Nanoscale Zero-valent Iron Concentration Research Articles

Enhanced removing of cyanobacterium by NZVI coupled with H2O2: Influencing factors and removal mechanisms

AbstractAs advanced oxidation processes (AOPs) is considered to be a highly effective approach for degrading organic pollutants, the simultaneous coagulation and oxidation process by the Fenton‐like reaction of nanoscale zero‐valent iron (NZVI) and hydrogen peroxide (H2O2) is investigated to eliminate the harmful cyanobacterium Microcystis aeruginosa in this study, and the process conditions are optimized using the central composite design of response surface methodology (RSM); in addition, the removal efficiency of M. aeruginosa (in terms of chlorophyll a, Chl a) and the verifications of the antioxidant abilities, as well as extracellular organic matters (EOM) and intracellular organic matters (IOM) are investigated under the optimized conditions. Results indicate that H2O2 concentration is the key factor affecting the Chl a removal efficiency, and the maximum Chl a removal reaches 98.10% under the optimized conditions: NZVI concentration 62.82 mg L−1, H2O2 concentration 54.2 mmol L−1, pH 4.38 and rotating speed 67 rpm. The high correlation coefficient (R2 > 0.80) of analysis of variance (ANOVA) demonstrates the RSM model is extremely significant and suitable for experimental results. Moreover, the total organic carbon (TOC) and fluorescent substances (soluble cyanobacteria metabolic byproducts, aromatic proteins II, humic and fulvic acid‐like compounds) for both EOM and IOM are enhanced removal. It is speculated the removal mechanisms of the Fenton‐like process of NZVI/H2O2 for cyanobacterium belongs to the combined actions of the oxidation of Fe(II)/H2O2 and the coagulation of Fe(III), which destroy the defense system and result in the removal of M. aeruginosa.

Impacts of engineered iron nanoparticles on oxidative stress, fatty acid composition, and histo-architecture of the smooth scallop Flexopecten glaber.

Engineered iron nanoparticles are widely used in environmental remediation, yet their potential toxic effects on marine biota remain poorly elucidated. This study aimed to gain insight into the nanoscale zero-valent iron (NZVI) toxicity mechanisms for marine invertebrates. Aside from the effect on oxidative status and histopathology, the effect of NZVI on lipid metabolism in bivalves was studied for the first time. To this end, specimens of Flexopecten glaber were exposed to ascending concentrations (0.5, 1, and 1.5 mg/L) of NZVI for 96 h. Results illustrate differential patterns of iron accumulation in the gills and the digestive gland. By increasing NZVI concentrations, the total iron level tended to markedly increase in the gills and decrease in the digestive gland, reaching 132 and 37.6 μg/g DW, respectively, in the specimens exposed to 1.5 mg/L. Biochemical and cellular biomarkers highlighted that NZVI caused oxidative stress (measured as hydrogen peroxide, malondialdehyde, and advanced oxidation protein product levels) and alterations of antioxidant defense systems, including reduced glutathione, non-protein thiol, glutathione peroxidase, superoxide dismutase, and catalase. Modulation of lipid metabolism with changed fatty acid compositions (mainly an increase in the saturation and a decrease in unsaturation levels) was also observed in both gills and digestive gland. Moreover, several histological damages, including lipofuscin accumulation, infiltrative inflammations, and digestive tubule alterations, were observed in the two studied organs, providing supplementary evidence regarding the toxic effect of NZVI. This study adds to the growing body of evidence pointing to the hazardous impacts of iron NPs on aquatic ecosystems.

Field-scale investigation of nanoscale zero-valent iron (NZVI) injection parameters for enhanced delivery of NZVI particles to groundwater

The effects of the injection parameters on delivery of nanoscale zero-valent iron (NZVI) to contaminated groundwater were investigated. The first two NZVI injections (gravity injection at low flow rates) resulted in NZVI being poorly mobile and gave total cumulative mass recoveries at the monitoring wells of 1.07%–2.43%. NZVI reached some wells (KDMW-3, MW-2, MW-4, and MW-7) earlier than the bromide tracer. The dominant travel directions for NZVI and the bromide tracer were very different. The NZVI transport characteristics suggested that targeted NZVI delivery requires preferential groundwater flow paths and local heterogeneity to be considered. In the gravity injection tests, the maximum NZVI concentrations and cumulative NZVI mass recoveries in the wells decreased markedly as the injected NZVI concentration and dose increased. In the third and fourth tests, in which NZVI was injected under pressure at high flow rates, NZVI was effectively delivered to the wells despite the injected NZVI concentration and dose being high. Relatively high cumulative mass recoveries of 26.0% and 74.5% were found for the third and fourth injections, respectively. Controlling the flow rate (pressure) and NZVI concentration and dose simply and effectively controlled NZVI mobility in the groundwater. The colloidal and electrostatic characteristics of the NZVI particles were monitored and modeled, and the results indicated that NZVI particles without Derjaguin–Landau–Verwey–Overbeek energy barriers were successfully delivered to the target zone and that decreased magnetic attractive forces between NZVI particles caused by iron corrosion probably decreased the degree of NZVI particle aggregation and therefore contributed to NZVI being delivered to the target zone.

Immobilization of uranium(VI) in a cementitious matrix with nanoscale zerovalent iron (NZVI)

We developed a novel solidification and stabilization process using a nanoscale zerovalent iron (NZVI)-cement system for reductive immobilization of hexavalent uranium (U(VI)) in a soil–cement matrix. The NZVI suspension without cement demonstrated high removal efficiency (100% in 2 h) and fast removal kinetics (53.7 Lm−2d−1), which surpassed those of other Fe-containing minerals (i.e., green rust, mackinawite, magnetite, and pyrite). Significant removal of aqueous U(VI) was observed in NZVI-cement slurries and minimal adsorbed U was desorbed by a bicarbonate/carbonate (CARB) solution. Surface analysis using scanning electron microscopy and X-ray photoelectron spectroscopy revealed U distributed homogeneously on the surface of the NZVI-cement and transformed considerably from U(VI) to reduced U species by coupled oxidation of Fe(0)/Fe(II) to Fe(III). Furthermore, the increase in pH and NZVI concentration, and presence of humic acid resulted in the enhanced U(VI) reduction in NZVI-cement slurries. The NZVI-cement system was tested with a soil matrix, resulting in successful immobilization of aqueous U(VI) in both batch and column experiments. Moreover, the U(VI) removed in the NZVI-cement system was not leached out by the CARB solution during long-term experiments. The results suggest an NZVI-cement system could represent a promising remediation alternative for effective and stable immobilization of U(VI) in contaminated sites.

Characteristics of Aggregate Size Distribution of Nanoscale Zero-Valent Iron in Aqueous Suspensions and Its Effect on Transport Process in Porous Media

Bare nanoscale zero-valent iron (NZVI) particles in aqueous suspensions aggregate into micron to submicron sizes. The transport process of enlarged aggregates or multi-sized aggregates is different from that of nanoparticles. In this work, we performed aggregate size distribution analysis of NZVI suspension using a laser grain size analyzer and conducted a series of continuous injection column experiments with different injected NZVI concentrations. The results show that aggregates in NZVI suspensions range from submicron to submillimeter size and are mainly distributed around 5–9 μm and 50–100 μm. Quantitative calculation of iron transport and retention showed that the retained iron linearly correlates with injected concentration. The cross-section images revealed that clogging weakened from inlet to outlet. Furthermore, larger aggregates (>40 μm) appeared more often in the rising-declining stages of breakthrough curves, whereas small aggregates (<30 μm) dominated the steady stage. Indeed, relatively preferential flow facilitated the transport and discharge of both large and small iron aggregates. Straining of glass beads especially for the large iron aggregates resulted in a decline in breakthrough. Moreover, the blocking of attached and plugged iron prevented later retention of iron, resulting in a certain concentration of iron in the effluents. Our study provides greater insight into the transport of NZVI.

The removal of lead and nickel from the composted municipal waste and sewage sludge using nanoscale zero-valent iron fixed on quartz

Reducing the concentration of heavy metals including lead (Pb) and nickel (Ni) in organic contaminants such as municipal wastes and sewage sludge is of health and environmental importance. Nanoscale zero-valent iron (NZVI) particles can effectively remove heavy metals from contaminated aqueous and solid media. It was accordingly hypothesized that it is possible to recycle and detoxify organic waste materials containing heavy metals using NZVI and NZVI fixed on quartz (QNZVI). The objective was to investigate the effects of NZVI type, concentration (2% and 5%) and contact time on the removal of Pb and Ni from raw compost, compost fermented with beet molasses, and leachate using a factorial design. The results indicated the significant reduction of DTPA- Pb and DTPA-Ni concentration, in all the organic compounds treated with NZVI and QNZVI (P= 0.01), compared with control. Increased concentration of NZVI in all treatments, increased the rate of DTPA-Pb and DTPA-Ni (P= 0.01) at 113.1% and 180% for Pb (NZVI at 2% and 5%), and at 16.3% and 23.3% for Ni, irrespective of the NZVI type. The reducing trend of extractable Pb and Ni in all the organic compounds was the same, quick reduction at the beginning, followed by a negligible rate. The highest reduction rates for Pb (at one hour) and Ni (at 672h) were equal to 72.93% and 23.27%, respectively. NZVI at 2% was more efficient than NZVI at 5%. There were not any significant differences between NZVI and QNZVI on the removal of Pb and Ni from the organic contaminants. It is possible to immobilize and reduce the concentration of heavy metals such as Pb and Ni in organic contaminants using NZVI, which is affected by NZVI properties, concentration, and contact time, as well as by organic contaminant type.

Reducing As availability in calcareous soils using nanoscale zero valent iron.

Different methods, including the use of nanoscale zero-valent iron (NZVI), have been used to treat arsenic (As)-contaminated environments, with much less data on the use of NZVI in arsenic-calcareous-polluted soils. Accordingly, two different experiments were conducted to investigate the effects of NZVI on the removal of As from three different calcareous-polluted soils. In the first experiment, the effects of soil type (differing in the rate of clay particles and organic carbon including S1 (8.0 and 0.05%), S2 (20 and 0.2%), and S3 (20.5 and 0.8%)) and NZVI concentration (0, 50, and 100g kg-1 of dry soil) on the removal of As extractable with distilled water were evaluated using a factorial design with three replicates. In the second experiment, the NZVI concentrations were reduced to 0, 2.5, 5.0, and 25gkg-1, and the NZVI contact time (0.5, 48, 96, 192, 384, and 768h) was also tested. The analysis of variance in both experiments indicated the significant effects (P<0.01) of the experimental treatments on the removal of As. The concentrations of available As in S3 (42.7mgkg-1), S2 (20.22mgkg-1), and S1 (24.22mgkg-1) after using the 50gkg-1 NZVI treatment decreased to 0, 0, and 0.05mgkg-1, respectively, which was not significantly different from the 100gkg-1 NZVI treatment. In the second experiment, using the 25gkg-1 NZVI treatment, the concentration of available As significantly decreased in S1 from 16.48 to 0.1767mgkg-1, in S2 from 13.34 to 0.31mgkg-1, and in S3 from 33.67 to 0.84mgkg-1. In the three soils, with increasing NZVI concentration and contact time, the concentration of available As in the solution phase significantly decreased (P=0.01). S3, due to a higher rate of organic matter, was less responsive to the NZVI treatments than the other soils. The effectiveness of the nanoremediation method, tested in this research work, on the stabilization of As in calcareous soils, is verified.

Unraveling the impact of nanoscale zero-valent iron on the nitrogen removal performance and microbial community of anammox sludge

Given the increasing use of nanoscale zero-valent iron (NZVI) particles for environmental remediation and wastewater treatment, their potential impact on anaerobic ammonium oxidation (anammox) bacteria was investigated in this study using anammox sludge. Batch assays showed that NZVI concentrations up to 200mgL−1 did not affect anammox activity, reactive oxygen species production, and cell membrane integrity. The nitrogen removal efficiency of the continuous-flow reactor fluctuated in the presence of 20 or 50mgL−1 NZVI, but it could return to normal over time, even at 200mgL−1 NZVI. 16S rDNA-based high-throughput sequencing indicated that although the presence of 10, 20, 50, and 200mgL−1 NZVI to some extent affected microbial composition, the anammox bacteria (Candidatus Kuenenia) never lost its dominance. The abundance of gene families that are related to the assimilation and utilization of iron was down-regulated in response to the stress of high-level NZVI.

Transport of carboxymethyl cellulose-coated zerovalent iron nanoparticles in a sand tank: Effects of sand grain size, nanoparticle concentration and injection velocity

The transport of nanoscale zerovalent iron (NZVI) particles colloidally stabilized with 70,000 Da carboxymethyl cellulose (CMC), through sands with mean grain diameters of 180, 340 and 1140 μm (referred to as fine, intermediate and coarse-sized sand, respectively) was investigated in a 70-cm long, two-dimensional tank. The effect of NZVI concentrations (1 and 3 g-Fe L−1) and CMC concentrations (1 and 2 g L−1) and injection velocities (0.96 and 0.40 cm min−1) on particle transport were also evaluated with the intermediate sand. The overall NZVI mass fractions eluted from the tank were 36%, 25% and 16% in the coarse, intermediate and fine sands, respectively, when injected with 1 g L−1 NZVI stabilized in 1 g L−1 CMC. However, the mass fraction eluted reduced to 2.33% when the injection velocity was reduced from 0.96 to 0.40 cm min−1 in the intermediate-sized sand. Maximum transport efficiency (38% NZVI mass eluted) in the intermediate-sized sand was achieved with 3 g L−1 NZVI suspended in 2 g L−1 CMC at an injection velocity of 0.96 cm min−1. The transport efficiency was substantially decreased (11% NZVI mass eluted) when 3 g L−1 NZVI was stabilized with only 1 g L−1 CMC. The NZVI mean particle diameters in the porewaters remained unchanged at different locations in the tank suggesting that straining or gravity settling did not influence NZVI deposition. After NZVI injection, the hydraulic conductivity in the tank reduced by 80%–96%, depending on the CMC concentration and injection velocity.

Comparison of the transport of the aggregates of nanoscale zerovalent iron under vertical and horizontal flow.

Direct injection of nanoscale zerovalent iron (NZVI) particles is being considered for remediation of contaminated sites. However, the transport characteristics of NZVI under horizontal flow conditions are not fully understood. In this study, NZVI particles were stabilized with carboxymethyl cellulose (CMC) and injected in vertical and horizontal columns to compare the effects of the flow direction on the transport. Columns were packed with sand of mean grain diameters of 180, 340 or 1140 µm (referred to as fine, intermediate and coarse sand, respectively), and were injected with CMC-NZVI suspensions of 0.3, 1 or 3 g Fe L(-1). Experimental breakthrough curves showed that with the coarse and intermediate sands, the steady-state effluent concentration in the horizontal column were up to 84% lower than those in the vertical column regardless of the initial NZVI concentration. However, in the fine sand the differences were insignificant, except at the highest NZVI particle concentration. Additionally, in the horizontally-oriented columns containing the coarse or intermediated sand, NZVI aggregates particles were non-uniformly distributed in the cross-section of the columns and there higher deposition in the bottom-half of the cross-section due to gravity effects. These deposition patterns can be accounted for, in part, by the gravitational settling of the large aggregates of NZVI, especially at high NZVI concentrations. A particle trajectory analysis in three dimensions demonstrated that under horizontal flow, gravity forces resulted in lower deposition of NZVI on the bottom-half of a single collector, as particles approaching the bottom-half of the collector were deflected by gravity to collectors below.

Modified MODFLOW-based model for simulating the agglomeration and transport of polymer-modified Fe0 nanoparticles in saturated porous media.

The solute transport model MODFLOW has become a standard tool in risk assessment and remediation design. However, particle transport models that take into account both particle agglomeration and deposition phenomena are far less developed. The main objective of the present study was to evaluate the feasibility of adapting the standard code MODFLOW/MT3D to simulate the agglomeration and transport of three different types of polymer-modified nanoscale zerovalent iron (NZVI) in one-dimensional (1-D) and two-dimensional (2-D) saturated porous media. A first-order decay of the particle population was used to account for the agglomeration of particles. An iterative technique was used to optimize the model parameters. The model provided good matches to 1-D NZVI-breakthrough data sets, with R 2 values ranging from 0.96 to 0.99, and mass recovery differences between the experimental results and simulations ranged from 0.1 to 1.8%. Similarly, simulations of NZVI transport in the heterogeneous 2-D model demonstrated that the model can be applied to more complicated heterogeneous domains. However, the fits were less good, with the R 2 values in the 2-D modeling cases ranging from 0.75 to 0.95, while the mass recovery differences ranged from 0.7 to 6.5%. Nevertheless, the predicted NZVI concentration contours during transport were in good agreement with the 2-D experimental observations. The model provides insights into NZVI transport in porous media by mathematically decoupling agglomeration, attachment, and detachment, and it illustrates the importance of each phenomenon in various situations. Graphical Abstract ᅟ.

Reactivity of Nanoscale Zero-Valent Iron in Unbuffered Systems: Effect of pH and Fe(II) Dissolution.

While most published studies used buffers to maintain the pH, there is limited knowledge regarding the reactivity of nanoscale zerovalent iron (NZVI) in poorly buffered pH systems to date. In this work, the effect of pH and Fe(II) dissolution on the reactivity of NZVI was investigated during the reduction of 4-nitrophenol (4-NP) in unbuffered pH systems. The reduction rate increased exponentially with respect to the NZVI concentration, and the ratio of dissolved Fe(II)/initial NZVI was related proportionally to the initial pH values, suggesting that lower pH (6-7) with low NZVI loading may slow the 4-NP reduction through acceleration of the dissolution of NZVI particles. Additional experiments using buffered pH systems confirmed that high pH values (8-9) can preserve the NZVI particles against dissolution, thereby enhancing the reduction kinetics of 4-NP. Furthermore, reduction tests using ferrous ion in suspensions of magnetite and maghemite showed that surface-bound Fe(II) on oxide coatings can play an important role in enhancing 4-NP reduction by NZVI at pH 8. These unexpected results highlight the importance of pH and Fe(II) dissolution when NZVI technology is applied to poorly buffered systems, particularly at a low amount of NZVI (i.e., <0.075 g/L).

Effects of nanoscale zero-valent iron particles on biological nitrogen and phosphorus removal and microorganisms in activated sludge

The use of nanoscale zero-valent iron (NZVI) particles in environmental remediation and wastewater treatment has recently increased. The effects of NZVI on nitrogen and phosphorus removal were examined under continuous aerobic/anaerobic conditions by employing activated sludge. NZVI did not display any measurable effect on nitrogen removal at the concentration of 50mg/L and below. However, 200mg/L of NZVI inhibited NH4+-N removal. The addition of NZVI at 20mg/L and above significantly (p<0.05) improved the phosphorous removal. The microbial activities were inhibited upon exposure to NZVI according to the ATP and reactive oxygen species (ROS) results. In comparison to control, the ATP content decreased by around 13%, 31% and 43% at the NZVI doses of 20, 50, and 200mg/L, respectively, probably due to ROS production under NZVI exposure. Lactate dehydrogenase (LDH) release assay suggested that NZVI concentration of 200mg/L cast adverse effects on microorganisms. Interestingly, lower concentrations of NZVI (20 and 50mg/L) boosted the dehydrogenase activity; however, approximately 19% depression in dehydrogenase activity was detected at 200mg/L. The high throughput 16S rDNA pyrosequencing results indicated that uncultured bacterial genera Sinobacteraceae, Xanthomonadaceae, Alcaligenaceae and Propionivibrio were sensitive to NZVI particles.

A New Ultrasound-Assisted Method of Wastewater Treatment By Air-Stable Nanosized Zero-Valent Iron

In this research, the ultrasonic-assisted treatment of multiple model systems by air-stable nanosized zero-valent iron was investigated. The sample of air-stable nanosized zero-valent iron was produced by chemical precipitation of iron (III) at oxide-hydroxide phase, reduction in hydrogen flow at 400 C, and passivation in technical grade nitrogen. The ions of lead (II), copper (II) and zinc (II) were selected as contaminants. The maximum removal rates of the contaminant ions were observed during ultrasonic treatment. The optimum conditions of treatment (nanoscale zero-valent iron concentration and duration of treatment) have been found. The obtained results provide an opportunity of short-term, less reagent, less reagent-consuming ultrasound-assisted treatment for industrial applications.

Aqueous phosphate removal using nanoscale zero-valent iron

Nanoscale zero-valent iron (NZVI) particles have been used for the remediation of a wide variety of contaminants. NZVI particles have high reactivity because of high reactive surface area. In this study, NZVI slurry was successfully used for phosphate removal and recovery. Batch studies conducted using different concentrations of phosphate (1, 5, and 10 mg PO4 3−-P/L with 400 mg NZVI/L) removed ~96 to 100 % phosphate in 30 min. Efficacy of the NZVI in phosphate removal was found to 13.9 times higher than micro-ZVI (MZVI) particles with same NZVI and MZVI surface area concentrations used in batch reactors. Ionic strength, sulfate, nitrate, and humic substances present in the water affected in phosphate removal by NZVI but they may not have any practical significance in phosphate removal in the field. Phosphate recovery batch study indicated that better recovery is achieved at higher pH and it decreased with lowering of the pH of the aqueous solution. Maximum phosphate recovery of ~78 % was achieved in 30 min at pH 12. The successful rapid removal of phosphate by NZVI from aqueous solution is expected to have great ramification for cleaning up nutrient rich waters.

Removal of a Di-Azo Dye Acid Red 73 Synthetic Wastewater by Advanced Fenton Process Based on Nanoscale Zero-Valent Iron

In this study, the removal of a di-azo dye, C.I. Acid Red 73 synthetic wastewater was investigated using advanced Fenton process based on nanoscale zero-valent iron (NZVI) that was synthesized by the aqueous phase borohydride reduction method in the laboratory. NZVI has been characterized by SEM. The influences of NZVI dosage, H2O2 concentration and initial pH value in the process of dye removal by advanced Fenton process were studied in a batch setting. The color removal efficiency was found to be decreased with increase of initial pH, and increased with increase of NZVI and H2O2 concentration. By using proposed process with NZVI dose of 0.02 g/L and H2O2 concentration of 1.0 mM, at 30 min the Acid Red 73 color removal was more than 90%.

Arsenic(V) Removal from Groundwater Using Nano Scale Zero-Valent Iron as a Colloidal Reactive Barrier Material

The removal of As(V), one of the most poisonous groundwater pollutants, by synthetic nanoscale zero-valent iron (NZVI) was studied. Batch experiments were performed to investigate the influence of pH, adsorption kinetics, sorption mechanism, and anionic effects. Field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy were used to characterize the particle size, surface morphology, and corrosion layer formation on pristine NZVI and As(V)-treated NZVI. The HR-TEM study of pristine NZVI showed a core-shell-like structure, where more than 90% of the nanoparticles were under 30 nm in diameter. Mössbauer spectroscopy further confirmed its structure in which 19% were in zero-valent state with a coat of 81% iron oxides. The XRD results showed that As(V)-treated NZVI was gradually converted into magnetite/maghemite corrosion products over 90 days. The XPS study confirmed that 25% As(V) was reduced to As(III) by NZVI after 90 days. As(V) adsorption kinetics were rapid and occurred within minutes following a pseudo-first-order rate expression with observed reaction rate constants (Kobs) of 0.02-0.71 min(-1) at various NZVI concentrations. Laser light scattering analysis confirmed that NZVI-As(V) forms an inner-sphere surface complexation. The effects of competing anions revealed that HCO3-, H4SiO4(0), and H2PO4(2-) are potential interfering agents in the As(V) adsorption reaction. Our results suggest that NZVI is a suitable candidate for As(V) remediation.

Removal of Arsenic(III) from Groundwater by Nanoscale Zero-Valent Iron

Nanoscale zero-valent iron (NZVI) was synthesized and tested for the removal of As(III), which is a highly toxic, mobile, and predominant arsenic species in anoxic groundwater. We used SEM-EDX, AFM, and XRD to characterize particle size, surface morphology, and corrosion layers formed on pristine NZVI and As(III)-treated NZVI. AFM results showed that particle size ranged from 1 to 120 nm. XRD and SEM results revealed that NZVI gradually converted to magnetite/maghemite corrosion products mixed with lepidocrocite over 60 d. Arsenic(III) adsorption kinetics were rapid and occurred on a scale of minutes following a pseudo-first-order rate expression with observed reaction rate constants (K(obs)) of 0.07-1.3 min(-1) (at varied NZVI concentration). These values are about 1000x higher than K(obs) literature values for As(III) adsorption on micron size ZVI. Batch experiments were performed to determine the feasibility of NZVI as an adsorbent for As(III) treatment in groundwater as affected by initial As(III) concentration and pH (pH 3-12). The maximum As(III) adsorption capacity in batch experiments calculated by Freundlich adsorption isotherm was 3.5 mg of As(III)/g of NZVI. Laser light scattering (electrophoretic mobility measurement) confirmed NZVI-As(III) inner-sphere surface complexation. The effects of competing anions showed HCO3-, H4SiO4(0), and H2P04(2-) are potential interferences in the As(III) adsorption reaction. Our results suggest that NZVI is a suitable candidate for both in-situ and ex-situ groundwater treatment due to its high reactivity.