Search Results (777)

Industrial wastewater containing refractory organic compounds, heavy metals, and emerging contaminants poses a significant challenge to conventional treatment methods due to their high chemical stability and toxicity. This review systematically summarizes recent advances in Fenton-based advanced oxidation processes (AOPs) for industrial wastewater treatment, with a particular focus on the paradigm shift from homogeneous to heterogeneous catalytic systems. Homogeneous Fenton processes, which rely on Fe²⁺/H₂O₂ reactions, exhibit rapid reaction kinetics but are severely limited by a narrow operational pH range (2–4) and the generation of substantial iron sludge. In contrast, heterogeneous Fenton systems employing immobilized or supported catalysts—such as iron-loaded zeolites, metal–organic frameworks, and carbon-based composites—broaden the applicable pH range to near-neutral conditions (4–8), enable catalyst recovery and reuse over multiple cycles, and enhance process sustainability by reducing iron leaching and sludge production. Integration with external energy inputs—such as photo, electricity, or ultrasound—can further promote radical generation and mass transfer, improving degradation efficiency while reducing chemical consumption. Practical applications in treating wastewater from textile, pharmaceutical, and electroplating industries have demonstrated effective contaminant removal and enhanced biodegradability. However, most current research remains at the laboratory scale, with long-term catalyst stability, operational costs, and scalability representing major barriers to large-scale implementation. Future research should focus on developing stable and regenerable catalysts, advancing pilot-scale studies of integrated systems, and conducting long-term evaluations under real wastewater conditions to promote the development of efficient, low-carbon, and sustainable solutions for industrial wastewater treatment. Full article

Constructed wetlands (CWs) are widely used for wastewater treatment but can also serve as significant sources of nitrous oxide (N₂O), a potent greenhouse gas. Balancing efficient nitrogen removal with N₂O mitigation remains a critical challenge for sustainable wastewater management. This review systematically elucidates the key microbial mechanisms underlying N₂O emissions in CWs and summarizes corresponding mitigation strategies. Mechanistically, N₂O production is primarily driven by hydroxylamine oxidation and nitrifier denitrification mediated by ammonia-oxidizing microorganisms, as well as incomplete heterotrophic denitrification resulting from electron-donor limitation. These pathways are tightly regulated by spatiotemporal redox gradients, carbon-to-nitrogen ratios, and influent strength conditions. To address these emissions, this review synthesizes mitigation strategies from an engineering perspective. Optimization of operational parameters, such as intermittent aeration and water-level regulation, together with the application of novel functional substrates, such as biochar and iron-carbon micro-electrolysis, can effectively facilitate electron transfer and improve micro-redox conditions. Furthermore, optimized plant species selection and community design, along with emerging low-carbon biological nitrogen removal processes, such as autotrophic denitrification and partial denitrification coupled with anammox, offer promising approaches for substantial emission reduction. Overall, this review provides practical guidance for designing efficient, low-carbon CWs toward carbon neutrality. Full article

Anatase-bearing lateritic ores from Qinglong, Guizhou Province, China, are characterized by extremely low TiO₂ grade, high clay content, fine-grained dissemination, and complex intergrowths with iron oxides, which severely hinder efficient beneficiation. In particular, anatase commonly occurs as ultra-fine particles encapsulated by clay minerals or closely associated with iron oxides, and its surface is often covered by nanoscale goethite films, resulting in surface passivation and pseudo-magnetic behavior. These characteristics lead to a pronounced contradiction between mineral liberation and excessive slime generation during conventional grinding processes. To address these challenges, a high-efficiency pre-concentration flowsheet was developed based on selective desliming, stage grinding, intensive scrubbing, flotation, and weak magnetic separation. Selective desliming via hydrocyclones was adopted, which is inferred to preferentially discard true slimes finer than 10 μm while potentially retaining most fine anatase particles within the underflow. Stage grinding was then applied, which may promote the improved liberation of anatase and early rejection of coarse gangue, and may help reduce overgrinding. Intensive scrubbing was introduced, which is expected to weaken or partially remove iron oxide coatings from the anatase surface, thereby potentially restoring surface activity and reducing pseudo-magnetic interference. Subsequent flotation and low-intensity magnetic separation were optimized to increase the concentrate TiO₂ grade and cut iron impurities, which may be associated with improved surface selectivity and weakened pseudo-magnetic responses. Closed-circuit beneficiation tests demonstrated that a TiO₂ concentrate with a grade of 29.62% and a recovery of 65.4% could be obtained from an ore with an initial TiO₂ grade of only 4.39%. Moreover, approximately 40% of the feed mass was rejected at the pre-concentration stage, significantly reducing the load on downstream separation processes. The proposed process demonstrates promising potential as a technical route for the beneficiation of similar refractory anatase-bearing lateritic ores. Full article

To explore a new approach to reducing the use of external carbon sources and phosphorus removal chemicals in conventional wastewater treatment, this study developed an anaerobic–oxic–anoxic sequencing batch reactor (AOA-SBR) system (Rf) with iron shavings addition (180 g, 60 g/L), using a blank reactor (R0) as the control. Synthetic wastewater with a C/N ratio of 7.5 was used as the influent. The operating cycle of the AOA-SBR reactor consisted of a 120 min anaerobic phase, a 120 min aerobic phase, and a 60 min anoxic phase, with a hydraulic retention time (HRT) of 12 h. Results showed that the SVI₃₀ of Rf remained at approximately 35 mL/g. The average removal efficiencies of TN and TP in Rf reached 70% and 96%, respectively, which were higher than those of the control. The addition of waste iron shavings improved sludge settleability and nitrogen and phosphorus removal performance of the biochemical system. Fe-C microelectrolysis significantly enriched Candidatus_Competibacter and Candidatus_Nitrocosmicus while inhibiting nitrite-oxidizing bacteria (NOB). This triggered persistent low-level nitrite accumulation within the system, diversified nitrogen-removal pathways, and ultimately improved the total nitrogen-removal efficiency. The extended anaerobic period in the anaerobic–oxic–anoxic (AOA) mode enriched phosphate-accumulating organisms, achieving synergistic chemical and biological phosphorus removal. This study provides a novel strategy for advanced wastewater treatment without external carbon sources or phosphorus additives. Full article

The persistence of refractory organic pollutants (e.g., antibiotics) in aquatic environments necessitates efficient and sustainable remediation strategies. In this study, a circular economy approach was adopted to convert iron sludge into a value-added carbon residue (CR) composite via one-step co-pyrolysis. The resulting material was designed as dual-functional, enabling synergistic pollutant removal through adsorption and catalytic oxidation. Experimental results demonstrated that the CR composite effectively adsorbed and degraded organic pollutants. The primary adsorption sites were attributed to surface functional groups, porous structure, and electrostatic interactions. Meanwhile, iron species, surface functional groups, and persistent free radicals facilitated the generation of singlet oxygen (¹O₂) and hydroxyl radicals (·OH), which in turn promoted pollutant degradation. The CR/PDS system exhibited excellent performance in real wastewater remediation, which was attributed to the high interference resistance of ¹O₂. Furthermore, the application of CR did not pose any significant environmental risk in aqueous solutions. Taken together, these findings present a novel material for pollutant removal and provide a cost-effective strategy for the valorization of waste iron sludge. Full article

The growing global population has increased energy and food demand, leading to a higher production of waste streams such as fly ash from the energy sector and wastewater from food and beverage industries. Without proper treatment, these wastes pose significant environmental concerns. One promising strategy is to repurpose industrial byproducts for wastewater treatment. Winery wastewater, for instance, contains acidic organic compounds and alcohol that are difficult to remove using conventional methods, while large amounts of fly ash remain underutilized. This study, therefore, examines a hybrid system that combines fly ash-assisted Fenton oxidation with membrane filtration for winery wastewater treatment. The process involved sequential Fenton pre-treatment followed by lab-scale nanofiltration using a 1 kg/mol ceramic membrane (13.1 cm²). A Design of Experiments approach was applied to evaluate system performance under varying H₂O₂ dosages (10–30 mL/L), fly ash loadings (1–3 g/L), and membrane fluxes (40–80 LMH). Filtration was performed through multiple constant-flux cycles, with energy requirements ranging from 400 to 800 kWh/m³ for the flux variations calculated from the lab-scale pump operating at a constant power supply. The hybrid method showed strong performance, achieving 70% TOC removal and 90% reduction of color and iron. However, considerable membrane fouling was observed, likely due to increased retention and deposition of organic matter, iron, and fly ash during filtration. Full article

Iron-based Fischer–Tropsch synthesis (Fe-FTS) catalysts are central to coal-to-liquid (CTL) processes but suffer from rapid and complex deactivation under industrial conditions. This review critically examines the key deactivation mechanisms, including carbon/wax deposition, hydrothermal sintering, chemical poisoning (S, Cl, As), and mechanical attrition, and evaluates modern regeneration strategies. These strategies include supercritical fluid extraction for wax removal, controlled oxidative decoking, reductive reconstruction of active iron carbides (χ-Fe₅C₂), chemical de-poisoning, and structural upcycling. We also discuss emerging techniques such as non-thermal plasma and supercritical fluid-assisted reactivation. Finally, we highlight challenges in irreversible phase transformation, in -situ regeneration engineering, and economic feasibility, and outline future directions toward regeneration-friendly catalyst design and advanced syngas purification for a circular CTL economy. Full article

Hydrogen–steel interactions remain a critical concern for the safe deployment of hydrogen–natural gas mixtures in pipeline infrastructures. Thermally grown iron oxides may be a good barrier to hydrogen ingress into the crystalline lattice of pipeline steels, but their actual effectiveness depends strongly on their composition and stability under service conditions. Several experimental approaches have been proposed to investigate the correlation between thermally grown oxides and hydrogen permeation. Among these, electrochemical permeation testing offers a more complex but safer methodology compared to pressurized hydrogen gas tests. However, when the oxide is directly exposed to the charging side (cathodic charging conditions), permeation behaviour often appears comparable to that of bare steel, and rapid oxide degradation occurs. This study introduces an alternative permeation testing configuration that enables direct assessment of thin thermally grown oxides while preserving their structural integrity. By deliberately placing the oxide on the anodic detection side, mechanical removal during hydrogen evolution is suppressed, allowing the intrinsic resistance of the oxide to hydrogen transport to be evaluated. Carbon steel samples were thermally oxidized at 250 °C for controlled exposure times, and the resulting oxide scales were characterized by Raman spectroscopy, revealing variations in hematite and magnetite fractions. Hydrogen permeation was evaluated using a Devanathan–Stachurski cell by positioning the oxidized surface either on the cathodic charging side or on the anodic detection side. Under these conditions, significant variations in apparent steady-state permeation current density were observed as a function of oxidation time and oxide composition. Full article

The contamination of aquatic environments by cadmium and other toxic heavy metals represents a major environmental concern requiring efficient and operationally sustainable remediation strategies. In this work, iron oxide materials were synthesized through a microwave-assisted hydrothermal method and evaluated for Cd(II) removal from aqueous systems. Different precursor compositions and organic additives were initially screened in order to identify the most suitable adsorbent formulation. The selected Fe-Tart material was characterized by FTIR, SEM-EDS, and XRD analyses, revealing hydroxylated and poorly crystalline iron oxide structures with heterogeneous surface organization. Batch adsorption experiments were performed under controlled conditions to investigate the influence of pH and equilibrium adsorption behavior, while adsorption data were analyzed using Langmuir and Freundlich isotherm models. Cd(II) uptake showed strong pH dependence, with adsorption progressively increasing from acidic to near-neutral conditions and reaching approximately 80% removal at pH 7–8. The Langmuir model provided the best fitting results (R² = 0.988), suggesting preferential occupation of energetically comparable surface sites with a maximum adsorption capacity of 6.51 mg g⁻¹. The adsorption behavior was interpreted within a pH-dependent surface complexation framework involving hydroxylated iron oxide surfaces. Although the adsorption capacity remained lower than that reported for some highly engineered adsorbents, the results indicate that microwave-assisted synthesis may provide a relatively simple and rapid route for preparing iron oxide-based materials potentially applicable to water remediation systems. Full article

Chlorpyrifos, a widely used organophosphate pesticide, poses significant environmental risks due to its persistence and the formation of toxic transformation products. Despite extensive research on iron-based Fenton systems, the application of manganese oxides, particularly α-Mn₂O₃, in chlorpyrifos degradation remains insufficiently explored. In this study, we investigated the catalytic performance of α-Mn₂O₃ in Fenton and visible-light-driven photo-Fenton processes for the degradation of chlorpyrifos in aqueous systems. Chlorpyrifos oxon was identified as a transient intermediate, detected at trace levels, supporting an oxidative degradation pathway. Kinetic analysis revealed pseudo-first-order behavior, with comparable rate constants for Fenton reactions at different catalyst loadings (0.0033 min⁻¹ for 5 mg and 0.0028 ± 0.0006 min⁻¹ for 10 mg), indicating that the process is not limited by catalyst concentration under the investigated conditions. In contrast, the photo-Fenton system exhibited a higher rate constant (0.0042 min⁻¹) and significantly improved degradation efficiency, highlighting the role of visible-light activation. The highest removal rates of chlorpyrifos were 86.24% for Fenton experiments and 96.05% for the photo-Fenton experiment, respectively. The enhanced performance is attributed to the photocatalytic properties of α-Mn₂O₃, including its narrow bandgap and the facilitation of Mn³⁺/Mn²⁺ redox cycling, which promotes reactive oxygen species generation. These findings demonstrate that α-Mn₂O₃ is a promising non-iron catalyst for advanced oxidation processes and provide new insights into manganese-mediated Fenton-like mechanisms for the removal of organophosphate contaminants. Full article

Synthetic textile dye solutions are commonly used as controlled model systems to evaluate adsorbent performance before application to real textile wastewater matrices. In this study, a magnetic adsorbent was developed by functionalizing pomegranate peel-derived biochar with iron oxide (Fe₃O₄) nanoparticles and was applied for chemical oxygen demand (COD) removal from synthetic aqueous solutions containing three individual acid dyes: Buracid Yellow BGL, Buracid Navy Blue RL, and Buracid Red FN. The effects of adsorbent loading, pH, contact time, and dye type on COD removal were systematically evaluated and optimized using Response Surface Methodology (RSM). The experimental results showed that adsorbent loading, pH, and contact time significantly influenced COD removal efficiency. The developed quadratic model showed good explanatory performance, with R² = 83.42% and adjusted R² = 79.28%, while the predicted R² value of 72.65% indicated moderate predictive capability. Under the identified optimum operating region (pH 7.4, contact time 35 min, and adsorbent loading 80 g/L), COD removal efficiency reached up to 84%, depending on dye type. These findings indicate that Fe₃O₄-modified pomegranate peel biochar is a promising adsorbent for COD reduction from synthetic textile dye solutions. However, further validation using real textile wastewater is required to evaluate matrix effects caused by salts, surfactants, suspended solids, mixed dyes, and other textile auxiliaries. Full article

This study investigates the degradation and mineralization of sulfamethazine (SMT) by an electrochemically assisted Fe³⁺/persulfate (electro/Fe³⁺/PDS) process. Experiments were conducted in a single-compartment electrochemical cell equipped with a carbon felt anode and a stainless steel cathode under constant current conditions. Compared with PDS alone and Fe³⁺/PDS, the combined electro/Fe³⁺/PDS system exhibited a strong synergistic effect, achieving up to 89.4% SMT removal within 90 min at a current intensity of 1.6 A. The enhanced performance was attributed to electrochemical Fe²⁺ regeneration enabling continuous activation of persulfate and generation of sulfate radicals (SO₄^•−). Operational parameters significantly influenced process efficiency. Increasing current intensity accelerated SMT degradation but reduced mineralization efficiency due to parasitic reactions. Under optimized conditions (I = 3 A and [Fe³⁺] = 1 mM), SMT degradation reached 96.83% after 60 min, while the mineralization yield attained 72.05%. Excess iron promoted radical scavenging. Similarly, a PDS concentration of 5 mM was sufficient, with higher dosages leading to self-scavenging effects. Kinetic analysis followed a pseudo first order model, with apparent rate constants decreasing at higher SMT concentrations due to radical competition. Biodegradability assays revealed a substantial increase in the BOD₅/COD ratio from initially low values to 0.34 after 300 min of pretreatment, indicating improved suitability for biological post-treatment. Overall, the electro/Fe³⁺/PDS process represents an efficient pre-oxidation strategy for the removal of refractory antibiotics from aqueous media. Full article

Petroleum hydrocarbons contamination in soil is difficult to remediate due to strong adsorption and limited bioavailability. This study investigated the coupled remediation of diesel contamination in an alkaline kaolin-based model substrate using a silica gel-loaded, iron-catalyzed sodium percarbonate composite (SPC^SF) and Bacillus subtilis. The alkaline model substrate was used as a simplified representation of difficult-to-reclaim hydrocarbon- and reagent-impacted matrices that may occur at oil drilling or production sites. In this study, a combined remediation strategy integrating a silica gel-loaded, iron-catalyzed sodium percarbonate composite (SPC^SF) with Bacillus subtilis ATCC 11774 was developed for diesel-contaminated soil. The remediation performance of chemical oxidation, microbial remediation, and their combined application was systematically evaluated. The simultaneous SPC^SF–microbial treatment achieved the highest removal efficiency, reaching 65.1% after 31 d, which was markedly higher than that of chemical oxidation (22.5%) or microbial remediation alone (31.1%). Within the mineral model substrate used in this study, SPC^SF effectively regulated pH and oxidation–reduction potential, creating conditions more favorable for microbial activity. Spectroscopic analyses (three-dimensional fluorescence spectrum, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy) indicated that SPC^SF promoted the transformation of diesel hydrocarbons into bioavailable intermediates, which were further converted by microorganisms into carboxyl-rich organic matter. Bacillus subtilis was associated with a higher Fe(II) proportion in the coupled system, which may have favored maintenance of Fe redox activity and sustained Fenton-like reactivity. However, direct measurements of reactive oxygen species and Fe(II)/Fe(III) dynamics were not performed; therefore, this interpretation should be regarded as a plausible hypothesis based on indirect evidence. The specific microbial contribution to Fe redox transformation was inferred from indirect evidence and may also have been influenced by medium-derived components or microbial metabolites. This study presents a coupled supported sodium percarbonate and microbial remediation strategy providing mechanistic evidence for the compatibility of supported chemical oxidation and microbial degradation in diesel-contaminated soil. Full article

The purpose of this study was to investigate the effectiveness and mechanism of iron-based catalysts in the treatment of phenolic wastewater by catalyzing ozone oxidation. The removal rates of phenolics and COD were systematically examined using simulation experiments with water and actual wastewater, which involved analyzing the effects of reaction time, pH, ozone dosage, catalyst dosage, and initial concentration. The phenol and COD removal rates in the simulated wastewater were 95.9% and 93.5%, respectively, respectively, while the ozone dosage was 16 mg/L/min, pH was 6.7–6.8, and catalyst dosage was 0.3 g/L. The phenol and COD removal rates in the actual wastewater were 68.6% and 68.0%, respectively. The reaction time was 30 min. The system’s efficient removal ability for phenolic compounds, polycyclic aromatic hydrocarbons, and others was confirmed through three-dimensional fluorescence and ultraviolet spectroscopy. The iron-based catalyst generates ·OH through three pathways: adsorption of activated ozone on surface active sites, continuous production of free radicals by Fe²⁺/Fe³⁺ cycling, and direct activation of ozone by Fe²⁺. This mechanism analysis showed that the catalyst generates ·OH. These pathways convert pollutants into small molecules or mineralized by attacking the aromatic rings and conjugated structures of pollutants. Technical references for the deep treatment of phenol-containing wastewater are provided in this study. Full article

The catalytic removal of refractory VOCs in gas–solid reactions usually suffers from the formation of toxic byproducts and catalyst deactivation. The advanced oxidation process (AOP) wet scrubber has recently attracted interest in VOCs purification due to its high efficiency and inhibited gaseous byproducts emission. MOFs/metal sulfides (termed M50C50) were designed to activate peroxymonosulfate (PMS) for toluene removal in a wet scrubber. The heterojunction interface synergistically couples MIL-100(Fe) and CoS for dual functions, the M50C50 enabled the rapid transfer the toluene from the gas phase to the aqueous phase, where they were subsequently mineralized by SO₄^•− and •OH radicals. The primary active sites responsible for PMS activation were identified as reducing sulfur species, along with low-valence cobalt and iron species. Over 90% of toluene were removed with a wide pH range, while •OH and SO₄^•− were involved in the mineralization of intermediates. The process showed high mineralization efficiency (75% CO₂ evolution) and effectively reduced the formation of toxic byproducts, underscoring its potential for minimizing secondary pollution risks. This work provides a novel route to designing composite catalysts for deep VOC oxidation via AOP wet scrubbers, greatly facilitating their use in environmental remediation. Full article