•CT could be effectively removed in the UV/S2O82−/HCOOH process.•CO2− was generated in the UV/S2O82− process with the addition of formic acid.•CT degradation performance was influenced by solution matrix.•The dechlorination of CT was 80.6% while no volatile intermediates were detected.The reduction performance of carbon tetrachloride (CT) mediated by carbon dioxide radical anion (CO2−) was investigated in this study, and CO2− was generated by the reaction of formic acid and sulfate radical produced in the UV/S2O82− process. The effects of various factors including persulfate and formic acid concentrations, solution pH, and anions such as Cl−, HCO3−, NO3−, and SO42− were evaluated. The experimental results showed that CT could be almost completely removed in 60 min with 1.50 mM persulfate and 2.25 mM formic acid. CT degradation efficiency was found to increase with increasing persulfate (0.75−4.50 mM) and formic acid (0.75−2.25 mM) concentrations. In the pH adjusted solutions (from pH 6–8), maximum CT degradation occurred at pH 6. Both Cl− and NO3− (1−100 mM), as well as HCO3− at high concentrations (10 and 100 mM), adversely affected CT degradation performance. The addition of methyl viologen as CO2− scavengers proved the presence of CO2− in this UV/S2O82−/HCOOH process, and the dechlorination of CT was not complete as Cl− release rate was 80.6% after 240 min.

In this study, an environmentally friendly complexing agent, S,S′-ethylenediamine-N,N′-disuccinic acid (EDDS), was applied in Fe(III)-mediated activation of persulfate (PS), and the degradation performance of trichloroethylene (TCE) was investigated. The effects of PS concentration, Fe(III)/EDDS molar ratio, and inorganic anions on TCE degradation were evaluated, and the generated reactive oxygen species responsible for TCE removal were identified. The results showed that nearly complete TCE degradation was achieved with PS of 15.0 mM and a molar ratio of Fe(III)/EDDS of 4:1. An increase in PS concentration or Fe(III)/EDDS molar ratio to a certain value resulted in enhanced TCE degradation. All of the anions (Cl−, HCO3−, SO42−, and NO3−) at tested concentrations had negative effects on TCE removal. In addition, investigations using radical probe compounds and radical scavengers revealed that sulfate radicals (SO4·−), hydroxyl radicals (·OH), and superoxide radical anions (O2·−) were all generated in the Fe(III)–EDDS/PS system, and ·OH was the primary radical responsible for TCE degradation. In conclusion, the Fe(III)–EDDS-activated PS process is a promising technique for TCE-contaminated groundwater remediation.

•A novel heterogeneous catalyst (Z-nZVFe-Cu) was prepared using ion exchange method.•The combined effect of iron and copper enhanced the catalytic activity of Z-nZVFe-Cu.•Z-nZVFe-Cu demonstrated an excellent performance for TCE degradation.•The hydroxyl radicals (OH) played the major role in TCE degradation.•The low leaching of Fe and Cu suggested its prolonged stability.Zeolite supported nano zero valent iron copper bimetallic composite (Z-nZVFe-Cu) was synthesized using an ion exchange method. The morphology and physico-chemical properties of the Z-nZVFe-Cu composite were determined using transmission electron microscopy (TEM), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET), energy dispersive X-ray spectra (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD). The results showed that iron and copper nano particles were well dispersed on the zeolite sheet. The degradation efficiency of trichloroethylene (TCE) achieved was more than 95% using Z-nZVFe-Cu as a heterogeneous Fenton like catalyst. An efficient removal of total organic carbon (TOC) was promoted as compared to zeolite supported iron nano composite (Z-nZVFe) and unsupported nano iron (nZVFe). Electron spin resonance (ESR) detection confirmed the intensity of hydroxyl radicals (OH) in the system. While benzoic acid (BA), a probe indicator for the quantification of OH, demonstrated the higher intensity of hydroxyl radicals in Z-nZVFe-Cu as compared to Z-nZVFe and nZVFe. The less iron and copper leaching of from Z-nZVFe-Cu presented its higher stability and better catalytic activity, displaying its potential long term applications for TCE degradation in groundwater.

Graphene-oxide-supported nano zero-valent iron (nZVI) composite (nZVI–rGO) was synthesized and tested as an efficient percarbonate activator for degradation of 1,1,1-trichloroethane (TCA). Significant dispersion of nZVI on the surface of reduced graphene oxide (rGO) was observed, with good limitation of nanoparticle agglomeration and aggregation. Good TCA degradation efficiency of 90% was achieved in 2.5 h in presence of 0.8 g/l nZVI–rGO catalyst and 30 mM sodium percarbonate (SPC) oxidant; however, excessive catalyst or oxidant concentration reduced the degradation efficiency. Investigation of reactive oxygen species using radical probe compounds as well as radical scavengers confirmed presence of hydroxyl (OH·) and superoxide (\({\text{O}}_{2}^{\cdot - }\)) radicals that are responsible for the TCA degradation. The morphology and surface characteristics of the heterogeneous catalyst were analyzed by transmission electron microscopy and scanning electron microscopy. Brunauer–Emmett–Teller analysis revealed that the synthesized catalyst had large surface area and small particle size of 299.12 m2/g and 20.10 nm, respectively, compared with 5.33 m2/g and 1.12 µm for bare graphene oxide. X-ray diffraction analysis revealed good dispersion of nZVI on the surface of rGO. Fourier-transform infrared characteristic peaks confirmed strong attachment of Fe onto the rGO surface. Energy-dispersive spectroscopy analysis validated the stoichiometric composition of the prepared Fe/rGO material. In conclusion, use of nZVI–rGO-activated SPC could represent an alternative technique for remediation of TCA-contaminated groundwater.

•Addition of ascorbic acid accelerated the transformation of Fe(III) to Fe(II).•Enhanced production of HO was responsible for promotion of TCE degradation.•TCE degradation was a complete Cl-releasing process.•CP/Fe(III)/AA system may be applicable in chemical groundwater remediation.The enhancement effect of an environmentally friendly reducing agent, ascorbic acid (AA), on trichloroethene (TCE) degradation by Fe(III)-activated calcium peroxide (CP) was evaluated. The addition of AA accelerated the transformation of Fe(III) to Fe(II), and the complexation of Fe(III)/Fe(II) with AA and its products alleviated the precipitation of dissolved iron. These impacts enhanced the generation of reactive oxygen species (ROSs). Investigation of ROSs using chemical probe tests, electron paramagnetic resonance (EPR) tests, and radical scavenger tests strongly confirm large production of hydroxyl radicals (HO) that is responsible for TCE degradation. The generation of Cl− from the degraded TCE was complete in the enhanced CP/Fe(III)/AA system. The investigation of solution matrix effects showed that the TCE degradation rate decreases with the increase in solution pH, while Cl−, SO42− and NO3− anions have minor impact. Conversely, HCO3− significantly inhibited TCE degradation due to pH elevation and HO scavenging. The results of experiments performed using actual groundwater indicated that an increase in reagent doses are required for effective TCE removal. In summary, the potential effectiveness of the CP/Fe(III)/AA oxidation system for remediation of TCE contaminated groundwater has been demonstrated. Additional research is needed to develop the system for practical implementation.

•Effective benzene degradation was achieved in Fe(III)-activated SPC system.•HO was the leading species responsible to degrade benzene.•Formation of HO depended on the generation of R and O2− in the system.•Proposed degradation routes agree with radical formation and organic products.•Efficient removal of benzene in groundwater was attained.Complete degradation of benzene by the Fe(III)-activated sodium percarbonate (SPC) system is demonstrated. Removal of benzene at 1.0 mM was seen within 160 min, depending on the molar ratios of SPC to Fe(III). A mechanism of benzene degradation was elaborated by free-radical probe-compound tests, free-radical scavengers tests, electron paramagnetic resonance (EPR) analysis, and determination of Fe(II) and H2O2 concentrations. The degradation products were also identified using gas chromatography-mass spectrometry method. The hydroxyl radical (HO) was the leading species in charge of benzene degradation. The formation of HO was strongly dependent on the generation of the organic compound radical (R) and superoxide anion radical (O2−). Benzene degradation products included hydroxylated derivatives of benzene (phenol, hydroquinone, benzoquinone, and catechol) and aliphatic acids (oxalic and fumaric acids). The proposed degradation pathways are consistent with radical formation and identified products. The investigation of selected matrix constituents showed that the Cl− and HCO3− had inhibitory effects on benzene degradation. Natural organic matter (NOM) had accelerating influence in degrading benzene. The developed system was tested with groundwater samples and it was found that the Fe(III)-activated SPC has a great potential in effective remediation of benzene-contaminated groundwater while more further studies should be done for its practical application in the future because of the complex subsurface environment.Download high-res image (69KB)Download full-size image

•SPC activated with EDDS–Fe(III) complex was applied to stimulate EB degradation.•The addition of EDDS significantly increased EB degradation in SPC/Fe(III) system.•EB degradation hinges on the dosages of SPC, EDDS, Fe(III) and solution pH.•The HCO3− anion and humic acid inhibited EB degradation.•The primary EB degradation mechanism was oxidized by OH.Ethylbenzene (EB) degradation performance in (S,S)-ethylenediamine-N,N-disuccinic acid (EDDS) chelated Fe(III) activated sodium percarbonate (SPC) system was investigated in this study. The effects of various factors, such as the dosages of SPC and Fe(III), molar ratio of EDDS/Fe(III), anions (Cl−, HCO3−, SO42−, and NO3−) concentration, natural organic matters (NOM), and initial solution pH were evaluated. The results showed that the addition of EDDS remarkably improved the EB removal in Fe(III)/SPC system. Both HCO3− anions and NOM had significantly inhibitive effect, while the influence of SO42−, Cl− and NO3− could be negligible on EB degradation. The EB removal was inhibited at extremely low and high initial solution pH. Moreover, the results of free radical probe tests, scavenger tests and electron paramagnetic resonance (EPR) detection indicated that OH was the predominant species responsible for EB degradation even though both OH and O2− were generated in the SPC/EDDS–Fe(III) system. The oxidation products were analyzed and possible EB degradation pathways were proposed. In conclusion, this study provides an important insight into the application of SPC/EDDS–Fe(III) system in the removal of EB contaminant, especially for in situ remediation of BTEX-contaminated groundwater.Download high-res image (76KB)Download full-size image

•Novel heterogeneous graphene supported iron and iron-copper nanocomposites were synthesized.•Solvothermal technique showed better catalytic performance compared to chemical reduction.•Aggregation was significantly eliminated in ST synthesized composite.•The surface area of the ST composites increased significantly.•Significantly improved efficiency with lower catalyst dosage.Experiments were conducted to investigate the use of graphene-oxide supported metallic nanocomposites for improving the degradation of trichloroethane (TCA) by sodium percarbonate (SPC). Two methods of production, chemical reduction (CR) and solvo-thermal (ST), were tested for preparation of single (Fe) and binary (Fe-Cu) nanocomposites supported by reduced graphene oxide (rGO). A variety of analytical techniques including N2 adsorption Brunauer-Emmett-Teller (BET), x-ray diffraction (XRD), fourier-transfrom infrared spectroscopy (FTIR), and transmisison electron microscopy (TEM) were applied to characterize the physicochemical and microstructural properties of the synthesized nanocomposites. The characterization indicated that the CR method produced nanocomposites that comprised only mesoporous structure. Conversely, both micro and mesoporous structures were present for samples produced with the ST method. The synthesized single and bimetallic composites produced from the ST method showed higher surface areas, i.e. 93.6 m2/g and 119.2 m2/g as compared to the ones synthesized via the CR method, i.e. 13.8 m2/g and 38.0 m2/g respectively. The results of FTIR and XRD analyses confirmed that the ST method produced highly crystalline nanocomposites. SEM and TEM analysis validated that metallic particles with definite morphology well distributed on the surface of rGO. X-ray photoelectron spectroscopy (XPS) analysis confirmed the homogeneity nanocomposites and occurrence of variation in copper oxidation states during degradation process. EDS mapping validate the homogeneous distribution of Cu and Fe at reduced graphene oxide surface. The Fe-Cu/rGO (ST) activated SPC system effectively degraded TCA (92%) in 2.5 h at low nanocomposite dose compared to the Fe-Cu/rGO (CR) and only Fe, for which the maximum degradation efficiencies achieved were 81% and 34%. In conclusion, excellent catalytic characteristics were observed for the ST-synthesized single and bimetallic (Fe/rGO, Fe-Cu/rGO) catalysts. These catalysts were successful in improving the degradation of TCA via activated SPC.Download high-res image (190KB)Download full-size image

•Recent advances in CP application in water and soil treatment are reviewed.•Removal of a wide range of contaminants from water and soil are achieved.•Various CP action modes in contaminants removal are summarized.•Future perspectives about CP application are suggested.Calcium peroxide (CP) has been progressively applied in terms of environmental protection due to its certain physical and chemical properties. This review focuses on the latest progresses in the applications of CP in water and soil treatment, including wastewater treatment, surface water restoration and groundwater and soil remediation. The stability of CP makes it an effective solid phase to supply H2O2 and O2 for aerobic biodegradation and chemical degradation of contaminants in water and soil. CP has exerted great performance in the removal of dyes, chlorinated hydrocarbons, petroleum hydrocarbons, pesticides, heavy metals and various other contaminants. The research progress in the encapsulation technologies of CP with other materials and the preparation of CP nanoparticles were also presented in this review. Based on the summarized research progresses, the perspective of CP application in the future was proposed.Download high-res image (93KB)Download full-size image

This work demonstrates the impact of hydroxylamine hydrochloride (HAH) addition on enhancing the degradation of trichloroethene (TCE) by the citric acid (CA)-chelated Fe(II)-catalyzed percarbonate (SPC) system. The results of a series of batch-reactor experiments show that TCE removal with HAH addition was increased from approximately 57 to 79% for a CA concentration of 0.1 mM and from 89 to 99.6% for a 0.5 mM concentration. Free-radical probe tests elucidated the existence of hydroxyl radical (HO•) and superoxide anion radical (O2•-) in both CA/Fe(II)/SPC and HAH/CA/Fe(II)/SPC systems. However, higher removal rates of radical probe compounds were observed in the HAH/CA/Fe(II)/SPC system, indicating that HAH addition enhanced the generation of both free radicals. In addition, increased contribution of O2•- in the HAH/CA/Fe(II)/SPC system compared to the CA/Fe(II)/SPC system was verified by free-radical scavengers tests. Complete TCE dechlorination was confirmed based on the total mass balance of the released Cl− species. Lower concentrations of formic acid were produced in the later stages of the reaction for the HAH/CA/Fe(II)/SPC system, suggesting that HAH addition favors complete TCE mineralization. Studies of the impact of selected groundwater matrix constituents indicate that TCE removal in the HAH/CA/Fe(II)/SPC system is slightly affected by initial solution pH, with higher removal rates under acidic and near neutral conditions. Although HCO3− was observed to have an adverse impact on TCE removal for the HAH/CA/Fe(II)/SPC system, the addition of HAH reduced its inhibitory effect compared to the CA/Fe(II)/SPC system. Finally, TCE removal in actual groundwater was much significant with the addition of HAH to the CA/Fe(II)/SPC system. The study results indicate that HAH amendment has potential to enhance effective remediation of TCE-contaminated groundwater.

Trichloroethene (TCE) degradation by Fe(III)- activated calcium peroxide (CP) in the presence of citric acid (CA) in aqueous solution was investigated. The results demonstrated that the presence of CA enhanced TCE degradation significantly by increasing the concentration of soluble Fe(III) and promoting H2O2 generation. The generation of HO• and O2–• in both the CP/Fe(III) and CP/Fe(III)/CA systems was confirmed with chemical probes. The results of radical scavenging tests showed that TCE degradation was due predominantly to direct oxidation by HO•, while O2–• strengthened the generation of HO• by promoting Fe(III) transformation in the CP/Fe (III)/CA system. Acidic pH conditions were favorable for TCE degradation, and the TCE degradation rate decreased with increasing pH. The presence of Cl–, HCO3–, and humic acid (HA) inhibited TCE degradation to different extents for the CP/Fe(III)/CA system. Analysis of Cl–production suggested that TCE degradation in the CP/Fe (III)/CA system occurred through a dechlorination process. In summary, this study provided detailed information for the application of CA-enhanced Fe(III)-activated calcium peroxide for treating TCE contaminated groundwater.

The role of reactive oxygen species (ROSs) and effect of solution matrix have been investigated for the degradation of trichloroethylene (TCE). Zeolite-supported nano iron (Z-nZVI) was synthesized as an activator to catalyze sodium percarbonate (SPC) with or without hydroxylamine, i.e. as reducing agent (RA). The probe tests confirmed the generation of OH· and O2−· in the Z-nZVI activated SPC system in absence of the RA, while the presence of RA significantly increased the generation of OH· and O2−· radicals. Scavenger tests demonstrated that OH· was the main ROS responsible for TCE degradation, whereas O2−· also participated in TCE degradation. From the solution matrix perspective, the experimental results confirmed significant scavenging effects of Cl− (1.0, 10.0, and 100 mmol L−1) and HCO3− (1.0 and 10.0 mmol L−1), whereas the scavenging effects were fairly impeded at 100 mmol L−1 concentration of HCO3−. On the other hand, a considerable decline in scavenging effect was observed in the presence of RA in tested Cl− and HCO3− concentration ranges. In addition, negligible scavenging effects of NO3− and SO42− anions were found in all tested concentrations. The effect of initial solution pH on catalytic activity indicated a significant increase in the TCE degradation in the presence of RA even at higher pH value of 9. The results indicated that the Z-nZVI activated SPC system in presence of RA can effectively degrade chlorinated organic solvents, but it is important to consider the intensive existence of anions in groundwater.

The thermally activated persulfate (PS) degradation of carbon tetrachloride (CT) in the presence of formic acid (FA) was investigated. The results indicated that CT degradation followed a zero order kinetic model, and CO2– · was responsible for the degradation of CT confirmed by radical scavenger tests. CT degradation rate increased with increasing PS or FA dosage, and the initial CT had no effect on CT degradation rate. However, the initial solution pH had effect on the degradation of CT, and the best CT degradation occurred at initial pH 6. Cl– had a negative effect on CT degradation, and high concentration of Cl– displayed much strong inhibition. Ten mmol·L–1HCO3– promoted CT degradation, while 100 mmol·L–1NO3– inhibited the degradation of CT, but SO42– promoted CT degradation in the presence of FA. The measured Cl–concentration released into solution along with CT degradation was 75.8% of the total theoretical dechlorination yield, but no chlorinated intermediates were detected. The split of C-Cl was proposed as the possible reaction pathways in CT degradation. In conclusion, this study strongly demonstrated that the thermally activated PS system in the presence of FA is a promising technique in in situ chemical oxidation (ISCO) remediation for CT contaminated site.

•HA is the most efficient reducing agent in TCE removal with Fe(II) regeneration.•TCE degradation highly depends on the dosage of HA, Fe(II) and PS concentrations.•The primary reactive oxygen species are OH, SO4− and O2− in PS/Fe(II)/HA system.•The suppressive effect of anions on TCE degradation ranks NO3− < SO42− < Cl− < HCO3−.The persulfate (PS) activated by ferrous ion (Fe(II)) system could generate reactive oxygen species capable of degrading refractory organic contaminants trichloroethylene (TCE). Nevertheless, the slow conversion from ferric ion (Fe(III)) back to Fe(II) limits its widespread practical application. Therefore, different reducing agents, i.e., hydroxylamine (HA), sodium thiosulfate, ascorbic acid, sodium ascorbate and sodium sulfite, were added into PS/HA system for accelerating the Fe(II) regeneration, and HA was most efficient in TCE degradation. The effects of HA, Fe(II) and PS concentrations were also evaluated in PS/Fe(II)/HA system. The results indicated that a proper HA and Fe(II) concentrations were needed in practical application, too low or too high dosages were adverse to TCE degradation. Moreover, TCE degradation was increased with the increasing of PS dosage over the tested range. The radical scavenging tests confirmed that the primary reactive oxygen species were sulfate radicals (SO4−), hydroxyl radicals (OH) and superoxide radical (O2−) in PS/Fe(II)/HA process. Both inorganic anions (Cl−, HCO3−, SO42−, NO3− ions) and natural organic matter had inhibitory effects on TCE removal, and the suppressive effects of inorganic anions can be ranked in an ascending order of NO3− < SO42− < Cl− < HCO3− in PS/Fe(II)/HA system.

In this study, the degradation performance of 1,1,1-trichloroethane (TCA) involving both oxidation and reduction processes was investigated with an application of the persulfate–ZVI (zero-valent iron) system, in which it is generally believed that SO4−˙-induced oxidation was responsible for pollutant removal. The study was conducted with persulfate and un-pretreated ZVI through batch experiments. The results showed that TCA was stable in the presence of ZVI alone within 12 h and degraded with the addition of persulfate. TCA degradation efficiency was found to increase with increasing persulfate concentration, but to decrease with increasing ZVI dosage. A two-stage process involving persulfate oxidation and ZVI reduction was developed during TCA degradation. The addition of isopropanol and tert-butyl alcohol proved the existence of sulfate and hydroxyl radicals during the 1st-stage (0–2 h), which were absent in the 2nd-stage (2–12 h) when persulfate was exhausted. The degradation performance of carbon tetrachloride, a reduction probe compound, was evidence of the persulfate–ZVI system involving an enhanced ZVI reduction, and which was mainly responsible for TCA degradation in the 2nd-stage. 1,1-Dichloroethane was the only confirmed intermediate emerging during the 2nd-stage.

A thermally activated persulfate (PS) system was applied to degrade 1,1,1-trichloroethane (TCA) in aqueous solution. The generation of reactive oxygen species (ROS) in the system and their roles in TCA degradation were investigated. The experimental results showed that TCA (0.15 mM) could be completely oxidized in 1 h at 50 °C with a PS concentration of 30 mM. TCA degradation and PS decomposition well fitted a pseudo-first-order kinetic model. In addition, the chemical probe method was developed to identify the ROS. The results showed that SO4•–, HO•, and O2•– were all generated in the system and the generation intensities could be strengthened with the increase of PS concentration. The tests for PS persistence in solution indicated that oxidative species were intensified during the initial 2 h, suggesting more SO4•– and HO• were generated, whereas after 12 h SO4•– and HO• intensities were slightly reduced. In contrast, O2•– generated in the system was maintained at a stable level after reaction but at a slightly lower intensity simply due to quenching by PS or other species. Radical scavenger tests showed that HO• was the predominant radical species responsible for TCA degradation, and this was also confirmed by electron paramagnetic resonance (EPR) spectrum analysis in the system. Finally, two different pathways, dechlorination and C–C bond breakage, were proposed as the main TCA degradation mechanism. In conclusion, a thermally activated PS process is a highly promising technique for TCA degradation, and the potential to degrade highly oxidized organic contaminants greatly increases its application in in situ chemical oxidation (ISCO) remediation in contaminated sites.

Photocatalytic of Cu-TiO2 was tested for the degradation of 1.1.1-trichloroethane, tetrachloroethene, and trichloroethene in aqueous phase under UV illumination. Results indicated fast degradation rate of pollutants over TiO2 doped with 0.5 wt % of Cu compared to undoped TiO2 and Degussa P25. Fast degradation of nitrobenzene, a probe of hydroxyl radicals (•OH), over Cu-TiO2 suggested high concentration of •OH generated in UV/Cu-TiO2 system. Cu-TiO2, synthesized by simply hydrothermal solution containing tetrabutyl-titanate, hydrofluoric acid, and cupric nitrate, was characterized by X-ray diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). Results showed that Cu-TiO2 was in anatase form and consisted of well-defined sheet-shaped structures having a rectangular outline. XPS analysis showed that surface state of the synthesized products was not modified by Cu doping and Cu was in Cu+ oxidation state. Moreover, Cu-TiO2 product showed good stability through five cycles reuse in trichloroethene photodegradation, suggesting a great potential for its application in chlorinated solvent contaminated groundwater remediation.

The degradation of trichloroethylene (TCE) was evaluated in a thermally activated persulfate system and the generation of active oxygen species investigated using various probe compounds. The experimental results showed that TCE was completely degraded in 9 min at 50 °C with an initial TCE concentration of 0.15 mM and a dose of 0.3 M persulfate. The influence of the solution matrix on the degradation of TCE was evaluated and it was shown that concentrations of 100 mM Cl−, 10 mM HCO3− and 100 mg L−1 humic acid (HA) affect the degradation of TCE. In addition, tests investigating the effects of Cl−, HCO3− and HA on the generation and intensity of active oxygen species showed that HCO3− affected the degradation of TCE by decreasing the intensities of ˙SO4− and ˙OH, while increasing the intensity of ˙O2−. In contrast, Cl− and HA influenced the degradation of TCE by decreasing the intensities of ˙OH and ˙O2− while increasing the intensity of ˙SO4−. The results from this study provide a key foundation for further studies of the remediation of groundwater contaminated by chlorinated solvents using the thermally activated persulfate process.

The present study investigates the applicability of the synthesized titanium dioxide (TiO2) for the removal of tetrachloroethene (PCE), trichloroethene (TCE), and 1,1,1-trichloroethane (TCA) in aqueous phase under VUV illumination. The photo-degradation results indicated that these harmful chemicals can be effectively removed under VUV irradiation, and the addition of the synthesized TiO2 significantly enhanced their degradation. Moreover, using nitrobenzene (NB) as a probe of hydroxyl radical (·OH), the NB degradation rate was better over VUV/synthesized TiO2, suggesting the high concentration of OH generated. The TiO2 used has been synthesized by a simple hydrothermal solution containing tetrabutyl titanate and hydrofluoric acid and characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), and X-ray photo-electron spectroscopy (XPS). The characterization results showed that the synthesized TiO2 was in anatase form and consisted of well-defined sheet-shaped structures having a rectangular outline with a thickness of ~4 nm, side length of ~50 nm, and width of ~33 nm and has a surface of 90.3 m2 g−1. XPS analysis revealed the formation of ≡ Ti–F surface bonds. Moreover, the synthesized TiO2 nano-sheets have shown good stability after testing their photo-catalytic activity through five cycles of reuse in TCE degradation. In summary, it can be concluded from the results on both photo-catalytic activity and the surface analyses that the synthesized TiO2 nano-sheets have a great potential for application in chlorinated solvent-contaminated groundwater remediation.

The chemical oxidation of 1,1,1-trichloroethane (TCA), a widely detected groundwater pollutant, by UV/H2O2 and UV/S2O82– processes was investigated. The effects of various factors were evaluated, including peroxide/TCA molar ratio, solution pH, Cl– and HCO3– anions, and humic acid (HA). The results showed that TCA oxidation fit to a pseudo-first-order kinetic model. The optimum H2O2/TCA molar ratio was 5:1, with TCA removal of 54.2% in 60 min. In the UV/S2O82– process, higher molar ratios (from 1/1 to 10/1) resulted in higher TCA oxidation rates, and TCA could be completely removed after 60 min with a S2O82–/TCA molar ratio of 3/1. In addition, acidic conditions were favorable for TCA removal in the UV/S2O82– process, while maximum TCA removal was observed at pH 6 in the UV/H2O2 process. Both Cl– and HCO3– anions adversely affected TCA oxidation performance, and higher concentration of HA resulted in a lag phase for TCA oxidation in both processes. Several reaction intermediates, including 1,1,1,2-tetrachloroethane, carbon tetrachloride, chloroform, tetrachloroethylene, 1,1-dichloroethylene, and tri- and dichloroacetic acids, were first identified during TCA oxidation by S2O82– chemistry, while only monochloroacetic acid was detected in the UV/H2O2 process. The results indicated that the UV/S2O82– process was much more effective than the UV/H2O2 process, but the latter was more environmentally friendly because fewer toxic intermediates were produced.

The aim of this study was to identify the intermediates in clofibric acid degradation under various advanced oxidation processes, namely ultraviolet (UV), UV/H2O2, vacuum ultraviolet (VUV), VUV/H2O2, and solar/TiO2 processes, as well as to assess the toxicity of these intermediates. Eleven intermediates have been detected by gas chromatography-mass spectrometer, most of which were reported for the first time to our best knowledge. Combining the evolution of the dissolved organic carbon, Cl− and specific ultraviolet absorption at 254 nm, it could be deduced that cleavage of aromatic ring followed by dechlorination was the mechanism in solar/TiO2 process, while dechlorination happened first and accumulation of aromatic intermediates occurred in the other processes. Different transformation pathways were proposed for UV-, VUV-assisted and solar/TiO2 processes, respectively. The acute toxicity was evaluated by means of Photobacterium phosphoreum T3 spp. bioassay. It was believed that aromatic intermediates increased the toxicity and the ring-opening pathway in solar/TiO2 process could relieve the toxicity.

The performance of clofibric acid (CA) degradation in Milli-Q water and wastewater treatment plant (WWTP) effluent by solar/TiO2 and solar/ZnO was investigated in summer and winter seasons. The effects of NO3− and HCO3− anions, humic acid (HA), and H2O2 on CA photocatalysis were evaluated. Significant difference in CA degradation in two seasons was observed. Both NO3− and HCO3− anions adversely affected CA degradation, particularly at high HCO3− concentration. CA degradation slightly increased with 0.5 mg L−1 HA in solar/TiO2 in summer, but was significantly inhibited in winter at 20 mg L−1 HA. However, the inhibitive effect of 20 mg L−1 HA on CA removal in solar/ZnO had no remarkable difference in two seasons. The degradation in solar/TiO2/H2O2 was similar to that in solar/TiO2, but was inhibited obviously in solar/ZnO/H2O2. When applying photocatalytic process into WWTP effluent, degradation rates were apparently lower compared to Milli-Q water and temperature caused a great adverse effect on CA elimination.

In this study, thermally activated persulfate (PS) to stimulate the oxidation of 1,1,1-trichloroethane (TCA) in groundwater remediation was investigated. The effects of various factors including temperature; initial TCA concentration; PS/TCA molar ratio; solution pH; and common constituents in groundwater such as Cl–, HCO3–, SO42–, and NO3– anions and humic acid (HA) were evaluated. The experimental results showed that TCA can be completely oxidized in 2 h at 50 °C with a PS/TCA molar ratio of 100/1, indicating the effectiveness of thermally activated PS oxidation for TCA removal. TCA oxidation was fitted with a pseudo-first-order kinetic model, and the rate constant was found to increase with increasing temperature and PS/TCA molar ratio, but to decrease with increasing initial TCA concentration. In addition, acidic conditions were favorable to TCA removal and elevating, the initial solution pH value (from pH 3 to 11) decreased the TCA degradation rate. Anions Cl– and HCO3– had negative effects on TCA removal, whereas the effects of both SO42– and NO3– were negligible. With 5–10 mg L–1 concentrations of HA in solution, an inhibitive effect was observed, indicating that dissolved organic matter consumed some of the oxidant. However, the anticipated effective thermally activated PS oxidation of TCA in groundwater from a real contaminated site was not achieved because of the complex solution matrix. On the other hand, the TCA degradation mechanism derived from GC/MS analytical results confirmed formic acid, dichloromethane, and trichloromethane as the primary intermediates, and therefore, two TCA decomposition pathways were proposed. In conclusion, thermally activated PS oxidation is a highly promising technique for TCA-contaminated groundwater remediation, but more complex constituents in in situ groundwater should be carefully considered for its practical application.

Soluble microbial products (SMPs) are considered as the main organic components in wastewater treatment plant effluent from biological wastewater treatment systems. To investigate and explore SMP metabolism pathway for further treatment and control, two innovative mechanistically based activated sludge models were developed by extension of activated sludge model no.3 (ASM3). One was the model by combining SMP formation and degradation (ASM3-SMP model) processes with ASM3, and the other by combining both SMP and simultaneous substrate storage and growth (SSSG) mechanisms with ASM3 (SSSG-ASM3-SMP model). The detailed schematic modification and process supplements were introduced for comprehensively understanding all the mechanisms involved in the activated sludge process. The evaluations of these two models were demonstrated by a laboratory-scale sequencing batch reactor (SBR) operated under aerated/non-aerated conditions. The simulated and measured results indicated that SMP comprised about 83% of total soluble chemical oxygen demand (SCOD) in which biomass-associated products (BAPs) were predominant compared with utilization-associated products (UAPs). It also elucidated that there should be a minimum SMP value as the reactive time increases continuously and this conclusion could be used to optimize effluent SCOD in activated sludge processes. The comparative results among ASM3, ASM3-SMP and SSSG-ASM3-SMP models and the experimental measurements (SCOD, ammonia and nitrate nitrogen) showed clearly the best agreement with SSSG-ASM3-SMP simulation values (R = 0.993), strongly suggesting that both SMP formation and degradation and SSSG mechanisms are necessary in biologically activated sludge modeling for municipal wastewater treatment.

The recovery of H2SO4 from waste anodic aluminum oxidation solution using diffusion dialysis process was investigated by a series of batch, dynamic and pilot-scale tests. Experimental results from batch tests indicated that to some extent agitation could reduce concentration polarization phenomenon and CuSO4 could enhance proton permeability throughout the DF120 anion exchange membrane. Dynamic experimental results showed that both acid recovery and H+ concentration in recovered acid decreased with flow rate increase when the flow rate ratio of water to feed was kept at 1.0, and the optimal flow rate range of 3.0 × 10−4 m3/h to 5.0 × 10−4 m3/h (corresponding to the membrane flux of 9.4 × 10−5 m3/h m2 to 1.56 × 10−4 m3/h m2) was obtained. Although acid recovery efficiency could be improved by increasing the flow rate ratio, the recovered acid concentration decreased and metal leakage increased. And it is confirmed that the optimal flow rate ratio of water to feed should be controlled at 1.0–1.2. Pilot-scale tests performed very well when using the wastewater from a real anodic aluminum oxidation plant. H2SO4 recovery, recovered acid concentration and Al3+ leakage in steady-state condition were 85.25%, 4.08 mol/L and 4.98%, respectively, suggesting that diffusion dialysis is a cost-effective technique for acid recovery from waste anodic aluminum oxidation solution.

Lab-scale experiments were conducted to investigate the effect of initial concentration, temperature and pH on the removal of bezafibrate (BF) by activated sludge under aerobic condition. The results showed that adsorption of BF onto activated sludge was negligible, and biodegradation was the main removal mechanism of BF. The removal of BF in the aqueous phase by the activated sludge can be described by a pseudo-first-order reaction. The reaction rate constants had a negative relationship with the initial concentration of BF, and dramatically reduced from 0.050 to 0.007 h−1, when the temperature dropped from 20 °C to 10 °C. Variation of pH between 5.0 and 9.0 did not have significant influence on the removal of BF, indicating a high adaptation of microorganism in the activated sludge responsible for BF degradation to a wide pH range. The findings of this study are helpful to improve the removal of pharmaceuticals during the wastewater treatment plants by selecting the appropriate process variables, and eventually eliminate their release to the environment.

•Carbon tetrachloride can be readily degraded in the thermally activated persulfate system.•The predominant radical species responsible for CT degradation was identified.•Effects of initial persulfate, carbon tetrachloride and solution matrix were studied.•Effects of solvents addition to the solution were studied.Thermal activation of persulfate (PS) has been identified to be effective in the destruction of organic pollutants. The feasibility of carbon tetrachloride (CT) degradation in the thermally activated PS system was evaluated. The experimental results showed that CT could be readily degraded at 50 °C with a PS concentration of 0.5 M, and CT degradation and PS consumption followed the pseudo-first order kinetic model. Superoxide radical anion (O2−) was the predominant radical species responsible for CT degradation and the split of CCl was proposed as the possible reaction pathways for CT degradation. The process of CT degradation was accelerated by higher PS dose and lower initial CT concentration. No obvious effect of the initial pH on the degradation of CT was observed in the thermally activated PS system. Cl−, HCO3−, and humic acid (HA) had negative effects on CT degradation. In addition, the degradation of CT in the thermally activated PS system could be significantly promoted by the solvents addition to the solution. In conclusion, the thermally activated PS process is a promising option in in-situ chemical oxidation/reduction remediation for degrading highly oxidized organic contaminants such as CT that is widely detected in contaminated sites.

•Occurrence of 18 PPCPs in landfill leachate collected in Shanghai was determined.•Concentrations of some PPCPs in the leachate were higher than in other countries.•Good removal of PPCPs in landfill leachates was achieved by membrane bioreactor.•Concentrations of some PPCPs were still high in the treated landfill leachates.Knowledge on the pharmaceuticals and personal care products (PPCPs) in landfill leachates, which are an important source of PPCPs in the environment, was very limited. Hence, four sampling campaigns were conducted to determine eighteen PPCPs in the landfill leachates from a landfill reservoir in Shanghai. Five of the target PPCPs were first included in a landfill leachate study. Additionally, their removal from landfill leachates by a full-scale membrane bioreactor (MBR) was illustrated. The results showed fourteen out of eighteen PPCPs were detectable in at least one sampling campaign and achieved individual concentrations ranging from 0.39 to 349 μg/L in the landfill leachates. Some PPCPs exhibited higher contamination levels than those reported in other countries. Good removal of PPCPs by MBR led to a largely reduced contamination level (