Mass balance assessment for mercury in Lake Champlain

A mass balance model for mercury in Lake Champlain was developed in an effort to understand the sources, inventories, concentrations, and effects of mercury (Hg) contamination in the lake ecosystem. To construct the mass balance model, air, water, and sediment were sampled as a part of this project and other research/monitoring projects in the Lake Champlain Basin. This project produced a STELLA-based computer model and quantitative apportionments of the principal input and output pathways of Hg for each of 13 segments in the lake. The model Hg concentrations in the lake were consistent with measured concentrations. Specifically, the modeling identified surface water inflows as the largest direct contributor of Hg into the lake. Direct wet deposition to the lake was the second largest source of Hg followed by direct dry deposition. Volatilization and sedimentation losses were identified as the two major removal mechanisms. This study significantly improves previous estimates of the relative importance of Hg input pathways and of wet and dry deposition fluxes of Hg into Lake Champlain. It also provides new estimates of volatilization fluxes across different lake segments and sedimentation loss in the lake.     

Increased remineralization of tooth enamel by milk containing added casein phosphopeptide-amorphous calcium phosphate

Casein phosphopeptide amorphous calcium phosphate nano-complexes (CPP-ACP) in chewing gum, lozenges and mouthrinses have been shown to re-mineralize enamel subsurface lesions in human in situ experiments. The aim of this double-blind, randomized clinical study was to investigate the capacity of CPP-ACP added to bovine milk to re-mineralize enamel subsurface lesions in situ. Ten subjects drank milk containing either 2.0 or 5.0 g CPP-ACP/l or a control milk whilst wearing removable appliances with enamel slabs containing subsurface demineralized lesions. Each 200 ml milk sample was consumed once a day for each weekday over three consecutive weeks. After each treatment and one weeks rest the subjects crossed over to the other treatments. At the completion of the treatments the enamel slabs were removed and remineralization determined using microradiography and microdensitometry. The results demonstrated that all three milk samples re-mineralized enamel subsurface lesions. However, the milk samples containing CPP-ACP produced significantly greater remineralization than the control milk. The re-mineralizing effect of CPP-ACP in milk was dose-dependent with 2.0 and 5.0 g CPP-ACP/l producing an increase in mineral content of 70 and 148%, respectively, relative to the control milk. The differences in remineralization following exposure to the three milk samples were all statistically significant (P<0.001). In conclusion, this study shows that the addition of 2.0-5.0 g CPP-ACP/l to milk substantially increases its ability to re-mineralize enamel subsurface lesions.     

Hurricane Katrina's impact on New Orleans soils treated with low Lead Mississippi River alluvium

Before Hurricane Katrina flooded 80% of New Orleans, 25 heavily Pb contaminated properties were treated with 15 cm of low Pb Mississippi River alluvium from the Bonnet Carré Spillway (BCS). Four phases of soil collection on the properties included pretreatment (phase 1) median surface soil Pb was 1051 mg/kg (range 5-19 627); after BCS cover (phase 2) the median soil Pb decreased to 6.3 mg/ kg (range 3-18); just before Katrina, a soil collection was partially completed (phase 3); and finally, a post-Katrina collection (phase 4) on all 25 properties. Twenty-three properties were flooded. The objective was to compare Pb changes of phases 2 and 3 pre-Katrina with the post-Katrina (phase 4) soil collection. The post-Katrina soil Pb (phase 4) (median of 16.3, range 5.5-1,155) increased significantly (P-value = 3.7 x 10(-10)) from the clean soil, phase 2 results. Matched soil samples collected in phase 3 before flooding and phase 4 after flooding showed that on initially vacant lots the amounts of Pb were not significantly different (P-value = 0.97); but, on properties with homes, the changes were significant (P-value = 0.03). After catastrophic flooding, the clean soil remained relatively undisturbed; the soil Pb changes were small with increases of median Pb of 12 and 6 mg/kg for vacant lots and properties with homes, respectively. Processes accounting for Pb increases include Pb-based paint abatement on one property, home construction on the vacant lots, and resuspension and deposition of Pb dust. As part of the post-Katrina recovery, the combined benefits of Pb-safe paint abatement or renovation and clean soil cover should outweigh the estimated annual cost of Pb poisoning of children returning to New Orleans.     

Methane cracking using Ni supported on porous and non-porous alumina catalysts

Porous and non-porous alumina catalysts were used as nickel supports to catalyze methane cracking. Different operating parameters were studied in a thermal gravimetric analyzer, including methane and hydrogen partial pressures, temperature and flow rate. During CH₄ cracking, carbon builds up on the catalyst surface and therefore the catalyst requires periodic regeneration. Cycling tests were performed, using air during the regeneration phase to burn off the carbon. The results showed that the non-porous catalyst performed better than the porous catalyst in terms of cracking during the first cycle. Full regeneration of the catalysts by oxidizing the deposited carbon was achieved at 550 °C, while oxidation was very slow at 500 °C. After full regeneration, the performance of the porous catalyst became considerably better than the non-porous. The porous catalyst kept its activity for 24 cracking/regeneration cycles, while the non-porous catalyst lost half of its activity by the second cracking cycle and almost all of its activity after six cycles. NiAl₂O₄ formation and Ni sintering caused the non-porous catalyst activity loss. TPO results showed that two carbon types were deposited on the catalysts, namely Cβ and Cγ, where Cβ is more active than Cγ.     

Hydrogen production by methane cracking using Ni-supported catalysts in a fluidized bed

Nickel, supported on porous alumina (γAl₂O₃), non-porous alumina (αAl₂O₃), and porous silica, was used to catalyze methane cracking in a fluidized bed reactor for hydrogen production. The effects of temperature, PCH₄${\text{P}}_{{\text{CH}}_4}$, and particle diameter, and their interactions, on methane conversion were studied with each catalyst. Temperature was the dominant parameter affecting the hydrogen production rate for all catalysts and particle diameter had the strongest effect on the total amount of carbon deposited. Maximum methane conversion as a function of support type followed the order Ni/SiO₂ > Ni/αAl₂O₃ > Ni/γAl₂O₃. Nonetheless, better fluidization quality was obtained with Ni/γAl₂O₃. Methane conversion was increased by increasing temperature and particle size from 108 to 275 μm due to better fluidization achieved with 275 μm particles. Increasing the flow rate and methane partial pressure (PCH₄${\text{P}}_{{\text{CH}}_4}$) caused a drop in methane conversion. Tests were also run in a fixed bed reactor, and at constant weight hourly space velocity (WHSV), higher conversion was achieved in the fixed bed, but at the same time faster deactivation occurred since a higher methane conversion led to increase in carbon filament and encapsulating carbon formation rates. A critical problem with the fixed bed was the pressure build-up inside the reactor due to carbon accumulation. Finally, a series of cracking/regeneration cycle experiments were carried out in the fluidized bed reactor. The regeneration was performed through product carbon gasification in air. Ni/αAl₂O₃ and Ni/γAl₂O₃ activity decreased significantly with the first regeneration, which is attributed to Ni sintering during exothermic regeneration/carbon oxidation. However, Ni/SiO₂ was thermally stable over at least three cracking/regeneration cycles, but mechanical attrition was observed.     

Optimal experimental conditions for hydrogen production using low voltage electrooxidation of organic wastewater feedstock

The dependence of electrooxidation on experimental conditions of organic molecules was investigated to optimize the production of hydrogen from potential wastewater sources using low voltage sources (∼1 V dc). Electrooxidation on platinum, gold, and stainless steel anodes with hydrogen production on the cathode was investigated using several different organic reductants, including: methanol, ethanol, glycerol, isopropanol, propanal, glycerol, glucose, sucrose, citric acid, and propionic acid. The electrolyte pH was varied from 2 to 12 in a 1 M Na₂SO₄ supporting solution. At 1 V, glycerol, citric acid, ethanol and methanol were found to yield the highest currents at low pH values (pH 2 and 7) on platinum electrode, glucose on gold electrode at pH 12 in 1 M Na₂SO₄ solution produced the highest total current density at 1 V with measured Faradaic efficiency for 1 M glucose of 70%. The hydrogen energy production efficiency was 86%. Practical limitations of glucose oxidation at optimum experimental conditions are discussed.     

SrCe0.7Zr0.2Eu0.1O3-based hydrogen transport water gas shift reactor

Proton-transport-membrane water gas shift (WGS) reactors, based on thin dense SrCe_0.7Zr_0.2Eu_0.1O_3−δ membranes on tubular Ni–SrCe_0.8Zr_0.2O_3−δ supports, were developed to increase H₂ yields relative to thermodynamic limitations. Pure H₂ permeate, total H₂ production, and reactor side CO conversion and H₂/CO effluent ratio were measured as a function of temperature, flow rate, CO concentration and H₂O/CO feed ratios. CO conversion, total H₂ production and yield, and the H₂/CO in the reactor side effluent increased with increasing temperature and H₂O/CO feed ratios. CO conversions of 84% and 90% were achieved at 900 °C with H₂O/CO feed ratios of 1/1 and 2/1, respectively. These respective 77% and 44% increases in CO conversion compared to feed gas condition thermodynamics resulted in 73% and 42% increases in H₂ production. Permeated H₂ and total H₂ production increased with increasing flow rate and CO concentration. Finally, membrane stability under WGS conditions was significantly improved by Zr substitution.     

Hydrocolloids as emulsifiers and emulsion stabilizers

We consider the essential molecular features of hydrocolloids having the ability to act as emulsifying agents and emulsion stabilizing agents. The criteria for effectiveness in protecting newly formed droplets against flocculation and coalescence are contrasted with the requirements to maintain long-term stability against aggregation, creaming and Ostwald ripening. To illustrate various aspects of stability behaviour, comparison is made between the physico-chemical characteristics of hydrocolloid emulsifying agents and those of other kinds of food emulsifying agents – surfactants, proteins and nanoparticles. Interfacial complexation between protein and polysaccharide may occur through covalent bonding or electrostatic bonding. For the case of electrostatic protein–polysaccharide complexes, the interfacial nanostructure and the stabilizing properties of the adsorbed layer are dependent, amongst other things, on the sequence of adsorption of the biopolymers to the emulsion droplet surface.     

Smearing of soft cheese with Enterococcus faecium WHE 81, a multi-bacteriocin producer,against Listeria monocytogenes

Enterococcus faecium WHE 81, a multi-bacteriocin producer, was tested for its antimicrobial activity on Listeria monocytogenes in Munster cheese, a red smear soft cheese. The naturally delayed and superficial contamination of this type of cheese allowed the use of E. faecium WHE 81 at the beginning of the ripening as a surface culture. A brine solution inoculated at 10⁵ CFU of E. faecium WHE 81 per mL was sprayed on the cheese surface during the first smearing operation. On day 7, smearing of cheese samples with a brine solution at 10² CFU of L. monocytogenes per mL yielded initial cell counts of approximately 50 CFU g⁻¹ of the pathogen on the cheese surface. Although, in some instances, L. monocytogenes could survive (<50 CFU g⁻¹) in the presence of E. faecium WHE 81, it was unable to initiate growth. In control samples however, L. monocytogenes counts often exceeded 10⁴ CFU g⁻¹. In other respects, E. faecium WHE 81, which naturally existed in Munster cheese, did not adversely impact on the ripening process.