Katrin Mackenzie

Hydrophobic Fe-Zeolites for Removal of MTBE from Water by Combination of Adsorption and Oxidation

Several zeolites were evaluated as adsorbents for the removal of MTBE from water in a screening process. It was observed that the SiO2/Al2O3 molar ratio is a decisive factor for the adsorption properties, at least in the case of ZSM5 zeolites. ZSM5 zeolites with SiO2/Al2O3 ratios >200 were found to provide the best sorption properties for MTBE. To design a combined sorption/reaction method, regeneration of the loaded zeolites by selected advanced oxidation processes (AOP) was studied: (1) Fenton treatment using H2O2 with dissolved iron salts and (2) heterogeneous Fenton-like oxidation with Fe immobilized on the zeolites. The first was ineffective in regenerating loaded zeolites. However, heterogeneous catalysis using Fe species immobilized on the zeolite by liquid ion exchange was markedly more effective. Although these hydrophobic zeolites have a low ion exchange capacity, resulting in iron loadings of ≤ 0.09 wt %, it was possible to obtain sufficiently active catalysts. Hydrophobic Fe-zeolites can therefore be regarded as promising materials for the removal of MTBE from water, since they allow the combination of efficient adsorption and oxidative degradation of MTBE by H2O2. In contrast to the homogeneous catalysis by dissolved iron ions, these heterogeneous catalysts work at near-neutral pH and can be easily reused. Fe-zeolites as adsorbents/catalysts showed a good stability in both batch and column experiments.

Sorption and chemical reactions of PAHs with dissolved humic substances and related model polymers

Sorption coefficients measured for PAHs on dissolved humic substances by SPME and FQT were found to be inevitably different and method-dependent – SPME provides activity-based and FQT concentration-based sorption coefficients. Poly(acrylic acid) esters as well-defined model polymers were used in sorption experiments, leading to the conclusion that short aliphatic chains are more effective in binding PAHs than aromatic moieties. FQT was inappropriate to measure sorption coefficients for the interaction of pyrene with poly(acrylic acid) esters but the experiments revealed a characteristic shift in the fluorescence spectrum. Using pyrene as a probe for the molecular environment in the sorbed state, the observed spectral shift indicated a highly hydrophobic microenvironment. The empirical relationships between lg KDOC and lg KOW were generalized on the basis of a modified Flory-Huggins concept. Introducing only one sorbent-specific parameter, the solubility parameter δDOM, the calculation of sorption coefficients became possible for a wide range of HOCs using fundamental data readily available from the literature. Long-term experiments showed that reactive PAHs (such as acenaphthylene and 9-methylanthracene) are able to react with HAs under strictly abiotic and anoxic conditions, whereas less reactive PAHs (such as naphthalene and dihydroanthracene) do not form bound residues. The HA reveals two functions in the interaction, behaving as a reaction partner and as a protecting ligand. Sorption und chemische Reaktion von PAK mit gelosten Huminstoffen und Modellpolymeren Sorptionskoeffizienten, die mit SPME und FQT bestimmt werden, sind zwangsweise unterschiedlich und methodenabhangig – SPME liefert Sorptionskoeffizienten auf der Basis der Aktivitat und FQT Sorptionskoeffizienten auf Basis der Konzentration. Sorptionsexperimente mit Polyacrylsaureestern als definierten Modellpolymeren fuhrten zu der Schlussfolgerung, dass kurze aliphatische Ketten effektiver PAK binden als aromatische Reste. Die FQT dagegen erwies sich als ungeeignet zur Bestimmung von Sorptionskoeffizienten fur die Wechselwirkung zwischen Pyren und Polyacrylsaureestern. Die Fluoreszenzspektren zeigen eine charakteristische Verschiebung der Fluoreszenzintensitaten. Dabei konnte Pyren als Sonde fur die molekulare Umgebung im sorbierten Zustand dienen, die beobachteten spektralen Verschiebungen weisen auf eine hochhydrophobe Mikroumgebung des Pyrens. Empirische lg KDOC-lg KOW-Beziehungen wurden vereinheitlicht auf der Basis eines modifizierten Flory-Huggins-Konzeptes. Durch das Einfuhren eines einzelnen sorbensspezifischen Parameters, dem Loslichkeitsparameter δDOM, wurde die Berechnung von Sorptionskoeffizienten fur ein weites Spektrum an hydrophoben organischen Verbindungen moglich; alle anderen Parameter liegen in der Literatur tabelliert vor. Langzeitexperimente belegen, dass reaktive PAK (wie Acenaphthylen und 9-Methylanthracen) in der Lage sind, unter strikt abiotischen und anoxischen Bedingungen mit Huminsauren zu reagieren, wohingegen wenig reaktive PAK (wie Naphthalin und Dihydroanthracen) keine gebundenen Reste bilden. Die Huminsaure offenbart zwei Funktionen in der Wechselwirkung – zum einen ist sie Reaktionspartner, zum anderen schutzender Ligand.

Evaluating the cytotoxicity of palladium/magnetite nano-catalysts intended for wastewater treatment

Palladium/magnetite nanoparticulate catalysts were developed for efficient elimination of halogenated organic pollutants from contaminated wastewater. Particle recovery from treated water can be ensured via magnetic separation. However, in worst-case scenarios, this catalyst removal step might fail, leading to particle release into the environment. Therefore, a toxicological study was conducted to investigate the impact of both pure magnetite and palladium/magnetite nanoparticle exposure upon human skin (HaCaT) and human colon (CaCo-2) cell lines and a cell line from rainbow trout gills (RTgill-W1). To quantify cell viability after particle exposure, three endpoints were examined for all tested cell lines. Additionally, the formation of reactive oxygen species was studied for the human cells. The results showed only minor effects of the particles on the tested cell systems and support the assumption that palladium/magnetite nano-catalysts can be implemented for a new wastewater treatment technology in which advantageous catalyst properties outweigh the risks.

A field investigation on transport of carbon-supported nanoscale zero-valent iron (nZVI) in groundwater.

The application of nanoscale zero-valent iron (nZVI) for subsurface remediation of groundwater contaminants is a promising new technology, which can be understood as alternative to the permeable reactive barrier technique using granular iron. Dechlorination of organic contaminants by zero-valent iron seems promising. Currently, one limitation to widespread deployment is the fast agglomeration and sedimentation of nZVI in colloidal suspensions, even more so when in soils and sediments, which limits the applicability for the treatment of sources and plumes of contamination. Colloid-supported nZVI shows promising characteristics to overcome these limitations. Mobility of Carbo-Iron Colloids (CIC) - a newly developed composite material based on finely ground activated carbon as a carrier for nZVI - was tested in a field application: In this study, a horizontal dipole flow field was established between two wells separated by 5.3m in a confined, natural aquifer. The injection/extraction rate was 500L/h. Approximately 1.2kg of CIC was suspended with the polyanionic stabilizer carboxymethyl cellulose. The suspension was introduced into the aquifer at the injection well. Breakthrough of CIC was observed visually and based on total particle and iron concentrations detected in samples from the extraction well. Filtration of water samples revealed a particle breakthrough of about 12% of the amount introduced. This demonstrates high mobility of CIC particles and we suggest that nZVI carried on CIC can be used for contaminant plume remediation by in-situ formation of reactive barriers.

Hyphenated techniques for characterizing coal wastewaters and associated sediments

Abstract Capillary gas chromatography (cGC)-mass spectrometry (MS) and cGC-atomic emission detection (AED) were used for the analysis of extracts from highly contaminated wastewaters and associated sediments. The main extractable constituents in both the lignite wastewater and the sediments include phenols, PAHs, indenols and heterocyclic compounds. Pyrolysis (Py)-GC-MS and Py-GC-AED were used for characterizing the building blocks of the dissolved polymeric organic matter. Polymers of natural and anthropogenic origins could be clearly distinguished. The Py-MS studies performed with humic organic matter at both atmospheric pressure and high vacuum (in-source mode) indicate a high portion of pyrolysis residue (about 40%, w/w) upon heating to 700°C, irrespective of the pressure level. The products released include many low molecular weight compounds which are of limited value for characterizing the polymeric network.

Novel Organoaluminum Lewis Acids via Selective Aluminum-Tin Exchange Processes – Electrophilic Initiation by the Aluminum Halide and Ensuing Complexation by the Resulting Tin Halide

With the goals of preparing novel carbaluminating reagents and mono- and bidentate organoaluminum Lewis acids, the scope and limitations of synthesizing the requisite organoalanes by the aluminum-tin exchange between an aluminum halide and the appropriate organostannane have been examined in detail. The interactions of such tin precursors as 1,2-bis(trimethylstannyl)ethyne, allyltri-n-butyltin, benzyltrimethyltin, and 1,2-bis(trimethylstannyl)benzene and various aluminum chlorides of the type, RnAlCl3–n (R = Me, Et), gave selective aluminum-tin exchange at the sp- or sp2-hybridized carbon–tin bond and produced such organoalanes as allyl(methyl)aluminum chloride, benzylaluminum dichloride, 1,2-bis(diethylalumino)ethyne, 1,2-bis(dimethylalumino)benzene, 1,2-bis[chloro(methyl)alumino]benzene, and 1,2-bis(dichloroalumino)benzene in high yield. A complicating factor was the tendency of the R3SnCl by-product to complex with the resulting organoalane. In some cases, exemplified by allyl(methyl)aluminum chloride, such complexation did not interfere with the carbaluminating action of the reagent; in other cases, exemplified by 1,2-bis[chloro(methyl)alumino]benzene, the R3SnCl could be removed by means of π-bases and reduced pressures; and in still other structures, as with 1,2-bis(dichloroalumino)benzene, the tin chloride could not be dislodged at moderate temperatures. The structure and bonding in such tin halide–aluminum halide complexes in solution were investigated with the 1:1 adducts of AlCl3 with Me3SnCl and with nBu3SnCl, respectively, by means of multinuclear NMR spectroscopy. Furthermore, an XRD of the solid complex, Me3SnCl · AlCl3, was carried out. Such complexes were shown to consist of 1:1 ion pairs of the type [R3Sn+][AlCl4−] in dilute solution and of a chiral polymeric helix in the solid state wherein planar Me3Sn+ units are linked to each other via bridging tetrachloroaluminate anions, Cl–(AlCl2)–Cl−. Treatment of such complexes with either benzyltriethylammonium chloride (one or two equivalents) or tetramethylphosphonium chloride leads to the displacement of Me3SnCl and the formation of the expected ionic complexes. Finally, the importance of such novel reagents and chelating Lewis acids to organic synthesis and olefin polymerization is discussed and elucidated.

Application of surfactants to the supercritical fluid extraction of nitroaromatic compounds from sediments

Abstract Supercritical fluid extraction using supercritical carbon dioxide was applied to extract nitroaromatic compounds covering a wide range of polarity from soils having high humic organic matter content. Commercially available non-ionic, anionic and cationic surfactants were utilised as modifiers to enhance analyte solubility in the fluid. The applied surfactants turned out to have no significant beneficial impact on target analyte recoveries. On the contrary, surfactants exercise a detrimental effect on recovery by the formation of a “layer” on the soil or by “plugging” micropores, thus hampering analyte desorption. The surfactant deposition onto the soil under supercritical conditions was traced using electrospray ionisation mass spectrometry. The surfactant can be fully solubilised by adding polar methanol modifier to the fluid, but there was no synergetic effect between surfactant and modifier.

Debromination of duroplastic flame-retarded polymers

Epoxy resins containing the flame retardant Tetrabromobisphenol A chemically bound to their structures were successfully dehalogenated with Na/NH3 in an autoclave at elevated temperatures. Four loaded printed circuit boards of various origins and one unloaded circuit board were investigated. Debromination efficiencies of solvolysis with ethyl acetate (280°C, 15 MPa) and dehalogenation with Na/NH3 (100°C, 6 MPa) are compared.

Accelerated Catalytic Fenton Reaction with Traces of Iron: An Fe–Pd-Multicatalysis Approach

An accelerated catalytic Fenton (ACF) reaction was developed based upon a multicatalysis approach, facilitating efficient contaminant oxidation at trace levels of dissolved iron. Beside the Fe(II)/H2O2 catalyst/oxidant pair for production of OH-radicals, the ACF system contains Pd/H2 as catalyst/reductant pair for fast reduction of Fe(III) back to Fe(II) which accelerates the Fenton cycle and leads to faster contaminant degradation. By this means, the concentration of the dissolved iron catalyst can be reduced to trace levels (1 mg L(-1)) below common discharge limits, thus eliminating the need for iron sludge removal, which is one of the major drawbacks of conventional Fenton processes. ACF provides fast degradation of the model contaminant methyl tert-butyl ether (MTBE, C0 = 0.17 mM) with a half-life of 11 min with 1 mg L(-1) dissolved iron, 500 mg L(-1) H2O2, 5 mg L(-1) Pd (as suspended Pd/Al2O3 catalyst) and 0.1 MPa H2, pH 3. The effects of pH, H2 partial pressure and H2O2 concentration on MTBE degradation rates were studied. Results on kinetic deuterium isotope effect and quenching studies are in conformity with OH-radicals as main oxidant. The heterogeneous Pd/Al2O3 catalyst was reused within six cycles without significant loss in activity.

Carbo-Iron as improvement of the nanoiron technology: From laboratory design to the field test

In a first pilot-scale field test the use of Carbo-Iron® was successfully demonstrated. Carbo-Iron was developed with the goal to overcome significant shortcomings of nanoscale zero-valent iron (NZVI) for in-situ groundwater remediation. The composite material of colloidal activated carbon and embedded nanoiron structures has been tested for the remediation of a tetrachloroethene (PCE) contaminated field site in Lower Saxony, Germany. The results of the two-step field test confirmed the properties intended by its design and the particle performance achieved in the laboratory experiments. The material showed transport lengths of several metres in the field and fast PCE decomposition with no vinyl chloride formation. Extended longevity of the PCE decrease in the treated area and evidence for microbiological participation were found. Carbo-Iron is now under study in the framework of the EU-project NanoREM where its performance is being further optimized at various scales from laboratory via large-scale tank to field testing. Targeted property adjustment was successful for Carbo-Iron performance in both directions: plume treatment and source attack.