Fractured rock formations represent a valuable source of groundwater and can be highly susceptible to contamination by dense, non-aqueous phase liquids (DNAPLs). The goal of this research is to evaluate the effectiveness of three accepted remediation technologies for addressing DNAPL contamination in fractured rock environments. The technologies under investigation in this study are chemical oxidation, bioremediation, and surfactant flushing. Numerical simulations were employed to examine the performance of each of these technologies at the field scale. The numerical model DNAPL3D-RX, a finite difference multiphase flow-dissolution-aqueous transport code that incorporates RT3D for multiple species reactions, was modified to simulate fractured rock environments. A gridding routine was developed to allow the model to accurately capture DNAPL migration in fractures and aqueous phase diffusion gradients in the matrix while retaining overall model efficiency. Reaction kinetics code subroutines were developed for each technology so as to ensure the key processes were accounted for in the simulations. The three remedial approaches were systematically evaluated via simulations in two-dimensional domains characterized by heterogeneous orthogonal fracture networks parameterized to be representative of sandstone, granite, and shale. Each simulation included a DNAPL release at the water table, redistribution to pools and residual, followed by 20 years of ‘ageing’ under ambient gradient conditions. Suites of simulations for each technology examined a variety of operational issues including the influence of DNAPL type and remedial fluid injection protocol. Performance metrics included changes in mass flux exiting, mass destruction in the matrix versus the fractures, and percentage of injected remedial fluid interacting with the target contaminant. The effectiveness of the three remediation technologies covered a wide range; the mass of contaminants destroyed were found to range from 15% to 99.5% of the initial mass present. Effectiveness of each technology was found to depend on a variety of critical factors particular to each approach. For example, in-situ chemical oxidation was found to be limited by the organic material present in the matrix of the rocks, while the efficiency of enhanced bioremediation was found to be related to factors such as the location of indigenous bacteria present in the domain and rate of bioremediation. In the chemical oxidation study, the efficiency of oxidant consumption was observed to be poor across the suite of scenarios, with greater than 90% of the injected permanganate consumed by natural oxidant demand. This study further revealed that the same factors that contributed to forward diffusion of contaminants prior to treatment are critical to this remediation method as they can determine the extent of contaminant destruction during the injection period. Bioremediation in fractured rock was demonstrated to produce relatively good results under robust first-order decay rates and active microorganisms throughout the fractures and matrix. It was demonstrated that under ideal conditions, of the total initial mass present, up to 3/4 could be reduced to ethene, indicating bioremediation may be a promising treatment approach due to the effective penetration of electron donor into the matrix during the treatment period and the ongoing treatment that occurs after injection ceases. However, when indigenous bacteria was assumed to exist only within the fractured walls of sandstone, it was found that under the same conditions, the rate of dechlorination was 200 times less than the Base Case. Since the majority of the mass resided in the matrix, lack of bioremediation in the matrix significantly reduced the effectiveness of treatment. Surfactant treatment with Tween-80 was proven to be a relatively effective technique in enhanced solubilisation of DNAPL from the fractures within the domain. However, by comparing the aqueous and sorbed mass at the start and end of the Treatment stage, it is revealed that surfactant treatment is not efficient in removing these masses that reside within the matrix. Furthermore, DNAPLs identified in dead end vertical fractures were found to remain in the domain by the end of the simulations across all scenarios studied; indicating that the injected surfactant experiences difficulty in accessing DNAPLs entrapped in dead end fractures. Altogether, the results underscore the challenge of restoring fractured rock aquifers due to the field scale limitations on sufficient contact between remedial fluids and in situ contaminants in all but the most ideal circumstances.

[pt] Efluentes contendo cianeto estão presentes em indústrias de importância como a minero-metalúrgica, siderúrgica, entre outras, constituindo estes potenciais riscos para os ecossistemas, devido à elevada toxicidade do cianeto. O alvo do presente trabalho foi estudar a cinética de degradação do cianeto com ácido de Caro (H2SO5), um poderoso oxidante produto da reação entre o H2SO4 e H2O2, e desenvolver um modelo matemático que envolvesse a oxidação de CN - e a decomposição simultânea do H2SO5. Os ensaios foram realizados em regime de batelada, e as amostras utilizadas na degradação foram soluções sintéticas de CN - livre. A metodologia experimental envolveu um desenho fatorial 24, levando em conta 4 variáveis: [CN-] mg/L, razão molar [H2SO5]:[CN-], pH e tipo de ácido de Caro, com a finalidade de avaliar o efeito de cada variável na cinética da degradação. A análise estatística mostrou que as variáveis mais preponderantes na cinética de degradação foram [CN-] mg/L e [H2SO5]:[CN-]. Uma avaliação físicoquímica mostrou também uma maior velocidade de degradação a um pH 9 em relação a um pH 11, enquanto que um tipo de [H2SO5] de razão molar H2SO4//H2O2 igual a 3:1 teve uma maior eficiência que utilizando um [H2SO5] de razão estequiométrica 1:1. O ácido de Caro mostrou-se efetivo na degradação de cianeto, permitindo que em condições de: [CN-]o = 400 mg/L, , pH = 9, razão molar [H2SO5]/[CN-] = 3:1, e tipo de [H2SO5] = 3:1, atingi-se uma concentração final de [CN-] < 0,2 mg/L em um t = 10 min. / [en] Effluents containing cyanides are generated in important industrial áreas such as mining-metallurgical, steelmaking, petrochemical, amongst others, carrying potential risks to the environment due to the high toxicity of cyanide. The aim of the present work is to study the kinetics of cyanide degradation with Caro s Acid (H2SO5), a powerful oxidant generated by the reaction between concentrated grades of H2SO4 and H2O2, and to develop a mathematical model involving CN - oxidation and simultaneous self-decomposition of H2SO5. The experiments were conducted in batches using synthetic solutions of free cyanide. The experimental methodology employed involved a 24 factorial design with the four factors: initial [CN-] mg/L, molar rate [H2SO5]:[CN-], pH e type of Caro s acid, with the aim to evaluate the effect of these factors in the process reaction kinetics. The statistical analyses showed that the most affecting variables were initial [CN-] mg/L and [H2SO5]:[CN-] molar ratio. Nevertheless a physicalchemical evaluation showed that also pH and type of Caro s Acid made of 1 or 3 moles of H2SO4 with 1 mole of H2O2, had effect on the kinetics. The highest observed reaction rate was obtained in the following conditions: initial [CN-] = 400 mg/L, molar ratio [H2SO5]/[CN-]= 3:1, pH = 9 and type of Caro s acid = 3 moles H2SO4 to 1 mole H2O2, achieving a value of [CN-] < 0,2 mg/L in t = 10 min.

Recentemente, o uso de persulfato em processo de oxidação química in situ em áreas contaminadas por compostos orgânicos ganhou notoriedade. Contudo, a matriz sólida do solo pode interagir com o persulfato, favorecendo a formação de radicais livres, evitando o acesso do oxidante até o contaminante devido a oxidação de compostos reduzidos presentes no solo ou ainda pela alteração das propriedades hidráulicas do solo. Essa pesquisa teve como objetivos avaliar se as interações entre a solução de persulfato com três solos brasileiros poderiam eventualmente interferir sua capacidade de oxidação bem como se a interação entre eles poderia alterar as propriedades hidráulicas do solo. Para isso, foram realizados ensaios de oxidação do Latossolo Vermelho (LV), Latossolo Vermelho Amarelo (LVA) e Neossolo Quartzarênico (NQ) com solução de persulfato (1g/L e 14g/L) por meio de ensaios de batelada, bem como a oxidação do LV por solução de persulfato (9g/L e 14g/L) em colunas indeformadas. Os resultados mostraram que o decaimento do persulfato seguiu modelo de primeira ordem e o consumo do oxidante não foi finito. A maior constante da taxa de reação (kobs) foi observada para o reator com LV. Essa maior interação foi decorrente da diferença na composição mineralógica e área específica. A caulinita, a gibbsita e os óxidos de ferro apresentaram maior interação com o persulfato. A redução do pH da solução dos reatores causou a lixiviação do alumínio e do ferro devido a dissolução dos minerais. O ferro mobilizado pode ter participado como catalisador da reação, favorecendo a formação de radicais livres, mas foi o principal responsável pelo consumo do oxidante. Parte do ferro oxidado pode ter sido precipitado como óxido cristalino favorecendo a obstrução dos poros. Devido à maior relação entre massa de persulfato e massa de solo, a constante kobs obtida no ensaio com coluna foi 23 vezes maior do que a obtida no ensaio de batelada, mesmo utilizando concentração 1,5 vezes menor no ensaio com coluna. Houve redução na condutividade hidráulica do solo e o fluxo da água mostrou-se heterogêneo após a oxidação devido a mudanças na estrutura dos minerais. Para a remediação de áreas com predomínio de solos tropicais, especialmente do LV, pode ocorrer a formação de radicais livres, mas pode haver um consumo acentuado e não finito do oxidante. Verifica-se que o pH da solução não deve ser inferior a 5 afim de evitar a mobilização de metais para a água subterrânea e eventual obstrução dos poros por meio da desagregação dos grãos de argila. / Recently the persulfate application for in situ chemical oxidation at areas contaminated by organic compounds gained notoriety. However, the persulfate can interact with the solid matrix of the soil favoring the formation of free radicals, avoiding the oxidant access to the contaminant due to the oxidation of reduced compounds present in the soil or by changing the hydraulic properties of the soil. This research aimed to evaluate if the interactions between the persulfate solutions and three Brazilian tropical soils could eventually interfere on the persulfate oxidation capacity and if the interaction between them could modify the hydraulic properties of the soil. For such, oxidation tests were performed with soils: Latossolo Vermelho (LV), Latossolo Vermelho Amarelo (LVA) and Neossolo Quartzarênico (NQ) with persulfate solution (1 and 14 g/L) through batch tests and LV oxidation by persulfate solution (9 and 14 g/L) on undisturbed columns. The results showed that persulfate decay followed a first order model and oxidant consumption was not finite. The higher reaction rate coefficient (kobs) was observed in the reactor with LV. This higher interaction was due to the difference in the mineralogical composition and surface area. Kaolinite, gibbisita and iron oxides showed greater interaction with persulfate. The pH reduction on the reactor solution caused the aluminum and iron leaching due to dissolution of minerals. The mobilized iron may have participated as a reaction catalyst favoring the formation of free radicals although it was the major responsible for the oxidant consumption. Part of oxidized iron may have been precipitated as crystalline oxide favoring the clogged pores. As a consequence of the higher mass proportion between persulfate and soil, the kobs constant obtained in the column test was 23 times higher than the one observed on the batch test, even utilizing a concentration 1.5 times lower than bath test. There was a reduction in the soil hydraulic conductivity and the water flow proved to be heterogeneous after oxidation due to changes in minerals structure. For remediation purposes in areas with predominance of tropical soils, especially LV, the formation of free radicals may occur but an accented and not finite oxidant consumption may happen. It is verified that the pH solution should not be inferior than 5 to prevent the mobilization of metals to the groundwater and a possible pores clogging by the breakdown of the clay grains.

Peptide mass fingerprinting (PMF) of protein digests is a widely-accepted method for protein identification in MS-based proteomic studies. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) is the technique of choice in PMF experiments. The success of protein identification in a PMF experiment is directly related to the amount of amino acid sequence coverage. In an effort to increase the amount of sequence information obtained in a MALDI PMF experiment, performic acid oxidation is performed on tryptic digests of known proteins. Performic acid was chosen as the chemical oxidant due to the ease of use and to the selective oxidation of cysteine, methionine, and tryptophan residues. In experiments performed in our laboratory, performic acid oxidation either increased or did not affect protein sequence coverage in PMF experiments when oxidized tryptic digests were analyzed by MALDI. Negative mode MALDI data were acquired, as well as positive mode MALDI data, due to the enhanced ionization of cysteic acid-containing peptides in negative mode. Furthermore, the confidence in a protein match is increased by observation of mass shifts indicative of cysteine, methionine, and/or tryptophan in oxidized peptide ion signals when comparing MALDI spectra prior to performic acid oxidation and after oxidation due to the low abundance of these residues in the majority of all known and hypothetical proteins.

In situ chemical oxidation (ISCO) is a leading-edge technology for soil and groundwater remediation, and involves injecting a chemical oxidant (e. g. , permanganate, hydrogen peroxide, or persulfate) into the subsurface to deplete contaminant mass through oxidation. Since the delivery of the chosen oxidant to the target treatment zone must occur in situ, the interaction between the injected oxidant and the aquifer material is a key controlling factor for a successful ISCO application. While many published ISCO studies have focused on the interaction between an oxidant and target contaminants, many questions still remain on the interaction between a potential oxidant and the aquifer material. Through a series of bench-scale experiments with aquifer materials collected from 10 sites throughout North America, the research presented in this thesis provides insight into the interaction between these aquifer materials and two widely used ISCO oxidants; permanganate and hydrogen peroxide. <br /><br /> The investigation into the interaction between aquifer materials and permanganate consisted of three series of bench-scale experiments: (1) long-term batch experiments which were used to investigate permanganate consumption in response to fundamental geochemical properties of the aquifer materials, (2) short-term batch experiments which were designed to yield kinetic data that describe the behavior of permanganate in the presence of various aquifer materials, and (3) column experiments which were used to investigate permanganate transport in a system that mimics the subsurface environment. The long-term experiments which involved more than 180 batch reactors monitored for ~300 days showed that the unproductive permanganate consumption by aquifer materials or natural oxidant demand (NOD) is strongly affected by the initial permanganate concentration, permanganate to solid mass ratio, and the reductive components associated with each aquifer material. This consumption cannot be represented by an instantaneous reaction process but is kinetically controlled by at least a fast and slow reactive component. Accordingly, an empirical expression for permanganate NOD in terms of aquifer material properties, and a hypothetical kinetic model consisting of two reaction components were developed. In addition, a fast and economical permanganate NOD estimation procedure based on a permanganate COD test was developed and tested. The investigation into short-term permanganate consumption (time scale of hours) was based on the theoretical derivation of the stoichiometric reaction of permanganate with bulk aquifer material reductive components, and consisted of excess permanganate mass experiments and excess aquifer material mass experiments. The results demonstrated that permanganate consumption by aquifer materials can be characterized by a very fast reaction on the order of minutes to hours, confirming the existence of the fast reaction component of the hypothetical kinetic model used to describe the long-term permanganate NOD observations. A typical experimental column trial consisted of flushing an aquifer-material packed column with the permanganate source solution until sufficient permanganate breakthrough was observed. The permanganate column results indicated the presence of a fast and slow consumption rate consistent with the long-term batch test data, and an intermediate consumption rate affecting the shape of the rising limb of the breakthrough curve. Finally, a comparison of the experimental results between batch and column systems indicated that permanganate NOD was significantly overestimated by the batch experiments; however, permanganate consumption displayed some similarity between the batch and column systems and hence an empirical expression was developed to predict permanganate consumption in physically representative column systems from batch reactor data. <br /><br /> The interaction between hydrogen peroxide and aquifer materials was also investigated with both batch and column experiments. A series of batch experiments consisting of a mixture of 2% hydrogen peroxide and 15 g of aquifer materials was used to capture the overall hydrogen peroxide behavior in the presence of various aquifer materials. The results indicated that the decomposition of hydrogen peroxide in the presence of various aquifer materials followed a first-order rate law, and was strongly affected by the content of amorphous transition metals (i. e. , Fe and Mn). Although hydrogen peroxide decomposition is related to the total organic carbon (TOC) content of natural aquifer materials, the results from a two-week long exposure to hydrogen peroxide suggests that not all forms of natural organic matter contributed to this decomposition. A multiple linear regression analysis was used to generate predictive relationships to estimate hydrogen peroxide decomposition rate coefficients based on various aquifer material properties. The enhanced stability of hydrogen peroxide was investigated under six scenarios with the addition of chelating reagents. The impact of a new green chelating reagent, S,S'-ethylenediaminedisuccinate (EDDS), on the stability of hydrogen peroxide in the presence of aquifer materials was experimentally examined and compared to that of the traditional and widely used chelating reagent, Ethylenediaminetetraacetic (EDTA). The results demonstrated that EDDS was able to significantly increase the stability of hydrogen peroxide, especially for aquifer materials with low TOC contents and/or high dissolvable Fe and Mn contents. Finally, to complement and expand the findings from the batch experiments, column experiments were conducted with aquifer materials from five representative sites. Each column was flushed with two types of source solutions (with or without EDDS addition) at two flow rates. The column experiments showed that the use of EDDS resulted in an earlier breakthrough and a higher stable concentration of hydrogen peroxide relative to the case without the addition of EDDS. The hydrogen peroxide decomposition rate coefficients generated from the column data were significantly higher than those generated from the batch test data and no correlation between hydrogen peroxide decomposition coefficients obtained from column and batch experiments was observed. Based on the column experimental results, a one-dimensional transport model was also calibrated to capture the hydrogen peroxide breakthrough process. <br /><br /> Data from bench-scale tests are routinely used to support both ISCO design and site screening, and therefore the findings from this study can be used as guidance on the utility of these tests to generate reliable and useful information. In general, the behavior of both permanganate and hydrogen peroxide in the presence of aquifer materials in batch and the column systems clearly indicates that the use of batch test data for ISCO system design is questionable since column experiments are believed to mimic in situ conditions better since column systems provide more realistic aquifer material contact. Thus the scaling relationships developed in this study provide meaningful tools to transfer information obtained from batch systems, which are widely employed in most bench-scale studies, to column systems.

Reagent injections designed to provide in stiu mass destruction of soil and groundwater contaminants are commonly prone to failure due to inadequate distribution of the injected reagent. Reagent injections, in particular in situ chemical oxidation (ISCO) injections, require contact between the treatment reagent and targeted contaminant to allow for mass destruction in source zones and plumes. Subsurface heterogeneities that exist at all spatial scales prevent remediation specialists from accurate prediction of reagent distribution in the subsurface, even when significant site characterization and hydraulic testing has previously taken place. A prototype probe system was developed to provide real-time monitoring of the distribution of injected reagents. This thesis focused on laboratory testing of the system to verify that the design was capable of indicating the presence of an injected reagent in the field. Temperature and two-wire dipole resistance sensors were developed with low-cost materials to provide feedback on the electrical conductivity (EC) signatures produced by typical reagents mixed as salt solutions. Sensors were attached to sections of PVC conduit and wired to a data acquisition system to control measurements and store data. The temperature sensor was found to accurately respond to temperature changes in comparison to a commercial datalogger. Measured temperature differences between the constructed sensor and commercial datalogger were relatively constant, indicating that the constructed sensor could be calibrated to measurements from a commercial logger. Static cell experiments were conducted in beakers with varying concentration sodium chloride (NaCl), potassium permanganate (KMnO4) and sodium persulfate (Na2S2O8) solutions to determine dipole resistance sensor response to variations in EC. Different fixed resistors were wired with the dipole sensor circuit to determine the impact on sensor readings. Results indicated a nonlinear correlation between two-wire dipole resistance sensor response and increasing EC. Each constructed dipole sensor behaved uniquely. Raw sensor response was calibrated to EC by accounting for the influence of the fixed resistor. Data was fit to a second-order polynomial with form y = aEC2 + bEC + c, with r2 ranging from 0.92-1.00 for experiments with 4-6 measurement points. Calibrations were accurate within the range of EC for each static cell experiment; trends extrapolated beyond the measurement range were subject to significant error. The choice of fixed resistor did not appear to alter the accuracy of probe calibrations. Flow cell experiments were designed to analyze dipole resistance sensor response to continuous changes in EC. EC breakthrough curves (BTCs) were produced by injecting NaCl tracer solutions into the flow cell. Initial flow cell experiments conducted in an open water system showed agreement between dipole sensor measurement and handheld EC measurements on the rising limb of BTCs and divergence between the two datasets on the falling limb of BTCs. To resolve these issues, a more sophisticated tank with a porous medium was built and tested to compare sensor response from s prototype probe and a commercial EC datalogger. EC BTCs were measured under two scenarios: (1) conditions with deionized water (DI) circulating through the tank as the background solution, and (2) conditions with a simulated groundwater solution with elevated EC circulating through the tank as the background solution. BTCs produced agreement between EC recorded by the commercial logger and dipole resistance measurements for both the rising and falling limbs of BTCs. Results indicated the dipole resistance sensor was not capable of resolving fine changes in EC that occurred during breakthrough. A calibration of all in situ measurements from the experiments with porous medium confirmed the simulated groundwater experiments were subject to significantly less variability than the deionized water experiments. The calibration applied to the simulated groundwater measurements produced BTCs that matched very closely with those recorded by the commercial logger. Two field trials were also conducted during ISCO injections at contaminated sites where probes were installed in existing monitoring wells. The field trials did not successfully correlate dipole resistance sensor measurements with oxidant concentration. Observations from the second trial indicated the dipole sensor measurements correlated with EC of water samples. This work has provided a theoretical representation of two-wire dipole resistance sensor response to EC and has verified expected results through laboratory experiments. It has analyzed the influence of temperature and choice of fixed resistors on two-wire dipole resistance sensor readings, has extensively tested sensor response to EC during static cell and BTC experiments, and has displayed the prototype probe is capable of indicating the presence of injected reagents that have an EC signature. Further research avenues include pilot-scale testing in the field and developing a design for use with a direct-push rig.

In situ chemical oxidation (ISCO) is a leading-edge technology for soil and groundwater remediation, and involves injecting a chemical oxidant (e. g. , permanganate, hydrogen peroxide, or persulfate) into the subsurface to deplete contaminant mass through oxidation. Since the delivery of the chosen oxidant to the target treatment zone must occur in situ, the interaction between the injected oxidant and the aquifer material is a key controlling factor for a successful ISCO application. While many published ISCO studies have focused on the interaction between an oxidant and target contaminants, many questions still remain on the interaction between a potential oxidant and the aquifer material. Through a series of bench-scale experiments with aquifer materials collected from 10 sites throughout North America, the research presented in this thesis provides insight into the interaction between these aquifer materials and two widely used ISCO oxidants; permanganate and hydrogen peroxide. <br /><br /> The investigation into the interaction between aquifer materials and permanganate consisted of three series of bench-scale experiments: (1) long-term batch experiments which were used to investigate permanganate consumption in response to fundamental geochemical properties of the aquifer materials, (2) short-term batch experiments which were designed to yield kinetic data that describe the behavior of permanganate in the presence of various aquifer materials, and (3) column experiments which were used to investigate permanganate transport in a system that mimics the subsurface environment. The long-term experiments which involved more than 180 batch reactors monitored for ~300 days showed that the unproductive permanganate consumption by aquifer materials or natural oxidant demand (NOD) is strongly affected by the initial permanganate concentration, permanganate to solid mass ratio, and the reductive components associated with each aquifer material. This consumption cannot be represented by an instantaneous reaction process but is kinetically controlled by at least a fast and slow reactive component. Accordingly, an empirical expression for permanganate NOD in terms of aquifer material properties, and a hypothetical kinetic model consisting of two reaction components were developed. In addition, a fast and economical permanganate NOD estimation procedure based on a permanganate COD test was developed and tested. The investigation into short-term permanganate consumption (time scale of hours) was based on the theoretical derivation of the stoichiometric reaction of permanganate with bulk aquifer material reductive components, and consisted of excess permanganate mass experiments and excess aquifer material mass experiments. The results demonstrated that permanganate consumption by aquifer materials can be characterized by a very fast reaction on the order of minutes to hours, confirming the existence of the fast reaction component of the hypothetical kinetic model used to describe the long-term permanganate NOD observations. A typical experimental column trial consisted of flushing an aquifer-material packed column with the permanganate source solution until sufficient permanganate breakthrough was observed. The permanganate column results indicated the presence of a fast and slow consumption rate consistent with the long-term batch test data, and an intermediate consumption rate affecting the shape of the rising limb of the breakthrough curve. Finally, a comparison of the experimental results between batch and column systems indicated that permanganate NOD was significantly overestimated by the batch experiments; however, permanganate consumption displayed some similarity between the batch and column systems and hence an empirical expression was developed to predict permanganate consumption in physically representative column systems from batch reactor data. <br /><br /> The interaction between hydrogen peroxide and aquifer materials was also investigated with both batch and column experiments. A series of batch experiments consisting of a mixture of 2% hydrogen peroxide and 15 g of aquifer materials was used to capture the overall hydrogen peroxide behavior in the presence of various aquifer materials. The results indicated that the decomposition of hydrogen peroxide in the presence of various aquifer materials followed a first-order rate law, and was strongly affected by the content of amorphous transition metals (i. e. , Fe and Mn). Although hydrogen peroxide decomposition is related to the total organic carbon (TOC) content of natural aquifer materials, the results from a two-week long exposure to hydrogen peroxide suggests that not all forms of natural organic matter contributed to this decomposition. A multiple linear regression analysis was used to generate predictive relationships to estimate hydrogen peroxide decomposition rate coefficients based on various aquifer material properties. The enhanced stability of hydrogen peroxide was investigated under six scenarios with the addition of chelating reagents. The impact of a new green chelating reagent, S,S'-ethylenediaminedisuccinate (EDDS), on the stability of hydrogen peroxide in the presence of aquifer materials was experimentally examined and compared to that of the traditional and widely used chelating reagent, Ethylenediaminetetraacetic (EDTA). The results demonstrated that EDDS was able to significantly increase the stability of hydrogen peroxide, especially for aquifer materials with low TOC contents and/or high dissolvable Fe and Mn contents. Finally, to complement and expand the findings from the batch experiments, column experiments were conducted with aquifer materials from five representative sites. Each column was flushed with two types of source solutions (with or without EDDS addition) at two flow rates. The column experiments showed that the use of EDDS resulted in an earlier breakthrough and a higher stable concentration of hydrogen peroxide relative to the case without the addition of EDDS. The hydrogen peroxide decomposition rate coefficients generated from the column data were significantly higher than those generated from the batch test data and no correlation between hydrogen peroxide decomposition coefficients obtained from column and batch experiments was observed. Based on the column experimental results, a one-dimensional transport model was also calibrated to capture the hydrogen peroxide breakthrough process. <br /><br /> Data from bench-scale tests are routinely used to support both ISCO design and site screening, and therefore the findings from this study can be used as guidance on the utility of these tests to generate reliable and useful information. In general, the behavior of both permanganate and hydrogen peroxide in the presence of aquifer materials in batch and the column systems clearly indicates that the use of batch test data for ISCO system design is questionable since column experiments are believed to mimic in situ conditions better since column systems provide more realistic aquifer material contact. Thus the scaling relationships developed in this study provide meaningful tools to transfer information obtained from batch systems, which are widely employed in most bench-scale studies, to column systems.

Petroleum hydrocarbons (PHCs) such as gasoline are ubiquitous organic compounds present at contaminated sites throughout the world. Accidental spills and leakage from underground storage tanks results in the formation of PHC source zones that release hundreds of organic compounds, including the high impact, acutely toxic and highly persistent aromatics (e.g., benzene, toluene, ethylbenzene, xylenes, trimethylbenzenes and naphthalene) into groundwater. Contamination by these compounds continues to persist until the PHC source zone is treated in place or removed. In situ chemical oxidation (ISCO) employing persulfate was identified as a potentially viable technology for the treatment of PHC source zones. The effectiveness and efficiency and, therefore, the overall economic feasibility of a persulfate-based ISCO treatment system depend upon the reactivity of the target organic compounds and the interaction of persulfate with aquifer media. The objective of this research was to investigate the persistence of unactivated and activated persulfate in the presence of aquifer materials, and to examine persulfate oxidation of PHC compounds at both the bench- and pilot-scales. A series of bench-scale studies were performed to estimate persulfate degradation kinetic parameters in the presence of seven well-characterized, uncontaminated aquifer materials and to quantify the changes in specific properties of these materials. Batch experiments were conducted in an experimental system containing 100 g of solids and 100 mL of persulfate solution at 1 or 20 g/L. Column experiments were designed to mimic in situ conditions with respect to oxidant to solids mass ratio and were performed in a stop-flow mode using a 1 g/L persulfate solution. The degradation of persulfate followed a first-order rate law for all aquifer materials investigated. An order of magnitude decrease in reaction rate coefficients was observed for systems that used a persulfate concentration of 20 g/L as compared to those that used 1 g/L due to ionic strength effects. As expected, the column experiments yielded higher reaction rate coefficients than batch experiments for the same persulfate concentration due to the lower oxidant to solids mass ratio. Bench-scale data was used to develop a kinetic model to estimate the kinetic response of persulfate degradation during these tests. The push-pull tests involved the injection of persulfate (1 or 20 g/L) and a conservative tracer into a hydraulically isolated portion of the sandy aquifer at CFB Borden, Canada. The kinetic model developed from the bench-scale data was able to reproduce the observed persulfate temporal profiles from these push-pull tests. This implies that persulfate degradation kinetics is scalable from bench-scale to in situ scale, and bench tests can be employed to anticipate in situ degradation. The estimated reaction rate coefficients indicate that persulfate is a persistent oxidant for the range of aquifer materials explored with half lives ranging from 2 to 600 days, and therefore in situ longevity of persulfate will permit advective and diffusive transport in the subsurface. This is critical for successful delivery of oxidant to dispersed residuals in the subsurface. Activation of persulfate is generally recommended to enhance its oxidation potential and reactivity towards organic compounds. This approach may influence the stability of persulfate-activator system in the presence of aquifer materials. A series of batch tests were performed to investigate persistence of persulfate at two concentrations (1 or 20 g/L) using three contemporary activation strategies (citric acid chelated-ferrous, peroxide and high pH ) in the presence of 4 well-characterized, uncontaminated aquifer materials. Chelation by citric acid was ineffective in controlling the interaction between persulfate and Fe(II) and a rapid loss in persulfate concentration was observed. Higher Fe(II) concentration (600 mg/L) led to greater destabilization of persulfate than lower Fe(II) concentration (150 mg/L) and the persulfate loss was stoichiometrically equivalent to the Fe(II) concentration employed. Subsequent to this rapid loss of persulfate, first-order degradation rate coefficients (kobs) were estimated which were up to 4 times higher than the unactivated case due to the interaction with Fe(III) and CA. Total oxidation strength (TOS) was measured for peroxide activation experiments and was observed to decrease rapidly at early time due peroxide degradation. This was followed by slow degradation kinetics similar to that of unactivated persulfate implying that the initial TOS degradation was peroxide dominated and the long-term kinetics were dominated by persulfate degradation. The kobs used to capture TOS degradation for later time were shown to depend upon unactivated persulfate and peroxide degradation rate coefficients, and peroxide concentration. Either a slow peroxide degradation rate and/or higher peroxide concentration allow a longer time for peroxide and persulfate to interact which led to kobs ~1 to 100 times higher than kobs for unactivated persulfate. For alkaline activation, kobs were only 1 to 4 times higher than unactivated persulfate and therefore alkaline conditions demonstrated the least impact on persulfate degradation among the various activation strategies used. For all activation trials, lower stability of persulfate was observed at 1 g/L as compared to 20 g/L due to insufficient persulfate and/or ionic strength effects. A series of batch reactor trials were designed to observe the behavior of the nine high impact gasoline compounds and the bulk PHC fraction measures subjected to various persulfate activation strategies over a 28-day period. This bench-scale treatability used unactivated persulfate (1 or 20 g/L) and activated persulfate (20 g/L). Activation employed chelated-Fe(II), peroxide, high pH or two aquifer materials as activators. No significant oxidation of the monitored compounds was observed for unactivated persulfate at 1 g/L, but 20 g/L persulfate concentration resulted in their near-complete oxidation. Oxidation rates were enhanced by 2 to 18 times by activation with peroxide or chelated-Fe(II). For alkaline activation, pH 11 trials demonstrated ~2 times higher oxidation rates than the unactivated results. For pH 13 activation the oxidation rates of benzene, toluene and ethylbenzene were reduced by 50% while for the remaining monitored compounds they were enhanced by 5 to 100%. Natural activation by both aquifer materials produced oxidation rates similar to the unactivated results, implying that either activation by minerals associated with aquifer material was not significant or that any potential activation was offset by radical scavenging from aquifer material constituents. Acid-catalyzation at pH <3 may enhance oxidation rates in weakly buffered systems. Oxidation of the monitored compounds followed first-order reaction kinetics and rate coefficients were estimated for all the trials. Overall, activated and unactivated persulfate appear to be suitable for in situ treatment of gasoline. Persulfate under unactivated or naturally activated conditions demonstrated significant destruction of gasoline compounds and showed higher persulfate persistence when in contact with aquifer solids as compared to chelated-Fe(II) or peroxide-activated persulfate systems. This observation was used as the basis for selecting unactivated sodium persulfate for a pilot-scale treatment of gasoline-contaminated source zone at CFB Borden, Canada where a ~2000 L solution of persulfate (20 g/L) was injected into a PHC source zone. Concentration of organics and inorganics were frequently monitored over a 4 month period across a 90 point monitoring fence line installed down-gradient. Treatment performance was measured by estimating organic and inorganic mass loading across the monitoring fence. Increased mass loading for sodium was observed over time as the treatment volume moved across the fence-line indicating transport of the inorganic slug created upon oxidant injection. The mass loading also increased for sulfate which is a by-product generated either due to persulfate degradation during oxidation of organic compounds or during its interaction with aquifer materials. Oxidation of organic compounds was evident from the enhanced mass loading of dissolved carbon dioxide. More importantly, a significant (45 to 86%) decrease in mass loading of monitored compounds was observed due to oxidation by injected persulfate. The cumulative mass crossing the monitoring fence-line was 20 to 50% lower than that expected without persulfate treatment. As the inorganic slug was flushed through the source zone and beyond the monitoring fence, the mass loading rate of sodium, sulfate and carbon dioxide decreased and approached background condition. Mass loading of the monitored compounds increased to within 40 to 80% of the pre-treatment conditions, suggesting partial rebound. These investigations assessed the impact of activation on persulfate persistence and treatability of gasoline and served to establish guidelines for anticipating field-scale persulfate behavior under similar conditions. In summary, unactivated persulfate is a stable oxidant in the presence of aquifer materials and its persistence depends upon TOC and Fe(Am) content of the materials, ionic strength, and aquifer to solids mass ratio. Persulfate exhibits significant destruction of gasoline compounds and can be employed for the remediation of gasoline-contaminated sites. Peroxide and chelated-Fe(II) enhance oxidation rates of these compounds, but reduce stability of the persulfate-activator system. Persulfate activation using high pH conditions does not significantly impact persulfate persistence but reduces the overall destruction of gasoline compounds. Therefore, activation imposes a trade-off between enhanced oxidation rates and reduced persulfate persistence. Kinetic model is representative of persulfate degradation at bench- and pilot-scales and can be used for estimation of in situ degradation. The quantification of oxidation rates for gasoline compounds under activated and unactivated persulfate conditions will assist decision-making for identification of appropriate remediation options when targeting contamination by gasoline or by specific high impact gasoline compounds. While persulfate oxidation resulted in partial treatment of a small gasoline source zone, aggressive persulfate load will be required during injection for a complete clean-up. Overall, persulfate-based in situ chemical oxidation was demonstrated to be an effective and a viable technology for the remediation of contaminated soil and groundwater.

The contamination of aquifer systems by petroleum hydrocarbons is a global problem. Underground storage tanks used for storing these hydrocarbons often leak, resulting in subsurface contamination. The hazards associated with petroleum hydrocarbon contamination are mainly attributable to the BTEX compounds, namely benzene, toluene, ethylbenzene and xylenes together with trimethylbenzenes (TMBs) and naphthalene due to their potential to impact human health and the ease with which they can enter the groundwater system. In situ chemical oxidation (ISCO) is the delivery of strong chemical oxidants to the subsurface for the purpose of treating organic contaminants. ISCO can be an effective way to remediate organic contaminants from the soil and groundwater. Sodium persulphate is one of the newer oxidants to gain widespread use in treating petroleum hydrocarbon contamination, though without being fully understood. This investigation tested the ability of unactivated sodium persulphate in treating dissolved phase and residual BTEX contamination through bench-scale laboratory tests and a pilot-scale field study. A degradation potential batch reactor test was carried out to assess the efficacy of unactivated sodium persulphate in oxidizing petroleum hydrocarbons present in contaminated groundwater as well as its effect on aquifer material from a field site. This test was carried out at a sodium persulphate concentration of 20 g/L. Results from this test did not follow the expected first-order degradation, and so subsequent experiments were carried out using a sodium persulphate concentration of 100 g/L. A test to determine the degree of interaction between the oxidant and aquifer material was also conducted. It was found that the degree of natural oxidant interaction for the field site in question was very low. 1000 kg of sodium persulphate was dissolved in nearly 10,000 L of water and injected into the subsurface. Electrical conductivity (EC), pH, sodium, persulphate, sulphate and BTEX were all monitored during the subsequent 152-day post-injection monitoring period. An empirical relationship was determined between EC and the concentration of sodium in groundwater. This enabled the use of EC as a real-time tracer to track the progress of the injectate. Field results supported predictions based on a simulation model that density-driven flow would play an important role in the delivery of the injectate. A portion of the injectate was believed to have been missed by the monitoring network. Areas that did show elevated tracer results in some cases showed a decrease in BTEX concentrations. Results were categorized in four ways. The first category had wells that showed strong evidence of injectate presence but little to no change in BTEX levels. The second category was comprised of wells that showed a reduction in BTEX levels along with the presence of injectate. BTEX levels in some wells rebounded towards the end of the study period. The third category consisted of wells that showed the presence of dilute injectate but did not show any reduction in BTEX concentrations. The fourth and final category was of wells that showed no evidence of having been affected by the injectate in any way. BTEX levels were the same as background. The oxidation of BTEX by unactivated sodium persulphate was found to be successful, though the vagaries of oxidant delivery and field sampling made difficult the accurate determination of the degree of success.

Groundwater at many existing and former industrial sites and disposal areas is contaminated by halogenated organic compounds that were released into the environment. The chlorinated solvent trichloroethylene (TCE) is one of the most ubiquitous of these compounds. In situ chemical oxidation (ISCO) has been successfully used for the removal of TCE. The objective of this study was to apply the ISCO technology to remediate TCE-contaminated groundwater. In this study, potassium permanganate (KMnO4) was used as the oxidant during the ISCO process. The study consisted bench-scale and pilot-scale experiments. In the laboratory experiments, the major controlling factors included oxidant concentrations, effects of soil oxidant demand (SOD) on oxidation efficiency, and addition of dibasic sodium phosphate on the inhibition of production of manganese dioxide (MnO2). Results show that higher molar ratios of KMnO4 to TCE corresponded with higher TCE oxidation rate under the same initial TCE concentration condition. Moreover, higher TCE concentration corresponded with higher TCE oxidation rate under the same molar ratios of KMnO4 to TCE condition. Results reveal that KMnO4 is a more stable and dispersive oxidant, which is able to disperse into the soil materials and react with organic contaminants effectively. Significant amount of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Results show that the increase in the first-order decay rate was observed when the oxidant concentration was increased, and the half-life was approximately 24.3 to 251 min. However, the opposite situation was observed when the second-order decay rate was used to describe the reaction. Results from the column experiment show that the breakthrough volumes were approximately 50.4 to 5.06 pore volume (PV). Injection of KMnO4 would cause the decrease in TCE concentration through oxidation. Results also indicate that the addition of Na2HPO4 would not inhibit the TCE removal rate. In the second part of this study, a TCE-contaminated site was selected for the conduction of pilot-scale study. A total of eight remediation wells were installed for this pilot-scale study. The initial TCE concentrations of the eight wells were as follows: C1 = 0.59 mg/L, C1-E = 0.64 mg/L, C1-W = 0.61 mg/L, EW-1 = 0.65 mg/L, EW-1E = 0.62 mg/L, EW-1W = 0.57 mg/L, C2 = 0.62 mg/L, C3 = 0.35 mg/L. C1, EW-1, C2, and C3 were located along the groundwater flow direction from the upgradient (C1) to the downgradient location (C3), and the distance between each well was 3 m. C1-E and C1-W were located in lateral to C1 with a distance of 3 m to C1. EW-1E and EW-1W were in lateral to EW-1 with a distance of 3 m to EW-1. In the first test, 2,700 L of KMnO4 solution was injected into each of the three injection wells (C1, C1-E, and C1-W) with concentration of 5,000 mg/L. Three injections were performed with an interval of 6 hr between each injection. After injection, the TCE concentrations in those three wells dropped down to below detection limit (<0.0025 mg/L). However, no significant variations in TCE concentrations were observed in other wells. In the second test, 2,700 L of KMnO4 solution was injected into injection well (EW-1) with concentration of 5,000 mg/L. Six injections were performed with an interval of 6 hr between each injection. After injection, the TCE concentrations in the injection well dropped down to below detection limit (<0.0025 mg/L). TCE concentrations in (C1, C1-E, C1-W, EW-1E, EW-1W, C2, and C3) dropped to 0.35-0.49 mg/L. After injection, no significant temperature and pH variation was observed. However, increase in conductivity and oxidation-reduction potential (ORP) was observed. This indicates that the KMnO4 oxidation process is a potential method for TCE-contaminate site remediation. The groundwater conductivity increased from 500 £gS/cm to 1,000 £gS/cm, and ORP increased from 200 to 600 mv. Increase in KMnO4, MnO2, and total Mn was also observed in wells. Results from the slug tests show that the hydraulic conductivity remained in the range from 10-4 to 10-5 m/sec before and after the KMnO4 injection.