Nano Zero-valent Iron Research Articles

Advancements and Challenges in Nanoscale Zero-Valent Iron-Activated Persulfate Technology for the Removal of Endocrine-Disrupting Chemicals

Endocrine-disrupting chemicals are a new class of pollutants that can affect hormonal metabolic processes in animals and humans. They can enter the aquatic environment through various pathways and gradually become enriched, thus posing a serious threat to the endocrine and physiological systems of both animals and humans. Nano zero-valent iron has promising applications in endocrine disruptor removal due to its excellent reducing properties and high specific surface area. However, given the dispersed focus and fragmented results of current studies, a comprehensive review is still lacking. In this paper, it was analyzed that the types of endocrine disruptors and their emission pathways reveal the sources of these compounds. Then, the main technologies currently used for endocrine disruptor treatment are introduced, covering physical, chemical, and biological treatment methods, with a special focus on persulfate oxidation among advanced oxidation technologies. Also, the paper summarizes the various activation methods of persulfate oxidation technology and proposes the nZVI-activated persulfate technology as the most promising means of treatment. In addition, this paper reviews the research progress of different modification methods of nZVI in activating persulfate for the removal of EDCs. Finally, the discussion includes recycling studies of nZVI/PS technology and emphasizes the urgency and importance of endocrine disruptor treatment. The review of this paper provides further scientific basis and technical support for nZVI/PS technology in the field of endocrine disruptor management.

Mechanisms of nano zero-valent iron in enhancing dibenzofuran degradation by a Rhodococcus sp.: Trade-offs between ATP production and protection against reactive oxygen species.

Nano zero-valent iron (nZVI) can enhance pollutants biodegradation, but it displays toxicity towards microorganisms. Gram-positive (G+) bacteria exhibit greater resistance to nZVI than Gram-negative bacteria. However, mechanisms of nZVI accelerating pollutants degradation by G+ bacteria remain unclear. Herein, we explored effects of nZVI on a G+ bacterium, Rhodococcus sp. strain p52, and mechanisms by which nZVI accelerates biodegradation of dibenzofuran, a typical polycyclic aromatic compound. Electron microscopy and energy dispersive spectroscopy analysis revealed that nZVI could penetrate cell membranes, which caused damage and growth inhibition. nZVI promoted dibenzofuran biodegradation at certain concentrations, while higher concentration functioned later due to the delayed reactive oxygen species (ROS) mitigation. Transcriptomic analysis revealed that cells adopted response mechanisms to handle the elevated ROS induced by nZVI. ATP production was enhanced by accelerated dibenzofuran degradation, providing energy for protein synthesis related to antioxidant stress and damage repair. Meanwhile, electron transport chain (ETC) was adjusted to mitigate ROS accumulation, which involved downregulating expression of ETC complex I-related genes, as well as upregulating expression of the genes for the ROS-scavenging cytochrome bd complex and ETC complex II. These findings revealed the mechanisms underlying nZVI-enhanced biodegradation by G+ bacteria, offering insights into optimizing bioremediation strategies involving nZVI.

Synergizing carbon sequestration mechanisms during the remediation of Cr(VI) by nano zero-valent iron loaded biochar (nZVI-BC)

Applying nano zero-valent iron loaded biochar (nZVI-BC) to remediate soil heavy metal pollution has been frequently tested in current studies. However, little knowledge has been disclosed regarding the effect of nZVI-BC on soil organic carbon (SOC) mineralization/sequestration. In this study, the dual effect of nZVI-BC addition on Cr(VI) removal and SOC mineralization/sequestration and the underlying mechanisms were explored, based on a 90 days laboratory soil incubation. The results confirmed that nZVI-BC significantly improved the Cr(VI) removal rate while markedly reducing the cumulative CO2 emissions. Following the 90 days incubation, nZVI-BC addition notably increased the contents of Fe-oxides, Fe-bound organic carbon (Fe-OC), and SOC. Pearson correlation and PLS-SEM analyses indicated that the enhanced Fe-OC content, resulting from increased Fe-oxides, was a critical abiotic mechanism for improved SOC preservation. Additionally, the observed decrease in enzymatic activity and the shift in bacterial community from unstable carbon-dominant taxa (e.g., Proteobacteria and Actinobacteria) to stable carbon-dominant taxa (e.g., Firmicutes) in the nZVI-BC treatments suggested that SOC bio-mineralization was also inhibited. Overall, this study demonstrates that nZVI-BC not only aids in heavy metal remediation but also promotes long-term SOC preservation.

Kirkendall effect enhanced sustained-release Fe-C composites for long-term reductive dechlorination of trichloroethylene: Interfacial reactions and slow-release degradation

Rebounding and lagging during the process of remediating contaminated sites are challenging problems. A potential solution is developing slow-release materials that could assist in the long-term remediation of contaminated sites. This study synthesised a slow-release Fe-C composite (CSBC-nZVI@β-CD), which exhibits a synergistic effect of encapsulated layers and nanocracks, using a liquid-phase reduction method. Furthermore, the reduction and dechlorination mechanism of trichloroethene (TCE) was systematically investigated. The introduction of β-cyclodextrin (β-CD) intensified the Kirkendall effect, forming nano zero-valent iron (nZVI) with abundant radial nanocracks and a litchi-like appearance on the biochar surface. Additionally, β-CD created an encapsulation layer measuring 5–7 nm on the surface of nZVI, improving its electron transport capacity and hydrophobic properties. The CSBC-nZVI@β-CD nanocomposite successfully removed 99 % of TCE in solution within 2 h and accomplished a degradation efficiency of 98.9 % within 15 d. The synergistic effect of the β-CD encapsulating layer and nanocracks facilitated the reactivity and electron-retarding capacity, resulting in a broad pH tolerance and anti-interference ability. Density-functional theory (DFT) calculations and experimental methods were used to study the mechanism of TCE reduction dechlorination; the unique structure of β-CD tended to bind with Fe as well as adsorb TCE, thereby facilitating electron transfer and the enrichment of TCE at the reaction interface. In addition, the sustained-release Fe-C composites reduced the bonding energy required during the TCE degradation reaction and promoted the complete reaction of the product. Overall, CSBC-nZVI@β-CD exhibited significant potential for the long-term remediation of groundwater.

Mechanisms of action of chlorella biochar-loaded nano zero-valent iron systems on Escherichia coli: Insights from cell biology and untargeted metabolomics

Mechanisms of action of chlorella biochar-loaded nano zero-valent iron systems on Escherichia coli: Insights from cell biology and untargeted metabolomics

2,4-Dinitrotoluene (DNT) Removal Efficiency Using the Sono-photo-fenton Process Combined with Nano Zero Valent Iron (nZVI) Heterogeneous Catalysis

2,4-Dinitrotoluene (DNT) is a highly toxic compound of nitrotoluene group causing negative impacts on mammals, fish, and human health that needs to be treated before discharging. The study aimed to evaluate the affecting factors on efficiency of DNT treatment by Sono-Photo-Fenton process using zero-valent iron catalysts (nZVI), including: pH, intial DNT concentration, nZVI catalyst concentration, hydrogen peoxide concentration, light power, and ultrasonic power. After 20 minutes of Sono-Photo-Fenton reaction, the DNT removal efficiency was 100% with optimal operating conditions as following: pH=3.0, CDNT = 50 mg/L, CH2O2 = 20 mM, CnZVI = 1 mM, UV power of 10 W, ultrasonic power of 80 W.

Removal of Cr(VI) in groundwater by controlled release materials based on nano zero-valent iron and activated carbon

ABSTRACT The use of nano zero-valent iron (nZVI) materials for groundwater Cr(VI) removal encountered challenges of agglomeration and low removal efficiency. Controlled release materials (CRMs) gradually release reactive substances or reducing agents, prolonging the release time. Here, we report the development of novel CRMs containing nZVI and activated carbon (AC). During the removal of Cr(VI) in groundwater, the prepared AC/nZVI/CRMs slowly released nZVI, greatly reducing the agglomeration of nZVI. The adsorption capacity of AC-containing CRMs prolonged the residence time of Cr(VI) in water, improving the removal efficiency of the AC/nZVI/CRMs. We found that lower pH enhanced the removal of Cr(VI) by the AC/nZVI/CRMs from simulated groundwater. The removal efficiency of the AC/nZVI/CRMs was also affected by the simulated groundwater environment and decreased with the increasing flow rate of the groundwater. Our results suggested that these novel nZVI-containing CRMs minimized agglomeration during the removal of Cr(VI) by nZVI, exhibited enhanced efficiency under acidic conditions, and facilitated Cr(VI) removal from similar groundwater environments.

Pharmaceutical effluent degradation using hydrogen peroxide-supported zerovalent iron nanoparticles catalyst

Pharmaceutical effluents generated during drugs production and application are often times released into the water systems with little or no treatment, which could pose potential danger to the ecosystem. Advanced oxidation processes for organic pollutants treatment have gained wide consideration due to their effectiveness. In this work, hydrogen peroxide (H2O2) and hydrogen peroxide-supported nano zerovalent iron (H2O2@nZVIs) were deployed to study pharmaceutical effluents (PE) degradation via batch experiments, under various reaction time, (H2O2) and (H2O2@nZVIs) concentrations, pH, PE concentration, and temperature. The nZVIs was prepared from the green synthesis of Vernonia amygdalina leaf extract and characterized using different analytical tools such as Fourier Transform-Infrared Spectroscopy (FT-IR), Gas Chromatography Mass Spectroscopy (GC-MS), Scanning Electron Microscopy (SEM), and X-Ray Diffraction Spectroscopy (XRD). The FT-IR results showed the presence of -C = O, -NH, -OH, -C = C and, -C-O functional groups, SEM report showed that the morphology of the nZVIs is round in shape, while GC-MS revealed the presence of several phytochemicals. When the concentration of the effluent was increased from 10 to 30 ml, the percentage decolourization decreased from 74.74 to 51.96% and from 80.36 to 54.38% for H2O2 and H2O2@nZVI respectively, whereas when the contact time was increased from 10 to 60 min, the percentage decolourization rose from 70.39 to 83.49% for H2O2 and from 85.19 to 89.73% when H2O2@nZVI was used. When the effect of pH was assessed, it was observed that on increasing the pH from 2 to 10, the percentage decolourization rose from 74.5 to 80.25% for H2O2, however, with H2O2@nZVI, the percentage decolourization decreased from 81.50 to 68%. Maximum percentage decolourization of 57.10% and 94.56% for H2O2 and H2O2@nZVI was achieved at catalyst volume of 25 ml. For all the parameters tested, the H2O2@nZVIs performed much better indicating that the nZVIs enhanced the decolourization ability of the H2O2. The kinetic results showed that the decolorization of pharmaceutical effluent by both catalysts fitted very well with the second-order model, while thermodynamic properties of enthalpy change were found to be 10.025 and 27.005 kJ/mol/K for H2O2 and H2O2@nZVIs respectively suggesting that the oxidation process is endothermic in nature. This technique employed in using hydrogen peroxide-supported zero valent iron, proved to be highly efficient not only for pharmaceutical effluent degradation but also in the elimination of lead from the effluent.

Enhanced anaerobic digestion for energy recovery from brewery wastewater employing nano zero-valent iron loaded biochar prepared by residual sludge

Anaerobic digestion is an effective wastewater energization technology, but suffers from low energy conversion efficiency. In this study, a novel biochar was successfully prepared by incorporating extracellular polymeric substances (EPS) to residual sludge, and the anaerobic digestion performance could be significantly improved by employing this biochar loaded with nano zero-valent iron (NZVI@EPSBC). In comparison to the control, the cumulative methane production with 100 mg/L NZVI@EPSBC was raised by approximately 1.4-fold. The NZVI@EPSBC did not significantly change the morphology of the inoculated granular sludge, but induced the secretion of proteins and humic substances in the extracellular EPS, which are beneficial for carbon conversion and extracellular electron transport at the microscopic scale. Meanwhile, the quantitative analysis of the electron transport system also confirmed that NZVI@EPSBC could significantly improve the electron transfer efficiency in microbial respiratory chain throughout the experimental cycle, in which the highest respiratory efficiency increase of 26.51 % at 48 h. Taxonomic analysis of microbial communities showed that NZVI@EPSBC exhibited complete retention of bacteria and archaea compared to the raw sludge, while realizing an efficient cooperative pattern of syntrophic bacteria by regulating the relative abundance of specific functional bacteria, like Anaerolineaceae and Methanosaeta. Overall, the study offers a valuable strategy for achieving resourcefulness of residual sludge and EPS along with facilitating efficient energy recovery from brewery wastewater.

The Application of Nano Zero-Valent Iron in Synergy with White Rot Fungi in Environmental Pollution Control.

Developing efficient and sustainable pollution control technologies has become a research priority in the context of escalating global environmental pollution. Nano zero-valent iron (nZVI), with its high specific surface area and strong reducing power, demonstrates remarkable performance in pollutant removal. Still, its application is limited by issues such as oxidation, passivation, and particle aggregation. White rot fungi (WRF) possess a unique enzyme system that enables them to degrade a wide range of pollutants effectively, yet they face challenges such as long degradation cycles and low degradation efficiency. Despite the significant role of nZVI in pollutant remediation, most contaminated sites still rely on microbial remediation as a concurrent or ultimate treatment method to achieve remediation goals. The synergistic combination of nZVI and WRF can leverage their respective advantages, thereby enhancing pollution control efficiency. This paper reviews the mechanisms, advantages, and disadvantages of nZVI and WRF in pollution control, lists application examples, and discusses their synergistic application in pollution control, highlighting their potential in pollutant remediation and providing new insights for combined pollutant treatment. However, research on the combined use of nZVI and WRF for pollutant remediation is still relatively scarce, necessitating a deeper understanding of their synergistic potential and further exploration of their cooperative interactions.

ZnO/nZVI nanoparticle-enhanced double-slope U-shaped solar distillation: A thermodynamic investigation of cephalexin adsorption

The increasing need for sustainable methods to remove pharmaceutical contaminants like cephalexin and improve water desalination is critical. This study explores ZnO/nZVI nanoparticles synthesized with Jackfruit peel extracts as eco-friendly, cost-effective adsorbents, enhancing water purification in solar desalination systems. This work used a matte black paint coating within a double slope U-shaped solar distiller (DSUD) in a discontinuous experimental setting to examine potential improvements in solar distillation performance. Activated carbon (AC) and bioactive powdered nanoparticles of ZnO/nZVI (nano zerovalent iron), produced from jackfruit peel extracts (JP) were combined in a synergistic way. The effectiveness of cephalexin removal was assessed taking into account the JPAC solution parameters, reaction duration, ZnO/nZVI concentrations in the nanocomposite dosage, and initial nanocomposite concentration. The best conditions for cephalexin adsorption were found to be pH 5 and reaction time of 50 min, which resulted in high absorption efficiencies of 94.74% (nZVI) and 97.53% (ZnO) at room temperature with a JPAC dose of 2.50 g L⁻1. The efficiency of the eco-friendly adsorbent in getting rid of cephalexin was calculated using “pseudo-second-order kinetics” for nanocomposites, which is consistent with the “Langmuir” isothermal absorption process. The nanocomposites as absorbent materials in solar thermal desalination processes, efficient heat transmission and energy storage have been established. JPAC and the addition of steel balls (S) with a silver hue to the DSUD improved the internal heat transfer mechanisms. Thermodynamic of Gibbs free energy and the Laplacian method (TGL), two thermodynamic concepts, were used to extensively study the temperature dynamics of the DSUD with SJPAC components. For ZnO/JPAC, an exceptional distillate production rate was noted from 8:00 to 18:00, with a noteworthy 4.932 L/m2 output in winter and 5.833 L/m2 per day in summer. Using silver balls, ZnO/JPAC generated significant yields over a 24-h period: 8.957 L/m2 in summer and 7.253 L/m2 in winter, with an ideal energy efficiency of 51.05%. The unique advancements in TGL procedures and their environmental consequences are presented in this paper. The field of thermal energy transduction will advance if silver balls are used in DSUD for the synthesis of JPAC, ZnO/JPAC, and nZVI/JPAC, as supported by the theoretical insights presented here.

High stability and reactivity of porous calcium tartrate supported nano zero-valent iron in aerobic environment and alkaline wastewater

Nano zero-valent iron (nZVI) has remarkable reactivity, but its practical application is severely hindered by its easy aggregation and rapid oxidation after exposure in air. In this study, spherical porous calcium tartrate (CaTr) was synthesized with ultrasound technology and used to support nZVI. It was found that the as-obtained nZVI@CaTr was highly stable and reactive in oxygen-rich water under neutral/alkaline conditions. In the pH range of 4–9, the degradation efficiency of p-nitrophenol (PNP, 50 mg/L) by nZVI@CaTr7 exceeded 98.1 %. Importantly, nZVI@CaTr could be stored in air for a long time without inert gas protection. After 60 days and 120 days of air exposure, the removal efficiency of PNP still reached 83.3 % and 63.3 %, which was 2.8 and 9.7 times that of bare nZVI, respectively. Such an excellent performance could be attributed to two reasons: (i) spherical CaTr effectively inhibited the oxidation and aggregation of nZVI by favorable interactions with nZVI, and (ii) the abundant functional groups on the surface of CaTr acted as electronic mediators to significantly promote charge transfer between nZVI (electron donor) and PNP (electron acceptor). Therefore, cheap, air stable and highly effective nZVI@CaTr7 provided a potential application prospect for the degradation of environmental pollutants in aerobic environment and alkaline wastewater.

Activation of persulfate by a layered double oxide supported sulfidated nano zero-valent iron for efficient degradation of 2,2′,4,4′-tetrabromodiphenyl ether in soil

The nano zero-valent iron (nZVI) activated persulfate (PS) is recognized as a promising approach to degrade 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in the soil at electronic waste sites. However, all the reported studies were performed in liquids, gaps in the real behaviour and microbial contribution to the degradation of BDE-47 in soil media need to be urgently filled. The removal efficiency of BDE-47 is low using traditional nZVI as activator because of its aggregation and corrosion. Herein, we designed a novel layered double oxide supported sulfidated nano zero-valent iron (S-nZVI@LDO) composite and explored the performance of S-nZVI@LDO/PS to remediate BDE-47 contaminated soil. The results showed that S-nZVI@LDO has excellent stability and superior reduction capability. It could couple PS to achieve a rapid and efficient degradation of BDE-47, and the removal efficiency reached 92.31 % (5 mg/kg) within 6 h, which was much higher than that of n-ZVI/PS (53.38 %) or S-nZVI/PS (75.69 %). The kinetic constant of BDE-47 degradation by S-nZVI@LDO/PS was 23.6 and 3.7 times higher than that by single S-nZVI@LDO and nZVI/PS, respectively. It is attributable to the efficient production of SO4•-, •OH, O2•-, and 1O2 in the system, in which SO4•- and •OH dominated. The bioinformatic analysis demonstrate that soil remediation by S-nZVI@LDO/PS significantly enriched aromatic compounds-degrading bacteria and increased the abundance of hydrocarbon degradation functions. Microbial degradation may play important roles in the BDE-47 degradation and soil quality recovery. The identification of degradation pathways suggests that BDE-47 was degraded to very low-toxic products based on GHS toxicity prediction through a series process of debromination, hydroxylation, cleavage central oxygen, and ring opening, or even completely mineralized. The findings may provide significant implications for the in-situ clean-up of brominated flame retardants in contaminated soil using S-nZVI@LDO/PS Fenton-like system.

Synergistic adsorption and degradation of sulfonylurea herbicides by biochar-supported nano zero-valent iron composites in in-situ soil remediation

The extensive and continuous application of sulfonylurea herbicide is crucial for weed management but has resulted in widespread non-point source pollution. In this study, nano zero-valent iron/biochar (nZVI/BC) was synthesized by using FeCl3-impregnated corn stalks under anoxic pyrolysis conditions, which was applied in the in-situ remediation of bensulfuron methyl (BSFM) and sulfometuron methyl (SMTM) polluted soil. The results show that nZVI/BC with a 2.7 ratio of Fe/C had the highest efficiency in removing sulfonylurea herbicides. The removal efficiencies of BSFM and SMTM by nZVI/BC were negatively correlated to initial concentrations of sulfonylurea herbicides and positively correlated to nZVI/BC addition amount in the soil. Moreover, nZVI/BC could remove 53 % of BSFM and 72 % of SMTM at the concentration of 5 mg/kg after 21 d, which was much higher than that of BC. Notably, the removal efficiency of BSFM by nZVI/BC reached 36 % within 7 d, while the removal efficiency of SMTM by nZVI/BC was up to 68 % even within 3 d. The adsorption of herbicides by nZVI/BC was mainly driven by chemical processes involving multilayer adsorption. Furthermore, the removal mechanisms of BMTM and SMTM by nZVI/BC also involved C = O and C–O groups and oxidation of nZVI to FeO and Fe3O4 along with the cleavage of the sulfonylurea bridge. This study provides a promising application of nZVI/BC in in-situ remediating sulfonylurea herbicide- polluted soil.

Degradation kinetics, influencing factors, and mechanisms of polycyclic aromatic hydrocarbons in a Fe3O4-nZVI Fenton-like system

To improve the catalytic performance of nano zero-valent iron (nZVI) in a Fenton-like system, Fe3O4 supported nZVI (Fe3O4-nZVI) was produced by the liquid-phase reduction method and co-precipitation method, then characterized by SEM, EDS, XRD, XPS, and VSM. Fe3O4-nZVI was used as the catalyst in a Fenton-like system to degrade polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap), phenanthrene (Phe), and pyrene (Pyr) in simulated wastewater. The results showed that under the optimization conditions, which were 25℃, 0.6g/L of Fe3O4-nZVI dosage, 3 of the pH in the reaction system, and 10-15mmol/L of the concentration of H2O2, the sequence of degradation efficiency in this system was Phe (99.76%)>Pyr (99.71%)>Nap (98.01%). The reused experiments on Fe3O4-nZVI showed that the degradation efficiency for PAHs remained above 87% after 4 reuses of Fe3O4-nZVI. These results indicated that nanoscale magnetic composites of Fe3O4-nZVI had excellent reactivity, stability, and reuse performance. The fitting parameters of kinetics showed that the degradation of PAHs in the Fenton-like system with the Fe3O4-nZVI catalyst fitted well with the Behnajady-Modirshahla-Ghanbery kinetic model. The radial quenching experiment proved that ·OH was the dominant free radical for the degradation of PAHs in the Fe3O4-nZVI Fenton-like system. Based on the degradation products of PAHs and the related literature, the possible degradation paths of the three PAHs in the Fe3O4-nZVI Fenton-like system were inferred. The above results could provide a reference and basis for the treatment of wastewater containing PAHs by Fe3O4-nZVI Fenton-like technology.

Carbothermally synthesized, lignin biochar-based, embedded and surface deposited nano zero-valent iron composites: Comparative material characterization, selective gas adsorption and nitroaromatics remediation

Biochar (BC) with nanoscale zero valent iron (nZVI) incorporation offers advantageous materials for water purification. Even though the most common approach for nZVI incorporation is the deposition on the carrier surface, embedding in the support matrix has also been reported. However, the behavior of the embedded material in contaminant removal has not been adequately studied while characteristics and the remediation capabilities of the two materials have not been compared. Present study focuses on preparing and extensively characterizing two materials: nZVI embedded in (Lig-e-nZVI) and surface deposited on (Lig-s-nZVI) lignin BC with subsequent comparative study of remedial action for two nitroaromatics, p-nitroaniline (pNA) and p-nitrophenol (pNP). The synthesis of Lig-e-nZVI and Lig-s-nZVI involved simultaneous and subsequent pyrolysis of lignin and carbothermal reduction of the iron salt, respectively. Lig-e-nZVI showed enhanced porosity. XRD confirmed the formation of Fe0. HR-TEM images proved the core-shell structure of nZVI, and an interlayer spacing of 0.36nm of the shell verified that the Fe0 particles are encapsulated with graphene while an iron carbide inner layer was also observed, thinner in Lig-e-nZVI and thicker in Lig-s-nZVI. Band gap energy of 2.54eV suggested a photocatalytic activity of both materials. Best fitted Sips isotherms showed 23.1 and 13.1mgg-1 capacities for Lig-s-nZVI in pNP and pNA adsorption respectively. Highest stability was portrayed by Lig-e-nZVI over 4 regeneration cycles. The physicochemical features of the developed materials further enable selective gas adsorption. Findings provide new insights into physicochemical characteristics and remedial actions of differently synthesized nZVI-BC composites.

Mechanisms of horizontal gene transfer and viral contribution to the fate of intracellular and extracellular antibiotic resistance genes in anaerobic digestion supplemented with conductive materials under ammonia stress

The addition of conductive materials (CMs) is an effective strategy for mitigating ammonia inhibition during anaerobic digestion (AD). However, the introduction of CMs can result in increased antibiotic resistance genes (ARGs) pollution, potentially facilitated by enhanced horizontal gene transfer (HGT). The complex dynamics of intracellular and extracellular ARGs (iARGs/eARGs) and the mechanisms underlying their transfer, mediated by CMs, in ammonia-stressed AD systems remain unclear. In this study, we investigated the effects of three commonly used CMs—nano magnetite (Mag), nano zero-valent iron (nZVI), and granular activated carbon (GAC)—on the fate of iARGs and eARGs during the AD of waste activated sludge under ammonia stress. The results revealed an unexpected enrichment of iARGs by 1.5 %–10.9 % and a reduction of eARGs by 14.1 %–25.2 % in CM-supplemented AD. This discrepancy in the dynamics of iARGs and eARGs may be attributed to changes in microbial hosts and the horizontal transfer of ARGs. Notably, CMs activated prophages within antibiotic-resistant bacteria (ARB) and their symbiotic partners involved in vitamin B12 provision, leading to the lysis of ARB and the subsequent release of eARGs for transformation. Additionally, the abundance of potentially mobile ARGs, which co-occurred with mobile genetic elements, increased by 56.6 %–134.5 % with CM addition, highlighting an enhanced potential for the HGT of ARGs. Specifically, Mag appeared to promote both transformation and conjugation processes, while nZVI only promoted conjugation. Moreover, none of the three CMs had any discernible impact on transduction. GAC proved superior to both nano Mag and nZVI in controlling the enrichment of iARGs, reducing eARGs, and limiting HGTs simultaneously. Overall, these findings provide novel insights into the role of viruses and the mechanisms of ARG spread in CM-assisted AD, offering valuable information for developing strategies to mitigate ARG pollution in practical applications.

Activated carbon fiber loaded nano zero-valent iron for Microcystis aeruginosa removal: Performance and mechanisms

Cyanobacterial blooms caused by Microcystis aeruginosa threaten environmental safety and daily life. In this study, an activated carbon fiber-supported nano zero-valent iron composite (ACF-nZVI) was developed to remove Microcystis aeruginosa. The results showed that nZVI was evenly distributed on the activated carbon fibers, preventing aggregation and oxidation. ACF-nZVI achieved a removal efficiency of more than 90 % within a pH range of 3–7. During the reaction, H2O2, which was generated by Fe0, was activated to form ·OH and ·O–2, which dismantled antioxidant enzymes and induced lipid peroxidation. Additionally, ACF-nZVI destroyed the cell wall and membrane, resulting in protein and humus leakage and causing 92.34 % cell damage and death. In this study, an environmentally friendly and stable nanomaterial was developed, offering a novel approach for the safe, cost-effective, and efficient removal of cyanobacteria.

Biological self-protection inspired engineering of nanomaterials to construct a robust bio-nano system for environmental applications.

Nanomaterials can empower microbial-based chemical production or pollutant removal, e.g., nano zero-valent iron (nZVI) as an electron source to enhance microbial reducing pollutants. Constructing bio-nano interfaces is critical for bio-nano system operation, but low interfacial compatibility due to nanotoxicity challenges the system performance. Inspired by microorganisms' resistance to nanotoxicity by secreting extracellular polymeric substances (EPS), which can act as electron shuttling media, we design a highly compatible bio-nano interface by modifying nZVI with EPS, markedly improving the performance of a bio-nano system consisting of nZVI and bacteria. EPS modification reduced membrane damage and oxidative stress induced by nZVI. Moreover, EPS alleviated nZVI agglomeration and probably reduced bacterial rejection of nZVI by wrapping camouflage, contributing to the bio-nano interface formation, thereby facilitating nZVI to provide electrons for bacterial reducing pollutant via membrane-anchoring cytochrome c. This work provides a strategy for designing a highly biocompatible interface to construct robust and efficient bio-nano systems for environmental implication.

A novel strategy for enhancing high solid anaerobic digestion of fecal slag and food waste using percolate recirculation and dosage of nano zero-valent iron

To speed up reaching UN Sustainable Development Goal 6 for safe sanitation by 2030, integrating high-solid anaerobic digestion (HSAD) into decentralized systems could recycle fecal slag (FS) and food waste (FW), aiding a circular economy and toilet revolution. In this study, a percolate recirculation system and conductive material were used to improve mass transfer, stability, and enhance methane production in HSAD of FS and FW. This setup consists of a percolate tank and a digester tank, where nano-zero valent iron (nZVI) was dosed in the percolate tank (PnZVI in P) and the digester tank (PnZVI in D) and compared with a control with no additive (PControl). The highest cumulative methane yield of 519.43 mL/gVS was achieved in PnZVI in D, which was 4.52 and 3.59 times higher than that of PControl (144.59 mL/gVS) and PnZVI in P (114.96 mL/gVS). This finding demonstrates that the dosing strategy of PnZVI in D facilitated effective interaction among organic matter, microbial communities, and nZVI, resulting in organics removal efficiencies of 67.42 % (total solid) and 77.22 % (volatile solid). Moreover, microbial community analysis supported the efficacy of the PnZVI in D strategy, revealing the enrichment of Clostridium sensu stricto 1 (46.91 %), which potentially engaged in interspecies electron transport (Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET)) with Methanobacterium (81.19 %) and Methanosarcina (17.11 %). These interactions contribute to enhanced methane yield and stability maintenance in the HSAD system with percolate recirculation. The findings of this study demonstrate that the implementation of HSAD of FS and FW, coupled with percolate recirculation and the addition of nZVI, holds promise for enabling sustainable sanitation practices in developing regions. Moreover, this approach not only facilitates resource recovery but also eliminates the requirement for water.