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Walter J Weber

Publications and source records attributed to Walter J Weber.

At least 19 recordsLinked to original sources
PubMed2006

Breakeven costs for distributed advanced technology water-treatment systems.

Breakeven costs associated with the strategic distribution of advanced treatment units in a water supply network to manage network-derived water quality degradation were investigated. Disinfections by-product (DBP) formation was used as a representative water quality degradation parameter. A basic DBP formation model was used to predict that fraction of residential service population receiving water degraded below required quality levels within a hypothetical water utility service population. The costs of upgrading centralized treatment facilities to meet DBP water quality standards were estimated and then apportioned over that population fraction to estimate breakeven or equivalent cost allowances for an alternative distributed treatment approach. Breakeven costs for single-connection treatment units were calculated for a range of service populations. A sensitivity analysis of the impacts of various network parameters on breakeven costs revealed the existence of singularities--sudden shifts in optimal technology selection--resulting from relatively small variations in required treatment levels.

Costs and Cost Analysis↗
PubMed2006

Quantitative structure-activity relationship based quantification of the impacts of enzyme-substrate binding on rates of peroxidase-mediated reactions of estrogenic phenolic chemicals.

The initial rates of horseradish peroxidase (HRP)-mediated enzymatic reactions of 15 assorted aqueous phase phenolic chemicals were studied. The associated reaction rate constants were found to correlate quantitatively with two independent variables: the highest-occupied molecular orbital energy (E(HOMO)) defining the intrinsic redox reactivities of the phenolic substrates and the distance between a substrate and the deltaN of HIS42's imidazole ring in an HRP/substrate binding complex, obtained through molecular simulations. Highly correlated quantitative structure-activity relationship (QSAR) equations were thus developed. This work provides insights into the impacts that HRP/substrate binding may have on HRP-mediated reactions. Additionally, the QSAR equations developed in the work may serve as a basis to further explore the potential use of HRP-mediated reactions in the treatment of estrogenic contaminants, and they constitute an important tool for redesign and screening of potential proteomic modifications to the wild-type HRP structure intended to enhance reactivity toward selected substrates.

Estrogens↗
PubMed2006

Development of engineered natural organic sorbents for environmental applications. 1. Materials, approaches, and characterizations.

A technology for effecting diagenesis-like transformations in young natural organic matter (NOM) derived from common plant materials is described. Thirteen such materials were processed in liquid-phase water at superheated temperature/pressure conditions. In all cases significant changes in the physical and chemical properties of the raw NOM source materials occurred. Their carbon and nitrogen contents increased, their hydrogen and oxygen contents decreased, their surface areas initially increased dramatically, then sharply decreased, and their bulk densities and equilibrated aqueous phase pH values increased as functions of increasing temperature and pressure. Spectroscopic analyses confirmed marked changes in the molecular structures of the NOMs resulting from superheated water processing; e.g., fractions of alkyl and aromatic carbons increased while oxygen-associated functional organic carbon decreased. These changes in elemental composition and molecular structure indicate that the organic fractions of the raw materials became less polar, increasingly condensed, and more aromatic as a result of the reactions induced by superheated water processing, the changes correlating directly with the temperature/ pressure conditions employed. The results presented confirm that the long-term biogeochemical processes that in nature effect geologically slow advances in the chemical states of organic carbon can be simulated and markedly accelerated by superheated water processing.

Ecosystem↗
PubMed2006

Development of engineered natural organic sorbents for environmental applications. 2. Sorption characteristics and capacities with respect to phenanthrene.

The effects of superheated water processing on enhancement of phenanthrene sorption by various source materials of natural organic matter (NOM) were systematically examined. Sorption capacities and subsequent phenanthrene retention characteristics of all organic materials tested were markedly increased by superheated water processing. Temperature effects on enhancement of the sorption behaviors of the test materials were greater than those of processing time, moisture content, and the presence of mineral catalysts. Greatest enhancement was observed for processing at 250 degrees C for 5 h with a moisture content of 50%. Strong correlations of sorption capacities and isotherm nonlinearities with processing temperature, and with the atomic ratios of oxygen to carbon (O/C), aromaticity, and hydrophobicity of the processed materials were observed. The sorption/desorption hysteresis indices of the processed materials also increased linearly with processing temperatures and O/C ratios. This is consistent with our observations of increased condensation and aromatization of NOM during superheated water processing presented in the first paper of this series. The relationships described provide direct experimental evidence that the sorption-desorption properties of NOM geosorbents are closely related to their degree of aromatization and condensation, and the work suggests strong potential for production of efficient and cost-effective engineered natural organic sorbents for environmental applications.

Ecology↗
PubMed2005

Reduction of disinfection byproduct formation by molecular reconfiguration of the fulvic constituents of natural background organic matter.

Experiments were performed to assess the effects of treating the fulvic acid fractions of background natural organic matter (NOM) by catalyst-induced oxidative coupling reactions. Changes in the molecular characteristics of the fulvic acids and related disinfection byproduct formation potentials of these important NOM constituents were investigated. The coupling reactions were induced by addition of horseradish peroxidase (HRP) and hydrogen peroxide to aqueous solutions of the fulvic acids (FAs) in semicontinuous flow reactors. Subsequent removal of organic matter by ultrafiltration was found to be markedly enhanced for FA solutions subjected to oxidative coupling treatment. Uniform formation condition tests further indicated that the disinfection byproducts formed upon chlorination of FAs treated via induced oxidative coupling were reduced significantly on a unit carbon basis relative to those formed upon chlorination of their untreated counterparts. Spectroscopic examinations revealed thatthe FA molecules were effectively reconfigured in the oxidative coupling reactions. Substantial conversion of aromatic hydroxyl groups into ether-bonded moieties is evident, and a loss of primary amine groups, probably through conversion into secondary or tertiary amines, was also observed. These conversions apparently result in cross-linking of the natural FA moieties to form stable species of larger sizes, thus rendering them more readily removable by ultrafiltration and less reactive with chlorine. The results of the study may be interpreted as indicating that catalytically induced oxidative coupling reactions of the type conducted in this work can be combined with ultrafiltration to provide an effective scheme for removal of disinfection byproduct precursors.

Adsorption↗
PubMed2005

Transformation and removal of bisphenol A from aqueous phase via peroxidase mediated oxidative coupling reactions: efficacy, products, and pathways.

A systematic investigation of the feasibility of and mechanisms for transformation and removal of bisphenol A (BPA) from aqueous phase via oxidative coupling mediated by horseradish peroxidase is described. It is demonstrated that BPA can be effectively transformed into precipitable solid products in HRP-mediated oxidative coupling reactions. A total of 13 reaction intermediates and products are identified using LC/MS and GC/MS techniques, and with the help of ab initio molecular modeling, detailed reaction pathways are proposed. It is postulated that two BPA radicals are coupled primarily by the interaction of an oxygen atom on one radical and propyl-substituted aromatic carbon atom on another, followed by elimination of an isopropylphenol carboncation. All intermediates or products detected can be interpreted as resulting from either coupling or substitution reactions between BPA and other intermediates or products. The efficacy of the reaction at low substrate concentrations is demonstrated using a sensitive analytical procedure involving solid-phase extractions. The results suggest that catalyzed oxidative coupling reactions may be important natural transformation pathways for estrogenic phenolic compounds and indicate their potential use as an efficient means for removal of estrogenicity from waters and wastewaters.

Benzhydryl Compounds↗
PubMed2005

Accelerated transformation and deactivation of erythromycin in superheated water. 2. Transformation reactions and bioassays.

The work presented in this second part of a two-part series on the accelerated transformation of erythromycin in superheated water focuses on the chemical nature and resultant antimicrobial implications of the overall reaction observed. Analyses of reactor effluents employing infrared spectroscopy and liquid chromatography/mass spectrometry indicated that the initial step in the decomposition pathway is one of dehydration. Subsequent hydrolysis in the presence of an acetate buffer appeared to result in the loss of the sugar cladinose. Chemical transformation under superheated conditions was tied to the loss of antibiotic function by an agar dilution test. The sensitivity of this test was verified by determination of the minimum inhibitory concentration (MIC) of erythromycin corresponding to each of two test microorganisms. MIC values for the selected strains of Escherichia coli and Bacillus subtilis were 35 and 0.5 mg/L, respectively. To relate the loss of antimicrobial activity to increased reaction temperature and thus to increased extent of parent compound transformation to microbially benign intermediates, bioassays using E. coli as test microorganism were performed on flow reactor effluents resulting from reaction of initial erythromycin concentrations of 75-150 mg/L.

Amino Sugars↗
PubMed2005

Accelerated transformation and deactivation of erythromycin in superheated water. 1. Temperature effects, transformation rates, and the impacts of dissolved organic matter.

The presence of antibiotics and other pharmaceuticals in the environment is of increasing concern. The stringent treatment of point discharges of antibiotic wastes holds promise as an approach for curtailing growing trends of microbial resistance. The work described in this two-part series explores the use of superheated water as a medium forthe accelerated transformation and deactivation of a specific target antibiotic, erythromycin. Part 1 of the series focuses on parent compound conversion, and Part 2 examines transformation mechanisms and reaction products. This paper, Part 1, highlights the results of reactor studies performed in both batch and flow-through modes. The data presented confirm that accelerated conversion of erythromycin, based on parent compound disappearance as measured by high-pressure liquid chromatography, occurs in water under superheated conditions. Given an initial erythromycin concentration of 50 mg/L, greaterthan 85% apparent conversion was achieved within 30 min in the batch system at all temperatures investigated in the range from 125 to 200 degrees C. The presence of dissolved organic matter extracted from two natural soil materials, at concentrations of 2.5-20 mg/L, was shown to have little effect on the overall extent of transformation of erythromycin in the batch system. The rates of decomposition observed were found to be best described by a psuedo-first-order expression, one in which the rate coefficient increased linearly with increasing initial concentration of the antibiotic. First-order rate behavior was verified in subsequent flow reactor experiments. The temperature dependence of rate was also examined, and an activation energy of 68.8 kJ/mol was determined.

Anti-Bacterial Agents↗
PubMed2005

Optimizing contaminant desorption and bioavailability in dense slurry systems. 2. PAH bioavailability and rates of degradation.

The effects of mechanical mixing on rates of polycyclic aromatic hydrocarbon (PAH) biodegradation in dense geosorbent slurry (67% solids content, w/w) systems were evaluated using laboratory-scale intermittently mixed batch bioreactors. A PAH-contaminated soil and a phenanthrene-sorbed mineral sorbent (alpha-Al2O3) were respectively employed as slurry solids in aerobic and anaerobic biodegradation studies. Both slurries exhibited a characteristic behavior of pseudoplastic non-Newtonian fluids, and the impeller revolution rate and its diameter had dramatic impacts on power and torque requirements in their laminar flow mixing. Rates of phenanthrene biodegradation were markedly enhanced by relatively low-level auger mixing under both aerobic and anaerobic (denitrifying) conditions. Parameters for empirical models correlating biodegradation rate coefficient (k(b)) values to the degree of mixing were similar to those for correlations between mass transfer (desorption) rate coefficient (k(r)) values for rapidly desorbing fractions of soil organic matter and degree of mixing reported in a companion study, supporting a conclusion that performance-efficient and cost-effective enhancements of PAH mass transfer (desorption) and its biodegradation processes can be achieved by the introduction of optimal levels of reactor-scale mechanical mixing.

Aluminum Oxide↗
PubMed2005

Optimizing contaminant desorption and bioavailability in dense slurry systems. 1. Rheology, mechanical mixing, and PAH desorption.

Intermittently mixed batch reactor (IMBR) systems were employed to evaluate the effects of mechanical mixing and corresponding power consumption on rates of phenanthrene desorption from natural and synthetic model sorbent phases to the aqueous phase in dense slurry reactors. Sorbent slurries comprising 57-67% (w/w) solids exhibited non-Newtonian (pseudoplastic) fluid behaviors, with apparent viscosities varying with shear rate. Dimensionless power numbers varied inversely with the Reynolds number under laminar flow conditions, indicating that small increases in mixing revolution number and auger size effect significant increases in power and torque requirements for the mechanical mixing of dense slurries. Rates of release of phenanthrene associated with rapidly desorbing or labile fractions of sorbent organic matter (SOM) to the aqueous phase were markedly enhanced by relatively low-level auger mixing, but significantly less further enhancement was observed as higher levels of mixing were applied. Conversely, desorption of phenanthrene associated with slowly desorbing or resistant fractions of SOM was relatively unaffected by auger mixing, being limited as it is by slow intraparticle-scale diffusion processes that are not enhanced by reactor-scale mixing. The experimental results lead to and support a conclusion that auger mixing at relatively low intensity is an attractive strategy for optimizing dense slurry reactor systems for remediation of hydrophobic organic contaminants associated with labile (rapidly desorbing) fractions of SOM with respect to performance efficiency and cost-effectiveness.

Adsorption↗
PubMed2005

Inactivation of horseradish peroxidase by phenoxyl radical attack.

To test the hypothesis that horseradish peroxidase (HRP) can be inactivated by phenoxyl radicals upon reaction with H(2)O(2)/phenol, we probed HRP-catalyzed phenol oxidation at various phenol/H(2)O(2) concentrations. To this end the total protein, phenolic product, active protein, and iron concentrations in the aqueous phase were determined by protein assay, phenol-(14)C isotopic labeling, resonance Raman and atomic absorption spectroscopy, respectively. Additionally, resonance Raman and FTIR measurements were carried out to probe possible structural changes of the enzyme during the reaction. The data obtained provide the first experimental support for the hypothesis that HRP can be inactivated by a phenoxyl radical attack. The heme macrocycle destruction involving deprivation of the heme iron occurs as a result of the reaction. An intermediate type of the active protein was observed by Raman difference spectra at low concentrations which features a stabilization of the quantum mixed state of the heme iron and a significant amount of phenoxylphenol-type oligomers in solution and probably also in the heme pocket. This work provides a basis for evaluating the relative contributions of different HRP inactivation mechanisms and is thus critical for optimizing engineering applications involving HRP reactions.

Enzyme Activation↗
PubMed2005

Precipitation of enzyme-catalyzed phenol oxidative coupling products: background ion and pH effects.

The effects of solution pH and background ion types and concentrations on the precipitation of polymeric products generated in the catalytically facilitated oxidative coupling of phenol were investigated systematically. The coupling reactions mediated by horseradish peroxidase were carried out under a specific predetermined experimental condition. Acids, bases, and/or selected salts of ions having different valences were then added to the resulting product solutions to adjust pH and ionic conditions. Subsequent analyses of product distributions between dissolved and precipitated forms revealed that ionic conditions and pH significantly impact those distributions, and associated mechanisms are discussed. The findings reported will assist feasibility assessments and process optimization with respect to engineering applications of catalyzed oxidative coupling reactions for wastewater treatment and soil decontamination.

Catalysis↗
PubMed2005

Polycyclic aromatic hydrocarbon behavior in bioactive soil slurry reactors amended with a nonionic surfactant.

The effects of an ethoxylated sorbitan fatty ester nonionic surfactant (Tween 80) on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) were examined by using soil-free and dense-slurry (67% solids content, by wt) systems containing a creosote-contaminated field soil. The dispersed-micelle-phase PAHs in soil-free systems were not readily bioavailable to the mixed consortium of microbes indigenous to the creosote-contaminated soil. Instead, the microbes partially and preferentially utilized readily available portions of the surfactant as carbon sources (16-18% of the initial surfactant dose). This selective microbial attack resulted in destabilization of dispersed-phase micelles and significant decreases in molar solubilization ratio and micelle-water partition coefficient values. Remarkably high dosages (>20 g/L) of Tween 80 were required to enhance mobilization of the sorbed PAHs via micelle association because of the sorption of Tween 80 to the soil employed. The PAHs released from the destabilized micelles in soil-slurry systems either associated with sorbed-phase surfactants or readsorbed to soil organic matter too rapidly to be biologically accessed, even by the acclimated PAH-degrading microbes present. The work provides important new information and practical insights to surfactant solubilization and mobilization technology applications for the bioremediation of PAH-contaminated soils and sediments.

Biodegradation, Environmental↗
PubMed2004

Peroxidase-catalyzed coupling of phenol in the presence of model inorganic and organic solid phases.

Peroxidase-catalyzed oxidative coupling reactions of phenol in aqueous systems variously containing silica sand, cellulose, lignin, and polymethylstyrene were investigated. These four solid phase materials represent a broad spectrum of different natural geosorbent types in terms of their physicochemical characteristics. Each solid was found to influence peroxidase-catalyzed phenol coupling, either by mitigation of enzyme inactivation, by participation in cross-coupling, or by a combination of these two activities. Mitigation of enzyme inactivation was observed for those three of the four model solids found to adsorb the enzyme effectively; i.e., cellulose, silica sand, and lignin. Two solids, polymethylstyrene and lignin, were found to participate significantly in cross-coupling reactions. It is postulated that relatively hydrophilic solids can mitigate peroxidase inactivation by forming enzyme-solid associations. Aromatic structures or unsaturated C-C bonds were found to be features of the solid-phase materials that allowed them to participate in cross-coupling. The results have important implications for process feasibility assessment and the engineering design of soil/sediment remediation systems employing enzymatic coupling schemes.

Biodegradation, Environmental↗
PubMed2004

Interactions of soil-derived dissolved organic matter with phenol in peroxidase-catalyzed oxidative coupling reactions.

The influence of dissolved soil organic matter (DSOM) derived from three geosorbents of different chemical composition and diagenetic history on the horseradish peroxidase (HRP) catalyzed oxidative coupling reactions of phenol was investigated. Phenol conversion and precipitate-product formation were measured, respectively, by HPLC and radiolabeled species analysis. Fourier transform infrared (FTIR) spectroscopy and capillary electrophoresis (CE) were used to characterize the products of enzymatic coupling, and the acute toxicities of the soluble products were determined by Microtox assay. Phenol conversion and precipitate formation were both significantly influenced by cross-coupling of phenol with dissolved organic matter, particularly in the cases of the more reactive and soluble DSOMs derived from two diagenetically "young" humic-type geosorbents. FTIR and CE characterizations indicate that enzymatic cross-coupling in these two cases leads to incorporation of phenol in DSOM macromolecules, yielding nontoxic soluble products. Conversely, cross-coupling appears to proceed in parallel with self-coupling in the presence of the relatively inert and more hydrophobic DSOM derived from a diagenetically "old" kerogen-type shale material. The products formed in this system have lower solubility and precipitate more readily, although their soluble forms tend to be more toxic than those formed by dominant cross-coupling reactions in the humic-type DSOM solutions. Several of the findings reported may be critically important with respect to feasibility evaluations and the engineering design of associated remediation schemes.

Biodegradation, Environmental↗
PubMed2003

Sorption and manganese-induced oxidative coupling of hydroxylated aromatic compounds by natural geosorbents.

The sorption/desorption equilibria and solvent extractabilities of phenol, o-cresol, and p-chlorophenol with respect to natural sorbents having different types of soil organic matter were investigated. Parallel tests in systems amended with birnessite (delta-MnO2), a solid-phase oxidative coupling catalyst, were also conducted. Sorption/desorption isotherms and solvent extraction data reveal that the relative isotherm linearities, desorption hysteresis, and extractabilities of these compounds are related to the geochemical nature of the sorbent organic matter and to the existence of system conditions that promote oxidative coupling reactions. When suitable coupling catalysts are present, soils containing primarily diagenetically "young" and highly amorphous organic matter (e.g., humic materials) are more likely to retain those solutes than are those containing primarily diagenetically "old" and more condensed organic matter (e.g., kerogens). The sorption/desorption properties of the solutes were significantly altered in the presence of birnessite as a result of both cross-coupling reactions with reactive soil organic matter components and self-coupling reactions with each other to form polymeric species. Under appropriate conditions, mineral-catalyzed oxidative coupling may exert a dominant influence on the sorption and transport of hydroxylated aromatic compounds in soil and sediment systems.

Adsorption↗
PubMed2003

Inclusion of persistent organic pollutants in humification processes: direct chemical incorporation of phenanthrene via oxidative coupling.

The participation of phenanthrene in phenol-coupling reactions mediated by horseradish peroxidase was investigated. Aqueous-phase concentrations of phenanthrene were observed to decrease dramatically with phenol as a result of the formation of precipitated products, suggesting a potential means for simultaneous treatment of phenolic contaminants and polycyclic aromatic hydrocarbons (PAHs) using peroxidase-mediated oxidative coupling processes. The studies reveal that phenanthrene removal from the aqueous phase occurs by a combination of sorption by and chemical bonding to precipitated reaction products. In that the oxidative coupling reactions of phenolics comprise an important step in the initiation of humification processes, the results obtained provide insights to potential roles that natural humification may play in the sorption, sequestration, and environmental fate of PAHs and other organic xenobiotics of similar nature.

Adsorption↗