Groundwater Remediation Technologies Research Articles

Physical modeling of organics-contaminated groundwater remediation by ozone micro-nano-bubbles enhanced oxidation

Ozone micro-nano-bubbles (MNBs) enhanced oxidation is a promising in-situ remediation technology for organics-contaminated groundwater. The transport behavior of MNBs and contaminant removal effect in actual groundwater scene is not yet comprehensively understood, although one-dimensional column experiments and batch tests were conducted to investigate the migration of MNBs and contaminant degradation in previous studies. Here, a novel two-dimensional (2D) physical modeling facility was developed, which can characterize the tempo-spatial distribution of MNBs and contaminant in groundwater. The facility was used to explore the migration of MNBs under different hydraulic gradients and the removal of methyl orange, a representative organic pollutant, using ozone MNBs. The experimental results show that groundwater flow velocity has a significant influence on the migration behavior of MNBs. A model including groundwater flow, MNBs transport, and dissolved gas transport can well capture the migration and distribution of MNBs under different hydraulic gradients. The longitudinal and transverse dispersivities of the MNBs were calculated to be 1.14 cm and 0.18 cm, respectively. MNBs are able to migrate with groundwater flow to long distances and exhibit strong dispersion in the lateral and longitudinal directions. The increase in hydraulic gradient greatly enhances the transport of MNBs in groundwater and relieves the deposited MNBs on the surface of porous media. At a hydraulic gradient increasing from 0.033 to 0.1, the range of influence of MNBs increased from about 80 cm × 40 cm to 140 cm × 39 cm after 36 h of injection of oxygen MNBs water. The methyl orange in groundwater is effectively removed by ozone MNBs enhanced oxidation, showing the remarkable remediation ability of ozone MNBs. The area of influence and pollutant removal of the ozone MNBs expanded with injection, and the area of influence was approximately 48 cm × 30 cm after 48 h of treatment. We also discuss the effect of groundwater matrix on ozone MNB migration and degradation of contaminants. The 2D model tests illustrate the mechanism of MNB migration and indicate that ozone MNBs enhanced oxidation technology has great potential in the remediation of organics-contaminated groundwater.

Assessing the electrode configuration in a sandbox system for the removal of sulfanilamide: A pilot study

Electrochemical oxidation has emerged as an effective and straightforward technology for groundwater remediation. While recent studies have investigated parameters such as current, electrolyte composition, and electrode materials, most have been conducted using small-scale batch or flow reactors, limiting their applicability to real-world conditions. In this study, a pilot-scale sandbox reactor was employed to simulate realistic groundwater conditions and assess the removal of sulfanilamide, a model organic contaminant. Various electrode configurations were systematically evaluated to identify the key operational parameters influencing pollutant removal efficiency, providing insights for practical applications in groundwater treatment. This study proposes three configurations, including a single well with the anode and cathode, a double well with the separated anode and cathode, and an e-barrier with electrodes separately mounted inside a permeable barrier. Single well had the lowest removal efficiency (60%) because cathodic reaction inhibited the anodic oxidation. A double well with a separate anode and cathode can achieve 80% removal efficiency. However, effluent pH can reach up to 13.2, which can adversely impact groundwater. Meanwhile, the e-barrier not only achieved complete removal, but also maintained a neutral pH of 7.0 over 30 days. The e-barriers proved to be the most effective configuration based on their removal efficiency (100%) while yielding an effluent with neutral pH. The energy consumption of the e-barrier was most effective at 1.54 kWh/m3, while the other configurations were 5.40 and 22.18 kWh/m3. E-barriers are deemed a very reasonable configuration, both in terms of removal efficiency and practical application in groundwater.

Superior nitrate and chromium reduction synergistically driven by multiple electron donors: Performance and the related biochemical mechanism

Nitrate and Cr(VI) are the typical and prevalent co-contaminants in the groundwater, how to synchronously and effectively diminish them has received growing attention. The most problem that currently limits the nitrate and Cr(VI) reduction technology for groundwater remediation is with emphasis on exploring the optimal electron donors. This study investigated the feasibility of utilizing the synergistical effect of inorganic electron donors (pyrite, sulfur) and inherently limited organics to promote synchronous nitrate and Cr(VI) removal, which meets the requirement of naturally low-carbon and eco-friendly technologies. The NO3−-N and Cr(VI) removal efficiencies in the pyrite and sulfur involved mixotrophic biofilter (PS–BF: approximately 90.8 ± 0.6% and 99.1 ± 2.1%) were substantially higher than that in a volcanic rock supported biofilter (V–BF: about 49.6% ± 2.8% and 50.0% ± 9.3%), which was consistent with the spatial variations of their concentrations. Abiotic and biotic batch tests directly confirmed the decisive role of pyrite and sulfur for NO3−-N and Cr(VI) removal via chemical and microbial pathways. A server decline in sulfate production correlated with decreasing COD consumption revealed that there was sulfur disproportionation induced by limited organics. Metagenomic analysis suggested that chemoautotrophic microbes like Sulfuritalea and Thiobacillus were key players responsible for sulfur oxidation, nitrate and Cr(VI) reduction. The metabolic pathway analysis suggested that genes encoding functional enzymes related to complete denitrification, S oxidation, and dissimilatory sulfate reduction were upregulated, however, genes encoding Cr(VI) reduction enzymes (e.g. chrA, chrR, nemA, and azoR) were downregulated in PS-BF, which further explained the synergistical effect of multiple electron donors. These findings provide insights into their potential cooperative interaction of multiple electron donors on greatly promoting nitrate and Cr(VI) removal and have implications for the remediation technology of nitrate and Cr(VI) co-contaminated groundwater.

Unlocking the power of activated carbon-mediated peracetic acid activation for efficient antibiotics abatement in groundwater: Coupling the processes of electron transfer, radical production, and adsorption

The activation of peracetic acid (PAA) by activated carbon (AC) is a promising approach for reducing micropollutants in groundwater. However, to harness the PAA/AC system’s potential and achieve sustainable and low-impact groundwater remediation, it is crucial to quantify the individual contributions of active species. In this study, we developed a combined degradation kinetic and adsorption mass transfer model to elucidate the roles of free radicals, electron transfer processes (ETP), and adsorption on the degradation of antibiotics by PAA in groundwater. Our findings reveal that ETP predominantly facilitated the activation of PAA by modified activated carbon (AC600), contributing to ∼61% of the overall degradation of sulfamethoxazole (SMX). The carbonyl group (CO) on the surface of AC600 was identified as a probable site for the ETP. Free radicals contributed to ∼39% of the degradation, while adsorption was negligible. Thermodynamic and activation energy analyses indicate that the degradation of SMX within the PAA/AC600 system requires a relatively low energy input (27.66 kJ/mol), which is within the lower range of various heterogeneous Fenton-like reactions, thus making it easily achievable. These novel insights enhance our understanding of the AC600-mediated PAA activation mechanism and lay the groundwork for developing efficient and sustainable technologies for mitigating groundwater pollution. Environmental ImplicationThe antibiotics in groundwater raises alarming environmental concerns. As groundwater serves as a primary source of drinking water for nearly half the global population, the development of eco-friendly technologies for antibiotic-contaminated groundwater remediation becomes imperative. The innovative PAA/AC600 system demonstrates significant efficacy in degrading micropollutants, particularly sulfonamide antibiotics. By integrating degradation kinetics and adsorption mass transfer models, this study sheds light on the intricate mechanisms involved, emphasizing the potential of carbon materials as sustainable tools in the ongoing battle for clean and safe groundwater.

Machine learning vs. statistical model for prediction modeling and experimental validation: Application in groundwater permeable reactive barrier width design

Permeable reactive barrier (PRB) is an effective in-situ technology for groundwater remediation. The important factors in PRB design are the width and reactive material. In this study, the beaded coal mine drainage sludge (BCMDS) was employed as the filling material to adsorb arsenic pollutants in groundwater, aiming to design the width of PRB. The design methods involving traditional continue column experiments and empirical formulas, as well as machine learning (ML) predictions and statistical methods, which are compared with each other. Traditional methods are determined based on breakthrough curves under several conditions. ML method has advantages in predicting the width of mass transfer zone (WMTZ), which simultaneously consider the characteristics of material, pollutant, and environmental conditions, with data collected from articles. After data preprocessing and model optimizing, selected the XGBoost algorithm based on the high accuracy, which shows good prediction for WMTZ (R2 = 0.97, RMSE = 0.15). The experimentally derived WMTZ values were also used to validate the predictions, demonstrating the ML low error rate of 7.04 % and the feasibility. Subsequent statistical analysis of multiple linear regression (MLR) showed the error rate of 39.43 %, interpret superiority of ML due to the complexity of influencing factors and the insufficient precision of math regression. Compared to traditional width design methods, ML can improve design efficiency and save experimental time and manpower. Further expansion of the dataset and optimization of algorithms could enhance the accuracy of ML, overcoming existing limitations and gaining broader applications.

Influencing factors and controlled release kinetics of H2O2 from PVP-coated calcium peroxide NPs for groundwater remediation

Calcium peroxide nanoparticles (nCP) as a versatile and safe solid source of hydrogen peroxide (H2O2) receive substantial attention from researchers as a potential groundwater remediation reagent. In this study, we synthesized polyvinylpyrrolidone-coated calcium peroxide nanoparticles (PVP@nCP-PVP) to control the release rate of H2O2 and modulate pH fluctuation simultaneously. The PVP@nCP-PVP is fully characterized and the H2O2 releasing kinetics and mechanisms are investigated. The H2O2 release longevity of nCP increased with the concentration of controlled release material (CRM) encapsulated shell, while the production of H2O2 decreased inversely. The acidic condition is favorable for increasing H2O2 production by promoting the complex decomposition of nCP. The low temperature prolonged the longevity of nCP and suppressed the competitive side reaction for producing O2. The release of H2O2 is consistent with zero-order reaction kinetics and the release of O2 is consistent with first-order reaction kinetics. At last, different nCP composites were employed to construct a Fenton-like system for the degradation of nitrobenzene (NB). The degradation rate was raised from 57.6% by Fe (II)/nCP to 70.0% and 93.7% by Fe (II)/nCP-PVP and Fe (II)/PVP@nCP-PVP systems, respectively. These findings demonstrate that PVP@nCP-PVP has significant advantages in repairing organically contaminated groundwater. Environmental implicationGroundwater contamination poses a great threat to human health and ecosystems. In-situ chemical oxidation (ISCO) is a widely used groundwater remediation technology. Calcium peroxide (CP) as solid hydrogen peroxide showed merits of low cost and high stability, but the further application was limited due to its violent chemical reaction and short longivity in groundwater . In this work, we prepared polyvinylpyrrolidone-coated controlled release nCP (PVP@nCP-PVP) for modulating the release of H2O2. The investigation of H2O2 release kinetics under various environmental conditions enhances the understanding of the inherent relationship between the H2O2 release performance of controlled-release materials and contamination remediation. The feasibility using macromolecules preparing controlled-release oxidizing agents was confirmed, providing a novel solution for groundwater contamination remediation.

Carbon Nanocoil-Based Photothermal Conversion Carrier for Microbubble Transport

Carbon nanocoil (CNC), a kind of quasi-one-dimensional carbon nanomaterial with a unique micro-scale helical structure, has wide application prospects in biological and environmental governance fields, due to its excellent photothermal conversion characteristics. We combine a carbon nanocoil as the laser irradiation carrier (i.e., the substance for absorbing light energy and converting light energy into heat to allow the creation of microbubbles) and a light-induced method to realize the radial short-distance transport of microbubbles. The results confirm that controlling the size of the microbubbles by laser power enables the radial transport of multiple microbubbles in a row. Light-induced CNC allows the creation of microbubbles at the start of the transport and the elimination of the microbubbles at the end of the transport, and the distance of transport between the laser irradiation site on the CNC and the location of the bubbles disappearing ranges from 10 µm to 30 µm. The circulation process of creating, transporting, and eliminating bubbles is expected to become a promising technology for soil and groundwater remediation.

Remediation of Groundwater Contaminated with Copper Ions by Waste Foundry Sand Permeable Barrier

The permeable reactive barrier (PRB) is one of the promising innovative in situ groundwater remediation technologies, in removing of copper from a contaminated shallow aquifer. The 1:1- mixture of waste foundry sand (WFS) and Kerbala’s sand (KS) was used for PRB. The WFS was represented the reactivity material while KS used to increase the permeability of PRB only. However, Fourier-transform infrared (FTIR) analysis proved that the carboxylic and alkyl halides groups are responsible for the sorption of copper onto WFS. Batch tests have been performed to characterize the equilibrium sorption properties of the (WFS+KS) mix in copper- containing aqueous solutions. The sorption data for Cu+2 ions, obtained by batch experiments, have been subjected to the Langmuir and Freundlich isotherm models. The Langmuir model was chosen to describe the sorption of solute on the solid phase of PRB. COMSOL Multiphysics 3.5a based on finite element method was used for formulation the transport of copper ions in two- dimension physical model under equilibrium condition. Numerical and experimental results proved that the PRB plays a potential role in the restriction of the contaminant plume migration. A good agreement between the predicted and experimental results was recognized with mean error (ME) not exceeded 10 %.

Revisiting the Role of Dissolved Silicate in Catalyzing the Hydrogen Peroxide Process with Iron-Bearing Minerals.

Injecting H2O2 into aquifers is a widely used in-situ chemical oxidation (ISCO) technology for groundwater remediation. Dissolved silicate was reported to decrease the reactivity of iron (Ⅲ)-bearing minerals toward H2O2. In this study, the effect of naturally occurring levels of dissolved silicate (≤1 mM) on the catalyzing hydrogen peroxide (CHP) with Fe(II) minerals is revaluated, and new observations that contradict with previous studies are reported. Specifically, dissolved silicate enhanced the CHP process by Fe(II) minerals. In the presence of Fe(II) minerals, siderite and ferrous oxide (FeO), which had a stronger dissolution tendency than Fe(III) minerals, dissolved silicate could prevent the dissolved iron species from precipitation through a coordinating effect, therefore reinforcing the homogeneous CHP process and the degradation of 2,4-dichlorophenol. The solution pH decreased due to the generation of degradation intermediates, and the solution acidification in turn promoted further dissolution of Fe(II) minerals. FeO particles exhibited the strongest silicate adsorption among the minerals, therefore a higher initial silicate concentration of 1 mM was needed to observe the enhancing effect. This study redefines the role of dissolved silicate on CHP process and provides clues to the design of efficient H2O2-based ISCO system for the remediation of groundwater.

Remediation of petroleum hydrocarbon-contaminated groundwater by biochar-based immobilized bacteria

It is essential to research the technology for effective remediation of petroleum hydrocarbon-contaminated groundwater because the petroleum hydrocarbon contamination of groundwater is becoming more and more serious. The petroleum hydrocarbon-degrading bacteria screened in this experiment were identified as Pseudomonas spp. by 16 S rDNA sequencing. Using wheat straw biochar as the carrier, a highly stable immobilized bacteria integrating adsorption and degradation was prepared by microbial immobilization technology. The results of scanning electron microscopy and Fourier transform infrared spectroscopy analysis showed that the microorganisms were adsorbed on the biochar. Degradation of petroleum hydrocarbon by immobilized bacteria conformed to the second-order kinetic model. For the manufacture of immobilized bacteria, the following immobilization parameters worked best: immobilization pH of 7 and immobilization time of 24 h. Finally, the produced immobilized bacteria were added to four groundwater samples with various initial concentrations of petroleum hydrocarbon, and it was found that all of the petroleum hydrocarbon degradations were above 95%. The study can serve as a useful resource for groundwater petroleum hydrocarbon remediation technology since the immobilized bacteria can successfully adapt to the groundwater petroleum hydrocarbon environment and significantly reduce the concentration of petroleum hydrocarbon.

Cyclic solubilization and release of polycyclic aromatic hydrocarbons (PAHs) using gemini photosensitive surfactant combined with micro-nano bubbles: a promising enhancement technology for groundwater remediation

Polycyclic aromatic hydrocarbons (PAHs) have posed serious risks to the groundwater environment. Surfactant-enhanced remediation (SER) is a promising strategy, as it can increase the solubilization efficiency of PAHs contaminants. However, this technology is still hampered due to low efficiency and high cost for the separation of pollutants after solubilization. Through the combination of micro-nano bubbles (MNBs) with a gemini photosensitive surfactant (N1, N2-bis[4-[4-[(4-butylphenyl) azo] phenoxy] butyl]-N1, N2-tetramethylethane-1,2-diammonium bromide, AzoPBT), herein we present a significantly enhanced efficiency of phenanthrene (Phe) solubilization and surfactant cycling. Notably, the presence of MNBs was conducive to the dissolution and release of Phe by reducing the CMC and γ of trans-AzoPBT (from 0.52 mmol/L and 28.94 mN·m−1 to 0.39 mmol/L and 27.88 mN·m−1) and increasing the difference of interfacial properties between trans and cis-AzoPBT, which was owing to the electrostatic interaction. Groundwater chemical parameters, i.e., ions, pH and organic matter would affect the solubilization ability of trans-AzoPBT. Mg2+ and Ca2+ inhibited the solubilization while SO42− promoted the solubilization, depending on their radius, electronic quantity and solution pH. A change in the HA level up to 8 mg/L had a negatively effect on the solubilization ability. High release rate (69.39 %) of cis-AzoPBT for Phe and high recovery rate (89.37 %) for tans-AzoPBT were obtained in the AzoPBT/MNBs mixed aqueous solution. Compared to MNBs combined with conventional cationic surfactants, AzoPBT/MNBs mixed aqueous solution exhibited better synergistic solubilization performance, and the apparent solubility of Phe increased from 26.74 % to 31.61 %. Overall, this study demonstrates the enhanced solubilization of PAHs by photosensitive surfactants combined with MNBs, which provides valuable insights of the effective utilization of surfactants in the remediation of PAHs-contaminated groundwater with SER technology.

Degradation of 1,2,3-trichloropropane by unactivated persulfate and the implications for groundwater remediation

Persulfate (PS) is widely used as an in situ chemical oxidation (ISCO) technology for groundwater and soil remediation. While conventional theory generally assumes that PS needs to be “activated” to produce reactive radicals for pollutant degradation, herein, PS without explicit activation system was discovered for the degradation of 1,2,3-TCP with the generation of reactive oxidation species (ROS). Comparison of five common ISCO oxidants (PS, peroxymonosulfate, hydrogen peroxide, potassium permanganate, and sodium percarbonate) indicated that only unactivated PS was able to degrade 1,2,3-TCP in both pure water and 12 natural water samples. 50 μM 1,2,3-TCP degradation can be continued as long as there is enough PS (50 mM). The degradation rate of 1,2,3-TCP increased 450 % when the PS concentration increased from 10 mM to 50 mM and 500 % when the temperature increased from 25 °C to 45 °C. Electron paramagnetic resonance (EPR) analyzes, hydroxyl radicals (·OH) probe reaction and radical quenching experiments confirmed the involvement of both sulfate radicals (SO4·-) and ·OH that were responsible for 1,2,3-TCP degradation and ·OH played a more important role. HCO3−, Cl− and NOM are three groundwater matrix species that are most likely to inhibit PS oxidation of 1,2,3-TCP. Compared to activated PS, unactivated PS is more promising and more practical for groundwater remediation, since it has several advantages: (1) longer lifetime and better long-term availability; (2) ability of enduring contaminant degradation; (3) applicable for low-permeability zones remediation and potential to alleviate contaminant rebound or tailing problems; (4) environmental friendly; and (5) lower cost. Overall, results of this study show that unactivated PS is a promising in situ remediation technology that may be a good candidate for the most challenging low permeable zone remediation.

A pore-scale investigation of the effect of nanoparticle injection on properties of sandy porous media

Nanoremediation is a new groundwater remediation technology in which nanoparticles (NPs) are injected into the sub-surface to promote in-situ degradation of aquifer contaminants. Although nanoremediation is an effective process to eliminate contaminants in-situ, its success relies on sufficiently mobile NPs that can reach the contaminated zones and remain there to facilitate chemical degradation of contaminants. Therefore, understanding the main parameters that control the mobility and retention of NPs in saturated porous media is a key component of designing a successful nanoremediation process.This work presents the outcome of a pore-scale study of nZVI NP (zero-valent iron) transport in sandy porous media using the non-destructive 3D imaging technique, X-ray computed micro-tomography (X-ray micro-CT). We investigate the effect of grain size (fine, coarse, carbonate and mixed sand) and composition (carbonate vs sand grains) on the mobility and retention of NPs in sand columns. To achieve this, we used four columns packed with grains of different sizes and compositions. The main contribution of this work is, therefore, to understand the effect of NP injection on the structural and geometric properties of sandy porous media and to identify the main pore-scale mechanisms controlling NP transport and entrapment.Our experiment shows that the pore geometries change because of NP injection. Pore clogging is evidenced through pore size and throat size distribution displaying a shift to the left with a noticeable reduction in pore connectivity in all the columns. The porosity and permeability of the columns studied display significant reduction as result of the NP injection.

Opportunities and critical issues related to the use of amendments as sustainable remediation techniques

This study aims to analyse the opportunities and critical issues related to the use of amendments as remediation techniques. The performance of amendments (Aerobic Bioremediation, In Situ Chemical Oxidation and Surfactants) was compared with the performance of other groundwater remediation technologies (Air Sparging, Pump&Treat, Multi-Phase Extraction, Pump&Reinjection, Monitoring Natural Attenuation) based on a dataset of 180 contaminated sites. The considered factors are: effectiveness of the remediation; cost to remediate; operational time; environmental sustainability. The occurrence and types of amendment-related issues analyzed were studied on the 40 sites where the amendments had been applied. Issues occurred in 20% of the 40 analyzed cases and consisted of: a) partial or total occlusion of the monitoring wells and by-product formation, for example heavy metals (5%); b) uncontrolled increase in contaminant concentrations and potential downstream migration (8%); c) byproduct formation without well obstruction (7%). For each critical event, a detailed analysis was conducted to understand the processes (pH-Eh equilibria, contaminant desorption, hydraulic conductivity reduction), to highlight the design and procedural gaps (surplus of amendment, injection method selection, contaminant removal by purge). However, it has been observed that the issues can be avoided or mitigated with an accurate design, pilot tests performance, with the application of delivery and monitoring protocols, and at least with a prompt response adopting a corrective action plan, if necessary. The use of amendments turns out to be an effective solution: in 64% of the analyzed sites, it led to a significative reduction of the contamination within one year from the application. The cost is about one third if compared to the average of the other technologies. The operational time is about half the average operational time of the other technologies. Based on the results of sustainability analysis, amendments technologies reduce the production of waste, energy and water consumption, and they minimize air emissions. Considering the sustainability in its broadest sense (environmental, economic, and temporal), it is possible to state that the remediation by amendments is the most sustainable and would meet the interest of all the stakeholders.

Effects of different permeable lenses on nitrobenzene transport during air sparging remediation in heterogeneous porous media

Air sparging (AS) is considered an effective remediation technology for groundwater contaminated by volatile organic compounds. However, the effects of AS remediation of heterogeneous aquifers with lenses of different permeability are still unclear, which limits the application of AS technology. In this study, the effects of different permeable lenses on nitrobenzene (NB) transport were quantitatively analysed by tracking the temporal and spatial evolutions of the NB concentration and using light transmission visualisation technology to observe airflow. Experimental results showed that the NB outside the airflow zone of the heterogeneous aquifer containing a gravel lens was rapidly removed, which is a special phenomenon. Through moisture content monitoring and colour tracer technology, the bubble-induced water circulation zone in a gravel lens was discovered during AS. At this time, the zone of influence (ZOI) included air flow zone and water circulation zone, while previous studies believed that the ZOI only contained the air flow zone. The presence of water circulation zone in the heterogeneous aquifer with a gravel lens increased the ZOI area and average contaminant removal flux by 5 and 2.3 times, respectively, compared with those in homogeneous aquifer. These findings have modified the conventional cognition about the ZOI and are conducive to an in-depth understanding of the remediation mechanisms and a better design of AS technology in heterogeneous aquifers with different permeable lenses.

PFAS Experts Symposium 2: PFAS Remediation research – Evolution from past to present, current efforts, and potential futures

AbstractDue 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.

Thermal based remediation technologies for soil and groundwater: a review

Thermal based remediation technologies for soil and groundwater: a review

Developing an approach for the sustainability assessment of groundwater remediation technologies based on multi criteria decision making

Groundwater is regarded as an important supply of drinking water, as well as for agricultural and industrial purposes. Groundwater pollution worsens as a result of several contaminants such as industrial, urban, and agricultural activities, and the difficulty is to select appropriate groundwater remediation methods. This research develops a technique for assessing the sustainability of groundwater remediation methods by integrating the Multi-Criteria Decision Making (MCDM) method with a Fuzzy Inference Engine. A standard approach for assessing the sustainability of groundwater remediation systems has been developed, consisting of four major criteria: economic, technical, environmental, and social. Following the calculations and determining the priority of all the criteria and techniques based on the weights, the results show the sequence of technologies in which Pump and Treat is the best with 7.83, followed by air stripping with 7.04, and monitored natural attenuation and permeable reactive barrier were the last with 3.70 and 3.19, respectively. The criteria that give P&T the most weight is both the technical and social criterion, with a weight of 8.18, while the criterion with the lowest weight was the economic criterion, with a weight of 4.22. The technical, environmental, and social aspects of P&T were all high, making it the optimum technology where the decision-maker or stakeholder can deal with the decline in the economic component, which is also proof of P&T's preferability and the most sustainable one, and It was also feasible to examine all options to determine which factors are reducing their sustainability and which should be addressed in order to enhance sustainability.

Rapid reactivation of aged NZVI/GO by Shewanella CN32 for efficient removal of tetrabromobisphenol A and associated reaction mechanisms

Tetrabromobisphenol A (TBBPA) is one of the most widely applied brominated flame retardants, which has consequently resulted in severe environmental contamination. Graphene oxide-loaded nanoscale zero-valent iron (NZVI/GO) has previously shown excellent performance for potential TBBPA removal. However, the aging of NZVI/GO resulted in reduced reaction rates. In this study, Shewanella CN32 was used to reactivate the performance of aged NZVI/GO. The results demonstrated that CN32 significantly reactivated aged NZVI/GO (27%) and consequently improved the removal of TBBPA by 240% in aged NZVI/GO+CN32 (92%). Compared to aged NZVI (0.07 mM), CN32 rapidly decomposed the iron oxide passivation layer of aged NZVI/GO, with a subsequent increase in the release of Fe2+ ions (0.12 mM). Moreover, Fe(II) vivianite (FeII3(PO4)2·8H2O) and SO42− type green rust (Fe3.6Fe0.9(O,OH,SO4)9) formed at the surface of aged NZVI/GO+CN32. GO accelerated the reduction of dissimilatory iron (α-Fe2O3) and the formation of vivianite crystals. Vivianite further improved the debromination of TBBPA. Furthermore, the semiquinone radicals (C=O) in the interface of the aged NZVI/GO effectively mediated electron transfer and reactivated the performance of aged NZVI/GO by CN32. It could therefore be concluded that CN32-induced iron oxide reduction and NZVI exposure, C=O mediated electron transfer, and vivianite-induced debromination were the main removal mechanisms of TBBPA in the system. It is a potential technology for convenient remediation of soil, groundwater, and lake.

Performance testing of mesh anodes for in situ electrochemical oxidation of PFAS

Groundwater remediation technologies that can destroy per- and polyfluoroalkyl substances (PFAS) in situ are in high demand. To address this need, using flow-through electrochemical reactors we compared the performance of three mesh electrode materials that may be implemented in the subsurface as permeable reactive barriers. A Magnéli-phase titanium suboxides TinO2n-1 anode achieved higher perfluorooctane sulfonate (PFOS) oxidation rates and lower energy consumption than boron-doped ultrananocrystalline diamond and IrO2-Ta2O5 mixed metal oxides, and was thus selected for more detailed testing regarding the impacts of varying current density, flow velocity, electrolyte conductivity, and PFOS concentration. Over 99% of PFOS removal was achieved under continuous flow conditions. The fluorine mass balance showed that most PFOS-bonded F was released as fluoride, while no organic intermediates were detected in the aqueous phase. Each ∼2% of fluorine was recovered as HF and organofluorine intermediates in the gas phase. A comparison of 10 PFAS revealed a hydrophobicity-driven increase in oxidation rate with increasing perfluoroalkyl chain length as well as faster oxidation kinetics for perfluoroalkyl carboxylic acids compared to perfluoroalkane sulfonic acids, likely due to contributions from electrochemically activated sulfate. The energy consumption of PFAS treatment under simulated slow-flow groundwater conditions was substantially higher than in ex situ electrochemical systems optimized for enhanced mass transfer. Consequently, future work should focus on in situ treatment design optimization with an emphasis on power requirements. Collectively, our investigations demonstrate that among the few water treatment technologies capable of breaking the carbon-fluorine bond, electrochemical treatment is a promising approach for in situ destruction of PFAS in the subsurface.