This dissertation examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) to various chlorinated aliphatic hydrocarbons (CAHs) that are common chemicals of concern at contaminated sites. The research focuses on the transformation of 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2,2-tetrachloro-ethane (1,1,2,2-TetCA) and 1,2-dichloroehtane (1,2-DCA) by Fe(II) in cement slurries. It also investigates the degradation of 1,1,1-TCA by a mixture of Fe(II), cement and three iron-bearing phyllosilicates. Transformation of 1,1,1-TCA and 1,1,2,2-TetCA by Fe(II) in 10% cement slurries was characterized using batch reactors. Dechlorination kinetics of 1,1,1-TCA and TCE* (TCE that was produced by transformation of 1,1,2,2-TetCA) was strongly dependent on Fe(II) dose, pH and initial target organic concentration. Degradation of target organics in DS/S-Fe(II) process was generally described by a pseudo-first-order rate law. However, saturation relationships between the rate constants and Fe(II) dose or between the initial degradation rates and target organic concentration were observed. These behaviors were properly described by a modified Langmuir-Hinshelwood kinetic model. This supports the working hypothesis of this research that reductive dechlorination of chlorinated ethanes occurs on the surface of active solids formed in mixtures of Fe(II) and cement. Transformation products for 1,1,1-TCA and 1,1,2,2-TetCA in mixtures of Fe(II) and cement were identified. The major product of the degradation of 1,1,1-TCA was 1,1-DCA, which indicates that the reaction followed a hydrogenolysis pathway. However, a small amount of ethane was also observed. TCE* was rapidly produced by degradation of 1,1,2,2-TetCA and is expected to undergo β-elimination to produce acetylene. Dechlorination of 1,1,1-TCA in suspension of Fe(II), cement and three soil minerals (biotite, vermiculite, montmorillonite) was characterized using batch reactors. A first-order rate model was generally used to describe the dechlorination kinetics of 1,1,1-TCA in this heterogeneous system. The rate constants for 1,1,1-TCA in mixtures of Fe(II), cement and soil minerals were influenced by soil mineral types, Fe(II) dose and the mass ratio of cement to soil mineral. It was demonstrated that structural Fe(II) and surface-bound Fe(II) in the soil minerals affect dechlorination kinetics and the effects vary with mineral types. Furthermore, it suggests that the reductant formed from Fe(II) and cement hydration components is also effective in systems that include soil minerals.

This dissertation examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) to various chlorinated aliphatic hydrocarbons (CAHs) that are common chemicals of concern at contaminated sites. The research focuses on the transformation of 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2,2-tetrachloro-ethane (1,1,2,2-TetCA) and 1,2-dichloroehtane (1,2-DCA) by Fe(II) in cement slurries. It also investigates the degradation of 1,1,1-TCA by a mixture of Fe(II), cement and three iron-bearing phyllosilicates. Transformation of 1,1,1-TCA and 1,1,2,2-TetCA by Fe(II) in 10% cement slurries was characterized using batch reactors. Dechlorination kinetics of 1,1,1-TCA and TCE* (TCE that was produced by transformation of 1,1,2,2-TetCA) was strongly dependent on Fe(II) dose, pH and initial target organic concentration. Degradation of target organics in DS/S-Fe(II) process was generally described by a pseudo-first-order rate law. However, saturation relationships between the rate constants and Fe(II) dose or between the initial degradation rates and target organic concentration were observed. These behaviors were properly described by a modified Langmuir-Hinshelwood kinetic model. This supports the working hypothesis of this research that reductive dechlorination of chlorinated ethanes occurs on the surface of active solids formed in mixtures of Fe(II) and cement. Transformation products for 1,1,1-TCA and 1,1,2,2-TetCA in mixtures of Fe(II) and cement were identified. The major product of the degradation of 1,1,1-TCA was 1,1-DCA, which indicates that the reaction followed a hydrogenolysis pathway. However, a small amount of ethane was also observed. TCE* was rapidly produced by degradation of 1,1,2,2-TetCA and is expected to undergo β-elimination to produce acetylene. Dechlorination of 1,1,1-TCA in suspension of Fe(II), cement and three soil minerals (biotite, vermiculite, montmorillonite) was characterized using batch reactors. A first-order rate model was generally used to describe the dechlorination kinetics of 1,1,1-TCA in this heterogeneous system. The rate constants for 1,1,1-TCA in mixtures of Fe(II), cement and soil minerals were influenced by soil mineral types, Fe(II) dose and the mass ratio of cement to soil mineral. It was demonstrated that structural Fe(II) and surface-bound Fe(II) in the soil minerals affect dechlorination kinetics and the effects vary with mineral types. Furthermore, it suggests that the reductant formed from Fe(II) and cement hydration components is also effective in systems that include soil minerals.

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater pollution. TCE in environment can be removed by physical, chemical and biological procedures. The objective of this pilot-scale study was to apply an enhanced in situ bioremediation technology to remediate TCE-contaminated groundwater. Both aerobic and anaerobic remedial systems were evaluated at a TCE-spill site located in southern Taiwan. In the aerobic test zone, the effectiveness of air, nutrient, and sugarcane molasses injection to enhance the aerobic cometabolism on TCE degradation was evaluated. In the anaerobic test zone, the effectiveness of nutrient and sugarcane molasses injection to enhance the anaerobic reductive dechlorination on TCE degradation was also evaluated. Polymerase chain reaction was applied to analyze the gene variation in TCE-microbial degraders during the treatment process. Results from this study indicate that the aerobic TCE-degraders (type ¢º methanotrophs) and the gene of degradation enzymes (toluene monooxygenase, toluene dioxygenase, particulate methane monooxygenase) were detected after the treatment process in the aerobic test zone. Moreover, TCE concentration dropped from approximately 0.1 mg/L to below 0.05 mg/L in the aerobic test zone after six months of treatment. In the anaerobic treatment zone, Dehalococcoides (anaerobic TCE-degrader) and the gene of degradation enzyme (vcrA) were detected and a significant drop of TCE concentration was also observed. Results reveal that both the aerobic cometabolism and anaerobic dechlorination are feasible and applicable technologies to clean up TCE contaminated aquifers.

Enhanced Reductive Bioremediation (ERB) is a sustainable remediation technology for the in situ treatment of chlorinated solvent contamination in aquifers. However, monitoring efforts employed to measure performance metrics rely on inferences of the subsurface environment from water samples collected at monitoring wells, ignoring the microbial activity that occurs at the granular level of aquifer sediment. This study compared potential bioavailable organic carbon (PBOC) and microbial diversity of two ERB sites. A two-sample t-test and a one-way ANOVA test with Tukey's HSD were performed to show differences between ERB and non-ERB samples and their degree of variability at selected geospatial locations downgradient of ERB treatment. Non-parametric multidimensional scaling (MDS) with similarity analysis was performed along with other data visualization plots to show microbial diversity. At Tinker AFB, results from the t-test showed that the PBOC concentrations from the ERB samples were statistically significantly greater than the samples without treatment (95% confidence; p-value = 0.018). For Dover AFB, results from the ANOVA with Tukey's HSD showed that there is a significant difference between the sample (DV3) collected in the ERB treatment zone to all other samples upgradient and downgradient of the ERB treatment. MDS and similarity analysis performed on relative abundance results from the Illumina MiSeq Sequencing of 16S rRNA genes showed large similarities among the samples within each site and the only observed differences occurred when comparing any sample to DV3, nearest to treatment. / Master of Science / Enhanced Reductive Bioremediation (ERB) is a sustainable remediation technology for the treatment of chlorinated solvent contamination in groundwater within the subsurface. ERB acts as a stimulant of microbial communities to accelerate remediation. Current ways to measure the success of remediation technologies use water from monitoring wells and they ignore the microbial activity that occurs within the subsurface sediment, where the water is stored. This study compared potential bioavailable organic carbon (PBOC) and microbial diversity of two ERB sites. PBOC is the amount of carbon in sediment that is consumable by bacteria. Microbial diversity are the various communities of microscopic organisms present in a sediment sample. A two-sample t-test and a one-way ANOVA test with Tukey’s HSD were performed to show differences between ERB and non-ERB samples and their degree of variability at selected geospatial locations downgradient of ERB treatment. A two-sample t-test determined if there is a statistical difference between two values. A one-way ANOVA test compared multiple values to each other and all their possible combinations. The Tukey’s HSD showed how different those values were from each other, from the ANOVA test results. Non-parametric multidimensional scaling (MDS) with similarity analysis was performed along with other data visualization plots to show microbial diversity. These visualization techniques helped determine similarities and demostrate microbial diversity. At Tinker AFB, results from the t-test showed that the PBOC concentrations from the ERB samples were statistically significantly greater than the samples without treatment (95% confidence; pvalue = 0.018). For Dover AFB, results from the ANOVA with Tukey’s HSD showed that there is a significant difference between the samples (DV3) collected in the ERB treatment zone to all other samples upgradient and downgradient of the ERB treatment. MDS and similarity analysis performed on relative abundance results from the Illumina MiSeq Sequencing of 16S rRNA genes showed large similarities among the samples within each site and the only observed differences occurred when comparing any sample to DV3, nearest to treatment.

The purpose of this thesis was to conduct preliminary research into the feasibility of using MCM-41 as a catalyst support material in the treatment of organochloride contaminated water. Specifically, the stability of MCM-41 in water and its efficiency as a Pd metal catalyst support in the degradation of trichloroethylene (TCE) was examined. MCM-41 is a mesoporous siliceous material that was developed by scientists with the Mobile Corporation in 1992. Since its development, MCM-41 has been the subject of a great deal of research into its potential application in catalytic sciences. The material possesses two especially notable characteristics. First, the diameter of its pores can be adjusted between 2 and 10 nm depending on the reagents and procedure used in its synthesis. Second, MCM-41 has an exceptionally high surface area, often in excess of 1 000 m2/g in well-formed samples. Other researchers have succeeded in grafting a variety of different catalytic materials to the surfaces and pores of MCM-41 and reported dehalogenation reactions proceeding in the presence of hydrogen. Thus, MCM-41 shows promise in treating a variety of chlorinated volatile organic compounds (cVOCs), such as chlorinated benzenes, trichloroethylene (TCE), perchloroethylene (PCE) and some polychlorinated biphenyls (PCBs). Preliminary stages of this research were devoted to synthesising a well-formed sample of MCM-41. The method of Mansour et al. (2002) was found to be a reliable and repeatable procedure, producing samples with characteristic hexagonal crystallinity and high surface areas. Crystallinity of all materials was characterized by small angle X-ray powder diffraction (XRD). Samples of MCM-41 prepared for this research exhibited a minimum of three distinct peaks in their XRD traces. These peaks are labelled 100, 110, and 200 according to a hexagonal unit cell. The 100 peak indicates that the sample is mesoporous. The 100, 110, and 200 peaks together indicate a hexagonal arrangement of the mesopores. An additional peak, labelled 210, was also observed in materials prepared for this research, reflecting a high degree of crystallinity. The position of the 100 peak was used to calculate the unit cell parameter - ???a??? - of the samples according to Bragg???s Law. The value of the unit cell parameter corresponds to the centre to centre distance of the material???s pores and thus the relative diameter of the pores themselves. The unit cell parameter of samples prepared for this research ranged from 4.6 nm to 5.3 nm with an average value of 4.8 nm. Surface areas of prepared samples were determined by BET nitrogen adsorption analysis and ranged from 1 052 to 1 571 m2/g with an average value of 1 304 m2/g. Field emission scanning electron microscope (SEM) images of a representative sample of MCM-41 revealed a particle morphology referred to as ???wormy MCM-41??? by other researchers. A sample of aluminum-substituted MCM-41 (Al-MCM-41) was also synthesized. The crystallinity of Al-MCM-41 was characterized by small angle XRD. The XRD trace of the material showed only one distinct peak centred at 2.1 degrees 2??. The 110 and 200 peaks seen in MCM-41 were replaced by a shoulder on the right hand side of the 100 peak. The shape of this trace is typical of Al-MCM-41 prepared by other researchers and is indicative of the lower structural quality of the material, i.e. a less-ordered atomic arrangement in Al-MCM-41 compared to that of regular MCM-41. The unit cell parameter of the Al-MCM-41 sample was 4.9 nm. The surface area of the sample was determined through BET nitrogen adsorption analysis and found to be 1 304 m2/g. Attempts were made to synthesize an MCM-41 sample with enlarged pores. Difficulties were encountered in the procedure, specifically with regards to maintaining high pressures during the crystallization stage. Higher temperatures used during these procedures caused failure of the O-ring used in sealing the autoclave, allowing water to be lost from the reaction gel. Samples generated in these attempts were amorphous in character and were subsequently discarded. A solubility study involving MCM-41 was undertaken to determine the stability of the material in water at ambient temperature and pressure. The experiment included several different solid/water ratios for the dissolution experiments: 1/200, 1/100, 1/75, 1/25. Results indicated that MCM-41 is metastable at ambient temperatures and more soluble than amorphous silica in water. The maximum silica concentration observed during the experiment was used to calculate a minimum Gibbs free energy of formation for MCM-41 of - 819.5 kJ/mol. The higher free energy value compared to quartz (- 856.288 kJ/mol) is indicative of the metastability of the material in water. Supersaturation with respect to amorphous silica was observed in samples prepared with relatively high concentrations of MCM-41. A subsequent decrease in dissolved silica concentration with time in these samples represented precipitation of amorphous silica, driving the concentration downward towards saturation with respect to this phase (120 ppm). The equilibrium concentration of 120 ppm recorded in these samples represented 4.8 mg out of 200, 400, 500, and 1 600 mg of initial MCM-41 dissolving into solution in the solid/liquid ratios of 1/200, 1/100, 175, and 1/25, respectively. Supersaturation with respect to amorphous silica did not occur in experiments with very low solid/water ratios. It also did not occur in higher solid/water experiments from which the SiO2 saturated supernatant was decanted and replaced with fresh deionized water after two weeks of reaction. The difference in dissolution behaviour is believed to result from deposition of a protective layer of amorphous silica from solution onto the MCM-41 surfaces, which reduces their dissolution rate. Thus, supersaturation with respect to amorphous silica is only manifested at early time and only when relatively large amounts of fresh MCM-41 are added to water. The solubility experiment was repeated using samples of Al-MCM-41 to determine the effect of Al substitution on the stability of the MCM-41. Dissolution curves for the Al-MCM-41 samples revealed behaviour that was analogous to that of the silica-based MCM-41 at similar solid/water ratios. Substitution of Al into the structure of MCM-41 appeared to have no positive or negative effects on the stability of the material in water. Solid MCM-41 material was recovered on days 28 and 79 of the solubility experiment and dried under vacuum. Solid material was also recovered from the Al-MCM-41 solubility experiment on day 79. These recovered samples were characterized by XRD and BET nitrogen adsorption analysis. An increase in background noise in the XRD plot of MCM-41 from the fresh to the 79 d sample indicated an increased proportion of an amorphous phase in the sample. The XRD plot of the 79 d sample of Al-MCM-41 also showed increased background noise corresponding to an increased proportion of an amorphous phase. The increased amorphous phase would have resulted from the continuous dissolution of the crystalline MCM-41 and reprecipitation as amorphous silica in the samples. BET surface area analysis of recovered MCM-41 compared to the freshly prepared material showed no significant change in surface area after 28 and 79 days in water. Analysis of the 79 d Al-MCM-41 indicated a 10% decrease in surface area relative to the as-prepared material. A set of SEM images were taken of the day 28 and 79 MCM-41 samples and compared to a sample of freshly prepared material. No substantial change in morphology was observed in the day 28 sample when compared to the fresh material. Some change was noted in the day 79 sample particle morphology, with worm-like structures appearing to be better developed than in the as-synthesized material. A series of palladized MCM-41 (Pd/MCM-41) samples with varying mass percent loadings of Pd was prepared to investigate the dehalogenation efficiency of Pd/MCM-41 in contact with TCE. TCE degradation was investigated in batch experiments. MCM-41 samples were prepared with calculated Pd loadings of 0.1, 1, and 5 mass %. The actual palladium content of the materials was determined using an EDAX-equipped SEM. The success of the loading technique was better at lower mass loadings of Pd, i.e. there was a greater deviation of actual Pd content from targeted or calculated contents at higher loadings of Pd. It was found that a procedure designed to yield 1% by mass Pd/MCM-41 produced an average loading of 0.95% Pd by mass. A procedure designed to produce a 5% Pd/MCM-41 sample resulted in an average loading of 2.6 mass %. These deviations were attributed to error inherent in the EDAX analysis and reduced effectiveness of the loading technique at higher Pd concentrations. All batch experiment reaction bottles were prepared with solid/liquid ratios of 1/800. The various Pd/MCM-41 samples induced rapid dehalogenation reactions, with the maximum extent of TCE degradation occurring before the first sample was taken at 7 to 12 min and within 35 min in the case of 0.1% Pd/MCM-41. The 0.1% Pd/MCM-41 sample degraded 70% of total TCE in solution with an estimated degradation half-life of 14 min. The 1% Pd/MCM-41 sample degraded 92% of total TCE in solution with an estimated half life of between 3 and 6 min. The 5% Pd/MCM-41 sample degraded only 22% of total TCE in solution; degradation half-life could not be determined. The seemingly paradoxical result of lower degradation efficiency at higher Pd loadings is proposed to result from absorption of hydrogen from solution by Pd, which is unreactive relative to the dissolved hydrogen in solution. Production of reaction intermediates and daughter products was also lower in the 1% by mass Pd/MCM-41 experiment compared to the 0.1 and 5% by mass Pd/MCM-41. Analysis of degradation products results from the experiments indicated that TCE degrades to ethane in the presence of Pd/MCM-41 with relatively low concentrations of chlorinated daughter products resulting from a random desorption process. A batch experiment using pure silica MCM-41 was also conducted to determine if there was adsorption of TCE to the support material itself. A lack of change in TCE concentration between the control sample and the MCM-41 sample during the experiment indicated no significant adsorption of TCE onto MCM-41. The conclusion of this research is that although MCM-41 is relatively unstable in water, its high TCE degradation efficiency shows promise for its application in developing water treatment technologies. However, more research needs to be conducted to fully determine the potential use of MCM-41 in water treatment and to investigate ways to improve its long-term stability in water.

M.Sc. (Chemistry) / Zero-valent nanoscale metal, especially iron nanoparticles have attracted significant attention with regards to remediation of organochlorinated compounds in drinking water. For a more rapid and complete dechlorination, a second and usually electronegative element is often added, resulting in the formationof bimetallic nanoparticles. However, in the absence of surfactants,the bimetallic nanoparticles easily aggregate into large particles (if they are not anchored on solid supports) with wide size distributions, thus losing their reactivity. This work reports an in-situ synthesis method of bimetallic nanoparticles immobilized on L-lysine functionalized microfiltration membranes by chemical reduction of metal ions chelated by amine and hydroxyl functional groups of L-lysine on the composite. The immobilization of the nanoparticles on membranes offers many advantages: reduction of particle loss, prevention of particle agglomeration and application under convective flow. The objective of this research wasto produce catalytic filtration membranes for dechlorination of organic compound, PCB-77. This was achieved first by (i) the modification of commercial PVDF to introduce functional groups that render the membrane more hydrophilic and have the ability to capture metal ions through chelation, and secondly (ii) the controlled introduction of catalytic nanoparticles onto the composite membrane surface, anchored through chelation to the surface functional groups. This approach was selected with aview to produce uniform surface distribution of monodispersed bimetallic nanoparticles that are resistant to leaching during the reduction reactions. The modification of the PVDF membrane was achieved by firstly performing an in situ polymerization of acrylic acid followed by covalently bonded L-lysine to the polymerized acrylic acid chains using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The Fe ions were introduced to the composite by L-lysine chelation and subsequently reduced to Fe0 with NaBH4, and finally deposition of Ni2+ which later were also reduced to Ni0 with NaBH4. The Fe/Ni bimetallic NPs system was chosen based on its proven ability for the total dechlorination of chlorinated organic compounds. Systematic characterization of the composite was performed using ATR-FTIR, FESEM, EDS, HRTEM, XRD, AFM and Contact Angle measurements. A relatively uniform distribution of Fe/Ni nanoparticles was found in L-lysine/PAA/PVDF membrane. The diameter of Fe/Ni nanoparticles was predominantly within the range 20-30 nm. Furthermore, the mechanism of the catalytic dechlorination of the model compound, PCB 77, was investigated by careful analysis of the reaction products. It is generally known that zero-valent iron undergoes corrosion to provide hydrogen atoms and electrons for the reductive catalytic hydrodechlorination reaction. The second metal in the bimetallic system on the other hand, acts as...

Chloroethenes such as tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene (DCE) and vinyl chloride (VC), are major contaminants in subsurface systems threatening water quality and human health. Under anaerobic conditions, PCE and TCE can be reductively dechlorinated to ethene. Recent findings indicate that members of the Dehalococcoides group are responsible for ethene formation at chloroethene-contaminated sites. Dehalococcoides species exhibit diverse dechlorination activities, but share highly similar 16S rRNA genes. Hence, additional gene targets that go beyond the 16S rRNA gene are needed to reliably detect and quantify Dehalococcoides populations involved in high rate chloroethene detoxification at contaminated sites. Dehalococcoides sp. strain BAV1 couples growth to reductive dechlorination of VC to ethene. To shed light on the genes involved in reductive dechlorination in strain BAV1, degenerate primers targeting reductive dehalogenase (RDase) genes of Dehalococcoides were designed using available sequence information. PCR amplification with these primers yielded seven putative RDase genes with genomic DNA from strain BAV1 as template. Transcription analysis identified one RDase gene possibly involved in VC dechlorination, which was named bvcA. The bvcA gene was not present in Dehalococcoides strains that failed to couple growth with reductive dechlorination of VC (i.e., Dehalococcoides isolates CBDB1, FL2 and 195). Primers specific for bvcA detected this gene in several, but not all, Dehalococcoides-containing, ethene-producing mixed cultures. Apparently, the bvcA-targeted primers do not capture the diversity of VC RDase genes. Nevertheless, a relevant target was identified, and bvcA-targeted primers are commercially applied to monitor Dehalococcoides sp. strain BAV1 and related organisms at contaminated sites undergoing bioremediation treatment. Additional RDase genes were identified in Dehalococcoides sp. strain FL2, and expression analysis was performed when FL2 was grown with cis-DCE and TCE as electron acceptors. Multiple RDase genes were transcribed with each electron acceptor. This work identified novel process-specific target genes that are useful for site assessment and bioremediation monitoring at chloroethene-contaminated sites. In particular, bvcA emerged as a relevant target for monitoring the critical detoxification step from VC, to ethene. Additionally, the RDase genes retrieved in this work form a basis for further exploration of the specific functions and regulation mechanisms involved in reductive dechlorination processes.

M.Sc. (Nanoscience) / Supported bimetallic Fe/Ni nanoparticles have been used for years as catalysts for the dechlorination of organochlorine compounds in ground water remediation. However, their fate and potential harm to the environment is of concern, hence, ways of reducing these negative aspects are being explored. As a way to solve this problem, catalytic nanoparticles are immobilised on a variety of substrates ranging from membranes, clays, silica, etc. In the current effort, the immobilisation of Fe/Ni bimetallic nanoparticles on electospun cellulose-based nanofibers was examined with the ultimate view to apply the materials for dechlorination studies. Fe/Ni bimetallic nanoparticles were anchored on ligand-functionalised cellulose nanofibers by the successive reduction of Fe(II) and Ni(II) ions from their respective solutions using NaBH₄...

The objective of this thesis is to aid in the development of Remedial Extraction And Catalytic Hydrodehalogenation (REACH), a green remediation technology used to remove and destroy halogenated hydrophobic organic compounds from soil. REACH has no secondary waste streams, uses an environmentally benign solvent, and aims to catalytically destroy rather than transfer the organic contaminants into a different phase. In this thesis, a bench-top semicontinuous model of the proposed remediation technology was constructed and used to extract the model contaminant, 1,2,4,5-tetrachlorobenzene, from soil and to convert it to an acceptable end product, cyclohexane. Palladium was used as a catalyst for hydrodehalogenation, which converted the tetrachlorobenzene to benzene. Rhodium was used to catalyze the hydrogenation of benzene to cyclohexane. A novel method, ultraviolet solvent treatment, was proposed to mitigate catalyst deactivation that occurs because of extracted chemicals contained in the contaminated soil. The goal of this treatment is to degrade organic matter that is suspected of causing catalyst deactivation. The REACH process was found to successfully extract TeCB from the soil, but only partial conversion from TeCB to cyclohexane occurred. Catalyst deactivation was the suspectedcause of the low amount of conversion observed. Hydrogen limitation was also tested as a cause of limited conversion, but was not found to be a contributor. Ultraviolet solvent treatment was tested as a means of mitigating catalyst deactivation. However, the treatment was not effective in making a profound difference in stopping the catalyst from deactivating. The experiments conducted in this research show that REACH has the potential to become a viable technology for cleaning soil contaminated with halogenated organic compounds. However, future research needs to be done to greatly reduce the severity of catalyst deactivation and to determine with which other halogenated organic compounds the technology works well.

The purpose of this thesis was to conduct preliminary research into the feasibility of using MCM-41 as a catalyst support material in the treatment of organochloride contaminated water. Specifically, the stability of MCM-41 in water and its efficiency as a Pd metal catalyst support in the degradation of trichloroethylene (TCE) was examined. MCM-41 is a mesoporous siliceous material that was developed by scientists with the Mobile Corporation in 1992. Since its development, MCM-41 has been the subject of a great deal of research into its potential application in catalytic sciences. The material possesses two especially notable characteristics. First, the diameter of its pores can be adjusted between 2 and 10 nm depending on the reagents and procedure used in its synthesis. Second, MCM-41 has an exceptionally high surface area, often in excess of 1 000 m2/g in well-formed samples. Other researchers have succeeded in grafting a variety of different catalytic materials to the surfaces and pores of MCM-41 and reported dehalogenation reactions proceeding in the presence of hydrogen. Thus, MCM-41 shows promise in treating a variety of chlorinated volatile organic compounds (cVOCs), such as chlorinated benzenes, trichloroethylene (TCE), perchloroethylene (PCE) and some polychlorinated biphenyls (PCBs). Preliminary stages of this research were devoted to synthesising a well-formed sample of MCM-41. The method of Mansour et al. (2002) was found to be a reliable and repeatable procedure, producing samples with characteristic hexagonal crystallinity and high surface areas. Crystallinity of all materials was characterized by small angle X-ray powder diffraction (XRD). Samples of MCM-41 prepared for this research exhibited a minimum of three distinct peaks in their XRD traces. These peaks are labelled 100, 110, and 200 according to a hexagonal unit cell. The 100 peak indicates that the sample is mesoporous. The 100, 110, and 200 peaks together indicate a hexagonal arrangement of the mesopores. An additional peak, labelled 210, was also observed in materials prepared for this research, reflecting a high degree of crystallinity. The position of the 100 peak was used to calculate the unit cell parameter - “a” - of the samples according to Bragg’s Law. The value of the unit cell parameter corresponds to the centre to centre distance of the material’s pores and thus the relative diameter of the pores themselves. The unit cell parameter of samples prepared for this research ranged from 4.6 nm to 5.3 nm with an average value of 4.8 nm. Surface areas of prepared samples were determined by BET nitrogen adsorption analysis and ranged from 1 052 to 1 571 m2/g with an average value of 1 304 m2/g. Field emission scanning electron microscope (SEM) images of a representative sample of MCM-41 revealed a particle morphology referred to as ‘wormy MCM-41’ by other researchers. A sample of aluminum-substituted MCM-41 (Al-MCM-41) was also synthesized. The crystallinity of Al-MCM-41 was characterized by small angle XRD. The XRD trace of the material showed only one distinct peak centred at 2.1 degrees 2θ. The 110 and 200 peaks seen in MCM-41 were replaced by a shoulder on the right hand side of the 100 peak. The shape of this trace is typical of Al-MCM-41 prepared by other researchers and is indicative of the lower structural quality of the material, i.e. a less-ordered atomic arrangement in Al-MCM-41 compared to that of regular MCM-41. The unit cell parameter of the Al-MCM-41 sample was 4.9 nm. The surface area of the sample was determined through BET nitrogen adsorption analysis and found to be 1 304 m2/g. Attempts were made to synthesize an MCM-41 sample with enlarged pores. Difficulties were encountered in the procedure, specifically with regards to maintaining high pressures during the crystallization stage. Higher temperatures used during these procedures caused failure of the O-ring used in sealing the autoclave, allowing water to be lost from the reaction gel. Samples generated in these attempts were amorphous in character and were subsequently discarded. A solubility study involving MCM-41 was undertaken to determine the stability of the material in water at ambient temperature and pressure. The experiment included several different solid/water ratios for the dissolution experiments: 1/200, 1/100, 1/75, 1/25. Results indicated that MCM-41 is metastable at ambient temperatures and more soluble than amorphous silica in water. The maximum silica concentration observed during the experiment was used to calculate a minimum Gibbs free energy of formation for MCM-41 of - 819.5 kJ/mol. The higher free energy value compared to quartz (- 856.288 kJ/mol) is indicative of the metastability of the material in water. Supersaturation with respect to amorphous silica was observed in samples prepared with relatively high concentrations of MCM-41. A subsequent decrease in dissolved silica concentration with time in these samples represented precipitation of amorphous silica, driving the concentration downward towards saturation with respect to this phase (120 ppm). The equilibrium concentration of 120 ppm recorded in these samples represented 4.8 mg out of 200, 400, 500, and 1 600 mg of initial MCM-41 dissolving into solution in the solid/liquid ratios of 1/200, 1/100, 175, and 1/25, respectively. Supersaturation with respect to amorphous silica did not occur in experiments with very low solid/water ratios. It also did not occur in higher solid/water experiments from which the SiO2 saturated supernatant was decanted and replaced with fresh deionized water after two weeks of reaction. The difference in dissolution behaviour is believed to result from deposition of a protective layer of amorphous silica from solution onto the MCM-41 surfaces, which reduces their dissolution rate. Thus, supersaturation with respect to amorphous silica is only manifested at early time and only when relatively large amounts of fresh MCM-41 are added to water. The solubility experiment was repeated using samples of Al-MCM-41 to determine the effect of Al substitution on the stability of the MCM-41. Dissolution curves for the Al-MCM-41 samples revealed behaviour that was analogous to that of the silica-based MCM-41 at similar solid/water ratios. Substitution of Al into the structure of MCM-41 appeared to have no positive or negative effects on the stability of the material in water. Solid MCM-41 material was recovered on days 28 and 79 of the solubility experiment and dried under vacuum. Solid material was also recovered from the Al-MCM-41 solubility experiment on day 79. These recovered samples were characterized by XRD and BET nitrogen adsorption analysis. An increase in background noise in the XRD plot of MCM-41 from the fresh to the 79 d sample indicated an increased proportion of an amorphous phase in the sample. The XRD plot of the 79 d sample of Al-MCM-41 also showed increased background noise corresponding to an increased proportion of an amorphous phase. The increased amorphous phase would have resulted from the continuous dissolution of the crystalline MCM-41 and reprecipitation as amorphous silica in the samples. BET surface area analysis of recovered MCM-41 compared to the freshly prepared material showed no significant change in surface area after 28 and 79 days in water. Analysis of the 79 d Al-MCM-41 indicated a 10% decrease in surface area relative to the as-prepared material. A set of SEM images were taken of the day 28 and 79 MCM-41 samples and compared to a sample of freshly prepared material. No substantial change in morphology was observed in the day 28 sample when compared to the fresh material. Some change was noted in the day 79 sample particle morphology, with worm-like structures appearing to be better developed than in the as-synthesized material. A series of palladized MCM-41 (Pd/MCM-41) samples with varying mass percent loadings of Pd was prepared to investigate the dehalogenation efficiency of Pd/MCM-41 in contact with TCE. TCE degradation was investigated in batch experiments. MCM-41 samples were prepared with calculated Pd loadings of 0.1, 1, and 5 mass %. The actual palladium content of the materials was determined using an EDAX-equipped SEM. The success of the loading technique was better at lower mass loadings of Pd, i.e. there was a greater deviation of actual Pd content from targeted or calculated contents at higher loadings of Pd. It was found that a procedure designed to yield 1% by mass Pd/MCM-41 produced an average loading of 0.95% Pd by mass. A procedure designed to produce a 5% Pd/MCM-41 sample resulted in an average loading of 2.6 mass %. These deviations were attributed to error inherent in the EDAX analysis and reduced effectiveness of the loading technique at higher Pd concentrations. All batch experiment reaction bottles were prepared with solid/liquid ratios of 1/800. The various Pd/MCM-41 samples induced rapid dehalogenation reactions, with the maximum extent of TCE degradation occurring before the first sample was taken at 7 to 12 min and within 35 min in the case of 0.1% Pd/MCM-41. The 0.1% Pd/MCM-41 sample degraded 70% of total TCE in solution with an estimated degradation half-life of 14 min. The 1% Pd/MCM-41 sample degraded 92% of total TCE in solution with an estimated half life of between 3 and 6 min. The 5% Pd/MCM-41 sample degraded only 22% of total TCE in solution; degradation half-life could not be determined. The seemingly paradoxical result of lower degradation efficiency at higher Pd loadings is proposed to result from absorption of hydrogen from solution by Pd, which is unreactive relative to the dissolved hydrogen in solution. Production of reaction intermediates and daughter products was also lower in the 1% by mass Pd/MCM-41 experiment compared to the 0.1 and 5% by mass Pd/MCM-41. Analysis of degradation products results from the experiments indicated that TCE degrades to ethane in the presence of Pd/MCM-41 with relatively low concentrations of chlorinated daughter products resulting from a random desorption process. A batch experiment using pure silica MCM-41 was also conducted to determine if there was adsorption of TCE to the support material itself. A lack of change in TCE concentration between the control sample and the MCM-41 sample during the experiment indicated no significant adsorption of TCE onto MCM-41. The conclusion of this research is that although MCM-41 is relatively unstable in water, its high TCE degradation efficiency shows promise for its application in developing water treatment technologies. However, more research needs to be conducted to fully determine the potential use of MCM-41 in water treatment and to investigate ways to improve its long-term stability in water.