Key Takeaways & Executive Findings
- •• • Achieved 91% decolorization of Congo red within 20 min and 82% mineralization within 60 min under optimal conditions (5 mA·cm−2, 480 L·(m2·h)−1, 0.15 mmol·L−1 CR, 75 mmol·L−1 NaCl), demonstrating high efficiency for high-salinity wastewater treatment. • • Flow-through mode enhanced mass transfer with a rate constant of 2.23×10−4 m·s−1, three times higher than conventional mode, and reduced diffusion layer thickness to 2.68 μm, significantly improving pollutant-anode contact. • • Active chlorine and H2O2 production increased by 32.8% and 66.7% respectively, reaching 0.61 mmol·L−1 and 0.24 mmol·L−1, enabling efficient generation of singlet oxygen (1O2) as the dominant reactive species. • • The system achieved >90% decolorization for five typical dyes with an energy consumption of only 0.16 kWh·m−3, indicating cost-effectiveness and broad applicability for industrial textile effluents.
Abstract
To address the challenges of high salinity, recalcitrance, limited mass transfer, and coating detachment in traditional anodes for textile wastewater treatment, a porous RuO2@r-TiO2 nanotube array (NTA) anode was fabricated via anodic oxidation, electrochemical reduction, and thermal decomposition. A flow-through electrochemical oxidation system was constructed using this anode and a graphite felt cathode. The material's morphology and physicochemical properties were characterized by SEM, XRD, and XPS. Congo red (CR) was used as a model pollutant to evaluate degradation performance under various conditions. Optimal conditions were identified as current density 5 mA·cm−2, permeate flux 480 L·(m2·h)−1, initial CR concentration 0.15 mmol·L−1, and NaCl concentration 75 mmol·L−1. Under these conditions, the system achieved 91% decolorization within 20 min and 82% mineralization within 60 min. Mass transfer tests showed a rate constant of 2.23×10−4 m·s−1 in flow-through mode, three times higher than conventional mode, with active chlorine and H2O2 production increased by 32.8% and 66.7%, respectively. Radical quenching experiments indicated that singlet oxygen (1O2) was the primary reactive species. The degradation mechanism was proposed based on quenching and UV spectral analysis. The system achieved >90% decolorization for five typical dye pollutants with an energy consumption of only 0.16 kWh·m−3. Cyclic voltammetry confirmed long-term stability. These findings provide theoretical support for applying electrochemical advanced oxidation to high-salinity textile wastewater.
1. Introduction
Textile wastewater, characterized by high salinity, intense color, and poor biodegradability, poses a significant environmental challenge. Conventional treatment methods, including biological processes, often fail to meet discharge standards due to the recalcitrance of synthetic dyes. Advanced oxidation processes (AOPs) such as Fenton and ozonation are effective but suffer from high chemical consumption and secondary pollution. Electrochemical advanced oxidation processes (EAOPs) offer a promising alternative due to their mild conditions, no external chemical addition, and flexible operation. However, the performance of EAOPs is critically dependent on the anode material. Traditional plate anodes, such as DSA electrodes, exhibit limited mass transfer due to thick boundary layers (>100 μm), and their catalytic coatings often delaminate from the titanium substrate, leading to electrode deactivation and poor long-term stability.
To overcome these bottlenecks, this study introduces a porous RuO2@r-TiO2 nanotube array anode fabricated on a porous titanium foam substrate. The in-situ growth of TiO2 nanotube arrays enhances coating adhesion and provides a high surface area. Operating in flow-through mode, the porous structure significantly reduces the diffusion layer thickness, thereby improving mass transfer and the utilization of electrogenerated oxidants. This design directly addresses the limitations of conventional EAOPs, offering a more efficient and stable solution for the treatment of high-salinity dye wastewater.
Loading authentic research manuscript (Pages 1–5)...
HUANG Zijiao, WEI Jiaqi, KONG Xinyi, CUI Jiayi, ZHANG Yuanyuan, WEI Qiaoyan, ZHENG Junjian, JU (2026). Electrocatalytic Oxidation Performance and Mechanism of Porous Active Metal Oxide Coated Anode for Congo Red Degradation. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202506064
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the long-term stability of the RuO2@r-TiO2 NTAs anode under continuous operation?
Cyclic voltammetry tests confirmed the electrode's long-term stability, indicating that the RuO2 coating remains adhered to the TiO2 nanotube array substrate, preventing delamination and maintaining catalytic activity over extended periods.
How does the flow-through mode enhance mass transfer compared to conventional plate electrodes?
Flow-through mode reduces the diffusion layer thickness to 2.68 μm, significantly lower than the >100 μm boundary layer in conventional mode. This results in a mass transfer rate constant of 2.23×10−4 m·s−1, three times higher, thereby increasing the contact efficiency between pollutants and reactive species.
What is the energy consumption and scalability potential of this system for industrial application?
The system achieves an energy consumption of only 0.16 kWh·m−3, which is highly competitive. The use of porous titanium foam and scalable fabrication steps suggests potential for scale-up, though further pilot-scale studies are needed to assess long-term operational costs and electrode replacement frequency.
What is the dominant degradation mechanism for Congo red in this system?
Radical quenching experiments revealed that singlet oxygen (1O2) is the primary reactive species, generated from the reaction of electrogenerated H2O2 with active chlorine. The contribution of free radicals (·OH, Cl·, O2·−) is minor, accounting for only 19.8% of degradation.
How does the system perform with other dye pollutants besides Congo red?
The system achieved >90% decolorization for five typical dyes, including methyl orange, methylene blue, Coomassie brilliant blue, and malachite green, demonstrating broad-spectrum applicability for various dye structures and functional groups.
Related Chinese Research & Cross-Citations
Analysis of National and Local Policies for Medical Waste Treatment and Disposal in China
The escalating generation of medical waste, driven by healthcare expansion and frequent medical activities, poses significant environmental and public health risks. Under the framework of ecological civilization, China is developing a comprehensive policy system for medical waste treatment and disposal, yet the current framework remains nascent and exhibits inconsistencies between national and local policies. This study systematically analyzes the status of national and local policies from 2003 to 2024, collecting 413 policy documents (166 from national ministries and 247 from provincial governments). The analysis examines temporal evolution, regional distribution, and policy focus, alongside the influence of medical waste output, treatment technologies, facility infrastructure, and major epidemic responses. Findings reveal distinct policy phases: initial self-disposal, exploratory management, foundational system building, and rapid development. Regional disparities are pronounced, with eastern coastal areas showing more advanced policies due to greater technical and financial resources. The surge in medical waste, particularly during the COVID-19 pandemic, underscores the need for enhanced regulatory guidance. Non-incineration technologies are gaining traction for their environmental and cost benefits, and facility coverage has improved but remains uneven. The study proposes five policy principles to foster technological innovation and industrial upgrading, ensuring safe medical waste management and environmental protection.
Kinetic Analysis and Simulation of Pollutant Removal in Sewage Networks
This study investigates pollutant removal characteristics and kinetic behaviors in sewage networks, and analyzes their impact on the carbon-to-nitrogen ratio (C/N, as COD/TN) of influent to wastewater treatment plants. Source water quality sampling at drainage outlets revealed spatial and temporal variations in C/N, with domestic sewage exhibiting higher C/N than industrial sewage, and diurnal peaks reaching 6.92 versus 4.71 during off-peak hours. Using a pilot-scale adjustable sewage network system in Kunshan, experiments were conducted under high (0.491 m·s−1) and low (0.089 m·s−1) flow velocities, monitoring pollutant removal over 144 hours. Pseudo-first-order kinetics were applied to model COD and TN removal. Results showed that COD (including SCOD and PCOD), BOD5, and SS achieved approximately 80% removal within 144 h, with higher removal at low flow velocity. TN, NH3-N, and TP exhibited lower overall removal rates. Kinetic fitting revealed that COD removal rate constants (kCOD) were significantly higher than those for TN (kTN), and both decreased with increasing flow velocity: at low velocity, kCOD=0.0167 h−1 and kTN=0.0029 h−1; at high velocity, kCOD=0.0127 h−1 and kTN=0.0020 h−1. Simulations based on actual source pollutant concentrations indicated that the time for C/N to drop to the denitrification critical value of 4.50 was 12.24 h at high velocity, but shortened to 9.49 h at low velocity. These findings demonstrate that increasing flow velocity effectively retards the decline of C/N. Therefore, regulating network flow velocity to reduce hydraulic retention time is a key strategy for maintaining adequate C/N at the terminal and ensuring denitrification efficiency in wastewater treatment plants.
Preparation of Trimetallic-Carbon Composite Catalysts and Their Application in Catalytic Ozonation of Industrial Wastewater
Advanced oxidation processes (AOPs) are promising for degrading organic pollutants in water treatment. Heterogeneous catalytic ozonation (HCO) has gained attention due to its high oxidation efficiency, strong interference resistance, and low secondary pollution. In this study, a series of trimetallic-carbon composite ozone catalysts were prepared via an organic precursor calcination method using γ-Al2O3 as support. This method enhanced catalytic activity and mechanical strength while overcoming the limitations of carbon materials (low mechanical strength) and metal-based materials (poor mass transfer). The optimized catalyst, CA-FeCoCu, comprising Fe, Co, Cu, carbon, and alumina, exhibited excellent performance in phenol degradation and real industrial wastewater treatment. Characterization revealed that the synergistic effect of trimetals and the introduction of multiple carbon types increased specific surface area and hydroxyl radical (·OH) generation. In a pilot-scale fixed-bed reactor, the CA-FeCoCu/O3 system reduced COD from 120 mg·L−1 to below 40 mg·L−1, with an O3 consumption ratio (O/C) of less than 1, effectively lowering operational costs. This work provides a new strategy for developing efficient and stable heterogeneous O3 catalysts and offers a reference for the practical application of HCO in industrial wastewater treatment.
Differentiated Characteristics of Suspended Particulate Matter and Their Effects on Water Quality in the Middle and East Routes of the South-to-North Water Diversion Project
This study investigates the spatiotemporal differentiation of suspended particulate matter (SPM) characteristics, sources, and their impacts on water quality between the Middle Route (closed artificial channel) and East Route (open natural water system) of the South-to-North Water Diversion Project. Thirty sampling sites (13 on the Middle Route, 17 on the East Route) were established, and samples were collected during dry and wet seasons. Water quality parameters and SPM characteristics were analyzed, including particle size distribution, total suspended solids (TSS), chlorophyll a, and stable carbon and nitrogen isotopes. Results show that the Middle Route maintains good and stable water quality, with SPM dominated by coarse particles (>63 μm, 61.43%–94.68%), total phosphorus (TP) <0.01 mg·L−1, and a significant positive correlation between chlorophyll a and coarse particles (r=0.60), indicating algal aggregation dominates particle formation. In contrast, the East Route exhibits high and fluctuating nitrogen and phosphorus concentrations, with SPM dominated by fine particles (<20 μm, 51.26%–88.61%), TP ranging from 0.03 to 1.11 mg·L−1, and a positive correlation with fine particles, suggesting significant external inputs. Carbon and nitrogen isotope analysis reveals that Middle Route SPM primarily originates from autochthonous algae (contribution >46.75%), while East Route SPM is influenced by both terrestrial C3 plants and algae. The distinct engineering and management approaches of the two routes lead to significant differences in SPM characteristics and sources, thereby affecting water quality dynamics. The Middle Route requires an 'algal reduction and hydrodynamic optimization' strategy to control algal-derived coarse particle deposition, whereas the East Route benefits from 'retention-sedimentation and wetland purification' to reduce external fine particles and pollutant inputs. This research provides theoretical support and practical guidance for differentiated SPM management in long-distance water diversion systems.
Combined Ozone Micro-Nano Bubble Oxidation and Powdered Activated Carbon Adsorption for Removal of Taste and Odor Compounds from Drinking Water
Algal-derived taste and odor compounds (2-methylisoborneol, 2-MIB, and geosmin, GSM) in drinking water sources are poorly removed by conventional treatment. This study systematically evaluated the standalone and combined performance of ozone micro-nano bubbles (O3-MNBs) oxidation and powdered activated carbon (PAC) adsorption for removing 2-MIB, GSM, and algal cells from source water. Results showed that O3-MNBs pre-oxidation achieved >97.5% removal of odorants at 400 ng·L−1 and 67.2% algal cell removal within 30 min. When applied as a deep treatment stage, the degradation rate constant (k) was 10.1%–25.6% higher than in pre-oxidation due to lower background matrix interference. Both pre-oxidation and deep treatment reduced effluent concentrations of 2-MIB and GSM to below 10 ng·L−1, with oxidation kinetics fitting pseudo-first-order models (R²>0.95). PAC adsorption of both compounds followed pseudo-second-order kinetics (R²>0.99), with GSM equilibrium adsorption capacity approximately 20.0% higher than that of 2-MIB. In pure water, adsorption capacity increased by >10.0% compared to raw water. Based on kinetic models, a quantitative prediction method was established for O3-MNBs oxidation and PAC adsorption processes, aiming to achieve efficient odorant removal and cost optimization, providing theoretical support for advanced drinking water purification and smart water plant construction.
Pulsed Electric Field Enhancement of Nitrogen Removal Performance and Microbial Community Structure Response in Anammox Granular Sludge
This study investigated the effects of a ring-shaped pulsed electric field (PEF) (1.5 V, 4 h on-time per cycle) on nitrogen removal performance and microbial community structure of anammox granular sludge (AnGS). Two anaerobic sequencing batch reactors (R1 control, R2 with PEF) were operated under stepwise increasing nitrogen loading rates (NLR). At NLR below 1,155 mg·(L·d)−1, R2 exhibited total nitrogen removal efficiency (TRE) 7.5%–17.0% higher than R1, with biomass, specific anammox activity (SAA), and extracellular polymeric substances (EPS) increased by 5%–7%, 21%–71%, and 54%–77%, respectively. However, at NLR above 1,320 mg·(L·d)−1, the toxic effect of nitrite dominated, and PEF enhancement diminished or even reversed to inhibition. Microbial community analysis revealed that at low-to-moderate NLR, PEF increased the relative abundance of Planctomycetes and key anammox bacteria (Candidatus Brocadia and Candidatus Jettenia), along with enhanced community richness (Chao1) and diversity (Shannon/Simpson indices). At high NLR, PEF decreased microbial richness compared to R1. Principal component analysis and redundancy analysis indicated that PEF was the key factor driving community differences at low-to-moderate NLR, whereas nitrite concentration became the dominant factor at high NLR. This study provides theoretical support for enhancing the resilience and engineering application of anammox processes.