Nano Zero-valent Iron Research Articles

Soil Remediation by Nanotechnology: Valuating Materials, Mechanisms, and Environmental Impacts

The rapid growth of the human population and industrial activities has resulted in considerable environmental degradation. Processes such as industrialization, mining, agriculture, and waste disposal introduce harmful chemicals that contaminate soil, groundwater, and surface waters. Consequently, soil remediation has become a critical priority for many nations, given that soil quality directly affects agriculture and public health. Nanotechnology presents promising solutions to the shortcomings of traditional soil remediation methods by offering innovative materials and mechanisms for the removal or neutralization of contaminants. This review intends to evaluate the use of nanotechnology in soil remediation, emphasizing the nanomaterials employed, their reaction mechanisms, and potential environmental effects. Nanomaterials like nano zero-valent iron, metal oxides, and carbon-based materials have shown effectiveness in immobilizing, degrading, or extracting pollutants from soil and water through processes such as adsorption, photocatalysis, and filtration. However, certain nanomaterials raise concerns about toxicity and bioaccumulation, which may negatively affect ecosystems and human health. Therefore, additional research is needed to confirm the safety, compatibility, and sustainability of these technologies. This review also identifies significant challenges in the implementation of nanotechnologies for soil remediation and examines future directions and recommendations for addressing these challenges.

Enhanced removal of Cr(VI) from aqueous solutions using a zero-valent nickel/iron-PDA@PVDF membrane prepared via a simple blending method

Nano zero-valent iron (nZVI) is extensively employed in the realm of wastewater treatment. However, conventional synthesis methods involve inherent risks of nZVI oxidation and aggregation, resulting in challenging recovery and potential waste generation. To address these concerns and improve stability, nano zero-valent nickel (nZVNi) was employed as a modifier for nZVI. The modified nZVNi/nZVI was successfully blended with polydopamine (PDA)-modified polyvinylidene fluoride (PVDF) powder, enabling the preparation of a novel hydrophilic composite membrane termed nZVNi/nZVI-PDA@PVDF (NFPP). PDA played a crucial role in effectively immobilizing nZVI particles and preventing their oxidation and aggregation. Scanning electron microscopy was used to confirm the consistent dispersion of nZVNi/nZVI particles both on the surface of the membrane and within its pores. Moreover, the NFPP membrane exhibited excellent performance in removing Cr(VI), with a maximum adsorption capacity of 75.65 mg/g. The presence of PDA endowed the NFPP membrane with a plentiful supply of hydroxyl and amino groups, enhancing its hydrophilicity, antioxidation properties, and loading capacity for nZVNi/nZVI. Additionally, the NFPP membrane demonstrated remarkable resistance to interference under different pH and ionic conditions. The removal of Cr(VI) by the NFPP membrane followed a pseudo-second-order kinetics and Langmuir isotherm adsorption model. Furthermore, the NFPP membrane retained good performance and stability in Cr(VI) removal even after undergoing five cycles. This study indicates that the highly efficient NFPP composite material holds promising potential for application as a functional material in heavy metal wastewater treatment.

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.

Nano zerovalent iron boosts methane content in biogas and reshapes microbial communities in long-term anaerobic digestion of pig slurry

Nano zerovalent iron boosts methane content in biogas and reshapes microbial communities in long-term anaerobic digestion of pig slurry

Silica-coated nano zero-valent iron as a slow-release electron donor for sustained enhancement of aerobic denitrification in oligotrophic source water: Performance and mechanism

Limited organic carbon in drinking water constrains the removal of nitrate‑nitrogen (NO3−-N) via aerobic denitrification. This paper reports the use of silica-coated nano zero-valent iron (nZVI@SiO2) as a stable and sustainable electron donor to enhance aerobic denitrification. The nZVI@SiO2, synthesized via a one-step method, was resistant to oxidation and exhibited excellent stability. In conjunction with aerobic denitrifying bacteria, nZVI@SiO2 achieved NO3−-N and total nitrogen TN removal efficiencies of 90.64 % and 80.94 %, respectively. This represents an increase of 24.15 % in the efficiency of TN removal compared with that of the nZVI system. The activity of the nZVI system diminished gradually after just three cycles, whereas nZVI@SiO2 maintained NO3−-N and TN removal efficiencies of 89.33 % and 78.08 %, respectively, after four cycles, respectively, indicating its sustainable ability to enhance aerobic denitrification. Cyclic voltammetry and electrochemical impedance spectroscopy demonstrated enhanced electron transfer efficiency of nZVI@SiO2. Furthermore, nZVI@SiO2 significantly promoted the activity of the electron transfer system, ATP levels, nitrate/nitrite reductase activity, contents of complexes I and III, and extracellular polymeric substances. nZVI@SiO2 significantly enhanced electron generation, transfer, and consumption during biological denitrification by functioning as both an electron donor and mediator. The findings implicate nZVI@SiO2 as a means to enhance nitrogen removal by aerobic denitrifying microorganisms in oligotrophic water via sustained donation of electrons.

Efficient As(III) removal using graphene oxide supported sulfidated nano zero-valent iron: potential role of the single-electron pathway

As(III) removal by graphene oxide loaded sulfidated nano zero-valent iron (S-nZVI@GO) was studied in this study. The results indicated that S-nZVI@GO exhibited significant As(III) removal ability, and the removal effect under aerobic conditions (91.2%) was higher than that under hypoxia conditions (44.79%). The maximum adsorption capacity of S-nZVI@GO can reach 444.68mg/g, and arsenic removal was higher than 95% under different pH (3-9). The mechanism of S-nZVI@GO removing As(III) was oxidation-adsorption-coprecipitation. S-nZVI@GO can active molecular oxygen in solution to generate active species (•O2-, H2O2) by a single-electron pathway, and then As(III) was oxidized to As(V) and separated from water by synergies of adsorption and co-precipitation.

Synthesis and characterization of eco-friendly cathodic electrodes incorporating nano Zero-Valent iron (NZVI) for the electro-fenton treatment of pharmaceutical wastewater

The electro-Fenton process has the potential to be an efficient effluent treatment method, contingent on effective process optimization. It relies on two critical components: efficient in-situ H2O2 generation and the integration of highly reactive heterogeneous catalysts into electrode synthesis. In this study, several cathodic electrodes were synthesized, including those using zero-valent iron nanoparticles (P-NZVI), zero-valent iron nanoparticles supported on activated carbon (AC-NZVI), and El Hamma Bentonite clay loaded with zero-valent iron nanoparticles (HB-NZVI). These electrodes were fabricated using sustainable, straightforward methods and subjected to thorough physicochemical and electrochemical characterization. The goal of this research was to develop environmentally friendly cathodes, employing either pressed catalyst techniques or supporting the catalyst on carbon felt (CF) or titanium foil. These electrodes were evaluated within a heterogeneous electro-Fenton-like process, with a boron-doped diamond (BDD) anode, targeting the efficient degradation of the pharmaceutical pollutant Antipyrine (ATP). Among the tested configurations, the AC-NZVI/CF electrode demonstrated the highest degradation efficiency. Key experimental parameters, such as pH, current density, and water matrices, were systematically studied to optimize the process. Under optimal conditions (pH 7, current density of 55 mA A/cm2), 80 % mineralization of a 40 mg/L ATP solution was achieved within 150 min, with an energy consumption of just 0.3502 kWh/g. The performance of the AC-NZVI/CF electrode remained stable when applied to real wastewater and after five consecutive cycles. Comprehensive analyses using FTIR, SEM-EDS, and XPS confirmed the stability and recyclability of the electrode, showcasing its potential for sustainable wastewater treatment applications.

Catalytic generation of adsorbed atomic H for degradation of 2,2′,4,4′-tetrabromodiphenyl ether by mechanochemically prepared Ni-doped oxalated zero-valent iron

In the homologous series of polybrominated diphenyl ethers (PBDEs), the debromination of low-brominated diphenyl ethers with higher toxicity remains a challenge. Nano zero-valent iron (nZVI) has been extensively studied for the debromination of PBDEs, but its inherent direct electron transfer mechanism is less efficient for low-brominated diphenyl ethers, and there are issues with high preparation costs. In this work, we synthesize Ni-doped oxalated submicron ZVI (FeOXbm/Ni) using a low-cost ball-milling method. FeOXbm/Ni exhibits a debromination rate constant of 0.48 day−1 for 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) in tetrahydrofuran (THF)/water. The debromination rate of FeOXbm/Ni for BDE-47 in water is even faster (0.98 day−1), with the yield of the complete debromination product, diphenyl ether, reaching 76.71%. In real groundwater, FeOXbm/Ni also shows high reactivity toward BDE-47, with a rate constant of 0.33 day−1. Kinetic experiments, quenching experiments, and degradation pathway indicate that the attack of atomic hydrogen on C-Br bonds is the primary degradation mechanism. Electrochemical analysis further show that Ni0 sites could cleave hydrogen into absorbed atomic hydrogen (H∗ABS) and adsorbed atomic hydrogen (H∗ADS), with H∗ADS playing the main role. These findings contribute valuable insights into advancing the large-scale application of ZVI and offer promising strategies for thorough remediation of PBDEs pollution.

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.

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.

Zero Valent Iron/Ni (FeNi) bimetallic heterostructure for scalable fabrication of polyvinylidene fluoride/FeNi films and efficient organic contaminant removal under UV/persulfate system

Surface heterogeneity on nano zero-valent iron (nZVI) with an additional metal is expected to enhance the catalytic performance and stability by inhibiting metal corrosion and leaching. The influence of passivation by Ni/NiO on the stability of nZVI is examined through degradation performance of uniformly aged nZVI and nZVI/Ni (FeNi) samples via photo-Fenton like reactions under UV/potassium persulfate (PS) system. FeNi bimetallic nanoparticles (BNPs) exhibits enhanced degradation than bare nZVI as thin layers of Fe3O4 and NiO which contribute towards photocatalytic degradation and anticorrosive effects by nickel inclusion. FeNi BNPs achieve 98 % degradation for pharmaceutical antibiotic levofloxacin (LEVO) within 120 min and 93 % degradation for Methylene Blue dye (MB) within 60 min, outperforming nZVI. To overcome secondary pollution, a stable polyvinylidene fluoride (PVDF)/FeNi film was fabricated to treat the contaminated water. The free-floating PVDF/FeNi film achieved 95 % degradation of MB and 98.3 % degradation of LEVO, maintaining a degradation efficiency of 95.9 % after five successive cycles. FeNi BNPs are also immobilized in the dialysis membrane resulting in 99.9 % and 99 % removal of MB and LEVO respectively. MB degradation using PVDF/FeNi film is validated through the micro reactor model developed in COMSOL Multiphysics. The parameters determined from the Langmuir-Hinshelwood (L-H) kinetic model include an intrinsic rate constant of 2.18 ×10−6 mol m−3 min−1 and an adsorption constant of 1.43 ×1019 m3 mol−1. This work introduces a cost-effective and scalable technique for the efficient remediation of contaminants in wastewater.

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

Surface modification can significantly improve nano zero-valent iron (nZVI) stability. However, different methods and materials significantly affect nZVI toxicity, and the effects on bacterial metabolic processes and corresponding molecular mechanisms require further study. In this study, Chlorella biochar-loaded nano zero-valent iron (nZVI/BC) was prepared, showing optimum removal of Microcystis aeruginosa (M. aeruginosa) at a dosing rate of 12.5 g L−1. The toxicity against Escherichia coli (E. coli) was investigated, revealing time-dependent inactivation efficiency, achieving −3.60 log at 30 min and −5.0 log for a single nZVI. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) analyses revealed that nZVI exhibited stronger adsorption to cells compared to nZVI/BC, with both nZVI and nZVI/BC primarily interacting with amine, carboxyl, and ester groups on the cell surface. Physiological, biochemical, ROS quenching, and metabolomics experiments indicated that ROS played a key role in the inactivation of E. coli. This study proposes a strategy to balance the stability of nZVI with its biocompatibility.

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.

Highly selective nitrate reduction to N2 by Cu-nZVI/LDH bimetallic composite: Mechanism, reaction pathway and strategy for enhanced N2 formation

Due to the highly reductive capacity of nano zero-valent iron (nZVI), the reduction of nitrate (NO3--N) is prone to produce ammonia (NH4+-N) as a by-product and has low selectivity for nitrogen gas (N2). Selective conversion of NO3--N to harmless N2 by regulating reaction pathway is the key to improve the reduction and nitrogen removal performance of nZVI-based materials. In this study, metal copper (Cu) was added to nZVI to prepare Cu-nZVI/LDH bimetallic composites. Cu was used as a catalyst to form a galvanic coupling with nZVI to accelerate electron transfer and improve the electron utilization efficiency. Synergism of adsorption and reduction of NO3--N was achieved through adsorption of layered bimetallic hydroxide (LDH) and reduction of nZVI. The results showed that the NO3--N removal and N2 product selectivity by Cu-nZVI/LDH was as high as 95.6 % and 80.3 %, respectively. The critical reaction pathway of N2 generation on the Cu surface of Cu-nZVI/LDH composite was further revealed by DFT theoretical calculations. Experiments on actual micro-polluted water showed that the removal of NO3--N by Cu-nZVI/LDH reached 85.2 %. The NO3--N removal of the composite material slightly decreased to 78.6 % after 15 d of aging, verifying that the composite material had good potential for practical applications.

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.

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.

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.

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.

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.