Perchlorate contamination is widespread. Perchlorate, a water contaminant, disrupts iodide uptake to the thyroid, inhibiting growth and mental development. Recent studies have demonstrated autohydrogenotrophic perchlorate reduction to chloride. Hydrogen gas can be produced in-situ via the corrosion of zero-valent iron (ZVI), thereby avoiding problems related to the low aqueous solubility of hydrogen gas. The presence of nitrate has been shown inhibit autohydrogenotrophic perchlorate reduction. However, no studies have modeled the effects of nitrate on autohydrogenotrophic perchlorate biokinetics or developed a model to function as a design tool to predict long-term performance of ZVI/biotic perchlorate treatment systems in the presence of nitrate. Batch experiments demonstrated the presence of nitrate significantly inhibited perchlorate degradation by an autohydrogenotrophic microbial consortium. However, the consortium was capable of significant perchlorate reduction while the bulk of the nitrate was still present. A modified competitive inhibition model successfully predicted autohydrogenotrophic perchlorate degradation in the presence of nitrate. The model describes perchlorate degradation as a function of the biomass, perchlorate, hydrogen, and nitrate concentrations, as well as the single-component perchlorate, hydrogen, and nitrate half-saturation coefficients and perchlorate maximum substrate utilization rate. To obtain the single-component parameters, a series of batch experiments were performed under perchlorate-, nitrate-, and hydrogen-limiting conditions. The single-component biokinetic parameters and model predictions indicate the consortium could treat perchlorate-contaminated water with concentrations in the low hundreds of μg/L and in states with perchlorate treatment goals in the low μg/L range. The consortium biokinetic parameters and modified competitive inhibition model were used in the development of an AQUASIM based biofilm model. The model also integrated physical parameters, ZVI hydrogen production, and abiotic nitrate reduction. The model was calibrated using the long-term performance results of a laboratory-scale ZVI/biotic column. Both laboratory and modeling results showed when the column becomes hydrogen-limited, the presence of nitrate decreases perchlorate removal efficiency. Full-scale simulations demonstrated the model could prove useful as a predictive design tool. Simulations suggest that a permeable reactive barrier that includes 10% ZVI and additional media capable of pH buffering could remove typical contaminated ground water concentrations of perchlorate in the presence of typical oxygen and nitrate concentrations. / text

Perchlorate is a threat to public health through water but also food. However, there is no effective chemical treatment process which can destroy perchlorate found in groundwater and surface water. Thus, there is growing interest in developing effective technologies, especially chemical treatments, to completely destroy trace levels of perchlorate present in drinking and groundwater. The research on perchlorate reduction by zero-valent titanium (Ti(0)) showed that perchlorate was effectively reduced to chloride using electrochemically developed pitting corrosion on Ti(0). Perchlorate reduction was believed to be caused by an active reductant (dissolved Ti(II)) during the pitting corrosion of Ti(0). The rate of perchlorate reduction was independent on the imposed potential as long as the potential was maintained above the pitting potential of Ti(0), but it was proportional to the applied current. The perchlorate reduction on the pitting developed Ti(0) was inhibited by the presence of chloride and bromide. Inhibition mechanism of perchlorate reduction inhibition was believed to be caused either by competitive adsorption of aggressive anions on bare Ti(0) surface or Ti(II) consumption by electrochemically produced chlorine. Kinetic models were developed based surface coverage of aggressive anions on bare Ti(0) and Ti(II) oxidation by chlorine. These kinetic models supported the perchlorate concentration change in the solution, but Ti(II) consumption model was not able to predict chloride concentration due to insufficient information describing complex nature of pitting on Ti(0). These results shown in this research demonstrate that pitting corrosion developed Ti(0) has the capability to chemically reduce perchlorate present in natural water and engineered systems as well as possible problems associated with electric input. This research may be a starting point for development of a new treatment process that applies titanium or titanium metal ions as a chemical reductant to abate contaminants present in natural and engineering systems. Further developments can be achieved by alloying titanium metal with other metals such as iron and aluminum, and finding a methodology producing stable Ti(II) in ambient conditions.

The decomposition of Ammonium Perchlorate (AP), a strong oxidizer used in solid rocket propellant, is widely studied in an attempt to increase the burn characteristics of propellants. Many materials have been shown to catalyze its decomposition, but little is known about the mechanism by which AP decomposition becomes catalyzed. In this study, Boron Nitride (BN) nanostructures, a material previously unknown to act as a catalyst, is studied. The decomposition reaction is studied by thermo-gravimetric analysis / differential scanning calorimetry, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The goal of this study is to discover the activation energy of this catalyst reaction, intermediary products of the reaction, mechanism of reaction and end state of the boron nitride nanostructures (ie, if the BN acts as a true catalyst, or participates on the overall reaction and has some end state that*s different from the initial state). Four variations of BN have been synthesized using a hydrothermal process; BN nanoribbons, Boron Rich BN, Nitrogen-Rich BN, and high surface area BN. It is shown that the decomposition of AP is significantly altered when in the presence of BN and the mechanism through which BN catalyzes the decomposition is most likely the presence of oxidized nitrogen species on the BN material.

No description available.

Energetic materials are a class of material that have large amounts of chemical energy stored within their molecular structure. This energy is released upon decomposition, generally in the form of rapidly expanding, hot gases. They are therefore used for a wide range of applications such as; mining, military, and space exploration, and there is therefore a strong desire to improve the overall performance and safety of such materials. On account of reduced sensitivity to initiation by shock and impact, 2,4-dinitroanisole (DNAN) is a potential replacement for 2,4,6-trinitrotoluene (TNT) in melt-cast formulations for military applications. However, up to 15 % irreversible growth of DNAN has been previously observed upon thermal cycling and is a key reason why DNAN has not yet been universally accepted as a replacement for TNT. DNAN exhibits a complex system of polymorphism. One particular transition from DNAN-II to DNAN-III, which occurs at 266 K, has been observed in these studies to cause 8 - 10 % growth of DNAN-II pellets when temperature cycled for 30 cycles between 256 K and 276 K. What was even more concerning was the appearance of cracking of DNAN pellets after being temperature cycled. Doping the crystal structure of DNAN-II with related molecules, such as 2,4-dinitrotoluene or 2,4-dinitroaniline, was investigated in order to probe how steric and electronic factors affect the transition. The addition of varying amounts of 2,4-dinitroaniline suppressed this transition to varying extents and ultimately as low as 150 K with 10 mol% 2,4-dinitroaniline, and potentially eliminated entirely. This doped material has been designated as phase-stabilised DNAN (PS-DNAN). Temperature cycling of PS-DNAN was conducted over the same 256-276 K range, and this material showed no evidence of irreversible growth compared to undoped DNAN pellets, on account of suppression of the II-III transition. The production of PS-DNAN is therefore a possible route to avoiding problematic irreversible growth in DNAN formulations. Melt-casting of DNAN in a sealed environment consistently results in the metastable form-II, which has proven to be stable for in excess of 32 weeks. However, exposure to seeds of form-I, either via deliberate or accidental seeding, rapidly converted the material to the thermodynamically more stable form-I. This transition was accelerated by increasing temperature which rapidly converted pellets of DNAN-II to DNAN-I. When DNAN-I pellets were temperature cycled, they did not undergo a transition to form-III, and as a result did not illustrate irreversible growth. This presents another approach to avoiding problematic growth in DNAN-based materials. Whilst being one of the most widely used oxidisers in propellant formulations, ammonium perchlorate (AP) has several issues; the formation of porous ammonium perchlorate (PAP) can seriously affect the sensitivity of propellants, the hygroscopicity of AP makes handling and manufacture of formulations difficult, and spherical AP exhibits poor binding properties to the polymer binders used in propellant formulations. Several different approaches were taken to combat these issues. Co-crystallisation of AP was attempted in order to produce new AP co-crystals with reduced reactivity towards the formation of PAP. A theoretical based approach using COSMOtherm was used for rapid screening and selection of potential co-formers to be used in lab-based co-crystallisation trials. Co-crystallisation was attempted using multiple stoichiometries and multiple solvents by solvent evaporation, cooling crystallisation, and Resonant Acoustic Mixing methods. Unfortunately no new co-crystals were obtained, presumably on account of the ionic nature of AP which makes co-crystallisation difficult. The mass of untreated AP increased by 0.027% in a humid environment (90% RH) due to the uptake of water, which resulted in significant caking and hence hindering the processability of AP. In an attempt to counteract the hygroscopicity and improve the processability of AP, particles of AP were coated in graphene nanoplatelets using the technique of Resonant Acoustic Mixing. Low mixing energy (G-force) (30 G) resulted in poor coating of AP, but the flowability of this mixure after exposure to moisture was significantly enhanced, most probably as a result of graphene acting as an effective lubricant. Higher mixing energy (90-100 G) was required to break up agglomerates of graphene nanoplatelets and resulted in AP particles efficiently coated with graphene (APGR). Differential scanning calorimetry showed that the energy released upon decomposition of APGR was greater than pure AP, or AP mixed with graphene, due to the intimacy of the AP particle surface and the graphene coating.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Daniel K. Cha, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Perchlorate is known to adversely affect the thyroid gland functions including iodide take up, thus perchlorate should be removed from drinking water. Bituminous coal-based activated carbon (AC) has been used for perchlorate removal in past years. Virgin carbon and carbon modified by oxidation with HNO3, NaOH and H2O2 were examined in this study for their ability to remove perchlorate by reduction or adsorption mechanisms. Surface functional groups formed on the modified AC (MAC) were examined with diffuse reflectance infrared spectrometry. Inhibition of perchlorate removal onto MAC by various anions ( - Cl , - 3 NO , and - 2 4 SO ) and solution pH (4.5, 7.2 and 10.5) were examined to characterize the MACs before an electrochemical reaction was performed. Surface functional groups were increased by oxidation. Groups that were found on the carbon include, but are not limited to lactone, quinine, carboxylate, and nitrogenoxygen groups. The effect of pH on removal of perchlorate by MAC was greatly affected by the change in the zero point charge (ZPC) induced on the carbon by modification. Virgin carbon also experienced difficulty in removing perchlorate when solution pH was above the ZPC. Anion inhibition varied with the modification process. - 3 NO inhibited perchlorate removal only by the virgin carbon. The other anions showed no major effects on the removal efficiency of perchlorate by the carbons. Electrochemical processes did not show favorable results in removal of perchlorate. The dominant mechanism of perchlorate removal during desorption tests was adsorption onto the carbon surfaces via ion exchange.

Perchlorate is one of the major emerging contaminants of concern and has been found in soil and water systems throughout the United States. Human exposures to perchlorate could occur by ingestion of contaminated water and food as well as by skin contact. Studies show that perchlorate blocks the sodium iodide symporter (NIS) protein in human body, which results in several diseases. It has been demonstrated that perchlorate can be removed by Advanced Reduction Processes (ARPs) that combine chemical reductants (e.g. sulfite) with activating methods (e.g. UV light) in order to produce highly reactive reducing free radicals that are capable of rapid and effective perchlorate reduction. However, other compounds in a real system might inhibit or promote this reduction process. Natural organic matter (NOM) widely exists in the environment and it can absorb UV light, so it has the potential to influence the process of perchlorate reduction by ARPs that use UV light as the activating method. Therefore, batch experiments were conducted to obtain data on the impacts of natural organic matter and light intensity on destruction of perchlorate by the ARPs that use sulfite activated by ultraviolet light produced by low-pressure mercury lamps or KrCl excimer lamps. The results indicate that NOM strongly inhibits perchlorate removal by either the sulfite/UV-KrCl or the sulfite/UV-L ARP, because NOM competes with sulfite for UV light and can possibly scavenge sulfite radicals. Even though the absorbance of sulfite is much higher at UV wavelength of 222 nm than that at 254 nm, the results indicate that a higher portion of perchlorate was removed with the UV-L lamp than with the UV-KrCl lamp. The results of this study will help to develop the proper way to apply the ARPs in a real wastewater treatment plant.

Thesis (Ph. D.)--University of Michigan, 1926.

Thesis (Ph. D.)--University of Michigan, 1926.