Peroxydisulfate Process Research Articles

Photocatalytic degradation of methyl orange and methyl violet dyes by UV/Cu2+/PDS process

ABSTRACT This research is focused on the application of the UV/Cu2+/peroxydisulfate (PDS) system for the successful decolorization of methyl orange (MO) and methyl violet (MV) dyes in aqueous media. The effects of different parameters such as the equilibrium time, initial catalyst amount, PDS concentration and pH of the media in terms of MO and MV degradation were studied. Furthermore, the photocatalytic performance of the UV/Cu2+/PDS system was also investigated by performing the degradation of MO and MV in different water systems including distilled water, synthetic wastewater and industrial wastewater samples. The results revealed 94 and 89% degradation for MO and MV dyes in the UV/Cu2+/PDS system, respectively. The radical quenching experiments showed sulfate radicals (SO4·-) as the prominent species involved in the degradation of MO and MV dyes. Overall, it was concluded that the UV/Cu2+/PDS process has the ability to be adopted for the effective elimination of contaminants from the aquatic system.

Role of surfactants on Fe2+ mediated oxidative decolorization of Acid Red 13 by peroxydisulfate

Over the past few years, environmental concerns regarding dye contamination have grown. Removing dye from wastewater from industry is crucial for environmental sustainability. The removal of Acid Red 13 (AR13) dye was achieved through its oxidative degradation utilizing peroxydisulfate. While there are few reports on the Fe2+-mediated oxidation of azo dyes by peroxydisulfate, further investigation is needed to understand the effect of surfactants on their degradation. The present study focuses on investigating the influence of cationic, anionic, and neutral surfactants on the decolorization of Acid Red 13 (AR13) in aqueous solutions using peroxydisulfate. The decolorization kinetics of AR13 in the peroxydisulfate process adhered to the principles of second-order reaction kinetics, with a rate constant of 2.96 × 10−4 M−1 min−1 at 4.0 mM S2O8 2− concentration. A decolorization efficiency of 92.9 ± 3.6% was achieved in 120 min under optimal reaction conditions. The rate constants of the second-order chemical process demonstrated a positive association with both S2O8 2− concentration and temperature. Fe2+ activates S2O8 2− to generate sulfate radical ion, amplifying AR13 decolorization. At higher pH, sulfate-free radical production decreases, limiting AR13 decolorization. Recent findings show that CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) retard Fe2+-catalyzed S2O8 2− activation, whereas no discernible impact on S2O8 2− activation was observed in the case of TX-100 (triton X-100). Peroxydisulfate decolorized AR13 with a low activation energy of 45.10 ± 1.71 kJ mol−1 at 2.0 mM starting concentration. The positive ΔG value indicates the non-spontaneity of the decolorization process.

Visible light-driven Cl-g-C3N4 activated peroxydisulfate process for TMP efficient degradation in a wide pH range

A narrow pH-applicability range can impact the actual treatment efficiency of AOPs, so the application of a wide pH range in AOP technology has garnered significant attention. In this study, the Cl-doped g-C3N4 as a visible light catalyst to activate the peroxydisulfate (PDS) process, named Vis/Cl-g-C3N4/PDS, was developed for trimethoprim (TMP) degradation in a wide pH range of 3–11. Results show that the Vis/Cl-g-C3N4/PDS process exhibited degradation efficiencies for TMP that were 1.39 times and 7.74 times higher than those of the Vis/Cl-g-C3N4 process and the Vis/g-C3N4 process, respectively. The Vis/Cl-g-C3N4/PDS process perfectly achieved degradation rates of over 98 % for TMP within a wide pH range of 3–11. It concluded that the high efficiency of the Vis/Cl-g-C3N4/PDS process in degrading TMP over a wide pH range was caused by the two co-existing reactive oxygen species (ROS) generation mechanism pathways: the photocatalytic activation of PDS and the light-assisted hydrolysis of PDS. Moreover, after 3 h of illumination in the Vis/Cl-g-C3N4/PDS process, a degradation range of 85.7 %–97.8 % was demonstrated in various real water matrices including of tap water, secondary sedimentation tank effluent, surface water, and aquaculture water. This study provided practical significance for the practical application of AOPs in water environmental pollution control.

Removal of Reactive Black 5 by UV-C assisted peroxydisulfate process: Effect of parameters, kinetic study, and phytotoxicity assessment

ABSTRACT Photochemical removal of Reactive Black 5 (RB5) was investigated by the UV-C assisted peroxydisulfate (UV-C/PDS) process. Parameters affecting the removal of RB5 were examined. Activation of PDS by UV-C light significantly improved the removal efficiency compared to direct photolysis or PDS alone. The removal of RB5 by UV-C/PDS process fitted well with the pseudo first-order kinetic model under all tested conditions. Almost complete removal of RB5 was achieved at the end of 120 min within the pH range of 3–7, whereas 90.7 and 89.4% removal efficiency values were observed at pH = 9 and 11, respectively. An increase in PDS dosage in the range of 0.25–1 mM led to a rise in removal from 48.5 to 97.3% after 120 min, and a complete removal was observed with a dosage higher than 2 mM. Pseudo firstorder rate constant (kobs) increased linearly with PDS dosage from 0.0058 to 0.0518 min−1 in the 0.25 mM − 2.3 mM concentration range. The removal efficiency decreased with an increase in the initial concentration of RB5 from 20 to 50 mg L−1 and an exponential correlation was observed between kobs and initial concentration of RB5. Scavenging experiments conducted using t-butyl alcohol and ethyl alcohol implied that both sulphate and hydroxyl radicals were involved in the removal of RB5. Adding HCO3 − decreased the removal of RB5 within the range of 1–30 mM. The presence of CI− showed a negative impact on the removal at low concentrations (1–15 mM) and NO3 − slightly inhibited the removal of RB5. With corresponding stoichiometric PDS dosage, almost a complete mineralisation was achieved for RB5 solution and simulated dyebath effluent after 720 min of reaction time. EE/O values were determined to be 91.0, 76.8, and 41.1 kWh m−3 order−1 for UV-C/H2O2, UV-C/PMS, and UV-C/PDS processes, respectively. The phytotoxicity tests indicated that the intermediates could be more toxic than the parent compound.

Novel non-radical elimination mechanism of phosphorus flame retardant parent compound in Triton X-100 enhanced solar activated peroxydisulfate process: Key role of energy transfer from singlet oxygen to Triton X-100

The elimination mechanism of emerging contaminants by triplet excited state organic compounds generated from non-radical pathway was rarely concerned in advanced oxidation process (AOP). This study proposed Triton X-100 (TX-100, a nonionic surfactant) enhanced solar activated persulfate process (Solar/PDS/TX-100 process) as a novel method to rapidly eliminate 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO, an organic phosphorus flame retardant parent compound), which mainly depended on 3TX-100* as a new reactive intermediate, instead of reactive oxygen species and SO4•−. The results of DOPO degradation and probe compounds experiments, EPR spectra as well as triplet excited state compound scavenge experiments demonstrated that the observed degradation rate constant (kobs-DOPO) was 3.70 × 10-3 s−1 in Solar/PDS/TX-100 process, 4.86 times higher than that in Solar/PDS process where kobs-DOPO was 7.61 × 10-4 s−1, and 3TX-100* was the dominant reactive intermediate leading to the enhancement of DOPO degradation where the second order rate constant of 3TX-100* vs. DOPO was 6.98 × 109 M−1s−1. Singlet oxygen was the energy precursor to trigger the transformation from TX-100 to 3TX-100*, which promoted the yield of 3TX-100*. The degradation pathways and products toxicity assessment demonstrated that Solar/PDS/TX-100 process had better performance on DOPO detoxification than Solar/PDS process.

Rapid spectrophotometric determination of peroxydisulfate in water via oxidative coloration of 2,2′azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) using ferrous ion as catalyst

In this study, a rapid, sensitive and reliable spectrophotometric method for peroxydisulfate (PDS) determination in water was established. The proposed spectrophotometric method was based on the oxidation of 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) to form stable and green-colored ABTS radical (ABTS•+) by ferrous ion (Fe(II))-catalyzed PDS. The formed ABTS•+ performed well linear relationship with PDS concentration (R2 > 0.999) in the range of 0–60 μM at four wavelengths of 415, 650, 732, and 820 nm under optimized conditions. The proposed Fe(II)-ABTS spectrophotometric method was highly sensitive with the absorptivity of 3.595 × 104 M−1 cm−1, 1.530 × 104 M−1 cm−1, 1.945 × 104 M−1 cm−1 and 1.768 × 104 M−1 cm−1 at four detection peaks of 415, 650, 732 and 820 nm, respectively. Additionally, the proposed Fe(II)-ABTS spectrophotometric method possessed well anti-interference capacity to common natural water constituents and was reliable to determine PDS concentration in water. What’s more, the proposed Fe(II)-ABTS spectrophotometric method was successfully applied in monitoring the change of PDS concentration during the degradation of diclofenac in heat-activated PDS process. In a word, the proposed Fe(II)-ABTS spectrophotometric method could be employed as a promising approach for the rapid and accurate measurement of PDS in water, and this study provided a new perspective for the measurement of PDS by the visible spectrophotometry.

Application of heat-activated peroxydisulfate process for the chemical cleaning of fouled ultrafiltration membranes

NaClO has been widely used to restore membrane flux in practical membrane cleaning processes, which would induce the formation of toxic halogenated byproducts. In this study, we proposed a novel heat-activated peroxydisulfate (heat/PDS) process to clean the membrane fouling derived from humic acid (HA). The results show that the combination of heat and PDS can achieve almost 100% recovery of permeate flux after soaking the HA-fouled membrane in 1 mmol/L PDS solution at 50 °C for 2 h, which is attributed to the changes of HA structure and enhanced detachment of foulants from membranes. The properties of different treated membranes are characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS), demonstrating that the reversible and irreversible foulants could be effectively removed by heat/PDS cleaning. The filtration process and fouling mechanism of the cleaned membrane were close to that of the virgin membrane, illustrating the good reusability of the cleaned membrane. Additionally, heat/PDS which can avoid the generation of halogenated byproducts shows comparable performance to NaClO on membrane cleaning and high performance for the removal of fouling caused by sodium alginate (SA), HA-bovine serum albumin (BSA)-SA mixture and algae, further suggesting that heat/PDS would be a potential alternative for membrane cleaning in practical application.

Heat-activated peroxydisulfate and peroxymonosulfate-mediated degradation of benzotriazole: Effects of chloride on kinetics, pathways and transformation product toxicity

The impact of chloride (Cl⁻) in heat-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) processes for benzotriazole (BTA) degradation was investigated. Results showed that 0.42 mM BTA could be degraded by PDS and PMS under 70 °C in presence and absence of Cl⁻. The PMS-mediated BTA degradation rate increased with increasing Cl⁻ concentration up to 1000 mg/L, while a further increase of Cl⁻ concentration decreased the BTA degradation rate. In contrast, Cl⁻ inhibited PDS-mediated BTA degradation at concentrations tested between 100 and 10,000 mg/L. Radical scavenging experiments indicated that BTA degradation was mainly driven by hydroxyl and sulfate radicals in PDS and PMS systems without Cl⁻. However, reactive chlorine species (RCS) significantly boosted the PMS system for BTA degradation in presence of Cl⁻. Variation in pH substantially influenced the PMS system, but not the PDS system, whether in presence and absence of Cl⁻. By LC-MS/MS analysis, forty-two transformation products (TPs) were identified resulting from BTA degradation. Based on the TPs, polymerization, hydroxylation, benzene ring-opening, and carboxylic acid formation were hypothesized to be the main degradation mechanisms in absence of Cl⁻, whereas chlorination, triazole ring-opening, and nitration were the additional degradation steps in presence of Cl⁻. These findings help understand the influence of Cl⁻ on BTA removal rate and degradation pathway in saline wastewater. Moreover, more chlorinated TPs were found in PMS/Cl⁻ system than in PDS/Cl⁻ system, which was also reflected in absorbable organic halides (AOX) and end-product toxicity analyses. The PMS/Cl⁻ process also produced other undesirable by-products, such as chlorates which were not detected in the PDS/Cl⁻ process. This shows that PDS and PMS-based advanced oxidation processes can notably differ in terms of toxic by-product formation. Thus, they need to be critically evaluated before applying for organic pollutant degradation under saline conditions.

A Comparison Study between Wood Flour and Its Derived Biochar for the Enhancement of the Peroxydisulfate Activation Capability of Fe3O4

In this study, both wood flour (WF) and wood flour-derived biochar (WFB) were used as supports for Fe3O4 to activate peroxydisulfate (PDS). The role of different carriers was investigated emphatically from the aspects of catalyst properties, the degradation kinetics of bisphenol A (BPA), the effects of important parameters, and the generation of reactive oxygen species (ROS). Results showed that both WF and WFB could serve as good support for Fe3O4, which could control the release of iron into solution and increase the specific surface areas (SSAs). The WFB/Fe3O4 had stronger PDS activation capability than WF/Fe3O4 mainly due to the larger SSA of WFB/Fe3O4 and the PDS activation ability of WFB. Both radical species (•OH and SO4•−) and non-radical pathways, including 1O2 and high-valent iron-oxo species, contributed to the degradation of BPA in the WFB/Fe3O4–PDS process. Moreover, the WFB/Fe3O4 catalyst also showed stronger ability to control the iron release, better reusability, and higher BPA mineralization efficiency than WF/Fe3O4.

Efficient activation of peroxodisulfate by novel bionic iron-encapsulated biochar: The key roles of electron transfer pathway and reactive oxygen species evolution.

In this study, a novel iron-encapsulated biochar (Fe@BC) was prepared using the biomass cultivated with an iron-containing solution. The iron in Fe@BC showed the phase change from Fe3O4 to α-Fe, and to CFe15.1, with the increase of pyrolysis temperature (500-900°C), and a graphene shell formed on the surface of Fe@BC. In addition, the signals assigned to the π-π*shake up, pyridinic N, graphitic N, and defects of Fe@BC were found to be stronger as the pyrolysis temperature increased. The F4@B9 sample, which was prepared at 900°C, exhibited an excellent performance (98.01%) to activate peroxydisulfate (PDS) for the degradation of 2,4-dichlorophenol. Electron paramagnetic resonanceand chemical quenching experiments revealed that reactive oxygen radicals (ROS) including sulfate radical (•SO4-), hydroxyl radical (•OH), superoxide radical (•O2-), and singlet oxygen (1O2) existed in the F4@B9/PDS system. Furthermore, the micro-electrolysis process facilitated the generation of •O2- (12.35%) and 1O2 (6.49%) compared with the pure PDS system. Density functional theory revealed that, for the F4@B9-activated PDS process, the graphene shell of F4@B9 served as catalytic active sites as well. According to the correlation analysis, the iron specie of CFe15.1 was more favorable for the generation of ROS than α-Fe. Also, π-π*shake up, pyridinic N, graphitic N, and defects participated in the PDS activation. This study provides a new method for the preparation of high-performance catalysts from naturally grown biomass with high iron contents.

Promoted elimination of metronidazole in ferrous ions activated peroxydisulfate process by gallic acid complexation

We applied gallic acid (GA) as the complexing agent to stabilizing the regeneration of Fe2+ during the Fe2+/peroxydisulfate (PDS) Fenton-like reaction for promoting the removal of metronidazole (MTZ). This research evaluated the elimination of MTZ by optimizing the dose of GA and Fe2+ and pH condition. MTZ removal reached 83% at the GA: Fe2+ molar ratio of 1:1 (30 μM) and initial pH 5 and 6.2 after 120 min, and the kinetics showed two degradation phases (kobs1 = 0.09636 for the rapid stage and kobs2 = 0.01056 for the slow stage). The Fe2+ and GA complexes could expand the range of pH applicability and effectively stabilize the regeneration of Fe2+, which ultimately promoted the decontamination of MTZ. Sulfate radical (SO4.-), hydroxyl radicals, and singlet oxygen were proved to exist in this ternary system and contribute to MTZ removal, and SO4.- played the dominant role. Furthermore, the possible pathways and mechanisms for MTZ degradation were proposed, and the simulation result indicated that the toxicity of degradation intermediates of MTZ were declined. The GA assisted Fe2+/PDS system provided an improved promising advanced oxidation process for organic wastewater disposal.

FeNi3 foam as cathode catalyst in electrocatalytic peroxydisulfate system for enhanced Hg0 removal from simulated flue gas

The feasibility of elemental mercury (Hg0) removal from simulated flue gas in electrocatalytic peroxydisulfate (PDS) system employing FeNi3 foam as cathode catalyst was studied for the first time. The electrocatalytic (EC) performance of FeNi3 foam activating PDS process was evaluated to remove Hg0 using Pt anode, FeNi3 cathode, and Na2SO4 electrolyte at room temperature. The results showed that the FeNi3 foam/PDS/EC system was superior to the other removal processes. According to the influence of experimental parameters, it was found that about 94% of Hg0 was removed within 20 min under the conditions of voltage = 2 V, PDS = 1 mM, Na2SO4 = 0.05 M. Theoretical calculations showed that the Ni atom of the FeNi3 cluster would improve its reactivity. The chemical adsorption and hybridization between PDS and FeNi3 had contributed to an efficient production of SO4•− free radical. The high removal efficiency of Hg0 was due to the following assistances: (i) the O2 gas adsorbed on the FeNi3 foam cathode surface was able to generate radicals •O2– and •OH by single electron reduction reaction, (ii) FeNi3 foam catalyst could afford Fe(II) and Ni(II) ions via two electron transfer, activating PDS to produce SO4•−, and (iii) the copresence of Fe and Ni was useful to accelerate the ion cycles of Fe(III)/Fe(II) and Ni(II)/Ni(I), which played a crucial role in FeNi3 foam/PDS/EC system. The novel proposed FeNi3 foam cathode electro-catalyzing PDS system provided a promising prospect in the pollutant control field of Hg0 removal.

Unveiling the enhancement of sulfidation for Fe(IV) production in a sulfidated microscale zero-valent iron activated peroxydisulfate process

Ferryl ion species (Fe(IV)) is considered as an important reactive species in zero-valent iron activated peroxydisulfate (PDS) process that has great potential for decontamination due to its merits. Sulfidation is an effective chemical reaction process to improve the activity of microscale zero-valent iron (mZVI). In this subject, the effect of sulfidation on the production of Fe(IV), and the key reaction pathways of Fe(IV) generation in sulfidated mZVI (S-mZVI)/PDS system are still unclear. In this work, by using methyl phenol sulfoxide as a probe, we found that sulfidation could greatly change the pathway of Fe(IV) generation, in which the heterogeneous process was proposed to play an important role in activating PDS to produce Fe(IV). In comparison, the production of Fe(IV) in mZVI/PDS system was dependent on aqueous Fe(II) released from mZVI corrosion. Further analysis indicated that the improvement of Fe(IV) production caused by sulfidation could be ascribed to the acceleration of Fe(II) release as well as electron transfer. Sulfur species especially S(-II) could participate in the Fe(II)/Fe(III) cycle for Fe(II) regeneration, and underwent oxidation according to X-ray photoelectron spectroscopy analysis. In addition, we investigated the influence of key parameters (initial pH, PDS dosage, S-mZVI dosage) and coexisting anions (Cl−, SO42−, HCO3−) on Fe(IV) production in S-mZVI/PDS system. This study not only distinguishes the interface activation of PDS for Fe(IV) production from the homogeneous process, but also provides a new insight for the sulfidation to enhance the performance of iron-based materials on advanced oxidation processes.

Fe–Mn Oxide Composite Activated Peroxydisulfate Processes for Degradation of p-Chloroaniline: The Effectiveness and the Mechanism

The chemical co-precipitation method was used to prepare magnetically separable Fe–Mn oxide composites, and the degradation of p-chloroaniline (PCA) using MnFe2O4 activated peroxydisulfate (PDS). The MnFe2O4 catalyst exhibited highly catalytic activity in the experiments. XRD, FTIR, SEM and TEM were used to characterize the catalytic materials. MnFe2O4 calcined at 500 °C was more suitable as a catalytic material for PCA degradation. The elevated reaction temperature was beneficial to the degradation of PCA in neutral pH solution. The reaction mechanism of the MnFe2O4 catalyzed oxidative degradation of PCA by PDS was investigated by free radical quenching experiments and XPS analysis. The results showed that sulfate radicals (SO4•−), hydroxyl radicals (•OH) and singlet oxygen (1O2) may all be participated in the degradation of PCA. XPS spectra showed that the electron gain and loss of Mn2+ and Fe3+ was the main cause of free radical generation. The possible intermediates in the degradation of PCA were determined by HPLC-MS, and possible degradation pathways for the degradation of PCA by the MnFe2O4/PDS system were proposed.

Photothermal activation of peroxydisulfate using iron nanoparticles/MXene@polyurethane sponge module for treatment of landfill leachate: From lab to pilot scale

Treatment of landfill leachate and recovery of recycled water in photothermal activation of peroxydisulfate (PDS) process using iron nanoparticles/MXene-coated polyurethane sponge module (Fe NPs/MXene@PU) were investigated from lab to pilot scale for the first time. In the module preparation process, nanoscale zero-valent iron (NZVI) and iron oxides were in situ generated on Ti3C2 MXene surface. Fe NPs/MXene@PU module reached the 147.7 °C interfacial temperature due to the synergistic effect of MXene and in-situ generated Fe NPs. Sulfate radical (SO4•-) and hydroxyl radical (HO•) were generated in photothermal activation of PDS process. Under optimized reaction conditions, almost complete removal of chemical oxygen demand (COD), nitrate nitrogen (NO3–), ammonia nitrogen (NH3-N) and total phosphorus (TP) of landfill leachate was achieved after about 40 d pilot-scale experiment in the open air. The recycled water collected by natural condensation was also purified, which contained ultralow concentrations of COD, NH3-N, NO3–, TP and heavy metals and met the discharge limits of various countries. This study provides an eco-friendly and energy-efficient technology for treatment of landfill leachate and recovery of recycled water.

Effect of peroxydisulfate oxidation catalyzed with ordered mesoporous carbons on controlling ultrafiltration membrane fouling by algal organic matter.

As typical ordered mesoporous carbons (OMCs) materials, CMK-3 and CMK-8 were proposed for catalyzing peroxydisulfate (PDS), and the OMCs/PDS process was combined with membrane filtration to remove algal extracellular organic matter and mitigate membrane fouling. The CMK-3/PDS process achieved substantial reduction of dissolved organic carbon and UV254, followed by CMK-8/PDS. The degradation behavior of fluorescent organics demonstrated the superior performance of OMCs/PDS, while the decomposition of high molecular weight (MW) compounds and generation of lower MW organics were observed. Generally, CMK-3 possessed higher catalytic activity on PDS compared with CMK-8 and powdered activated carbon. The CMK-3/PDS process distinctly decreased the fouling resistances for polyether sulfone and polyvinylidene fluoride membranes, with the reversible resistance reduced by 59.5-83.2% and irreversible resistance declined by 71.7-73.0%. In the meanwhile, CMK-3/PDS prolonged the volumes to the transition period, and postponed the cake layer's generation. The characterization of the membrane morphologies and chemical compositions also showed effective alleviation of fouling. The generated SO4-, OH, O2- and 1O2 as major active oxidation species provided radical as well as non-radical reaction ways for pollutants removal. Overall, our study provides some new ideas for membrane-based combined water purification processes.

Nano- and micro-scale zerovalent iron-activated peroxydisulfate for methyl phenyl sulfoxide probe transformation in aerobic water: Quantifying the relative roles of SO4·−, Fe(IV), and ·OH

Multiple reactive intermediates have been proposed to be involved in peroxydisulfate (PDS) activation by zerovalent iron (ZVI), including sulfate radical (SO4·−) produced via iron-oxide shell mediated electron transfer, ferryl ion species (Fe(IV)) formed from Fe(II)-PDS interaction, and hydroxyl radical (·OH) generated by ZVI aerobic oxygenation. In this study, evolution of the relative role of these intermediates in microscale and nanoscale ZVI (mZVI vs. nZVI) activated PDS processes is comparatively investigated by using a methyl phenyl sulfoxide (PMSO) probe that selectively reacts with Fe(IV) to produce methyl phenyl sulfone (PMSO2). Interestingly, during PMSO transformation by mZVI/PDS process, yields of PMSO2 (η(PMSO2)) exhibit three-stage behavior that they first increase to a maximum (∼80% but lower than 100%) (Stage I) and then plateau for a period (Stage II) followed by a decrease phase (Stage III). Accordingly, the relative role of Fe(IV) in PMSO transformation is unceasingly improved in Stage I and subsequently reaches equilibrium with that of free radicals in Stage II, while it finally decreases in Stage III. Similar η(PMSO2) evolution trends are obtained in nZVI/PDS process, except that the η(PMSO2) increase in Stage I is negligible, possibly due to the exceptional fast nZVI dissolution. It was further clarified by tert-butyl alcohol scavenging assay that, in addition to Fe(IV), the free radical involved in Stages I and II is SO4·−, while ·OH was dominant in Stage III. Moreover, studies on O2 effect reveal that ZVI aerobic oxygenation participates in mZVI corrosion during the entire process, while it is only involved in nZVI corrosion when PDS content is reduced to a low concentration, indicating that the reactivities of PDS and O2 are similar in mZVI corrosion, but differ greatly in nZVI corrosion. Additionally, effects of reactant dose and pH on η(PMSO2) evolution are also explored. Dynamics of the relative role of different reactive oxidants should be taken into account in further applications of ZVI/PDS in situ chemical remediation technology considering their different chemistries.

Investigation of the Performance of Organic Contaminant Degradation by Fe2+/PDS Under Environmentally Relevant pH Conditions

Peroxydisulfate (PDS) activation by Fe2+ has proven to be a promising method to abate emerging organic contaminants by generating reactive oxidation species. Nevertheless, this process may only achieve good decontamination performance under acidic conditions, which has markedly limited its application in real practice. To address this issue, we comprehensively investigated the performance of the Fe2+/PDS process toward some probe contaminants at different pH levels and explored the potential change in reactive oxidative species and the influence of oxygen. Both SO4-· and Fe(Ⅳ) were identified to be involved in the Fe2+/PDS process, and the types of these oxidative species did not change with varying pH values. Although dissolved oxygen could compete with PDS for Fe2+, especially at high pH values, this competition process was not the major reason for the declined performance of the Fe2+/PDS process, since 37.6%-100% of PDS could also be activated with the presence of oxygen. Instead, the overdosing of Fe2+could greatly inhibit carbamazepine removal, indicating that the nonproductive consumption of reactive oxidants by Fe2+should account for the declined performance of Fe2+/PDS under environmentally relevant pH conditions. Accordingly, the feasibility of applying zero-valent iron and sulfidated zero-valent iron was further evaluated, and the formation of corrosion products was characterized using X-ray absorption fine structure spectroscopy. All these findings will improve our understanding about the Fe2+/PDS process and thus facilitate its application.

A comparative study of the degradation of refractory organic matter in MBR effluent from landfill leachate treatment by the microwave-enhanced iron-activated hydrogen peroxide and peroxydisulfate processes

This study applied two advanced oxidation processes dominated by different reactive oxygen species (ROS), microwave-iron-hydrogen peroxide (Microwave/ZVI/H2O2) and microwave-iron-peroxydisulfate (MW Microwave/ZVI/PDS), to the degradation of refractory organic matter in the membrane bioreactor (MBR) effluent from landfill leachate treatment. The two processes were systematically compared according to their degradation efficiencies and transformation mechanisms toward refractory organic matter in MBR effluent. Controlled experiments and an influential factor analysis showed that the total organic carbon (TOC) removal efficiencies of the Microwave/ZVI/H2O2 and Microwave/ZVI/PDS processes were 74.48% and 64.40%, respectively. After treatment by the two processes, fulvic-like substances with a low molecular weight and high fluorescence frequency, and humic-like substances with a large molecular weight, stable chemical structure, and high aromaticity were substantially degraded. In addition, the Microwave/ZVI/H2O2 process had a better TOC removal efficiency than the Microwave/ZVI/PDS process over a wider pH range (3−11), which was mainly attributed to the different dominant ROS in the two processes. Both Fe3O4 and FeOOH were found in the reacted ZVI of the two processes, and the reaction mechanisms included Fenton-like reactions and adsorption-precipitation by iron (hydro)oxides, which were promoted by microwave irradiation. This study provided a theoretical reference for the efficient treatment of MBR effluent.

Degradation of Ibuprofen by the Electro/Fe3+/Peroxydisulfate Process: Reactive Kinetics, Degradation Products and Mechanism

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is one of the most widely used and frequently detected pharmaceuticals and personal care products in water bodies. This study examined the IBU degradation in aquatic solutions via ferric ion activated peroxydisulfate (PDS) coupled with electro-oxidation (EC/Fe3+/PDS). The degradation mechanisms involved three synergistic reactions in the EC/Fe3+/PDS system, including: (1) the electro-oxidation; (2) SO4•− generated from the activation of PDS by ferrous ions formed via cathodic reduction; (3) SO4•− generated from the electron transfer reaction. The radical scavenging experiments indicated that SO4•− and •OH dominated the oxidation process. The effects of the applied current density, PDS concentration, Fe3+ dosage, initial IBU concentration and initial pH as well as inorganic anions and humic acid on the degradation efficiency, were studied, and the degradation process of IBU followed the pseudo-first-order kinetic model. About 99.37% of IBU was removed in 60 min ((Fe3+ concentration) = 2.0 mM, (PDS concentration) = 12 mM, (initial IBU concentration) = 30 mg/L, current density = 15 mA/cm2, initial pH = 3). Finally, seven intermediate compounds were identified and probable IBU degradation pathways in the EC/Fe3+/PDS system were speculated.