Modified Nanoscale Zero-valent Iron Research Articles

Multistage stabilization of Cd, Pb, Zn, Cu and As in contaminated soil by phosphorus-coated nZVI layered composite materials: characteristics, process and mechanism

This study developed a shell-like slow-release material, PF@ST/Fe-0.5, by encapsulating nanoscale zero-valent iron composites (NZC) with phosphate fertilizer (PF) and a starch binder (ST). The material dissolved in soil in stages, first releasing P and Ca to increase the soil pH from 4.95 to 7.14. This was followed by the formation of phosphates and hydroxides precipitates with Pb, Cu, Zn, and Cd in soil, reducing their bioavailable forms by 81.73 %, 79.58 %, 91.05 %, and 86.47 %, respectively. The process also involved the competitive adsorption between PO43-/HPO42- and arsenate/arsenite led to the release of specifically adsorbed arsenic, increasing the probability of reaction with the material. Afterwards, the exposure of the NZC core reacted with arsenate/arsenite to form ferric arsenates, thus reducing the content of bioavailable arsenic in the soil by 73.57 %. Excess PO43- and alkali metal cations were captured and mineralized by the iron (hydro) oxides and reactive silicates in NZC, enhancing the remediation effect. Furthermore, the wet-dry alternation test had demonstrated the adaptability of PF@ST/Fe-0.5 to the rainy dry-wet soil environment in Yunnan, which enabled the bioavailable content of As, Pb, Cu, Zn, and Cd decreased by 71.2 %, 94.8 %, 84.1 %, 79.8 %, and 83.9 %, respectively. The layered structure minimized internal reactive substance consumption and protected the internal nZVI from oxidation. The phased release of phosphate and Fe0 stabilized Pb, Cu, Zn, and Cd, enhancing As stabilization and providing a new perspective for the synchronous stabilization of soil contaminated.

Study on the enhancement of citric acid chemical leaching of contaminated soil by modified nano zero-valent iron.

This study aimed to evaluate the effect of modified nanoscale zero-valent iron (SAS-nZVI) on chemical leaching of lead and cadmium composite contaminated soil by citric acid (CA). The synthesized SAS-nZVI was used as a leaching aid to improve the removal rate of soil heavy metals (HMs) by CA chemical leaching. The effects of various factors such as SAS-nZVI dosage, elution temperature and elution time were studied. At the same time, the effect of chemical leaching on the basic physical and chemical properties of soil and the morphology of HMs was evaluated. The results show that when the SAS-nZVI dosage is 2.0g/L, the leaching temperature is 25°C, and the leaching time is 720min, the maximum removal rates of Pb and Cd in the soil are 77.64% and 97.15% respectively. The experimental results were evaluated using elution and desorption kinetic models (Elovich model, double constant model, diffusion model). The elution and desorption process of Pb and Cd in soil by SAS-nZVI-CA fitted well with the double-constant model, indicating that the desorption kinetic process of Pb and Cd is a heterogeneous diffusion process, and the elution process is controlled by diffusion factors. After leaching with SAS-nZVI-CA, the physical and chemical properties of the soil changed little, the mobility and toxicity of HMs in the soil were reduced, and the HMs content in the leaching waste liquid was reduced. It can be concluded that SAS-nZVI enhances the efficiency of CA in extracting Pb and Cd from soil, minimizes soil damage resulting from chemical leaching technology, and alleviates the challenges associated with treating leaching waste liquid.

Immobilization of cadmium in river sediments by different modified nanoscale zero-valent iron: performance, mechanisms, and Fe dissolution.

Modified nanoscale zero-valent iron (NZVI) exhibited great potential for the remediation of heavy metal contaminated river sediments, but its mechanisms and environmental risks are still unclear. This study systematically discussed the performance and the mechanisms of modified NZVI materials, i.e., sodium alginate-coated NZVI (SNZVI), rhamnolipid-coated NZVI (RNZVI), and graphene oxide-loaded NZVI (GNZVI), for the stabilization of Cd in sediment, with the exploration of their stability to Cd at various pH values and Fe dissolution rate. Compared with the control, the toxicity characteristic leaching procedure (TCLP) leachable Cd decreased by 52.66-96.28%, and the physiologically based extraction test (PBET) extractable Cd decreased by 44.68-70.21% after 56 days of incubation with the immobilization efficiency varying according to GNZVI > RNZVI > SNZVI > NZVI. Besides, the adsorption behavior of Cd on materials was fitted with the Freundlich model and classified as an endothermic, spontaneous, and chemical adsorption process. SEM-EDX, XRD, and FTIR results verified that the stabilization mechanisms of Cd were principally based on the adsorption, complexation of Cd2+ with secondary Fe minerals (including Fe2O3, γ-Fe2O3, and γ-FeOOH) and precipitation (Cd(OH)2). From the risk assessment results, it was observed that the materials were favorable for Cd stabilization at a pH range from 7 to 11, meanwhile, the leaching concentration of Fe in the overlying water was detected below the limit value. These findings pave the way to developing an effective strategy to remediate Cd contaminated river sediments.

Characterization and mechanism of p-nitrophenol removal based on modified nanoscale zero-valent iron electrocoagulation

p-Nitrophenol (PNP) is a toxic chemical and is difficult to degrade naturally when it enters the environment. It is of great importance to develop methods to remove PNP efficiently and safely. Electrocoagulation has been widely used for the removal of PNP, but challenges remain in the improvement of anode materials and solid-liquid separation of PNP-containing precipitates. In this work, the characteristics and mechanism of activated biochar (ABC) and sulfide dual-modified nanoscale zero-valent iron (nZVI) electrocoagulation anode for the removal of PNP were systematically investigated. The synergistic effect of magnetic iron oxide generated by zero-valent iron oxidation and electrochemical oxidation technique was used to rapidly reduce the PNP concentration for water purification. The results showed that the modified nZVI anode had higher electrocoagulation activity than the iron sheet anode, and the S-nZNI/ABC anode had the highest PNP removal efficiency. The main component of the precipitate after the reaction was Fe3O4, which facilitated the magnetic solid-liquid separation of the precipitate and scum. The seed germination test confirmed that the electrocoagulation material synthesized in this work had almost no adverse effects on the ecological environment. The electrocoagulation process had good degradation performance for PNP, which could significantly attenuate the ecotoxicity of PNP in the aquatic environment and thus improve the water quality. It is expected that this work may provide design references and ideas for the efficient degradation of PNP and the application of electrocoagulation.

Efficient degradation of hexabromocyclododecane using montmorillonite supported nano-zero-valent iron and Citrobacter sp. Y3

The coupling of modified nanoscale zero-valent iron (nZVI) with organohalide-degrading bacteria provides a promising solution for the remediation of hexabromocyclododecane (HBCD)-contaminated environments. However, the interactions between modified nZVI and dehalogenase bacteria are intricate, and the mechanisms of synergistic action and electron transfer are not clear, and requires further specific investigation. In this study, HBCD was used as a model pollutant, and stable isotope analysis revealed that organic montmorillonite (OMt)-supported nZVI coupled with the degrading bacterial strain Citrobacter sp. Y3 (nZVI/OMt–Y3) can use [13C]HBCD as the sole carbon source and degrade or even mineralise it into 13CO2 with a maximum conversion rate of 100% within approximately 5 days. Analysis of the intermediates showed that the degradation of HBCD mainly involves three different pathways: dehydrobromination, hydroxylation, and debromination. The proteomics results showed that nZVI introduction promoted the transport of electrons and debromination. Combining the results from XPS, FTIR, and Raman spectroscopy with the analysis results of proteinomics and biodegradation products, we verified the process of electron transport and proposed a metabolic mechanism of HBCD degradation by the nZVI/OMt–Y3. Moreover, this study provides insightful avenues and models for the further remediation of HBCD and other similar pollutants in the environment.

Enhanced degradation of monobrominated diphenyl ether by sophorolipid modified nanoscale zerovalent iron: Reactivity, electron selectivity, and mechanism

Nanoscale zero-valent iron (nZVI) is regard as a promising reductant for halogenated organic compounds remediation, while it still suffers from low reactivity and poor electron selectivity toward monobrominated diphenyl ether. In this paper, the modified nZVI was successfully prepared via introducing sophorolipid during the synthesis of nZVI by a one-step method (SL-nZVI). The experimental results demonstrated that the degradation efficiency of SL-nZVI for BDE-3 could reach up to 99.96%, which was significantly higher than that of nZVI (59.60%). TEM and BET characterizations indicated that the modified nZVI possessed excellent dispersion properties and higher specific surface area, while the electrochemical tests results revealed that the sophorolipid modification reduced the charge transfer resistance of nZVI and favored the electron transfer. Besides, the introduced sophorolipid enhanced solubilization of hydrophobic organic contaminants via halogen bonding interaction also contributes to the increasement of BDE-3 degradation. More importantly, the experimental results also indicated that the utilization efficiency and electron selectivity of nZVI particles for the BDE-3 were significantly improved after sophorolipid modification (from 56.64% and 2.69% to 74.14% and 7.39%, respectively), and this could be owned to more accessible active sites, as well as the increased hydrophobicity of nZVI, which is not conducive to the adsorption of hydrophobic BDE-3 onto the nZVI surface, but reduces the occurrence of side reaction between nZVI and water. Those results demonstrate that the sophorolipid modification is an efficient strategy for nZVI in the remediation of hydrophobic BDE-3, and also highlight the promising prospects of sophorolipid in increasing the reactivity and electron selectivity of nZVI.

Removal of nitrate nitrogen from wastewater by green synthetic hydrophilic activated carbon supported sulfide modified nanoscale zerovalent Iron: Characterization, performance and mechanism

In this study, A green reducing agent green tea extract is used instead of traditional sodium borohydride and porous activated carbon was supported to prepare nano-zero valent iron (nZVI) combined with sulfate (GT-PAC-nZVI/S) to remove Nitrate Nitrogen (NO3–-N) in wastewater. SEM-EDS, BET, XRD and FTIR characterization results confirmed that effective preparation of porous and high specific surface area and successful loading of sulfide nZVI on PAC. Batch experiments were conducted to measure the effects on the removal of nitrate nitrogen of different parameters including pH, temperature, dosage, interfering agents, carbon-iron ratio and iron-sulfur ratio. The experimental results demonstrate that GT-PAC-nZVI/S has a high nitrate nitrogen removal rate and reduction product gaseous nitrogen can reach 93.00% and 22.10%, respectively, at pH = 7, the dosage of GT-PAC-nZVI/S = 4 g/L, temperature of 60 ℃, iron-sulfur ratio = 1:0.3 and time of 95 min. And interfering ion HPO42- have the strong inhibition for NO3–-N degradation. The adsorption isotherm and kinetic data for GT-PAC-nZVI/S was fitted well with the Langmuir and pseudo-second order model, respectively, indicating that the adsorption process for nitrate was chemisorption. Furthermore, GT-PAC-nZVI/S enhanced the removal of nitrate nitrogen through complexation, redox, and adsorption co-precipitation. This work highlights the efficient remediation of nitrate-nitrogen water pollution by porous activated carbon loaded with sulfide nZVI.

Synergistic removal of As(III) and Cd(II) by sepiolite-modified nanoscale zero-valent iron and a related mechanistic study.

Arsenic (As) and cadmium (Cd) are two highly toxic elements. In recent years, many newly synthesized chemical materials have been used widely for treatments of As- and Cd-contaminated effluents. However, most materials do not exhibit high efficiencies for simultaneous removal of As and Cd from water systems. Our study established a simple scheme for synthesizing a sepiolite (SEP)-modified nanoscale zero-valent iron (S-nZVI) for simultaneous removal of coexisting As and Cd from water and illuminated a possible underlying mechanism. Batch experiments showed that the maximum capacities for adsorption of As(III) and Cd(II) by S-nZVI were 230.29mg/g and 11.37mg/g, respectively, which represented better effects than those of other materials, as reported previously. Removal of Cd(II) depended on pH, but As(III) removal showed little dependence on pH. Coexisting ions such as phosphate (PO43-) and the conjugate base of humic acid (HA) significantly inhibited simultaneous removal of As(III) and Cd(II). In the mixed As(III)-Cd(II) system, the presence of As(III)-pretreated S-nZVI significantly enhanced Cd(II) adsorption by a factor of four over that seen for aqueous solution without As(III). XRD and XPS results showed that CdFe2O4 (Fe-O-Cd), Fe2As2O14 or FeAsO4 (Fe-O-As) were formed after As(III) and Cd(II) were captured by S-nZVI. However, a further zeta (ζ) potential analysis showed that the mechanism for As(III) and Cd(II) adsorption by S-nZVI is not just simple formation of the above chemicals, since the adsorbed As(III) increased the negative charge of S-nZVI; this suggested an electrostatic attraction between S-nZVI and Cd(II) and indicated that adsorbed As(III) created new sorption sites for Cd(II), which enhanced Cd(II) sorption via formation of ternary complexes (Fe-As-Cd). These results suggested that S-nZVI is a promising material for in situ remediation of heavy metal-contaminated groundwaters or paddy soils.

Promotion of ciprofloxacin adsorption from contaminated solutions by oxalate modified nanoscale zerovalent iron particles

Water contamination by ciprofloxacin (CIP) is a global and emerging issue because it increases the risk of infection by antimicrobial resistant bacteria. CIP removal from water by iron nanoparticles (Fe0) with the presence of oxalate hasn't been reported yet. The present study demonstrated that the addition of oxalate to Fe0 nanoparticles improved the removal of 100 mg L−1 of CIP from 45.04% to 95.74% under the following optimum conditions: [Fe0] = 0.3 g L−1, [oxalate] = 0.3 mM, initial pH = 7, and temperature = 25 ℃. Furthermore, the experimental results illustrated that high concentrations of dissolved oxygen in the aqueous solution greatly decreased the removal efficiency of CIP by (Fe0/oxalate) system from 97.69% (N2 atmosphere) to 67.47%. Similarly, the performance of (Fe0/oxalate) system declined from 95.43% to 85.23% because of increasing the ionic strength of the solution from 0 to 100 mM. In contrast, the influence of humic acid (0 – 40 mg L−1) on the removal of CIP by (Fe0/oxalate) system was neglectable. Also, the negative impact of coexisting ions on the competence of (Fe0/oxalate) system was in the following order: Mg2+ > NO3– > SO₄2- > Ca2+ > CO32– > K+. In addition, the desorption experiments and the results of SEM-EDS, XRD, and FTIR revealed that physisorption and chemisorption were responsible for CIP removal by (Fe0/oxalate) system as the addition of 0.3 mM of oxalate boosted the surface complexation between Fe0 nanoparticles and the carboxylic, ketone, and piperazinyl groups in CIP. These results were supported by the outcomes of kinetics, isotherm, and thermodynamic analysis. Moreover, oxalate addition significantly reduced the treatment cost of 1 L of 100 mg L−1 of CIP and the generated sludge by approximately 55.68% and 57%, respectively. Finally, this study proved that (Fe0/oxalate) system is inexpensive, practical, and more efficient than most of the reported Fe0-based systems with a maximum adsorption capacity of 294.66 mg g−1.

Pyrogallic acid modified nanoscale zero-valent iron efficiently removed Cr(VI) by improving adsorption and electron selectivity

Pyrogallic acid (pyGA) was firstly introduced into nanoscale zero-valent iron (nZVI) synthesis process by sodium borohydride to obtain a new catalyst pyGA-nZVI. The characterization of the material indicated successful coating of pyGA on nZVI surface. pyGA-nZVI could completely remove 50 mg·L−1 Cr(VI) within 4 min, while only 41.4% of Cr(VI) was removed by nZVI within 30 min. The material presented high Cr(VI) removal in a wide pH range of 3–12. Ortho-phenol hydroxyl groups played a crucial role in synthesizing highly effective nZVI. Fe(II) and Fe0 were mainly responsible for Cr(VI) removal in the pyGA-nZVI and nZVI systems, respectively. pyGA modification reduced the charge transfer resistance and enhanced electron transfer of nZVI. Density functional theory calculation indicated enhanced Cr(VI) adsorption on pyGA-nZVI. The reactivity of pyGA-nZVI toward H2O was hindered, increasing the electron selectivity for Cr(VI) removal. This article provides a new strategy for synthesizing highly reactive nZVI using polyphenols to remove Cr(VI).

Superhigh Adsorption of Cadmium(II) Ions onto Surface Modified Nano Zerovalent Iron Composite (CNS-nZVI): Characterization, Adsorption Kinetics and Isotherm Studies

The efficiency of surface modified nanoscale zerovalent iron (nZVI) composite by cashew nut shell (CNS) was tested for the removal of cadmium ions from the aqueous solutions. 2 g/l CNS-nZVI was efficient for 98% removal. The adsorption capacity was 35.58 mg/g. The Freundlich isotherm (R2 = 0.9769) and the pseudo-second order adsorption kinetics data fitted well. This proved CNS-nZVI has a high removal efficiency for Cd(II) from aqueous solutions.

Experimental study of the effect of nanoscale zero-valent iron injected on the permeability of saturated porous media

Abstract In a comparison of modified nanoscale zero-valent iron (NZVI), bare NZVI used to remediate deep contaminated groundwater source areas has more advantages. However, the influence of injected bare NZVI deposition on the permeability of aquifer remains unclear, together with which are still the key factors of engineering cost and contamination removal. Hence, this study sought to assess a method of measuring hydraulic conductivity with a constant head device and to examine the permeability loss mechanism of NZVI injected into different saturated porous media, using column tests. The results showed that it was feasible to determine hydraulic conductivity by the constant head device. The permeability loss caused by NZVI injection increased with a decrease in the grain size of the porous media, and was determined by the amount and distribution of NZVI deposition. The NZVI distribution area had a good linear correlation with dispersivity of the porous media. Additionally, although surface clogging occurred in all porous media, the amount of NZVI deposition at the injection point was largest in fine sand, so that its permeability loss was the most; this was more likely to cause hydraulic fracturing and expand the area of the contaminant source zone. These results have implications for NZVI field injection for successful groundwater remediation.

Remediation of Cd-Contaminated Soil by Modified Nanoscale Zero-Valent Iron: Role of Plant Root Exudates and Inner Mechanisms.

In this study, the role of exogenous root exudates and microorganisms was investigated in the application of modified nanoscale zero-valent iron (nZVI) for the remediation of cadmium (Cd)-contaminated soil. In this experiment, citric acid (CA) was used to simulate root exudates, which were then added to water and soil to simulate the pore water and rhizosphere environment. In detail, the experiment in water demonstrated that low concentration of CA facilitated Cd removal by nZVI, while the high concentration achieved the opposite. Among them, CA can promote the adsorption of Cd not only by direct complexation with heavy metal ions, but also by indirect effect to promote the production of iron hydroxyl oxides which has excellent heavy metal adsorption properties. Additionally, the H+ dissociated from CA posed a great influence on Cd removal. The situation in soil was similar to that in water, where low concentrations of CA contributed to the immobilization of Cd by nZVI, while high concentrations promoted the desorption of Cd and the generation of CA–Cd complexes which facilitated the uptake of Cd by plants. As the reaction progressed, the soil pH and cation exchange capacity (CEC) increased, while organic matter (OM) decreased. Meanwhile, the soil microbial community structure and diversity were investigated by high-throughput sequencing after incubation with CA and nZVI. It was found that a high concentration of CA was not conducive to the growth of microorganisms, while CMC had the effect of alleviating the biological toxicity of nZVI.

Modified nanoscale zero-valent iron in persulfate activation for organic pollution remediation: a review

Under the action of different activators, persulfate can produce sulfate radicals (SO4·-) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation.

Erratum on “Reductive immobilization of Re(VII) by graphene modified nanoscale zero-valent iron particles using a plasma technique”

We regret that our article “Reductive immobilization of Re(VII) by graphene modified nanoscale zero-valent iron particles using a plasma technique” (Sci. China Chem., 2016, 59: 150–158) [1] contained errors. The corrections in an erratum do not change or affect the result or conclusion of the paper.

Migration experiment and numerical simulation of modified nanoscale zero-valent iron (nZVI) in porous media

A packed column experiment was carried out to study the migration process of modified nano-zero-valent iron (nZVI) in porous media and the change process of hydraulic characteristics of porous media. In view of the complexity of the migration mechanism of modified nZVI in porous media, an unsteady variable parameter mathematical model considering the effects of interception, Brownian diffusion, gravity settling and the change of porous media properties was established. By fitting the model with the experimental data, the changes of various mechanisms in the experimental process were studied. The results show that the higher the injection flow rate, the higher the concentration at the outlet, and the lower the injection concentration, the higher the throughput. The distribution of iron particles in porous media is not uniform, the maximum at the entrance and the lowest at the exit. The model fits the test results well under various test conditions. The model analysis shows that in the process of particle injection, the particle size is small at the beginning, and the particles are mainly attached to the surface of the medium due to Brownian motion. As the experiment proceeds, the particle size increases, the Brownian motion effect decreases, but the interception and gravity settlement effect strengthens. In addition, during the whole process, the porosity of the medium decreases gradually, and the probability of collision between particles and porous media increases, which leads to the increase of the deposition rate coefficient.

New insights into the activity of green supported nanoscale zero-valent iron composites for enhanced acid blue-25 dye synergistic decolorization from aqueous medium

This work investigates how organic and inorganic support for innovatively modified nanoscale zero-valent iron (Fe0) as an integrated green technology to play a constructive role in the remediation of Acid Blue-25 (AB-25) dye in an aqueous solution. Silica gel and starch are used as a support material to solve the problem of aggregation and de-stabilization of Fe0 which has limited the application in an industrial scale. The modified Fe0 is successfully fabricated via a facile, one-step and environmentally-friendly approach. The systematic characterization, including SEM, TEM, STEM-XEDS and XRD for modified Fe0 compared with unmodified bare Fe0 is applied to study the morphological and structural properties. This study is also demonstrated that Fe0 and modified dosage, initial pH value, and reaction temperature and time have played an important role in the reduction of AB-25. Batch experiments showed that the removal efficiency of AB-25 has reached 100% at 6 min. under the optimum condition. Studies on the kinetics and isotherms of AB-25 reduction are well fitted using pseudo-first-order kinetics and Langmuir model, respectively. Thermodynamic studies indicated that these processes are endothermic, spontaneous and naturally favorable. Starch and silica do not only work as a carrier for Fe0 nanoparticles, but also contributes to the decolorization through an “adsorption–enhanced reduction, oxidative degradation, corrosion, and precipitation” mechanisms. The unmodified and modified Fe0 also exhibited easily regeneration and recycling at least for ten adsorption-desorption recycles. This study offers new insights into the promising green technology as a good performance for potential long term applications and magnetic separation for efficiently applied to dye-contaminated water.

Effects of persulfate treatment on antibiotic resistance genes abundance and the bacterial community in secondary effluent

Secondary effluents as one of the main ‘hotspots’ of spreading antibiotic resistance genes (ARGs) into the environment have attracted considerable attentions. However, conventional disinfection methods may be inadequate for the successful removal of ARGs. Therefore, this study investigated the removal efficiency and the regeneration potential of ten ARGs in secondary effluent using sodium persulfate activated by Ginkgo biloba L. modified nanoscale zero-valent iron. Moreover, the role of bacterial community was not yet clear when ARGs were removed by persulfate treatment (PT). Therefore, quantitative PCR and Illumina MiSeq sequencing were applied for further exploration. The results depicted that 98.6% bacterial 16S rRNA gene was removed within 10 min. After 0.5 h PT, the removal efficiency of target ARGs decreased in the following order: Tn916/1545 = aac (below the limit of detection) > int I1 (99.99%) > tet E (99.64%) > mex F (99.10%) > tet W (94.57%) > qnr S (90.18%) > van G (82.21%) > bla-TEM (64.15%) > cat A1 (23.13%). Even upon after 48 h storage, ARGs abundances were stable. The influence of pH on ARGs removal efficiency was not significant. The results of heatmap and principal coordinate analysis depicted that the abundance of ARGs did not increase with the changes of community structure. This study revealed PT as an effective method could reduce abundance of ARGs. The ARGs carried by bacteria did not multiply in their hosts and pass on to other bacterial populations further.

Interaction between pollutants during the removal of polychlorinated biphenyl-heavy metal combined pollution by modified nanoscale zero-valent iron

Modified nanoscale zero-valent iron (nZVI) is a promising functional material for the remediation of combined pollutants involving polychlorinated biphenyls (PCBs) and heavy metals. However, the interaction between the two types of pollutants has not been systematically studied for this method of treatment. In this study, 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153), Cu2+, and Ni2+ were selected as the target pollutants. To understand the interaction between pollutants, the efficiencies of nZVI, sulfidated nZVI (S-nZVI), and carboxymethylcellulose stabilized nZVI (CMC-nZVI) were investigated for removal of PCB153, Cu2+/Ni2+, and combined pollution system (PCBs-Cu2+/Ni2+). Results showed that the removal kinetics of the two types of pollutants by the three materials fitted a pseudo-first-order model well and that the reaction mechanisms were similar. Among the three materials, CMC-nZVI showed the highest reactivity to degrade PCB153 (pseudo-first-order kinetic constants (kobs) = 2.7 × 10−4 min−1) and remove Cu2+ (kobs = 2.890 min−1), while S-nZVI showed higher affinity for the removal of Ni2+ (kobs = 0.931 min−1). For the combined pollution system, PCB153 had little effect on the removal of heavy metals by the three materials, while the effect of heavy metals on PCB153 degradation was related to the types of heavy metals and the materials. Cu2+ had no significant effect on PCB153 degradation by the three materials, while the coexistence of Ni2+ promoted PCB153 degradation by nZVI and CMC-nZVI. XPS and electrochemical analysis showed that Cu0 and Ni0 were produced on the surface of the three materials. Ni is a more effective catalyst and promoted the electron transfer efficiency of the materials and had a positive impact on the dechlorination reaction.

Characteristics of trichloroethene (TCE) dechlorination in seawater over a granulated zero-valent iron

The accumulation of halogenated organic contaminants in estuaries near harbor areas has been receiving increasing attention. This work demonstrates the reductive treatment of trichloroethene (TCE) within seawater and freshwater using a polymeric surfactant (polyvinyl alcohol-co-vinyl acetate-coitaconic acid) modified nanoscale zero-valent iron (GnZVI). Experimental parameters included the ratio of seawater to freshwater, reaction pH, dosage of GnZVI and initial TCE concentration. It was found that the rate of TCE reduction decreased with increasing weight ratio of seawater to freshwater (ka = 0.075 min−1 in freshwater and 0.01 min−1 in seawater); however, the rate substantially improved by increasing the dosage of GnZVI. A consecutive reaction model of adsorption/desorption and reductive dechlorination was established to assess the chemical kinetics of TCE and the intermediates over the GnZVI. The experimental results suggested that both the amount of free sites on the reductant and reactivity of iron to TCE dominated the degradation efficiency. Desorption was a rate-limiting step for the intermediates that evolved (DCE, VC and ethene) in the bulk solution. Under conditions: GnZVI = 5 g/L, reaction pH around 8 and initial TCE = 10 mg/L, the removal efficiency attained 95%, while the decline in the removal rate of TCE from the seawater could be simply improved by increasing GnZVI dosage (10 g/L). As a role of electron donor for water and TCE, ZVI might passivate with contact time, leading to formation of the main crystalline phase magnetite (Fe3O4) by the coprecipitation of oxidized iron (Fe(II)/Fe(III)) over the surfaces of ZVI particles.