Removal of antibiotic resistant bacteria and genes by nanoscale zero-valent iron activated persulfate: Implication for the contribution of pH decrease

Rapid charge transfer and O3 selective catalysis induced by B-doped nanoconfined reactor realized complete Cu-EDTA decomplexation: Significant role of BC3 conformation

Nanoconfinement strategy that overcomes the defects of conventional heterogeneous catalysts in electron and mass transport provides a new outlet to enhance REDOX processes. Nonetheless, limitations in the activity and selectivity of effective catalytic sites are still the drawbacks of nanoconfined catalysts. In this study, a B-doped carbon nanotubes-confined-FexOy catalyst (B500Fe200@CNTs-L) coupled with a dielectric barrier discharge (DBD) plasma system (DBD/B500Fe200@CNTs-L) was developed for Cu-EDTA removal. The DBD/B500Fe200@CNTs-L system realized 100% Cu-EDTA decomplexation within 3 min, which was 3.6 times kinetically faster than without B doping. The system emphasized extensive pH adaptability, maintaining 100% Cu-EDTA removal at a pH of 3-9. B doping increased the selectivity to O3 and promoted active species generation, in which •OH and O2•- prominently contributed to Cu-EDTA decomplexation, as well as FeIV=O. The strong electronic activity induced by BC3 conformation enhanced charge transfer, regulating the positive charge and d-band center of central Fe atoms to decline the energy barriers of H2O2 and O3 adsorption and active species formation. Moreover, this system emphasized the superior catalytic stability under different matrix water (Cl⁻, CO₃²⁻, NO₃⁻, SO₄²⁻, and PO₄³⁻).

Differing envelope composition of Gram-negative and Gram-positive bacteria controls the adhesion and bactericidal performance of nanoscale zero-valent iron

Zero-valent-iron (nZVI) is a candidate antimicrobial agent, and previous works revealed its varying inactivation performance on Gram-negative (G-) and Gram-positive (G+) bacteria, but the underlying mechanism remains ambiguous. Herein, we reported the easier inactivation of Escherichia coli (G-, E. coli) than Staphylococcus aureus (G+, S. aureus) by nZVI, and revealed the key role of cell-nZVI adsorption. nZVI adhered more massively on E. coli surface than on S. aureus, and subsequently led to more pronounced membrane damage of E. coli. Investigations of pH, zeta potential, and ionic strength ruled out the essential contribution of nZVI-bacteria electrostatic interaction due to the different surface charges of E. coli and S. aureus. Three-dimensional excitation emission matrix suggested that the extracellular polymeric substances of E. coli suffered more severe damage by nZVI and lead to greater exposure of membrane. Infrared spectra indicated that nZVI strongly bound with the membrane proteins of E. coli and destroyed the membrane components. By contrast, the bonding between nZVI and S. aureus was minimal because of the dominant multi-layered peptidoglycan. The enhanced nZVI adsorption and membrane disruption would result in magnified reactive oxygen species (ROS) generation and oxidative stress of E. coli. Moreover, the catalase activity normalized by ROS concentration of S. aureus was 14.9-fold higher than that of E. coli after nZVI treatment, suggesting the stronger antioxidative capability of S. aureus. Our findings highlight that the different envelope compositions and antioxidant capacities between G- and G+ bacteria were responsible for their varying susceptibility to nZVI.

Combating Antibiotic Resistance in Persulfate-Based Advanced Oxidation Processes: Activation Methods and Energy Consumption

Antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) have become increasing concerning issues, threatening human health. Persulfate-based advanced oxidation processes (PS-AOPs), due to their remarkable potential in combating antibiotic resistance, have garnered significant attention in the field of disinfection in recent years. In this review, we systematically evaluated the efficacy and underlying mechanism of PS integration with various activation methods for the elimination of ARB/ARGs. These approaches encompass physical methods, catalyst activation, and hybrid techniques with photocatalysis, ozonation, and electrochemistry. Additionally, we employed Chick's model and electrical energy per log order (EE/O) to assess the performance and energy efficiency, respectively. This review aims at providing a guide for future investigation on PS-AOPs for antibiotic resistance control.

Performance of nano zero-valent iron activated peroxydisulfates prepared by carbothermal reduction using various bagasse components

Biomass has been utilized in the carbothermal reduction method to reduce iron cations, thereby synthesizing nano zero-valent iron (nZVI). The effect of the biomass components on the regulation of the performance of prepared nZVI is not clear and the mechanism of action remains to be explored. Biomass components such as cellulose, hemicellulose, lignin, and amylum were used to prepare carbon-loaded nano zero-valent iron. It was demonstrated that increasing the cellulose content of the mixture led to higher Fe0 content by 2-6 times and a greater activation efficiency of peroxydisulfate (PDS) by 2-5 times. nZVI prepared by carbothermal reduction using bagasse (Fe0/CB) removed 99.8 % of metronidazole in 60 min. The bagasse's cellulose content was found to be 59.5 % and the results demonstrated that the composites prepared with the cellulose content exceeded 60 % had unusual properties. The pyrolysis process of the mixtures showed that cellulose promotes the production of nZVI by generating more reducing gases (e.g. CO, CH4). Furthermore, the efficiency of activated PDS in removing metronidazole was confirmed, with cellulose-prepared nZVI (c-Fe0/C) proving to be the most effective activator. Its removal rate was 1.3 times higher than that of Fe0/CB. Physical characterization and mechanistic investigations demonstrated that c-Fe0/C has the same active sites as Fe0/CB and produces the same type and amount of reactive oxygen species. These demonstrates that cellulose is a critical component in the preparation of nZVI during carbothermal reduction. This study provides guidelines for preparing carbothermal reduced nZVI and establishes a theoretical basis for its engineering application.

Deciphering Multidrug-Resistant Plasmids in Disinfection Residual Bacteria from a Wastewater Treatment Plant

Current disinfection processes pose an emerging environmental risk due to the ineffective removal of antibiotic-resistant bacteria, especially disinfection residual bacteria (DRB) carrying multidrug-resistant plasmids (MRPs). However, the characteristics of DRB-carried MRPs are poorly understood. In this study, qPCR analysis reveals that the total absolute abundance of four plasmids in postdisinfection effluent decreases by 1.15 log units, while their relative abundance increases by 0.11 copies/cell compared to investigated wastewater treatment plant (WWTP) influent. We obtain three distinctive DRB-carried MRPs (pWWTP-01-03) from postdisinfection effluent, each carrying 9-11 antibiotic-resistant genes (ARGs). pWWTP-01 contains all 11 ARGs within an ∼25 Kbp chimeric genomic island showing strong patterns of recombination with MRPs from foodborne outbreaks and hospitals. Antibiotic-, disinfectant-, and heavy-metal-resistant genes on the same plasmid underscore the potential roles of disinfectants and heavy metals in the coselection of ARGs. Additionally, pWWTP-02 harbors an adhesin-type virulence operon, implying risks of both antibiotic resistance and pathogenicity upon entering environments. Furthermore, some MRPs from DRB are capable of transferring and could confer selective advantages to recipients under environmentally relevant antibiotic pressure. Overall, this study advances our understanding of DRB-carried MRPs and highlights the imminent need to monitor and control wastewater MRPs for environmental security.

Magnetic MoS2/Fe3O4 composite as an effective activator of persulfate for the degradation of tetracycline: performance, activation mechanisms and degradation pathways

The activated persulfate (PS) process could produce sulfate radical (SO4·-) and rapidly degrade organic pollutants. The application of Fe3O4 as a promising PS activator was limited due to the rapid conversion of Fe2+ to Fe3+ on its surface. Mo4+ on MoS2 surface could be used as a reducing site to convert Fe3+ to Fe2+, but the separation and recovery of MoS2 was complex. In this study, MoS2/Fe3O4 was prepared to accelerate the Fe3+/Fe2+ cycle on Fe3O4 surface and achieved efficient separation of MoS2. The results showed that MoS2/Fe3O4 was more effective for PS activation compared to Fe3O4 or MoS2, with a removal efficiency of 91.8% for 20 mg·L-1 tetracycline (TC) solution under the optimal conditions. Fe2+ and Mo4+ on MoS2/Fe3O4 surface acted as active sites for PS activation with the generation of SO4•-, •OH, •O2-, and 1O2. Mo4+ acted as an electron donor to promote the Fe3+/Fe2+ cycling and thus improved the PS activation capability of MoS2/Fe3O4. The degradation pathways of TC were inferred as hydroxylation, ketylation of dimethylamino group and C-N bond breaking. This study provided a promising activated persulfate-based advanced oxidation process for the efficient degradation of TC by employing MoS2/Fe3O4 as an effective activator.

Affecting factors and mechanism of removing antibiotics and antibiotic resistance genes by nano zero-valent iron (nZVI) and modified nZVI: A critical review

Antibiotics and antibiotic resistance genetic pollution have become a global environmental and health concern recently, with frequent detection in various environmental media. Therefore, finding ways to control antibiotics and antibiotic resistance genes (ARGs) is urgently needed. Nano zero-valent iron (nZVI) has shown a positive effect on antibiotics degradation and restraining ARGs, making it a promising solution for controlling antibiotics and ARGs. However, given the current increasingly fragmented research focus and results, a comprehensive review is still lacking. In this work, we first introduce the origin and transmission of antibiotics and ARGs in various environmental media, and then discuss the affecting factors during the degradation of antibiotics and the control of ARGs by nZVI and modified nZVI, including pH, nZVI dose, and oxidant concentration, etc. Then, the mechanisms of antibiotic and ARGs removal promoted by nZVI are also summarized. In general, the mechanism of antibiotic degradation by nZVI mainly includes adsorption and reduction, while promoting the biodegradation of antibiotics by affecting the microbial community. nZVI can also be combined with persulfates to degrade antibiotics through advanced oxidation processes. For the control of ARGs, nZVI not only changes the microbial community structure, but also affects the proliferation of ARGs through affecting the fate of mobile genetic elements (MGEs). Finally, some new ideas on the application of nZVI in the treatment of antibiotic resistance are proposed. This paper provides a reference for research and application in this field.

Synthesis of stabilized zero-valent iron particles and role investigation of humic acid-Fex+ shell in Fenton-like reactions and surface stability control

Herein, a novel humic acid-Fex+ complex-coated ZVI (HA-Fex+@ZVI) was synthesized and used to activate peroxydisulfate (PDS) for phenol degradation. The HA-Fex+ shell selectively reacted with PDS rather than O2, leading to the formation of modified ZVI with excellent surface stability in storage and ultraefficient PDS activation in advanced oxidation processes (AOPs). As a result, the phenol degradation and PDS activation efficiencies of HA-Fex+@ZVI/PDS were ∼14.4 and ∼1.8 times higher than those of ZVI/PDS, respectively. Mechanistic explorations revealed that the replacement of the HA-Fex+ shell relative to the original passivation layer of ZVI greatly changed the SO4•- generation pathway from a heterogeneous process to a homogeneous process, resulting from the slow exposure of Fe0 (generating dissolved Fe2+) and the depolymerized HA (enhancing the Fe3+/Fe2+ cycle). Based on experimental analysis and density functional theory (DFT) calculations, the Fe3+ in HA-Fex+ could be reduced to Fe2+ by PDS, resulting in the disintegration of the HA-Fex+ shell and exposure of Fe0 core active sites. Furthermore, compared to similar catalysts synthesized with commercial HA and traditional chemicals, HA-Fex+@ZVI synthesized with multiple waste biomasses exhibited better performance. This research provides valuable insights for designing ZVI-based catalysts with excellent storage stability and ultraefficient PDS catalytic activity for AOPs.

Green synthesis of zero valent iron using tannins to activate persulfate for sulfamethoxazole degradation

Majority zero-valent iron (ZVI) materials are prepared by reducing agents in liquid phase, resulting in the high environmental pollution and poor particle size distribution uniformity. Therefore, this study employed a green synthesis method to prepare ZVI. Tannins (TA) with phenolic hydroxyl groups that are characterized by strong reducing capacity were employed to synthesize ZVI (TA@ZVI). The dispersity and stability of ZVI was improved by TA, which inhibited the agglomeration of ZVI. Meanwhile, the specific surface area of TA@ZVI was higher than chemical prepared ZVI, increasing the reactive sites. The organic matter components enriched on TA could promote the adsorption of pollutants and complex with Fe(II/III) to enhance the reactivity of TA@ZVI. Also, the polyphenol structure in TA was oxidized to quinone, which facilitated electron transport. In order further test the performance of TA@ZVI, SMX was chosen as a target pollutant to study the oxidative degradation performance of TA@ZVI. SO4•- degraded about 16.4%-25.5% SMX and •OH degraded about 49.8%-63.9% SMX in the pH range of 4-6 while •OH played a dominant role in the neutral and alkaline conditions. Moreover, the presence of TA reduced Fe(III) to Fe(II) and promoted the release of Fe(II), providing a continuous source of •OH for the oxidative degradation of SMX. Besides, the conversion of Fe(II/III) was accelerated due to TA, which delayed the formation of passivation layer. Thus, TA enhanced the antioxidant capacity of ZVI. Generally, this study provided an environmental-friendly technology to synthesize and improve the reactivity of ZVI.