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

Antibiotic Degradation via Fenton Process Assisted by a 3-Electron Oxygen Reduction Reaction Pathway Catalyzed by Bio-Carbon-Manganese Composites

Bio-carbon-manganese composites obtained from olive mill wastewater were successfully prepared using manganese acetate as the manganese source and olive wastewater as the carbon precursor. The samples were characterized chemically and texturally by N2 and CO2 adsorption at 77 K and 273 K, respectively, by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Electrochemical characterization was carried out by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The samples were evaluated in the electro-Fenton degradation of tetracycline in a typical three-electrode system under natural conditions of pH and temperature (6.5 and 25 °C). The results show that the catalysts have a high catalytic power capable of degrading tetracycline (about 70%) by a three-electron oxygen reduction pathway in which hydroxyl radicals are generated in situ, thus eliminating the need for two catalysts (ORR and Fenton).

Highly efficient heterogeneous electro-Fenton reaction for tetracycline degradation by Fe-Ni LDH@ZIF-67 modified carbon cloth cathode: Mechanism and toxicity assessment

In this work, a novel and efficient Fe-Ni LDH@ZIF-67 catalyst modified carbon cloth (CC) cathode was developed for tetracycline (TC) degradation in heterogeneous electro-Fenton (Hetero-EF) process. Compared to Fe-Ni LDH/CC (75.7%), TC degradation rate of Fe-Ni LDH@ZIF-67/CC cathode increased to 95.6% within 60 min. The synergistic effect of hetero-EF and anodic oxidation process accelerated electron transfer, the maximum H2O2 production of Fe-Ni LDH@ZIF-67/CC electrode reached 264 mg/L, improving utilization efficiency of H2O2. The cathode possessing a satisfied TC degradation performance over a wide pH (3-9). Free radical capture experiment revealed the collaboration of ·O2-, ·OH, and 1O2 play a significant role in TC degradation. The 5 cycles experiment and metal ion leaching experiment showed that the proposed Fe-Ni LDH@ZIF-67/CC has good recyclability and stability. In addition, the proposed Fe-Ni LDH@ZIF-67/CC cathode achieved satisfying performance in real water (tap water: 97.3%, lake water: 97.7%), demonstrating the possibility for practical application. TC degradation pathways were proposed by theory analysis and experimental results. The toxicity of TC intermediates was reduced by Hetero-EF degradation according to Toxicity Estimation Software Tool and Escherichia coli growth inhibition experiments. This work provides a novel modified cathode to improve removal efficiency of antibiotics in wastewater.

Progress of improving waste activated sludge dewaterability: Influence factors, conditioning technologies and implications and perspectives

Large amounts of waste activated sludge (WAS) as a by-product generated from the biological treatment in wastewater treatment plants (WWTPs) is of high moisture content (MC), organic pollutants, heavy metals and pathogenic bacteria, it may cause serious environmental ecological risk without appropriate disposal. More than one half of the total operation cost is accounted for sludge disposal in a WWTP. Dewatering is an essential and important step during the sludge treatment and disposal process for it could efficiently reduce its volume, and be beneficial to the subsequent treatment and disposal of sludge. However, sludge should be conditioned before mechanical dewatering because of its high hydrophilicity. In this work, it presented a comprehensive review on sludge dewatering including summarizing the dewaterability measurement indexes, affecting factors, conditioning technologies, the improvement mechanisms. Finally, based on the eventual disposal and low carbon emission target, the implications and perspectives development of sludge conditioning were discussed. Based on the above discussion, there is no unified theoretical insight of the improvement mechanism of sludge dewaterability. In addition, the relationship between the microstructure of organic matters in sludge floc and the dewaterability should be deepened. Especially, how to choose the optimal conditioning technology for sludge dewatering lies in the physical and chemical properties of sludge, however, the carbon emission of the conditioning and dewatering process also needs to be considered. Accordingly, green, low-cost and organic conditioning agents are the direction of future research, and the establishment of automatic operating system and real-time evaluation index system is the key challenge.

Combination of coagulation, Fe0/H2O2 and ultra-high lime aluminium processes for the treatment of residual pollutants in biologically-treated landfill leachate

Refractory substances (humus) and salts (chloride (Cl-) and sulphate (SO42-) ions) remain in the biotreated landfill leachate treatment, and it is necessary to carry out further treatments by a suitable method before discharge. In this study, the effect and operational mechanism of a combination of the coagulation Fe0/H2O2 and ultra-high lime aluminium (UHLA) processes for the treatment of refractory organic substances and salts in the leachate effluent of a semi-aerobic aged refuse biofilter (SAARB) were investigated. The results showed that polyferric sulphate is a relatively efficient coagulant comparing to FeCl3, Al2(SO)4, and polyaluminium chloride. The Fe0/H2O2 process further removed refractory organics from wastewater, achieving 49.8% of total organic carbon removed. Further treatment by the UHLA process was carried. The results demonstrated that the amount of precipitant, reaction duration, and temperature had a significant impact on the Cl- and SO42- removals. After three treatments, the cumulative SO42- and Cl- removal efficiencies were 98% and 80%, respectively. The SO42- and Cl- were removed in the form of precipitates such as UHLA, specific components of which included calcium alumina, Fremy's salt of calcium, aluminium chloride, and calcium hydroxide. Overall, the UV254, CN, Cl-, and SO42- removal efficiencies from the SAARB effluent were 94.08%, 98.73%, 79.96%, and 98.44%, respectively, for the combined coagulation Fe0/H2O2 and UHLA processes. Therefore, the combined processes could effectively remove residual pollutants in the biologically-treated landfill leachate, and the study provides a useful reference for the removal of refractory organic matter and salts in landfill leachate.HighlightsCoagulation-Fe0/H2O2-UHLA process is effective to SAARB effluent treatment.Refractory organics are substantially degraded by the coagulation-Fenton-like stage.Both Cl- and SO42- in SAARB effluent are greatly removed by UHLA process.

Boron promoted Fe3+/peracetic acid process for sulfamethazine degradation: Efficiency, role of boron, and identification of the reactive species

In this work, boron (B) was used to promote Fe3+/peracetic acid (Fe3+/PAA) for the degradation of sulfamethazine (SMT). An SMT degradation efficiency of 9.1% was observed in the Fe3+/PAA system over 60 min, which was significantly increased to 99.3% in the B/Fe3+/PAA system over 10 min. The B/Fe3+/PAA process also exhibited superior resistance to natural substances, excellent adaptability to different harmful substances, and good removal of antibiotics in natural fresh water samples. The mechanism of action of boron for Fe3+ reduction was determined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, density functional theory (DFT) calculations, and electrochemical tests. The dominant role of •OH was confirmed using quenching experiments, electron spin resonance (EPR) spectroscopy, and quantitative tests. Organic radicals (R-O•) and Fe(IV) also significantly contribute to the removal of SMT. DFT calculations on the reaction between Fe2+ and the PAA were conducted to further determine the contribution from •OH, R-O•, and Fe(IV) from the perspective of thermodynamics and the reaction pathways. Different boron dosages, Fe3+ dosages, and initial pH values were also investigated in the B/Fe3+/PAA system to study their effect of SMT removal and the production of the reactive species. Fe(IV) production determined the kR-O•+Fe(IV) value suggesting that Fe(IV) may play a more important role than R-O•. A comparison of the results with other processes has also proved that the procedure described in this study (B/Fe3+/PAA) is an effective method for the degradation of antibiotics.

FeMo@porous carbon derived from MIL-53(Fe)@MoO3 as excellent heterogeneous electro-Fenton catalyst: Co-catalysis of Mo

An ultra-efficient electro-Fenton catalyst with porous carbon coated Fe-Mo metal (FeMo@PC), was prepared by calcining MIL-53(Fe)@MoO₃. This FeMo@PC-2 exhibited impressive catalytic performance for sulfamethazine (SMT) degradation with a high turnover frequency value (7.89 L/(g·min)), much better than most of reported catalysts. The mineralization current efficiency and electric energy consumption were 83.2% and 0.03 kWh/g_TOC, respectively, at low current (5 mA) and small dosage of catalyst (25.0 mg/L). The removal rate of heterogeneous electro-Fenton (Hetero-EF) process catalyzed by FeMo@PC-2 was 4.58 times that of Fe@PC/Hetero-EF process. Because the internal-micro-electrolysis occurred between PC and Fe⁰, while the co-catalysis of Mo accelerated the rate-limiting step of the Fe³⁺/Fe²⁺ cycle and greatly improved the H₂O₂ utilization efficiency. The results of radical scavenger experiments and electron paramagnetic resonance confirmed the main role of surface-bound hydroxyl radical oxidation. This process was feasible to remove diverse organic contaminants such as phenol, 2,4-dichlorophenoxyacetic acid, carbamazepine and SMT. This paper enlightened the importance of the doped Mo, which could greatly improve the activity of the iron-carbon heterogeneous catalyst derived from metal-organic frameworks in EF process for efficient removal of organic contaminants.

Enhancement of iron-based nitrogen removal with an electric-magnetic field in an upflow microaerobic sludge reactor (UMSR)

Traditional denitrification often produces high operating costs and excessive sludge disposal expenses due to conventional carbon sources. A novel electric-magnetic field (MF) 48 mT with Fe⁰ and C-Fe⁰ powder in an upflow microaerobic sludge reactor (UMSR) improved nitrogen removal from wastewater without organic carbon resources and gave richness to the heterotrophic bacterial community. In the current study, the reactor was operated for 78 ± 2 days, divided into five stages (without Fe⁰, with Fe⁰, coupling with MF, without coupling with MF, and coupling with MF again), at a hydraulic retention time (HRT) of 2.5 h, with an influent loading of ammonium (NH₄⁺-N) 50 ± 2 mg/L, at 25-27 °C, and less than 1.0 mg/L dissolved oxygen (DO). The results demonstrated nitrogen removal efficiency enhanced after coupling with MF on the levels of NO₃^--N by 76% with an effluent concentration of 8.7 mg/L, NH₄⁺-N by 72% with an effluent concentration of 13.6 mg/L, and total nitrogen removal (TN) by 76%, respectively. After coupling the MF with the reactor, the microbial community data analysis showed the dominant abundance of ammonia-oxidizing bacteria, heterotrophic nitrifying bacteria, and denitrifying bacteria on the level of Anaerolineaceae_uncultured 2%, which is capable of denitrification that uses Fe²⁺ as an electron source, Gemmatimonadaceae_uncultured 4%, Hydrogenophaga 4% which is capable of catalyzing hydrogenotrophic denitrification and correlating to nitrate removal, denitrification and desulfurization bacteria SBR1031_norank 18%, anammox-bacteria Saccharimonadales_norank 2%, and (AOM) Limnobacter 3% in the sludge.

Effect and mechanism of norfloxacin removal by guava leaf extract in the ZVI/H2O2 system

To overcome the bottlenecks of the conventional zero-valent iron Fenton-like (ZVI/H₂O₂) process, such as low reagent utilization, low applicable pH, and iron sludge contamination, guava leaf extract (GLE) was used as a green promoter to enhance ZVI/H₂O₂ process in this study. Compared with the ZVI/H₂O₂ system, the removal rate and k_obs of norfloxacin by the ZVI/H₂O₂/GLE system were increased by 33.76% and 2.19 times, respectively. The experimental investigation of the mechanism showed that the attack of reactive oxygen species was the main pathway for the removal of pollutants, and three types of reactive oxygen species (¹O₂, O₂^-,·OH) generations in the ZVI/H₂O₂/GLE system were effectively promoted by the introduction of GLE. The reactivity improvement was mainly due to the decrease of pH. At the same time, the chelation of iron ions by GLE promoted the Fe(III)/Fe(II) cycle on the catalyst surface was also a minor mechanism to improve the reactivity. This study provides a crucial reference for the practical application of guava leaf to promote the ZVI/H₂O₂ process in environmental pollution control.

Floating sandwich-type electro-Fenton: A feasible process to remove micro-pollutants through adsorption enrichment and enhanced oxidation efficiency

To improve the removal efficiency of low-concentration organic pollutants and enhance the oxidation efficiency of electro-Fenton (EF) process, a floating sandwich-type EF system (N/(A)/D-EF) without aeration was constructed for the first time. This EF system electro-synthesized H₂O₂ through the floating natural air diffusion electrode (NADE) without aeration, and regenerated Fe(II) effectively by the activated carbon fiber (ACF) interlayer, which significantly enhanced the process oxidation capacity since its ^•OH yield was 8.7 times that of the conventional EF system. In addition, the ACF interlayer could adsorb and enrich micro-pollutants and the generated ^•OH directly oxidize the pollutants adsorbed on the ACF, which enabled regeneration of ACF and maintained removal stability in 20 consecutive experiments. The removal rate constant (k) of carbamazepine by N/(A)/D-EF process was 7.6 times and 2.1 times higher than that of conventional EF and ACF adsorption process, respectively. This process could efficiently remove mixed low-concentration organic pollutants (0.1 mg L^-1) in domestic sewage and lake water with rate constant 1.6-7.1 times that of the conventional EF process but lower energy consumption. Meanwhile, the N/(A)/D-EF process had a wider application range of sewage pH and conductivity, which was a promising process for removing low-concentration pollutants in wastewater.

Binary Adsorption and Migration Simulation of Levofloxacin with zinc at Concentrations Simulating Wastewater on Silty Clay and The Potential Environmental Risk in Groundwater

Migration of soil pollutants can cause groundwater pollution, which is dominated by the soil adsorption of pollutants. Heavy metals and fluoroquinolone antibiotics exist in the soil and form compound pollution, with different adsorption behaviors in the soil. It may make the levofloxacin (LVFX) migration and potential risk of LVFX to groundwater change. Therefore, this research on Zinc (Zn/Zn²⁺) and LVFX studied the binary adsorption on silty clay in the vadose zone using the batch equilibrium adsorption method. Besides, Hydrus-1D simulate vertical migration. As the results show: (1) Silty clay has excellent storage capacity (adsorption rate>90%) for LVFX and is a natural barrier to reducing groundwater risk; (2) Binary adsorption of LVFX with Zn on silty clay had could be influenced by metallic oxide, pH value, and cation species. The metallic oxides adsorption rate decreased by 10.3%; Compared with single adsorption, Zn²⁺ promoted the adsorption of LVFX on silty clay, with the exception that the pH value was 2.0; Based on the simulated migration, subtle changes in adsorption may lead to a significant difference in migration and impact on the environmental risk of LVFX to groundwater. This paper proposed three aspects of the research should be strengthened to further develop the potential of silty clay in the prevention and control of groundwater pollution.

Degradation of carbamazepine over MOFs derived FeMn@C bimetallic heterogeneous electro-Fenton catalyst

A highly efficient heterogeneous electro-Fenton (Hetero-EF) catalyst with core-shell structure was successfully prepared by calcination of Mn-doped Mil-53 (Fe) precursor at high temperature. FeMn@C-800/2 prepared at pyrolysis temperature of 800 °C and Fe:Mn molar doping ratio of 2:1 showed the best catalytic performance for the degradation of carbamazepine (CBZ). The characterization, properties and stability of FeMn@C-800/2 were systematically investigated, obtaining the apparent first-order reaction rate of Hetero-EF was 8.9 and 17.8 times higher than that on Fe@C-800 and Mn@C-800 at the optimized conditions of current density 10 mA cm^-2, catalyst dosage of 50 mg L^-1 and initial pH 4.0, respectively. The incorporation of Mn promoted the generation of more Fe⁰ and Fe₃C during the pyrolysis process, and enhanced the internal micro-electrolysis between Fe⁰ and carbon shell. At the same time, the presence of Mn⁰ also promoted the regeneration of Fe²⁺, and improved the activity of iron-carbon heterogeneous catalysis in the EF process, so as to degrade organic pollutants more effectively. This work would help to gain insight into the design of MOFs derived Fe-Mn bimetal catalyst and its mechanism for enhanced heterogeneous electro-Fenton.

Kinetic study on methylene blue removal from aqueous solution using UV/chlorine process and its combination with other advanced oxidation processes

This study investigated the kinetic degradation of methylene blue (MB) by a UV/chlorine process and its combination with other advanced oxidation processes. The ∙OH and reactive chlorine species (RCS: Cl∙, ClO∙, etc.) were the primary reactive species, which accounted for 56.7% and 37.6% of MB degradation at pH 7, respectively. The second-order rate constant of Cl∙ towards MB was calculated to be 2.8 × 10⁹ M^-1 s^-1. When the pH increased from 3 to 7, k_MB by ∙OH increased from 0.15 to 0.21 min^-1 before being reduced to 0.11 min^-1 at pH 11. k_MB by RCS continuously reduced from 0.16 to 0.13 min^-1 when the pH was increased to 11. Humic acid (HA), Br^-, and Cl^- inhibited the degradation with k_MB in the order: k_MB (in HA) < k_MB (in Br^-) < k_MB (in Cl^-). HCO₃^- increased k_MB from 0.37 to 0.48 min^-1. The experimental and modeling methods fit well, indicating the effectiveness of using Kintecus® in predicting concentrations of free radicals in complex water matrices. TOC removal was achieved at 60% after 30 min in a control process and it was strongly inhibited by the presence of HA, with 22% removal achieved at 5 mg_c L^-1 HA. UV/chlorine/electrochemical oxidation (UV/chlorine/EO) significantly improves k_MB from 0.37 to 0.94 min^-1 at a high current (240 mA), while UV/chlorine/H₂O₂ decreased k_MB at a low concentration of 0.01 mM H₂O₂ (k_MB decreased by 6.1%). The results indicate that the energy cost for UV irradiation was the main cost in MB treatment in both UV/chlorine and UV/persulfate (UV/PS) processes, accounting for 91% and 84%, respectively.

Rapid degradation of tetracycline in aqueous solution by Fe/Cu catalysis enhanced by H2O2 activation

Tetracycline (TC) is widely detected in the environment because of its abuse and persistence. There is an urgent need to efficiently treat TC due to its potential threat to the ecosystem and human health. In this study, microscale Fe/Cu bimetallic particles' (mFe/Cu) catalysis enhanced by H₂O₂ was proposed to remove TC in an aqueous solution. Based on the pre-experiment, the effect of theoretical Cu mass loading (TML_Cu) and some key operating parameters on the TC removal efficiency were investigated thoroughly. The degradation rates of TC by mFe/Cu with different TML_Cu followed the pseudo-first-order kinetics model, and the optimal TML_Cu (0.34 g Cu/g Fe) was obtained. The optimal operating parameters of mFe/Cu dosage, concentration of H₂O₂, initial concentration of TC, stirring speed and operating temperature were 5 g/L, 50 mM, 50 ppm, 400 r/min, and 55°C, respectively. Compared with the control system, the system of mFe/Cu catalysis enhanced by H₂O₂ (mFe/Cu-H₂O₂) presented excellent performance due to its synergistic effect. Also, the fresh and reacted mFe/Cu was characterized by scanning electron microscope, which showed the surface of mFe/Cu was rougher after reaction, indicating mFe/Cu participated in the degradation reaction. Besides, with the presence of inorganic anions, the degradation of TC in mFe/Cu-H₂O₂ system did not change much. And mFe/Cu presented good stability and recyclability after 10 repeated tests. Therefore, mFe/Cu-H₂O₂ system had a great potential for cost-effective removal of antibiotics in wastewater.

Effect of dielectric barrier discharge plasma on persulfate activation for rapid degradation of atrazine: Optimization, mechanism and energy consumption

Dielectric barrier discharge plasma (DBDP) is an emerging and promising advanced oxidation process (AOP) for wastewater treatment. After investigating the effect of input voltage, O₃ (generated by dielectric barrier discharge), and peroxydisulfate (PDS) dosage, the DBDP_O3/PDS system was established. With the assistance of PDS, the atrazine (ATZ) removal efficiency increased from 69.67% to 82.46% within 25 min. Synergistic effect calculation suggests that there were markedly synergies between DBDP, O_3, and PDS. Under the effect of SO₄^-•, the total organic carbon (TOC) removal and dechlorination efficiency were significantly improved. In addition, the DBDP_O3/PDS system maintained the ATZ removal efficiency at a high level over a wide range of initial pH values. According to quenching experiments and electron paramagnetic resonance (EPR) detection, the dominant radical for ATZ degradation in the DBDP_O3/PDS system was HO^•. A possible degradation pathway of ATZ was proposed based on density functional theory (DFT) analysis, quadrupole-time of flight-liquid chromatography/mass spectrometry (Q-TOF-LC/MS) results, and related literature. The acute toxicity to aquatic minnows and the developmental toxicity of intermediate products prediction confirmed that the DBDP_O3/PDS system could effectively reduce ATZ toxicity. The electrical energy per order (E_EO) was 7.10 kWh m^-3 order^-1 illustrating that the DBDP_O3/PDS was a more energy-economic system than other energy-intensive processing technologies.

Surface-catalyzed electro-Fenton with flexible nanocatalyst for removal of plasticizers from secondary wastewater effluent

Activation of H₂O₂ with metal-free catalysts is an efficient and environmentally benign alternative to electron-Fenton (EF) for organics degradation. In the present study, flexible nanocatalysts were synthesized with self-regulated metal oxide nanoparticles (FeOx NPs) for efficient removal of plasticizers from secondary wastewater effluent (SWE). Compared with NGr/EF and FeOx@Gr/EF systems, FeOx@NGr/EF could enhance the decay kinetics of plasticizers by 3.9-4.4 times and reduce 48-59% of the disposal cost. Reactive oxygen species tests and trapping experiments proved that the surface-catalyzed EF effectively broadened the range of solution pH. Density functional theory calculations coupled with electrochemical measurements indicated that the electron transfer rates between Fe-O-C atoms were enhanced with N-doping due to strong interactions between N-Fe bond. The synergistic effects of FeOx and N could improve the oxygen reduction activity for H₂O₂ generation, and accelerate electron transfer between FeOx/NGr and H₂O₂ for ^•OH generation, offering an alternative for wastewater treatment.

Insights into a novel CuS/percarbonate/tetraacetylethylenediamine process for sulfamethazine degradation in alkaline medium

This work presents a novel CuS/percarbonate/tetraacetylethylenediamine (CuS/SPC/TAED) process for the degradation of sulfamethazine (SMT). Results indicated that the CuS/SPC/TAED process enabled the efficient generation of peracetic acid (PAA), which can be efficiently activated by CuS in alkaline reaction media, and 93.6% of SMT was degraded in 30 min. Mechanism study revealed that the available reactive oxygen species (ROS) including hydroxyl radical (^•OH), carbonate radical (CO₃^•-), superoxide radical (O₂^•-), singlet oxygen (¹O₂), and organic radicals (R-O^•). Among them, R-O^• (acetyloxyl radical (CH₃CO₂^•) and acetylperoxyl radical (CH₃CO₃^•)) were confirmed to be the primary species that contributed to SMT degradation. Simultaneously, the role of sulfur species and carbonate ions were explored. It was found that the reductive O₂^•- and sulfur species rendered the efficient redox of Cu species. Besides, the effects of key influencing factors including SPC/TAED mole ratio, CuS dosage, initial pH, temperature, and nontarget matrix constituents on SMT degradation were examined. Finally, the degradation intermediates of SMT was identified, and the toxicity of these products was estimated by quantitative structure-activity relationship (QSAR) analysis. Overall, this work offers a new and simple strategy for antibiotic-polluted water remediation.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

Derivatives of metal-organic frameworks for heterogeneous Fenton-like processes: From preparation to performance and mechanisms in wastewater purification - A mini review

Organic pollution is an ever-growing issue in aquatic environment, Fenton-like processes have gained widespread acceptance due to their high oxidative potential and environmental compatibility. Derivatives of metal-organic frameworks (MOFs) are emerging heterogeneous Fenton-like catalysts, which have advantages of large surface area, diversity of structures, and abundant active sites. This work focuses on the recent advances in MOFs derivatives including metal compounds and metal incorporated carbons for Fenton-like processes. First, preparation strategies, structures and compositions are introduced. And then, the removal of organic pollutant in Fenton, electro-Fenton, and photo-Fenton process catalyzed by MOFs derivative is summarized, respectively. The contents particularly devote efforts to build connections among preparation, structures, compositions, and performance. Furthermore, the mechanisms of improving performance are discussed in detail. Finally, the perspectives of MOFs derivatives toward Fenton-like applications are proposed.

S-doped MIL-53 as efficient heterogeneous electro-Fenton catalyst for degradation of sulfamethazine at circumneutral pH

The reduced S-modified MIL-53(Fe) was prepared by sulfurizing MIL-53(Fe) at low temperature, which was an efficient electro-Fenton catalyst at wide pH range (3-9) for sulfamethazine (SMT) degradation. The best temperature and MIL-53(Fe)/S ratio were 350 °C and 1:2, at which the BET surface area was much enlarged. The MIL-53(Fe) surface was etched by S to many 2D nanosheets with the thickness of ~50 nm, while S_2-2 replaced OH^- to coordinate with Fe²⁺ and increased the Fe²⁺ content, which improved the catalytic performance. Even at initial pH of 7.0, the SMT removal was 95.8%, and the rate constant (k) in the Hetero-EF process was 16-folds of that in the Homo-EF process. The turnover frequency (TOF_d) value of MIL-53(Fe)/S(1:2)-350 was 0.48 L g^-1 min^-1, which was 6.8 times that of commercial FeS₂. The S_2-2in catalyst adjusted the pH superfast, and promoted the generation of Fe²⁺ and thus efficiently activating H₂O₂ to form surface ^·OH, which was verified to be the main radical by EPR and radical scavenger experiments. This catalyst showed promising prospect for environmental application and could be regenerated by sulfidation method. S-doped MIL-53(Fe) was an excellent pH regulator, thus promoting promising application in Hetero-EF processes.

When microbial electrochemistry meets UV: The applicability to high-strength real pharmaceutical industry wastewater

Wastewater from pharmaceutical and related industries contains many residual pharmaceutical components rich in color and high COD contents, which cannot be removed through the traditional wastewater treatment processes. Recently, microbial electrolysis ultraviolet cell (MEUC) process has shown its promising potential to remove recalcitrant organics because of its merits of wide pH range, iron-free, and without complications of iron sludge production. However, its application to the real pharmaceutical-rich industrial wastewater is still unknown. In this study, the MEUC process was validated with real ciprofloxacin-rich (6863.79 ± 2.21 µg L^-1) industrial wastewater (6840 ± 110 mg L^-1 of COD). The MEUC process achieved 100% removal of ciprofloxacin, 100% decolorization, and 99.1% removal of COD within 12, 60 and 30 h, respectively, when it was operated at pH-controlled at 7.8, applied voltage of 0.6 V, UV intensity of 10 mW cm^-2, and cathodic aeration velocity of 0.005 mL min^-1 mL^-1. Moreover, fluorescence analysis showed that protein- and humic-like substances in such wastewater were effectively removed, providing further evidence of its high treatment efficiency. Furthermore, eco-toxicity testing with luminescent bacteria Vibro Feschri confirmed that the treated effluent was utterly non-toxic. The results demonstrated the broad application potential of MEUC technology for treating industrial wastewater.

Sulfadiazine removal by peroxymonosulfate activation with sulfide-modified microscale zero-valent iron: Major radicals, the role of sulfur species, and particle size effect

Sulfide-modified zero-valent iron (S-Fe⁰) is regarded as a promising method to enhance the catalytic activity of Fe⁰ for peroxymonosulfate (PMS) activation. However, the roles of sulfidation and the application of the sulfidation treatment method are worth to further investigation. In our study, the effects of the S/Fe ratio, Fe⁰ dosage, and initial pH on sulfadiazine (SDZ) removal were investigated. The characterization of S-Fe⁰ with SEM, XPS, contact angle and Tafel analysis confirmed that the formation of sulfur species on the Fe⁰ surface could enhance the catalytic performance of Fe⁰. S^2- played the major role and SO₃^2- played the minor role in accelerating the conversion of Fe³⁺ to Fe²⁺. EPR tests, radical quenching and quantitative determination experiments identified ^•OH as playing the major role and SO₄^•- also playing an important role in SDZ removal in S-Fe⁰/PMS system. Sulfidation produced no notable change in the role of ^•OH and SO₄^•-. A possible degradation pathway of SDZ was proposed. Effect of sulfidation on various sizes of Fe⁰ was also studied which demonstrated that the smaller sizes of Fe⁰ (< 8 µm) were more effective in the sulfidation method treatment. S-Fe⁰/PMS system also showed a good performance in removing antibiotics in natural fresh water.

Investigation of Antibiotic-Resistant Bacterial Communities and Antibiotic-Resistant Genes in Wastewater Treatment Plants: Removal of Antibiotic-Resistant Genes by the BBR Process

The antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) in Wastewater treatment plants (WWTPs) have attracted increasing attention. In this study, the abundance of ARB and resistance genes tet32 and defA1 were investigated using high-throughput sequencing and high-throughput qPCR in water samples collected from the inlet of the biological treatment pool and outlet of Beilun Yandong WWTP in Ningbo, China. The result shows there was a high level of ARGs in the water of both the inlets and outlets in 2017 and 2018, whereas no ARGs were detected after adding a new baffled bioreactor (BBR) water treatment process in 2019. The BBR process uses Bacillus subtilis, B. thuringiensis, B. megaterium, B. licheniformis and B. amyloliquefaciens to effectively eliminate the ARGs in wastewater. Notably, this process did not significantly change the bacterial community structure of outlet water samples. The findings demonstrate an effective new method for removing ARGs from sewage.

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

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

High-efficiency oxidation of norfloxacin by Fe3+/H2O2 process enhanced via vacuum ultraviolet irradiation: Role of newly formed Fe2

Fluoroquinolones in water environments have caused worldwide concern due to negative effects on human health and ecological environment. Heretofore, synergistic mechanisms of Fe³⁺/H₂O₂ process enhanced via vacuum ultraviolet (VUV) irradiation for fluoroquinolones removal, and generation ways and contribution evaluations of reactive oxygen species (ROS) in integrated VUV/Fe³⁺/H₂O₂ were not reported systematically. This work comparatively investigated norfloxacin (NOR, typical fluoroquinolones) degradation in VUV/Fe³⁺/H₂O₂ and its sub-processes. Compared with its sub-processes, VUV/Fe³⁺/H₂O₂ process could not only increase degradation rate constant by 2.1-10.2 times and increase mineralization rate by 14.5%-49.5%, but also reduce energy consumption by 53.1%-89.9% and reduce economic cost by 33.3%-68.0%. Effect mechanisms of Fe³⁺ and H₂O₂ doses on decontamination capability of VUV/Fe²⁺/H₂O₂ were elaborated, and 3 mM H₂O₂ and 90 μM Fe³⁺ were determined as optimal doses. The synergetic factor in integrated VUV/Fe³⁺/H₂O₂ was 3.33, which was mainly ascribed to VUV photons accelerating iron cycle. In VUV/Fe³⁺/H₂O₂ process, superoxide radical and hydroxyl radical were confirmed as primary ROS, contributing 20.86% and 76.32% to NOR oxidation, separately. Organic and inorganic products of NOR and its degradation pathways in integrated VUV/Fe³⁺/H₂O₂ were also investigated. Besides, the synergistic reaction pathways in VUV/Fe³⁺/H₂O₂ were elaborated. Effects of water matrices on decontamination capability of VUV/Fe³⁺/H₂O₂ were also studied. All results indicated VUV/Fe³⁺/H₂O₂ as an efficient and cost-effective process suitable for NOR removal.

Photocatalytic Degradation of Tetracycline in Aqueous Solution Using Copper Sulfide Nanoparticles

In this paper, spherical-shaped pure phase djurleite (Cu31S16) and roxbyite (Cu7S4) nanoparticles were prepared by a solvothermal decomposition of copper(II) dithiocarbamate complex in dodecanthiol (DDT). The reaction temperature was used to control the phases of the samples, which were represented as Cu31S16 (120 °C), Cu31S16 (150 °C), Cu7S4 (220 °C), and Cu7S4 (250 °C) and were characterized by using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and absorption spectroscopy. The samples were used as photocatalysts for the degradation of tetracycline (TC) under visible light irradiation. The results of the study showed that Cu7S4 (250 °C) exhibited the best activity in the reaction system with the TC degradation rate of up to 99% within 120 min of light exposure, while the Cu31S16 (120 °C) system was only 46.5% at the same reaction condition. In general, roxbyite Cu7S4 (250 °C) could be considered as a potential catalyst for the degradation of TC in solution.

Ultrasonic role to activate persulfate/chlorite with foamed zero-valent-iron: Sonochemical applications and induced mechanisms

The novel system, consisting of composite oxidants (persulfate/chlorite, S2O82-/ClO2-) and stationary phase activator (zero-valent-iron foam, Fe0f) driven by ultrasonic (US) field, was applied to treat the triphenylmethane derivative effectively even at low temperature (≈ 289 K). By comparisons of sub-systems, the US roles to S2O82-, ClO2-, and Fe0f were seriatim analyzed. US made the reaction order of multi-component system tend to within 1 (leading to de-order reaction), and widened pH activating range of the Fe0f by sonicate-polishing during the process of ClO2- co-activating S2O82-. US and Fe0f were affected by fluid eddy on activating S2O82-/ClO2-. The Fe0f had slight effect on the temperature of US bubble-water interface but the addition of ClO2- lowered it. The partitioning capacity of the above US reactive zone increased during the reaction. US and ClO2- could enrich the kinds of degradation intermediates. The contributions of free radicals (ClOx-based radicals, sulfate radicals (SO4-), and hydroxyl radicals (OH)) and non-free radicals (ClO2, and O = FeIV/V from ionic Fe under "-O-O-" of S2O82- and cyclic adjustment reaction of ClO2-) processes by sonochemical induction were equally important by corresponding detection means. Especially, real-time and online high-resolution mass spectrum by self-developing further confirmed the chain transfers of different free radicals due to US role. The findings expanded the application of sono-persulfate-based systems and improved understanding on activation mechanism.

Targeted degradation of refractory organic compounds in wastewaters based on molecular imprinting catalysts

Efficient removal of low-concentration refractory pollutants is a crucial problem to ensuring water safety. The use of heterogeneous catalysis of molecular imprinting technology combined with traditional catalysts is a promising method to improve removal efficiency. Presently, the research into molecular imprinting targeting catalysts focuses mainly on material preparation and performance optimization. However, more researchers are investigating other applications of imprinting materials. This review provides recent progress in photocatalyst preparation, electrocatalyst, and Fenton-like catalysts synthesized by molecular imprinting. The principle and control points of target catalysts prepared by precipitation polymerization (PP) and surface molecular imprinting (S-MIP) are introduced. Also, the application of imprinted catalysts in targeted degradation of drugs, pesticides, environmental hormones, and other refractory pollutants is summarized. In addition, the reusability and stability of imprinted catalyst in water treatment are discussed, and the possible ecotoxicity risk is analyzed. Finally, we appraised the prospects, challenges, and opportunities of imprinted catalysts in the advanced oxidation process. This paper provides a reference for the targeted degradation of refractory pollutants and the preparation of targeted catalysts.

Rapid degradation of norfloxacin by VUV/Fe2+/H2O2 over a wide initial pH: Process parameters, synergistic mechanism, and influencing factors

Vacuum UV (VUV) technology has attracted much attention because it effectively splits water to generate reactive oxygen species (ROS) in situ and has the advantages of UV. So far, the synergistic mechanisms, formation pathways and contributions of ROS in VUV/Fe²⁺/H₂O₂ process have not been extensively studied. Herein, complete removal (at 4 min) and 63.3% mineralization (at 8 min) of 45 μM norfloxacin (NOR) were achieved at neutral pH by VUV/Fe²⁺/H₂O₂ (90 μM Fe²⁺ and 3 mM H₂O₂). Compared with its subsystems, VUV/Fe²⁺/H₂O₂ can not only increase the pseudo-first-order reaction rate constant of NOR removal by 2.3-14.9 times and increase the mineralization by 20.4-59.4%, but also reduce the residual ratio of H₂O₂ by 19.9-70.1% and reduce total cost by 20.0-68.0%. The synergy factor of VUV/Fe²⁺/H₂O₂ was 3.97, which was attributed to the VUV irradiation promoting iron redox cycle and H₂O₂ decomposition. Moreover, hydroxyl radical and superoxide radical, which were identified as the main ROS, contributed 79.07% and 18.47% to NOR removal, respectively. Degradation pathways of NOR were proposed. Furthermore, effects of coexisting ions and dissolved organic matter were investigated. As an energy-saving and efficient process, the satisfactory results of VUV/Fe²⁺/H₂O₂ applied in real waters also highlight its application potential.

Enhanced Fenton-like degradation of sulfadiazine by single atom iron materials fixed on nitrogen-doped porous carbon

The use of single-atom iron catalysts in heterogeneous Fenton-like reactions has demonstrated tremendous potential for antibiotic wastewater treatment. In this study, single-atom iron fixed on nitrogen-doped porous carbon materials (Fe-ISAs@CN) was synthesised using a metal organic framework (MOF) as a precursor. Fe-ISAs@CN was applied as a heterogeneous Fenton catalyst to activate H₂O₂ for the degradation of sulfadiazine (SDZ) in an aqueous solution. The physical and chemical properties of Fe-ISAs@CN were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disk electrode (RDE) measurements. The results of our degradation experiments indicated that Fe-ISAs@CN exhibited remarkable activity and stability for the degradation of SDZ over a wide pH range; even after five cycles, Fe-ISAs@CN retained a high catalytic efficiency (>80%). The 5,5-dimethyl-1-oxaporphyrin-n-oxide (DMPO)-X signal captured by electron paramagnetic resonance (EPR) spectroscopy indicated that a large amount of hydroxyl radicals (OH) was produced in the reaction system. Quench tests indicated that the OH was the main active substance in the degradation of SDZ. The degradation products of the reaction were analysed by High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS), and possible degradation pathways for the SDZ degradation were proposed.

Recent advancement in remediation of synthetic organic antibiotics from environmental matrices: Challenges and perspective

Continuous discharge and persistence of antibiotics in aquatic ecosystem is identified as emerging environment health hazard. Partial degradation and inappropriate disposal induce appearance of diverse antibiotic resistant genes (ARGs) and bacteria, hence their execution is imperative. Conventional methods including waste water treatment plants (WWTPs) are found ineffective for the removal of recalcitrant antibiotics. Therefore, constructive removal of antibiotics from environmental matrices and other alternatives have been discussed. This review summarizes present scenario and removal of micro-pollutants, antibiotics from environment. Various strategies including physicochemical, bioremediation, use of bioreactor, and biocatalysts are recognized as potent antibiotic removal strategies. Microbial Fuel Cells (MFCs) and biochar have emerged as promising biodegradation processes due to low cost, energy efficient and environmental benignity. With higher removal rate (20-50%) combined/ hybrid processes seems to be more efficient for permanent and sustainable elimination of reluctant antibiotics.

Peroxide/Zero-valent iron (Fe0) pretreatment for promoting dewaterability of anaerobically digested sludge: A mechanistic study

Peroxide/Zero-valent iron (Fe⁰) was reported to promote dewaterability of anaerobically digested sludge (ADS), but the mechanism of how Peroxide/Fe⁰ facilitates ADS dewatering is unknown. This study therefore aims to uncover the details of how Peroxide/Fe° elevates ADS dewaterability. Experimental results showed that with 0.6 g Fe⁰/g TSS and 0.08 g peroxide/g TSS, capillary suction time, specific resistance to filtration, and time to filtration of ADS was 50.7 %, 41.4 %, and 54.4 % of that in the control, respectively. In this condition, water content of sludge cake decreased from 91.2 % ± 0.5 % (the control) to 68.6 % ± 1.3 %. The mechanism explorations revealed that the elevated dewaterability was mainly caused by role of OH and Fe(II)/Fe(III) species during Peroxide/Fe° pretreatment. OH decreased the polysaccharides and proteins in extracellular polymeric substance (EPS), then injured the cytoderm & cytomembrane through the releases of lactate dehydrogenase and N-acetylglucosamine, and further facilitated the decrease of intracellular substances, which disengaged the water trapped in ADS. In addition, the cell lysis caused by OH facilitated forming macro-pores. Moreover, OH converted the conformational structure of extracellular proteins, which may strengthen the ADS hydrophobicity, promoting the discharge of unbound water and ADS flocculation. Meanwhile, Fe(II)/Fe(III) benefited aggregating the denatured ADS particulates.

Kinetic and mechanism study of UV/pre-magnetized-Fe0/oxalate for removing sulfamethazine

In this study, UV irradiated photochemical reactions of oxalate (Ox) with premagnetized-Fe⁰ (pre- Fe⁰) as the catalyst was used to degrade sulfamethazine (SMT). Magnetic field promoted the release of iron ion from Fe⁰ thus enhanced SMT and Ox removal in UV/pre- Fe⁰/Ox process. X-ray photoelectron spectroscopy demonstrated that the presence of UV and Ox promoted the transformation of Fe³⁺ to Fe²⁺ on Fe⁰, which enhanced the surface bound •OH (•OH_surf) generation. Ox inhibited the formation of iron (hydro)xides and enhanced the hydroxylation of Fe⁰ surface. •OH_surf was mainly responsible for SMT removal (44%), while UV direct photolysis and •OH in the solution both caused around 28% SMT removal. The process with Ox exhibited much higher efficiency in SMT degradation than that added with H₃PO₄, citric acid and ethylenediaminetetraacetic acid, which greatly expanded the chelate-modified Fenton processes and their treatment efficiency.

A flow-through electro-Fenton process using modified activated carbon fiber cathode for orange II removal

This study investigated the removal of Orange II by an electro-Fenton process using a novel recirculation flow-through reactor. The hydrogen peroxide was generated in-situ on the activated carbon fiber (ACF) modified with carbon black and polytetrafluoroethylene (PTFE). The modified ACF cathode was characterized by scanning electron microscopy (SEM) and nitrogen adsorption-desorption study. In light of the production of H₂O₂ and removal of Orange II, the optimum weight percentage of PTFE in the mixture of carbon black and PTFE was 75%. The effects of some important operating parameters such as current and flow rate were investigated. The best Orange II removal reached 96.7% with mineralization efficiency of 55.4% at 120 min under the current of 100 mA, initial pH 3, Fe²⁺ 0.3 mM and the flow rate of 7 mL min^-1. The cathode exhibited good regeneration ability and stability. OH was proved to be the main oxidizing species in this flow-through electro-Fenton system. This work demonstrated that such electro-Fenton process using modified ACF cathode was promising for the degradation of organic pollutants.

Discovering the Importance of ClO• in a Coupled Electrochemical System for the Simultaneous Removal of Carbon and Nitrogen from Secondary Coking Wastewater Effluent

Inorganic constituents in real wastewater, such as halides and carbonates/bicarbonates, may have negative effects on the performance of electrochemical systems because of their capability of quenching HO^•. However, we discovered that the presence of Cl^- and HCO₃^- in an electrochemical system is conducive to the formation of ClO^•, which plays an important role in promoting the simultaneous elimination of biorefractory organics and nitrogen in secondary coking wastewater effluent. The 6-h operation of the coupled electrochemical system (an undivided electrolytic cell with a PbO₂/Ti anode and a Cu/Zn cathode) at a current density of 37.5 mA cm^-2 allowed the removal of 87.8% of chemical oxygen demand (COD) and 86.5% of total nitrogen. The electron paramagnetic resonance results suggested the formation of ClO^• in the system, and the probe experiments confirmed the predominance of ClO^•, whose steady-state concentrations (8.08 × 10^-13 M) were 16.4, 26.5, and 1609.5 times those of Cl₂^•- (4.92 × 10^-14 M), HO^• (3.05 × 10^-14 M), and Cl^• (5.02 × 10^-16 M), respectively. The rate constant of COD removal and the Faradaic efficiency of anodic oxidation obtained with Cl^- and HCO₃^- was linearly proportional to the natural logarithm of the ClO^• concentration, and the specific energy consumption was inversely correlated to it, demonstrating the crucial role of ClO^• in pollutant removal.

Recovery of phosphorus and metallic nickel along with HCl production from electroless nickel plating effluents: The key role of three-compartment photoelectrocatalytic cell system

A three-compartment photoelectrocatalytic (PEC) cell system combined with ion exchange and chemical precipitation was proposed to recover phosphorus and nickel from electroless nickel plating effluents containing hypophosphite (H₂PO₂^-) and nickel ions (Ni²⁺). Ion exchange was used to concentrate and separate Ni²⁺ and H₂PO₂^-. As a key unit, the established PEC system consisted of TiO₂/Ni-Sb-SnO₂ photoanode and Ti cathode. With 25.8 mM NaH₂PO₂ and 500 mM NiCl₂, 100 % H₂PO₂^- was oxidized to PO₄^3- in the anode cell, 78 % Ni²⁺ was recovered as metallic Ni in the cathode cell, and 900 mM HCl was obtained in the middle cell within 24 h at 3.0 V. Based on quenching experiments and ESR technique, OH radicals were mainly responsible for H₂PO₂^- oxidation. In situ Raman spectroscopy indicated that Ni²⁺ initially reacted with OH^- to form α-Ni(OH)₂, which was gradually reduced to metallic Ni. Fortunately, a slight pH decrease in the cathode cell in the three-compartment cell system was beneficial for Ni²⁺ reduction to Ni°. The obtained PO₄^3- was recovered by chemical precipitation. Finally, recovery of phosphorus and metallic nickel along with HCl production from an actual electroless nickel plating effluents in terms of efficiency, cost-benefit, and stability assessment were demonstrated.

Electro-Fenton and photoelectro-Fenton degradation of sulfamethazine using an active gas diffusion electrode without aeration

A novel superhydrophobic gas diffusion electrode based on carbon black (CB)- polytetrafluoroethylene (PTFE) modified graphite felt cathode was prepared to increase oxygen mass transfer efficiency and produce hydrogen peroxide at the gas-liquid-solid three-phase interface without aeration. The gas diffusion electrode system was further tested for the degradation of sulfamethazine (SMT) by electro-Fenton (EF) and photoelectro-Fenton (PEF). In the EF process, SMT was removed effectively, but the mineralization degree was not high due to the generation of organic acids which were difficult to be further degraded. While in the PEF process, organic contaminant can be destroyed by the combined action of Fe²⁺/H₂O₂, UV/H₂O₂ and UV radiation, and more efficient mineralization (>83.5%) at low current (50 mA) was attained, which might be attributed to the high H₂O₂ utilization (70-90%), rapid regeneration of Fe²⁺ and photolysis of intermediates. In addition, it was verified that the PEF system had a good adaptability to pH and pollutant concentration. Compared with aeration system, the use of this active gas diffusion cathode in electrochemical advanced oxidation processes significantly reduced energy consumption.

EDTA, oxalate, and phosphate ions enhanced reactive oxygen species generation and sulfamethazine removal by zero-valent iron

The activation rate of oxygen by zero-valent iron (Fe°) was very low. In this study, ethylenediaminetetraacetic acid (EDTA), oxalate (Ox), and phosphate ions (Na₂HPO₄) were used to enhance the oxygen activation by Fe° for sulfamethazine (SMT) removal. The addition of these ligands could significantly enhance the SMT degradation. SMT removal was improved from 10.5 % in the Fe° system (360 min) to 70.3 %, 85.2 % and 77.8 % in the Fe°/EDTA (60 min), Fe°/Ox (180 min) and Fe°/phosphate (360 min) systems, respectively. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier transform infrared reflection (FTIR), contact angle and X-ray photoelectron spectra (XPS) of Fe° in different systems were recorded. The presence of chelating agents hydroxylated Fe°, inhibited the iron oxide formation on the Fe° surface and promoted iron ion release from the solid. Moreover, the agents improved the recovery of surface Fe²⁺ which could subsequently enhance the activation of O₂ to produce more H₂O₂ and reactive oxygen radicals for SMT removal. OH radical produced mainly through H₂O₂ decomposition was primarily responsible for removing SMT in all three systems. The Fe° system added with chelating agents is a new and promising approach for treating wastewaters containing ligands.

High-level waste activated sludge dewaterability using Fenton-like process based on pretreated zero valent scrap iron as an in-situ cycle iron donator

A novel, recyclable, and rapid pre-ultrasound-thermal-acid-washed zero valent scrap iron/hydrogen peroxide (UTA-ZVSI/H2O2) method has been developed to effectively enhance waste activated sludge (WAS) dewaterability. The effects of UTA ultrasound densities, UTA temperature, newly generated iron solution, H2O2 concentrations, and WAS conditioning time on the WAS dewaterability were investigated using a bench-scale system. Results indicated that the UTA-ZVSI/H2O2 treatment significantly improved the WAS dewaterability. The water content of the dewatered cake decreased to 44.15 ± 0.98 wt% during optimal operational conditions, which was significantly lower than that achieved using Fenton-based processes. Based on this outcome, a three-step treatment mechanism involving UTA-ZVSI/H2O2 has been developed, including iron flocculation, hydroxyl radical oxidation, and skeleton building. The dewatering efficiencies of three types of representative WAS were consistently effective in the UTA-ZVSI/H2O2 reactor for up to 15 cycles. Efficiencies levels were significantly higher than those achieved with Fenton-based processes. Economic analysis illustrated that the developed UTA-ZVSI/H2O2 system was the most cost-effective among other WAS dewatering treatments. In addition, the treatment system significantly alleviated toxicity of heavy metals and phytotoxicity in the dewatered sludge. This supported subsequent agricultural use. In summary, this study provided a comprehensive and useful basis for improving WAS dewatering and subsequent disposal.

Enhanced isophthalonitrile complexation-reduction removal using a novel anaerobic fluidized bed reactor in a bioelectrochemical system based on electric field activation (AFBR-EFA)

On account of the recalcitrant and highly toxicity of organonitrile substrates, traditional processes are limited by HCN poisoning thus inefficient. This article proposed a novel anaerobic fluidized bed reactor with electric field activation (AFBR-EFA) which had a 260-day continuous operation. The operation aims to explore the practicability of the enhanced reduction of isophthalonitrile (IPN), with emphasis on the optimum operation parameters and synergistic effect between electric field and anaerobic processes. The results showed that relatively higher voltage (1.0 V < V < 1.6 V) had a positive impact on reduction enhancement. High removal could be obtained at high initial concentration, low methanol dosage and short HRT which indicated that tolerance to shock loading was significantly enhanced in AFBR-EFA. Furthermore, EFA visibly motivated the enrichment of electrochemically active bacteria and various autotrophic IPN degradation-related species. The significantly efficient performance makes the potential for full-scale application of the AFBR-EFA markedly improved, particularly for treating hard-biodegraded contaminants.

Supported Atomically-Precise Gold Nanoclusters for Enhanced Flow-through Electro-Fenton

Gold (Au) has been considered catalytically inert for decades, but recent reports have described the ability of Au nanoparticles to catalyze H₂O₂ decomposition in the Haber-Weiss cycle. Herein, the design and demonstration of a flow-through electro-Fenton system based on an electrochemical carbon nanotube (CNT) filter functionalized with atomically precise Au nanoclusters (AuNCs) is described. The functionality of the device was then tested for its ability to catalyze antibiotic tetracycline degradation. In the functional filters, the Au core of AuNCs served as a high-performance Fenton catalyst; while the AuNCs ligand shells enabled CNT dispersion in aqueous solution for easy processing. The hybrid filter enabled in situ H₂O₂ production and catalyzed the subsequent H₂O₂ decomposition to HO·. The catalytic function of AuNCs lies in their ability to undergo redox cycling of Au⁺/Au⁰ under an electric field. The atomically precise AuNCs catalysts demonstrated superior catalytic activity to larger nanoparticles; while the flow-through design provided convection-enhanced mass transport, which yielded a superior performance compared to a conventional batch reactor. The adsorption behavior and decomposition pathway of H₂O₂ on the filter surfaces were simulated by density functional theory calculations. The research outcomes provided atomic-level mechanistic insights into the Au-mediated Fenton reaction.

Low-Fe(III) driven UV/Air process for enhanced recovery of heavy metals from EDTA complexed system

The efficient recovery of heavy metals from complexed wastewater is an essential but challenging task. In this study, a novel low-Fe(III) driven UV/Air process (LFUA) was developed to break the strong complexation between ethylenediamine tetracetic acid (EDTA) and heavy metal ions (HMIs) and enable the enhanced recovery of HMIs via chelating resin adsorption (CRA). The inside mechanism of the LFUA process includes: 1) displacement of HMIs from HMI-EDTA complexes by Fe(III); 2) direct photolysis of Fe(III)-EDTA through a ligand-to-metal charge transition reaction (LMCT) and indirect photolysis of EDTA by HO₂·/O₂·^-. The iron dosage was orders of magnitude lower than that previously reported, due to the Fe(II)/Fe(III) redox cycle in the LFUA process. Fe(II) formed during the LMCT reaction of Fe(III)-EDTA was oxidized back to Fe(III) by O₂ and HO₂·, and the reformed Fe(III) was then recombined with EDTA to sustains the LMCT reaction. EDTA was completely removed in 20 min at a molar ratio of Fe(III)/EDTA = 0.05. In addition, following the LFUA process, the adsorption amounts of various HMIs onto D463 resin were at least two orders of magnitude higher than those reported using the direct adsorption process. Employing the integrated technique of LFUA + CRA enabled the efficient removal of up to 64.5 mg/L of Cu(II) from inlet wastewater, and residual Cu(II) was below 0.5 mg/L. The results of desorption experiments showed that over 90% of Cu(II) was recovered, and the desorption solution had a Cu concentration of 2.1 g/L and purity of 99%. Furthermore, the economic and practical feasibility of using the combined process of LFUA + CRA was analyzed to substantiate that the technique is highly efficient and clean (produces no harmful sludge). Therefore, it is an appropriate and practical process in removing HMIs-EDTA complexes and recovering HMIs from wastewater.

Nitrofurazone degradation in the self-biased bio-photoelectrochemical system: g-C3N4/CdS photocathode characterization, degradation performance, mechanism and pathways

In this study, a self-biased bio-photoelectrochemical system (SB-BPES) was constructed using a bioanode and the g-C₃N₄/CdS heterojunction photocathode for nitrofurazone (NFZ) degradation under solar irradiation. The physio-chemical properties and optical performance of photocatalysts were characterized, and photo-electrochemical properties of various photocathodes were analyzed. Results showed that g-C₃N₄/CdS exhibited the broadest visible light absorption range (to 594 nm) and the most efficient e^--h⁺ separation; and its corresponding photocathode showed the highest photocurrent (9.8 μA), and the lowest charge transfer resistance (5.43 ☓ 10³ Ω). In the solar-illuminated SB-BPES with g-C₃N₄/CdS photocathode, about 80% of NFZ removal rate was achieved within 10 h. More importantly, TOC removal of 62.6% was achieved in 24 h, which was 1.8 times of that from the open circuit SB-BPES, and 4.3 folds of that from microbial degradation; also, about 1.5 times of those from SB-BPES with g-C₃N₄ and CdS photocathodes. Besides, reproducible current generations (∼1.0 mA) were produced. These verified that it was a self-sustained system for spontaneously pollutants degradation and electricity generation. Moreover, possible degradation mechanism and pathways were proposed according to the identified intermediates. This study provides inspiration for synchronic improving refractory organics degradation and net energy recovery.