Flow-through heterogeneous electro-Fenton system based on the absorbent cotton derived bulk electrode for refractory organic pollutants treatment

Innovative treatment of industrial effluents through combining ferric iron and attapulgite application

The escalation of industrial activities has escalated the production of pharmaceutical and dyeing effluents, raising significant environmental issues. In this investigation, a hybrid approach of Fenton-like reactions and adsorption was used for deep treatment of these effluents, focusing on effects of variables like hydrogen peroxide concentration, catalyst type, pH, reaction duration, temperature, and adsorbent quantity on treatment effectiveness, and the efficacy of acid-modified attapulgite (AMATP) and ferric iron (Fe(III))-loaded AMATP (Fe(III)-AMATP) was examined. Optimal operational conditions were determined, and the possibility of reusing the catalysts was explored. Employing Fe3O4 as a heterogeneous catalyst and AMATP for adsorption, CODCr was reduced by 78.38-79.14%, total nitrogen by 71.53-77.43%, and phosphorus by 97.74-98.10% in pharmaceutical effluents. Similarly, for dyeing effluents, Fe(III)-AMATP achieved 79.87-80.94% CODCr, 68.59-70.93% total nitrogen, and 79.31-83.33% phosphorus reduction. Regeneration experiments revealed that Fe3O4 maintained 59.48% efficiency over three cycles, and Fe(III)-AMATP maintained 62.47% efficiency over four cycles. This work offers an economical, hybrid approach for effective pharmaceutical and dyeing effluent treatment, with broad application potential.

Preparation of Mn-doped sludge biochar and its catalytic activity to persulfate for phenol removal

In recent years, the increasing prevalence of phenolic pollutants emitted into the environment has posed severe hazards to ecosystems and living organisms. Consequently, there is an urgent need for a green and efficient method to address environmental pollution. This study utilized waste sludge as a precursor and employed a hydrothermal-calcination co-pyrolysis method to prepare manganese (Mn)-doped biochar composite material (Mn@SBC-HP). The material was used to activate peroxydisulfate (PDS) for the removal of phenol. The study investigated various factors (such as the type and amount of doping metal, pyrolysis temperature, catalyst dosage, PDS dosage, pH value, initial phenol concentration, inorganic anions, and salinity) affecting phenol removal and the mechanisms within the Mn@SBC-HP/PDS system. Results indicated that under optimal conditions, the Mn@SBC-HP/PDS system achieved 100% removal of 100 mg/L phenol within 180 min, with a TOC removal efficiency of 82.7%. Additionally, the phenol removal efficiency of the Mn@SBC-HP/PDS system remained above 90% over a wide pH range (3-9). Free radical quenching experiments and electron spin resonance (ESR) results suggested that hydroxyl radicals (·OH) and sulfate radicals (SO4-) yed a role in the removal of phenol through radical pathways, with singlet oxygen (1O2) being the dominant non-radical pathway. The phenol removal efficiency remained above 90%, demonstrating the excellent adaptability of the Mn@SBC-HP/PDS system under the interference of coexisting inorganic anions or increased salinity. This study proposes an innovative method for the resource utilization of waste, creating metal-biochar composite catalysts for the remediation of water environments. It provides a new approach for the efficiency of organic pollutants in water environments.

Efficient multi-stage electrochemical flow-through system for refractory organic pollutant treatment: Kinetics, mass transfer, and thermodynamic analysis

Improving the kinetics rate and mass transfer is essential for expanding the potential of electrochemical technologies in wastewater treatment. The electrochemical flow-through configuration promises a high oxidation efficiency and low energy consumption. We aimed to provide a thorough understanding of the enhanced kinetics, mass transfer, and thermodynamic parameters during the degradation of amoxicillin (AMX) in a multi-stage flow-through (MSFT) system using porous Ti-ENTA/SnO2-Sb anodes. All operating conditions strongly influenced the kinetics of AMX degradation and followed pseudo-first-order rate kinetic model (R2 > 0.85), with the highest kobs of 0.228 min-1 at high temperature (318 K). In comparison to the flow-by mode, the AMX removal rate in the three-stage flow-through mode was greatly enhanced by 70%, exhibiting the superior capacity of a porous anode. This system exhibited outstanding performance regarding the high kinetics rate and mass transfer rate (km), which increased by factors of 3.46 and 10.74, respectively, obtained in the flow-by mode. It also revealed that •OH generation was 5.64 times higher, and the EE/O was 19.89-fold lower than those in flow-by mode. Temperature plays a vital role in the reaction process, and thermodynamic features found the positive enthalpy (ΔHo) of +27.06 kJ mol-1, signifying the process was endothermic. A Hatta number (Ha) of >0.02 at all temperatures proved this finding, confirming an undeniable role in mass transfer. Finally, these findings reveal the system's performance and offer the possibility of establishing a multi-stage flow-through for wastewater treatment.

Flow-through heterogeneous electro-Fenton system using a bifunctional FeOCl/carbon cloth/activated carbon fiber cathode for efficient degradation of trimethoprim at neutral pH

The synthesis of multifunctional cathode with high-efficiency and stable catalytic activity for simultaneously producing and activating H₂O₂ is an effective way for promoting the performance of heterogeneous electro-Fenton process (HEF). In addition, accelerating mass transfer by adopting a flow-through reactor is also great importance because of its better utilization of catalysts and adequate contact of the contaminant with the oxidants generated on the electrode surface. Herein, a novel flow-through HEF (FHEF) system was designed for the degradation of trimethoprim (TMP) using bifunctional cathode with a sandwich structure FeOCl nanosheets loaded onto carbon cloth (CC) and activated carbon fiber (ACF) (FeOCl/CC/ACF). The cathode exhibited excellent performance in activating H₂O₂ for the in-situ generation of hydroxyl radicals (^•OH). The electron spin resonance (ESR) measurements and radical quenching tests proved that the high production of ^•OH in the FHEF process was favorable to the high catalytic efficiency. 25 mg L^-1 TMP was entirely degraded after 60 min, with the TOC removal of 62.6% (180 min) at pH 6.8, 9.0 mA cm^-2, and flux rate 210 mL min^-1. Moreover, the degradation rate still could reach 83% (60 min) after 10 cycles without obvious valence and crystal phase changes. Simultaneously, the current utilization rate has also been greatly enhanced, with an average current efficiency of 69.9% and a low energy consumption of 0.28 kWh kg^-1. The reasonable degradation pathways for TMP were proposed based on the UPLC-QTOF-MS/MS results. Finally, the results of toxicological simulation showed a declining trend in the toxicity of the samples during TMP degradation. These results claim that the FeOCl/CC/ACF-FHEF system is an efficient and economical technology for the treatment of organic contaminants in effluents.

Degradation of antibiotics by electrochemical advanced oxidation processes (EAOPs): Performance, mechanisms, and perspectives

Global consumption and discharge of antibiotics have led to the rapid development and spread of bacterial antibiotic resistance. Among treatment strategies, electrochemical advanced oxidation processes (EAOPs) are gaining popularity for treating water/wastewater containing antibiotics due to their high efficiency and easiness of operation. In this review, we summarize various forms of EAOPs that contribute to antibiotic degradation, including common electrochemical oxidation (EO), electrolyte enhanced EO, electro-Fenton (EF) processes, EF-like process, and EAOPs coupling with other processes. Then we assess the performance of various EAOPs in antibiotic degradation and discuss the influence of key factors, including electrode, initial concentration and type of antibiotic, operation conditions, electrolyte, and water quality. We also review mechanisms and degradation pathways of various antibiotics degradation by EAOPs, and address the species and toxicity of intermediates produced during antibiotics treatment. Finally, we highlight challenges and critical research needs to facilitate the application of EAOPs in antibiotic treatment.

Enhanced tetracycline removal using membrane-like air-cathode with high flux and anti-fouling performance in flow-through electro-filtration system

The membrane-like air-cathodes modified with different polyaniline were prepared using phase inversion method, which possessed dual functions of interception and electrochemical degradation, and showed good conductivity (15.9 ± 0.4 to 25.7 ± 0.5 mS cm^-1) and porosity (77.0 ± 0.1 to 87.8 ± 0.1%) compared to the unmodified control one (13.2 ± 0.5 mS cm^-1, and 63.1 ± 0.7%). At tetracycline 50 mg L^-1, the cathode with 25 wt% polyaniline exhibited the highest rejection rate and final removal (71.1% and 92.9%, 35.9% and 31.4% higher than the control), the highest water flux recovery (97.9%), and the lowest attenuation of porosity and conductivity. The modified cathode also showed an autocatalytic effect on H₂O₂, an obvious ^·OH peak appeared on the electron paramagnetic resonance curves. It also had good anti-fouling performance because it exhibited a high durability (the final removal was decreased by 4.0% after 15 cycles) with a long service life of 124 periods (372 h, 15.5 d). The tetracycline (0.5 mg L^-1) removal in the river background was near 100%, and the chemical oxygen demand removal was 91.9%, supporting that it was suitable for treating antibiotics in natural water without adding agents but only for electricity consumption.