Green cleanup of styrene-contaminated soil by carbon-based nanoscale zero-valent iron and phytoremediation: Sunn hemp (Crotalaria juncea), zinnia (Zinnia violacea Cav.), and marigold (Tagetes erecta L.).

Accidental chemical spills can result in styrene-contaminated soil. Styrene negatively affects human health and the environment. The objective of this study was to remediate styrene-contaminated soil using a combination of activated carbon-based nanoscale zero-valent iron (nZVI-AC) and phytoremediation by sunn hemp (Crotalaria juncea), zinnia (Zinnia violacea Cav.) and marigolds (Tagetes erecta L.). The results showed that all three plant types could potentially increase the removal efficiency of styrene-contaminated soil. At 28 days, all three plants showed complete removal of styrene from the soil with 1 g/kg of nZVI-AC, activated carbon-based nZVI synthesized by tea leaves (Camellia sinensis) (T-nZVI-AC), or activated carbon-based nZVI synthesized by red Thai holy basil (Ocimum tenuiflorum L.) (B-nZVI-AC). However, styrene removal efficiencies of sunn hemp, zinnia, and marigold without carbon-based nZVI were 30%, 67%, and 56%, respectively. Statistical analysis (ANOVA) revealed that the removal efficiencies differed significantly from those of phytoremediation alone. With the same removal efficiency (100%), the biomass of sunn hemp in nano-phytoremediation treatments differed by approximately 55%, whereas the biomass of zinnia differed by >67%, compared with that of the control experiment. For marigold, the difference in biomass was only 30%. Styrene was adsorbed on surface of soil and AC and then further oxidized under air-water-nZVI environment, while phytovolatilization played an important role in transporting the remaining styrene from the contaminated soil to the air. Marigold was used as an alternative plant for the nano-phytoremediation of styrene-contaminated soil because of its sturdy nature, high biomass, tolerance to toxic effects, and ease of cultivation. Remediation of one cubic meter of styrene-contaminated soil by a combination of carbon-based nanoscale zero-valent iron and phytoremediation by marigolds emitted 0.0027 kgCO2/m3.

Dual Activation of Peroxymonosulfate Using MnFe2O4/g-C3N4 and Visible Light for the Efficient Degradation of Steroid Hormones: Performance, Mechanisms, and Environmental Impacts.

Single activation of peroxymonosulfate (PMS) in a homogeneous system is sometimes insufficient for producing reactive oxygen species (ROS) for water treatment applications. In this work, manganese spinel ferrite and graphitic carbon nitride (MnFe2O4/g-C3N4; MnF) were successfully used as an activator for PMS under visible light irradiation to remove the four-most-detected-hormone-contaminated water under different environmental conditions. The incorporation of g-C3N4 in the nanocomposites led to material enhancements, including increased crystallinity, reduced particle agglomeration, amplified magnetism, improved recyclability, and increased active surface area, thereby facilitating the PMS activation and electron transfer processes. The dominant active radical species included singlet oxygen (1O2) and superoxide anions (O2•-), which were more susceptible to the estrogen molecular structure than testosterone due to the higher electron-rich moieties. The self-scavenging effect occurred at high PMS concentrations, whereas elevated constituent ion concentrations can be both inhibitors and promoters due to the generation of secondary radicals. The MnF/PMS/vis system degradation byproducts and possible pathways of 17ß-estradiol and 17α-methyltestosterone were identified. The impact of hormone-treated water on Oryza sativa L. seed germination, shoot length, and root length was found to be lower than that of untreated water. However, the viability of both ELT3 and Sertoli TM4 cells was affected only at higher water compositions. Our results confirmed that MnF and visible light could be potential PMS activators due to their superior degradation performance and ability to produce safer treated water.

Adsorptive-Photocatalytic Performance for Antibiotic and Personal Care Product Using Cu0.5Mn0.5Fe2O4.

The amount of antibiotics and personal care products entering local sewage systems and ultimately natural waters is increasing and raising concerns about long-term human health effects. We developed an adsorptive photocatalyst, Cu0.5Mn0.5Fe2O4 nanoparticles, utilizing co-precipitation and calcination with melamine, and quantified its efficacy in removing paraben and oxytetracycline (OTC). During melamine calcination, Cu0.5Mn0.5Fe2O4 recrystallized, improving material crystallinity and purity for the adsorptive-photocatalytic reaction. Kinetic experiments showed that all four parabens and OTC were removed within 120 and 45 min. We found that contaminant adsorption and reaction with active radicals occurred almost simultaneously with the photocatalyst. OTC adsorption could be adequately described by the Brouers-Sotolongo kinetic and Freundlich isotherm models. OTC photocatalytic degradation started with a series of reactions at different carbon locations (i.e., decarboxamidation, deamination, dehydroxylation, demethylation, and tautomerization). Further toxicity testing showed that Zea mays L. and Vigna radiata L. shoot indexes were less affected by treated water than root indexes. The Zea mays L. endodermis thickness and area decreased considerably after exposure to the 25% (v/v)-treated water. Overall, Cu0.5Mn0.5Fe2O4 nanoparticles exhibit a remarkable adsorptive-photocatalytic performance for the degradation of tested antibiotics and personal care products.

Enhanced degradation of herbicides in groundwater using sulfur-containing reductants and spinel zinc ferrite activated persulfate.

A challenge to successfully implementing an injection-based remedial treatment in aquifers is to ensure that the oxidative reaction is efficient and lasts long enough to contact the contaminated plume. Our objective was to determine the efficacy of zinc ferrite nanocomposites (ZnFe2O4) and sulfur-containing reductants (SCR) (i.e., dithionite; DTN and bisulfite; BS) to co-activate persulfate (S2O82-; PS) and treat herbicide-contaminated water. We also evaluated the ecotoxicity of the treated water. While both SCRs delivered excellent PS activation in a 1:0.4 ratio (PS:SCR), the reaction was relatively short-lived. By including ZnFe2O4 in the PS/BS or PS/DTN activations, herbicide degradation rates dramatically increased by factors of 2.5 to 11.3. This was due to the SO4- and OH reactive radical species that formed. Radical scavenging experiments and ZnFe2O4 XPS spectra results revealed that SO4- was the dominant reactive species that originated from S(IV)/PS activation in solution and from the Fe(II)/PS activation that occurred on the ZnFe2O4 surface. Based on liquid chromatography mass spectrometry (LC-MS), atrazine and alachlor degradation pathways are proposed that involve both dehydration and hydroxylation. In 1-D column experiments, five different treatment scenarios were run using 14C-labeled and unlabeled atrazine, and 3H2O to quantify changes in breakthrough curves. Our results confirmed that ZnFe2O4 successfully prolonged the PS oxidative treatment despite the SCR being completely dissociated. Toxicity testing showed treated 14C-atrazine was more biodegradable than the parent compound in soil microcosms. Post-treatment water (25 %, v/v) also had less impact on both Zea Mays L. and Vigna radiata L. seedling growth, but more impact on root anatomies, while ≤4 % of the treated water started to exert cytotoxicity (<80 % viability) on ELT3 cell lines. Overall, the findings confirm that ZnFe2O4/SCR/PS reaction is efficient and relatively longer lasting in treating herbicide-contaminated groundwater.

Developing a Slow-Release Permanganate Composite for Degrading Aquaculture Antibiotics.

Copious use of antibiotics in aquaculture farming systems has resulted in surface water contamination in some countries. Our objective was to develop a slow-release oxidant that could be used in situ to reduce antibiotic concentrations in discharges from aquaculture lagoons. We accomplished this by generating a slow-release permanganate (SR-MnO4-) that was composed of a biodegradable wax and a phosphate-based dispersing agent. Sulfadimethoxine (SDM) and its synergistic antibiotics were used as representative surrogates. Kinetic experiments verified that the antibiotic-MnO4- reactions were first-order with respect to MnO4- and initial antibiotic concentration (second-order rates: 0.056-0.128 s-1 M-1). A series of batch experiments showed that solution pH, water matrices, and humic acids impacted SDM degradation efficiency. Degradation plateaus were observed in the presence of humic acids (>20 mgL-1), which caused greater MnO2 production. A mixture of KMnO4/beeswax/paraffin (SRB) at a ratio of 11.5:4:1 (w/w) was better for biodegradability and the continual release of MnO4-, but MnO2 formation altered release patterns. Adding tetrapotassium pyrophosphate (TKPP) into the composite resulted in delaying MnO2 aggregation and increased SDM removal efficiency to 90% due to the increased oxidative sites on the MnO2 particle surface. The MnO4- release data fit the Siepmann-Peppas model over the long term (t < 48 d) while a Higuchi model provided a better fit for shorter timeframes (t < 8 d). Our flow-through discharge tank system using SRB with TKPP continually reduced the SDM concentration in both DI water and lagoon wastewater. These results support SRB with TKPP as an effective composite for treating antibiotic residues in aquaculture discharge water.

Fabrication of Ternary Nanoparticles for Catalytic Ozonation to Treat Parabens: Mechanisms, Efficiency, and Effects on Ceratophyllum demersum L. and Eker Leiomyoma Tumor-3 Cells.

The use of parabens in personal care products can result in their leakage into water bodies, especially in public swimming pools with insufficient water treatment. We found that ferrite-based nanomaterials could catalytically enhance ozone efficiency through the production of reactive oxygen species. Our objective was to develop a catalytic ozonation system using ternary nanocomposites that could minimize the ozone supply while ensuring the treated water was acceptable for disposal into the environment. A ternary CuFe2O4/CuO/Fe2O3 nanocomposite (CF) delivered excellent degradation performance in catalytic ozonation systems for butylparaben (BP). By calcining with melamine, we obtained the CF/g-C3N4 (CFM) nanocomposite, which had excellent magnetic separation properties with slightly lower degradation efficiency than CF, due to possible self-agglomeration that reduced its electron capture ability. The presence of other constituent ions in synthetic wastewater and actual discharge water resulted in varying degradation rates due to the formation of secondary active radicals. 1O2 and •O2− were the main dominant reactive species for BP degradation, which originated from the O3 adsorption that occurs on the CF≡Cu(I)−OH and CF≡Fe(III)−OH surface, and from the reaction with •OH from indirect ozonation. Up to 50% of O3-treated water resulted in >80% ELT3 cell viability, the presence of well-adhered cells, and no effect on the young tip of Ceratophyllum demersum L. Overall, our results demonstrated that both materials could be potential catalysts for ozonation because of their excellent degrading performance and, consequently, their non-toxic by-products.

Enrofloxacin and Sulfamethoxazole Sorption on Carbonized Leonardite: Kinetics, Isotherms, Influential Effects, and Antibacterial Activity toward S. aureus ATCC 25923.

Excessive antibiotic use in veterinary applications has resulted in water contamination and potentially poses a serious threat to aquatic environments and human health. The objective of the current study was to quantify carbonized leonardite (cLND) adsorption capabilities to remove sulfamethoxazole (SMX)- and enrofloxacin (ENR)-contaminated water and to determine the microbial activity of ENR residuals on cLND following adsorption. The cLND samples prepared at 450 °C and 850 °C (cLND450 and cLND550, respectively) were evaluated for structural and physical characteristics and adsorption capabilities based on adsorption kinetics and isotherm studies. The low pyrolysis temperature of cLND resulted in a heterogeneous surface that was abundant in both hydrophobic and hydrophilic functional groups. SMX and ENR adsorption were best described using a pseudo-second-order rate expression. The SMX and ENR adsorption equilibrium data on cLND450 and cLND550 revealed their better compliance with a Langmuir isotherm than with four other models based on 2.3-fold higher values of qmENR than qmSMX. Under the presence of the environmental interference, the electrostatic interaction was the main contributing factor to the adsorption capability. Microbial activity experiments based on the growth of Staphylococcus aureus ATCC 25923 revealed that cLND could successfully adsorb and subsequently retain the adsorbed antibiotic on the cLND surface. This study demonstrated the potential of cLND550 as a suitable low-cost adsorbent for the highly efficient removal of antibiotics from water.

Solvothermal-Based Lignin Fractionation From Corn Stover: Process Optimization and Product Characteristics.

Fractionation of lignocellulosic is a fundamental step in the production of value-added biobased products. This work proposes an initiative to efficiently extract lignin from the corn stover using a single-step solvothermal fractionation in the presence of an acid promoter (H2SO4). The organic solvent mixture used consists of ethyl acetate, ethanol, and water at a ratio of 30: 25:45 (v/v), respectively. H2SO4 was utilized as a promoter to improve the performance and selectivity of lignin removal from the solid phase and to increase the amount of recovered lignin in the organic phase. The optimal conditions for this extraction, based on response surface methodology (RSM), are a temperature of 180°C maintained for 49.1 min at an H2SO4 concentration of 0.08 M. The optimal conditions show an efficient reaction with 98.0% cellulose yield and 75.0% lignin removal corresponding to 72.9% lignin recovery. In addition, the extracted lignin fractions, chemical composition, and structural features were investigated using Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, and two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance spectroscopy (2D-HSQC NMR). The results indicate that the recovered lignin primarily contains a ß-O-4 linking motif based on 2D-HSQC spectra. In addition, new C-C inter-unit linkages (i.e., ß-ß, and ß-5) are not formed in the recovered lignin during H2SO4-catalyzed solvothermal pretreatment. This work facilitates effective valorization of lignin into value-added chemicals and fuels.

Fractionation and characterization of lignin from sugarcane bagasse using a sulfuric acid catalyzed solvothermal process.

Conversion of lignocellulosic residue to bioenergy and biofuel is a promising platform for global sustainability. Fractionation is an initial step for isolating lignocellulosic components for subsequent valorization. The aim of this research is to develop the solvothermal fractionation of sugarcane bagasse to produce high purity lignin. The physio-chemical structure of isolated lignin from this process was determined. In this study, a central composite design-based response surface methodology (RSM) was used to optimize an acid promoter for isolating lignin from sugarcane bagasse using a solvothermal fractionation process. The reaction was carried out with sulfuric acid, at a concentration of 0.01-0.02 M and a reaction temperature of 180-200 °C for 30-90 min. The optimal conditions for the experiment were obtained at the acid concentration of 0.02 M with a temperature of 200 °C for 90 min in methyl isobutyl ketone (MIBK)/methanol/water (35% : 25% : 40% v/v%). The results showed that 88% of lignin removal was done in the solid phase, while 87% of lignin recovery was conducted in the organic phase. Furthermore, the changes in the physico-chemical characteristics of solid residue and lignin recovery were analyzed using various techniques. GPC analysis of recovered lignin from the organic fraction showed a lower M w (1374 g mol-1) and polydispersity index (1.75) compared to commercial organosolv lignin. The major lignin degradation temperature of commercial organosolv lignin was estimated to be 410 °C, whereas BGL showed two main degradations at 291 °C and 437 °C, which could point to potential relationships with the degradation of ß-O-4 cross-links. The results indicated that recovered lignin was mostly cross-linked by ß-O-4 cross-links. In addition, Py-GC/MS and 2D HSQC NMR gave more information regarding the compositional and structural features of recovered lignin. The development of the sulfuric acid catalyzed solvothermal process in this study provides efficient extraction of high-value organosolv lignin from sugarcane bagasse and the production of recovered lignin in the organic phase with low contamination from other contents. The lignin characteristic data can contribute to the development of lignin valorization in value-added applications.

Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in freshwater crocodiles (Crocodylus siamensis) after intravenous and intramuscular administration.

To the best of the authors' knowledge, pharmacokinetic information to establish suitable therapeutic plans for freshwater crocodiles is limited. Therefore, the purpose of this study was to clarify the pharmacokinetic characteristics of enrofloxacin (ENR) in freshwater crocodiles, Crocodylus siamensis, following single intravenous and intramuscular administration at a dosage of 5 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168 hr. The plasma concentrations of ENR and its metabolite ciprofloxacin (CIP) were measured by liquid chromatography tandem-mass spectrometry. The concentrations of ENR and CIP in the plasma were quantified up to 144 hr after both the administrations. The half-life was long (43-44 hr) and similar after both administrations. The absolute i.m. bioavailability was 82.65% and the binding percentage of ENR to plasma protein ranged from 9% to 18% with an average of 10.6%. Percentage of CIP (plasma concentrations) was 15.9% and 19.9% after i.v. and i.m. administration, respectively. Based on the pharmacokinetic data, susceptibility break point and PK-PD indexes, i.m. single administration of ENR at a dosage of 5 mg/kg b.w. might be appropriate for treatment of susceptible bacteria (MIC > 1 µg/mL) in freshwater crocodiles, C. siamensis.

Multiclass analysis of antimicrobial drugs in shrimp muscle by ultra high performance liquid chromatography-tandem mass spectrometry.

A reliable, selective and rapid multiclass method has been developed for the simultaneous determination of 55 antibacterial drug residues in shrimp muscle samples by ultra high performance liquid chromatography-tandem mass spectrometry. The investigated compounds comprise of eight different classes, namely fluoroquinolones, sulfonamides and synergistic agents, tetracyclines, macrolides, lincosamides, penicillins, nitroimidazole and amphenicols. A simple liquid extraction procedure was developed consisting of extraction with a mixture of acetonitrile and ethylenediaminetetraacetic acid (EDTA), followed by a defatting step with n-hexane. Chromatographic conditions were optimized, obtaining a running time <10 min. Mean recoveries ranged from 74.3% to 113.3%. For precision test, relative standard deviations (RSD, %) were lower than 15.0% and 24.0% for repeatability and reproducibility, respectively. Limits of detection and quantification ranged from 1.0 to 5.0 ng/g and 3.0-10.0 ng/g, respectively. Finally, the method was applied to real samples and the results demonstrated that enrofloxacin, ciprofloxacin, pefloxacin and doxycycline were quantifiable in shrimp samples.

Hexavalent chromium adsorption from aqueous solution using carbon nano-onions (CNOs).

The capacity of carbon nano-onions (CNOs) to remove hexavalent chromium (Cr(VI)) from aqueous solution was investigated. Batch experiments were performed to quantify the effects of the dosage rate, pH, counter ions, and temperature. The adsorption of Cr(VI) onto CNOs was best described by a pseudo-second order rate expression. The adsorption efficiency increased with increasing adsorbent dosage and contact time and reached equilibrium in 24 h. The equilibrium data showed better compliance with a Langmuir isotherm than a Freundlich isotherm. Effective removal of Cr(VI) was demonstrated at pH values ranging from 2 to 10. The adsorption capacity of Cr(VI) was found to be highest (82%) at pH 3.4 and greatly depended on the solution pH. We found that Cr(VI) adsorption decreased with increasing pH over the pH range of 3.4-10. The adsorption capacity increased dramatically when the temperature increased from 10 °C to 50 °C regardless of the amount of CNOs used. Cr(VI) removal decreased by ∼13% when Zn(II), Cu(II), and Pb(II) were present, while there were no significant changes observed when NO3- or SO42- was present. The overall results support that CNOs can be used as an alternative adsorbent material to remove Cr(VI) in the water treatment industry.

Removing PAHs from urban runoff water by combining ozonation and carbon nano-onions.

Ozone (O3) is a chemical oxidant capable of transforming polycyclic aromatic hydrocarbons (PAHs) in urban runoff within minutes but complete oxidation to CO2 can take days to weeks. We developed and tested a flow-through system that used ozone to quickly transform PAHs in a runoff stream and then removed the ozone-transformed PAHs via adsorption to carbon nano-onions (CNOs). To quantify the efficacy of this approach, (14)C-labeled phenanthrene and benzo(a)pyrene, as well as a mixture of 16 unlabeled PAHs were used as test compounds. These PAHs were pumped from a reservoir into a flow-through reactor that continuously ozonated the solution. Outflow from the reactor then went to a chamber that contained CNOs to adsorb the ozone-transformed PAHs and allowed clean water to pass. By adding a microbial consortium to the CNOs following adsorption, we observed that bacteria were able to degrade the adsorbed products and release more soluble, biodegradable products back into solution. Control treatments confirmed that parent PAH structures (i.e., non-ozonated) were not biologically degraded following CNO adsorption and that O3-transformed PAHs were not released from the CNOs in the absence of bacteria. These results support the combined use of ozone, carbon nano-onions with subsequent biological degradation as a means of removing PAHs from urban runoff or a commercial waste stream.

Modeling improved ISCO treatment of low permeable zones via viscosity modification: assessment of system variables.

A major challenge to successfully using in situ chemical oxidation (ISCO) for groundwater treatment is achieving uniform contact between the oxidant and contaminants in a heterogeneous aquifer. Viscosity modification technology, where a water-soluble polymer is mixed with remedial fluids, has been introduced in recent years to improve oxidant coverage of the target zone (i.e., sweep efficiency) and thus, treatment efficacy. In this work, we developed a numerical model to simulate the remedial fluid coverage from an ISCO injection with viscosity modification. Specifically, solution mixtures of xanthan and NaMnO4 were injected into a two-dimensional (2D) transport flow box that contained heterogeneous layers. Xanthan solutions were simulated as shear-thinning non-Newtonian fluids, where viscosity is a function of shear rate, polymer and NaMnO4 concentrations. Reactive transport of the polymer, NaMnO4, TCE, and reaction products were simultaneously modeled using advection dispersion reaction (ADR) equations coupled with the simulated flow field. The numerical model was validated using experimental data from the 2D cell experiments. Sensitivity analysis was conducted to investigate the relative contributions of system variables, such as polymer and permanganate concentrations, flow rate, permeability contrast, and different geometry settings. Results showed that higher concentration of permanganate and slower flow rate of the shear-thinning non-Newtonian fluids improved the oxidants ability to enter low permeable zones and react with the TCE. Higher permeability contrast decreased the velocity of the xanthan-MnO4(-) mixture inside the low permeable zone (LPZ), which increased TCE oxidation and product recovery. Changing the architecture of the LPZ from one zone to two smaller zones separated by a transmissive zone increased the overall product recovery. Thus, viscosity modification can improve both the sweeping efficiencies and TCE removal.

A combined chemical and biological approach to transforming and mineralizing PAHs in runoff water.

The water quality of lakes, rivers and streams associated with metropolitan areas is declining from increased inputs of urban runoff that contain polycyclic aromatic hydrocarbons (PAHs). Our objective was to transform and mineralize PAHs in runoff using a combined chemical and biological approach. Using (14)C-labeled phenanthrene, (14)C-benzo(a)pyrene and a mixture of 16 PAHs, we found that ozone transformed all PAHs in a H2O matrix within minutes but complete mineralization to CO2 took several weeks. When urban runoff water (7.6 mg CL(-1)) replaced H2O as the background matrix, some delays in degradation rates were observed but transforming a mixture of PAHs was still complete within 10 min. Comparing the biodegradability of the ozonated products to the parent structures in unsaturated soil microcosms showed that the 3-ring phenanthrene was more biodegradable (as evidence by (14)CO2 released) than its ozonated products but for the 5-ring benzo(a)pyrene, the products produced by ozone were much more biodegradable (22% vs. 3% mineralized). For phenanthrene, we identified diphenaldehyde as the initial degradation product produced from ozonation. By continuing to pump the ozonated products ((14)C-labeled diphenaldehyde or ozone-treated benzo(a)pyrene) onto glass beads coated with microorganisms, we verified that biological mineralization could be achieved in a flow-through system and mineralization rates improved with acclimation of the microbial population (i.e., time and exposure to the substrate). These results support a combined ozone and biological approach to treating PAHs in urban runoff water.

Improving the treatment of non-aqueous phase TCE in low permeability zones with permanganate.

Treating dense non-aqueous phase liquids (DNAPLs) embedded in low permeability zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate (MnO4(-)) into LPZs to treat high concentrations of TCE. This was accomplished by conducting transport experiments that quantified the penetration of various permanganate flooding solutions into a LPZ that was spiked with non-aqueous phase (14)C-TCE. The treatments we evaluated included permanganate paired with: (i) a shear-thinning polymer (xanthan); (ii) stabilization aids that minimized MnO2 rind formation and (iii) a phase-transfer catalyst. In addition, we quantified the ability of these flooding solutions to improve TCE destruction under batch conditions by developing miniature LPZ cylinders that were spiked with (14)C-TCE. Transport experiments showed that MnO4(-) alone was inefficient in penetrating the LPZ and reacting with non-aqueous phase TCE, due to a distinct and large MnO2 rind that inhibited the TCE from further oxidant contact. By including xanthan with MnO4(-), the sweeping efficiency increased (90%) but rind formation was still evident. By including the stabilization aid, sodium hexametaphosphate (SHMP) with xanthan, permanganate penetrated 100% of the LPZ, no rind was observed, and the percentage of TCE oxidized increased. Batch experiments using LPZ cylinders allowed longer contact times between the flooding solutions and the DNAPL and results showed that SHMP+MnO4(-) improved TCE destruction by ∼16% over MnO4(-) alone (56.5% vs. 40.1%). These results support combining permanganate with SHMP or SHMP and xanthan as a means of treating high concentrations of TCE in low permeable zones.

Improving the sweeping efficiency of permanganate into low permeable zones to treat TCE: experimental results and model development.

The residual buildup and treatment of dissolved contaminants in low permeable zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat dissolved-phase TCE. This was accomplished by conducting transport experiments that quantified the ability of xanthan-MnO4(-) solutions to penetrate and cover (i.e., sweep) an LPZ that was surrounded by transmissive sands. By incorporating the non-Newtonian fluid xanthan with MnO4(-), penetration of MnO4(-) into the LPZ improved dramatically and sweeping efficiency reached 100% in fewer pore volumes. To quantify how xanthan improved TCE removal, we spiked the LPZ and surrounding sands with (14)C-lableled TCE and used a multistep flooding procedure that quantified the mass of (14)C-TCE oxidized and bypassed during treatment. Results showed that TCE mass removal was 1.4 times greater in experiments where xanthan was employed. Combining xanthan with MnO4(-) also reduced the mass of TCE in the LPZ that was potentially available for rebound. By coupling a multiple species reactive transport model with the Brinkman equation for non-Newtonian flow, the simulated amount of (14)C-TCE oxidized during transport matched experimental results. These observations support the use of xanthan as a means of enhancing MnO4(-) delivery into LPZs for the treatment of dissolved-phase TCE.

Developing slow-release persulfate candles to treat BTEX contaminated groundwater.

The development of slow-release chemical oxidants for sub-surface remediation is a relatively new technology. Our objective was to develop slow-release persulfate-paraffin candles to treat BTEX-contaminated groundwater. Laboratory-scale candles were prepared by heating and mixing Na(2)S(2)O(8) with paraffin in a 2.25 to 1 ratio (w/w), and then pouring the heated mixture into circular molds that were 2.38 cm long and either 0.71 or 1.27 cm in diameter. Activator candles were prepared with FeSO(4) or zerovalent iron (ZVI) and wax. By treating benzoic acid and BTEX compounds with slow-release persulfate and ZVI candles, we observed rapid transformation of all contaminants. By using (14)C-labeled benzoic acid and benzene, we also confirmed mineralization (conversion to CO2) upon exposure to the candles. As the candles aged and were repeatedly exposed to fresh solutions, contaminant transformation rates slowed and removal rates became more linear (zero-order); this change in transformation kinetics mimicked the observed dissolution rates of the candles. By stacking persulfate and ZVI candles on top of each other in a saturated sand tank (14×14×2.5 cm) and spatially sampling around the candles with time, the dissolution patterns of the candles and zone of influence were determined. Results showed that as the candles dissolved and persulfate and iron diffused out into the sand matrix, benzoic acid or benzene concentrations (C(o)=1 mM) decreased by >90% within 7 d. These results support the use of slow-release persulfate and ZVI candles as a means of treating BTEX compounds in contaminated groundwater.

Transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by permanganate.

The chemical oxidant permanganate (MnO(4)(-)) has been shown to effectively transform hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at both the laboratory and field scales. We treated RDX with MnO(4)(-) with the objective of quantifying the effects of pH and temperature on destruction kinetics and determining reaction rates. A nitrogen mass balance and the distribution of reaction products were used to provide insight into reaction mechanisms. Kinetic experiments (at pH ∼ 7, 25 °C) verified that RDX-MnO(4)(-) reaction was first-order with respect to MnO(4)(-) and initial RDX concentration (second-order rate: 4.2 × 10(-5) M(-1) s(-1)). Batch experiments showed that choice of quenching agents (MnSO(4), MnCO(3), and H(2)O(2)) influenced sample pH and product distribution. When MnCO(3) was used as a quenching agent, the pH of the RDX-MnO(4)(-) solution was relatively unchanged and N(2)O and NO(3)(-) constituted 94% of the N-containing products after 80% of the RDX was transformed. On the basis of the preponderance of N(2)O produced under neutral pH (molar ratio N(2)O/NO(3) ∼ 5:1), no strong pH effect on RDX-MnO(4)(-) reaction rates, a lower activation energy than the hydrolysis pathway, and previous literature on MnO(4)(-) oxidation of amines, we propose that RDX-MnO(4)(-) reaction involves direct oxidation of the methylene group (hydride abstraction), followed by hydrolysis of the resulting imides, and decarboxylation of the resulting carboxylic acids to form N(2)O, CO(2), and H(2)O.