrogen, and industrial chemicals. Based on the source of feedstock, biorefineries has evolved through three main phases. The first generation of bioethanol is produced from corn and has been the main source of ethanol in US. Several second generation bioethanol plants have been established at pilot scale using feedstocks such as switchgrasses, woody crops and agriculture residues. A third generation of biorefinery producing bioproducts from algae is believed to have potential, but continues to face challenges in commercial feasibility.
There is a growing consensus that carbon emission, if left unchecked, will lead to major changes in the climate system. As a result, governments are under growing pressure to enact legislation to curb the amount of carbon emissions, and energy producers worldwide are obliged to adjust their production policy in response to the change of carbon emission policy.
A challenge associated with both corn and ethanol, is the existing drastic price fluctuations on the commodity markets. For a biorefinery that consumes corn and produces ethanol, if fully exposed to this price variation, could suffer from great financial loss resulting from the sudden price changes. Therefore, managing financial risk becomes an essential task for a biorefinery. Financial derivatives, such as forwards, futures, swap and options are commonly used tools in financial risk management, which help to transfer the price uncertainty to the counterparty based on mutual financial agreement.
Motivated by the complications of environmental policy and financial uncertainty, the goal of this work is the development of a systematic optimization framework to help manage the financial risk for both first generation and second generation biorefineries. The solution will maximize economic viability of the process under a specified risk level and with specified carbon tax constraints. Considering different time horizons and derivative types, the framework consists of a price model, a process model, and a hedging model, which interact to generate the optimal operational and hedging strategies. The approach will be demonstrated with results from case studies and is also validated from backtesting with historical price data
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