Kanwartej S. Sra

Persistence of persulfate in uncontaminated aquifer materials.

Batch and stop-flow column experiments were performed to estimate persulfate decomposition kinetic parameters in the presence of seven well-characterized aquifer materials. Push-pull tests were conducted in a sandy aquifer to represent persulfate decomposition under in situ conditions. The decomposition of persulfate followed a first-order rate law for all aquifer materials investigated. Reaction rate coefficients (k(obs)) increased by an order of magnitude when persulfate concentration was reduced from 20 g/L to 1 g/L, due to ionic strength effects. The column experiments yielded higher k(obs) than batch experiments due to the lower oxidant to solids mass ratio. The kinetic model developed from the batch test data was able to reproduce the observed persulfate temporal profiles from the push-pull tests. The estimated k(obs) indicate that unactivated persulfate is a persistent oxidant for the range of aquifer materials explored with half-lives ranging from 2 to 600 d.

Carbon isotope fractionation of 1,1,1-trichloroethane during base-catalyzed persulfate treatment.

The extent of carbon isotope fractionation during degradation of 1,1,1-trichloroethane (1,1,1-TCA) by a base-catalyzed persulfate (S₂O₈(2-)) treatment system was investigated. Significant destruction of 1,1,1-TCA was observed at a pH of ∼12. An increase in the NaOH:S₂O₈(2-) molar ratio from 0.2:1 to 8:1 enhanced the reaction rate of 1,1,1-TCA by a factor of ∼5 to yield complete (>99.9%) destruction. An average carbon isotope enrichment fractionation factor which was independent of the NaOH:S₂O₈(2-) molar ratio of -7.0 ± 0.2‰ was obtained. This significant carbon isotope fractionation and the lack of dependence on changes in the NaOH:S₂O₈(2-) molar ratio demonstrates that carbon isotope analysis can potentially be used in situ as a performance assessment tool to estimate the degradation effectiveness of 1,1,1-TCA by a base-catalyzed persulfate system.

Carbon isotope fractionation of chlorinated ethenes during oxidation by Fe2 + activated persulfate

The increased use of persulfate (S(2)O(8)(2-)) for in situ chemical oxidation to treat groundwater and soils contaminated by chlorinated hydrocarbon compounds (CHCs) requires unbiased methods to assess treatment performance. Stable carbon isotope analysis offers a potential tool for assessing the in situ treatment performance of persulfate at sites contaminated with CHCs. This study investigated the extent of C isotope fractionation during oxidation of tetrachloroethene (PCE), trichloroethene (TCE) and cis-dichloroethene (cis-DCE) by persulfate activated by ferrous ion (Fe(2+)). An average carbon isotope enrichment factor ε(bulk) of -4.9‰ for PCE, -3.6‰ for TCE and -7.6‰ for cis-DCE were obtained in batch experiments. Variations in the initial S(2)O(8)(2-)/Fe(2+)/CHC molar ratios did not result in any significant differences in carbon isotope fractionation. The occurrence of carbon isotope fractionation during oxidation and the lack of dependence of enrichment factors upon the S(2)O(8)(2-)/Fe(2+)/CHC molar ratio demonstrate that carbon isotope analysis can potentially be used at contaminated sites as an additional technique to estimate treatment efficacy during oxidation of CHCs by Fe(2+) activated persulfate.

Persulfate injection into a gasoline source zone

One pore volume of unactivated sodium persulfate was delivered into an emplaced gasoline residual source zone at CFB Borden. Concentrations of inorganic species (S2O8(2-), SO4(2-), Na(+), dissolved inorganic carbon (DIC)) and selected gasoline compounds (benzene, toluene, ethylbenzene, xylenes, trimethylbenzenes and naphthalene) were monitored across a transect equipped with 90 multilevel sampling points for >10months post-injection. Mass loading (M˙) of compounds constructed from the transect data was used for assessment purposes. Breakthrough of inorganic species was observed when the injection slug crossed the monitoring transect. An increase in [Formula: see text] indicated persulfate consumption during oxidation of gasoline compounds or degradation due to the interaction with aquifer materials. M˙DIC increased by >100% suggesting some mineralization of gasoline compounds during treatment. Mass loading for all the monitored gasoline compounds reduced by 46 to 86% as the inorganic slug crossed the monitoring transect. The cumulative mass discharge across the monitoring transect was 19 to 58% lower than that expected without persulfate injection. After the inorganic injection slug was flushed from the source zone a partial rebound (40 to 80% of baseline levels) of mass discharge of the monitored gasoline compounds was observed. The ensemble of data collected provides insight into the fate and transport of the injected persulfate solution, and the accompanying treatment of a gasoline the source zone.

Persulfate Treatment of Dissolved Gasoline Compounds

AbstractBench-scale treatability of an ensemble of gasoline compounds was investigated using unactivated and activated persulfate. The activation strategies explored were chelated-iron, peroxide, alkaline conditions, and the presence of aquifer solids. Batch reactor trials were designed with an initial total petroleum hydrocarbon (TPH) concentration of ∼25  mg/L, and nine organic compounds were monitored over a 28-day reaction period. First-order oxidation rate coefficients (kobs) were estimated for all experimental trials. Unactivated persulfate at a concentration of 20  g/L resulted in almost complete oxidation of benzene, toluene, ethylbenzene, and xylenes (BTEX) (>99%), trimethylbenzenes (>95%), and significant oxidation of naphthalene (∼70%). Oxidation rate coefficients were enhanced by 2–15 times using the peroxide or chelated-iron activation strategy. Alkaline activation at pH 11 or 13 yielded kobs that were ∼2 times higher than the unactivated case, except for the kobs for benzene, toluene, and et...

Stability of Activated Persulfate in the Presence of Aquifer Solids

Bench-scale experiments were performed to investigate the persistence of activated persulfate using citric acid (CA) chelated ferrous (Fe(II)), peroxide (H2O2), or hydroxide (OH−) activation in the presence of well-characterized aquifer solids. Chelation by citric acid was ineffective in controlling the interaction between persulfate and Fe(II), and oxidation of Fe(II) was observed, causing a rapid initial decrease in persulfate concentration. Subsequent to this loss, first-order persulfate degradation rate coefficients (kobs) were estimated, which were up to four times higher than the unactivated case due to the interaction with Fe(III), Fe(II), or CA. Total oxidation strength (TOS) was measured for peroxide activation experiments and was observed to decrease rapidly early due to 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 later used to capture TOS degradation were ∼1 to 100 times higher than kobs for unactivated persulfate. For alkaline activation, kobs were only one to four times higher than unactivated persulfate, and therefore alkaline conditions demonstrated the least overall impact on persulfate stability among the various activation strategies explored.

Targeted nanoparticle binding & detection in petroleum hydrocarbon impacted porous media

Targeted nanoparticle binding has become a core feature of experimental pharmaceutical product design which enables more efficient payload delivery and enhances medical imaging by accumulating nanoparticles in specific tissues. Environmental remediation and geophysical monitoring encounter similar challenges which may be addressed in part by the adoption of targeted nanoparticle binding strategies. This study illustrates that engineered nanoparticles can bind to crude oil-impacted silica sand, a selective adsorption driven by active targeting based on an amphiphilic polymer coating. This coating strategy resulted in 2 mg/kg attachment to clean silica sand compared to 8 mg/kg attachment to oil-impacted silica sand. It was also shown that modifying the surface coating influenced the binding behaviour of the engineered nanoparticles - more hydrophobic polymers resulted in increased binding. Successful targeting of Pluronic-coated iron oxide nanoparticles to a crude oil and silica sand mixture was demonstrated through a combined quantitative Orbital Emission Spectroscopy mass analysis supported by Vibrating Scanning Magnetometer magnetometry, and a qualitative X-ray micro-computed tomography (CT) visualization approach. These non-destructive characterization techniques facilitated efficient analysis of nanoparticles in porous medium samples with minimal sample preparation, and in the case of X-Ray CT, illustrated how targeted nanoparticle binding may be used to produce 3-D images of contaminated porous media. This work demonstrated successful implementation of nanoparticle targeted binding toward viscous LNAPL such as crude oil in the presence of a porous medium, a step which opens the door to successful application of targeted delivery technology in environmental remediation and monitoring.