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.

Water recycling has become a global trend because of water scarcity and increased demand of water supply. Therefore, attentions to the improvement of reclaimed water quality have been paid. In the past decade various environmental hormones and PPCPs (pharmaceuticals and personal care products) have been detected in different aquatic environments. Even though their concentrations are in the range of ng/L to £gg/L, these emerging contaminants might cause harm to human health and the environment. Nanoscale contaminants are another type of emerging contaminants cannot be neglected because many nanomaterials have been used in household goods of our daily lives. Thus, how to effectively separate and/or recover those nanomaterials from aqueous solution to reduce their potential hazards is an important issue The first objective of this study was to assess the efficiency of nano-Fe3O4/S2O82- oxidation against selected environmental hormones (i.e., di(2-ethylhexyl)phthalate (DEHP) and perfluorooctane sulphonates (PFOS)) and pharmaceuticals (i.e., erythromycin (ERY) and sulfamethoxazole (SMX)) in aqueous solution. The optimal operating conditions obtained from the above-indicated oxidation process were then transferred to a simultaneous electrocoagulation and electrofiltration (EC/EF) treatment module into which a tubular TiO2/Al2O3 composite membrane was incorporated. The purpose of this practice was to evaluate whether the EC/EF process could further enhance the removal of target contaminants. In this work nanoscale magnetite (nano-Fe3O4) used for activation of S2O82- oxidation was prepared by chemical coprecipitation. Then, X-ray powder diffractometry was used to confirm the crystal structure of the prepared particles as magnetite. The employment of 3 wt% soluble starch was found to be sufficient to stabilize nano-Fe3O4 for later uses. Further, slurries of nano-Fe3O4 and S2O82- (sodium persulfate) were prepared with three dosage ratios, namely 1:2.5, 1:5 and 1:10. Nano-Fe3O4/S2O82- slurries thus prepared were used for evaluating their efficiencies in removing target contaminants (i.e., DEHP, PFOS, ERY, and SMX) of two concentration levels. In this study the high concentration level referred to 38 mg/L for DEHP and 10 mg/L each for the rest of target contaminants, whereas 10 £gg/L as the low concentration level for each of target contaminants. Batch experiments of nano-Fe3O4/S2O82- oxidation against target contaminants were first carried out in glass beakers. In the case of high concentration level with a nano-Fe3O4-to-S2O82- dosage ratio of 1:10, the respective removal efficiencies for all target contaminants were greater than 98%. Using the same dosage ratio for the case of low concentration level, however, the respective removal efficiencies for all target contaminants decreased to 78-91% except for ERY. When all target contaminants of low concentration level co-existed in the reaction vessel, the residual concentrations of environmental hormones were found to be greater than that of pharmaceuticals. Under the circumstances, the removal efficiency of DEHP dropped to 70% or so. The reaction pathways of nano-Fe3O4/S2O82- oxidation against each of target contaminants with a high concentration level were also investigated. The degradation intermediates detected for all target contaminants were all in line with the literature. Besides, the degradation intermediates were all close to their respective end products except those originated from DEHP. In other words, nano-Fe3O4/S2O82- per se had a phenomenal oxidation rate against each target contaminant. The performance of EC/EF-assisted nano-Fe3O4/S2O82- oxidation against target contaminants of low concentration level was also evaluated in this study. In each test every contaminated aqueous solution was physically preconditioned within the EC/EF treatment module for 20 min prior to the application of an electric field to enact electrocoagulation and electrofiltration. The optimal operating conditions obtained were given as follows: aluminum anode, electric field strength of 60 V/cm, transmembrane pressure of 98 kPa, and crossflow velocity of 3.33 cm/s. Under such conditions, the removal efficiencies for DEHP, PFOS, ERY, and SMX were determined to be 95%, 99%, 100%, and 99%, respectively. In the case of mixed environmental hormones and pharmaceuticals, the respective removal efficiencies slightly decreased to 85-99%. It is evident that the coupling of the EC/EF process with nano-Fe3O4/S2O82- oxidation yielded a substantial removal increase for selected target contaminants. Additionally, in all tests of EC/EF-assisted nano-Fe3O4/S2O82- oxidation against target contaminants, no residual nano-Fe3O4 was found in permeate. After a simple adjustment of pH, permeate thus treated would be ready for reuse in cooling towers.

Contamination of soil/groundwater supplies by gasoline and other petroleum-derived hydrocarbons released from underground storage tanks (USTs) is a serious and widespread environmental problem. Corrosion, ground movement, and poor sealing can cause leaks in tanks and associated piping. Petroleum hydrocarbons contain methyl tertiary-butyl ether (MTBE) (a fuel oxygenate), benzene, toluene, ethylbenzene, and xylene isomers (BTEX), the major components of gasoline, which are hazardous substances regulated by many nations.The objective of this proposed study is to assess the potential of using a passive in situ oxidation barrier system. This passive active barrier system has advantages over conventional systems including less maintenance, cost-effectiveness, no above-ground facilities, no groundwater pumping and reinjection, and groundwater remediation in situ. The oxidation barrier system included a persulfate-releasing barrier, which contains persulfate-releasing materials. The slow-released persulfate would oxidize MTBE and benzene in aquifer. The persulfate-releasing materials would release persulfate when contacts with groundwater, thus oxidizes the MTBE and benzene. In the first part of this study, bench scale experiment was also performed to produce the persulfate-releasing materials high persulfate-releasing rate. The components of the persulfate-releasing materials and optimal concentrations of those components were determined in this study. Results indicate that the highest persulfate releasing rate can be obtained when the mass ratio of cement/sand/water was 1.4/0/0.7. Result obtained from the persulfate-releasing materials test and bench-scale were used for the design and operation of the following column experiments. Results from the column experiment indicate that approximately 98% of MTBE and 99% of benzene could be removed during the early persulfate-releasing stage. Results also reveal that the produced oxidation byproducts of MTBE, tert-butyl formate (TBF) and tert-butyl alcohol (TBA), can also be produce an acetone. Results from this study suggest that extra Fe(II) would cause the decrease in oxidation rates due to the reaction of sulfate with Fe(II). Results show that the parameters, which would affect the oxidation rate include persulfate concentration, oxidant reduction potential (ORP), conductivity, sulfate concentration, and contaminant concentration. The proposed treatment scheme would be expected to provide a more cost-effective alternative to remediate MTBE and other petroleum-hydrocarbon contaminated aquifers. Knowledge obtained from this study will aid in designing a persulfate oxidation system for site remediation.

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.

In this Thesis either advanced oxidation or reductive processes are investigated for the degradation of two pesticides considered persistent in the environment: amicarbazone (AMZ) and chlorpyrifos (CP). In chapter I, different advanced oxidation processes (AOPs) driven by sulfate (SO4o-) and hydroxyl radicals (oOH) were applied to the degradation of AMZ. In the first study, several persulfate (PS) activated reactions were explored for AMZ degradation, namely activation with UVA radiation, Fe(II) and H2O2, as well as the combination of UVA radiation with Fe(II), Fe(III) and Fe(III)-complexes. Here, the influence of different reaction variables, such as solution pH, reactants and pesticide initial concentrations, addition of a second oxidant (H2O2) and the addition of different iron catalysts were also investigated. Control experiments regarding the photolysis of iron species in the absence of PS captured our interest and, with the aim of exploring more deeply this process on AMZ degradation, a second investigation was carried out. In this second study, a Doehlert experimental design was applied to investigate the simultaneous effects of two variables on AMZ degradation: pH and Fe(III):carboxylate ratio, where the carboxylate could be oxalate, citrate or tartrate. A response surface model for the observed degradation rate (kobs) as a function of pH and Fe(III):carboxylate ratio was obtained. The processes explored in both aforementioned studies revealed to be effective for AMZ removal, although nothing is known yet about their effectiveness regarding toxicity removal. Given that, a third study was carried out, where the toxicity of AMZ solutions, before and after submission to the processes studied was evaluated towards five microorganisms: Vibrio fischeri (acute toxicity), Tetrahymena thermophile, Chlorella vulgaris (chronic toxicity), Escherichia coli and Bacilus subtilis (antimicrobial activity). The last investigation detailed in chapter I is related with the application of zero-valent-metals on PS activation, which is a subject that links this chapter with the following one. For that, zero-valent-iron (ZVI) was investigated as a PS activator and the influence of variables that help to assess the environmental applicability of this process. In general, organochlorine pesticides reveal a higher resistance to oxidation than reduction, the latter process preferred when the aim is to degrade that important class of contaminants. Therefore, in chapter II the reductive degradation of CP by means of zero-valent-metals and bimetallic particles was investigated. ZVI has been extensively applied for that purpose. However, besides iron, other zero-valent metals can be potential reactive materials for reductive degradation and hence, in this study, the effectiveness of Zn0 and Cu0 was also explored in comparison to that widely reported for ZVI. Furthermore, two different ways of enhancing metals reactivity were here explored: i) by coating ZVI or Zn0 with a more noble metal (Cu), in order to analyze the copper catalytic effect on the bimetallic system; ii) by different surface pretreatments. / Na presente Tese de Doutorado foram abordados tanto processos oxidativos avançados (POA), como processos redutivos por metais de valência zero, na degradação de dois pesticidas considerados persistentes no meio ambiente: amicarbazona (AMZ) e clorpirifós (CP). No capítulo I são apresentados os estudos realizados com diversos POA, mediados por radicais sulfato (SO4o-) e hidroxila (oOH), aplicados da AMZ. Num primeiro estudo foi explorada a ativação do oxidante persulfato (PS), de diferentes formas, tais como radiação UVA, H2O2 e Fe(II), assim como a combinação de radiação UVA com Fe(II), Fe(III) e complexos de Fe(III). Aqui também foram investigados os efeitos de diversas variáveis reacionais, tais como pH, concentração inicial de reagentes e de pesticida, adição de um segundo oxidante (H2O2) e adição de diferentes espécies de ferro. Os testes realizados, para efeito de controle, referentes à irradiação das espécies de Fe(III) na ausência de PS, despertaram o interesse para um estudo mais aprofundado sobre o efeito da fotólise destas espécies na degradação da AMZ, surgindo assim o segundo trabalho. Neste utilizou-se um projeto experimental de Doehlert, para avaliar o efeito de duas variáveis em simultâneo quanto à degradação da AMZ: pH e proporção Fe(III): ligante, sendo o ligante um dos seguintes carboxilatos: oxalato, citrato ou tartarato. Um modelo de superfície de resposta, que correlaciona a taxa de degradação observada (kobs) em função do pH e proporção Fe(III):ligante foi obtido para cada um dos complexos de Fe(III) estudados. Os processos explorados, tanto no primeiro como no segundo estudo, se mostraram eficazes na remoção da AMZ, porém nada se sabe acerca da remoção da toxicidade. Para tal, foi desenvolvido um terceiro estudo dedicado à avaliação da toxicidade da solução de AMZ, antes e após a aplicação de cada um dos processos anteriormente abordados, contra cinco micro-organismos: Vibrio fischeri (toxicidade aguda); Tetrahymena thermophila, Chlorella vulgaris (toxicidade crônica); Escherichia coli e Bacilus subtilis (atividade antimicrobiana). O último estudo abordado no capitulo I é referente à aplicação de metais de valência zero também nos POA, correlacionado assim o capítulo I e o capítulo II. Como tal, foi feito um estudo de ativação de PS por meio de ferro de valência zero (Fe0), em que se investigou a influência de diversas variáveis por forma a inferir sobre a aplicabilidade prática deste processo. Pesticidas organoclorados apresentam maior resistência à degradação por processos oxidativos do que redutivos, sendo preferível o último na degradação desta importante classe de contaminantes. Como tal, o capítulo II se refere à degradação redutiva, por meio de diferentes metais de valência zero e partículas bimetálicas, do pesticida organoclorado CP. Além do amplamente explorado Fe0, outros metais podem ser aplicados neste processo, pelo que, neste estudo, explorou-se a potencialidade de Zn0 e Cu0 comparativamente ao primeiro. Ainda neste estudo foram investigadas duas formas de aumentar a reatividade dos metais: i) no caso do Fe0 e Zn0, revestindo com um metal mais nobre (Cu), por forma a observar o efeito catalisador do último no sistema bimetálico; ii) realizando um pré-tratamento à superfície dos metais.

During the construction of the new urban area in the north-eastern part of Stockholm, Stockholm Royal Seaport, groundwater with extremely elevated levels of the carcinogenic aromatic hydrocarbon benzene was discovered in the area Hjorthagen. Such a contamination can be remediated in-situ by the use of chemical oxidation and biodegradation. Due to the fact that many factors such as contaminant composition, groundwater characteristics and temperature vary between sites, smaller bench scale studies are usually conducted before the full scale remediation on site. Little published research exists on the ability of these remediation techniques in areas with lower groundwater temperature such as Stockholm, why the need of a bench-scale study in this case is even larger. The objective of this master thesis is to, out of three investigated remediation agents, find the most suitable one for remediation of the benzene-contaminated groundwater in Hjorthagen. This was made in the form of a bench-scale study and the techniques studied were chemical oxidation, for which the two agents hydrogen peroxide (uncatalyzed and catalyzed in the form of Fenton’s reagent) and persulfate (activated with iron (II)) were used, and biological degradation by the use of a calcium peroxide-based compound. The study showed that the benzene-contaminated groundwater was best remediated with Fenton’s reagent, which was able to degrade the benzene with great success.

The efficiency of boron-doped diamond electrodes (BDD) has been investigated by electrolysis of an aqueous solution containing sodium sulfate. A Synthesis StarterKit from Condias was used, which contained the BDD anode with an active surface area of 3.14 cm2, and electrosynthesis was performed in a batch mode reactor. In this report, the electrooxidation of sodium sulfate to sodium persulfate is well reported. The production of persulfate was studied at different cell voltages and electrolyte concentrations. The amount of persulfate produced was determined by the iodometric titration and itwas found that its concentration in the electrolyte was directly proportional to the persulfate concentration, i.e, a larger amount of persulfate could be obtained when the electrolyte was highly concentrated, up to 1 M. For each of the samples the amount of persulfate that theoretically is possible to produce was calculated and subsequently compared to the actual amount of persulfate that was formed, ie. current efficiencies. These current efficiencies were unexpectedly low for all experiments except for one data point. Hydrogen gas was also produced as a by-product at the cathode, but it couldn ot be collected in the present setup. The results and some possible improvements are discussed in the report. / Effektiviteten av att använda bor-dopad diamant (BDD) för elektrosyntes med en vattenlösning innehållande natriumsulfat för att producera persulfat har undersökts. Den utrustningen som använde svar ett Syntes StarterKit från företaget Condias, denna innehöll en cell med BDD som anodmaterial vilken hade en aktiv area på 3,14 cm2. Produktionen av persulfat studerades vid olika cellspänningar och elektrolytkoncentrationer. Mängden av producerad persulfat bestämdes genom titrering. Detv isade sig att koncentrationen av elektrolyten var proportionell mot persulfatkoncentrationen, dvs. mer persulfat producerades vid högre elektrolytkoncentrationer. För varje prov beräknades även det teoretiska antalet mol persulfat som kan åstadkommas och jämfördes sedan med det faktiska antalet mol som producerades, detta gav strömeffektiviteten för den önskade reaktionen. Denna effektivitet var oväntat låg för alla prov förutom ett i experiment 4. Vätgas producerades som en biprodukt vid katoden, men på grund av begränsad tillgång till utrustning och tid kunde denna gas inte samlas uppför vidare analys. Resultaten och möjliga förbättringar diskuteras även i rapporten.

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