Pyrite enables persulfate activation for efficient atrazine degradation

Efficient removal of naphthenic acids from real petroleum wastewater by natural pyrite activated persulfate system

The petroleum wastewater (PWW) contains a diverse range of recalcitrant organic contaminants. Of particular concern is the removal of naphthenic acids (NAs) due to the high toxicity and persistence. Persulfate (PS) based oxidation processes have shown promising in treating refractory wastewater, while the high costs of prepared catalysts limited their widespread implementation. This study aims to develop a cost-effective natural pyrite activated PS system for PWW treatment. The removal of NAs by pyrite/PS system was initially investigated. More than 90% of cyclohexanoic acid (CHA), a model NA, was removed in pyrite/PS system (2.0 g/L pyrite, 4.0 mM PS) at initial pH of 3-11. Scavenging experiments revealed that Fe(II) on pyrite surface was the reactive site for PS activation to generate reactive species, including sulfate radical (SO4·-), Fe(IV) and hydroxyl radical (·OH) for CHA degradation. Reactions of Fe(III) with S helped restore Fe(II) and enhance PS activation, resulting in the sustained catalytic activity of pyrites over five cycles. Cl-, SO42- and NO3- below 10 mM had minimal impact on CHA degradation in pyrite/PS system. However, over 1 mM of HCO3- inhibited 80% of CHA removal due to the buffer effect to maintain the high solution pH. Removing HCO3- from real PWW restored the removal of CHA and of total organic carbon (TOC) to over 90% and 71.3% in pyrite/PS system, respectively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results indicated that O2‒6 species including NAs were primarily eliminated through mineralization and oxygen addition. Besides, O3-5S, NO3-5S and N3O2‒4 species were the most susceptible to oxidation in PWW, resulting in the increase of the oxidation level (i.e., O/Cwa) from 0.41 to 0.56 after treatment. This study provides valuable insights into the treatment of NAs in real PWW, and potential application of natural minerals in the treatment of industrial wastewater.

Enhanced degradation of reactive black 5 via persulfate activation by natural bornite: Influencing parameters, mechanism and degradation pathway

Reactive black 5 (RBk5) is a refractory azo dye that constitutes a serious threat to the environment and humans. Herein, natural bornite (Nbo) was utilized to activate persulfate (PDS) for the RBk5 removal. The particle size of the Nbo catalyst was optimized and the RBk5 degradation rate constant that responded positively to the particle size of the Nbo catalyst was exhibited. Then, the operational factors affecting RBk5 removal were comprehensively investigated. With the addition of 1.5 g·L^-1 Nbo and 1.5 mM PDS, 99.05% of the RBk5 (20 mg·L^-1) was removed in 150 min compared with 0.46% removal with PDS only, which was caused by the additional reactive oxygen species (ROS) produced by the synergistic action of Fe-Cu bimetallic metal and reductive sulfur species. The Nbo catalyst presented high stability and reusability toward RBk5 removal. Identification of reactive oxygen species revealed that SO₄^·-, ·OH, O₂^·- and ¹O₂ collectively participated in RBk5 removal. Additionally, a possible degradation pathway for RBk5 was proposed, including cleavage of the azo, C-S and S-O bonds, hydroxylation, hydrolyzation, direct oxidation and other pathways. This work developed a highly effective and low-cost natural mineral-based bimetallic sulfide material for PDS activation for the degradation of contaminants and environmental remediation.

Original nanostructured bacterial cellulose/pyrite composite: Photocatalytic application in advanced oxidation processes

The development of an original catalytic composite of bacterial cellulose (BC) and pyrite (FeS₂) for environmental application was the objective of this study. Nanoparticles of the FeS₂ were synthesized from the hydrothermal method and immobilized on the BC structure using ex situ methodology. In the BC, the FTIR and XRD analyzes showed the absorption band associated with the Fe-S bond and crystalline peaks attributed to the pyrite. Thus, the immobilization of the iron particles on the biopolymer was proven, producing the composite BC/FeS₂. The use of the SEM technique also ratifies the composite production by identifying the fibrillar structure morphology of the cellulose covered by FeS₂ particles. The total iron concentration was 54.76 ± 1.69 mg L^-1, determined by flame atomic absorption analysis. TG analysis and degradation tests showed respectively the thermal stability of the new material and its high catalytic potential. A multi-component solution of textile dyes was used as the matrix to be treated via advanced oxidative processes. The composite acted as the catalyst for the Fenton and photo-Fenton processes, with degradations of 52.87 and 96.82%, respectively. The material proved stability by showing low iron leaching (2.02 ± 0.09 and 2.11 ± 0.11 mg L^-1 for the respective processes). Thus, its high potential for reuse is presumed, given the remaining concentration of this metal in the BC. The results showed that the BC/FeS₂ composite is suitable to solve the problems associated with using catalysts in suspension form.

Efficient degradation of atrazine through in-situ anchoring NiCo2O4 nanosheets on biochar to activate sulfite under neutral condition

Sulfite (S(IV)) is a promising substitute for sulfate radical-based advanced oxidation processes. Here, a composite of in-situ anchoring NiCo₂O₄ nanosheets on biochar (BC) was firstly employed as a heterogeneous activator for sulfite (NiCo₂O₄@BC-sulfite) to degrade atrazine (ATZ) in the neutral environment. The synergistic coupling of BC and NiCo₂O₄ endows the resulting composite excellent catalytic activity. 82% of the degradation ratio of ATZ (1 mg/L) could be achieved within 10 min at initial concentrations of 0.6 g/L NiCo₂O₄@BC, 3.0 mmol/L sulfite in neutral environment. When further supplementing sulfite into the system at 20 min (considering the depletion of sulfite), outstanding degradation efficiency (∼ 100%) were achieved in the next 10 min without any other energy input by the NiCo₂O₄@BC-sulfite system. The features of the prepared catalysts and the effects of some key parameters on ATZ degradation were systematically examined. A strong inner-sphere complexation (Co²⁺/Ni²⁺-SO₃^2-) was explored between sulfite and the metal sites on the NiCo₂O₄@BC surface. The redox cycle of the surface metal efficiently mediated sulfite activation and triggered the series radical chain reactions. The generated radicals, in particular the surface-bound radicals were involved in ATZ degradation. High performance liquid chromatography-tandem mass spectrometry (LC-MS) technique was used to detect the degradation intermediates. Density functional theory (DFT) calculations were performed to illustrate the possible degradation pathways of ATZ. Finally, an underlying mechanism for ATZ removal was proposed. The present study offered a low-cost and sustainable catalyst for sulfite activation to remove ATZ in an environmentally friendly manner from wastewater.

New insight into the activation mechanism of hydrogen peroxide by greigite (Fe3S4) for benzene removal: The combined action of dissolved and surface bounded ferrous iron

Iron sulfides have attracted growing concern in heterogeneous Fenton reaction. However, the structure of iron sulfides is different from that of iron oxides and how the structures affect the activation property of hydrogen peroxide (H₂O₂) remains unclear. This study investigated benzene removal through the activation of H₂O₂ by the synthesized magnetite (Fe₃O₄) and greigite (Fe₃S₄). The structures of Fe₃O₄ and Fe₃S₄ were characterized by XRD and EPR, the electron transfer properties of Fe₃O₄ and Fe₃S₄ were analyzed by electrochemical workstation, XPS and DFT. It is revealed that the effective benzene removal rate of 88.86％ in the Fe₃S₄/H₂O₂ was achieved, which compared to 15.58％ obtainable from the Fe₃O₄/H₂O₂, with the apparent rate constant in the Fe₃S₄/H₂O₂ being approximately 65 times over that in the Fe₃O₄/H₂O₂. The better H₂O₂ activation by Fe₃S₄ was attributed to the significant roles of S (-II) and S vacancies in regulating the dissolution of ferrous iron ions, thus generating abundant free •OH radical. In addition, surface bounded ferrous iron of Fe₃S₄ could transfer more electrons to H₂O₂ and O₂ to generate more surface bounded •OH and •O₂^-. This study revealed the combined action of dissolved and surface bounded ferrous iron of greigite on H₂O₂ activation, and provides an efficient heterogeneous H₂O₂ activator for the remediation of organic contaminants in groundwater.

FeMoS2 micoroparticles as an excellent catalyst for the activation of peroxymonosulfate toward organic contaminant degradation

The FeMoS₂ catalyst for activating peroxymonosulfate (PMS) is a promising pathway for removing organic pollutants in wastewater, however, the dominant FeS₂ phases and sulfur (S) vacancies in it are little involved. Herein, for the first time, novel bimetallic FeMoS₂ microparticles were synthesized by a simple method and then applied for PMS activation for degrading organic pollutants. The catalysts were characterized by several techniques, including X-ray diffraction and X-ray photoelectron spectroscopies. The results revealed that new FeMoS₂ microparticles containing S vacancies in the main FeS₂ phases were obtained. FeS₂ and S vacancies were found to play important roles for activating PMS by radical and nonradical pathways. More Fe²⁺ and Mo⁴⁺ were formed in the presence of S vacancies, which offered a new strategy for exploring novel heterogeneous catalysts in the activation of PMS for environmental remediation.

Real-Time Monitoring of the Atrazine Degradation by Liquid Chromatography and High-Resolution Mass Spectrometry: Effect of Fenton Process and Ultrasound Treatment

High resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (uHPLC) to monitor atrazine (ATZ) degradation process of Fenton/ultrasound (US) treatment in real time. Samples were automatically taken through a peristaltic pump, and then analysed by HPLC-HRMS. The injection in the mass spectrometer was performed every 4 min for 2 h. ATZ and its degradation metabolites were sampled and identified. Online Fenton experiments in different equivalents of Fenton reagents, online US experiments with/without Fe²⁺ and offline Fenton experiments were conducted. Higher equivalents of Fenton reagents promoted the degradation rate of ATZ and the generation of the late-products such as Ammeline (AM). Besides, adding Fe²⁺ accelerated ATZ degradation in US treatment. In offline Fenton, the degradation rate of ATZ was higher than that of online Fenton, suggesting the offline samples were still reacting in the vial. The online analysis precisely controls the effect of reagents over time through automatic sampling and rapid detection, which greatly improves the measurement accuracy. The experimental set up proposed here both prevents the degradation of potentially unstable metabolites and provides a good way to track each metabolite.

Benzoquinone-assisted heterogeneous activation of PMS on Fe3S4 via formation of active complexes to mediate electron transfer towards enhanced bisphenol A degradation

Benzoquinone (BQ) is of great significance for enhancement of contaminants degradation in the homogeneous oxidation system of peroxymonosulfate (PMS). However, the role of BQ in the heterogeneous activation of PMS for contaminants oxidation is still not clear. Herein, this work reported that the addition of BQ into the Fe₃S₄/PMS system could effectively enhance the degradation and mineralization of bisphenol A (BPA). Mechanistic study uncovered that the BQ and PMS would form active complexes (BQ-PMS*) on the surface of Fe₃S₄ and the excited BQ-PMS* can oxidize the BPA. To be specific, the electron of BPA was extracted by BQ-PMS* and then transfer to the surface of Fe₃S₄. The surface electron can induce the change of valence state of S and Fe elements, which can trigger the degradation of BPA and inhibit the decomposition of BQ itself. To the best of our knowledge, it is the first time to unveil the positive role of BQ in the heterogeneous activation of PMS, which may shed new light on the establishment of high-efficient PMS-based oxidation technology for remediation of organic pollutant.

Degradation of ciprofloxacin by persulfate activated with pyrite: mechanism, acidification and tailwater reuse

Residues of ciprofloxacin (CIP) in the environment pose a threat to human health and ecosystems. This study investigated the degradation of CIP by persulfate (PS) activated with pyrite (FeS₂). Results showed that when [CIP] = 30 μM, [FeS₂] = 2.0 g L^-1, and [PS] = 1 mM, the CIP removal rate could reach 94.4% after 60 min, and CIP mineralization rate reached 34.9%. The main free radicals that degrade CIP were SO₄˙^- and HO˙, with contributions of 34.4% and 35.7%, respectively. Additionally, compared to the control (ultrapure water), CIP in both tap water and river water was not degraded. However, acidification could eliminate the inhibition of CIP degradation in tap water and river water. Furthermore, acidic tailwater from CIP degradation could be utilized to adjust the pH of untreated CIP, which could greatly promote the degradation of CIP and further reduce disposal costs. The reaction solution was not significantly biotoxic and three degradation pathways of CIP were investigated. Based on the above results and the characterization of FeS₂, the mechanism of CIP degradation in the FeS₂/PS system was that FeS₂ activated PS to generate Fe(iii) and SO₄˙^-. The sulfide in FeS₂ reduced Fe(iii) to Fe(ii), thus achieving an Fe(iii)/Fe(ii) cycle for CIP degradation.

BCOFGs loaded with nano-FexSy for the catalytic degradation of QNC: Contribution and mechanism of OFGs for reductive iron regeneration

Biochar currently served as the support for dispersed metal nanoparticles and cooperated with pyrite to generate more reactive radicals in organic pollution degradation system. But the mechanism of interaction between biochar and pyrite has not been elucidated. In this paper, biochar with oxygen-containing functional groups (OFGs) served as a stable dispersant to prepare nano-Fe_xS_y loaded biochar materials (BC_OFGs@nano-Fe_xS_y). BC_OFGs coordinated with nano-Fe_xS_y to overcome its drawbacks, boosting QNC removal efficiency from 28.64% to 100%. The XPS and the linear sweep voltammetry (LSV) results revealed higher Fe(II) content and higher electron transfer rate on used BC_OFGs@nano-Fe_xS_y, further validating that hydroxyl functional groups on biochar surface provided electrons to Fe(III) to achieve efficient Fe(II)/Fe(III) cycling. Based on comparative experiments and studies on the roles of iron, S(II) species and OFGs, we clearly revealed that OFGs on biochar materials surface coordinated with nano-Fe_xS_y to catalyze the degradation of QNC. The degradation efficiency of BC_OFGs@nano-Fe_xS_y for QNC was still as high as 91.39% after five cycles, providing full demonstrations that OFGs and S(II) as the abundant electron donor coordinated with Fe species for QNC catalytic degradation and further enhanced the catalytic performance and stability of nano-Fe_xS_y.

FeC2O4•2H2O enables sustainable conversion of hydrogen peroxide to hydroxyl radical for promoted mineralization and detoxification of sulfadimidine

Safe treatment of antibiotics requires efficient removal of both antibiotics and their degraded intermediates. In this study, we demonstrate that FeC₂O₄•2H₂O enables the more sustainable conversion of H₂O₂ to ^•OH than commonly used FeSO₄•7H₂O, promoting the detoxification of a typical antibiotic sulfadimidine. It was found that the FeC₂O₄/H₂O₂ system could completely degrade 250 mg L^-1 of sulfadimidine within 40 min at pH 3.0, along with decreasing the contents of chemical oxygen demand and total organic carbon by 295.0 and 33.5 mg L^-1, respectively, more efficient than those in a classical Fenton system (FeSO₄/H₂O₂). Analysis of sulfadimidine degraded intermediates and toxicity evaluation suggested that the FeC₂O₄/H₂O₂ treatment could more effectively decrease the overall toxicity of the sulfadimidine solution than the FeSO₄/H₂O₂ counterpart. The sustainability of FeC₂O₄•2H₂O in H₂O₂ conversion to ^•OH was attributed to its controlled release of Fe²⁺ into the solution to prevent the quenching of ^•OH by excessive Fe²⁺, as well as the simultaneous release of C₂O₄^2- to complex with Fe²⁺ and Fe³⁺, which could inhibit iron sludge formation and accelerate Fe³⁺/Fe²⁺ redox cycle. This study provides a promising Fenton system for the safe treatment of antibiotics and sheds light on the potential of FeC₂O₄•2H₂O in environmental remediation.

Degradation of Residual Herbicide Atrazine in Agri-Food and Washing Water

Atrazine, an herbicide used to control grassy and broadleaf weed, has become an essential part of agricultural crop protection tools. It is widely sprayed on corn, sorghum and sugar cane, with the attendant problems of its residues in agri-food and washing water. If ingested into humans, this residual atrazine can cause reproductive harm, developmental toxicity and carcinogenicity. It is therefore important to find clean and economical degradation processes for atrazine. In recent years, many physical, chemical and biological methods have been proposed to remove atrazine from the aquatic environment. This review introduces the research works of atrazine degradation in aqueous solutions by method classification. These methods are then compared by their advantages, disadvantages, and different degradation pathways of atrazine. Moreover, the existing toxicological experimental data for atrazine and its metabolites are summarized. Finally, the review concludes with directions for future research and major challenges to be addressed.

Activation of Persulfate for Degrading Tetracycline Using the Leaching Residues of the Lead-Zinc Flotation Tailing

Inappropriate disposal of leaching residues from the lead-zinc tailings recovery process may result in environmental pollution. Its recycling and reuse remain a prevalent topic in environmental science and technology. It was roasted to prepare leaching residues-based materials (TLRS) in this work, and the TLRS were creatively used as the catalyst to active sodium persulfate (PS) to degrade organic pollutants. Degradation of tetracycline using the TLRS–PS system was evaluated, and the treating parameters were optimized. Roasting resulted in the exposure of active sites on TLRS surface, in which transition metals can donate electrons to PS to form SO₄^·−. SO₄^·− can further react with OH⁻ to form ·OH. Formation of these radicals was confirmed by both quenching experiments and EPR analysis. Under optimized conditions, 85% of the TC can be degraded in 3.0 h, and ~50% of degraded TC was mineralized to CO₂ and H₂O. The performance of TLRS barely changed after four reuses, suggesting the chemical stability of TLRS. The presence of dissolved substance in the water matrix could weaken the performance of the TLRS–PS system. A mechanism of TC degradation was proposed based on the experimental results and literature. These preliminary results provide us new insight on the reuse of lead-zinc flotation tailings.

Degradation of methyl orange by pyrite activated persulfate oxidation: mechanism, pathway and influences of water substrates

Degradation mechanism of methyl orange (MO), a typical azo dye, with pyrite (FeS₂) activated persulfate (PS) was explored. The results showed that when the initial concentration of MO was 0.1 mM, FeS₂ was 1.6 g/L and PS was 1.0 mM, the removal rate of MO could reach 92.9% in 150 min, and the removal rate of total organic carbon could reach 14.1%. In addition, both pH ≤ 2 and pH ≥ 10 could have an inhibitory effect in the FeS₂/PS system. Furthermore, Cl^- and low concentrations of HCO^-₃ had little effect on the degradation of MO with FeS₂/PS. However, H₂PO^-₄ and high concentrations of HCO^-₃ could inhibit the degradation of MO in the system. Besides, MO in river water and tap water were not degraded in FeS₂/PS system, but acidification (pH = 4) would greatly promote the degradation. In addition, the removal rate of MO with FeS₂/PS could still reach about 90% after five cycles of FeS₂. Furthermore, the intermediates and possible degradation pathways were speculated by LC-MS, and the degradation mechanism of MO by FeS₂/PS was that the cycle of Fe(III)/Fe(II) could continuously activate persulfate to produce SO₄^•-. The results could provide technical support for azo dye degradation in the FeS₂/PS system.

A novel preparation process of straw-based iron material for enhanced persulfate activation of reactive black 5 degradation

In this study, a new straw-iron composite material (ST@Fe) was synthesized through impregnation and freeze-drying process for persulfate (PS) activation to degrade reactive black 5 (RB5). Scanning electron microscope, Brunauer-Emmett-Teller, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy confirmed that straw owns huge pore structure and varieties of organic functional groups, including hydroxyl carboxyl groups, which could effectively adsorb and complex iron ions. The interaction between the active iron particles in ST@Fe and straw generated Fe²⁺ for PS activation, effectively degrading over 94.80% of RB5 at an initial concentration of 20 ppm in 100 min with a specific degradation capacity of 18.97 min^-1 per unit of iron ions. ST@Fe/PS system demonstrated high tolerance in a wide initial pH range, which could gradually attack the RB5 molecular structure and significantly reduce the mineralization of water. Quenching experiments and electron paramagnetic resonance demonstrated the efficient generation of ROS including sulfate radicals, hydroxyl radicals, and singlet oxygen, and confirmed the dominance of sulfate radicals in the degradation process. The continuous degradation capacity and reusability of ST@Fe were also evaluated, which proved that the contaminant could be effectively degraded even after multiple cycles in the simulated textile wastewater, indicating its potential for use in practical remediation. This work provided a new method for the preparation of modified functional materials for the degradation of organic pollutants in textile wastewater and posed a novel strategy for the utilization of waste biomass.

Effective degradation of Direct Red 81 using FeS-activated persulfate process

As a burgeoning advanced oxidation process (AOP), heterogeneous activation of persulfate (PS) for synthetic refractory contaminants decontamination has recently received much attention. In this study, FeS was selected as a heterogeneous PS activator to facilitate the degradation of a typical recalcitrant contaminant of diazo dye Direct Red 81 (DR 81). The results showed that approximately 95% of 0.03 mM DR 81 was removed within 60 min with FeS and PS doses of 1.5 × 10^-3 M. The efficient decomposition of DR 81 by the FeS/PS system was assumed to be mainly attributed to the highly reactive SO₄^-• and •OH, which was related to PS cleavage by both dissolved Fe²⁺ leached from FeS and Fe²⁺ bound on the FeS surface. Except for strongly alkaline conditions, DR 81 decolorations by FeS/PS were insignificantly affected by operational parameters such as temperature, initial solution pH, and rotate speed. Meanwhile, the presence of five inorganic anions being studied had distinct impacts on DR 81 degradation and followed a strict order of NO₃^- < Cl^- < SO₄^2- < CO₃^2- < PO₄^3-. However, FeS/PS system was highly adaptable, and FeS, which is used as a PS activator was more stable. GC/MS and TOC data revealed that thorough mineralization of DR 81 by PS/FeS in an initial fast reaction phase to transform DR 81 to aromatic intermediates, followed by a slow reaction phase that mineralized these organic intermediates into carboxylic acids and carbon dioxide through further oxidation.

Peroxymonosulfate (PMS) activation by mackinawite for the degradation of organic pollutants: Underappreciated role of dissolved sulfur derivatives

The internal Fe²⁺/Fe³⁺ cycle is important for peroxymonosulfate (PMS) activation by iron-based materials to produce the reactive oxidative species (ROS) for the breakdown of organic contaminants. Previous studies have focused on the contribution of heterogeneous sulfur species to the Fe²⁺/Fe³⁺ cycle such as lattice S(-II) and surface SO₃^2- of iron sulfides. In this study, we found that the dissolved S(-II) from mackinawite (FeS) had a substantial contribution to the Fe²⁺/Fe³⁺ cycle. Furthermore, the oxidation intermediates of the dissolved S(-II) such as S₂O₃^2- and SO₃^2- ions could convert Fe³⁺ to Fe²⁺ in solution. The elimination of target organic pollutant bisphenol A (BPA) derived from PMS activation triggered by the dissolved Fe²⁺ might be enhanced by the equivalent dissolved S(-II) in the FeS/PMS system. These results revealed that previous studies underestimated the significance of PMS activation by dissolved Fe²⁺ of iron sulfides to organic pollutant degradation. Moreover, SO₄^•- and •OH were more likely to be the main ROS for BPA degradation in the FeS/PMS system compared with FeO²⁺. Considering that the metal sulfides have been widely used to activate PMS, H₂O₂ and peroxydisulfate, this study offers a new perspective on the function of sulfur in these advanced oxidation processes.

Pyrite-mediated advanced oxidation processes: Applications, mechanisms, and enhancing strategies

Proper treatment of wastewater is one of the key issues to the sustainable development of human society, and people have been searching for high-efficiency and low-cost methods for wastewater treatment. This article reviews recent studies about pyrite-mediated advanced oxidation processes (AOPs) in removing refractory organics from wastewater. The basic information of pyrite and its characteristics for AOPs are first introduced. Then, the performance and mechanisms of pyrite-mediated Fenton oxidation, electro-Fenton oxidation, and persulfate oxidation processes are carefully reviewed and presented. Natural pyrite is an abundant low-cost heterogeneous catalyst for AOPs, and the slow release of Fe²⁺ and the self-regulation of solution pH are highlighted characteristics of pyrite-mediated AOPs. In AOPs, the interaction between Fe³⁺ and pyrite facilitates the Fe²⁺ regeneration and the Fe²⁺/Fe³⁺ cycle. Making pyrite into nanoparticles, assisting by ultrasound and light irradiation, and adding exogenous Fe³⁺, organic chelating agents, or biochar is effective to enhance the performance of pyrite-mediated AOPs. Based on the analyses of those pyrite-mediated AOPs and their enhancing strategies, the future development directions are proposed in the aspects of toxicity research, mechanism research, and technological coupling.

Pyrite-activated persulfate oxidation and biological denitrification for effluent of biological landfill leachate treatment system

The feasibility of pyrite as catalysts in the persulfate oxidation and electron donor for subsequent bacterial denitrification was investigated. The results demonstrated that pyrite-activated persulfate oxidation could efficiently degrade the organic matter in the effluent of biological landfill leachate treatment system, and COD removal efficiency of about 45% was achieved at the optimum parameters: pH = 6, pyrite dosage = 9.28 mM, dimensionless oxidant dose = 0.25. Among the dissolved organic matter, hydrophobic dissolved organic carbon (HO DOC), humic acids and building blocks were the main components. After the pyrite-activated persulfate oxidation, humic acids and HO DOC were primarily degraded, followed by building blocks, while low molecular weight neutrals were probably the degradation products. In the subsequent biological process, nitrate reduction was satisfactorily accomplished with autotrophic denitrification as the main pathway. When the influent nitrate concentration was about 180 mg L^-1, the effluent nitrate concentration was stable below 20 mg L^-1 with the nitrogen removal rate of about 108 mg L^-1 d^-1. To sum up, the pyrite-activated persulfate oxidation and the following biological denitrification was a feasible application in the effluent of biological landfill leachate treatment system.

Activation of peroxydisulfate by ball-milled α-FeOOH/biochar composite for phenol removal: Component contribution and internal mechanisms

Persulfate-based advanced oxidation process is considered as a promising technology for the degradation of phenol, where efficient, cost effective, and green methods with high peroxydisulfate (PS) activation capacity is of increasing demand. In this work, an in-situ liquid phase precipitation combined with ball milling method was applied for the synthesized of α-FeOOH/biochar, as be the PS activator for phenol degradation. Results showed that the ball-milled α-FeOOH and red pine wood biochar prepared at 700 °C (BM-α-FeOOH/PBC700) exhibited the highest catalytic property with PS for phenol oxidation (a phenol removal rate of 100%), compared with the BM-α-FeOOH (16.0%) and BMPBC700 (66.3%). The presence of intermediate products such as hydroquinone and catechol, and total organic carbon (TOC) removal rate (88.9%) proved the oxidation of phenol in the BM-α-FeOOH/PBC700+PS system. The characterization results showed that the functional groups (e.g., CO, C-O, Fe-O, and Si-O), the dissolved organic matter (DOM) in biochar, the loading of Fe element, and higher degree of graphitization and defect structures, contributed to the activation of PS to form free radicals (i.e., SO₄^·-, ·OH, ·O₂^-, and h_VB⁺) for phenol oxidation, of which, SO₄·^- and ·OH account for 72.1% of the phenol removal rate. The specific contribution to the PS activation for phenol oxidation by each part of the materials was calculated based on the "whole to part" experiment. The contribution of DOM, acid-soluble substance, and carbon matrix and basal part in BM-α-FeOOH/PBC700 were 6.0%, 40.9%, and 53.1%, respectively. The reusability experiments of BM-α-FeOOH/PBC700 demonstrated that the composite was relatively stable after four cycles of reuse. Among three co-existing anions (NO₃^-, Cl^-, and HCO₃^-), HCO₃^- played the most significant inhibition effects on phenol removal through reducing the phenol removal rate from 89.6% to 77.9%. This work provides guidance for the design of high active and stable carbon materials that activate PS to remove phenol.

Sulfite activation by oxidized pyrite for dye degradation assisted by oxygen

Fe(iii) on the surface of pyrite, instead of Fe(ii), acted as the active site of sulfite activation.

Fe(II) Redox Chemistry in the Environment

Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.

Decolorization of azo dyes in a heterogeneous persulfate system using FeS as the activator

Textile effluents containing synthetic refractory azo dyes are one of the most important sources of water pollution. However, these kinds of refractory organic pollutants did not resist a persulfate (PS) oxidation process which was correctly activated. In this study, PS was activated by ferrous sulfide (FeS) in a heterogeneous system to break down azo dyes wastewater. The results showed that all five selected azo dyes were efficiently broken down using the PS/FeS system, except for DY 12, and more than 95% of azo dyes were decolored within 60 minutes. The decolorization efficiency of DR 81 in the PS/FeS system was comparable to PS activated with heat (60 °C) or Fe²⁺, and was slightly superior to Fe⁰ powders under the same conditions. Quenching studies indicated that both SO4^-• and •OH were formed in the FeS surface and diffused into the solution to facilitate the successive transformation of DR 81, the •OH reaction with DR 81 might the crucial reaction. The coexisting chelating agents in real azo dye effluents at high concentrations had a negative influence on azo dye decolorization by PS/FeS. However, the superior factor of the PS/FeS system was the regenerability and reusability of the heterogeneous catalyst.

Iron-based persulfate activation process for environmental decontamination in water and soil

Sulfate radical based advanced oxidation processes have been extensively studied for the degradation of environmental contaminants. Iron-based materials such as ferrous, ferric, ZVI, iron oxides, sulfides etc., and various natural iron minerals have been explored for activating persulfate to generate sulfate radicals. In this review, an overview of different iron activated persulfate systems and their application in the removal of organic pollutants and metals in water and soil are summarised. The chemistry behind the activation of persulfate by homogenous and heterogeneous iron-based materials with/without the assistance of electrochemical techniques are also discussed. Besides, the soil decontamination by iron persulfate system and a brief discussion on the ability of the persulfate system to reduce metals presence in wastewater are also summarised. Finally, future research prospects, believed to be useful for all researchers in this field, based on up to date research progress is also given.

Modeling and simulation of atrazine biodegradation in bacteria and its effect in other living systems

Atrazine is the most commonly used herbicide worldwide in the agricultural system. The increased environmental concentration of the atrazine showed the toxic effects on the non-target living species. Biodegradation of the atrazine is possible with the bacterial systems. The present study investigated biodegradation potential of atrazine degrading bacteria and the impact of atrazine on environmental systems. Model of atrazine fate in ecological systems constructed using the cell designer. The used model further analyzed and simulated to know the biochemistry and physiology of the atrazine in different cellular networks. Topological analysis of the atrazine degradation confirmed the 289 nodes and 300 edges. Our results showed that the overall biomagnification of the atrazine in the different environmental systems. Atrazine is showing toxic effects on humans and plants, whereas degraded by the bacterial systems. To date, no one has analyzed the complete degradation and poisonous effects of the atrazine in the environment. Therefore, this study is useful for overall system biology based modeling and simulation analysis of atrazine in living systems.Communicated by Ramaswamy H. Sarma.