Photo-Fenton like degradation of catechol using persulfate activated by UV and ferrous ions: Influencing operational parameters and feasibility studies

Activating peroxymonosulfate with Fe-doped biochar for efficient removal of tetracycline: Dual action of reactive oxygen species and electron transfer

If pharmaceutical wastewater is not managed effectively, the presence of residual antibiotics will result in significant environmental contamination. In addition, inadequate utilization of agricultural waste represents a squandering of resources. The objective of this research was to assess the efficacy of iron-doped biochar (Fe-BC) derived from peanut shells in degrading high concentrations of Tetracycline (TC) wastewater through activated peroxymonosulfate. Fe-BC demonstrated significant efficacy, achieving a removal efficiency of 87.5% for TC within 60 min without the need to adjust the initial pH (20 mg/L TC, 2 mM PMS, 0.5 g/L catalyst). The degradation mechanism of TC in this system involved a dual action, namely Reactive Oxygen Species (ROS) and electron transfer. The primary active sites were the Fe species, which facilitated the generation of SO4•-, •OH, O2•-, and 1O2. The presence of Fe species and the C=C structure in the Fe-BC catalyst support the electron transfer. Degradation pathways were elucidated through the identification of intermediate products and calculation of the Fukui index. The Toxicity Estimator Software Tool (T.E.S.T.) suggested that the intermediates exhibited lower levels of toxicity. Furthermore, the system exhibited exceptional capabilities in real water and circulation experiments, offering significant economic advantages. This investigation provides an efficient strategy for resource recycling and the treatment of high-concentration antibiotic wastewater.

Degradation of Ampicillin with antibiotic activity removal using persulfate and submersible UVC LED: Kinetics, mechanism, electrical energy and cost analysis

Effective water treatment to remove antibiotics and its activity from contaminated water is urgently needed to prevent antibiotic-resistant bacteria (ARB) emergence. In this study, we investigated degradation of Ampicillin (AMP), an extensively used β-lactam antibiotic, using submersible Ultraviolet C Light Emitting Diode (λmax = 276 nm) irradiation source, and Persulfate (UVC LED/PS system). Pseudo first order rate constant (kobs) for degradation of AMP (1 ppm) by UVC LED/PS system was determined to be 0.5133 min-1 (PS = 0.2 mM). kobs value at pH 2.5 (0.7259 min-1) was found to be higher than pH 6.5 (0.5133 min-1) and pH 12 (0.1745 min-1). kobs value for degradation of AMP in deionized water spiked with inorganic anions (Cl-=0.5369 min-1,SO42-=0.4545 min-1, NO3-=0.1526 min-1, HCO3-=0.0226 min-1), in real tap water (0.1182 min-1) and simulated ground water (0.0372 min-1) were presented. Radical scavenging experiment reveal involvement of sulfate radical anion and hydroxyl radical in UVC LED/PS system. EPR analysis confirms the generation of sulfate radical anion and hydroxyl radical. Importantly, 74% reduction of total organic carbon (TOC) occurred within 60 min of AMP treatment by UVC LED/PS system. Seven degradation by-products were identified by high resolution mass spectrometry, and degradation pathways were proposed. Antibacterial activity of AMP towards Bacillus subtilis and Staphylococcus aureus was completely removed after UVC LED/PS treatment. ECOSAR model predicted no very toxic degradation by-products generation by UVC LED/PS system. Electrical Energy per order (EEo) and cost of UVC LED/PS system were determined to be 0.9351 kW/m3/order and ₹ 7.91/m3 ($ 0.095/m3 or € 0.087/m3), respectively. Overall, this study highlights, UVC LED/PS system as energy efficient, low-cost, and its potential to emerge as sulfate radical anion based advanced oxidation process (AOP) to treat water with antibiotics.

Persulfate-assisted heterogeneous photocatalytic degradation of furfural from aqueous solutions using TiO2-ZnO/biochar composite

This study evaluated the performance of TiO2-ZnO/biochar as activator of persulfate (PS) for degradation of furfural. After the successful synthesis of the catalyst, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) methods were used to investigate the properties of TiO2-ZnO/biochar. The findings of this research suggests that under optimal conditions (pH = 3, catalyst dosage = 1 g/L, persulfate concentration = 1.2 mM, and furfural concentration = 10 mg/L), the PS/Catalysts/UV system can remove 96 % of furfural within 15 min. Under ideal conditions, the experimental results fit well with the first-order kinetic model (R2 > 0.95), and the rate constant (Kobs) was derived as 0.195 min-1. The quenching experiments provided further insights that confirmed the participation of SO4°- and OH° radicals in the degradation process. Nevertheless, the evidence strongly supports the idea that SO4°- plays a more prominent and dominant role as the primary radical species responsible for furfural degradation. Based on the obtained results, it can be concluded that the PS/Catalysts/UV system has an appropriate ability to remove furfural from aqueous solutions, which suggests promising perspectives for its practical application in pollutant treatment scenarios.

Generation and engineering applications of sulfate radicals in environmental remediation

Sulfate radical (SO4•-)-based advanced oxidation processes (AOPs) have become promising alternatives in environmental remediation due to the higher redox potential (2.6-3.1 V) and longer half-life period (30-40 μs) of sulfate radicals compared with many other radicals such as hydroxyl radicals (•OH). The generation and mechanisms of SO4•- and the applications of SO4•--AOPs have been examined extensively, while those using sulfite as activation precursor and their comparisons among various activation precursors have rarely reviewed comprehensively. In this article, the latest progresses in SO4•--AOPs were comprehensively reviewed and commented on. First of all, the generation of SO4•- was summarized via the two activation methods using various oxidant precursors, and the generation mechanisms were also presented, which provides a reference for guiding researchers to better select two precursors. Secondly, the reaction mechanisms of SO4•- were reviewed for organic pollutant degradation, and the reactivity was systematically compared between SO4•- and •OH. Thirdly, methods for SO4•- detection were reviewed which include quantitative and qualitative ones, over which current controversies were discussed. Fourthly, the applications of SO4•--AOPs in various environmental remediation were summarized, and the advantages, challenges, and prospects were also commented. At last, future research needs for SO4•--AOPs were also proposed consequently. This review could lead to better understanding and applications of SO4•--AOPs in environmental remediations.

UV/Fe(II) synergistically activated S(IV) per-treatment on HA-enhanced Ca2+ scaling in NF filtration: Fouling mitigation, mechanisms and correlation analysis of membrane resistance in different filtration stage

The aim of this study was to investigate the feasibility and fouling mitigation mechanisms of UV/Fe(II) synergistically activated sulfite (S(IV)) (UFS) pretreatment to alleviate membrane fouling caused by HA-enhanced Ca²⁺ scaling. After UFS treatment, hydrophobic substances and carboxyl groups structure were destroyed by the in-situ-generated SO•-4, resulted in a significant reduction of hydrophobic substances ratio and carboxyl group concentration. Due to the formation of more electropositive in-situ-generated Fe(III), the complexation between Ca²⁺ and carboxyl groups was weakened so that the bulk crystallization size on the membrane surface was greatly reduced. The filter cake enhanced osmotic pressure effect (CEOP) and concentration polarization effect were hence alleviated, as well as the surface roughness. At the microcosmic perspective, as the energy barrier between the membrane and foulants was increased significantly after pretreatment, the anti-foulants adsorption ability of the membrane was enhanced. Correlation analysis showed that the carboxyl concentration and density, HPO ratio, larger particle size (>100 nm) ratio, the Ca²⁺ concentration in the scaling layer and energy barrier all had a good correlation with the membrane resistance. This research not only provides an advanced oxidation technology that can effectively alleviate the synergistically-fouling effect of HA and Ca²⁺ of nanofiltration process, but also proposes a guidance for the UV/Fe(II) synergistically activated sulfite.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Cascade Reaction of "Mn2+ -Catechol" Triggered by H2 O2 to Integrate Firm Tumor Vessel Embolization and Hypoxic Response Relief

Transcatheter arterial embolization (TAE) therapy requires firm and long-term vessel embolization without recanalization. However, firm embolization usually leads to unanticipated hypoxic response which promotes tumor recurrence and metastasis. Herein, an injectable thermosensitive hydrogel containing catechol groups and Mn²⁺ (PNDM) has been developed to enhance embolization and inhibit hypoxic response utilizing augmented H₂ O₂ after TAE. This novel embolic agent converts H₂ O₂ into hydroxyl radicals via Mn²⁺ -dependent Fenton-like reaction, which are subsequently scavenged through a "catechol-quinone" transition to supress hypoxic responses. Quinone structure can not only make hydrogel internal structure more compact, but also enhance hydrogel adhesion to vessel wall. In vivo experiments confirm that the rabbit renal artery can be firmly embolized for 84 days. Studies in liver VX2 tumor-bearing rabbits demonstrate the PNDM-based TAE can promote tumor necrosis, inhibit angiogenesis and tumor metastasis, and greatly prolong rabbit survival. This strategy opens new sights in the TAE therapy for liver cancer. This article is protected by copyright. All rights reserved.

Photo-persulfate oxidation and mineralization of benzoic acid: Kinetics and optimization under UVC irradiation

The strong oxidant, persulfate (PS, S₂O₈^2-), was applied to treat the synthetic wastewater of benzoic acid (BA) under UV irradiation. UVC light initiated a chain reaction that derived the sulfate radical (SO₄•^-) and hydroxyl radical (HO•) from S₂O₈^2- ion. The experiment parameters, including light irradiation (UVA and UVC), pH, dose ratio ([PS]₀/[BA]₀), initial concentration ([BA]₀, mg/L), was optimized based on degradation efficiency and total organic carbon (TOC) removal of BA, which reached up to 100% and 96%, respectively, under pH 3.0. The best dose ratio was close to equivalent stoichiometry (and [PS]₀/[BA]₀ = 15) for the treatment of 100 mg-BA/L, suggesting that UV/S₂O₈^2- was able to completely convert BA to carbon dioxide and water. The scavenging test showed that SO₄•^- contributed to about 60% of degradation rate, which the HO• predominated the mineralization rate, i.e., TOC removal. A consecutive kinetic model was proposed to clarify the reaction sequence and rate-determining factor of photo-persulfate oxidation for benzoic acid.

Sustainable and effective degradation of aniline by sodium percarbonate activated with UV in aqueous solution: Kinetics, mechanism and identification of reactive species

In recent decades, sodium percarbonate (SPC) has been widely applied as a solid replacement for H₂O₂ in advanced oxidation process (AOPs). In this study, ultraviolet (UV) light was utilized for SPC activation to investigate the aniline degradation performance. The effects of SPC dosages and UV irradiation on aniline degradation were elaborated. The removal efficiency was significantly improved by increasing either the SPC dosage or UV irradiation intensity. Moreover, scavenging experiments showed that •OH, CO₃^•-, and O₂^•- were the predominant reactive species for aniline degradation. Meanwhile, the variation in the amount of •OH in the UV/SPC system was monitored, which revealed the dominant role of •OH. As a result, the mechanism of aniline degradation by the UV/SPC system was demonstrated based on confirmed free radicals. Furthermore, aniline degradation by the UV/H₂O₂ and UV/H₂O₂/Na₂CO₃ system were compared with the UV/SPC system, and an enhancement by the addition of Fe(II) in the UV/SPC system was verified. Aniline degradation was not significantly affected by the initial pH or the presence of Cl^-, SO₄^2- while NO₃^-, HCO₃^- and humid acid (HA) suppressed the reaction. In general, the UV/SPC system is a novel, green, and promising technology for aniline removal from aqueous solutions.

Unravelling the effects of complexation of transition metal ions on the hydroxylation of catechol over the whole pH region

Catechol pollutants (CATPs) serving as chelating agents could coordinate with many metal ions to form various CATPs-metal complexes. Little information is available on the effects of complexation of metal ions on CATPs degradation. This work presents a systematical study of •OH-mediated degradation of catechol and catechol-metal complexes over the whole pH range in advanced oxidation processes (AOPs). Results show that the pH-dependent complexation of metal ions (Zn²⁺, Cu²⁺, Ti⁴⁺ and Fe³⁺) promotes the deprotonation of catechol under neutral and even acidic conditions. The radical adduct formation (RAF) reactions are both thermodynamically and kinetically favorable for all dissociation and complexation species, and OH/O^- group-containing C positions are more vulnerable to •OH attack. The kinetic results show that the complexation of the four metal ions offers a wide pH range of effectiveness for catechol degradation. At pH 7, the apparent rate constant (k_app) values for different systems follow the order of catechol+Ti⁴⁺ ≈ catechol+Zn²⁺ > catechol+Cu²⁺ > catechol+Fe³⁺ > catechol. The mechanistic and kinetic results would greatly improve our understanding of the degradation of CATPs-metal and other organics-metal complexes in AOPs. The toxicity assessment indicates that the •OH-based AOPs have the ability for decreasing the toxicity and increasing the biodegradability during the processes of catechol degradation.

UV-assisted nitrogen-doped reduced graphene oxide/Fe3O4 composite activated peroxodisulfate degradation of norfloxacin

We reported the preparation of NGO-Fe₃O₄ by simple hydrothermal-co-precipitation. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). It was demonstrated that norfloxacin (NOR) could be effectively degraded by the UV/NGO-Fe₃O₄/PDS system. The degradation efficiency reached 100% within 13 min (the concentration of NOR and S2O82- were 100 mg L^-1 and 1 mM, respectively; m(NGO-Fe₃O₄): m(PDS) = 4: 1; pH: 3.0). In addition, NGO-Fe₃O₄ showed stable catalytic activity in recycling. The analysis found that the in-situ generated ·OH was the main active free radicals but SO4-⋅ also participated in the NOR degradation. Based on the identified intermediates, the NOR degradation pathways were proposed with UV/NGO-Fe₃O₄/PDS system.

Different activation methods in sulfate radical-based oxidation for organic pollutants degradation: Catalytic mechanism and toxicity assessment of degradation intermediates

With the continuous development of industrialization, a growing number of refractory organic pollutants are released into the environment. These contaminants could cause serious risks to the human health and wildlife, therefore their degradation and mineralization is very critical and urgent. Recently sulfate radical-based advanced oxidation technology has been widely applied to organic pollutants treatment due to its high efficiency and eco-friendly nature. This review comprehensively summarizes different methods for persulfate (PS) and peroxymonosulfate (PMS) activation including ultraviolet light, ultrasonic, electrochemical, heat, radiation and alkali. The reactive oxygen species identification and mechanisms of PS/PMS activation by different approaches are discussed. In addition, this paper summarized the toxicity of degradation intermediates through bioassays and Ecological Structure Activity Relationships (ECOSAR) program prediction and the formation of toxic bromated disinfection byproducts (Br-DBPs) and carcinogenic bromate (BrO₃^-) in the presence of Br^-. The detoxification and mineralization of target pollutants induced by different reactive oxygen species are also analyzed. Finally, perspectives of potential future research and applications on sulfate radical-based advanced oxidation technology in the treatment of organic pollutants are proposed.

Iron powder activated peroxymonosulfate combined with waste straw to improve sludge dewaterability

In an activated sludge system, the high hydrophilicity of extracellular polymeric substances (EPS) and the high compressibility of sludge greatly hinder sludge dewatering. A new method for improving the dehydration of waste activated sludge was explored by using iron powder activated peroxomonosulfate combined with waste straw (Fe⁰+PMS + WS). Specific resistance to filtration (SRF) and water content (Wc) were used to characterize the dewatering performance of sludge. Under the optimal measurement, Wc and SRF were significantly reduced. To reveal the synergistic effect of this joint treatment, zeta potential, particle size distribution, three-dimension excitation emission matrix (3D-EEM) fluorescence spectroscopy, bound water content analysis, and scanning electron microscopy (SEM) were used to investigate the mechanism of sludge dewatering. Results showed that the tightly bound EPS (TB-EPS) was oxidized by sulfate radicals (SO4-∙) to loose bound EPS (LB-EPS) and soluble EPS(S-EPS). SEM analysis displayed that the Fe⁰+PMS + WS combination regulated the formation of a more porous sludge filter cake structure. In addition, the low calorific value of the dewatered sludge after 12 h in open air was significantly increased, and the Wc of the dewatered sludge cake was reduced to 25%. These parameters were beneficial to the subsequent disposal of sludge.

Degradation of Bisphenol A in an Aqueous Solution by a Photo-Fenton-Like Process Using a UV KrCl Excilamp

Bisphenol A (BPA), a precursor to important plastics, is regarded as a common aquatic micropollutant with endocrine-disrupting activity. In the present study, we explored the capability of a UV KrCl excilamp (222 nm) to degrade BPA by a photo-Fenton-like process using persulfate under flow-through conditions. The first-order rate constants of degradation were obtained and the mineralization of dissolved organic carbon (DOC) was estimated. The results showed complete BPA degradation and high DOC mineralization (70-97%). A comparative analysis of degradation rates and DOC removal in the examined systems (UV, Fe2+/S2O82-, UV/S2O82- and UV/Fe2+/S2O82-) revealed a significant synergistic effect in the photo-Fenton-like system (UV/Fe2+/S2O82-) without the accumulation of toxic intermediates. This indicated that the BPA was oxidized via the conjugated radical chain mechanism, which was based on the photo-induced and catalytic processes involving HO• and SO4-• radicals. The primary intermediates of BPA degradation in the UV/Fe2+/S2O82- system were identified by HPLC/MS and the oxidation pathway was proposed. The high performance of the photo-Fenton-like process employing a quasi-monochromatic UV radiation of a KrCl excilamp offers promising potential for an efficient removal of such micropollutants from aqueous media.

Photochemical reaction kinetics and mechanism of bisphenol A with K2S2O8 in aqueous solution: a laser flash photolysis study

The photochemical reaction kinetics and mechanism of bisphenol A (BPA) with potassium persulfate (K2S2O8) were investigated by using 266 nm laser flash photolysis and gas chromatography mass spectrum (GC-MS) technique. Sulfate radical (SO4•−), generated upon K2S2O8 photolysis, reacted with BPA with the overall rate constant of (1.61 ± 0.15) × 109 L mol−1 s−1, and two main reaction mechanisms were involved. One was addition channel to generate BPA–SO4•− adduct with a specific second-order rate constant of (1.09 ± 0.15) × 109 L mol−1 s−1. Molecular oxygen was involved in the decay of the BPA–SO4•− adduct with a rate constant of (1.28 ± 0.14) × 108 L mol−1 s−1. Another channel was the formation of BPA’s phenoxyl radical, likely derived from a deprotonation of the cation radical (BPA•+) generated from single electron transfer reactions. The specific rate constant of BPA’s phenoxyl radical formation was determined to be (6.16 ± 0.08) × 108 L mol−1 s−1. The overall rate constant was in line with the sum of aforementioned two specific rate constants for two main reaction channels. By comparing these rate constants, it was indicated that SO4•− addition channel accounted for ∼65% (1.09/1.61) to the overall reaction, and phenoxyl radical formation accounted for only ∼35% (0.62/1.61). The transformation products of BPA were identified by using GC-MS including 4-isopropylphenol, 4-isopropenylphenol, and 2,4-di-tert-butylphenol, and the reaction mechanism was proposed. These results may provide microscopic kinetics and mechanism information on BPA degradation using SO4•−-based advanced oxidation processes.

UV-Accelerated Photocatalytic Degradation of Pesticide over Magnetite and Cobalt Ferrite Decorated Graphene Oxide Composite

Pesticides are one of the main organic pollutants as they are highly toxic and extensively used worldwide. The reclamation of wastewater containing pesticides is of utmost importance. For this purpose, GO-doped metal ferrites (GO-Fe₃O₄ and GO-CoFe₂O₄) were prepared and characterized using scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopic techniques. Photocatalytic potentials of catalysts were investigated against acetamiprid’s degradation. A detailed review of the parametric study revealed that efficiency of overall Fenton’s process relies on the combined effects of contributing factors, i.e., pH, initial oxidant concentration, catalyst dose, contact time, and acetamiprid load. ~97 and ~90% degradation of the acetamiprid was achieved by GO-CoFe₂O₄ and GO-Fe₃O₄, respectively during the first hour under UV radiations at optimized reaction conditions. At optimized conditions (i.e., pH:3, [H₂O₂]: 14.5 mM (for Fe₃O₄, GO-Fe₃O_4, and GO-CoFe₂O₄) and 21.75 mM (for CoFe₂O₄), catalysts: 100 mgL⁻¹, time: 60min) the catalysts exhibited excellent performance, with high degradation rate, magnetic power, easy recovery at the end, and efficient reusability (up to 5 cycles without any considerable loss in catalytic activity). A high magnetic character offers its easy separation from aqueous systems using an external magnet. Moreover, the combined effects of experimental variables were assessed simultaneously and justified using response surface methodology (RSM).

Visible light-assisted NGO-Fe3O4 composite activated peroxydisulfate for degradation of oxytetracycline

A nitrogen-doped reduced graphene oxide/Fe₃O₄ composite (NGO-Fe₃O₄) was prepared through the simplified hydrothermal and deposition-precipitation method and characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The degradation efficiency of oxytetracycline (OTC) by NGO-Fe₃O₄ activated peroxodisulfate (PDS) under visible light irradiation was studied. The degradation efficiency reached 100% within 32.5 min (the initial OTC concentration 50 mg L^-1 and PDS 1 mM; [NGO-Fe₃O₄]:[ PDS] = 4:1; pH = 3.0). No apparent decrease in degradation efficiency was observed after five cycles. SO₄ ^-· and ·OH were the main active oxides for OTC degradation in this system. Moreover, four degradation pathways were proposed, namely hydroxylation, dehydration, decarbonylation and demethylation according to the analysis results of high-performance liquid chromatography mass spectrometry.

Photo-Fenton Degradation of AO7 and Photocatalytic Reduction of Cr(VI) over CQD-Decorated BiFeO3 Nanoparticles Under Visible and NIR Light Irradiation

In this work, the carbon quantum dot (CQD)-decorated BiFeO3 nanoparticle photocatalysts were prepared by a hydrothermal method. The TEM observation and XPS characterization indicate that the CQDs are well anchored on the surface of BiFeO3 nanoparticles. Acid orange 7 (AO7) and hexavalent chromium (Cr(VI)) were chosen as the model pollutants to investigate the photocatalytic/photo-Fenton degradation and photocatalytic reduction performances of the as-prepared CQD/BiFeO3 composites under visible and near-infrared (NIR) light irradiation. Compared with bare BiFeO3 nanoparticles, the CQD/BiFeO3 composites exhibit significantly improved photocatalytic and photo-Fenton catalytic activities. Moreover, the composites possess good catalytic stability. The efficient photogenerated charges separation in the composites was demonstrated by the photocurrent response and electrochemical impedance spectroscopy (EIS) measurements. The main active species involved in the catalytic degradation reaction were clarified by radicals trapping and detection experiments. The underlying photocatalytic and photo-Fenton mechanisms are systematically investigated and discussed.

Photo-Fenton-like degradation of bisphenol A by persulfate and solar irradiation

This work evaluates the feasibility of a solar-enhanced Fenton-like process using S₂O₈^2- (PS) and Fe²⁺ for the elimination of BPA, a model endocrine-disruption compound. This comparative study of BPA removal showed that among the approaches employed, the effectiveness of BPA degradation (10 mg/L) decreased in the order: Solar/PS/Fe²⁺> Solar/PS > PS/Fe²⁺> Solar/Fe²⁺> Solar. The complete degradation of BPA was achieved by Solar/PS/Fe²⁺ treatment at a [PS]:[BPA] ratio of 20 in less than t_30W 5 in deionised water. The high efficiency of the Solar/PS/Fe²⁺ process revealed a synergistic effect (ϕ = 2.38) between the applied activation agents on the formation of reactive oxygen species (ROS) and subsequent decomposition of BPA. The treatment was accompanied by total organic carbon (TOC) removal (44%) in 45 min. Sequential generation of reactive oxygen species has made Solar/PS/Fe²⁺ a kinetically effective process for removing BPA without accumulation of toxic intermediates. The reaction rate followed pseudo-first-order kinetics that increased with increasing PS and Fe²⁺ concentrations. Experimental evidence suggests that exposure to solar irradiation maintains suitable quantities of free Fe²⁺ in the reaction mixture, even at low catalyst concentrations (the molar ratio of [PS]:[Fe²⁺] varied from 1:0.01 to 1:0.08). The effects of HCO₃^-, SO₄^2-, and Cl^- were also examined. As expected, HCO₃^- and SO₄^2- inhibited BPA oxidation. The effect of Cl^- on the oxidation efficiency of BPA in Fenton-like systems depends not only on actual Cl^- concentrations but it is also highly influenced by molar ratios of Cl^- to oxidant and catalyst. Inhibition, which was caused by Cl^- in the mM range can be overcome by prolonging the reaction time or increasing the initial Fe²⁺concentration. Finally, the efficiency of Solar/PS/Fe²⁺ process was examined in diluted natural surface water and wastewater effluent. On eliminating the buffering action of HCO₃^-/CO₃^2- ions by lowering the pH value to 4.5, complete BPA degradation was achieved in all real water matrices.

Enhanced Activation of Persulfate by Meso-CoFe2O4/SiO2 with Ultrasonic Treatment for Degradation of Chlorpyrifos

Magnetic mesoporous CoFe₂O₄/SiO₂ (Meso-CoFe₂O₄/SiO₂) composites were simply synthesized. On the basis of previous studies, optimum preparation conditions of their structure and physical properties can be readily determined. CoFe₂O₄ nanocrystals and their mesoporous structure were authenticated by low-angle and wide-angle X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, element mapping, X-ray photoelectron spectroscopy, nitrogen adsorption isotherms, and so on. They were applied to degrade chlorpyrifos where Meso-CoFe₂O₄/SiO₂ composites provide a mesoporous microenvironment and combined with ultrasonic treatment can enhance heterogeneous activation of persulfate. Research findings showed that the system can be conducive to remove quickly chlorpyrifos and the removal ratios reached 99.99%. The results provided a strategy for the chlorpyrifos degradation and, similarly, pollution control of pesticide wastewater.

Efficient treatment of saline recalcitrant petrochemical wastewater using heterogeneous UV-assisted sono-Fenton process

An effective hybrid system was applied as a first report for successful treatment of recalcitrant petrochemical wastewater (PCW). In this regards, magnetic powdered activated carbon (MPAC), as a heterogeneous catalyst, was coupled with ultrasound (US) and UV irradiations for activation of H₂O₂ (marked as MPAC/US/UV/H₂O₂). Chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including solution pH, MPAC and H₂O₂ concentrations, US power and quenchers. A possible mechanism for catalytic degradation and generation of reactive species was proposed. To evaluate the biodegradability of both raw and treated PCWs, the activated sludge inhibition experiments were performed based on Zahn-Wellens test. MPAC indicated high catalytic activity, reusability and stability in the studied system. Over 87% of COD was removed under optimum conditions within 80 min treatment and the residual COD concentration reached 82.9 mg/L, which was permissible to discharge surface water sources based on the environmental standards. Leaching of transition metals from catalyst textural was negligible. Compared to homogeneous system (Fe²⁺/US/UV/H₂O₂), heterogeneous system (MPAC/US/UV/H₂O₂) represented a better performance in COD removal. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. A biodegradability ratio of 64% and the residual COD of 28 mg/L for treated PCW, indicating that the biodegradability was improved and refractory organic matters removed effectively. As conclusion, MPAC/US/UV/H₂O₂ hybrid system can be introduced as a successful advanced treatment process for efficient remediation of refractory PCWs.

Enhanced removal of antibiotics from secondary wastewater effluents by novel UV/pre-magnetized Fe0/H2O2 process

Antibiotics have been frequently detected in the aquatic environment and are of emerging concern due to their adverse effect and potential of inducing antibiotic resistance. In this study, we developed an UV/pre-magnetized Fe⁰/H₂O₂ process (UV/pre-Fe⁰/H₂O₂) valid for neutral pH conditions, which could remove sulfamethazine (SMT) completely within only 30 min and enhance 1.8 times of SMT removal. Meanwhile, this process demonstrated outstanding mineralization capability with the TOC removal of 92.1%, while for UV/H₂O₂ and UV/Fe⁰/H₂O₂ system it was 53.9% and 72.1%, respectively. Better synergetic effect between UV irradiation and pre-Fe⁰/H₂O₂ system was observed, and the value of synergetic factor was 6.3 in the presence of both ions and humic acid, which was much higher than that in deionized water (4.4), humic acid (5.5) and ions (1.5). Moreover, the process could efficiently remove various antibiotics (800 μg L^-1 oxytetracycline (OTC); 800 μg L^-1 tetracycline (TC); 400 μg L^-1 sulfadiazine (SD) and 400 μg L^-1 SMT) in the secondary wastewater effluent. After optimization of Fe⁰ and H₂O₂ dosage, these antibiotics could be removed within 10 min (k_app (10³) = 288.6 min^-1) with a very low treatment cost of 0.1 USD m^-3, and the EE/O value was only 1.22 kWh m^-3. Compared with O₃, UV/Fe²⁺/PDS, VUV/UV/Fe²⁺ and other US-based processes, the degradation rates by this process could enhance as high as 22.3 folds while the treatment cost or EE/O value could reduce greatly. Therefore, UV/pre-Fe⁰/H₂O₂ process is promising and cost-effective for the treatment of antibiotics in secondary wastewater effluents.

Photocatalytic and Photo-Fenton Catalytic Degradation Activities of Z-Scheme Ag₂S/BiFeO₃ Heterojunction Composites under Visible-Light Irradiation

Z-scheme Ag₂S/BiFeO₃ heterojunction composites were successfully prepared through a precipitation method. The morphology and microstructure characterization demonstrate that Ag₂S nanoparticles (30⁻50 nm) are well-decorated on the surfaces of polyhedral BiFeO₃ particles (500⁻800 nm) to form Ag₂S/BiFeO₃ heterojunctions. The photocatalytic and photo-Fenton catalytic activities of the as-derived Ag₂S/BiFeO₃ heterojunction composites were evaluated by the degradation of methyl orange (MO) under visible-light irradiation. The photocatalytic result indicates that the Ag₂S/BiFeO₃ composites exhibit much improved photocatalytic activities when compared with bare Ag₂S and BiFeO₃. The optimum composite sample was observed to be 15% Ag₂S/BiFeO₃ with an Ag₂S mass fraction of 15%. Furthermore, the addition of H₂O₂ can further enhance the dye degradation efficiency, which is due to the synergistic effects of photo- and Fenton catalysis. The results of photoelectrochemical and photoluminescence measurements suggest a greater separation of the photoexcited electron/hole pairs in the Ag₂S/BiFeO₃ composites. According to the active species trapping experiments, the photocatalytic and photo-Fenton catalytic mechanisms of the Ag₂S/BiFeO₃ composites were proposed and discussed.

Photo-Fenton like Catalyst System: Activated Carbon/CoFe2O4 Nanocomposite for Reactive Dye Removal from Textile Wastewater

The removal of dye from textile industry wastewater using a photo-Fenton like catalyst system was investigated wherein the removal efficiency of phenol and chemical oxygen demand (COD) was studied by varying various parameters of pH (3–11), reaction time (1–50 min), activated Carbon/CoFe2O4 (AC/CFO) nanocomposite dosage (0.1–0.9 g/L), and persulfate amount (1–9 mM/L). The highest removal rates of reactive red 198 and COD were found to be 100% and 98%, respectively, for real wastewater under the optimal conditions of pH = 6.5, AC/CFO nanocomposite dosage (0.3 g/L), reaction time, 25 min, and persulfate dose of 5 mM/L up on constant UV light irradiation (30 W) at ambient room temperature. The result showed that this system is a viable and highly efficient remediation protocol relative to other advanced oxidation processes; inexpensive nature, the ease of operation, use of earth-abundant materials, and reusability for removal of organic pollutants being the salient attributes.

Degradation of the Nonsteroidal Anti-Inflammatory Drug Piroxicam by Iron Activated Persulfate: The Role of Water Matrix and Ultrasound Synergy

This work examined the oxidation of Piroxicam (PIR), a representative nonsteroidal anti-inflammatory drug using iron activated persulfate. The effect of persulfate dosing was vital for the efficiency of the process. The addition of 20 mg/L sodium persulfate (SPS) eliminated 500 μg/L of PIR in less than 20 min at natural pH. PIR decomposition followed pseudo-first-order kinetics, and the observed kinetic constant increased by 2.1 times when the initial concentration of PIR decreased from 2000 to 250 μg/L. Acidic pH favored the PIR destruction, while both sulfate and hydroxyl radicals are involved in PIR destruction at natural pH. The effect of inorganic ions like bicarbonate and chlorides was almost insignificant on PIR removal. The presence of humic acid reduced PIR removal from 100% to 67% after 20 min of treatment with 2 mg/L Fe2+ and 20 mg/L SPS. The experiment that was performed with bottled water showed similar efficiency with ultrapure water, while in the case of secondary effluent, PIR removal decreased by 26% after 30 min of treatment. The Fe2+/SPS/ultrasound hybrid process showed a low degree of synergy (18.3%). The ecotoxicity of aqueous solution using the Vibrio fischeri as an indicator was reduced during the treatment, although with a different trend from the removal of PIR, possibly due to byproducts derived from the oxidation of secondary effluent and PIR.