Thesis (M.Sc.)--College of William and Mary. / Vita. Includes bibliographical references.

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The distribution of the physical and chemical properties in Tofino Inlet is examined in this study. The presence of shallow thresholds in the entrances to the inlet prevents the exchange of deep water in the inlet with oceanic water of the same depth and restricts the intrusion of oceanic water to that of the surface layer. Replacement of the bottom water of the inlet occurs in the summer, when the density of the oceanic surface water is highest for the year, and accounts for the relatively high bottom temperatures, which are observed throughout the year. Between replacements the bottom water in the upper basins of Tofino stagnates and becomes anoxic. Under these stagnant conditions the oxygen supply of this water is used up. Eventually heterotrophic bacteria use sulphate as hydrogen acceptor for the oxidation of organic matter and produce hydrogen sulphide and carbon dioxide. The production of these substances results in an increase In the alkalinity and a decrease in the pH of the water. Using certain assumptions regarding the oxidative processes, calculations are made which suggest that the observed anomalous increase in alkalinity is mainly due to the dissolution of calcium carbonate in these relatively acidic waters. A rate of oxygen utilization is calculated for the deep basin water and is used to determine whether or not replacement of the bottom water was likely during the summer of 1959. / Science, Faculty of / Chemistry, Department of / Graduate

Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2008. / Physics / unrestricted

Reverse osmosis (RO) desalination plants enable the production of high-quality freshwater from seawater, explaining the increasing global use of this technology. However, a major operational challenge for RO is biofouling, caused by excessive biomass accumulation. Membrane fouling simulators (MFSs), downsized membrane systems, were demonstrated to be suitable for biofouling studies using tap water. There is a need to investigate biofouling using natural seawater. The seawater MFS studies involved (i) an exploratory study to evaluate the MFS setup, (ii) long-term operation without feed water nutrient dosage, (iii) impact of nutrient concentration, and (iv) a comparison of biofouling development with freshwater. MFSs were operated parallel at constant feed flow (0.2 m/s), with feed spacer and RO membrane, at varying biodegradable organic nutrient concentrations (0, 50, and 200 µg C/L). The relative pressure drop (RPD) was monitored over time, and biofilm development was characterized through the MFS window applying optical coherence tomography (OCT). Results demonstrated for seawater that (i) the developed setup had a reliable operation and provided reproducible data, (ii) biofouling development presented a minimal effect when nutrient concentration was quadrupled, (iii) there was no correlation between the nutrient concentration and growth rate for seawater experiments, suggesting biofilm development under conditions close to the maximum growth rate. Compared to tap water at the same nutrient concentrations, seawater showed much faster biofilm development, pressure drop increase, and strongly different biofilm morphology. This research provides new insights, new research directions and underlines the importance of doing MFS research with natural seawater.

Aluminum is an attractive metal for use as an anode in the cathodic protection of steels in seawater due to its low cost and high current capacity. Zinc is often used for its ability to readily corrode, but it has a low current capacity and it operates at very negative voltages, leading to hydrogen generation at the steel cathode, which may cause hydrogen embrittlement. Aluminum can operate at less-negative voltages, therefore reducing hydrogen generation, but it forms a passive oxide film, preventing the anode from corroding. Ga is added to aluminum in small amounts (0.1 wt%) to destabilize this oxide film and allow for active corrosion. The mechanism of how Ga activates Al is still not well-known, though there are prevailing proposals. A previous study noted a difference in behavior between Al-Ga master heats and the alloys that were later produced by re-melting them. This study is focused on characterizing the corrosion behavior of Al-0.1 wt% Ga in synthetic seawater, with samples from a master heat and two subsequent remelts. Galvanostatic, potentiostatic, and open-circuit tests were run, as well as galvanic coupling with 1123 steel. It was found that the remelted anodes behaved more consistently and maintained stable corrosion behavior for longer times than the master heat. X-ray Photoelectron Spectroscopy analysis showed elevated concentrations of Ga inside the oxide layer. The findings support the mechanism in the literature of discrete particles of Ga forming under the oxide film but do not support the mechanism of an amalgam layer formation. This project was funded by NACE International, Virginia Tech project number 457789. / Master of Science

Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R-2, are 0.98 for pH from nitrate (pH(N)) and 0.97 for pH from oxygen (pH(Ox)) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.

Even at 3.3 ppb, seawater contains a uranium supply large enough to power the world’s nuclear fleet for 13,000 years. This large supply has prompted interest in technologies for recovering uranium from seawater. Since the 1960’s, economic models of such technologies have failed to produce an economically competitive strategy when compared to conventional uranium recovery from terrestrial mining. Thus, uranium from seawater is researched as a potential price ceiling because of the large supply but high recovery cost. Such an upper bound is still valuable research because it allows for more certainty in uranium prices for planning, research, development and deployment of nuclear power systems. This thesis explores past cost estimates for uranium recovery from seawater and adds a new cost estimate to the pool of literature. The past estimates showed a development from systems that actively moved seawater to systems that allowed adsorbent to sit passively in seawater. The adsorbent material changed from hydrous titanium oxide to the higher-capacity amidoxime ligand. Capacity was the strongest driver of cost. Early models with the amidoxime ligand used an acrylic substrate or backbone. This substrate was later replaced by polyethylene because of its increased durability and lower cost. However, each of those materials could contribute to the problem of plastics in the ocean. The new technology assessed for cost in this paper attempts to address the plastics concern by replacing the plastic with a high molecular weight chitin nanomat as the substrate for the amidoxime ligand. The cost assessment showed the technology is presently cost prohibitive largely due to the adsorption capacity and chitin nanomat production costs. To increase capacity, the grafting efficiency onto the chitin substrate must be improved in order to achieve capacities comparable to those observed for the amidoxime-polyethylene adsorbent. To reduce chitin nanomat production costs, the ionic liquid (IL) consumption must be reduced and the recyclability of IL must be achieved. / text

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