Presence Of Nanoscale Zero-valent Iron Research Articles

Mechanisms of nanoscale zero-valent iron mediating aerobic denitrification in Pseudomonas stutzeri by promoting electron transfer and gene expression

Aerobic denitrification and its mechanism by P. stutzeri was investigated in the presence of nanoscale zero-valent iron (nZVI). The removal of nitrate and ammonia was accelerated and the nitrite nitrogen accumulation was reduced by nZVI. The particle size and dosage of nZVI were key factors for enhancing aerobic denitrification. nZVI reduced the negative effects of low carbon/nitrogen, heavy metals, surfactants and salts to aerobic denitrification. nZVI and its dissolved irons were adsorbed into the bacteria cells, enhancing the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to nitrate reductase. Moreover, the activities of NADH-ubiquinone reductase involved in the respiratory system, and the denitrifying enzymes were increased. The expression of denitrifying enzyme genes napA and nirS, as well as the iron metabolism gene fur, were promoted in the presence of nZVI. This work provides a strategy for enhancing the biological denitrification of wastewater using the bio-stimulation of nanomaterials.

Synergistic degradation of chloramphenicol by ultrasound-enhanced nanoscale zero-valent iron/persulfate treatment

Ultrasonic (US) was used to activate persulfate (PS) in presence of nanoscale zero-valent iron (nZVI) to degrade chloramphenicol (CAP) in solution. Synergistic effects were observed of US and nZVI on PS activation (US-nZVI/PS) compared to US/PS, nZVI/PS, or US-nZVI alone, while replacement of nZVI with Fe(II) or Fe(III) ion was less efficient to degrade CAP. The US-nZVI/PS treatment exhibited a rapid and continuous oxidation of CAP in solution. Both OH and SO4− were considered to be primary reactive species responsible for CAP degradation, of which SO4− had a higher contribution than OH. Our results indicated that Fe2+ was continuously being recycled by reaction of nZVI and PS, accompanied by generation of SO4−. US accelerated the corrosion of nZVI and removed passive films on the nZVI surface. Under optimal conditions, 98.1% of CAP was degraded during 90 min. This was established in presence of 0.5 g/L nZVI and 1.0 mM PS, with an US intensity of 0.36 W/mL at 40 kHz and a pH of 7.0. When present, inorganic anions and natural organic matter partly inhibited CAP degradation, which was mainly attributed to their scavenging effects for SO4− and OH. The reusability of nZVI was examined in five consecutive cycles, showing a decrease in efficiency with each cycle. Seven major intermediate products were identified, and these indicated two degradation pathways. Finally, in-situ regeneration of CAP-saturated powdered activated carbon using US-nZVI/PS process was evaluated.

Enhanced denitrification performance of Alcaligenes sp. TB by Pd stimulating to produce membrane adaptation mechanism coupled with nanoscale zero-valent iron

The microbial reduction of nitrate in the presence of nanoscale zero-valent iron (nZVI) was evaluated to assess the feasibility of employing nZVI for biological denitrification treatment. The effect of modified nZVI on the growth, metabolism, and denitrification performance of Alcaligenes sp. TB under aerobic conditions was studied. Results showed that Alcaligenes sp. TB with nZVI/Pd had 31.5% increase in nitrate removal and 18.1% decrease in nitrite accumulation within 28 h. nZVI/Pd exhibited less inhibition on the cell growth (OD600 = 0.725), NADH/NAD+ ratio (86% of control), and electron transfer system activity (68.5% of control). In addition, nZVI/Pd decreased the membrane fluidity by increasing the trans/cis isomerization ratio (317.7% of control) to enhance the resistance of nZVI. This study underlines the effects of nZVI/Pd on membrane susceptibility via membrane fatty acid transformation during denitrification and suggests the influence of engineered nanomaterials on denitrification.

Simultaneous degradation of nitrogenous heterocyclic compounds by catalytic wet-peroxidation process using box-behnken design

The present study investigates the feasibility of nitrogenous heterocyclic compounds (NHCs) (Pyridine-Quinoline) degradation by catalytic wet peroxidation (CWPO) in the presence of nanoscale zerovalent iron supported on granular activated carbon (nFe<sup>0</sup>/GAC) using statistical optimization technique. Response surface methodology (RSM) in combination with Box-Behnken design (BBD) was used to optimize the process parameters of CWPO process such as initial pH, catalyst dose, hydrogen peroxide dose, initial concentration of pyridine (Py) and quinolone (Qn) were chosen as the main variables, and total organic carbon (TOC) removal and total Fe leaching were selected as the investigated response. The optimization of process parameters by desirability function showed the ~85% of TOC removal with process condition of initial solution pH 3.5, catalyst dose of 0.55 g/L, hydrogen peroxide concentration of 0.34 mmol, initial concentration of Py 200 mg/L and initial concentration of Qn 200 mg/L. Further, for TOC removal the analysis of variance results of the RSM revealed that all parameter i.e. initial pH, catalyst dose, hydrogen peroxide dose, initial concentration of Py and initial concentration of Qn were highly significant according to the <i>p</i> values (<i>p</i> < 0.05). The quadratic model was found to be the best fit for experimental data. The present study revealed that BBD was reliable and effective for the determination of the optimum conditions for CWPO of NHCs (Py-Qn).

Effects of the presence of nanoscale zero-valent iron on the degradation of polychlorinated biphenyls and total organic carbon by sediment microbial fuel cell

The degradation of polychlorinated biphenyls (PCBs) and total organic carbon (TOC) by sediment microbial fuel cell (SMFC) with/without nanoscale zero-valent iron (NZVI) addition was investigated. It was found that the combined application led to the highest removal efficiencies of PCBs (37.55 ± 1.11%) and TOC (49.72 ± 1.54%) in all circumstances and produced a higher power density (108.89 mW/m2) and a corresponding lower internal resistance (264 Ω) than operation employing SMFC only. The TOC removal efficiency and the total production of electricity were linear. High-throughput sequencing of anodic microbial communities indicated that the electrode participation can increase the abundance of electrogenic bacteria (Geobacter and Pseudomonas) and the NZVI addition can reduce the oxidation reduction potential of the system and therefore enrich some bacteria (Longilinea and Desulfofustis) beneficial to the degradation of organic matter.

Effect of dissolved oxygen/nZVI/persulfate process on the elimination of 4-chlorophenol from aqueous solution: Modeling and optimization study

4-Chlorophenol (4-CP) is a hazardous and toxic chemical that enters into water bodies mainly through industrial effluents. The present study investigated the effect of under pressure dissolved oxygen on 4-CP degradation in the presence of nanoscale zero-valent iron (nZVI) and sodium persulfate. The impact of oxygen pressure, as a qualitative variable at three levels (1, 1.5 and 2 atm), along with five quantitative variables, including persulfate concentration (0-2mM), nZVI dosage (0-1 g/L), pH (3-11), reaction time (5-90min) and 4-CP concentration (50-500mg/L) on the 4-CP elimination from aqueous solutions, was examined using response surface methodology. There was a direct relationship between the dissolved oxygen under pressure and the 4-CP removal efficiency. Also, the gained R2 and adjusted R2 for three developed models of 1, 1.5 and 2 atm oxygen pressure were 0.971 and 0.9569, 0.9689 and 0.9538, and 0.9642 and 0.9468, respectively. The best removal process conditions for pH 4.2, 1.6mM persulfate, 64.79 min reaction time, 97.89mg/L initial 4-CP and 1 g/L nZVI dosage. The results indicated that dissolved oxygen under pressure-nZVI-persulfate could be considered a promising process for elimination of organic compounds from aqueous solutions.

Bioaccumulation and toxic effects of decabromodiphenyl ether in the presence of nanoscale zero-valent iron in an earthworm–soil system

In this study, the bioaccumulation and toxic effects of decabromodiphenyl ether (BDE209) (1 and 10 mg kg−1) were investigated in the earthworm Eisenia fetida in the presence of different levels of nanoscale zero-valent iron (nZVI) (100, 500, and 1000 mg kg−1) in an earthworm–soil system. The results demonstrated that compared to single BDE209 exposure, the addition of high levels of nZVI significantly (P < 0.05) inhibited growth and respiration, while increased the avoidance response of earthworms. The perturbations of antioxidant enzyme activities (superoxide dismutase (SOD) and catalase (CAT)) and the malondialdehyde (MDA) content clearly revealed that oxidative stress was induced by the two chemicals. The histopathological observations of the body wall of earthworms under a combined exposure of 10 mg kg−1 BDE209 with 500 or 1000 mg kg−1 nZVI illustrated the presence of a serious injury in the intestinal tissues after a 28-day exposure. Additionally, a gas chromatography–mass spectrometry analysis revealed that the coexistence of high level of nZVI significantly (P < 0.05) decreased the bioaccumulation of BDE209 in earthworms; BDE208 and BDE206 were the predominant congeners of debrominated metabolites, and 4,6-dibromobenzene-1,2,3,5-tetraol along with benzene-1,2,4,5-tetraol were determined as the two main intermediates. The possible degradation pathways were proposed on the basis of the identified products. This work provides useful information on the biological effects of BDE209 and nZVI.

Inhibition or promotion of biodegradation of nitrate by Paracoccus sp. in the presence of nanoscale zero-valent iron

To investigate the effect of nanoscale zero-valent iron (nZVI) on the growth of Paracoccus sp. strain and biodenitrification under aerobic conditions, specific factors were studied, pH, concentration of nitrate, Fe (II) and carbon dioxide. Low concentration of nZVI (50mg/L) promoted both cell growth and biodegradation of nitrate which rose from 69.91% to 76.16%, while nitrate removal fell to 67.10% in the presence of high nZVI concentration (1000mg/L). This may be attributed to the ions produced in nZVI corrosion being used as an electron source for the biodegradation of nitrate. However, the excess uptake of Fe (II) causes oxidative damage to the cells. To confirm this, nitrate was completely removed after 20h when 100mg/L Fe (II) was added to the solution, which is much faster than the control (86.05%, without adding Fe (II)). However, nitrate removal reached only 45.64% after 20h, with low cell density (OD600=0.62) in the presence of 300mg/L Fe (II). Characterization techniques indicated that nZVI adhered to microorganism cell membranes. These findings confirmed that nZVI could affect the activity of the strain and consequently change the biodenitrification.

Stabilization of sewage sludge in the presence of nanoscale zero-valent iron (nZVI): abatement of odor and improvement of biogas production

The potential benefits of nanoscale zero-valent iron (nZVI) on sludge stabilization, either the abatement of odor or the improvement of biogas production, were investigated in this study. Two commercial-grade microscale iron powders were also utilized for comparison. Adding 0.10 wt% of nZVI in sludge during anaerobic incubation significantly reduced the concentration of H2S in biogas by 98.0 % (96.2–98.9 %), probably attributed by reactions between sulfides and the neo-formed hydrous Fe(II)/Fe(III) oxides layer at the surface of ZVI nanoparticles. Meanwhile, the percentage of P in bioavailable fractions decreased from 76.8 to 52.5 %, possibly due to the formation of vivianite [Fe3(PO4)2]. Furthermore, 0.10 wt% of nZVI in anaerobic digestion for 17 days enhanced the concentration of CH4 in biogas by 5.1–13.2 % and improved the production of biogas and methane by 30.4 and 40.4 %, respectively. The amendment of iron nanoparticles during anaerobic digestion can not only effectively reduce H2S in biogas, but also potentially boost methane production significantly.

나노영가철의 TCE 분해반응 시 지하수 용존물질의 영향

Nanoscale zero-valent iron (NZVI) particles were tested as remediation media for groundwater contaminated by organic pollutants (e.g., TCE, trichloroethylene). The contaminated groundwater contained anions (NO3, Cl, SO4, and HCO3) and natural organic matter (NOM). Treatability of commercial NZVI particles (NANOFER 25, Nanoiron, Czech) was tested by using a synthetic groundwater and the field groundwater samples. More than 95% of 1.8 mM TCE was removed within 20 hours with a NZVI dosage of 25 g/L (k = 0.15 hr). Repetitive degradation experiments revealed that the removal capacity of NANOFER 25 was 0.19 mmole TCE/g NZVI. TCE degradation reactions were not substantially affected by the presence of each anion with concentrations as high as 100 times the average field concentrations. However, when the four anions (NO3, Cl, SO4, HCO3) were present simultaneously. the degradation reactivity and removal capacity were decreased by 60% (k = 0.069 hr) and 10%, respectively. The k value of TCE degradation in the presence of NZVI (25 g/L) with dissovled organic carbon of 2.5 mg/L was also decreased by 84% (k = 0.025 hr). In the experiments with the field groundwater, more than 90% of 1.8 μM TCE, which is the concentration of TCE at the source zone, was removed within 10 hours with a NANOFER 25 dosage of 25 g/L. The results imply that the contaminated groundwater can effectively be treated by NANOFER 25 with more information on the hydrogeology of the site.

Impact of Nanoscale Zero Valent Iron on Geochemistry and Microbial Populations in Trichloroethylene Contaminated Aquifer Materials

Nanoscale zerovalent iron (NZVI) particles are a promising technology for reducing trichloroethylene (TCE) contamination in the subsurface. Prior to injecting large quantities of nanoparticles into the groundwater it is important to understand what impact the particles will have on the geochemistry and indigenous microbial communities. Microbial populations are important not only for nutrient cycling, but also for contaminant remediation and heavy metal immobilization. Microcosms were used to determine the effects of NZVI addition on three different aquifer materials from TCE contaminated sites in Alameda Point, CA, Mancelona, MI, and Parris Island, SC. The oxidation and reduction potential of the microcosms consistently decreased by more than 400 mV when NZVI was added at 1.5 g/L concentrations. Sulfate concentrations decreased in the two coastal aquifer materials, and methane was observed in the presence of NZVI in Alameda Point microcosms, but not in the other two materials. Denaturing gradient gel electrophoresis (DGGE) showed significant shifts in Eubacterial diversity just after the Fe(0) was exhausted, and quantitative polymerase chain reaction (qPCR) analyses showed increases of the dissimilatory sulfite reductase gene (dsrA) and Archaeal 16s rRNA genes, indicating that reducing conditions and hydrogen created by NZVI stimulate both sulfate reducer and methanogen populations. Adding NZVI had no deleterious effect on total bacterial abundance in the microcosms. NZVI with a biodegradable polyaspartate coating increased bacterial populations by an order of magnitude relative to controls. The lack of broad bactericidal effect, combined with the stimulatory effect of polyaspartate coatings, has positive implications for NZVI field applications.

Reductive Dechlorination of Chloroacetanilide Herbicide (Alachlor) Using Zero-Valent Iron Nanoparticles

Abstract Nanoscale zero-valent iron (NZVI) was used for the first time to reductively degrade the chloroacetanilide herbicide, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide], in laboratory studies. NZVI was synthesized by the borohydride reduction method and characterized using transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. Resulting particles had an average diameter of 35 nm and a Brunauer–Emmett–Teller surface area of 25 m2 g−1. Alachlor degradation in the presence of NZVI was rapid and complete. Parallel comparison trials with commercial microscale zero-valent iron (surface area = 1–2 m2/g−1) were also conducted. Surface area-normalized rate constants (kSA) for NZVI and microscale zero-valent iron were found to be 38.5 × 10−5 and 3.8–7.7 × 10−5 L h−1/m−2, respectively. A reaction product was identified as dechlorinated alachlor [N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide]. Based on results obtained in the research, the authors stipulate that N...

Microbial reduction of nitrate in the presence of nanoscale zero-valent iron

Microbial reduction of nitrate in the presence of nanoscale zero-valent iron (NZVI) was evaluated to assess the feasibility of employing NZVI in the biological nitrate treatment. Nitrate was completely reduced within 3 d in a nanoscale Fe(0)-cell reactor, while only 50% of the nitrate was abiotically reduced over 7 d at 25 °C. The removal rate of nitrate in the integrated NZVI-cell system was unaffected by the presence of high amounts of sulfate. Efficient removal of nitrate by Fe(II)-supported anaerobic culture in 14 d indicated that Fe(II), which is produced during anaerobic iron corrosion in the Fe(0)-cell system, might act as an electron donor for nitrate. Unlike abiotic reduction, microbial reduction of nitrate was not significantly affected by low temperature conditions. This study demonstrated the potential applicability of employing NZVI iron as a source of electrons for biological nitrate reduction. Use of NZVI for microbial nitrate reduction can obviate the disadvantages associated with traditional biological denitrification, that relies on the use of organic substrates or explosive hydrogen gas, and maintain the advantages offered by nano-particle technology such as higher surface reactivity and functionality in suspensions.