Browsing by Subject "Organic Carbon"

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    Effects of Organic Carbon on the Biodegradation of Estrone in Multiple Substrate, Mixed-Culture Systems
    (2014-08) Tan, Tat Ui
    This dissertation describes the study of the effect of organic carbon on the biodegradation of estrone (E1) in multiple substrate, mixed-culture systems. In exploring this topic, important degradation mechanisms related to organic carbon were tested to determine which, if any, play an important role. Additionally, the effects of organic carbon concentrations, loads, and quality on E1 degrading activity of cultures from a wastewater treatment system were determined. Catabolic repression effects on E1 degradation was studied by adding synthetic septage to an E1 degrading culture to determine if degradation rates were affected. No differences in first-order E1 degradation rates between test and control reactors were observed in the 2 h or 8 h period following the addition of synthetic septage, ruling out catabolic repression as an important mechanism in E1 degradation in wastewater treatment-like conditions. Cultures were grown in membrane bioreactors (MBRs) with and without exposure to E1 to determine if (i) E1 exposure is necessary for E1 degrading ability, and if so (ii) whether multiple substrate utilization and/or cometabolism play an important role in the degradation of E1. These cultures were capable of degrading E1 regardless of prior exposure. Higher rates of E1 degradation were observed in cultures with prior E1 exposure, and a lag phase of 6 h was observed in cultures without prior E1 exposure. These results indicate that E1 was degraded metabolically, demonstrating that multiple substrate utilization is the key mechanism for E1 degradation. Longer term effects of organic carbon concentrations on E1 degrading activity were explored by comparing cultures operating under starvation conditions and cultures operating on a daily feeding cycle. Cultures fed daily showed a large initial increase in E1 degradation activity, attributable to a corresponding increase in biomass. Subsequently, however, E1 degradation activity dropped substantially even though biomass continued to increase, suggesting that E1 degraders were outcompeted when subjected to repeated exposure to high organic carbon concentrations. Conversely, starvation cultures had moderate but sustained increases in E1 degradation rates. Another experiment using MBRs to distinguish organic loads from organic concentrations confirmed the positive effect of organic carbon loads on E1 degradation via biomass growth, indicating that high organic carbon concentrations rather than loads were responsible for the drop in E1 degradation rates. A follow-up study was carried out to determine if altering the duration between feeding cycles could mitigate the negative effects of high organic carbon concentrations on E1 degradation. When cultures were exposed to high organic carbon concentrations (600 mg COD/L over a 6 d period), increasing the duration between feeding cycles improved performance. Conversely, at lower organic carbon concentrations (180 mg COD/L over a 6 d period), no differences in E1 degrading activity was observed. Effects of organic carbon quality on E1 degradation were explored using aged synthetic septage and waters from various treatment and natural sources to culture mixed communities. In these experiments, spectrophotometric methods (specific UV absorbance, spectral slope ratios, excitation-emission matrices, and fluorescence index) were used to characterize organic carbon. Additional analyses and experiments were conducted to rule out organic carbon, nitrogen species, and trace element concentrations as complicating factors. These experiments showed that microbially-derived organic carbon was associated with E1 degrading ability, while organic carbon from natural water sources (river and lake) was not. Furthermore, the experiments with aged synthetic septage suggest that products from cell lysis and/or microbial products under stress by starvation may be important for E1 degradation. Overall, this work shows that multiple substrate utilizing bacteria are important for E1 degradation in wastewater treatment-like systems and indicates various organic carbon parameters that are vital for the selection of these bacteria.
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    Iron and Carbon Speciation in Non-Buoyant Hydrothermal Plumes along the East Pacific Rise: A Chemistry Love Story
    (2018-09) Hoffman, Colleen
    In the ocean, iron (Fe) is an important micronutrient for phytoplankton growth. Phytoplankton play a vital role in the global carbon (C) cycle, accounting for 50% of the total photosynthesis on the planet (Field et al. 1998; Moore et al. 2013; Fitzsimmons et al. 2014). When they die, phytoplankton sink and can become buried in the sediments of the deep ocean, removing C from the atmosphere and surface water. While Fe is an abundant element overall in the Earth’s crust (Edwards et al. 2004), it is extremely diluted in the surface ocean. Iron-poor surface waters limit phytoplankton growth (Vraspir and Butler 2009) and their ability to remove C from the atmosphere and surface ocean. Over the past few decades, research has focused on constraining the global Fe cycle and its impacts on the global C cycle (Tagliabue et al. 2010). Hydrothermal vents have become a highly debated potential source of Fe to the surface ocean. Initially, the hypothesis stated that hydrothermal Fe would all be oxidized and deposited locally upon being expelled from the vent. Therefore, hydrothermal vent would have a negligible effect on global biogeochemical cycles (Elderfield and Schultz 1996). However, as a variety of new sampling techniques were developed to preserve reduction-oxidation (redox) states and increase the ability to collect trace-metal clean samples (Johnson et al. 1997; Johnson et al. 2007; Breier et al. 2009), it was discovered that hydrothermal Fe could be protected from oxidation and removal to the sediments and be a potential source of Fe to the deep ocean and surface waters in some locations (Toner et al. 2009a; Toner et al. 2012a). With the amount of Fe released through hydrothermal venting to the ocean per year being similar in magnitude to that delivered by global riverine run-off (Elderfield and Schultz 1996), hydrothermal vents could be an unrecognized nutrient source to the surface ocean and play a role in global C cycling. Two main mechanisms, nanoparticles with slow settling rates, and complexation reactions with organic functional moieties, have been hypothesized to transport solid and aqueous phase Fe over long distances (Bennett et al. 2008; Toner et al. 2009a; Yücel et al. 2011). During the time interval of this dissertation, studies have investigated a large hydrothermal Fe source emanating from the East Pacific Rise (EPR; Resing et al. 2015; Fitzsimmons et al. 2017; Lee et al. 2018). This has informed current working geochemical models about the complexity of reaction pathways and transport mechanisms active in hydrothermal plumes with implications for basin-scale transport and bioavailability of hydrothermal Fe (Tagliabue and Resing 2016; Tagliabue et al. 2017). This dissertation will focus on investigating the chemical speciation and transport mechanisms of Fe in non-buoyant plume particles along the East Pacific Rise. Therefore, further informing the global impact of hydrothermal venting within ocean basins.