No description available.

The ability of supersaturated water injection (SWI) to recover non-aqueous phase liquids (NAPLs) was studied at the field scale as part of an ongoing program to evaluate its applicability to groundwater remediation. SWI uses Gas inFusionTM technology to efficiently dissolve gases into liquids at elevated pressures. SWI has been shown to both volatilize and mobilize residual NAPL ganglia (Li, 2004). During SWI pressurized water containing high concentrations of CO2 is injected into the subsurface below the zone of contamination. Once the injected water is in the aquifer the pressure drops substantially and the concentration of CO2 is no longer in equilibrium with the water and as a result CO2 bubbles nucleate. These bubbles then migrate upwards through the contaminated zone towards the water table. As they move they come into contact with residual NAPL ganglia and they either volatilize this NAPL, resulting in a bubble comprised of CO2 and gaseous NAPL, or mobilize this NAPL, resulting in a film of NAPL surrounding the bubble. In either case the bubbles continue to rise until they reach the water table at which point they are removed by a dual phase extraction system. In this work, a known amount of NAPL was emplaced below the water table at residual concentrations to represent a residual source of weathered gasoline. The source was created in a hydraulically isolated cell in an unconfined sand aquifer at CFB Borden, Ontario. After the source was emplaced SWI was used to remove as much of the contaminant mass as possible in 22.25 days of operation over three months. The goal of this project was to determine if SWI was capable of removing residual NAPL at a field site. It was successful in removing volatile NAPL but not non-volatile NAPL. 64% of the volatile compounds were removed but contaminant mass was still being removed when the system was shut down so with continued operation more mass would have been removed. There is no way of knowing how much more would have been removed had the project continued. These results indicate that continued development of the technology is warranted.

Methyl Tertiary-Butyl Ether (MTBE) contamination of groundwater and surface waters has become a relevant environmental and public safety concern in recent years. This anthropogenic compound is now persistent at low concentrations in several valuable ground and surface water locations within the United States due largely to the widespread production of MTBE for use as a fuel oxygenate in conjunction with negligent underground storage practices during the 1980's and 1990's. Though there are several treatment strategies for the remediation of MTBE spill sites, the most efficient strategy may be adsorption of MTBE by a packed column of silicalite-1 adsorbent. Effective adaption of this technology requires cheap production of silicalite-1 sorbent packing particles on the order of 3 millimeters diameter. This work entails the development of a new synthesis process which results in sufficient in-situ crystallization of silicalite-1 aggregates within a 3 millimeter spherical amorphous silica gel source. The crystal aggregates sizes can be tuned from 5 to 70 µm, depending on synthesis parameters, and the finished silicalite-1 aggregate particle takes the shape of the amorphous gel source. These aggregate particles, when containing a small amorphous core, should be suitable for packed adsorption column applications. Multiple hydrothermal synthesis experiments were performed by batch methods featuring silica gel spheres as the sole silica source for the batch. Zeolite nucleation and crystal growth were demonstrated throughout the amorphous bead. Synthesis parameters were optimized both for short synthesis times, optimal mechanical properties, and cost effectiveness. The influence of product crystal size on particle hardness was also investigated. The packing production process is sufficiently ready for supporting pilot scale adsorption studies.

The ability of supersaturated water injection (SWI) to recover non-aqueous phase liquids (NAPLs) was studied at the field scale as part of an ongoing program to evaluate its applicability to groundwater remediation. SWI uses Gas inFusionTM technology to efficiently dissolve gases into liquids at elevated pressures. SWI has been shown to both volatilize and mobilize residual NAPL ganglia (Li, 2004). During SWI pressurized water containing high concentrations of CO2 is injected into the subsurface below the zone of contamination. Once the injected water is in the aquifer the pressure drops substantially and the concentration of CO2 is no longer in equilibrium with the water and as a result CO2 bubbles nucleate. These bubbles then migrate upwards through the contaminated zone towards the water table. As they move they come into contact with residual NAPL ganglia and they either volatilize this NAPL, resulting in a bubble comprised of CO2 and gaseous NAPL, or mobilize this NAPL, resulting in a film of NAPL surrounding the bubble. In either case the bubbles continue to rise until they reach the water table at which point they are removed by a dual phase extraction system. In this work, a known amount of NAPL was emplaced below the water table at residual concentrations to represent a residual source of weathered gasoline. The source was created in a hydraulically isolated cell in an unconfined sand aquifer at CFB Borden, Ontario. After the source was emplaced SWI was used to remove as much of the contaminant mass as possible in 22.25 days of operation over three months. The goal of this project was to determine if SWI was capable of removing residual NAPL at a field site. It was successful in removing volatile NAPL but not non-volatile NAPL. 64% of the volatile compounds were removed but contaminant mass was still being removed when the system was shut down so with continued operation more mass would have been removed. There is no way of knowing how much more would have been removed had the project continued. These results indicate that continued development of the technology is warranted.

The potential of utilizing a new form of chemical processing technology called SpinChem® Rotating Bed Reactor (RBR), in combination with different reactive materials, for the purpose of remediating multi-contaminated aquifers under changing environmental conditions, was investigated using laboratory studies and geochemical models. Four different reactive materials, or combinations thereof, were tested: heat-treated peat powder combined with zero-valent iron (ZVI); IronPeat, which consists of peat powder coated with a ferriferous hydrosol (FFH); and a powdered steel waste product. Results showed that the powdered steel waste was compatible with the technology while the peat-based sorbents were not. However, there were no indications that the kinetics of the sorption reactions increased. This was attributed to the fact that the rate-limiting steps, for the binding of the studied metal(loid)s onto iron oxide, are generally considered to be dependent on the later stages of the sorption process related to diffusion mechanisms and not to the rate of mass transfer through the bulk liquid phase, which is what primarily is increased through application of the SpinChem® RBR technology.

No description available.

Permeable reactive barrier (PRB) technology is increasingly considered for in situ treatment of contaminated groundwater; however, current design formulas for PRBs are limited and do not properly account for all major physical and attenuation processes driving remediation. This study focused on developing a simple methodology to design PRBs that is easy to implement while improving accuracy and being more conservative than the available design methodologies. An empirical design equation and a simple analytical design equation were obtained to calculate the thickness of a PRB capable of degrading a contaminant from a source contaminant concentration to a maximum contaminant level at a Point of compliance . Both equations integrate the fundamental components that drive the natural attenuation process of the aquifer and the reactive capacity of the PRB.The empirical design equation was derived from a dataset of random hypothetical cases that used the solutions of the PRB conceptual model (Solution I). The analytical design equation was derived from particular solutions of the model (Solution II) which the study showed fit the complex solutions of the model well. Using the hypothetical cases, the analytical equation has shown that it gives an estimated thickness of the PRB just 15 % lower or higher than the real thickness of the PRB 95 percent of the time. To calculate the design thickness of a PRB, Natural attenuation capacity of the aquifer can be estimated from the observed contaminant concentration changes along aquifer flowpaths prior to the installation of a PRB. Bench-scale or pilot testing can provide good estimates of the required residence times ( Gavaskar et al. 2000) , which will provide the reactive capacity of the PRB needed for the calculation. The results of this study suggest also that the installation location downgradient from the source of contaminant is flexible. If a PRB is installed in two different locations, it will achieve the same remediation goals. This important finding gives engineers and scientists the choice to adjust the location of their PRBs so that the overall project can be the most feasible and cost effective. / Master of Science

Sites where 2-chlorobutadiene-1,3 (chloroprene) and 2,3-dichlorobutadiene-1,3 (DCBD) are synthesized for use in chlorobutyl rubber have the potential to release a mixture of at least five chlorinated butenes and butadienes including trans-1,4-dichlorobutene-2 (1,4-DCB-2), 3,4-dichlorobutene-1 (3,4-DCB-1), 2,3,4-trichlorobutene-1 (2,3,4-TCB-1), chloroprene and DCBD into the groundwater environment. Granular iron has been shown to be effective in the remediation of groundwater contaminated with chlorinated organic compounds by reductive dechlorination. To evaluate the possibility of using granular iron in the remediation of the above contaminants a series of batch and column experiments were conducted at the laboratory scale. Chlorine mass balance calculations showed that each compound, with the exception of DCBD, could be fully dechlorinated by the use of granular iron. Kinetic data and proposed reaction pathways, however, suggest that DCBD can also be fully dechlorinated by granular iron. Normalization of observed pseudo-first-order reaction half-lives indicated that compounds were degrading much slower in batch experiments than in column experiments. This, along with the observation that temperature did not affect degradation in batch experiments, led to the conclusion that mass transport to the iron surfaces was limiting degradation rates in batch experiments. Results showed that the three chlorinated butenes degraded much faster (normalized column half-lives ranged from 1.6 to 5.2 min) than the two chlorinated butadienes (normalized column half-lives ranged from 115 to 197 min). Chlorinated and non-chlorinated intermediates were identified. It was determined that all contaminants degrade to 1,3-butadiene as a reaction intermediate which then degraded to a mixture of non-harmful end products consisting of 1-butene, cis-2-butene, trans-2-butene and n-butane. The reaction pathway from 1,4-DCB-2 to 1,3-butadiene was proposed to be a reductive elimination similar to reductive β-elimination. 3,4-DCB-1 and 2,3,4-TCB-1 were proposed to undergo reductive β-elimination reactions resulting in 1,3-butadiene and chloroprene intermediates, respectively. Degradation of chloroprene and DCBD occurred via hydrogenolysis pathways while 1,3-butadiene underwent catalytic hydrogenation resulting in the observed end products. The results suggest that granular iron may be an effective treatment for groundwater contaminated with these compounds.

Sites where 2-chlorobutadiene-1,3 (chloroprene) and 2,3-dichlorobutadiene-1,3 (DCBD) are synthesized for use in chlorobutyl rubber have the potential to release a mixture of at least five chlorinated butenes and butadienes including trans-1,4-dichlorobutene-2 (1,4-DCB-2), 3,4-dichlorobutene-1 (3,4-DCB-1), 2,3,4-trichlorobutene-1 (2,3,4-TCB-1), chloroprene and DCBD into the groundwater environment. Granular iron has been shown to be effective in the remediation of groundwater contaminated with chlorinated organic compounds by reductive dechlorination. To evaluate the possibility of using granular iron in the remediation of the above contaminants a series of batch and column experiments were conducted at the laboratory scale. Chlorine mass balance calculations showed that each compound, with the exception of DCBD, could be fully dechlorinated by the use of granular iron. Kinetic data and proposed reaction pathways, however, suggest that DCBD can also be fully dechlorinated by granular iron. Normalization of observed pseudo-first-order reaction half-lives indicated that compounds were degrading much slower in batch experiments than in column experiments. This, along with the observation that temperature did not affect degradation in batch experiments, led to the conclusion that mass transport to the iron surfaces was limiting degradation rates in batch experiments. Results showed that the three chlorinated butenes degraded much faster (normalized column half-lives ranged from 1.6 to 5.2 min) than the two chlorinated butadienes (normalized column half-lives ranged from 115 to 197 min). Chlorinated and non-chlorinated intermediates were identified. It was determined that all contaminants degrade to 1,3-butadiene as a reaction intermediate which then degraded to a mixture of non-harmful end products consisting of 1-butene, cis-2-butene, trans-2-butene and n-butane. The reaction pathway from 1,4-DCB-2 to 1,3-butadiene was proposed to be a reductive elimination similar to reductive β-elimination. 3,4-DCB-1 and 2,3,4-TCB-1 were proposed to undergo reductive β-elimination reactions resulting in 1,3-butadiene and chloroprene intermediates, respectively. Degradation of chloroprene and DCBD occurred via hydrogenolysis pathways while 1,3-butadiene underwent catalytic hydrogenation resulting in the observed end products. The results suggest that granular iron may be an effective treatment for groundwater contaminated with these compounds.

A cylindrical electrochemical reactor with a 3 in diameter copper or nickel metal foam cathode and a concentric carbon cloth anode was used to destroy aqueous phase carbon tetrachloride (CT). The results show that a high CT conversion can be achieved in regions of the cathode near the anode, but a low CT conversion is obtained in the region around the center of the cathode. This CT conversion distribution in the radial current-conducting direction suggests that a portion of the cathode worked inefficiently even though the overall CT conversion is still adequate. Further research by changing the solution pH and conductivity suggests that the radial conversion distribution is due to radial variations in cathode surface availability. The inherent difficulties that these results imply with regards to reactor scale up suggested a new approach to the design. An annular reactor, consisting of a thin (3.2 mm) nickel foam cathode wrapped around an inert Plexiglas core and separated for an external concentric anode by a semi-permeable membrane was adopted. Under compatible operating conditions, the annular reactor showed a high overall effluent CT conversion. However, experiments at low pH (2.25) yielded higher conversions than under neutral pH conditions. This result suggests that CT conversion is favored by a relatively high proton concentration. This reactor can be simulated by a one dimensional model. The annular reactor was used to destroy PCE and TCE successfully, which suggests that this technique can be employed to treat groundwater contaminated with complex mixtures of chlorinated hydrocarbons.A multi-layer reactor based on the principle of the annular reactor was developed as an option for the scale up of the system. This reactor exhibited high and uniform radial CT conversion.