Heterogeneous fenton-like degradation of ofloxacin over sludge derived carbon as catalysts: Mechanism and performance

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

Solid-liquid redistribution and degradation of antibiotics during hydrothermal treatment of sewage sludge: Interaction between biopolymers and antibiotics

Waste activated sludge serves an important reservoir for antibiotics within wastewater treatment plants, and understanding the occurrence and evolution of antibiotics during sludge treatment is crucial to mitigate the potential risks of subsequent resource utilization of sludge. This study explores the degradation and transformation mechanisms of three typical antibiotics, oxytetracycline (OTC), ofloxacin (OFL), and azithromycin (AZI) during sludge hydrothermal treatment (HT), and investigates the influence of biopolymers transformation on the fate of these antibiotics. The findings indicate that HT induces a shift of antibiotics from solid-phase adsorption to liquid-phase dissolution in the initial temperature range of 25-90 °C, underscoring this phase's critical role in preparing antibiotics for subsequent degradation phases. Proteins (PN) and humic acids emerge as crucial for antibiotic binding, facilitating their redistribution within sludge. Specifically, the binding capacity sequence of biopolymers to antibiotics is as follows: OFL>OTC>AZI, highlighting that OFL-biopolymers display stronger electrostatic attraction, more available adsorption sites, and more stable binding strength. Furthermore, antibiotic degradation mainly occurs above 90 °C, with AZI being the most temperature-sensitive, degrading 92.97% at 180 °C, followed by OTC (91.26%) and OFL (52.51%). Concurrently, the degradation products of biopolymers compete for active sites to form novel amino acid-antibiotic conjugates, which inhibits the further degradation of antibiotics. These findings illuminate the effects of biopolymers evolution on intricate dynamics of antibiotics fate in sludge HT and are helpful to optimize the sludge HT process for effective antibiotics abatement.

Sphere-shaped ZnO photocatalyst synthesis for enhanced degradation of the Quinolone antibiotic, Ofloxacin, under UV irradiation

The sphere-shaped zinc oxide (ZnO) photocatalyst was synthesized by the homogeneous precipitation method, using Zn(CH3COO)2·2H2O as a zinc precursor and NH4OH as a precipitating agent. The morphology and crystal structure of the prepared ZnO sample were studied by XRD, SEM, FT-IR, XPS, zeta potential measurements, and a low-temperature nitrogen adsorption-desorption technique. The optical characteristics of ZnO were determined by UV - Vis diffuse reflectance spectroscopy. ZnO photocatalyst performance of up to 100% within 210 min was observed in the photodegradation of the ofloxacin antibiotic under ultraviolet (UV) irradiation. The effect of antibiotic concentration, heavy metal ions, and water sources on the photocatalytic activity of ZnO demonstrated both the potential of its application under different conditions, and a good adaptability of this photocatalyst. The photodegradation reaction correlated well with the first-order kinetics model, with a rate constant of 0.0173 min-1. The reusability of the photocatalyst was verified after three cycles of use. Admittedly, photogenerated electrons and holes played a key role in removal of the antibiotic. This work showed the suitability of prepared ZnO for antibiotic removal, and its potential use for environmental protection.

Photocatalytic Degradation of Quinolones by Magnetic MOFs Materials and Mechanism Study

With the rising incidence of various diseases in China and the constant development of the pharmaceutical industry, there is a growing demand for floxacin-type antibiotics. Due to the large-scale production and high cost of waste treatment, the parent drug and its metabolites constantly enter the water environment through domestic sewage, production wastewater, and other pathways. In recent years, the pollution of the aquatic environment by floxacin has become increasingly serious, making the technology to degrade floxacin in the aquatic environment a research hotspot in the field of environmental science. Metal-organic frameworks (MOFs), as a new type of porous material, have attracted much attention in recent years. In this paper, four photocatalytic materials, MIL-53(Fe), NH2-MIL-53(Fe), MIL-100(Fe), and g-C3N4, were synthesised and applied to the study of the removal of ofloxacin and enrofloxacin. Among them, the MIL-100(Fe) material exhibited the best photocatalytic effect. The degradation efficiency of ofloxacin reached 95.1% after 3 h under visible light, while enrofloxacin was basically completely degraded. The effects of different materials on the visible photocatalytic degradation of the floxacin were investigated. Furthermore, the photocatalytic mechanism of enrofloxacin and ofloxacin was revealed by the use of three trappers (▪O2-, h+, and ▪OH), demonstrating that the role of ▪O2- promoted the degradation effect of the materials under photocatalysis.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·- generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Facile introduction of coordinative Fe into oxygen-enriched graphite carbon nitride for efficient photo-Fenton degradation of tetracycline

Tetracycline (TC) antibiotics have been widely used over the past decades, and their massive discharge led to serious water pollution. Photo-Fenton process has gained ever-increasing attention for its excellent oxidizing ability and friendly solar energy utilization ability in TC polluted water treatment. This work introduced coordinative Fe into oxygen-enriched graphite carbon nitride (OCN) to form FeOCN composites for efficient photo-Fenton process. Hemin was chosen as the source to provide the source of coordinative Fe-Nx groups. The degradation efficiency of TC reached 82.1 % within 40 min of irradiation, and remained 76.9 % after five runs of reaction. The degradation intermediates of TC were detected and the possible degradation pathways were gained. It was found that h+, OH, and O2- played major roles in TC degradation. Notably, the photo-Fenton performance of FeOCN was stable in highly saline water or strong acid/base environment (pH 3.0-9.0). Besides, H2O2 can be generated in-situ in this photo-Fenton process, which is favorable for practical application. It can be anticipated that the coordinative FeOCN composites will promote the application of photo-Fenton oxidation process in TC polluted water treatment.

Dual-functional heterogeneous Fenton catalyst Cu/Ti co-doped Fe3O4@FeOOH for cyanide-containing wastewater treatment: Preparation, performance and mechanism

The dual-functional heterogeneous Fenton catalyst Cu/Ti co-doped iron-based Fenton catalyst (Cu/Ti -Fe3O4@FeOOH, FCT) were successfully prepared by precipitation oxidation method and characterized by XRD, XPS and XAFS. The prepared Cu/Ti co-doped Fe3O4@FeOOH nanoparticles consisted of goethite nanorods and magnetite rod octahedral particles, with Cu and Ti replacing Fe in the catalyst crystal structure, leading to the formation of the goethite structure. The heterogeneous Fenton catalyst FCT exhibited excellent degradation activity for cyanide in wastewater and showed different reaction mechanisms at varying pH levels. When treating 100 mL of 12 mg L-1 NaCN solution, complete degradation occurred within 40 min at 30 °C and pH ranging from 6.5 to 12.5 without external energy. Compared to Fe3O4, FCT shows superior degradation activity for cyanide. The surface Cu(Ⅰ) facilitated the electron transfer and significantly improved the catalytic activity of the catalyst. Additionally, the magnetic properties of the Ti-doped catalyst samples were greatly enhanced compared to the Cu@FeOOH catalyst doped with Cu, making them favorable for recycling and reuse. FCT maintains 100% degradation of cyanogen after three cycles, indicating its excellent stability. Furthermore, electron spin resonance spectroscopy, free radical quenching experiments and fluorescence probe techniques using terephthalic acid (TA) and benzoic acid (BA) confirmed that the presence of •OH and FeⅣ=O reactive species was responsible for the catalysts exhibiting different mechanisms at different pH conditions. Compared with other heterogeneous Fenton catalysts, FCT exhibits intentional degradation activity for cyanide-containing wastewater under different acid-base conditions, which greatly broadened the pH range of the heterogeneous Fenton reaction.

Synthesis of sewage sludge biochar in molten salt environment for advanced wastewater treatment: Performance enhancement, carbon footprint and environmental impact reduction

Sewage sludge (SS) pyrolysis to produce biochar is a vital approach for treating and utilizing SS, while reducing the carbon footprint of SS disposal. However, the high inorganic content in SS results in low carbon content and underdeveloped pore structure of biochar prepared under inert atmospheres. There is a significant risk of secondary pollutant emissions, including CO2, SO2, and NOx. In this study, we propose an innovative approach that utilizes excess molten salts, specifically a Li-Na-K molten carbonate (MC) and a Li-Na-K molten chloride (MCH), to create a medium-temperature liquid phase reaction environment (500 °C) for SS pyrolysis. This environment promotes the functional enhancement of biochar (SSB-MC and SSB-MCH) and in-situ absorption of secondary pollutants. The pore structure of SSB-MC and SSB-MCH are greatly optimized. Thanks to the dissolution of calcium-silicon-aluminum-based minerals by molten salt, the carbon content is also significantly increased. The increased specific surface area and surface-enriched functional groups (O, N, P, etc.) of SSB-MC result in greatly enhanced adsorption performance for Rhodamine B (27.9 to 89.1 mg g-1). SSB-MCH, due to the increased iron and phosphorus doping, also exhibits enhanced Fenton oxidation capability. Life cycle assessments demonstrate that the molten salt processes effectively reduce the carbon footprint, energy consumption, and environmental impact.

Selective oxidation of organic pollutants based on reactive oxygen species and the molecular structure: Degradation behavior and mechanism analysis

The selective and rapid elimination of refractory organic pollutants from surface water is significant. However, the relationship of between reactive oxygen species (ROSs) and diversified pollutants molecular structures still needs to be further clarified. Here, we utilize polydopamine (PDA)-assisted coating strategy to prepare hollow 2D carbon nanosheet (ZPL-HCNS) and 2D Co3O4 nanosheet (ZPL-Co3O4) by thermolysis of PDA coated ZIF-L (ZIF-L@PDA) precursor under different gas atmosphere, which realizes the controlled generation of radicals and non-radicals. Organic pollutants including bisphenols, sulfonamides, quinolones, tetracyclines, and azo dyes are applied to assess the catalytic performance. Results show that dyes containing azo structure are more likely to be degraded by radical process, which is due to that the energy (ΔE) requirements to break the azo bond is higher than energy released from singlet oxygen to oxygen molecule and lower than that of sulfate radical to sulfate. Frontier molecular orbital theory HOMO-LUMO and Fukui function expounded the possible selectivity mechanism. In addition, the degradation pathway and biotoxicity test are carried out. This work provides a reference to illustrate the selective degradation for ROSs and molecular structure of pollutants.

Activation of peroxymonosulfate by catalysts derived from water treatment plant sludge for the simultaneous removal of Disperse Blue 56 and phosphates

In this study, calcined water treatment plant sludge (C-WTPS) was used as a catalyst for peroxymonosulfate (PMS) activation to simultaneously remove Disperse Blue 56 (DB56) and phosphates. Firstly, the performance of the C-WTPS/PMS system was examined for the degradation of DB56. The results showed that 96.7% of DB56 (400 mg L^-1) was removed within 60 min in the presence of 4.8 g L^-1 PMS and 0.8 g L^-1 C-WTPS at pH 3 and 50 °C. Hydroxyl radicals (·OH), sulfate radicals (SO_4·^-), and singlet oxygen (¹O₂) were generated during the oxidation process, and ¹O₂ was the main active species. The relatively high surface area, proper Fe content, and abundant ketone groups on the catalyst surface were responsible for PMS activation. Furthermore, the possible degradation pathways of DB56 were proposed based on the gas chromatography-mass spectrometry (GC-MS) results. Secondly, the simultaneous removal of DB56 and phosphates by the C-WTPS/PMS system was investigated. Due to the different removal mechanisms, the effects of the initial phosphate concentration and water matrix species on the removal of DB56 and phosphates showed different trends. Reusability tests results showed that C-WTPS had relatively high stability. In addition, the C-WTPS/PMS system exhibited a high decolorization ratio and phosphate removal efficiency in real wastewater tests. This article offers a value-added approach for reusing WTPS as a catalyst for treating organic contaminants and phosphates.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Applications of Spent Lithium Battery Electrode Materials in Catalytic Decontamination: A Review

For a large amount of spent lithium battery electrode materials (SLBEMs), direct recycling by traditional hydrometallurgy or pyrometallurgy technologies suffers from high cost and low efficiency and even serious secondary pollution. Therefore, aiming to maximize the benefits of both environmental protection and e-waste resource recovery, the applications of SLBEM containing redox-active transition metals (e.g., Ni, Co, Mn, and Fe) for catalytic decontamination before disposal and recycling has attracted extensive attention. More importantly, the positive effects of innate structural advantages (defects, oxygen vacancies, and metal vacancies) in SLBEMs on catalytic decontamination have gradually been unveiled. This review summarizes the pretreatment and utilization methods to achieve excellent catalytic performance of SLBEMs, the key factors (pH, reaction temperature, coexisting anions, and catalyst dosage) affecting the catalytic activity of SLBEM, the potential application and the outstanding characteristics (detection, reinforcement approaches, and effects of innate structural advantages) of SLBEMs in pollution treatment, and possible reaction mechanisms. In addition, this review proposes the possible problems of SLBEMs in practical decontamination and the future outlook, which can help to provide a broader reference for researchers to better promote the implementation of “treating waste to waste” strategy.

New insights into the degradation and detoxification of methylene blue using heterogeneous-Fenton catalyzed by sustainable siderite

The huge application of synthetic dyes caused a severe impact in the environment. In the present study, a physico-chemical strategy of heterogeneous-Fenton catalyzed by the natural ferrous ore has been established for toxic chemical degradation, of which the complex and high-expense repetitive pH adjustment procedures were escaping. And this natural heterogeneous catalyst also could be recycled and sustainable for toxic substances treatment involved in synergetic adsorption and oxidation. The siderite, served as an adsorbent and catalyst for the degradation of methylene blue (MB). Siderite exhibited a better adsorption capacity with a saturated adsorption capacity of ∼11.08 mg/g. Batch adsorption experiments have verified that adsorption rate and adsorption equilibrium followed pseudo-second-order rate model and Langmuir isotherm equation, respectively. The combination with H₂O₂, showed significant enhancement of MB degradation without any pH adjustment. The effect of siderite dosage, H₂O₂ dosage, MB concentration, initial pH, and reaction temperature on MB degradation was investigated, which also has indicated the excellent catalytic performance of siderite. About 99.71% of MB was degraded in 480 min with initial pH of 7.0, reaction temperature of 25 °C, siderite, and H₂O₂ dosage of 2.5 g/L and 122.38 mM, respectively. It was found that siderite could be reused and remained high degradation efficiency on MB after 5 times reutilization, which also could demonstrate the sustainable and effective process to degrade organic pollution. The generation of reactive species including ·OH and O2·- have been confirmed based on scavenger test and electron spin resonance (ESR) analysis, which was dominated by heterogeneous reaction. The possible degradation mechanisms of MB have been predicted based on spectrum scanning and GC-MS analysis. Moreover, acute toxicity assessment with marine photobacterium Vibrio fisheri was conducted to investigate the toxicity change in the adsorption/oxidation coupled process. This sustainable heterogeneous-Fenton technology has been verified as a promising and applicable process for toxic organic chemicals removal due to effective mineralization and detoxification assisted with the natural ore mineral through the simple operation and mild condtions.

Removal of ofloxacin from wastewater by chloride electrolyte electro-oxidation: Analysis of the role of active chlorine and operating costs

Electro-oxidation (EO) has received increasing attention as an efficient and green method for removing pollutants from wastewater. Chloride anions (Cl^-), which commonly exist in wastewater, can act as an electrolyte for the EO process. However, the role of reactive chlorine species (RCS) generated near electrodes is often underestimated. In this study, we generated hydroxyl radicals (OH) and RCS in a boron-doped diamond (BDD) electrode system and investigated its degradation mechanism for ofloxacin (OFX) removal. The findings suggested that OFX degradation was dominated by OH existing near the anode in solution, with RCS playing a supporting role. Based on the produced intermediates, we proposed an OFX decomposition pathway. The biological toxicities of the intermediates were evaluated through the ECOSAR and T.E.S.T. procedure. Nearly half of the intermediates are less toxic than the parent compound. After optimizing the operating parameters by the response surface methodology, 20 mg/L OFX was almost completely degraded after 10 min of reaction in 1.45 g/L NaCl with a current density (j) of 18 mA/cm², and the total organic carbon was decreased by 30.55 %. The energy consumption and current efficiency were 0.648 kW·h/g_TOC and 8.65 %, respectively. Comparing the operating costs of the proposed and other EO methods, our method emerged as a viable new treatment scheme for similar polluted wastewaters. This study aims to comprehensively understand the potential application value of BDD electrodes in the treatment of Cl^- containing organic wastewater.

Enhanced photocatalytic degradation of malachite green dye by highly stable visible-light-responsive Fe-based tri-composite photocatalysts

A novel visible-light-sensitive ZnVFeO₄ photocatalyst has been fabricated by the precipitation method at different pH values for the enhanced photocatalytic degradation of malachite green (MG) dye as a representative pollutant under visible light irradiation at neutral pH conditions. The structure and optical characteristics of the prepared photocatalysts were investigated by XRD, FTIR, N2 adsorption-desorption, TEM, diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) analyses. In addition, the photocatalytic activity of ZnVFeO₄ photocatalysts superior the efficiency to be more than that of the mono and bi-metal oxides of iron and iron zinc oxides, respectively. The best sample, ZnVFeO₄ at pH 3, significantly enhances the degradation rate under visible light to be 12.7 × 10^-3 min^-1 and can retain a stable photodegradation efficiency of 90.1% after five cycles. The effect of the catalyst dose and the initial dye concentration on the photodegradation process were studied. This promising behavior under visible light may be attributed to the low bandgap and the decreased electron-hole recombination rate of the ZnVFeO₄ heterostructures. The scavenger experiment confirmed that the hydroxyl radicals induced the MG photodegradation process effectively. Hence, the ZnVFeO₄ is a reliable visible-light-responsive heterostructure photocatalyst with excellent potential for the photodegradation of organic pollutants in wastewater treatment.

Controlled carbonization of microplastics loaded nano zero-valent iron for catalytic degradation of tetracycline

Nano zero-valent iron loaded porous carbon derived from microplastics was designed as heterogeneous catalyst for degradation of persistent organic pollutants. Controlled carbonization of microplastics with molten salt was conducted to tune the morphology of carbon product. Controlled carbonization induces higher carbon yield (from 17.73% to 52.24%) and larger surface area (from 403.72 m²/g to 601.82 m²/g). The catalyst (Fe/MMPC) was characterized by Raman, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope. Loading nano zero-valent iron onto porous carbon are verified in the catalyst. The process factors including Fe/MMPC dosage, H₂O₂, pH, anions, and temperature were studied to estimate the catalytic performance. Tetracycline degradation (81.8% within 10 min) is effectively obtained in the Fe/MMPC and H₂O₂ system. The apparent rate constant is 0.1311-0.2999 min^-1 under different temperature, and the activation energy of catalytic process is 22 kJ/mol. Pollutants including rhodamine B, p-nitrophenol, and butylxanthate are efficiently degraded in the catalytic system. The predominant species of catalytic reactions are hydroxyl radicals, which are mainly produced from H₂O₂ activation enhanced by zero-valent iron in Fe/MMPC. This work offers an innovative strategy for microplastic management and wastewater treatment.

3D-printed heterogeneous Cu2O monoliths: Reusable supports for Antibiotic Treatmentantibiotic treatment of wastewater

In this study, surfactant stabilized dispersions of the Cu₂O microparticles in a commercially available photocurable resin were 3D printed into both porous and non-porous monoliths, and the heterogeneous Cu₂O catalytic monolith with improved mass transfer characteristics was applied for antibiotic wastewater treatment. The physicochemical properties of catalytic monoliths were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermogravimetric. Ten intermediates were analyzed and identified by GC-MS, and the corresponding degradation pathways were proposed. Both numerical simulation and degradation experiments were used to explore the mass transfer mechanism and catalytic performance of the monoliths. The results showed that the 3D-printed monolith with a well-defined porous network exhibited a high ofloxacin degradation efficiency (100%) based on the sulfate radical-based advanced oxidation processes. In addition, the catalytic monolith showed sustained high activity over 7 reusable cycles demonstrating its feasibility in removal of antibiotics from wastewater.

Synthesis of acidified magnetic sludge-biochar and its role in ammonium nitrogen removal: Perception on effect and mechanism

An acidified magnetic sludge-biochar (MSB) was prepared to enhance ammonium nitrogen (AN) removal efficiency in eutrophic water, and MSB was obtained by secondary pyrolysis of sludge biochar powder. A series of MSB were prepared under 300, 400, 500, 600 °C and different valence states of iron ions by impregnation pyrolysis, which is based on the deposition of unstable iron minerals on biochar matrix. Physicochemical properties of pristine biochar and MSB were revealed through characterization analysis, suggesting that MSB prepared by ferric chloride at 400 °C presented the largest adsorption capacity, and the acid-modification enhanced the ammonium adsorption capacity by 10.7%. Electrostatic attraction and ion-exchange processes were identified as the main adsorption mechanisms of MSB on AN. As the most dominant mechanism, ion exchange of AN with functional groups containing -OH and CO on the surface of MSB resulted in the relative content of -OH (61.3%) and CO (11.5%) bonds reduced to 34.2% and 7.0% respectively. The novel magnetic sludge-biochar with acid-modification possessed enhanced electron transfer capacity, revealing a removal pathway of ammonium by nitrification. The findings above demonstrated that MSB is a promising adsorbent for ammonium removal and can be applied to the natural nitrogen-rich water regulation.

Removal of methyl orange from water by Fenton oxidation of magnetic coconut-clothed biochar

Water pollution has become a serious environmental problem to date. Advanced oxidation processes (AOP) have been widely applied in water treatments.

Recent Development in Sludge Biochar-Based Catalysts for Advanced Oxidation Processes of Wastewater

Sewage sludge as waste of the wastewater treatment process contains toxic substances, and its conversion into sludge biochar-based catalysts is a promising strategy that merges the merits of waste reutilization and environmental cleanup. This study aims to systematically recapitulate the published articles on the development of sludge biochar-based catalysts in different advanced oxidation processes of wastewater, including sulfate-based system, Fenton-like systems, photocatalysis, and ozonation systems. Due to abundant functional groups, metal phases and unique structures, sludge biochar-based catalysts exhibit excellent catalytic behavior for decontamination in advanced oxidation systems. In particular, the combination of sludge and pollutant dopants manifests a synergistic effect. The catalytic mechanisms of as-prepared catalysts in these systems are also investigated. Furthermore, initial solution pH, catalyst dosage, reaction temperature, and coexisting anions have a vital role in advanced oxidation processes, and these parameters are systematically summarized. In summary, this study could provide relatively comprehensive and up-to-date messages for the application of sludge biochar-based catalysts in the advanced oxidation processes of wastewater treatment.

Heterogeneous ozonation of ofloxacin using MnOx -CeOx /γ-Al2 O3 as a catalyst: Performances, degradation kinetics and possible degradation pathways

In this study, the performance of ofloxacin (OFX) degradation in synthetic wastewater using synthesized MnO_x -CeO_x /γ-Al₂ O₃ as a heterogeneous ozonation catalyst was evaluated. The removal rates of OFX and chemical oxygen demand (COD) during 15-day continuous-flow experiments were 98.2% and 76.7% on average, respectively. An ozone index (mgCOD/mgO₃ ) of 1.09 with a high ozone utilization efficiency of 91.39% was achieved. The pseudo-first-order rate constant of ofloxacin degradation reached 15.216 × 10^-2  min^-1 , which was five times that (3.085 × 10^-2  min^-1 ) without catalysts. The results of gas chromatography-mass spectrometry (GC-MS) demonstrated that a variety of small-molecule organics occurred in the final oxidation products, such as 4-hydroxyl-4-methyl-2-pentanone and 2-oxoadipic acid in addition to homologs of OFX. The results of this study suggested that hydroxyl radicals played critical roles in the degradation and mineralization of OFX via four main pathways: (a) electrophilic addition of nitrogen; (b) breakdown of carbon-carbon double bonds; (c) hydrolysis of ether rings; and (d) halodecarboxylation of carboxyl groups. The biodegradability (BOD₅ /COD) of OFX after catalytic ozonation reached 0.54. PRACTITIONER POINTS: Ofloxacin wastewater was treated using catalytic ozonation in a 15-day continuous experiment with MnO_x -CeO_x /γ-Al₂ O₃ as a catalyst. The ozone index reached 1.09 mgCOD/mgO₃ during ozonation of ofloxacin. The presence of the catalyst increased the reaction rate constant by a factor of five. 4-hydroxy-4-methyl-2-pentanone was the primary ofloxacin oxidation product.

A novel strategy for enhancing heterogeneous Fenton degradation of dye wastewater using natural pyrite: Kinetics and mechanism

Hydrogen peroxide activation by pyrite for degradation of recalcitrant contaminants receives increasing attention. The improvement of catalytic efficiency of natural pyrite is still a challenging issue. This work provides a novel strategy of enhancing catalytic efficiency via pre-reaction between pyrite and hydrogen peroxide. Effects of process factors including pre-reaction time, hydrogen peroxide, solution pH and initial dye concentration were examined. Natural pyrite with low purity was characterized by Raman, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Reaction kinetic verifies tremendous improvement of the reaction rate through pre-reaction. Enhanced dye degradation is ascribed to hydroxyl radical production promoted by self-regulation of pH, Fe²⁺ releasing and Fe²⁺/Fe³⁺ cycle. The plausible mechanism was proposed based on multiple determinations. Dye degradation in different water matrix was efficiently obtained, as well as multicomponent dyes. Additionally, broad operation pH and good reusing performance make the developed process highly attractive for application. This work provides a solid step-forward of pyrite/hydrogen peroxide Fenton process for treatment of recalcitrant contaminants in wastewater.

The behavior of surface acidity on photo-Fenton degradation of ciprofloxacin over sludge derived carbon: Performance and mechanism

Sludge derived carbon (SC) has been widely used in advanced oxidation processes as an effective and economic catalyst. In this study, we applied surface modified SC for the first time to catalyze the heterogeneous photo-Fenton process with ciprofloxacin, a highly concerned emerging contaminant, as a model substance. H₂SO₄ was used to acidify the SCs under varying acid dosages, temperatures, and reaction time lengths. The surface acidity of SCs was quantitatively characterized with NH₃-TPD. A strong correlation between the surface acidity and the catalytic activity was clearly demonstrated. The highest catalytic activity was obtained with SC whose acidity was 0.149 mmol·g^-1 after being modified with 6 mol·L^-1 H₂SO₄ at -20 ℃ for 24 h. In addition, XRD, XRF, BET, XPS, and HRTEM were also used to characterize the obtained SC. ·OH radicals were found to be the main reactive species by EPR. Ten transformation products were identified by GC-MS, based on which three possible reaction pathways were proposed.

Improved Degradation Efficiency of Levofloxacin by a Self-Powered Electrochemical System with Pulsed Direct-Current

With the excellent structural design, rotary triboelectric nanogenerator (R-TENG) is suitable for harvesting mechanical energy such as wind energy and water energy to build a self-powered electrochemical system for environmental science. The electrochemical performance has been greatly improved by using the pulsed direct-current (PDC) output of a TENG; however, a full-wave PDC (FW-PDC) is hardly realized in R-TENG devices due to existence of phase superposition. Here, a R-TENG with FW-PDC output is reported to perform a self-powered electro-Fenton system for enhancing the removal efficiency of levofloxacin (OFL). By adjusting the rotation center angle ratio between each rotator and stator unit, the phase superposition of R-TENG caused by multiple parallel electrodes can be effectively eliminated, thus achieving the desired FW-PDC output. Because of the reduced electrode passivation effect, the removal efficiency of OFL is improved by 30% under equal electric charges through using the designed R-TENG with FW-PDC output compared to traditional R-TENG. This study provides a promising methodology to improve the performance of self-powered electrochemical process for treating environment pollutions.

Red mud modified sludge biochar for the activation of peroxymonosulfate: Singlet oxygen dominated mechanism and toxicity prediction

In this paper, red mud-sewage sludge derived biochar (RSDBC) was synthesized and employed as the heterogenous activator of peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. With the incorporation of red mud, 82.5% degradation of SMX was achieved by RSDBC/PMS system in a process dominated by ¹O₂, which was attributed to the participation of oxygen vacancy, ketone groups and graphitic carbon. On the other hand, in the absence of red mud, OH and SO₄^•- were dominantly accounted for SMX degradation in sewage sludge derived biochar (SDBC)/PMS system. In this case heterogeneous Fe species, ketone groups and graphitic carbon were responsible for PMS activation. Due to the different Reactive Oxygen Species (ROS), effects of reaction conditions including initial pH, common anions and natural organic matter (NOM) were not in full accord. Besides, Fe leaching from RSDBC (0.67 ppm) was much lower than that of SDBC (3.07 ppm), leading to a better reuse ability for RSDBC. Less degradation intermediates were disclosed in RSDBC/PMS system, along with lower residual toxicity. In addition, eco-toxicity of all the intermediates was predicted by ECOSAR program for the further understanding of the detoxification of SMX. Advantages of RSDBC/PMS system as disclosed in this paper further suggest its potential full-scale application of environmental remediation.

Acceleration of goethite-catalyzed Fenton-like oxidation of ofloxacin by biochar

While carbon materials have been well studied to stimulate the homogeneous Fenton-like processes, little was known about their impacts on iron mineral-catalyzed heterogeneous Fenton-like reactions. Here, it was found that biochar prepared at 300 °C or 600 °C (BC300 or BC600) greatly stimulated the degradation of ofloxacin (OFX) in a goethite (Gt)-mediated Fenton-like system. In 4 h, while only 38.4 % and 48.4 % OFX were removed in Gt/H₂O₂ and BC600/H₂O₂ systems, the removal efficiency reached over 94.0 % in Gt/BC600/H₂O₂ system. And the pseudo-first-order rate constant of Gt/H₂O₂, BC600/H₂O₂ and Gt/BC600/H₂O₂ systems were 0.12, 0.16 and 0.72 h^-1, respectively, indicating the occurrence of synergistically catalytic degradation. •OH was identified as the major oxidant. Both the •OH yield and the H₂O₂ utilization efficiency of Gt/BC600/H₂O₂ system were higher than those of Gt/H₂O₂ and BC600/H₂O₂ systems. BC600 showed better stimulation effects than BC300. The persistent free radicals (PFRs) of BC could activate H₂O₂ and partly contribute to •OH production in the Gt/BC/H₂O₂ system. While BC could not directly reduce Fe(III) in Gt, it improved the cycling of Fe(III)/Fe(II) through complexing Fe(III) with its carboxyl group. Potential pathways were proposed for OFX degradation in the Gt/BC/H₂O₂ system.

Study of polarized activated carbon filters as simultaneous adsorbent and 3D-type electrode materials for electro-Fenton reactors

Electro-Fenton (EF) based water treatment processes using activated carbon (AC) packed beds constitute an attractive approach for the development of competitive degradation technology of persistent pollutants in aqueous effluents. In this work, the results of a study aimed to assess the effect on the EF performance of different parameters of the reactor's operation are presented. By means of a factorial experimental design, the influence of the AC source (lignitic or vegetal), AC acid pre-treatment, particle size distribution and the amount of Fe loaded resin in the reactor were analyzed. From the resulting data it was found that the most influential parameter in the EF performance of the reactor is the AC source. Modest effects were observed for AC acid pre-treatment, which limits Fe ion adsorption on the AC substrate. The use of a wide particle distribution of AC particles was also found to improve inter-particle electrical contact, thus favoring the electrochemical processes that take place inside the reactor. An investigation on the effect of the amount of Fe in the reactor as well as its distribution dynamics, also revealed that an excess of Fe ions in the reactor decreases the EF performance of the system since Fe ions efficiently adsorb on the AC substrate, particularly in non- acid treated samples. The best operation conditions consisted on using un-meshed vegetable AC, without acid pretreatment in an EF reactor loaded with 0.25 g of Fe, which allowed to reach full color removal of bright blue FCP model dye in 70 min.

Fe3O4@S-doped ZnO: A magnetic, recoverable, and reusable Fenton-like catalyst for efficient degradation of ofloxacin under alkaline conditions

In this study, an efficient and reusable heterogeneous Fenton catalyst Fe₃O₄@S-doped ZnO magnetic composite was synthesized for the degradation of ofloxacin (OFX) under alkaline conditions without external energy input. The Fe₃O₄@S-doped ZnO exhibited excellent catalytic activity toward ofloxacin degradation within 120 min. Using 0.25 g/L of catalyst and 5.0 mL/L of H₂O₂ under optimized conditions, the catalyst was effective in pH values ranging from 5.2 to 9.0. The catalytic performance at optimal conditions was in accordance with a pseudo-first-order kinetics model. The reaction constant of Fe₃O₄@S-doped ZnO (0.0354 min^-1) was three times than that of Fe₃O₄@ZnO (0.0124 min^-1) under alkaline conditions (pH 8.2). The reactive oxygen species were the ·OH and O₂^·-, with ·OH dominating in the degradation of OFX. It is proposed that the catalyst acts as a Lewis acid, creating an acidic microenvironment on the catalyst's surface and widening the pH range of the Fenton reaction to alkaline conditions. Additionally, the catalyst was stable and reusable after six cycles of use. The Fenton-like Fe₃O₄@S-doped ZnO catalyst overcomes the problem of the narrow pH of the reaction system, thus providing promising environmental applications.

Significant enhancement of photo-Fenton degradation of ofloxacin over Fe-Dis@Sep due to highly dispersed FeC6 with electron deficiency

An efficient strategy for enhancing iron efficiency in heterogeneous Fenton reaction via the pyrolysis of ferrocene chemically modified sepiolite (Sep) was proposed in this study. Highly dispersed FeC₆ on sepiolite (Fe-Dis@Sep) was synthesized as an efficient photo-Fenton catalyst for the visible light degradation of ofloxacin (OFX). It exhibits an excellent Fenton activity and stability towards OFX degradation. The pseudo-first order reaction rate constant of Fe-Dis@Sep was 5.1-fold higher than that of the supported catalyst with aggregated iron oxides prepared by traditional impregnation method (Fe-Agg@Sep). Based on TEM images and density functional theory (DFT) calculation, the enhanced Fenton activity of Fe-Dis@Sep was attributed to the unique incorporation of FeC₆ on Sep via Si-O-C-Fe bond which not only favor the high dispersion of FeC₆ with an electron deficiency but also promote Fe(III) to Fe(II) cycle via the formation of surface Fe-H₂O₂ complex. OH and O₂^- were identified as active species for OFX degradation in Fe-Dis@Sep-H₂O₂-Vis system. 98.7% of F and 97.0% of N in OFX was converted into F^- and NO₃^- with a TOC removal efficiency of 89.35%. The possible degradation pathway of OFX was also proposed according to HPLC-MS results. Finally, the Fenton reaction mechanism over Fe-Dis@Sep was discussed.

Ultraviolet/peroxydisulfate degradation of ofloxacin in seawater: Kinetics, mechanism and toxicity of products

The ultraviolet/peroxydisulfate (UV/PDS) system was used to degrade ofloxacin (OFL) in fresh water, synthetic marine aquaculture water and synthetic seawater. The comparison of the reaction degradation rate constants proved that the order of reaction rate was the following: synthetic seawater (0.77 min^-1) > synthetic marine aquaculture water (0.74 min^-1) > freshwater (0.30 min^-1). Bromide (Br^-) and bicarbonate (HCO₃^-) promote the degradation of OFL, whereas chloride (Cl^-) inhibits the degradation. The piperazine ring of OFL was the main reactive group, and atoms N1, C6, C7 and N2 were identified as the reaction sites. Based on the intermediate and final products, the possible degradation pathways of OFL in the three kinds of water were proposed. Additionally, during the UV/PDS treatment of synthetic marine aquaculture water containing Cl^- and Br^-, the oxidation products of OFL showed a slight toxicity to Chlorella pyrenoidosa (C. pyrenoidosa) and Priacanthus tayenus (P. tayenus). The maximum growth inhibition rate of the products to C. pyrenoidosa was 9.72%. The products also caused liver cells of P. tayenus to be damaged and reduced the species richness and diversity of intestinal microorganism. Nevertheless, compared with the products degraded by traditional disinfection methods using NaClO, the biological toxicities were much lower. UV/PDS can be used for seawater as a new alternative disinfection method.

In-situ self-assembly of robust Fe (III)-carboxyl functionalized polyacrylonitrile polymeric bead catalyst for efficient photo-Fenton oxidation of p-nitrophenol

From the view of channel confinement and functional site capture, we develop an in-situ self-assembly strategy to fabricate the carboxyl functionalized Fe-HPAN bead catalyst with highly stable and uniformly dispersed metallic sites for efficient photo-Fenton oxidation of p-nitrophenol (p-NP). BET and FTIR analysis reveal that numerous carboxyl groups and mesopores exist in Fe-HPAN beads, which acts to capture and immobilize iron ions. Catalytic results show that the degradation rate and TOC removal for p-NP were up to 99.78 and 91.68% under the optimal condition. Even at near neutral pH, the degradation rate almost keep the same and the TOC removal can still reach 73.05%. Due to the autocatalytic cycle of Fe^III/Fe^II, the apparent rate constant of Fe-HPAN (0.2247 min^-1) was 5.4 times as high as unmodified Fe-PAN (0.0415 min^-1) in the presence of H₂O₂ and visible light irradiation, which was 2-3 orders of magnitude larger than that of other reaction systems. More importantly, Fe-HPAN bead catalyst exhibited little loss of activity even after 20 cycles of re-utilization. The possible degradation pathway of p-NP was also proposed based on GC/MS analysis. The present work may provide a new perspective for the use of synthetic polymer to prepare low-cost, efficient and robust photo-Fenton oxidation catalysts.

A novel discovery of a heterogeneous Fenton-like system based on natural siderite: A wide range of pH values from 3 to 9

Natural iron-bearing minerals have been proven to be effective for activating H₂O₂ to produce OH, which can be used to degrade organic pollutants. In this study, the performance of siderite to degrade sodium sulfadiazine via catalytic H₂O₂ degradation was investigated at different solution pH values from 3 to 9. An interesting discovery was made: the performance of the siderite-H₂O₂ system was excellent under acidic, neutral, and even alkaline conditions. The influence of various factors (e.g. initial concentration, anions, natural organic matters, etc.) on the system under different pH conditions was investigated, which confirmed that siderite exhibited an excellent catalytic performance. By combining EPR characterization with scavenger research, it was proposed that dissolved iron (Fe²⁺) mainly initiated the homogenous Fenton reaction to degrade pollutants under acidic conditions, while structural Fe²⁺ species present in siderite triggered Fenton-like reactions under neutral or even alkaline conditions. From the SEM and XPS characterizations, oxidation and dissolution of Fe²⁺ on the surface were also observed, confirming our inference concerning the different reaction mechanisms. The experimental findings show that this siderite-H₂O₂ system can be used in solutions with pH values from 3 to 9 and that siderite plays a positive role in soil and groundwater remediation when H₂O₂ is used as an oxidant.

Impact of pyrone group on H2S catalytic oxidization

The surface functional group plays an important role in H₂S catalytic oxidization. However, the specific effect of each group species has seldom been investigated. For the first time, we revealed by experimental and theoretical methods that the pyrone group was the most valuable group. An increase in the pyrone-group amount obviously decreased the kinetic reaction order of H₂S catalytic oxidization. The catalyst with the largest amount of pyrone group (0.1321 mmol·g^-1) showed the lowest reaction order (0.5896) and activation energy (16.25 kJ·mol^-1). By comparison, a catalyst with 0.0008 mmol·g^-1 of pyrone group had a reaction order of just 1.1852 and an activation energy of 81.22 kJ·mol^-1. The contribution of pyrone content to the kinetic reaction order had a negative correlation coefficient of -8.0665, which was three and five times larger than that of the quinone (-2.5568) and acidic groups (-1.7454), respectively. Moreover, density functional theory calculations showed that the pyrone group had the lowest energy gap (0.156 eV), far less than that (1.921 eV) of the carboxyl group. After H₂S was adsorbed, the pyrone group had a Mulliken atomic charge of 0.510, which was larger than that (0.236) of the carboxyl group. In other words, the pyrone group showed the best ability to facilitate electron transfer. As a result, the catalyst with 0.1321 mmol·g^-1 of the pyrone group removed 100% of the H₂S (450 ppm). This amount was 42% higher than a catalyst with 0.0008 mmol·g^-1 of the pyrone group. The main results of this work help to explain the mechanism of carbon material in various types of catalysis.

The Occurrence and Risks of Selected Emerging Pollutants in Drinking Water Source Areas in Henan, China

The occurrence of organic micropollutants (OMPs) in aqueous environments has potential effects on ecological safety and human health. Three kinds of OMPs (namely, pharmaceuticals, ultraviolet (UV) filters and organophosphate esters (OPEs)) in four drinking water source areas in Henan Province of China were analyzed, and their potential risks were evaluated. Among 48 target chemicals, 37 pollutants with total concentrations ranging from 403.0 to 1751.6 ng/L were detected in water, and 13 contaminants with total concentrations from 326.0 to 1465.4 ng/g (dry weight) were observed in sediment. The aqueous pollution levels in Jiangang Reservoir and Shahe Water Source Area were higher than that in Nanwan Reservoir and Baiguishan Reservoir, while the highest total amount of pollutants in sediment was found in Baiguishan Reservoir. Compared with pharmaceuticals and UV filters, OPEs presented higher concentrations in all investigated drinking water source areas. The highest observed concentration was triphenylphosphine oxide (TPPO, 865.2 ng/L) in water and tripentyl phosphate (TPeP, 1289.8 ng/g) in sediment. Moreover, the risk quotient (RQ) analysis implies that the determined aqueous contaminants exhibited high risks to algae and invertebrates, whereas moderate risk to fish was exhibited. The health risk assessment of aqueous OMPs by means of the hazard index (HI) indicates that the risks to adults and children were negligible. These observations are expected to provide useful information for the assessment of water quality in drinking water sources in Henan, China.

Editorial of the VSI "Antibiotics and heavy metals in the environment: Facing the challenge"

The Virtual Special Issue (VSI) "Antibiotics and Heavy Metals in the Environment: Facing the Challenge" received more than 100 submissions from research teams around the world. Finally, more than 50 papers were accepted and published. These very interesting research papers allow going ahead in the knowledge of different aspects which determine the fate of antibiotics and heavy metals in the environmental. The success of the VSI, as well as reports from scientific databases, indicate that this field of research is clearly growing, which is expected to continue, especially considering emerging pollutants as a whole.