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In situ chemical oxidation (ISCO) using peroxydisulfate has become more popular in the remediation of soils and shallow groundwater contaminated with organic chemicals. Researchers have studied the chemistry of peroxydisulfate and the oxidative species produced upon its decomposition (i.e., sulfate radical and hydroxyl radical) for over five decades, describing reaction kinetics, mechanisms, and product formation in great detail. However, if this information is to be useful to practitioners seeking to optimize the use of peroxydisulfate in the remediation of hazardous waste sites, the relevant conditions of high oxidant concentrations and the presence of minerals and solutes that affect radical chain reactions must be considered. The objectives of this Review are to provide insights into the chemistry of peroxydisulfate-based ISCO that can enable more efficient operation of these systems and to identify research needed to improve understanding of system performance. By gaining a deeper understanding of the underlying chemistry of these complex systems, it may be possible to improve the design and operation of peroxydisulfate-based ISCO remediation systems.

In-situ chemical oxidation with persulfate (PS-ISCO) is a preferred approach for the remediation of fuel-contaminated groundwater. Persulfate (PS) can be activated by various methods to produce stronger sulfate radicals for more efficient ISCO. Despite karst aquifers being widespread, there are few reports on PS-ISCO combined with Fe2+-activated PS. To better understand the effects of Fe2+-activated PS for the remediation of gasoline-contaminated aquifers in karst areas, a box-column experiment was conducted under flow conditions, using karst groundwater and limestone particles to simulate an aquifer. Gasoline was used as the source of hydrocarbon contaminants. Dissolved oxygen and nitrate were added to enhance bioremediation (EBR) and ferrous sulfate was used to activate PS. The effect of Fe2+-activated PS combined with biodegradation was compared during the periods of EBR + ISCO and ISCO alone, using the mass flow method for data analysis. The results showed that the initial dissolution of benzene, toluene, and xylene (BTX) from gasoline injection was rapid and variable, with a decaying trend at an average pseudo-first-order degradation rate constant of 0.032 d−1. Enhanced aerobic biodegradation and denitrification played a significant role in limestone-filled environments, with dissolved oxygen and nitrate utilization ratios of 59 ~ 72% and 12–70%, respectively. The efficiency of EBR + ISCO was the best method for BTX removal, compared with EBR or ISCO alone. The pseudo-first-order degradation rate constants of BTX reached 0.022–0.039, 0.034–0.070, and 0.027–0.036 d−1, during the periods of EBR alone, EBR + ISCO, and ISCO alone, respectively. The EBR + ISCO had a higher BTX removal ratio range of 71.0 ~ 84.3% than the ISCO alone with 30.1 ~ 45.1%. The presence of Fe2+-activated PS could increase the degradation rate of BTX with a range of 0.060 ~ 0.070 d−1, otherwise, with a range of 0.034–0.052 d−1. However, Fe2+-activated PS also consumed about 3 times the mass of PS, caused a further decrease in pH with a range of 6.8–7.6, increased 3–4 times the Ca2+ and 1.6–1.8 times the HCO3− levels, and decreased the BTX removal ratio of ISCO + EBR, compared to the case without Fe2+ activation. In addition, the accumulation of ferric hydroxides within a short distance indicated that the range of PS activated by Fe2+ may be limited. Based on this study, it is suggested that the effect of Fe2+-activated PS should be evaluated in the remediation of non-carbonate rock aquifers. [ABSTRACT FROM AUTHOR]

Peroxymonosulfate (PMS, HSO5-) is an increasingly popular oxidant for groundwater remediation via in situ chemical oxidation (ISCO). However, it is desired to evaluate the effect of phosphate on the PMS oxidation of organics in detail due to the saline characteristics of groundwater. In this study, ofloxacin (OFX) as a typical antibiotic was chosen as a model pollutant. The results indicated that 64% of OFX was degraded by PMS in the presence of HPO42- (PMS/HPO42- system), and the efficiency increased from 64% to 80% when the HPO42- concentration was increased from 0.1 mol/L to 0.3 mol/L. The corresponding pseudo-first-order reaction constants were 0.0086 and 0.02 min-1, respectively. In comparison, PO43- and H2PO4- showed almost no reactivity. Electron spin response (ESR) analysis and quenching tests proved that SO4·- and 1O2 were the main oxidizing species for OFX degradation in PMS/HPO42- system. Hence, HPO42- was the most effective form in PMS activation and its performance was highly pH and ionic strength sensitive. Given the ambient pH and phosphate concentration in saline groundwater, a considerable amount of HPO42- can be produced, which then serves as a homogeneous PMS activator in ISCO process. This finding provides new insights into ISCO process using PMS. [ABSTRACT FROM AUTHOR]

This article introduces a ternary nanocomposite‐based flexible thin film ammonia sensor developed on transparent polyethylene terephthalate (PET) substrate in the well‐known in situ chemical oxidative polymerization technique. The nanocomposite consists of three different materials: polyaniline (PANI), reduced graphene oxide (rGO), and zinc ferrite (ZF). Keeping the PANI amount constant, seven PANI/rGO/ZF (PRZ) samples are produced by performing stoichiometric variation between rGO and ZF. Later on, various structural, morphological, and spectroscopic analysis of all the composite materials is accomplished with field emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis). The sensing performance of the as‐produced sensors toward ammonia (NH3) is examined in the concentration range from 250 ppb to 100 ppm. The study reveals the excellent sensing ability of the PRZ3 sensor (rGO = 30%, ZF = 20%) achieving minimum and maximum responsivity values of ~51% and ~1052%, respectively, at the lowest (250 ppb) and highest (100 ppm) concentration of ammonia. The sensor also exhibits admirable repeatability, good dynamic responsivity, rapid response (tres ~2.9–5 s), moderately faster recovery (trec ~37.9–69.7 s), superb linearity against ppm variation (R2 ~ 0.989), low detection limit (~123 ppb), and exceptional selectivity toward ammonia. The substrate temperature variation divulges that room temperature (30°C) is the ideal temperature for getting outstanding responsivity of the sensor. The study is further accompanied by humidity variation in the incoming air and bending flexibility test of the substrate. A compulsory and legitimate model regarding the sensing mechanism is presented at the end. [ABSTRACT FROM AUTHOR]

Sustained-release materials are increasingly being used in the delivery of oxidants for in situ chemical oxidation (ISCO) for groundwater remediation. Successful implementation of sustained-release materials depends on a clear understanding of the mechanism and kinetics of sustained release. In this research, a columnar sustained-release material (PS@PW) was prepared with paraffin wax and sodium persulfate (PS), and column experiments were performed to investigate the impacts of the PS@PW diameter and PS/PW mass ratio on PS release. The results demonstrated that a reduction in diameter led to an increase in both the rate and proportion of PS release, as well as a diminished lifespan of release. The release process followed the second-order kinetics, and the release rate constant was positively correlated with the PS@PW diameter. A matrix boundary diffusion model was utilized to determine the PS@PW diffusion coefficient of the PS release process, and the release lifespan of a material with a length of 500 mm and a diameter of 80 mm was predicted to be more than 280 days. In general, this research provided a better understanding of the release characteristics and kinetics of persulfate from a sustained-release system and could lead to the development of columnar PS@PW as a practical oxidant for in situ chemical oxidation of contaminated aquifers. [ABSTRACT FROM AUTHOR]

In remote communities in the Canadian Arctic, petroleum hydrocarbons supply most household energy needs. Their transportation and use frequently incurs small volume spills in populated areas. The remediation method that is currently used when such spills affect the soil under northern villages’ stilted buildings is expensive and not well suited to local conditions. Here, we review local constraints and environmental considerations and select the best remediation technology for this context: in situ chemical oxidation, involving sodium persulfate (SPS) alkali activated with calcium peroxide (CP). Activated SPS presents a good reactivity and amenability to compounds found in diesel. Its high persistence allows a gradual contaminant degradation, regulating heat release from exothermic reactions associated with the oxidative reactions. CP provides suitable alkali activation, acts itself as an oxidant and provides O2 into the subsurface, which may favour a final smoothing bioremediation step. The SPS properties and the contaminant amenability mean that diesel is removed relatively efficiently, while the subsurface temperature increase is limited, thus preserving the residual permafrost. The solid form of the chemicals offers safe and economic transportation and operation, along with versatility regarding the preparation and distribution of the oxidizing solution into the subsurface. Finally, the oxidation by-products resulting from this method are not considered to be environmentally problematic in the context of the application, and they can be partly confined during the treatment.

Persulfate-based in situ chemical oxidation (ISCO) has been increasingly used for the remediation of contaminated groundwater and soil. In recent years, there have been numerous studies in the literature on all aspects of the activation of persulfate for contaminant removal at the laboratory scale, including the ways and mechanisms for the activation, the pathways of contaminant degradation, the factors associated with the activation performance, the methods characterizing the processes, etc. In contrast, studies in the literature on the practical use of the activated persulfate at the field scale are fewer, and at the same time have not been reviewed in an organized way. This review was initiated to summarize on the current research on the applications of activated persulfate for actual site remediation, and to extract the knowledge necessary for the formation of applicable technologies. The remediation efficiency and mechanism of activated persulfates by heat, alkaline, metal-based, and electrokinetic activated technologies are described. The major factors including pH, the persistence of persulfate, and the radius of influence and soil property during ISCO remediation applications were presented and discussed. Finally, the rebound process and impact towards microbial communities after in-situ chemical oxidation on site application were discussed. [ABSTRACT FROM AUTHOR]

Soil contamination with hazardous substances like phenol poses significant environmental and health risks. In situ soil mixing can be a promising technological solution to this challenge. A persulfate and sulfidated zero-valent iron (S-ZVI bm) system for remediating contaminated soil was developed and tested to be suited to in situ soil mixing. S-ZVI bm was synthesized using a ball mill process, and the optimal sulfur to iron molar ratio for effectively removing phenol from soil removal without pyrophoric risks was 0.12. Soil slurry experiments were performed, and the best phenol oxidation results (high stoichiometric efficiency and sustained oxidation after mixing) were achieved at a persulfate to S-ZVI bm molar ratio of 2:1 and a persulfate to phenol molar ratio of 8:1. A high organic matter content of the silty clay fraction of the soil strongly suppressed persulfate activation, so suppressed phenol removal and increased persulfate consumption. Electron spin resonance and radical scavenging tests confirmed that hydroxyl and sulfate radicals were present during the degradation of phenol. While sulfate radicals predominantly facilitated degradation in the soil, both sulfate and hydroxyl radicals were crucial in the aqueous phase in the absence of soil organic matter. In situ soil mixing simulation tests indicated that the persulfate and S-ZVI bm doses and the mixing rate and duration strongly affected the efficacy of the system, and the optimal conditions for phenol removal were determined. The results indicated that the persulfate/S-ZVI bm system could be tuned to achieve sustained persulfate activation and to remediate contaminated soil employing in situ soil mixing technique. [Display omitted] • A sulfidated ZVI activated persulfate system was developed for in situ remediation. • The optimal [persulfate]/[sulfidated ZVI] ratio for sulfidation was 0.12 • Soil organic matter hindered persulfate activation in the system. • SO 4.•− contributed more than OH• to remediation of contaminated soil • Optimal intensity and duration conditions for in situ soil mixing were identified. [ABSTRACT FROM AUTHOR]

Due to its adverse health and environmental impacts, groundwater contamination by toxic organic compounds such as chlorinated solvents is a global concern. The slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate (KMnO 4) and colloidal silica solution. The SRP-G is designed to radially spread after injection via wells, gelate in situ to form gel barriers containing permanganate (MnO 4 −), and slowly release MnO 4 − to treat plumes of chlorinated solvents in groundwater. This study aimed to characterize the effects of temperature on the dynamics of SRP-G in saturated porous media. In gelation batch tests, the viscosity of ambient-temperature (24 °C) SRP-G with 30 g/L-KMnO 4 was 21 cP at 70 min, 134 cP at 176 min, and peaked at 946 cP to solidification at 229 min. The viscosity of low-temperature (4 °C) SRP-G with 30 g/L-KMnO 4 was 71 cP at 273 min, 402 cP at 392 min, and peaked at 818 cP to solidification at 485 min. A similar pattern, e.g., increased gelation lag time with low-temperature SRP-G, was observed for SRP-Gs with 40 g/L, 50 g/L, and 60 g/L KMnO 4. In flow-through tests using a glass column filled with saturated sands, injection rates, spreading rates, and release durations were 0.6 mL/min, 46 mm/min, and 33 h for KMnO 4 (aq), 0.2 mL/min, 2 mm/min, and 38 h for ambient-temperature SRP-G, and 0.4 mL/min, 16 mm/min, and 115 h for low-temperature SRP-G, respectively. These results indicated that the injectability, injection rate, and gelation lag time of SRP-G and the size, release rate, and release duration of MnO 4 − gel barriers can be increased at low temperatures. The low-temperature SRP-G scheme can be useful for treating large or dilute dissolved plumes of chlorinated solvents or other pollutants in groundwater. [Display omitted] • Slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate and colloidal silica solution. • SRP-G solution spreads, gelates, and slowly releases permanganate in saturated porous media. • Cooling increases injectability, gelation lag time, spreading, release rate, and release duration of SRP-G in porous media. • Low-temperature SRP-G can be effective for treating large or dilute plumes of chlorinated solvents in groundwater. • Low-temperature SRP-G scheme can be used with other treatment agents to reduce different pollutants in groundwater. [ABSTRACT FROM AUTHOR]

Sustained-release materials are increasingly being used in the delivery of oxidants for in situ chemical oxidation (ISCO) for groundwater remediation. Successful implementation of sustained-release materials depends on a clear understanding of the mechanism and kinetics of sustained release. In this research, a columnar sustained-release material (PS@PW) was prepared with paraffin wax and sodium persulfate (PS), and column experiments were performed to investigate the impacts of the PS@PW diameter and PS/PW mass ratio on PS release. The results demonstrated that a reduction in diameter led to an increase in both the rate and proportion of PS release, as well as a diminished lifespan of release. The release process followed the second-order kinetics, and the release rate constant was positively correlated with the PS@PW diameter. A matrix boundary diffusion model was utilized to determine the PS@PW diffusion coefficient of the PS release process, and the release lifespan of a material with a length of 500 mm and a diameter of 80 mm was predicted to be more than 280 days. In general, this research provided a better understanding of the release characteristics and kinetics of persulfate from a sustained-release system and could lead to the development of columnar PS@PW as a practical oxidant for in situ chemical oxidation of contaminated aquifers.

Perfluoroalkyl acids (PFAAs) are a class of organic contaminants notable for their extreme persistence. The unique chemical properties of these compounds make them difficult to remove from water using most standard water treatment techniques. To gain insight into the possibility of remediating contaminated groundwater by in situ chemical oxidation with heat-activated persulfate, PFAA removal and the generation of transformation products were evaluated under laboratory conditions. Solution pH had a strong influence on the removal of perfluorooctanoic acid (PFOA), resulting in its transformation into shorter-chain perfluorocarboxylic acids (PFCAs) at pH values below 3. The presence of chloride and aquifer sediments decreased the efficiency of the process by less than 25% under conditions likely to be encountered in drinking water aquifers. Perfluorooctane sulfonic acid (PFOS) was not transformed by heat-activated persulfate under any of the conditions tested. Despite challenges related to the need to manipulate aquifer pH, the possible generation of undesirable short-chain PFCAs and chlorate, and metals mobilization, heat-activated persulfate may be a useful treatment technology for sites contaminated with PFCAs and fluorotelomer-based compounds, including those used in current-generation aqueous film-forming foams.

Bisphenol AF (BPAF) is degraded through the ultrasound-assisted in situ generation and activation of hydrogen peroxide (H 2 O 2 ) by the copper(II) catalysed oxidation of hydroxylamine (NH 2 OH) with dioxygen (O 2 ). Compared to added H 2 O 2 , in situ generated H 2 O 2 significantly improves the degradation of BPAF from 46.7% to 94.8% in ∼15 min. The reaction follows a pseudo-first-order kinetic model. This study examines the influence of solution pH, anions, humic acid, and different concentrations of the reactants on BPAF degradation. Mass spectrometry was used to identify the BPAF degradation products, and a degradation pathway is proposed. This work advances the understanding of in situ hydrogen peroxide generation and activation in advanced oxidation (Fenton-like) processes (AOPs)., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Ye CaO reports financial support was provided by China Scholarship Council. Tippu S Sheriff reports a relationship with Royal Society of Chemistry that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In this study, column experiments were conducted to explore on the method of emplacement of magnetite nanoparticles (MNPs) for in situ activation of persulfate (PS) in sand porous media to degrade 1,2-dichloroethane (DCA), a typical recalcitrant chlorinated compound. Different molar ratios between PS and DCA (0:1, 2:1, 5:1 and 20:1) and mass contents of MNPs in the sand (0 %, 1.9 % and 5.4 %) were tested. In the absence of MNPs, degradation of DCA was negligible for a hydraulic retention time of 7 h. Presence of MNPs at the content of 1.9 % enhanced degradation of DCA and the highest removal efficiency (34.2 %) was observed at the PS-to-DCA molar ratio of 5:1. At the MNPs content of 5.4 %, increase of the PS-to-DCA molar ratio from 2:1 to 20:1 lead to not only increase in DCA removal efficiency but also substantial enhancement in chloride production, indicating that high PS concentration could cause significant degradation of the Cl-containing intermediates. In contrast to MNPs, Fe 3 O 4 solids with much larger size (∼1 μm) were much less effective in activating PS for DCA removal even at a significantly higher content in the medium. The transport data could be well fitted by the one-site chemical nonequilibrium model, which showed kinetic DCA sorption to the MNPs as a key process for the transport. In the long-term injection experiment, a stable and significant removal of DCA (∼50 %) was observed for 254 days at the MNP content of 1.9 %. The results of this study show the potential of MNPs as a sustainable PS activator in injection-based in situ chemical oxidation for groundwater remediation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Persulfate oxidation technology is widely used in wastewater treatment, but there are still many disadvantages, such as high energy consumption, side reaction and narrow pH applicability. Copper oxides can activate persulfate steadily with higher efficiency. In this paper, a novel preparation method of shape-controlled cuprous oxide (Cu2O) nanoparticles featured with high catalytic performance was explored. It was found that adding ionic liquid 1-butyl-3-methylimidazolium bromide ([BMIM]Br) during preparation of Cu2O can improve the degradation rate of diclofenac (DCF). Cu2O nanoparticles possess good stability in consecutive cycling tests, which was confirmed by X-ray photoelectron spectroscopy. The possible mechanism of Cu2O activating persulfate at different initial pH conditions was discussed based on electron paramagnetic resonance spin-trapping experiment. It was found that DCF was efficiently degraded in the Cu2O/peroxydisulfate (PDS) system within a broad pH range from 5 to 11. It proved via a quenching experiment that the activation process of PDS mainly occurs on the surface layer of Cu2O nanoparticles. As a result, shape-controlled Cu2O nanoparticles prepared by ionic liquid are expected to be used for in situ chemical oxidation, which is an effective oxidation processes to degrade DCF remaining in surface water and ground water. HIGHLIGHTS This study provides a novel preparation method of shape-controlled cuprous oxide (Cu2O) particles featured with high catalytic performance to degrade diclofenac (DCF).; It overcomes the disadvantages of degradation of organic pollutants by the traditional Fe in situ chemical oxidation system to some extent, such as being unrecyclable and having a narrow application range of pH value.;

Non‐aqueous phase liquids (NAPLs), such as toluene, often contaminate the subsurface. In this study, we focus on the transformation of toluene NAPL trapped in a single glass replica of a rock fracture via in situ chemical oxidation (ISCO) with ferrous activated persulfate. The trapped toluene consisted of a main trapped blob surrounded by smaller blobs. Over 53 days, successive persulfate injections into the fracture were interspersed with periods of water flushing. During persulfate injections, effluent toluene concentrations were below 0.04 mM. The rebound toluene concentrations during intervening water flushing periods decreased from 0.9 to 0.3 mM over the study. The smaller toluene blobs were removed by dissolution and partial oxidation. The main toluene blob was reduced in area by 35.5% and in volume by 37.3% due to dissolution and partial oxidation. The main blob changed in shape with reduction in size and there was also formation of an oxidation by‐product zone around the blob. The reduction in toluene effluent concentrations with time over successive persulfate injections and periods of water flushing was attributed to reductions in the NAPL‐water interfacial area of the blob and the formation of the by‐product zone surrounding the blob, which resulted in limited toluene dissolution. Analysis of by‐products of toluene oxidation by ferrous activated persulfate suggests that oligomers were part of the by‐product zone formed in the fracture. Gas bubbles were also observed in the fracture and may have formed from toluene oxidation and persulfate decomposition. Key Points: Glass fracture allows visualization of toluene non‐aqueous phase liquid (NAPL) removal over timeToluene NAPL volume in the fracture and dissolved toluene flux decrease with successive persulfate injectionsBy‐product zone formed around the NAPL during persulfate injection [ABSTRACT FROM AUTHOR]

The effective approaches to eliminate impacts of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) are concerned in the bioremediation of groundwater contaminated with ethanol-blended gasoline. In situ chemical oxidation (ISCO) is a common technique widely used for the remediation of contaminated groundwater. However, the selectivity of ISCO for BTEX and ethanol removal is poorly understood. Therefore, a batch experiment was performed with different aquifer materials, including calcareous soil, basalt soil, granite soil, dolomite, and sand. Gasoline was used to provide dissolved BTEX and ethanol reagent was used as additive to improve the quality of gasoline and to reduce the possibility of air pollution caused by gasoline. Persulfate (PS) was used as a chemical oxidant to oxidize organic contaminants. The target concentrations of BTEX and ethanol were 20 mg/L and 1000 mg/L, respectively. The results showed that ethanol could be preferentially degraded in the absence of PS and inhibit BTEX biodegradation. However, BTEX could be preferentially removed prior to ethanol in all aquifer materials used at ambient temperature, when PS was added at a PS/BTEX molar ratio of 150. Over 94% BTEX in sand, dolomite, and granite soil was preferentially removed with the first-order decay rate constants of 0.890–2.703 day−1 within the first ~ 10 days, followed by calcareous and basalt soil at the constants of 0.123–0.371 day−1. Ethanol could compete with BTEX for sulfate radical at the first-order decay rate constants of 0.005–0.060 day−1 for the first 25 days, which was slower than that of BTEX. The pH quickly decreased to < 2.5 in dolomite, sand, and granite soil, but maintained > 6.2 in calcareous soil. Rich organic matter in calcareous and basalt soil had an inhibition effect on BTEX oxidation by PS. The pH buffer in calcareous soil may imply the potential of PS oxidation combined with bioremediation in carbonate rock regions. [ABSTRACT FROM AUTHOR]

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In remote communities in the Canadian Arctic, petroleum hydrocarbons supply most household energy needs. Their transportation and use frequently incurs small volume spills in populated areas. The remediation method that is currently used when such spills affect the soil under northern villages' stilted buildings is expensive and not well suited to local conditions. Here, we review local constraints and environmental considerations and select the best remediation technology for this context: in situ chemical oxidation, involving sodium persulfate (SPS) alkali activated with calcium peroxide (CP). Activated SPS presents a good reactivity and amenability to compounds found in diesel. Its high persistence allows a gradual contaminant degradation, regulating heat release from exothermic reactions associated with the oxidative reactions. CP provides suitable alkali activation, acts itself as an oxidant and provides O2 into the subsurface, which may favour a final smoothing bioremediation step. The SPS properties and the contaminant amenability mean that diesel is removed relatively efficiently, while the subsurface temperature increase is limited, thus preserving the residual permafrost. The solid form of the chemicals offers safe and economic transportation and operation, along with versatility regarding the preparation and distribution of the oxidizing solution into the subsurface. Finally, the oxidation by-products resulting from this method are not considered to be environmentally problematic in the context of the application, and they can be partly confined during the treatment. [ABSTRACT FROM AUTHOR]

Persulfate-based in situ chemical oxidation (ISCO) has been increasingly used for the remediation of contaminated groundwater and soil. In recent years, there have been numerous studies in the literature on all aspects of the activation of persulfate for contaminant removal at the laboratory scale, including the ways and mechanisms for the activation, the pathways of contaminant degradation, the factors associated with the activation performance, the methods characterizing the processes, etc. In contrast, studies in the literature on the practical use of the activated persulfate at the field scale are fewer, and at the same time have not been reviewed in an organized way. This review was initiated to summarize on the current research on the applications of activated persulfate for actual site remediation, and to extract the knowledge necessary for the formation of applicable technologies. The remediation efficiency and mechanism of activated persulfates by heat, alkaline, metal-based, and electrokinetic activated technologies are described. The major factors including pH, the persistence of persulfate, and the radius of influence and soil property during ISCO remediation applications were presented and discussed. Finally, the rebound process and impact towards microbial communities after in-situ chemical oxidation on site application were discussed.

The rising in situ chemical oxidation (ISCO) technologies based on polymerization reactions have advanced the removal of emerging contaminants in the aquatic environment. However, despite their promise, uncertainties persist regarding their effectiveness in eliminating structurally complex contaminants, such as sulfonamide antibiotics (SAs). This study elucidated that oligomerization, rather than mineralization, predominantly governs the removal of SAs in the carbon materials/periodate system. The amine groups in SAs played a crucial role in forming organic radicals and subsequent coupling reactions due to their high f - index and low bond orders. Moreover, the study highlighted the robust adhesion of oligomers to the catalyst surface, facilitated by enhanced van der Waals forces and hydrophobic interactions. Importantly, plant and animal toxicity assessments confirmed the nontoxic nature of oligomers deposited on the carbon material surface, affirming the efficacy of carbon material-based ISCO in treating contaminated surface water and groundwater. Additionally, a novel classification approach, Δlog  k , was proposed to differentiate SAs based on their kinetic control steps, providing deeper insights into the quantitative structure-activity relationship (QSAR) and facilitating the selection of optimal descriptors during the oligomerization processes. Overall, these insights significantly enhance our understanding of SAs removal via oligomerization and demonstrate the superiority of C-ISCO based on polymerization in water decontamination.

Benzophenone (BP) is an emerging contaminant that is widely distributed in soil, groundwater, sediment and surface water. In this study, the degradation kinetics, mechanisms, and influence of anions on thermally activated persulphate (TAP) oxidation of BP were systematically investigated. BP degradation was promoted by elevated temperature. The BP degradation data fitted well to the Arrhenius equation with calculated activation energy of 122.8 kJ/mol. BP degradation was also promoted by alkaline pH and high persulphate concentrations. Radical scavenging experiments suggested that both SO4•− and HO• were involved in BP oxidation. Ultra-high-performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC-Orbitrap-MS) identified six degradation intermediates. Based on these results, two possible reaction pathways were proposed. Water matrix anions had complex impacts on BP degradation by TAP. Cl− had dual effects on the reaction: low concentration promoted it while high concentration inhibited it. Br− strongly suppressed the reaction. SO42− and NO3− did not affect the reaction. Overall, this study shows that thermally activated persulphate can effectively remove BP and water matrix anions greatly influence the reaction. [ABSTRACT FROM AUTHOR]

Under the action of different activators, persulfate can produce sulfate radicals (SO4·–) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation. [ABSTRACT FROM AUTHOR]

To investigate the feasibility and effectiveness of applying in situ chemical oxidation (ISCO) on the remediation of sulfolane-contaminated groundwater, batch and pilot-scale studies were conducted in this study. The kinetics of sulfolane oxidation by Fenton and Fenton-like processes and optimal operational conditions were evaluated. The major control factors in the ISCO study included H2O2 concentrations, ratio of H2O2 to ferrous iron (mol/mol), molar ratios of oxidant to sulfolane, and catalyst effect. Results show that the Fenton reaction could obtain a complete sulfolane oxidation with the following operational conditions: 3% of H2O2, molar ratio of H2O2 to ferrous iron = 1:0.5, and initial sulfolane concentration = 72 mg/L. The calculated pseudo-first-order decay rate constants (k') were 1.32 × 10-1 and 6.69 × 10-2 min-1 for sulfolane degradation under Fenton and Fenton-like oxidation reaction processes with 3% of H2O2 concentration, respectively. However, the sequential Fenton-like operational pattern could be an alternate option to obtain a complete sulfolane removal efficiency. Results from the soil oxidant demand test show that approximately 25%-35% of supplied H2O2 (3%) was consumed by soil organic matter, and thus, higher oxidant concentration would be required for field application. Sulfolane oxidation would result in sulfuric acid production, which caused the decrease in solution pH, and this would be beneficial to Fenton reaction. A sulfolane-contaminated groundwater site was selected for the pilot-scale study and Fenton oxidation process was applied for sulfolane degradation. Approximately, 600 L of H2O2 solution (5%) [molar ratio of [H2O2]:[Fe2+] = 1:0.5] was injected into the injection well (IW) to oxidize sulfolane in situ. Up to 97% and 88% of sulfolane could be removed (initial sulfolane concentration = 68 mg/L) in the IW and a downgradient monitor well (located 5 m downgradient of the IW). Results from the batch and pilot-scale studies demonstrate that the Fenton reaction could be an applicable remedial option to oxidize sulfolane and cleanup sulfolane-contaminated groundwater. [ABSTRACT FROM AUTHOR]

Using natural minerals as persulfate activators can develop effective and economical in situ chemical oxidation technology for environmental remediation. Yet, few natural minerals can provide a high activation efficiency. Here, we demonstrate that brochantite (Cu 4 SO 4 (OH) 6), a natural mineral, can be used as a persulfate activator for the rapid degradation of tetracycline hydrochloride (TC-H). Approximately 70% of TC-H was removed in Cu 4 SO 4 (OH) 6 /PDS within 5 min, which much higher than that of Cu 3 P (61.99%), CuO (29.75%), CNT (25.83%), Fe 2 O 3 , (14.48%) and MnO 2 (9.76%). Experiments and theoretical calculations suggested that surface copper acts as active sites induce the production of free radicals. The synergistic effect of Cu/S promotes the cycle between Cu+/Cu2+. Sulfate radicals and hydroxyl radicals are the main reactive oxygen species that are responsible for the rapid removal of TC-H. The findings of this work show a novel persulfate/brochantite system and provide useful information for the environmental remediation. [ABSTRACT FROM AUTHOR]

In situ chemical oxidation using permanganate as an oxidant is a remediation technique often used to treat contaminated groundwater. In this paper, groundwater flow with a full hydraulic conductivity tensor and remediation process through in situ chemical oxidation are simulated. The numerical approach was verified with a physical sandbox experiment and analytical solution for 2D advection-diffusion with a first-order decay rate constant. The numerical results were in good agreement with the results of physical sandbox model and the analytical solution. The developed model was applied to two different studies, using multi-objective genetic algorithm to optimise remediation design. In order to reach the optimised design, three objectives considering three constraints were defined. The time to reach the desired concentration and remediation cost regarding the number of required oxidant sources in the optimised design was less than any arbitrary design. [ABSTRACT FROM AUTHOR]

Pollution of waters by chlorinated organic pollutants is difficult to clean using actual remediation methods because these pollutants are highly stable. For instance, chloroform (CHCl3) is poorly reactive with common oxidants such as iron-activated persulfate, ozone and Fenton's reagents. Therefore, there is a need to develop new oxidants. Here, we designed a new dechlorination system, in which tannic acid and NaOH work synergistically to activate persulfate. We tested the effect of temperature and concentrations of persulfate, NaOH and tannic acid, on chloroform removal from water. Free radical-quenching experiments were performed to identify active species. Results show that chloroform removal increased from 42.5 to 97.6 wt.% after the addition of 300 mg/L tannic acid in 0.4 M NaOH. Superoxide radicals (O2·−) was primarily responsible for the degradation of chloroform in the persulfate/NaOH/tannic acid system, in which tannic acid reacts with persulfate to produce hydroperoxide. Hydroperoxide then reduces persulfate to generate sulfate radicals (SO4·−), and produces O2·−. NaOH-activated persulfate produces hydroxyl radicals (HO·), which can oxidize chloroform. This dechlorination system showed excellent degradation efficiency for recalcitrant halogenated compounds, making it a very promising candidate for practical applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate the performance of a Fenton-like process carried out adding as amendments humic acids extracted from compost obtained from organic wastes. Namely, Fenton-like lab-scale tests with different dosages of the extracted humic acids and traditional stabilizing agent (KH2PO4) were performed on a diesel-contaminated soil collected in a former gasoline station. The performed tests showed a beneficial effect of the extracted humic acids on the hydrogen peroxide stability. Namely, the H2O2 lifetime in the tests carried out without the addition of any amendments proved to be quite limited, resulting equal to around 1 h. The adoption of the extracted humic acids alone entailed a limited increase of the hydrogen peroxide stability that anyhow was detected in solution for 24 h using 10 g/L of extracted HA. When the humic acids (10 g/L) were used in combination with KH2PO4 (8.2 g/L), the hydrogen peroxide lifetime increased up to around 150 h. A beneficial effect of the humic acids extracted from compost for a Fenton-like process was also observed in terms of diesel removal. Namely, without any amendment, a contaminant removal of around 55% was observed. Using KH2PO4 or HA alone, the contaminant removal raised up to around 75% while using the traditional stabilizer together with the humic acids extracted from compost, it was possible to remove up to 90% of the initial diesel content of the soil. [ABSTRACT FROM AUTHOR]

The phenolic compound is a priority toxic organic contaminant; it is of great significance to research on the in situ remediation of phenolic compound polluted groundwater. Chemical oxidation technology is an effective method to deal with phenol pollution. Commonly used chemical oxidation methods include Fenton oxidation, persulfate activation oxidation, and ozone oxidation. This paper systematically reviews the mechanism, impacting factors, remediation effect, application scope, advantages and disadvantages of various oxidation technologies of phenolic contaminated groundwater and suggests that combination of chemical oxidation remediation and electrokinetic remediation and surfactant enhanced aquifer remediation be the development direction when pollution expands deep into low-permeability soil. [ABSTRACT FROM AUTHOR]

The oxidation of chlorendic acid (CA), a polychlorinated recalcitrant contaminant, by heat-, mineral-, and base-activated persulfate was investigated. In pH 3–12 homogeneous (i.e., solid-free) solutions, CA was oxidized by •OH and SO 4 •- radicals, resulting in a nearly stoichiometric production of Cl−. The rate constants for the reaction between these radicals and CA were measured at different temperatures by electron pulse radiolysis, and were found to be k OH = (8.71 ± 0.17) × 107 M−1s−1 and k SO4 = (6.57 ± 0.83) × 107 M−1s−1 at 24.5 °C for •OH and SO 4 •-, respectively. CA was oxidized at much slower rates in solutions containing iron oxyhydroxide or aquifer soils, partially due to the adsorption of CA on these solids. To gain further insight into the effect of solids during in-situ remediation of CA, the adsorption of CA onto iron (hydr)oxide, manganese dioxide, silica, alumina, and aquifer soils was investigated. The fraction of CA that was adsorbed on these materials increased as the solution pH decreased. Given that the solution pH can decrease dramatically in persulfate-based remedial systems, adsorption may reduce the ability of persulfate to oxidize CA. Overall, the results of this study provide important information about how persulfate can be used to remediate CA-contaminated sites. The results also indicate that the groundwater pH and geology of the subsurface can have a significant influence on the mobility of CA. Image 1 • Activated persulfates (S 2 O 8 2−) could degrade CA only under certain conditions. • In homogeneous (i.e., solid-free) solutions, CA could be oxidized by.•OH and SO 4 •-. • In heterogeneous solutions, CA was removed mainly by adsorption to solids. • Adsorption of CA retarded/inhibited the oxidation of CA, especially at acidic pH. • CA desorption after S 2 O 8 2− is depleted may cause the CA concentration to rebound. [ABSTRACT FROM AUTHOR]

Abstract The objective of this research was to evaluate slow-release permanganate and unactivated persulfate for in situ treatment of dioxane and associated chlorinated solvents. Laboratory batch studies with unactivated persulfate in deionized water or in soil and groundwater demonstrated dioxane removal with pseudo second-order rate constants ranging from 10−5 to 10−3 M−1 s−1. Flow-through column studies demonstrated over 99% dioxane removal with slow-release unactivated persulfate but not with slow-release permanganate. The slow-release permanganate cylinders became coated with a rind that limited oxidant mass transfer and dioxane oxidation. A field study was conducted with slow-release persulfate cylinders transverse to groundwater flow. Over 99% removal of dioxane and chlorinated solvents was observed 2.5 m downgradient of the cylinders. Density-driven flow associated with the released persulfate was observed and was attributed to a low horizontal hydraulic gradient. Thus, most of the contaminant and persulfate flux was thought to be isolated to a deep aquifer zone that was bound by an underlying silt aquitard. Contaminant reductions were also observed in shallow groundwater samples, albeit at a lesser extent. The longevity of the persulfate oxidant cylinders was estimated to be 6–12 months. Results of this study demonstrate that dioxane and co-mingled chlorinated solvents can be effectively treated using slow-release persulfate cylinders. Careful consideration to cylinder placement during the design phase is essential to prevent the contaminant plume from bypassing and not coming into contact with the released oxidant. Highlights • Persulfate without added activators and permanganate promoted dioxane and chlorinated solvent destruction. • A rind formed around slow-release permanganate cylinders limited permanganate release, resulting in poor dioxane destruction. • 99% removal of dioxane and chlorinated solvents was observed in a field study using slow-release persulfate cylinders. • Density-driven flow was observed and was attributed to a low horizontal gradient at the site. [ABSTRACT FROM AUTHOR]

This study involved development of a computer program to determine optimal design variables for in situ chemical oxidation (ISCO) of dense nonaqueous phase liquid (DNAPL) sites to meet site-wide remediation objectives with minimum life-cycle remediation cost while taking uncertainty in site characterization data and model predictions into consideration. A physically-based ISCO performance model computes field-scale DNAPL dissolution, instantaneous reaction of oxidant with contaminant and with readily oxidizable natural oxidant demand (NOD), second-order kinetic reactions for slowly oxidizable NOD, and time to reach ISCO termination criteria. Remediation cost is computed by coupling the performance model with a cost module. ISCO termination protocols are implemented that allow different treatment subregions (e.g., zones with different estimated contaminant concentrations) to be terminated independently based on statistical criteria related to confidence limits of contaminant concentrations estimated from soil and/or groundwater sampling data. The ISCO model was implemented in the program called Stochastic Cost Optimization Toolkit, which includes modules for additional remediation technologies that can be implemented serially or in parallel coupled with a dissolved plume model to enable design optimization to meet plume-scale cleanup objectives. This study focuses on optimization of ISCO design to meet specified source zone remediation objectives. ISCO design parameters considered for optimization include oxidant concentration and injection rate, frequency and number of soil or groundwater samples, and cleanup criteria for termination of subregion injection. Sensitivity studies and example applications are presented to demonstrate the benefits of proposed stochastic optimization methodology. [ABSTRACT FROM AUTHOR]

Calcium peroxide (CaO 2 ) is a stable hydrogen peroxide (H 2 O 2 ) carrier, and the CaO 2 /Fe(II) system has been applied for treatment of various pollutants. It is commonly reported in the literature that hydroxyl radical (HO ) and superoxide radical anions (O 2 − ) are the two main reactive oxygen species (ROSs) generated in the CaO 2 /Fe(II) system. However, many of the reported results were deduced from degradation performance rather than specific testing of radical generation. Thus, the specific generation of ROSs and the influence of system conditions on ROSs yield are still unclear. To our knowledge, this is the first study specifically focusing on the generation of HO and O 2 − in the CaO 2 /Fe(II) system. Experimental conditions were optimized to investigate the production of HO and O 2 − . The results showed the influences of CaO 2 , Fe(II), and solution pH on HO and O 2 − generation, and the HO generation efficiency was reported for the first time. In addition, the ROSs generation pathways in the CaO 2 /Fe(II) system were elucidated. A strategy for enhancing HO yield is developed, based on the continuously dosing Fe(II). This proposed strategy has implications for the effective application of in situ chemical oxidation employing CaO 2 /Fe(II) for groundwater remediation. [ABSTRACT FROM AUTHOR]

In situ chemical oxidation using permanganate as an oxidant is a remediation technique often used to treat contaminated groundwater. In this paper, groundwater flow with a full hydraulic conductivity tensor and remediation process through in situ chemical oxidation are simulated. The numerical approach was verified with a physical sandbox experiment and analytical solution for 2D advection-diffusion with a first-order decay rate constant. The numerical results were in good agreement with the results of physical sandbox model and the analytical solution. The developed model was applied to two different studies, using multi-objective genetic algorithm to optimise remediation design. In order to reach the optimised design, three objectives considering three constraints were defined. The time to reach the desired concentration and remediation cost regarding the number of required oxidant sources in the optimised design was less than any arbitrary design.

In this study, we report the desirable conversion of H 2 O 2 to OH with aquifer sediment activated by ascorbic acid. Although aquifer sediment contained various iron minerals, such as goethite, hematite, montmorillonite, muscovite, chlorite and phlogopite, it could not efficiently activate H 2 O 2 to produce OH. Interestingly, the presence of ascorbic acid dramatically promoted the OH conversion efficiency of H 2 O 2 by aquifer sediment to remediate organic contaminants in groundwater, which was ascribed to the efficient iron cycle of aquifer sediment induced by ascorbic acid. Among these minerals in sediment, goethite and hematite were more reactive than other minerals to activate H 2 O 2 in the presence of ascorbic acid. Although the initial pH could affect the OH conversion efficiency of H 2 O 2 , H 2 O 2 could be decomposed by aquifer sediment at pH 3–11 after the introduction of ascorbic acid. Along with the complete degradation of organic contaminants, the final pH of solution increased to 8.3, which was close to the initial pH (8.9) of groundwater. Moreover, packed column of aquifer sediment could also catalyze the H 2 O 2 conversion to OH for the removal of different organic contaminants with adding ascorbic acid, suggesting a new strategy for in situ chemical oxidation remediation of organic contaminated groundwater. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl acids (PFAAs) are a class of organic contaminants notable for their extreme persistence. The unique chemical properties of these compounds make them difficult to remove from water using most standard water treatment techniques. To gain insight into the possibility of remediating contaminated groundwater by in situ chemical oxidation with heat-activated persulfate, PFAA removal and the generation of transformation products were evaluated under laboratory conditions. Solution pH had a strong influence on the removal of perfluorooctanoic acid (PFOA), resulting in its transformation into shorter-chain perfluorocarboxylic acids (PFCAs) at pH values below 3. The presence of chloride and aquifer sediments decreased the efficiency of the process by less than 25% under conditions likely to be encountered in drinking water aquifers. Perfluorooctane sulfonic acid (PFOS) was not transformed by heat-activated persulfate under any of the conditions tested. Despite challenges related to the need to manipulate aquifer pH, the possible generation of undesirable short-chain PFCAs and chlorate, and metals mobilization, heat-activated persulfate may be a useful treatment technology for sites contaminated with PFCAs and fluorotelomer-based compounds, including those used in current-generation aqueous film-forming foams. [ABSTRACT FROM AUTHOR]

Highlights • Mixing conditions significantly influence the kinetic expression of NOD. • NOD continues to be expressed as long as permanganate is present. • There appears to be reduced species that react very slowly with permanganate. • The fast and slow reactions can also provide insight into the complex kinetics. • The level of mixing was shown to significantly increase the initial rate of NOD. Abstract Excess oxidant requirements are commonly observed during field applications of in situ chemical oxidation by permanganate for the remediation of groundwater. This excess oxidant, generally referred to as natural or soil oxidant demand, is a direct result of organic matter and other naturally occurring reduced species present in the subsurface. Since site conditions vary widely, laboratory scale experiments are often used to determine the natural oxidant demand of soil at hazardous waste sites. Though many researchers have reported values in the literature, experimental conditions often go unreported and few take these factors into consideration. This study provides a broader perspective of the issues and concerns related to determining the permanganate natural oxidant demand of soil while evaluating the effects that initial oxidant concentration, soil to water ratio, and mixing have on the rate and extent of permanganate consumption. It was found that mixing conditions significantly influenced the kinetic expression of permanganate natural oxidant demand while soil to water ratios were not shown to have a significant effect as long as initial permanganate concentrations were sufficient to overcome the oxidant demand of the soil (i.e., were not limiting). [ABSTRACT FROM AUTHOR]

Recently, in situ chemical oxidation (ISCO) using peroxymonosulfate (PMS) for environmental decontamination has received increasing interest. In this study, oxidation kinetics and products of four steroid estrogens (i.e., estrone, 17β-estradiol, estriol, and 17α-ethinylestradiol) by PMS under various conditions were investigated. PMS could fairly degrade steroid estrogens over the pH range of 7–10, and the degradation rate increased with the increase of solution pH. This pH-dependence was well described by parallel reactions between individual acid-base species of steroid estrogens (E and E − ) and PMS (HSO 5 − and SO 5 2− ), where specific second-order rate constants for E − with HSO 5 − and SO 5 2− were in the range of 2.11–5.58 M −1 s −1 and 0.77–1.25 M −1 s −1 , respectively. Identification of oxidation products by liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometer showed that PMS readily oxidized the phenolic group of steroid estrogens, leading to the generation of hydroxylated and ring-opening products. The presence of bromide and chloride ions (Br − and Cl − ) at environmentally relevant levels could greatly accelerate the degradation of steroid estrogens by PMS with the formation of halogenated aromatic products. This effect was quantitatively estimated by a kinetic model, where the formation of free bromine and chorine and their rapid electrophilic substitution with steroid estrogens were taken into consideration. Eco-toxicity of transformation products of 17α-ethinylestradiol by PMS treatment in the absence and presence of bromide and chloride was estimated by quantitative structure–activity relationship analysis using ECOSAR. These findings advance the understanding of ISCO using PMS. [ABSTRACT FROM AUTHOR]

Sodium persulfate has become the most popular oxidant source for the in situ chemical oxidation (ISCO) treatment of organic contaminants in the subsurface. The most common persulfate activators, iron chelates and base, are often ineffective in initiating the generation of reactive oxygen species in field applications. In this study, glucose was investigated as a persulfate activator in systems containing varying concentrations of sodium hydroxide using nitrobenzene as a hydroxyl radical probe and hexachloroethane as a reductant + nucleophile probe. Glucose activation of persulfate increased as a function of sodium hydroxide addition, but was still effective at circumneutral pH regimes. Use of central composite rotatable experimental designs showed that hydroxyl radical and reductant + nucleophile generation rates increased as a function of persulfate at near-neutral pH regimes. Glucose activation of persulfate has the advantages over other activation pathways of more options and flexibility for effective process chemistry and of minimizing or eliminating the mass of sodium hydroxide added to the subsurface. The results of this research can be applied in the field by first evaluating glucose activation compared to base and iron chelate activation of persulfate in laboratory treatability studies. [ABSTRACT FROM AUTHOR]