Cores extracted from several species of deciduous and coniferous trees (n = 11) located immediately downgradient from an aqueous film forming foam (AFFF) contaminated source area were used to determine PFAS concentrations and compositions within these trees and evaluate the use of tree cores to forensically reconstruct past trends of PFAS concentrations in shallow, root-accessible porewater over time. The tree cores were divided into mostly decadal increments (n = 95), subjected to a solid-phase PFAS extraction process, and analyzed for 40 PFAS. PFBA, PFHxS, PFOA, and PFOS were the most detected PFAS. Variability in the tree core concentrations appear to be influenced by PFAS concentrations in root-accessible porewater, tree species, and growth rates. PFOS served as the most useful compound for reconstructing past trends of contamination due to relatively high detection rates and concentrations, and less radial translocation than PFBA, PFHxS, and PFOA, which were commonly found in decadal increments formed before the first purported usage of AFFF. Reconstructions from four trees (cedar, poplar, and white pine) were used to identify peak PFOS concentrations of 7, 15, 17, and 18 years after the first reported AFFF application in 1970 that systematically occur in sequence with increasing distance from the source. This time range appears feasible, particularly for the tight range of 15-18 years for the white pines and cedars which are located 450, 497, and 588 m along their respective groundwater flow paths.

Surface Water Foam (SWF) and underlying Surface Water (SW) were collected from six distinct sites across Michigan using a novel sampling device. PFAS were detected in all SWF samples (Σ41 compounds, n = 14; Avg total PFAS=54,895 ng/L). SWF samples were enriched in high and intermediate molecular volume PFAS relative to SW samples (n = 10) which were dominated by low molecular volume, short-chain PFAS (Avg total PFAS=21 ng/L). Ultra-long-chain and rarely detected PFAS were quantified in SWF that were not detected in SW. Wet and dry SWFs were distinguished by appearance, liquid content, and PFAS composition. Dry SWFs had higher total PFAS concentrations than wet SWFs (Avg total PFAS difference =158,330 ng/L). Intermediate molecular volume PFAS constituted a greater percentage of total PFAS concentrations in wet SWFs, whereas dry SWFs were dominated by high molecular volume PFAS. Principal component and cluster analyses show distinct compositional differences between SW, wet SWF, and dry SWF. A conceptual model is proposed to describe changes in PFAS composition during the evolution and aging of SWFs. Bubbles created from turbulence in surface waters initially accumulate to form wet SWFs. Liquid drains as wet SWFs evolve towards dry SWFs and lower molecular weight PFAS with lower air-water interface (AWI) adsorption drain with the liquid. This enriches dry SWFs with higher molecular volume PFAS that have higher AWI adsorption (up to five orders of magnitude). This study demonstrates the value of SWFs as a complementary sampling matrix for quantifying high and intermediate volume PFAS in natural surface water systems.

Road salt (e.g., NaCl) application in cold-temperature regions has increased Cl- concentrations in freshwater. Removing Cl- from water is challenging because it is highly soluble. This paper is the first to demonstrate and characterize the removal of Cl- from stormwater via Friedel's salt (Ca4Al2(OH)12Cl2(H2O)4) precipitation (FSP), achieved by adding calcium oxide (CaO) and sodium aluminate (NaAlO2). Laboratory tests were done on Cl- removal with FSP using a range of Ca/Al/Cl ratios in deionized (DI) water and stormwater samples impacted by road salt. Even the lowest doses resulted in significant removal of Cl- with maximum removal rates for comparable Ca/Al/Cl ratios of 72% and 84% in stormwater and DI water, respectively. Temporal experiments in stormwater and DI water indicate that most of the Cl- removal occurred within the first 10 min of reaction time. Potential applications of FSP were demonstrated for two hypothetical scenarios based on a well-characterized, salt-impacted lake. The first scenario indicates that a 30% reduction in stormwater Cl- mass is sufficient to maintain concentrations below 150 mg/L. A second scenario with an initial 300 mg/L lake water concentration shows the potential for implementing FSP in low-flow pump and treat systems for the rehabilitation of road-salt-impaired lakes.

Fate and transport of per- and polyfluoroalkyl substances (PFAS) in wastewater treatment plant (WWTP) effluent discharged to rapid infiltration basins (RIBs) is investigated using data from 26 WWTPs in Michigan, USA. PFAS were found to accumulate in groundwater downgradient from RIBs with median groundwater-effluent enrichment factors for ten commonly detected, terminal-form perfluoroalkyl acids (PFAAs) ranging from 1.3 to 5.2. Maximum contaminant levels for drinking water were exceeded in groundwater at all WWTPs with available PFAS data. Numerical models of unsaturated fluid flow and PFAS transport honoring RIB site properties, such as median vertical separation distance to the water table and a realistic range of area-normalized effluent fluxes, show long-chain PFAS undergo significant delays from air-water interface (AWI) adsorption, requiring up to 15 times longer to reach maximum mass flux to the saturated zone under low-flux conditions, where AWI area is 2.5 times greater. Short-chain PFAS commonly detected in effluent are only minimally affected by AWI adsorption and show little to no attenuation under high-flux conditions. The nonlinear inverse relationship between water content and AWI area highlights the important role of AWI adsorption in modulating unsaturated transport of long-chain PFAS to underlying groundwater due to the broad range of flux rates applied to RIB systems.

Trends in concentration, distribution, and variability of per-and polyfluoroalkyl substances (PFAS) in biosolids are characterized using an extensive dataset of 350 samples from 190 wastewater treatment plants (WWTPs) across Michigan. All samples are comprised of final treated solids generated at the end of the wastewater treatment process. Concentrations of both individual and sigma 24 PFAS are lognormally distributed, with sigma 24 PFAS concentrations ranging from 1-3200 ng/g and averaging 108 +/- 277 ng/g dry wt. PFAS with carboxyl and sulfonic functional groups comprise 29% and 71% of sigma 24 PFAS concentrations, respectively, on average. Primary sample variability in concentration is associated with long-chain PFAS with higher tendency for partitioning to biosolids. Short-chain carboxylic compounds, most notably PFHxA, are responsible for secondary concentration variability. Usage of FTSA and PFBS replacements to long-chain sulfonic compounds also contributes to variance in biosolids concentrations. Sulfonamide precursor compounds as a collective group are detected at a similar frequency as PFOS and often have higher concentrations. Trends in PFAS enrichment for individual PFAS vary at least 3 orders-of-magnitude and generally increase with compound hydrophobicity; however, partitioning of PFAS onto solids in WWTPs is a complex process not easily described nor constrained using experimentally derived partitioning coefficients.

Per- and polyfluorinated alkyl substances (PFAS) enrichment in foam was investigated for the first time at a wastewater treatment plant cascade. A novel sampling device was utilized to allow spatial and temporal heterogeneity in PFAS concentrations and liquid content to be characterized. Concentrations of 8 PFAS compounds were normalized to liquid content and fit to a power law model revealing strong correlation (R2 = 0.91) between drainage induced enrichment and PFAS molar volume. Short chain PFAS such as perfluorobutanoate (PFBA) exhibited minor to no enrichment factors in foam (0.24-5.9) compared to effluent concentrations across the range of foam liquid contents (0.28-6.24%), while long chain compounds such as perfluorooctane sulfonate (PFOS) became highly enriched with factors of 295-143,000. A conceptual model is proposed to explain higher than expected enrichment of more surface-active PFAS relative to liquid content, which combines continuous partitioning of PFAS to air bubbles during foam formation with additional partitioning during non-linear drainage and foam collapse, both controlled by their affinity for the air-water interface. Scoping calculations suggest the majority of PFOS and other long chain PFAS may be removed if foam is continuously collected with potential to reduce waste volume under economic barriers for current destructive technologies.

This paper describes research to characterize subsurface contamination caused by leaching of lead (Pb) from batteries disposed of at the surface, which has spread with groundwater movement. The contaminated soils and aquifer are located in the Matano formation (Sulawesi, Indonesia). Ground Penetrating Radar (GPR) was used to detect and delineate Pb-contaminated soils (i.e., solid-phase Pb). Lead in the solid and aqueous phase have different characteristics and responses when subjected to electromagnetic (EM) waves. Many studies have used GPR to map solid-phase Pb contamination in the subsurface. GPR uses EM as the base medium to receive subsurface images and is useful for the detection of solid-phase Pb contamination but cannot detect aqueous-phase Pb. The first step in the remediation process was to delineate solid-phase Pb contamination in the subsurface using GPR, which required a geotechnical survey to support GPR. Samples of soil and aquifer solids were then taken to quantify lead concentrations using X-ray fluorescence (XRF). We collected 15 lines of GPR measurements and 11 soil samples to quantify Pb. Frequencies of 600 MHz and 900 MHz were used for the GPR antenna. The results identified a clay layer at a depth of between 3 m and 4 m, which appears to have served as barrier to downward migration of Pb-contaminated groundwater. A shadow zone and low reflectance in the GPR subsurface section images were used to identify as the Pb contamination, which has a distinct wavelength ranging between 0.36 m and 0.45 m. We conclude from the results of this study that GPR was an effective tool for the delineation of the vertical and horizontal spread of Pb contamination eastward from the source.

Approximately 760 liters (200 gallons) of first-generation, PFOS-dominant, Aqueous Film-Forming Foam (AFFF) concentrate entered the sanitary sewer after an accidental release at the Kalamazoo/Battle Creek International Airport and migrated 11.4 km to the Kalamazoo Water Reclamation Plant. Near-daily sampling of influent, effluent, and biosolids generated a high-frequency, long-duration dataset used to understand the transport and fate of accidental PFAS releases to wastewater treatment plants, identify AFFF concentrate composition, and perform a plant-wide PFOS mass balance. Monitored influent concentrations exhibited sharp PFOS declines after 7 days post-spill, yet effluent discharges remained elevated due to return activated sludge (RAS) recirculation, resulting in the exceedance of Michigan's Surface Water Quality Value for 46 days. Mass balance estimates indicate 1.292 kg PFOS entering the plant and 1.368 kg leaving. Effluent discharge and sorption to biosolids account for 55% and 45% of estimated PFOS outputs, respectively. Identification of AFFF formulation and reasonable agreement between computed influent mass and reported spill volume demonstrates effective isolation of the AFFF spill signal and increases confidence in the mass balance estimates. These findings and related considerations provide critical insight for performing PFAS mass balances and developing operational procedures for accidental spills that minimize PFAS releases to the environment.

Observed trends in municipal solid waste landfills reveal a distinct disparity between PFAS composition entering in waste, mostly as diPAP and FTOH, and leaching out as FTCA and PFCA. These patterns are elucidated by compiling PFAS compositions in paper, textiles, and carpet, with known precursor transformations that generate FTCA and PFCA in leachate. Future research must assess the role of precursor PFAS like diPAP and FTOH in landfill mass balances, particularly in leachate, along with the potential release of semi-volatile PFAS to the atmosphere. Closing these knowledge gaps is critical as landfills will increasingly serve as PFAS sources.

Due to the diverse chemistries of per- and polyfluoroalkyl substances (PFAS) and their apparent recalcitrance to natural biological and abiotic transformation processes, remediation of this class of compounds in groundwater environments is much more challenging than that of other common contaminants such as chlorinated solvents, hydrocarbons, methyl tert-butyl ether, and 1,4-dioxane. Overall, the groundwater remediation community is faced with substantial challenges that will require both continued enhancement of existing technologies and development of new technologies and strategies to manage PFAS-impacted sites. Fortunately, an extraordinary breadth and depth of ongoing research in PFAS remediation is funded through a variety of different agencies and organizations. This research can be organized into three main categories: (1) nondestructive approaches that remove PFAS from water and other matrices; (2) destructive technologies that break carbon-fluorine and carbon-carbon bonds to create nontoxic products; and (3) coupled systems that concentrate and then destroy PFAS. As with previous groundwater contaminants, an initial focus on ex situ PFAS treatment is now slowly evolving to include more in situ research. However, as of 2021, there are no practical groundwater remediation technologies that have been shown to destroy target PFAS (i.e., mineralize and/or create nontoxic products) in situ at full-scale field application. While the historical goal of in situ treatment for most contaminants has been destruction, practitioners, facility owners, and regulators may need to alter their expectations and objectives for PFAS, at least in the short term, to management strategies that include treatment at receptor locations to avoid exposures and adsorption-based attenuation strategies for some plumes. These approaches can be used as practical alternatives to PFAS destruction or to buy time until promising technologies become both commercially available and accepted by the industry. The success of any remedial effort typically depends upon meeting regulatory criteria, which in the case of PFAS, are currently in flux at the federal level and differ by orders of magnitude among state regulatory bodies. While this is understandable given the uncertainty and complexity of this issue, setting firm, consistent, and attainable regulatory standards is necessary to provide researchers and practitioners with necessary benchmarks for remediation technology development and commercialization.

Concentrations of Per-and Polyfluorinated Alkyl Substances (PFAS) from public and private sources in Michigan compiled for wastewater treatment plants (WWTPs) (influent, effluent, biosolids), contaminated sites, and landfill leachates reveal complex cycling within the natural and engineered environment. Analysis of 171 contaminated sites in Michigan by source release indicate four dominant PFAS sources - landfills, aqueous film-forming foams (AFFF), metal platers, and automotive/metal stamping - account for 75% of the contamination. Diverse chemical signatures were observed for leachates collected from 19 landfills (mostly type II municipal) with the dominant PFAS ranging from perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) to shorter-chained compounds, perfluorohexanoic acid (PFHxA), perfluorobutanoic acid (PFBA), and per-fluorobutanesulfonic acid (PFBS). Analysis of PFAS carbon chain length as a function of landfill age shows the transition of C8s in leachate from older landfills to C4s and C6s in younger landfills, consistent with the phasing out and replacement of C8s. PFAS mass flux in leachate for landfills studied range between 5 - 2,000 g/yr and are highest for active landfills, which generate greater leachate volumes and contain fresh PFAS wastes. Detailed study of 10 WWTPs with industrial pretreatment programs indicate numerous chemical transformations across the plants that yield effluent PFAS concentrations as much as 19 times greater than influent, attributed to transformations of unmeasured precursors in the influent to measured, stable PFAS in the effluent. PFOA, PFHxA, perfluoropentanoic acid (PFPeA), PFBA, and PFBS show the greatest increases across the plant ranging from 20% to nearly 2,000%. PFOS concentrations decreased across 6 WWTPs, consistent with a strong tendency to adsorb onto biosolids. Estimated mass of discharge of (mostly unregulated) PFAS from WWTPs to receiving waters range from 40 g/yr to 128 kg/yr.

BACKGROUND Phenanthrene (PHE) is a widespread, highly-toxic, and biodegradable polycyclic aromatic hydrocarbon (PAH) that can be found with high concentrations in multiple industrial sites. For the efficient biodegradation of PHE, especially for the high concentrations, a PHE-degrading Acidovorax strain was isolated from a soil contaminated for decades with PAH; its ability to degrade PHE was investigated and the pathways involved were identified. RESULTS A PHE-degrading strain was isolated and identified as Acidovorax sp. JG5. The bacterium completely degraded 200 mg center dot L-1 PHE in 24 h and it degraded over 90% of PHE in solutions ranging from 500 to 1500 mg center dot L-1 in 48 h. Key metabolites, such as 9,10-phenanthraquinone, 2-hydroxy-1-naphthoic acid, protocatechuic acid, phthalic acid, pyruvic acid, and salicylic acid, were detected during PHE biodegradation. Twelve genes related to PHE biodegradation (e.g., nahAa, pht5, ligA, and dmp cluster) were also revealed. Two PHE degradation pathways are proposed based on these metabolites and genes. CONCLUSION Acidovorax sp. JG5 exhibits a high tolerance to PHE and high rates of degradation, along with a tremendous potential for the bioremediation of heavy PAH contamination. (c) 2021 Society of Chemical Industry

Interactive effects of inorganic arsenic (As) species and polycyclic aromatic hydrocarbons (PAHs) on their uptake, accumulation and translocation in the hyperaccumulator Pteris vittata L. (P. vittata) were studied hydroponically. The presence of PAHs hindered As uptake and acropetal translocation by P. vittata, decreasing As concentrations by 29.8%-54.5% in pinnae, regardless of the initial As speciation. The inhibitive effect of PAHs was 1.6-8.7 times greater for arsenite [As(III)] than for arsenate [As(V)]. Similarly, inorganic As inhibited the uptake of fluorene (FLU) and benzo[a]pyrene (BaP) by P. vittata roots by 0.4%-21.7% and by 33.1%-69.7%, respectively. Interestingly, coexposure to As and PAHs slightly enhanced the translocation of PAHs by P. vittata with their concentrations increased 0.3 to 0.8 times in shoots, except for the As(III)+BaP treatment. The antagonistic interaction between As and PAHs uptake is likely caused by competitive inhibition or oxidative stress injury. By using synchrotron radiation micro X-ray fluorescence imaging, high concentrations of As were found distributed throughout the microstructures far from main vein of the pinnae when coexposed with PAHs, the opposite of what was observed with exposure to As only. PAHs could also significantly inhibit the accumulation and distribution of As in vascular bundles in rachis treated with As(III). The results of two-photon laser scanning confocal microscopy revealed that PAHs were mainly distributed in the vascular cylinder, epidermal cells, vascular bundles, epidermis and vein tissues, and this was independent of As speciation and treatment. This work offers new positive evidence for the interaction between As and PAHs in P. vittata, presents new information on the underlying mechanisms for interactions of As and PAHs affecting their uptake and translocation within P. vittata L., and provides direction for future research on the mechanisms of PAHs uptake by plants.

This study quantified influences of interactions between anthropogenic and natural factors on trace element accumulation and pollution risk in karst soils at regional and local scales and identified the dominant interacting factors. A total of 513 soil samples were collected from Hechi, southern China to measure concentrations of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb), which were compared with published background values. Descriptive statistics and occurrence characteristics were developed with geostatistical methods and the comprehensive pollution risk was calculated using the Nemerow pollution index (NPI). Geo-detector models were used to further examine and quantify the influence of 14 factors (5 anthropogenic and 9 natural) on trace element concentrations and NPI, both individually and interacting with the other 13 factors. The results clearly demonstrate that anthropogenic factors interact with natural factors to enhance nonlinearly and significantly trace element accumulation in karst soils. Watershed was the natural factor that most enhanced trace element accumulation when interacting with anthropogenic factors. Land use and smelting industry were the anthropogenic factors that most enhanced trace element accumulation when interacting with natural factors. Land use-watershed interaction accounted for 56% of Cd accumulation and smelting industry-watershed interaction for 19% of As accumulation. Land use-watershed, land use-lithology, and pH-watershed interactions accounted for 51%, 19%, and 15%, respectively of NPI values. The findings indicate that changing land use and reducing pollutant discharge from the smelting industry should be considered.

Sixty leading members of the scientific, engineering, regulatory, and legal communities assembled for the PFAS Experts Symposium in Arlington, Virginia on May 20 and 21, 2019 to discuss issues related to per- and polyfluoroalkyl substances (PFAS) based on the quickly evolving developments of PFAS regulations, chemistry and analytics, transport and fate concepts, toxicology, and remediation technologies. The Symposium created a venue for experts with various specialized skills to provide opinions and trade perspectives on existing and new approaches to PFAS assessment and remediation in light of lessons learned managing other contaminants encountered over the past four decades. The following summarizes several consensus points developed as an outcome of the Symposium: Regulatory and policy issues: The response by many states and the US Environmental Protection Agency (USEPA) to media exposure and public pressure related to PFAS contamination is to relatively quickly initiate programs to regulate PFAS sites. This includes the USEPA establishing relatively low lifetime health advisory levels for PFAS in drinking water and even more stringent guidance and standards in several states. In addition, if PFAS are designated as hazardous substances at the federal level, as proposed by several Congressional bills, there could be wide-reaching effects including listing of new Superfund sites solely for PFAS, application of stringent state standards, additional characterization and remediation at existing sites, reopening of closed sites, and cost renegotiation among PRPs. Chemistry and analytics: PFAS analysis is confounded by the lack of regulatory-approved methods for most PFAS in water and all PFAS in solid media and air, interference with current water-based analytical methods if samples contain high levels of suspended solids, and sample collection and analytical interference due to the presence of PFAS in common consumer products, sampling equipment, and laboratory materials. Toxicology and risk: Uncertainties remain related to human health and ecological effects for most PFAS; however, regulatory standards and guidance are being established incorporating safety factors that result in part per trillion (ppt) cleanup objectives. Given the thousands of PFAS that may be present in the environment, a more appropriate paradigm may be to develop toxicity criteria for groups of PFAS rather than individual PFAS. Transport and fate: The recalcitrance of many perfluoroalkyl compounds and the capability of some fluorotelomers to transform into perfluoroalkyl compounds complicate conceptual site models at many PFAS sites, particularly those involving complex mixtures, such as firefighting foams. Research is warranted to better understand the physicochemical properties and corresponding transport and fate of most PFAS, of branched and linear isomers of the same compounds, and of the interactions of PFAS with other co-contaminants such as nonaqueous phase liquids. Many PFAS exhibit complex transport mechanisms, particularly at the air/water interface, and it is uncertain whether traditional transport principles apply to the ppt levels important to PFAS projects. Existing analytical methods are sufficient when combined with the many advances in site characterization techniques to move rapidly forward at selected sites to develop and test process-based conceptual site models. Existing remediation technologies and research: Current technologies largely focus on separation (sorption, ion exchange, or sequestration). Due to diversity in PFAS properties, effective treatment will likely require treatment trains. Monitored natural attenuation will not likely involve destructive reactions, but be driven by processes such as matrix diffusion, sorption, dispersion, and dilution. The consensus message from the Symposium participants is that PFAS present far more complex challenges to the environmental community than prior contaminants. This is because, in contrast to chlorinated solvents, PFAS are severely complicated by their mobility, persistence, toxicological uncertainties, and technical obstacles to remediation-all under the backdrop of stringent regulatory and policy developments that vary by state and will be further driven by USEPA. Concern was expressed about the time, expense, and complexity required to remediate PFAS sites and whether the challenges of PFAS warrant alternative approaches to site cleanups, including the notion that adaptive management and technical impracticability waivers may be warranted at sites with expansive PFAS plumes. A paradigm shift towards receptor protection rather than broad scale groundwater/aquifer remediation may be appropriate.

The delineation of contamination at a co-contaminated site is vital for designing remedial strategy and estimating costs. Backpropagation (BP) neural networks and the Nemerow pollution index (NPI) with 3-D kriging were combined in this study to delineate contaminant plumes, analyze the spatial distribution of pollutants in different layers and visualize them in three dimensions, quantify polluted areas and pollution levels, and identify hotspots of the contaminants of concern (COCs). The results of a comprehensive assessment performed using BP networks and NPI were compared. The analysis of the volumes of soil contaminated with specific COCs in different soil layers showed that arsenic (As) hardly migrated downgradient whereas benzo[a]pyrene (BaP) had a strong tendency to migrate. The tendency of fluorene (FLE), naphthalene (NAP), and phenanthrene (PHE) to migrate was between that for As and BaP. The volumes of earth contaminated with of all five of these COCs generally decreased with increasing pollution levels. The volumes of PHE, FLE, and NAP at different pollution levels exhibited similar trends, and most contaminated areas were safe. The volume of BaP at high pollution levels was markedly greater than that for the other four COCs, and the volume of As at low pollution levels was also notably greater than that for the other four pollutants. (3) The spatial patterns performed by the NPI and BP network comprehensive assessment methods were similar. However, BP networks can overcome the deficiencies of NPI, which are amplification of the effect of heavily polluted elements and narrowing the separability of polluted and unpolluted areas. After comparing performance and performing a cost-benefit analysis, we propose a model that integrates BP networks and geostatistics to delineate soil contaminant plumes at co-contaminated sites.

A simple surface-enhanced Raman spectroscopy (SERS) sensor based on an undecorated gold-colloid substrate was developed for the rapid and effective detection of polycyclic aromatic hydrocarbons (PAH). The SERS enhancement of the bare Au nanoparticles for PAH was achieved by adjusting chemical reduction conditions and Cl- content. The strongest SERS response of this system was achieved with 2.0 mL of trisodium citrate (1%) and 80 μL of NaCl (1 M). With this simple SERS sensor, qualitative and quantitative determination of trace-level naphthalene (NaP), phenanthrene (PHE) and pyrene (PYR) were achieved using a portable Raman spectrometer at detection limits of 1.38 μg L-1, 0.23 μg L-1, and 0.45 μg L-1, respectively. Plots of SERS intensity vs. PAH concentrations were linear, with correlation coefficients (R2) ranging from 0.8729 to 0.9994. More importantly, the SERS sensor was able to accurately identify each PAH in complex mixtures. This SERS technique shows great promise for the rapid and direct detection of aromatic hydrocarbons organic pollutants in field.

Accurate estimation of oxidant consumption during in situ chemical oxidation (ISCO) is the key to determining the treatment effectiveness in contaminated sites. We established the estimation model of soil oxidant demand (SOD) and simulation equations of potassium permanganate (KMnO4) dynamic consumption based on the reaction equation of KMnO4 with reductive minerals and the estimation model of SOD. Model validation, model application, and simulation assessment had been accomplished. Results indicated that the simulations are in good agreement with measured data. The confidence level of the SOD estimation model of KMnO4 was over 80%, with sensitivity in decreasing order as follows: organic matter content > initial KMnO4 concentration > reductive minerals (RMs). Particularly, the organic matter played a dominate role in the SOD model estimation. The coefficient of determination (R-2) of the SOD dynamic consumption simulation equation was above 0.9. Among the various types of soils, the overall trend of SOD value and reaction period decreased as follows: clay > loam > sand. However, the consumption rate of KMnO4 decreased in the order of clay > sand > loam. In addition, SOD value, reaction period, and reaction rate all increased as the initial concentration of KMnO4 went up. This work can provide a methodology and reference for selecting and estimating of the optimal oxidant doses and reaction period during field application.

A contaminated soil was treated in the laboratory with in situ chemical oxidation and in situ solidification/stabilization combined in a single application. Portland cement can activate the persulfate anion (S2O82-)in sodium persulfate (Na2S2O8), chemically oxidizing organic contaminants. Ten doses of Na2S2O8, ranging from 0.25% to 5% (by weight) with a cement: Na2S2O8 ratio of 2: 1, completely activated S2O82- within 2.5 h of mixing. Chemical oxidation removed a significant portion of the contaminants of concern (COCs), including BTEX, naphthalene, and 17 higher molecular weight PAHs. COC oxidation showed saturation-type dose-response curves, with pronounced contaminant removal at Na2S2O8 doses below 1.5%, and little removal at higher doses. Plots of reduced COC leachability vs. cement dose for combined oxidation and stabilization treatments were similar to those for COC oxidation, but for stabilization treatments the dose-response was roughly linear, and inversely related to the molecular weight of the COCs. Even with low Na2S2O8 doses, combined oxidation and stabilization treatments reduced COC leachability far more than stabilization treatments alone using the same PC dose, because of the COC removal achieved by Na2S2O8 oxidation. The increase in soil strength and decrease in hydraulic conductivity were unaffected by Na2S2O8. (C) 2016 Elsevier Ltd. All rights reserved.