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In this study, the degradation of trichloroethylene (TCE) with the existence of tween-80 (TW-80) or sodium dodecyl sulfate (SDS) using peroxymonosulfate (PMS) activated by nano-zero-valent iron (nZVI) was investigated. Over 87.6% TCE (with 1.3 g L−1 TW-80 presence) was degraded by 0.9 mM PMS and 0.12 g L−1 nZVI, while 89.7% TCE (with 2.3 g L−1 SDS presence) was degraded by 1.2 mM PMS and 0.20 g L−1 nZVI, in which more than 71.9% TCE with TW-80 existence and 87.5% TCE with SDS existence were dechlorinated. Besides, the effects of some factors (i.e., PMS and nZVI dosages, initial solution pH, and inorganic anions) on TCE removal were evaluated. The degradation of TCE was restrained continuously with increasing surfactant concentration, and TW-80 was more easily decomposed than SDS in PMS/nZVI system. Furthermore, sulfate radical (SO4–•) and hydroxyl radical (HO•) were demonstrated the main reactive oxygen species (ROS) contributing to TCE degradation and SO4–• played a dominant role through EPR tests and ROS scavenging experiments. Finally, the results of TCE degradation in actual groundwater confirmed that PMS/nZVI process has great advantages and potential in remediation of actual TCE-contaminated groundwater with TW-80 or SDS existence. [ABSTRACT FROM AUTHOR]

This study demonstrated that peroxymonosulfate (PMS) activated by Fe(II)/citric acid (CA) could effectively degrade trichloroethylene (TCE) in the presence of Tween-80 (TW-80) or sodium dodecyl sulfate (SDS). Significant TCE removal of 91.6% (90.1%) with 1.3 g L−1 TW-80 (2.3 g L−1 SDS) were achieved at the PMS/Fe(II)/CA/TCE molar ratio of 4/4/4/1 (20/20/20/1). TCE degradation could be greatly elevated by Fe(II) and CA addition, while the existence of surfactants restrained TCE removal and the inhibitory effect increased with the higher surfactant concentration. The tests of the electron paramagnetic resonance (EPR) and reactive radicals scavenging experiments proved that sulfate radical (SO4−•), hydroxyl radical (HO•), and superoxide radical (O2−•) were responsible for TCE degradation and SO4−• acted as the major one. The influences of initial solution pH and inorganic anions k(Cl− and HCO3−) on TCE removal were also investigated. Eventually, TCE removal in actual groundwater tests with surfactants confirmed that the PMS/Fe(II)/CA process has a huge potential of practical application in remediating the groundwater contaminated by TCE after the pretreatment by solubilization using surfactants. [ABSTRACT FROM AUTHOR]

Trichloroethene (TCE) degradation was investigated in Fe(II)/citric acid (CA) activated persulfate (PS) system containing surfactant sodium dodecyl sulfate (SDS). Only 37.7% removal of TCE was achieved at PS/Fe(II)/CA/TCE molar ratio of 40/20/20/1 in the presence of 2.3 g L−1 SDS with pH unadjusted (pH = 2.96). However, this result was significantly increased to 81% after adjusting the initial solution pH = 9.0. The presence of SDS inhibited TCE degradation and this inhibitory effect was initially increased and then declined with SDS concentration increase from 0 to 9.2 g L−1. Radical scavenger experiments revealed that the major reactive oxygen species (ROS) contributed to TCE degradation were HO• and SO 4 −•, while less contribution was owed to O 2 −•. The intermediates of SDS were identified with GC-MS and possible decomposition pathway of SDS was proposed. The performance of TCE degradation in other solution matrixes were investigated. Actual groundwater tests showed that PS/Fe(II)/CA system possessed huge potential in remediating groundwater contaminated by TCE with SDS presence. This research found that alkaline condition was more favorable for TCE degradation in PS/Fe(II)/CA system in the presence of SDS and the possible reasons for this phenomenon were explored from various aspects. [Display omitted] • The influence of solution pH on the CMC value of SDS was investigated. • The mechanism of higher TCE degradation in alkaline condition was explored. • HO• and SO 4 −• were the primary ROSs in PS/Fe(II)/CA system with the presence of SDS. • Significant TCE degradation in actual groundwater containing SDS was achieved after adjusting solution pH = 9. [ABSTRACT FROM AUTHOR]

Based on a few studies on the effect of different chelators on the Fenton system in a solution containing surfactants, sodium dodecyl sulfate (SDS) was selected as an exemplary surfactant to conduct a comparative study on trichloroethylene (TCE) degradation of Fe(II) catalyzed sodium percarbonate (SPC) system by citric acid (CA), oxalic acid (OA), and glutamic acid (GA) chelating agents, respectively. All these three chelators could relieve the inhibition of SDS on TCE removal. Due to the existence of SDS, GA had the most significant promoting effect on TCE degradation. According to Fe(II) concentration and the decomposition of chelators, it was proved that GA system combined with SDS could maintain the highest Fe(II) content and accelerate the formation of hydroxyl radical (HO•). Probe, scavenging, and EPR experiments demonstrated that SPC/chelated-Fe(II) systems produced more HO•. The hysteresis of the dechlorination process was found in the chloride ion release test, certifying that the degradation process of TCE in chelating systems was complicated. Through solution matrixes and actual groundwater experiments, the chelating systems could broaden the scope of pH application, reduce the influence of inorganic ions, and have a good practical application prospect. [Display omitted] • Comparing the effects of citric acid (CA), oxalic acid (OA), and glutamic acid (GA). • GA had the most significant promoting effect on trichloroethylene degradation. • SPC/chelated-Fe(II) system could maintain the high Fe(II) content and accelerate the formation of hydroxyl radical (HO•). • The chelating system could broaden the scope of pH application and have a good practical application prospect. [ABSTRACT FROM AUTHOR]

The degradation performance of trichloroethylene (TCE) by sodium percarbonate (SPC) activated with citric acid (CA) chelated Fe(II) in the presence of nonionic surfactant Tween-80 was investigated. The addition of CA successfully prevented the precipitation of iron and facilitated TCE degradation. However, Tween-80 had an inhibitory effect on TCE degradation mainly due to the competition of ∗OH between Tween-80 and TCE. The effect of SPC and Fe(II) dosage on TCE degradation was also explored and the results displayed that 87.2% of TCE could be degraded in 15 min at the SPC/Fe(II)/CA/TCE molar ratio of 3/4/2/1. Free radical probe tests confirmed that both O2−∗ and ∗OH were generated in the SPC/Fe(II)/CA system. Free radical scavenging tests implied that the degradation of TCE in the SPC/Fe(II)/CA system was mainly attributed to ∗OH, while O2−∗ was only partially involved in the degradation of TCE. In addition, TCE removal was suppressed with the raising of the initial solution pH from 3.0 to 9.0. The actual groundwater (containing Tween-80) tests confirmed that 93.2% of TCE degradation could be achieved at the SPC/Fe(II)/CA/TCE molar ratio of 30/40/10/1 and strongly demonstrated that the SPC/Fe(II)/CA process has potential for the in situ treatment of TCE contaminated groundwater in the presence of surfactant Tween-80. In conclusion, TCE degradation by Fe(II) activated SPC system in the presence of Tween-80 can be significantly enhanced with the addition of CA, and this finding offers an innovative direction for removing chlorinated organic contaminants from groundwater in contaminated site after surfactant solubilization treatment. Image 1 • SPC/Fe(II)/CA process was applied to remove TCE in the presence of Tween-80. • The addition of CA facilitated TCE degradation in SPC/Fe(II) system. • TCE removal was mainly attributed to. OH, while O 2 − also partially involved. • TCE degradation in actual groundwater was successfully achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • The presence of TW-80 improved the reductive degradation of CT in PS oxidation system. • The strengthening effect of CA or nZVI on CT removal in PS/Fe(II) system was confirmed. • Both the secondary surfactant radicals (R•CHOH) and O 2 −• were responsible for CT removal. • Efficient degradation of mixed TCE, PCE, and CT was achieved with TW-80 presence in both PS/Fe(II)/CA and PS/Fe(II)/nZVI systems. Despite the wide range of applications for persulfate-based advanced oxidation processes (PS-based AOPs) in groundwater remediation, the elimination of perchlorinated hydrocarbon contaminants such as carbon tetrachloride (CT) remains a challenge. In this research, we discovered that CT degradation in PS/Fe(II) system was greatly promoted with the presence of surfactant Tween-80 (TW-80), whereas it was hardly removed without TW-80 presence. The introduction of citric acid (CA) or nano zero-valent iron (nZVI) could both enhance the efficacy of PS/Fe(II) system. Through scavenging experiments and electron paramagnetic resonance analysis, the generated secondary surfactant radicals (R•CHOH) from TW-80 and superoxide radicals (O 2 −•) were identified as the driving factors behind CT degradation. CT dechlorination reached 70.6% and 71.8% in PS/Fe(II)/CA and PS/Fe(II)/nZVI systems, respectively, and the potential degradation routes of CT were offered. Additionally, the effect of TW-80 concentration and solution matrixes (solution pH and inorganic ions) on CT degradation was assessed. Furthermore, the removal of mixed chlorinated hydrocarbon contaminants and actual groundwater tests were also performed. Given that surfactants are commonly used in soil and groundwater remediation, this research provides a new prospect and theoretical support for the treatment of perchlorinated contaminants in groundwater with the presence of surfactants. [ABSTRACT FROM AUTHOR]

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO 4 －•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques. [Display omitted] • Simultaneous removal of CHCs (TCE, PCE, and CT) was achieved with TW-80 presence. • TCE and PCE were degraded by HO• and SO 4 －•, while CT was reductively eliminated by surfactant radicals. • The accelerated Fe(III)/Fe(II) cycle by the surfactant radicals was confirmed. • Possible degradation pathways of CHCs and TW-80 decomposition routes were proposed. [ABSTRACT FROM AUTHOR]

The performance of trichloroethylene (TCE) degradation by sodium percarbonate (SPC) activated with Fe(II) in the presence of 3.0 g/L sodium dodecyl sulfate (SDS) as well as the role of SDS in the SPC/Fe(II) system was investigated since SDS is a common surfactant used in groundwater remediation for improving TCE dissolution to the aqueous phase. The results showed that though the introduction of SDS could inhibit the TCE degradation, the inhibiting effect was less with the increasing SDS dose. In the presence of SDS, TCE could be completely removed with the SPC/Fe(II)/TCE molar ratio of 40/80/1. Experiments with free radical probe compounds and radical scavengers elucidated that TCE was mainly oxidized by both HO· and O2-·. A weakly acidic environment was more favorable to TCE degradation. Nevertheless, HCO3- at a high concentration had a strongly inhibitive effect on the TCE degradation but the influence of Cl− was negligible. Finally, the excellent TCE degradation achieved in actual groundwater demonstrated that Fe(II) activated SPC technique was applicable in the remediation of TCE contaminated groundwater in the presence of SDS. Practitioner points: The effects of SDS were evaluatedSPC/Fe(II)/SDS system applied to remediate TCEThe mechanism of HO· and O2-· generation had been investigatedCl− and HCO3- affected TCE degradation at different levelsThe performance of TCE removal in actual groundwater had been studied [ABSTRACT FROM AUTHOR]

• nZVI-Ni bimetallic composite showed better properties in activating SPS for TCE degradation in the presence of surfactant. • Nickel significantly enhanced the reactivity of nanocomposite. • OH radical was the major contributor to TCE degradation. • nZVI-Ni/SPS system is more effective than conventional Fenton system. Trichloroethylene (TCE) is chloride organic solvent used in industrial process and frequently detected as one of contaminants in groundwater. In present study, nano zero valent iron-nickel composite (nZVI-Ni) was prepared successfully by ion exchange process and investigated as a proficient sodium persulfate (SPS) activator for the removal of TCE in Fenton-like oxidation system. The physico-chemical characteristics, structure, and surface morphology of the prepared nZVI-Ni nanocomposite was analyzed through energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), N 2 adsorption-desorption, transition electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results obtained from batch tests in lab showed that more than 95% of TCE could be removed efficiently at nZVI-Ni/SPS/TCE molar ratio of 4/4/1 within 120 min at 20 °C. Further scavenging tests were designed to examine the presence of HO, SO 4 − and O 2 − radicals and verified the major role of HO radical in the nZVI-Ni/SPS system for the complete removal of TCE. Moreover, the generation of HO radicals in the system was confirmed through electrons paramagnetic resonance (EPR) of nZVI-Ni composite. The influence of surfactants on TCE removal was tested and the results showed that the percentage removal of TCE was recorded as 97.75%, 95.63% and 77.50% in the presence of Tween-80, BRIJ-35 and TX-100 surfactants at the nZVI-Ni/SPS/TCE molar ratio of 80/80/1, respectively. Results of TCE degradation in real groundwater revealed that nZVI-Ni can be applicable and is a promising catalyst for TCE removal in in-situ chemical oxidation (ISCO) practice. In Summary, these significant findings strongly demonstrate the feasibility and potential of nZVI-Ni activated SPS process as an alternative technique for TCE contaminated groundwater remediation. [ABSTRACT FROM AUTHOR]

[Display omitted] • CT removal could be effectively achieved with surfactant presence in Fenton system. • Radical scavenger and EPR tests revealed that surfactant radicals (R•CHOH) with TW-80 presence, and O 2 −• and CO 2 −• with SDS presence were responsible for CT degradation. • Surfactant solutions could be recycled for CT solubilization and degradation. • Significant CT removal in actual groundwater containing TW-80 or SDS was achieved. This study investigates the mechanisms of surfactants in surfactant-in situ chemical oxidation (S-ISCO) for enhanced degradation of perchlorinated organic contaminants. The addition of Tween-80 (TW-80) or sodium dodecyl sulfate (SDS) in Fenton system resulted in a significant improvement in carbon tetrachloride (CT) removal from 6.2 % to 97.2 % and from 8.2 % to 91.8 %, respectively. Upon further analysis of free radical quenching studies and electron paramagnetic resonance (EPR) tests, it was observed that surfactant radicals were responsible for CT removal with TW-80 presence, while superoxide radicals (O 2 −•) and carbon dioxide radicals (CO 2 −•) were the primary radicals with SDS presence. The dechlorination of CT reached 82.1 % and 75.3 % with TW-80 or SDS presence, respectively, indicating that most of the degraded CT could be completely mineralized. The possible degradation pathways of CT were proposed based on the detected intermediates. Additionally, degradation of various single or mixed chlorinated hydrocarbon contaminants with TW-80 or SDS presence in Fenton system was performed. The study also assessed the influence of different solution matrixes on CT degradation and the impact of the recovered surfactant solution after reaction on CT solubilization and removal. In summary, this study provides theoretical support for groundwater remediation with perchlorinated contaminants when containing surfactants. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influence of surfactants TW-80 and SDS on TCE degradation was investigated. • The strengthening effect of nZVI on TCE degradation in PS/Fe(II) system was proved. • HO and SO 4 − were the primary ROSs in PS/Fe(II)/nZVI system in the presence of TW-80 or SDS. • Significant TCE degradation in actual groundwater containing TW-80 or SDS was achieved. Trichloroethylene (TCE) removal performance in non-ionic surfactant Tween-80 (TW-80) and anionic surfactant sodium dodecyl sulfate (SDS) involved solution by Fe(II) activated persulfate (PS) was investigated through the strengthening of nanoscale zero valent iron (nZVI). 99.5% removal of TCE could be obtained at the PS/Fe(II)/nZVI/TCE molar ratio of 8/4/4/1 with 1.0 critical micelle concentration (CMC) of TW-80 presence (13 mg L−1), while this value was slightly decreased to 88.3% at the molar ratio of 40/20/20/1 with 1.0 CMC of SDS presence (2.3 g L−1) in 180 min. The addition of nZVI significantly promoted TCE degradation, while TW-80 or SDS definitely inhibited TCE removal. Further, TCE removal declined with TW-80 or SDS concentration increasing from 0 to 10 CMC, and continuously decreased at 20 CMC of TW-80 but elevated TCE removal at 20 CMC of SDS. Tests of radical scavengers revealed that HO and SO 4 − contributed a major part while O 2 − had less contribution to TCE degradation in PS/Fe(II)/nZVI system. The dichlorination of TCE in PS/Fe(II)/nZVI system was 94.5% with TW-80 and 97.2% with SDS. In addition, TCE (with TW-80) removal was decreased with the initial pH increase from 3.0 to 11.0, while TCE (with SDS) degradation was always beyond 83% in the initial pH change from 3.0 to 11.0. Moreover, the effects of inorganic anions (Cl−, HCO 3 −) in the solution were evaluated. Experimental results using the actual groundwater revealed the excellent availability of PS/Fe(II)/nZVI system in remediating TCE contaminated field involved with TW-80 or SDS surfactants. In summary, these findings provide a new direction in remediating groundwater from contaminated sites polluted by chlorinated organic solvents after pretreatment by surfactant solubilization. [ABSTRACT FROM AUTHOR]

The mechanism of surfactants in surfactant-in situ chemical oxidation (S-ISCO) coupled process for trichloroethene (TCE) degradation was firstly reported. The performance of TCE solubilization and inhibition of TCE degradation in three nonionic surfactants (TW-80, Brij-35, TX-100) in PS/Fe(II)/citric acid (CA) system was compared and TW-80 was evaluated to be the optimal surfactant in S-ISCO coupled process due to the best TCE solubilizing ability and minimal inhibition for TCE degradation (only 31.8% TCE inhibition in the presence of 1 g L−1 TW-80 surfactant). The inhibition mechanism in TCE degradation was also demonstrated by comparing the strength of ROSs and PS utilization. In the presence of TW-80 (1 g L−1), over 97.5% TCE was removed at the PS/Fe(II)/CA/TCE molar ratio of 30/4/4/1, in which more than 86.7% TCE was dechlorinated. The result of scavenger experiments revealed that the dominant radicals were HO• and SO 4 −• in PS/Fe(II)/CA system in TW-80 containing aqueous solution, among which SO 4 −• performed a greater role in TCE removal. Moreover, over 85.3% TCE degradation in actual groundwater revealed the potential of PS/Fe(II)/CA process for actual groundwater remediation in containing TW-80 of TCE contaminant. This research provided a novel alternative technology for groundwater remediation with TCE contaminant when containing surfactants. ga1 • TW-80 was evaluated to be the optimal surfactants in S-ISCO coupled process. • The mechanism of TW-80 in TCE solubilization and degradation was investigated. • HO• and SO 4 −• was the primary ROSs in PS/Fe(II)/CA system in the presence of TW-80. • Effective degradation of TCE in actual groundwater containing TW-80 was achieved. [ABSTRACT FROM AUTHOR]

• FeS significantly enhanced HO generation and TCE degradation. • The synergistic activation mechanism of Fe(II)/FeS was investigated. • HO was the primary ROSs in nCP/Fe(II)/FeS system. • Effective degradation of TCE in actual groundwater was achieved. The performance of trichloroethene (TCE) degradation was significantly improved with the addition of FeS in nanoscale calcium peroxide (nCP) environment and the enhancement of HO generation in nCP/Fe(II)/FeS system was confirmed by comparison with nCP/Fe(II) and nCP/FeS systems. The role of FeS in nCP/Fe(II)/FeS system demonstrated that the majority of reactive oxygen radicals (ROSs) was generated on the catalyst surface due to the heterogeneous reaction through FeS activated nCP in one hand, and the reductive FeS could promote TCE degradation by regenerating Fe(II) from Fe(III) in the other hand. The probe as well as scavenger test results suggested that the major ROSs was HO rather than O 2 −. Over 91.5% TCE could be degraded at the molar ratio of 2/2/4/1 of nCP/Fe(II)/FeS/TCE, in which more than 95.5% TCE was dechlorinated. The effect of surfactants on TCE degradation was evaluated. In contrast, further investigation found that BTEX removal was inhibited with the addition of FeS. In conclusion, this study revealed the well function and fundamental synergistic mechanism of FeS. Moreover, the degradation of TCE in actual groundwater confirmed that nCP/Fe(II)/FeS technique has a great advantage and potential in TCE contaminated groundwater remediation in ISCO practice. [ABSTRACT FROM AUTHOR]