Digital Commons Network^™

Mathematical Model Of Arsenic Adsorption In A Modified Zeolite / Microfiltration System, Miles B. Beamguard

USF Tampa Graduate Theses and Dissertations

Carcinogenic health concerns over arsenic in drinking water caused the USEPA to reduce the maximum contaminant level (MCL) from 50 to 10 ppb, effective on January 23, 2006. This has forced many smaller utilities into expensive treatment or discontinuation of water distribution. Researchers throughout the world are working to develop an inexpensive method for arsenic removal to meet this MCL. Aluminum silicates, or zeolites, are naturally occurring ionic sorbents. Modification of a zeolite may enhance adsorption capacities and ion selectivity. This research investigates the arsenic adsorption capacities of a modified Chabazite. This adsorption, coupled with a hollow fiber, microfiltration membrane …

Heme Biosynthesis: Structure-Activity Studies Of Murine Ferrochelatase, Zhen Shi

USF Tampa Graduate Theses and Dissertations

Ferrochelatase catalyzes the terminal step of heme biosynthesis by inserting ferrous iron into protoporphyrin IX. The current study is aimed at understanding the structural basis of porphyrin binding and distortion in ferrochelatase-catalyzed reaction by functional analysis of a highly conserved active site loop motif. The loop was shown to contact bound porphyrin based on crystallographic and molecular modelling observations, and its role in murine ferrochelatase was assessed by random mutagenesis and steady-state kinetic analysis. To overcome the limitations of conventional kinetic assay methods for ferrochelatase, a continuous assay was developed by monitoring porphyrin fluorescence decrease using natural substrates ferrous iron …

Saharan Dust And Phosphatic Fidelity: A Three Dimensional Biogeochemical Model Of Trichodesmium On The West Florida Shelf, Jason M. Lenes

USF Tampa Graduate Theses and Dissertations

The availability of iron within the surface waters of the broad, oligotrophic West Florida shelf (WFS) controls periodic blooms of the pelagic marine cyanobacterium Trichodesmium. Summer delivery of iron (Fe), in the form of Saharan dust, alleviates this growth constraint, shifting limitation to the efficiency of phosphorus (P) cycles. Florida's rivers drain Miocene phosphorus deposits to supply the WFS with freshwater nutrient supplies at molar dissolved inorganic nitrogen/phosphate (DIN/PO4) ratios of less than 6. These diazotrophs draw upon ubiquitous stocks of dissolved nitrogen gas, once stimulated by Fe-deposition within P-replete waters of the West Florida shelf. An extensive in situ …

Influence Of Solution And Surface Chemistry On Yttrium And Rare Earth Element Sorption, Kelly Ann Quinn

USF Tampa Graduate Theses and Dissertations

The sorption behavior of yttrium and the rare earth elements (YREEs) was investigated using a variety of hydroxide precipitates over a range of solution conditions. Experiments with amorphous hydroxides of Al, Ga, and In were conducted at constant pH (~6.0) and constant ionic strength (I = 0.01 M), while YREE sorption by amorphous ferric hydroxide was examined over a range of ionic strength (0.01 M <̲ I <̲ 0.09 M), pH (3.9 <̲ pH <̲ 7.1), carbonate concentration (0 M <̲ [CO32-]T <̲ 150 micro-M), and temperature (10°C <̲ T <̲ 40°C). Sorption results were quantified via distribution coefficients, expressed as ratios of YREE concentrations between the solid and the solution, and normalized to concentrations of the sorptive solid substrate. Distribution coefficient patterns for Al, Ga, and In hydroxides were well correlated with the pattern for YREE hydrolysis.

In contrast, amorphous ferric hydroxide developed a distinct pattern that was different than those for Al, Ga, and In precipitates but similar to the pattern predicted for natural marine particles. YREE sorption was shown to …