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

The effects of various pressure treatments (OK, 30K, 60K, 75K psig) and packing medium (water or cocktail sauce) on shucked oysters were investigated. The pH, moisture content, microbiological tests (including aerobic plate count (APC) and anaerobic plate count (ANPC)), enzyme assays (i.e. α-amylase, β-amylase, lipase and peroxidase activities) were conducted to determine the quality of pressure treated oysters during a 6 week shelf-life study. The moisture content in water-packed oysters under OK, 30K, 60K and 75K psig pressure treatments was slightly increased during storage, while that in cocktail sauce-packed samples was significantly lower than in water-packed samples. Addition of cocktail sauce lowered the pH in oysters, which effectively inhibited the microbial growth, but altered the appearance. The microbial shelf-life of water-packed oysters with pressure treatment of 60K and 75K psig was extended several weeks compared with the controls while 30K psig had less of an effect. Pressure treatments did not inhibit enzyme activities in oysters, however, the addition of cocktail sauce was significant in inhibiting the enzyme activities in this study. / Graduation date: 2000

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This article discusses the application of laser to trim the outer surface from tree-ring increment cores in preparation for dendrochemistry of certain metals. A source of contamination specific to dendrochemistry of metals is metal constituents, such as iron, tungsten, chromium, nickel, and cobalt, coming off tools used to collect and process cores and adhering to the sample surface. One method to eliminate this contamination is to trim off the outer surface of cores using laser. To test this application of laser, three tree-ring increment cores were collected from each of three trees. For each tree, one core was trimmed using a CO2 laser, one core was trimmed using a stainless steel razor blade, and one core was left untrimmed. The resultant cores were measured for metals using acid dissolution inductively coupled plasma mass spectroscopy. Trimmed cores had on average one-third the content of iron, tungsten, and chromium than that of untrimmed cores. Laser-trimmed cores had less of these metals than razor-trimmed cores. Razor-trimmed cores also had measurable nickel, but laser-trimmed cores had no nickel. Laser trimming is an ideal solution to potential contamination of cores with metals from increment borers without imparting other contamination from tools such as razor blades.

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