Suppressing Methane Production to Boost High-Purity Hydrogen Production in Microbial Electrolysis Cells.

Hydrogen gas (H2) is an attractive fuel carrier due to its high specific enthalpy; moreover, it is a clean source of energy because in the combustion reaction with oxygen (O2) it produces water as the only byproduct. The microbial electrolysis cell (MEC) is a promising technology for producing H2 from simple or complex organics present in wastewater and solid wastes. Methanogens and non-archaeal methane (CH4)-producing microorganisms (NAMPMs) often grow in the MECs and lead to rapid conversion of produced H2 to CH4. Moreover, non-archaeal methane production (NAMP) catalyzed by nitrogenase of photosynthetic bacteria was always overlooked. Thus, suppression of CH4 production is required to enhance H2 yield and production rate. This review comprehensively addresses the principles and current state-of-the-art technologies for suppressing methanogenesis and NAMP in MECs. Noteworthy, specific strategies aimed at the inhibition of methanogenic enzymes and nitrogenase could be a more direct approach than physical and chemical strategies for repressing the growth of methanogenic archaea. In-depth studies on the multiomics of CH4 metabolism can possibly provide insights into sustainable and efficient approaches for suppressing metabolic pathways of methanogenesis and NAMP. The main objective of this review is to highlight key concepts, directions, and challenges related to boosting H2 generation by suppressing CH4 production in MECs. Finally, perspectives are briefly outlined to guide and advance the future direction of MECs for production of high-purity H2 based on genetic and metabolic engineering and on the interspecific interactions.

Microbial compositions, ecological networks, and metabolomics in sediments of black-odour water in Dongguan, China.

Black-odour water with organic compounds and heavy metals caused by domestic and industrial activities has aroused people's attention in recent years, yet little is known about the ecological effects on aquatic organisms, especially microorganisms in sediments. To explore the response of microbial communities to environmental factors, the community and metabolites of nine river sediments with different pollution in Dongguan city, China were investigated using 16S rRNA gene sequencing and liquid chromatography tandem-mass. The results revealed that the composition and structure of sedimentary microbial communities significantly changed in rivers with varying pollution levels. Cyanobacteria were the most abundant organisms in the sediment of black-odorous rivers, while the relative abundance of Thaumarchaeota was gradually increased with the river quality gets better. The relative abundance of organic acids (including amino acids), alcohols, esters, and ketones associated with microbial metabolism in sediments of polluted rivers was increased. The 16S rRNA gene sequencing-based molecular ecological network analysis indicated that the interactions amongst bacteria were enhanced in severely contaminated communities. Sphingomonadaceae and Cyanobacteria have important roles in bacterial community structures of polluted rivers and those with ongoing treatment. The correlation analysis showed significant metal resistance and/or tolerance of the following bacteria species Thalassiosira weissflogii, Aminicenantes bacterium clone OPB95, 'Candidatus Halomonas phosphatis', and archaeal species Methanolinea and unidentified Thermoplasmata. These results indicated that sedimentary microbial communities may shift in composition and structure, as well as their interaction network, to adapt and resist environmental contamination and promote restoration.

Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river.

Microplastics (MPs) and heavy-metal contamination in freshwater is an increasing concern. Fe, Mn, Pb, Zn, Cr, and Cd are common heavy metals that can easily flow into rivers causing water pollution. Microplastics act as carriers for heavy metals and increase the transport of contaminants in freshwater systems. We investigated the adsorption mechanisms of three kinds of MPs having similar particle sizes, namely polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), with respect to trace heavy metals of Pb, Cu, Cr, and Cd under different temperature and salinity conditions. The reaction kinetics of the adsorption of different trace heavy metals on different MPs were consistent with both the quasi primary and quasi secondary kinetic models, indicating the complexity of heavy metal adsorption by MPs. The adsorption rate of heavy metal on MPs was mainly controlled by intra-particle diffusion, and the isotherm model indicated that the adsorption of Pb, Cu, Cr, and Cd by MPs occurred in the form of monolayer physical adsorption. Additionally, an increase in temperature and decrease in salinity were favourable to improve the affinity of MPs toward heavy metals (through adsorption). Zeta potential measurements and Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that electrostatic force interaction was the main mechanism of the adsorption process; oxygen-containing functional groups, π-π interaction, and halogen bonds played important roles in the process of adsorption. Furthermore, the growth inhibition and oxidative stress of microalgae Chlorella vulgaris (GY-D27) due to PP, PS, and PVC were analysed; notably, MPs or Pb inhibited the growth of Chlorella vulgaris. However, the reduced toxicity to Chlorella vulgaris, with respect to a mixture of Pb and MPs, was confirmed using superoxide dismutase and catalase enzyme activities. Our results can be applied for the risk assessment of heavy metals and MPs in aquatic environments.

Is HFPO-DA (GenX) a suitable substitute for PFOA? A comprehensive degradation comparison of PFOA and GenX via electrooxidation.

Due to the potential hazard of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) has become a typical alternative since 2009. However, GenX has recently been reported to have equal or even greater toxicity and bioaccumulation than PFOA. Considering the suitability of alternatives, it is quite essential to study and compare the degradation degree between PFOA and GenX in water. Therefore, in the present study, a comprehensive degradation comparison between them via electrooxidation with a titanium suboxide membrane anode was conducted. The degradation rate decreased throughout for PFOA, while it first increased and then decreased for GenX when the permeate flux increased from 17.3 L to 100.3 L m-2·h-1. The different responses of PFOA and GenX to flux might be attributed to their different solubilities. In addition, the higher kobs of PFOA demonstrated that it had a better degradability than GenX by 2.4-fold in a mixed solution. The fluorinated byproduct perfluoropropanoic acid (PFPrA) was detected as a GenX intermediate, suggesting that ether bridge splitting was needed for GenX electrooxidation. This study provides a reference for assessing the degradability of GenX and PFOA and indicates that it is worth reconsidering whether GenX is a suitable alternative for PFOA from the point of view of environmental protection.

Defect Engineering on a Ti4O7 Electrode by Ce3+ Doping for the Efficient Electrooxidation of Perfluorooctanesulfonate.

Defect engineering in an electrocatalyst, such as doping, has the potential to significantly enhance its catalytic activity and stability. Herein, we report the use of a defect engineering strategy to enhance the electrochemical reactivity of Ti4O7 through Ce3+ doping (1-3 at. %), resulting in the significantly accelerated interfacial charge transfer and yielding a 37-129% increase in the anodic production of the hydroxyl radical (OH•). The Ce3+-doped Ti4O7 electrodes, [(Ti1-xCex)4O7], also exhibited a more stable electrocatalytic activity than the pristine Ti4O7 electrode so as to facilitate the long-term operation. Furthermore, (Ti1-xCex)4O7 electrodes were also shown to effectively mineralize perfluorooctanesulfonate (PFOS) in electrooxidation processes in both a trace-concentration river water sample and a simulated preconcentration waste stream sample. A 3 at. % dopant amount of Ce3+ resulted in a PFOS oxidation rate 2.4× greater than that of the pristine Ti4O7 electrode. X-ray photoelectron spectroscopy results suggest that Ce3+ doping created surficial oxygen vacancies that may be responsible for the enhanced electrochemical reactivity and stability of the (Ti1-xCex)4O7 electrodes. Results of this study provide insights into the defect engineering strategy for boosting the electrochemical performance of the Ti4O7 electrode with a robust reactivity and stability.

Effective immobilization of hexavalent chromium from drinking water by nano-FeOOH coating activated carbon: Adsorption and reduction.

In this study, nano α-FeOOH (nFeOOH, 100-500 nm) was coated onto activated carbon (nFeOOH@AC) through a dipping means for enhanced Cr(VI) immobilization from drinking water. The nFeOOH@AC significantly improved the Cr(VI) removal from 19.9% (AC control) to 93.4%. XPS spectra and chromium speciation demonstrated that about 90% of adsorbed Cr(VI) was converted to Cr(III) by the nFeOOH@AC, accompanying with a reduction-oxidation of Fe3+/Fe2+ in the nFeOOH matrix due to electrons delivering between AC and surface-bound Cr(VI). The resultant Cr(III) subsequently reacted with Fe(III) to generate stable (CrχFe1-χ)(OH)3 precipitates, leading to a much lower Cr(III) release of 7.5% back to solution by the nFeOOH@AC as compared to the AC control of 33.8%, indicating that the nFeOOH@AC had a prospective potential for Cr(VI) immobilization and decreased Cr residue in treated drinking water. Results from column experiment also showed that the nFeOOH@AC afforded a 3.5 times higher capacity for Cr(VI) immobilization and a 3.4 times longer life-span than the pristine AC. Besides, Cr(VI) immobilization by the nFeOOH@AC was a pH-dependent process and the adsorbed Cr on the nFeOOH@AC could be readily desorbed with acetic acid. The disabled nFeOOH@AC could be refreshed by recoating nFeOOH particles with the above dipping method after stripping all the iron oxides with hydrochloric acid. This study demonstrated that nFeOOH coating is an efficient approach to enhance Cr(VI) elimination by AC during drinking water treatments.

Succession of functional bacteria in a denitrification desulphurisation system under mixotrophic conditions.

Large-scale use of ammonia, sulphate, and nitrate in industrial manufacturing has resulted in the generation of industrial wastewater pollutants. However, approaches to eliminate such contamination have not been extensively studied. Accordingly, in this study, we investigated the succession of bacteria under different influent loadings in a mixotrophic denitrification desulphurisation system. Four expanded granular sludge bed reactors were operated simultaneously. The sulphide loading of reactor I was 1.2 kg/m3‧day, the sulphide load of reactor II was 2.4 kg/m3‧day, and the sulphide load of reactor III was 3.6 kg/m3‧day. The molar ratio of carbon versus nitrogen in the influent under each condition was fixed at 1.26:1, and the molar ratio of sulphur versus nitrogen was fixed at 5:6; each reactor was operated for 90 days. Reactor IV was a verification reactor. The three conditions were repeated, and each condition was operated for 90 days. Middle- and late-stage samples under each condition were sequenced using a high-throughput sequencer. Azoarcus, Thauera, Arcobacter, and Pseudomonas were the core genera of the denitrification desulphurisation system under mixotrophic conditions. The genus Azoarcus was a cornerstone genus of mixotrophic conditions, as demonstrated using the random forest model and correlation network analysis.

Simultaneous Cu(II)-EDTA decomplexation and Cu(II) recovery using integrated contact-electro-catalysis and capacitive deionization from electroplating wastewater.

The complex of heavy metals and organic acids leads to high difficulty in heavy metals separation by traditional technologies. Meanwhile, alkaline precipitation commonly used in industry causes the great consumption of resources and extra pollution. Herein, the effective decomplexation of Cu(Ⅱ)-EDTA and synchronous recycling of Cu2+ were realized by contact-electro-catalysis (CEC) coupled with capacitive deionization (CDI) innovatively. In particular, fluorinated ethylene propylene (FEP) as dielectric powders could generate reactive oxygen species under ultrasonic stimulation, realizing continuous deaminization and decarboxylation of Cu(Ⅱ)-EDTA and accelerating the totally breakage of Cu-O and Cu-N bonds. Additionally, the degradation pathway and intermediates evolution of Cu(Ⅱ)-EDTA were investigated using various characterization methods. It was confirmed that decarboxylation predominantly governed the degradation process of Cu(Ⅱ)-EDTA in CEC. During the course of treatment, the degradation ratio of Cu(Ⅱ)-EDTA reached 86.4 % within 150 min. Impressively, this strategy had satisfactory applicability to other metal combinations and excellent cycle stability. Subsequently, the released Cu ions were captured by CuSe cathode electrode through CDI. This research elucidated the degradation mechanism of persistent organic pollutant during CEC, and provided a novel approach for efficiently treating industrial wastewater containing metal complexes and advancing the exploitation and utilization of new technologies for metal recovery.

Multi-omics analysis of nitrifying sludge under carbon disulfide stress: Nitrification performance and molecular mechanisms.

Carbon disulfide (CS2) is a widely used enzyme inhibitor with cytotoxic properties, commonly employed in viscose fibers and cellophane production due to its non-polar characteristics. In industry, CS2 is often removed by aeration, however, residual CS2 may enter the wastewater treatment plants, impacting the performance of nitrifying sludge. Currently, there is a notable dearth of research on the response of nitrifying sludge to CS2-induced stress. This study delves into the alterations in the performance of nitrifying sludge under short-term and long-term CS2 stress, scrutinizes the toxic effects of CS2 on microbial cells, elucidates the succession of microbial community structure, and delineates changes in microbial metabolic products. The findings from short-term CS2 stress revealed that low concentrations of CS2 induced oxidative stress damage, which was subsequently repaired in cells. However, at concentrations of 100-200 mg/L, CS2 inhibited reactive oxygen species, superoxide dismutase, and catalase, which are associated with metabolic and antioxidant activities. The inhibition of nitrite oxidoreductase activity by high concentrations of CS2 was attributed to its impact on the enzyme's conformation. Prolonged CS2 stress resulted in an increase in the secretion of soluble extracellular polymeric substances in sludge, while CS2 was assimilated into sulfate. The analysis of sludge microbial community structure revealed a decline in the relative abundance of Rhodanobacter, which is associated with nitrification, and an increase in Sinomonas, involved in sulfur oxidation. Metabolite analysis results demonstrated that high concentrations of CS2 affect pantothenate and CoA biosynthesis, purine metabolism, and glutathione metabolism. This study elucidated the microbial response mechanism of nitrifying sludge under short-term and long-term CS2 stress. It also clarified the composition and function of microbial ecosystems, and identified key bacterial species and metabolites. It provides a basis for future research to reduce CS2 inhibition through approaches such as the addition of metal ions, the selection of efficient CS2-degrading strains, and the modification of strain metabolic pathways.

Copper removal and recovery from electroplating effluent with wide pH ranges through hybrid capacitive deionization using CuSe electrode.

In modern industry, selective extraction and recovery of Cu from strongly acidic electroplating effluent are crucial to reduce carbon emissions, alleviate resource scarcity, and mitigate water pollution, yielding considerable economic and environmental benefits. This study proposed a high-efficiency CuSe electrode to selectively remove Cu from electroplating effluent via hybrid capacitive deionization (HCDI). The potential of this electrode was thoroughly evaluated to assess its effectiveness. The CuSe electrode exhibited superior deionization performance in terms of Cu adsorption capacity, selectivity, and applicability in various water matrices. Specifically, under strong acid conditions (1 M H+), the CuSe electrode maintained an optimal adsorption capacity of 357.36 mg g-1 toward Cu2+. In systems containing salt ions, heavy metals, and actual electroplating wastewater, the CuSe electrode achieved a remarkable removal efficiency of up to 90% for Cu2+ with a high distribution coefficient Kd. Notably, the capacitive deionization (CDI) system demonstrated the simultaneous removal of Cu-EDTA. The removal mechanism was further revealed using ex-situ X-ray diffraction and X-ray photoelectron spectroscopy analyses. Overall, this study presents a practical approach that extends the capabilities of CDI platforms for effectively removing and recovering Cu from acidic electroplating effluent.

Single-atom Zr embedded Ti4O7 anode coupling with hierarchical CuFe2O4 particle electrodes toward efficient electrooxidation of actual pharmaceutical wastewater.

Electrocatalytic oxidation is commonly restricted by low degradation efficiency, slow mass transfer, and high energy consumption. Herein, a synergetic electrocatalysis system was developed for removal of various drugs, i.e., atenolol, florfenicol, and diclofenac sodium, as well as actual pharmaceutical wastewater, where the newly-designed single-atom Zr embedded Ti4O7 (Zr/Ti4O7) and hierarchical CuFe2O4 (CFO) microspheres were used as anode and microelectrodes, respectively. In the optimal reaction system, the degradation efficiencies of 40 mg L-1 atenolol, florfenicol, and diclofenac sodium could achieve up to 98.8%, 93.4%, and 85.5% in 120 min with 0.1 g L-1 CFO at current density of 25 mA cm-2. More importantly, in the flow-through reactor, the electrooxidation lasting for 150 min could reduce the COD of actual pharmaceutical wastewater from 432 to 88.6 mg L-1, with a lower energy consumption (25.67 kWh/m3). Meanwhile, the electrooxidation system maintained superior stability and environmental adaptability. DFT theory calculations revealed that the excellent performance of this electrooxidation system could be ascribed to the striking features of the reduced reaction energy barrier by single-atom Zr loading and abundant oxygen vacancies on the Zr/Ti4O7 surface. Moreover, the characterization and experimental results demonstrated that the CFO unique hierarchical structure and synergistic effect between electrodes were also the important factors that could improve the system performance. The findings shed light on the single-atom material design for boosting electrochemical oxidation performance.

Fabrication and characterizations of Zn-doped SnO2-Ti4O7 anode for electrochemical degradation of hexafluoropropylene oxide dimer acid and its homologues.

Hexafluoropropylene oxide dimer acid (HFPO-DA) and its homologues, as perfluorinated ether alkyl substances with strong antioxidant properties, have rarely been reported by electrooxidation processes to achieve good results. Herein, we report the use of an oxygen defect stacking strategy to construct Zn-doped SnO2-Ti4O7 for the first time and enhance the electrochemical activity of Ti4O7. Compared with the original Ti4O7, the Zn-doped SnO2-Ti4O7 showed a 64.4% reduction in interfacial charge transfer resistance, a 17.5% increase in the cumulative rate of •OH generation, and an enhanced oxygen vacancy concentration. The Zn-doped SnO2-Ti4O7 anode exhibited high catalytic efficiency of 96.4% for HFPO-DA within 3.5 h at 40 mA/cm2. Hexafluoropropylene oxide trimer and tetramer acid exhibit more difficult degradation due to the protective effect of the -CF3 branched chain and the addition of the ether oxygen atom leading to a significant increase in the C-F bond dissociation energy. The degradation rates of 10 cyclic degradation experiments and the leaching concentrations of Zn and Sn after 22 electrolysis experiments demonstrated the good stability of the electrodes. In addition, the aqueous toxicity of HFPO-DA and its degradation products was evaluated. This study analyzed the electrooxidation process of HFPO-DA and its homologues for the first time, and provided some new insights.

Sludge source-redox mediators obtainment and availability for enhancing bioelectrogenesis and acidogenesis: Deciphering characteristics and mechanisms.

Anaerobic biological treatment was regarded as one of promising options for realizing concurrent WAS reduction, stabilization and bioenergy/bioresource recycle. But the relatively low treatment efficiency limited its spreading application toward larger scale considerably in China. Aimed at such barrier, this study offered a novel enhancing strategy for achieving high-efficiency of bioenergy/bioresource recycle from WAS anaerobic treatment via improving bioelectrogenesis/acidogenesis using sludge source-redox mediators (SSRMs). SSRMs not only facilitated bioeletrogenesis with an increasing efficiency of 36% for voltage output and 39% for bioelectricity bioconversion, but also enhanced acidogenesis of WAS with a mean elevating efficiency of 37.5% of volatile fatty acids (VFAs) production within 5 d Mechanistic investigations indicated that SSRMs had a potential influence on improving the protein and carbohydrate metabolisms-related genes' expression for enhancing bioelectrogenesis and acidogenesis. Moreover, SSRMs exerted roles of electrochemical "catalysts" or as terminal electron acceptors with affecting functional proteins of complexes of Ⅰ and Ⅳ in electron transfer chains for improving electron transfer efficiency. Meanwhile, the core members' abundance, microbial diversity and community distributive evenness were prompted concurrently for carrying out superior bioelectrogenesis and acidogenesis. A schematic illustration was established for demonstrating the mechanism of SSRMs for enhancing bioelectrogenesis and acidogenesis via changing microbial metabolism functions, enhancing electron transfer efficiency, and regulating functional genes' expression of functional proteins (up-regulating cytochrome c oxidase and down-regulating-NADH dehydrogenase). This study provided an effective enhancing strategy for facilitating WAS bioconversion to bioenergy/bioresource with well-process sustainability.

Column study of Cd(II) removal and longevity by nitrate-mediated zero-valent iron with mixed anaerobic microorganisms.

In this study, hydrogen-autotrophic microorganisms and zero-valent iron (Fe0) were filled into columns to investigate hydrogenotrophic denitrification effect on cadmium (Cd(II)) removal and column life-span with sand, microorganisms, Fe0 and bio-Fe0 columns as controls. In terms of the experiment results, the nitrate-mediated bio-Fe0 column showed a slow Cd(II) migration rate of 0.04 cm/PV, while the values in the bio-Fe0 and Fe0 columns were 0.06 cm/PV and 0.14 cm/PV respectively, indicating much higher Cd(II) removal efficiency and longer service life of the nitrate-mediated bio-Fe0 column. The XRD and SEM-EDX results implied that this improvement was attributed to hydrogenotrophic denitrification that caused more serious iron corrosion and larger amount of secondary mineral generation (e.g., green rust, lepidocrocite and goethite). These active minerals provided more reaction sites for Cd(II) adsorption and further immobilization. In addition, the decrease of Cd(II) migration front and the increase of removal capacity along the bio-Fe0 column mediated by nitrate presented an uneven distribution in reactive zone. The latter half part was identified to be a more active region for Cd(II) immobilization. The above results indicate that the introduction of nitrate and microorganisms will improve the performance of iron-based permeable reactive barriers for the remediation of Cd(II)-containing groundwater.

Synergic role of ferrate and nitrite for triggering waste activated sludge solubilisation and acidogenic fermentation: Effectiveness evaluation and mechanism elucidation.

Enhancing anaerobic treatment efficiency of waste activated sludge (WAS) toward preferable resource recovery would be an important requirement for achieving carbon-emission reduction, biosolids minimization, stabilization and security concurrently. This study demonstrated the synergic effect of potassium ferrate (PF) and nitrite on prompting WAS solubilisation and acidogenic fermentation toward harvesting volatile fatty acids (VFAs). The results indicated the PF+NaNO2 co-pretreatment boosted 7.44 times and 1.32 times higher WAS solubilisation [peak soluble chemical oxygen demand (SCOD) of 2680 ± 52 mg/L] than that by the single nitrite- and PF-pretreatment, respectively, while about 2.77 times and 2.11 times higher VFAs production were achieved (maximum VFAs accumulation of 3536.25 ± 115.24 mg COD/L) as compared with the single pretreatment (nitrite and PF)-fermentations. Afterwards the WAS dewaterability was improved simultaneously after acidogenic fermentation. Moreover, a schematic diagram was established for illustrating mechanisms of the co-pretreatment of PF and nitrite for enhancing the VFAs generation via increasing key hydrolytic enzymes, metabolic functional genes expression, shifting microbial biotransformation pathways and elevating abundances of key microbes in acidogenic fermentation. Furthermore, the mechanistic investigations suggested that the PF addition was conducive to form a relatively conductive fermentation environment for enhancing electron transfer (ET) efficiency, which contributed to the VFAs biotransformation positively. This study provided an effective strategy for enhancing the biodegradation/bioconversion efficiency of WAS organic matters with potential profitable economic returns.

Electro-activation of peroxymonosulfate by a graphene oxide/iron oxide nanoparticle-doped Ti4O7 ceramic membrane: mechanism of singlet oxygen generation in the removal of 1,4-dioxane.

Electro-activation of peroxymonosulfate (PMS) has been widely investigated for the degradation of organic pollutants. Herein, we employ graphene oxide (GO)/Fe3O4 nanoparticles (NPs) doped into a Ti4O7 reactive electrochemical membrane through strong chemical bonding as the cathode to activate PMS for the degradation of 1,4-dioxane (1,4-D). The strong chemical interaction between GO, Fe3O4-NPs, and Ti4O7 via Fe-O---GO---O-Ti bonds enhances the electron-transfer efficiency and provides catalytically active sites that boost the electro-activation of PMS. As a result, the 1,4-D oxidation rate of the GO/Fe3O4-NPs@Ti4O7 REM cathode is ~3 times higher (7.21 × 10-3 min-1) than those of other Ti4O7 ceramic membranes, and 1O2 plays a key role (59.9%) in the degradation of 1,4-D. The 1O2 generation mechanism in the electro-activation process of PMS was systematically investigated, and we claimed that 1O2 is mainly generated from the precursors H2O2 and O2•-/HO2• rather than by O2 or •OH, as has been reported in previous studies. A flow-through mode test in the PMS electro-activation system is firstly reported, and the 1,4-D decay efficiency is 7.1 times higher than that obtained by a flow-by mode, showing that an improved PMS mass transfer efficiency enhances the conversion to reactive oxygen species.

Interface engineering strategy of a Ti4O7 ceramic membrane via graphene oxide nanoparticles toward efficient electrooxidation of 1,4-dioxane.

Although Ti4O7 ceramic membrane has been recognized as one of the most promising anode materials for electrochemical advanced oxidation process (EAOP), it suffers from relatively low hydroxyl radical (•OH) production rate and high charge-transfer resistance that restricted its oxidation performance of organic pollutants. Herein, we reported an effective interface engineering strategy to develop a Ti4O7 reactive electrochemical membrane (REM) doped by graphene oxide nanoparticles (GONs), GONs@Ti4O7 REM, via strong GONs-O-Ti bonds. Results showed that 1% (wt%) GON doping on Ti4O7 REM significantly reduced the charge-transfer resistance from 73.87 to 8.42 Ω compared with the pristine Ti4O7 REM, and yielded •OH at 2.5-2.8 times higher rate. The 1,4-dioxane (1,4-D) oxidation rate in batch experiments by 1%GONs@Ti4O7 REM was 1.49×10-2 min-1, 2 times higher than that of the pristine Ti4O7 REM (7.51×10-3 min-1) and similar to that of BDD (1.79×10-2 min-1). The 1%GONs@Ti4O7 REM exhibited high stability after a polarization test of 90 h at 80 mA/cm2, and within 15 consecutive cycles, its oxidation performance was stable (95.1-99.2%) with about 1% of GONs lost on the REM. In addition, REM process can efficiently degrade refractory organic matters in the groundwater and landfill leachate, the total organic carbon was removed by 54.5% with a single-pass REM. A normalized electric energy consumption per log removal of 1,4-D (EE/O) was observed at only 0.2-0.6 kWh/m3. Our results suggested that chemical-bonded interface engineering strategy using GONs can facilitate the EAOP performance of Ti4O7 ceramic membrane with outstanding reactivity and stability.

Peroxymonosulfate activation by oxygen vacancies-enriched MXene nano-Co3O4 co-catalyst for efficient degradation of refractory organic matter: Efficiency, mechanism, and stability.

Cobalt-based catalysts have been widely explored in the degradation of organic pollutants based on peroxymonosulfate (PMS) activation. Herein, we report an MXene nano-Co3O4 co-catalyst enriched with oxygen vacancies (Ov) and steadily fixed in nickel foam (NF) plates, which is used as an efficient and stable PMS activator for the removal of 1,4-dioxane (1,4-D). Ti originating from MXene was doped into the Co3O4 crystal, generating large amounts of Ov, which could provide more active sites to enhance PMS activation and facilitate the transformation of Co2+ and Co3+, causing a high stability. As a result, the 1,4-D removal efficiency of the NF/MXene-Co3O4/PMS system (kapp: 2.41 min-1) was about four times higher than that of the NF/Co3O4/PMS system (kapp: 0.62 min-1). In addition, singlet oxygen was the predominant reactive oxygen species. Notably, the 1,4-D removal of the NF/MXene-Co3O4/PMS system was over 95% after 20 h operation in the single-pass filtration mode with only 3.72% accumulative Co leaching, showing excellent stability and reusability of NF/MXene-Co3O4. This work provides a defect engineering strategy to design a robust and stable catalytic system for water treatment, which expands the application of MXene in the field of environmental remediation.

Insight into the rapid elimination of low-concentration antibiotics from natural waters using tandem multilevel reactive electrochemical membranes: Role of direct electron transfer and hydroxyl radical oxidation.

Herein, we reported a tandem multilevel reactive electrochemical membrane (REM) system was promising for the rapid and complete removal of trace antibiotics from natural waters. Results indicate that a four-stage REM module-in-series system achieved steady over 98% removal of model antibiotic norfloxacin (NOR, 100 µg·L-1) from wastewater treatment plant final effluent and surface water with a residence time of 5.4 s, and the electric energy consumption was only around 0.007-0.011 kWh·m-3. As for the oxidation mechanism, direct electron transfer (DET) oxidation process played an important role in NOR rapid oxidation, enabling the REM system to tolerate various •OH scavenges in natural waters, including natural organic matters, Cl- and HCO3-, even at very high concentration levels. Meanwhile, •OH-mediated indirect oxidation process promotes the oxidation and mineralization of NOR. Although the DET-dominated oxidation mechanism makes the REM system cannot achieve the complete mineralization of NOR with residence times of few seconds, the antibacterial activity from NOR was completely eliminated. This REM system featured effective removal performance of trace contaminants with low energy cost and was tolerant to complex waster matrix, suggesting that it could be a powerful supplementary step for wastewater/water treatment.

Efficient adsorption of ciprofloxacin using Ga2S3/S-modified biochar via the high-temperature sulfurization.

Ga2S3 and sulfur co-modified biochar (Ga/S-BC) composites were prepared for enhancing the adsorption of ciprofloxacin from sugarcane bagasse via the high-temperature sulfurization. In contrast with sulfur-modified biochar, Ga/S-BC exhibited the better adsorption capacity for ciprofloxacin removal. The increasing Ga content induced to the climbing and then declining adsorption activity of Ga/S-BC. Among these obtained Ga/S-BC composites, optimal 3-Ga/S-BC with a Ga content of 7.40% and surface area of 681.67 m2 g-1 exhibited the superior capacity of 330.21 mg g-1. The adsorption capacity of 3-Ga/S-BC declined to 301.66 mg g-1 after nine cycles. pH and inorganic salts also affected the adsorption capacity of 3-Ga/S-BC for ciprofloxacin removal. The adsorption isotherms of obtained Ga/S-BC composites were well described by Langmuir isotherm, and their adsorption kinetics were well estimated via second-order model. The adsorption performance of 3-Ga/S-BC in ciprofloxacin removal was a physisorption and spontaneous process.