Enhanced Cr(VI) Removal by Nanozerovalent Iron-Immobilized

Article pubs.acs.org/IECR

Enhanced Cr(VI) Removal by Nanozerovalent Iron-Immobilized Alginate Beads in the Presence of a Biofilm in a Continuous-Flow Reactor K. V. G. Ravikumar, Deepak Kumar, Gaurav Kumar, P. Mrudula,* Chandrasekaran Natarajan, and Amitava Mukherjee* Centre for Nanobiotechnology, VIT University, Vellore, Tamil Nadu, India S Supporting Information *

ABSTRACT: Cr(VI) removal was investigated in a fixed-bed column using nanozerovalent iron-immobilized calcium alginate beads (nZVI−C−A beads) and a biofilm formed on nZVI−C−A beads. The removal studies were performed at various initial Cr(VI) concentrations, different flow rates, and bed heights. Under optimal conditions, nZVI−C−A beads showed 91.35 ± 1.57% Cr(VI) removal and 320.66 ± 3.87 mg/g removal capacity. For biofilm-coated nZVI−C−A beads, the removal percentage and removal capacity were found to be 97.84 ± 0.56% and 473.9 ± 4.84 mg/g, respectively. Breakthrough data were successfully described by the Thomas and Yoon−Nelson model for removal of Cr(VI) using nZVI−C−A and a biofilm on nZVI−C−A beads. Cr(VI) sorption on nZVI−C−A beads and biofilm-coated nZVI−C−A beads were confirmed by X-ray diffraction, energy-dispersive analysis of X-rays, and Fourier transform infrared.

1. INTRODUCTION Hexavalent chromium, being the most toxic form of chromium, is a significant environmental pollutant.1 According to the World Health Organization, the concentration of Cr(VI) in drinking water must not exceed 0.05 mg/L.2 The wide release of effluents from leather tanneries, metal finishing industries, and textile industries has resulted in the accumulation of Cr(VI) at higher concentrations in soil and water.3 Traditional types of Cr(VI) removal, including ion exchange, adsorption on alum or activated charcoal, chemical reduction, and precipitation, are not feasible from energy and economic points of view.3 On the other hand, bioremediation using microorganisms appears to be cost-effective and environmentally amiable and also has a promising future.4 Biofilm forms by the attachment of microbial cells to the surface of a substrate.5 The biofilm has important features that help in the adhesion to surfaces and arrangement of a defensive barrier, which provides resistance to biocides and element sorption from the environment. 6 Previous studies on bionanocomposites have proven that the use of bacterial strains (Shewanella oneidensis MR-1, Pseudomonas aeruginosa, etc.) and carbon nanotubes has improved the percentage of Cr(VI) removal in batch studies.7,8 The efficiency of Eschericha coli biofilm on zeolite, kaolin,9 and granular activated carbon (GAC)10 to remediate Cr(VI) has been proven in batch studies. Biofilms of Arthrobacter viscosus on zeolite11 and GAC9 are used in Cr(VI) removal in both batch and continuous-flow systems. Chirwa and Wang12 have utilized the biofilm of Bacillus sp. on GAC and pyrex glass beads for Cr(VI) removal © XXXX American Chemical Society

in column studies. In particular, specific bacteria isolated from the ecosystem of Cr(VI)-contaminated sites are particularly suitable for Cr(VI) because they have high tolerance to Cr(VI), and most of these bacteria are capable of forming a biofilm.13 From the above works, it can be seen that biofilms have the ability to enhance the adsorption of Cr(VI), and thereby its removal, when used in combination with nanoparticles. The use of nanoparticles can be employed for Cr(VI) remediation.1,14 Cr(VI) may readily be reduced to Cr(III) because of its higher redox potential (1.33 V).15,16 Hence, the reduction of Cr(VI) to Cr(III) is a practical approach to remediating Cr(VI) contamination.15,17 Nanozerovalent iron (nZVI) was found to be the most effective adsorbent for the removal of Cr(VI) from aqueous solutions compared to other adsorbents because of its oxidizing property.18−21 The compensation of nZVI over zerovalent iron (ZVI) includes elevated reactive surface area, faster and higher reactivity, and better injectability into aquifers.14 In Europe and the USA, nZVI was considered to be an emerging new option for groundwater (GW) remediation especially for Cr(VI).18 At high concentrations, because of magnetic and van der Waals forces, nZVI tends to agglomerate, which leads to the formation of large particles. Because of the agglomeration phenomenon, there was a decrease of the surface area and reactivity of nZVI, Received: March 14, 2016 Revised: April 30, 2016 Accepted: April 30, 2016

A

DOI: 10.1021/acs.iecr.6b01006 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research which will thereby decrease Cr(VI) removal.21,22 Hence, to overcome the agglomeration of nZVI and increase Cr(VI) removal, in the present study, nZVI was immobilized in calcium alginate beads (nZVI−C−A beads).23 Immobilization of nZVI in sodium alginate is a simple technique and cost-effective. Also, alginate is biodegradable, nontoxic, nonimmunogenic, a waterinsoluble gel, and thermally irreversible.24−26 Because of its porous nature, the solutes diffuse into the beads and come in contact with the entrapped nanoparticles.26 Our previous batch study on Cr(VI) removal using nZVI−C−A beads showed a higher removal percentage and removal capacity compared with other studies.23 Direct application of free nZVI for the removal of contaminants from aqueous or soil environments could also lead to the buildup of iron levels in the environment and possible agglomeration with an overall decrease in the efficiency of the removal of Cr(VI). In this context, immobilizing nZVI will prevent leaching of iron into the aquatic or GW system. Further combination of bioremediation and application of nanoparticles could improve the efficiency of the removal of Cr(VI). In this study, an immobilized bio- and nanocomposite with a specific Cr(VI)-tolerant bacterial consortium (biofilm) isolated from Cr(VI)-contaminated sites and nZVI has been designed, and their efficiency of Cr(VI) removal using this composite system was evaluated. Our current study tries to simulate the formation of a biofilm on a support system (nZVI−C−A beads) and its effect on Cr(VI) removal, which could be more relevant to the scenario in a real contaminated site. Although a few reports are available on the use of immobilized nZVI using alginate and chitosan for Cr(VI) removal in a batch reactor, to the best of our knowledge, none of the prior studies has evaluated Cr(VI) removal using immobilized nZVI in alginate beads in a continuous system. Furthermore, the effect of biofilm formation from a consortium of Cr(VI)-tolerant bacteria in such a continuous system for Cr(VI) removal has been reported in our present study. In the current study, the parameters [flow rate, bed height, and influent Cr(VI)] were optimized to get the highest removal of Cr(VI). Different mathematical models (Adam−Bohart, Thomas, and Yoon−Nelson) were applied to predict breakthrough curves. The efficiency of Cr(VI) removal in Cr(VI)spiked GW and lake water was also studied to determine the applicability of the sorbents in simulated conditions. The developed biofilm on nZVI−C−A beads can be utilized further for remediation of Cr(VI) in real sites through an in situ treatment approach by permeable-reactive-barrier technology.

immobilized in alginate beads by the method described in our previous report.23 Briefly, 0.1 M FeSO4 and 0.05 M disodium salt of EDTA were prepared and mixed, and then 0.75 M NaBH4 was added drop by drop at a speed of 1−2 drops/s into this mixture in a nitrogen atmosphere at 60 °C under vigorous and continuous stirring. The solution turned black as a result of precipitation of nZVI, the solution was filtered, and nZVI nanoparticles were quickly rinsed three times with absolute ethanol and dried. The different concentrations of nZVI colloidal solutions were mixed with a sodium alginate slurry and subjected to sonication for 20 min. The mixture was ejected dropwise into 0.2 M CaCl2 using a 0.55 × 25 mm gauge syringe for polymerization and bead formation. The beads were kept in the polymerizing medium (CaCl2) for 4 h at 4 °C, then washed with distilled water, and stored in distilled water at 4 °C for further use. 2.3. Formation of a Biofilm on nZVI-Immobilized Sodium Alginate Beads. The bacterial consortia (Bacillus subtilis VITSUKMW1, E. coli VITSUKMW3, and Acinetobacter junii VITSUKMW2) were isolated from the chromite mine27 (16S rRNA gene sequences JF309279, JF346549, and JN393206, respectively, deposited in GenBank) and grown together in nutrient broth overnight with agitation at 37 °C. The grown bacterial consortium was passed through a nZVI− C−A beads filled glass column. Because nZVI−C−A beads are not stable in nutrient broth, 0.05 M CaCl2 was added to the nutrient broth medium to stabilize the nZVI−C−A beads. The growth rates of bacterial consortia in nutrient broth and nutrient broth with 0.1 M CaCl2 were estimated. 2.4. Continuous-Flow Studies on Cr(VI) Removal by Sorbents (nZVI−C−A Beads and a Biofilm on nZVI−C−A Beads). Continuous-flow studies were conducted in a glass column with a 2.5 cm internal diameter and a 30 cm length with packed sorbents. Glass wool was used to prevent the loss of void space at the bottom of the glass column. A quartz sand bed was used on top of the sorbent to uniformly spread the mobile phase [Cr(VI) solution] in the column. Cr(VI) removal was done using a packed-bed column by varying the flow rates (0.5, 1, and 1.5 mL/min), initial Cr(VI) concentrations (10, 30, and 50 mg/L), and bed heights (6, 12, and 18 cm) to find out the best values for efficient Cr(VI) removal from the column. The Cr(VI) solution was pumped forward through the column at the desired flow rate by a peristaltic pump (PP 30 EX, Miclins, India). Figure 1 shows the experimental setup for

2. EXPERIMENTAL SECTION 2.1. Materials. Sodium borohydride (NaBH4) and 1,5diphenylcarbazide were procured from SD Fine Chemicals, Mumbai, India. Ferrous sulfate (FeSO4·7H2O) and ethylenediaminetetraacetic acid (EDTA; C10H14N2Na2O8·2H2O) were obtained from Sisco Research Laboratories Pvt. Ltd., India. The Cr(VI) solution for the experiments was prepared by dissolving potassium dichromate (K2Cr2O7; SRL Chemicals Pvt. Ltd., Mumbai, India) in deionized water. Quartz sand (CAS Number 14808-60-7, Sigma-Aldrich), glass wool, and sodium alginate (C6H7O6Na)n were procured from HiMedia Laboratories, Mumbai, India. All of the chemicals used were of analytical-grade, and the solutions were prepared with deionized water. 2.2. Synthesis of nZVI and Immobilization in Calcium Alginate Beads. The nZVI particles were synthesized and

Figure 1. Experimental setup for Cr(VI) removal by nZVI−C−A beads and a biofilm on nZVI−C−A beads in a continuous-flow reactor. B


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as the ratio of the volumetric flow rate Q (cm3/min) to the cross-sectional area of the bed A (cm2). KAB and N0 can be calculated from the linear plot of ln(Ct/C0) against time. 2.6.2. Thomas Model. The Thomas model assumes plugflow behavior in the bed. It is the most general theory that is widely used to describe the performance theory of the sorption process in a fixed-bed column.32 The linearized form of this model can be represented by the following expression:

Cr(VI) removal by wet nZVI−C−A beads and a biofilm on nZVI−C−A beads in a continuous-flow reactor. The nZVI dosage was increased from 1000 to 3000 mg/L and then to 5000 mg/L for attaining maximum removal of Cr(VI) using nZVI−C−A beads. The column experiments were run until exhaustion of the sorbent capacity, and the samples were collected at the exit at different time intervals and analyzed for Cr(VI) by the standard colorimetric 1,5-diphenylcarbazide method.28 The total chromium concentration was determined using a flame atomic absorption spectrophotometer (Analyst400/HGA 900, PerkinElmer, USA) equipped with a 35-mA chromium hollow cathode lamp at a wavelength of 359.9 nm. The entire experiments were carried at constant pH (7) and reaction temperature (27 ± 3 °C). The total amount of metal ions adsorbed in the column (Wad) was calculated from the area under the breakthrough curve (outlet metal concentration vs time) multiplied by the flow rate. The total amount of the metal ions (W) entering the column can be calculated from the equation

W=

C0Fte 1000

⎛ C0 ⎞ KThq0m ln⎜ ⎟= ⎝ C t − 1 ⎠ Q − KThC0t

where KTh = Thomas model constant (mL/min/mg), q0 = adsorption capacity (mg/g), and t = total flow time (min). The values of KTh and q0 can be determined from the linear plot of ln[C0/(Ct − 1)] against t. The Thomas model was suitable for adsorption process, which indicated that the external and internal diffusions were not the limiting steps. 2.6.3. Yoon−Nelson Model. The Yoon−Nelson model is less complicated than the other models and does not require detailed data concerning the characteristics of exchange, the type of exchanger, or the physical properties of the exchange bed. It is based on the hypothesis that the rate of decrease of adsorption for each adsorbate molecule is proportional to the probability of adsorption and adsorbate breakthrough on the adsorbent.33 The linearized model for a single-component system is expressed as

(1)

where C0 = inlet metal-ion concentration (mg/L), F = volumetric flow rate (mL/h), te = exhaustion time (h), and M = mass of the sorbent. The total metal removal (%) and removal capacity (mg/g) can be calculated from eqs 2 and 3).29 total metal removal (%) =

Wad × 100 W

W removal capacity q (mg/g) = ad M

⎛ Ct ⎞ ln⎜ ⎟ = KYNt − τKYN ⎝ C0 − C t ⎠

(2)

(6)

where KYN = rate constant (min) and s = time required for 50% adsorbate breakthrough (min). A linear plot of ln[Ct/(C0 − Ct)] against t was used to determine the values of KYN and τ from the intercept and slope of the plot, respectively. 2.7. Characterization of nZVI−C−A Beads and a Biofilm on nZVI−C−A Beads. 2.7.1. X-ray Diffraction (XRD). Powder XRD analysis was performed using a Bruker Advanced D8 (Germany) diffractometer using Cu Kα radiation (λ = 1.5418 Å) to identify the structure and composition of Cr(VI)-interacted and noninteracted nZVI−C−A beads and a biofilm on nZVI−C−A beads. Each sample was scanned within the range of 20−80°. 2.7.2. Scanning Electron Microscopy (SEM). The surface morphologies of Cr(VI)-interacted and noninteracted nZVI− C−A beads and a biofilm on nZVI−C−A beads were observed by a FEI QUANTA scanning electron microscope. The samples were mounted on metal stubs using carbon tape and sputtercoated with gold in an argon atmosphere for 1 h before analysis. 2.7.3. Energy-Dispersive Analysis of X-rays (EDX). Surface elemental analyses of nZVI−C−A beads and a biofilm on nZVI−C−A beads interacted with Cr(VI) were done by EDX spectroscopy. The gold sputtering was done before analysis of the samples. 2.7.4. Fourier Transform Infrared (FTIR) Analysis. The surface chemical characteristics of nZVI−C−A beads and a biofilm on nZVI−C−A beads before and after interaction with Cr(VI) were found by a FTIR spectrometer (IR Affinity-1, Shimadzu, Japan). Attenuated total reflection of the spectrometer was employed to analyze the powder samples in their native form. The spectra were recorded from 4000 to 600 cm−1. 2.8. Cr(VI) Removal in Environmental Water Matrixes (Lake Water and GW). Water samples were collected from

(3)

2.5. Viability of Biofilm Cells through Fluorescence Microscopy. The viability of cells after interaction with Cr(VI) was estimated by fluorescence microscopy (Leica DM-2500). The cells were stained with acridine orange (AO) and ethidium bromide (EtBr) according to the protocol described by Jakopec et al. with minor modifications.30 AO (5 μL) and EtBr (5 μL) were added to Cr(VI)-interacted biofilm cells (500 μL) and incubated for 5 min at room temperature. The cell suspension was centrifuged at 6000 rpm for 10 min, the supernatant was discarded to remove unbound dyes, and the pellet was washed with a PBS buffer. One drop of the washed pellet was taken on the glass slide and examined under a fluorescence microscope. The dark condition was maintained to avoid photobleaching. Fluorescence was observed using BP 450-490 and LP 590 filters, and the images were captured and processed using a Leica DFC-295 camera. 2.6. Modeling of Column Data for Cr(VI) Removal by Sorbents. 2.6.1. Adams−Bohart Model. In 1920, Bohart and Adams described the relationship between Ct/C0 and t in a continuous system, which was named the Adams−Bohart model. It is used for relating the initial part of the breakthrough curve.31 The model can be represented as ⎛C ⎞ ⎛Z⎞ ln⎜ t ⎟ = kABC0t − KABN0⎜ ⎟ ⎝ C0 ⎠ ⎝ U0 ⎠

(5)

(4)

where C0 and Ct = influent and effluent concentration (mg/L), kAB = kinetic constant (L/mg/min), N0 = saturation concentration (mg/L), Z = bed depth of the fix-bed column (cm), and U0 = superficial velocity (cm/min), which is defined C


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Figure 2. Cr(VI) removal using nZVI−C−A beads: experimental breakthrough curves and simulated model results for (A) different flow rates, (C) different initial Cr(VI) concentrations, and (E) different bed heights. Cr(VI) removal using a biofilm formed on nZVI−C−A beads: experimental breakthrough curves and simulated model results for (B) different flow rates, (D) different initial Cr(VI) concentrations, and (F) different bed heights.

to 320.66 ± 3.87 mg/g) (Table S1). The effect of different flow rates, initial Cr(VI) concentrations, and bed heights was evaluated in a packed column with 5000 mg/L nZVI−C−A beads. An increase in the nZVI concentration causes a decrease in the biofilm formation (1000 mg/L, 296 × 10−3 CFU/cm2; 3000 mg/L, 196 × 10−3 CFU/cm2; 5000 mg/L, 76 × 10−3 CFU/cm2) after 72 h. A higher concentration of nZVI in calcium alginate beads showed greater inhibition of biofilm growth.23,34 Hence, for Cr(VI) removal, 1000 mg/L nZVI was used for biofilm formation. All of the experiments were done in natural condition at pH 7 and a temperature of 27 ± 3 °C. After interaction of the biofilm with Cr(VI), the viable cell count of the biofilm was found to be 183 × 10−3 CFU/cm2, and the ratio of live/dead cells was found to be decreased to 38.18%. Because of the high Cr(VI) resistance of these bacterial strains, the biofilm exhibited good viability even after treatment with Cr(VI). 3.1.3. Effect of the Flow Rates. In order to determine the optimal contact time for Cr(VI) adsorption and removal in the column, the effects of different flow rates (0.5, 1, and 1.5 mL/ min) using two sorbents at a constant bed height (18 cm) and an initial influent Cr(VI) concentration of 10 mg/L were investigated. The breakthrough time and percentage of Cr(VI) removal dropped from 234 to 74 min and from 91.35 ± 1.57 to 73.67 ± 1.29%, respectively, when the flow rates increased from 0.5 to 1.5 mL/min (Figure 2A). However, in the presence of a biofilm, the breakthrough time increased significantly, and with an increase in the flow rate from 0.5 to 1.5 mL/min, decreases in the breakthrough time (from 440 to 120 min) and removal percentage (from 97.84 ± 0.56 to 78.28 ± 3.07%) were observed (Figure 2B). Parts A and B of Figure 2 indicate that the saturation and breakthrough times for Cr(VI) removal in nZVI−C−A and biofilm-coated beads decrease significantly (p

different locations around Vellore. The GW and lake water samples were collected from Sipcot and VIT University Vellore, respectively. The removal of Cr(VI)-spiked environmental water samples was carried out at optimal conditions [initial Cr(VI) concentration = 10 mg/L, flow rate = 0.5 mL/min, and bed height = 18 cm]. 2.9. Statistical Analysis. All of the experiments were performed in triplicate, and the data are given as mean ± standard deviation error. The data were analyzed by Student’s t test using Graph pad prism 5.0 with p < 0.05 to obtain the statistical significance.

3. RESULTS AND DISCUSSION 3.1. Continuous-Flow Studies of Cr(VI) Removal by Sorbents. 3.1.1. Biofilm Formation. The biofilm estimation was done by the plate−count method. After 24 h, the bacterial consortia cell count was found to be 287 × 10−3 CFU/mL (nutrient broth) and 278 × 10−3 CFU/mL (nutrient broth with 0.05 M CaCl2). There was no significant variation in the growth of bacterial consortia in the nutrient broth with and without CaCl2. However, nutrient broth with CaCl2 was chosen for the rest of the experiment because the nZVI−C−A beads were stable only under the presence of CaCl2. The cell counts in the biofilm on nZVI−C−A beads were found to be 148 × 10−3 CFU/cm2 (after 24 h), 221 × 10−3 CFU/cm2 (after 48 h), and 296 × 10−3 CFU/cm2 (after 72 h) at a flow rate of 1 mL/min. These results showed that 72 h was the most suitable condition for the formation of a biofilm on nZVI−C−A beads. 3.1.2. Effect of the nZVI Concentration in Calcium Alginate Beads. In the present study, as the nZVI concentration (from 1000 to 5000 mg/L) in calcium alginate beads increases, there was an increase in the breakthrough time (from 140 to 234 min), removal percentage (from 70.28 ± 3.39 to 91.35 ± 1.57%), and removal capacity (from 181.53 ± 3.62 D


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Table 1. Comparison of Cr(VI) Removal Capacities of Iron Nanoparticles and a Biofilm As Reported with the Current Study serial no. 1

sorbent used

2 3 4 5 6

iron-grown carbon nanofibers containing porous carbon microbeads chitosan beads supported Fe(0) nanoparticles E. coli biofilm supported on kaolin nZVI/graphene nanosheets nZVI nZVI−C−A beads

7

biofilm on nZVI−C−A beads

sorbent dosage (mg/L) 100 10000

pH

temperature (°C)

initial Cr(VI) concentration (mg/L)

removal capacity (mg/g)

5

30

10−150

6.40

20 37

20 116 25 0.90 10

44.80 4.60 21.72 47.20 320.66 ± 3.87

10

473.90 ± 4.84

1000 0.30 5000

2 3 7

1000

7

> 0.05) at higher flow rates because of insufficient solute interaction time.35,36 3.1.4. Effect of the Initial Cr(VI) Concentrations. In order to test the effect of the initial Cr(VI) concentration (from 10 to 50 mg/L) on Cr(VI) removal, Cr(VI) samples were collected at varying times (3 min) at a constant bed height (18 cm) and flow rate (0.5 mL/min), and the Cr(VI) content was estimated by a diphenylcarbazide test. Decreases in the breakthrough time (from 234 to 132 min) and removal percentage (from 91.35 ± 1.57 to 26.27 ± 1.97%) were observed with increasing initial Cr(VI) concentrations (Figure 2C). For biofilm-coated beads, the breakthrough time and Cr(VI) removal decreased from 440 to 200 min and from 97.84 ± 0.56 to 48.67 ± 1.77%, respectively (Figure 2D), with an increase in the initial Cr(VI). The increased removal percentage with an increase in the initial Cr(VI) concentration indicated that the higher influent concentration could saturate the biosorbent more quickly.13 These results are in disagreement with the conclusions of other studies, in which a positive correlation was found between the removal capacity and initial influent Cr(VI) concentration,37 but these results could not be compared on the same scale as those from batch experiments. However, the results clearly showed that there was significant (p > 0.05) Cr(VI) removal using nZVI−C−A and biofilm-coated beads at different influent initial Cr(VI) concentrations. 3.1.5. Effect of the Bed Heights. The effect of various bed heights filled with nZVI−C−A beads from 6 to 18 cm was investigated at a constant flow rate (0.5 mL/min) and initial influent Cr(VI) concentration (10 mg/L). Figure 2E shows the breakthrough graph of Cr(VI) removal at three different bed heights. The results indicate that the breakthrough time and percentage removal of Cr(VI) increased from 114 to 234 min and from 42.37 ± 1.51 to 91.35 ± 1.57%, respectively, with an increase in the bed heights from 6 to 18 cm. For a biofilm on nZVI−C−A beads, the breakthrough time increased from 170 to 440 min as the bed height increased from 6 to 18 cm. The Cr(VI) removal percentage also increased from 66.69 ± 1.54 to 97.84 ± 0.56% (Figure 2F). This can be explained by the increase in the amount of sorbents in the column, which correlates with an increase in the number of binding sites. The obtained experimental results showed that an increase in the bed height (6 to 18 cm) increased the removal capacity from 114.50 ± 5.32 to 321.66 ± 2.86 mg/g in nZVI−C−A beads. For a biofilm on nZVI−C−A beads, the removal capacity was increased from 218.93 ± 4.48 to 478.90 ± 3.04 mg/g. These results support the conclusions of other studies.36,37 The results demonstrated that there was a significant (p > 0.05) difference in the Cr(VI) removal using

24.10 room temperature room temperature

45.00

ref 1 46 9 47 17 current study current study

nZVI−C−A beads and a biofilm on nZVI−C−A beads at different bed heights. 3.2. Optimal Conditions for Cr(VI) Removal Using Sorbents. Column study of calcium alginate beads at optimal conditions (flow rate = 0.5 mL/min, initial Cr(VI) concentration = 10 mg/L, and bed height = 18 cm) showed 9.76 ± 1.96% of Cr(VI) removal and 12 ± 1.90 mg/g removal capacity. In the case of a biofilm on alginate beads, the Cr(VI) removal percentage and removal capacity were observed to be 49.50 ± 1.44% and 199.22 ± 3.47 mg/g, respectively, at optimal conditions. Column studies showed that the optimal conditions for removal of Cr(VI) using nZVI−C−A beads were found to be of 5000 mg/L nZVI concentration, 10 mg/L influent Cr(VI), 18 cm bed height, and 0.5 mL/min flow rate. The removal of 91.35 ± 1.57% and capacity of 320.66 ± 3.87 mg/g were observed at the optimal conditions. Removal of Cr(VI) in the presence of a biofilm on nZVI− C−A beads was maximum under optimal conditions (1000 mg/L nZVI on C−A beads, 10 mg/L influent Cr(VI), 18 cm bed height, and 0.5 mL/min flow rate). Higher Cr(VI) removal percentage (97.84 ± 0.56%) and capacity (473.90 ± 4.84 mg/ g) were found at optimal conditions. Moreover, nZVI−C−A beads (1000 mg/L) without a biofilm showed 70.28 ± 3.39% of Cr(VI) removal and 181.53 ± 3.62 mg/g of removal capacity. The current results demonstrate that the removal percentage and removal capacity of Cr(VI) were enhanced in the presence of a biofilm on nZVI−C−A beads. Compared to other studies using Fe(0) nanoparticle containing carbon nanofibers1 and calcium alginate immobilized Bacillus sp.38 for Cr(VI) removal, the current study shows high removal percentages and removal capacities (Table 1). The cell viability of biofilm was confirmed by live−dead cell discrimination assay. AO and EtBr stains were added to the interacted biofilm and were observed under a fluorescent microscope. Two types of cells were observed i.e. green colored cells, which were viable and orange colored cells that were dead (Figure 3). The results confirm that the cells of the biofilm were viable after interaction with Cr(VI). 3.3. Modeling of the Breakthrough Curves. The explanation of the initial part of breakthrough curves for Cr(VI) removal was investigated using the saturation concentration (N0) and kinetic constant (KAB) calculated from the Adams−Bohart adsorption model (Table S2). The values of correlation coefficients (R2) were found to be below 0.90 under all conditions. Table S2A indicates that N0 of the fixed bed increased with increasing initial Cr(VI) concentration (10, 30, and 50 mg/L) but decreased with increasing bed height (6, 12, and 18 cm) and flow rate (0.5, 1, and 1.5 mL/min). E


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with Cr(VI). XRD analyses of Cr(VI)-interacted and noninteracted nZVI−C−A beads and a biofilm on nZVI−C−A beads are shown in Figure 4. The nZVI−C−A beads show a 2θ

Figure 3. Fluorescence image of Cr(VI)−interacted biofilm.

However, KAB decreased with increasing initial Cr(VI) concentration and bed height and increased with increasing flow rate. As indicated from Table S2B, the biofilm-coated beads also showed a similar trend. These results indicate that the overall system kinetics was dominated by the external mass transfer in the early part of the sorption process in fixed-bed experiments.39 Therefore, the bed height should be higher while the flow rate should be lower to achieve better saturation concentration (N0) and lower kinetic constant (KAB) values for the column. The Thomas model for the column data could provide more accurate predictions of the breakthrough curve (R2> 0.9) and column uptake obtained for Cr(VI) removal at different flow rates (0.5, 1, and 1.5 mL/min) (Table S3A). The Thomas rate constant, KTh, decreased at a higher flow rate of Cr(VI) solution passing through the column. A similar type of trend has also been observed in a previous report upon the removal of Cu(II) using rice husk based activated carbon.40 However, for a biofilm-coated bead, the KTh value increased with increasing flow rate (Table S3B).13 In both sorbents, the removal capacity (q0) decreased with increasing flow rate of Cr(VI). The Thomas model was more suitable for relating the adsorption process, wherein external and internal diffusions were not the limiting steps13,40 because of the better fit (higher R2) for the two sorbents compared to the Adams−Bohart model. From these results, we can conclude that the external and internal diffusions are not the limiting steps for Cr(VI) removal using nZVI−C−A and biofilm-coated beads in a continuous-flow column. The Yoon−Nelson model was functional to explore the breakthrough behavior of Cr(VI) on the two sorbents. The rate constant (KYN) was found to increase with increasing initial Cr(VI) concentrations and decrease with increasing bed heights, whereas the τ value showed an opposite trend (Table S4A). A similar type of trend was also observed for biofilm-coated beads (Table S4B). In both cases, the τ values were found to be much lower than the experimental t values at 50% breakthrough for the different conditions tested, indicating that the Yoon−Nelson model is not very accurate in predicting the t value because of its relative simplicity.37 3.4. Characterization of nZVI−C−A Beads and a Biofilm on nZVI−C−A Beads before and after Reaction

Figure 4. XRD graphs of A) nZVI−C−A beads, (B) a biofilm on nZVI−C−A beads, (C) Cr(VI)-interacted nZVI−C−A beads, and (D) a Cr(VI)-interacted biofilm on nZVI−C−A beads.

peak at 46.27° (Figure 4A), which corresponds to the (110) phase of the body-centered-cubic (BCC) structure of iron. Further, the obtained results were compared with the database of JCPDS (no. 00-006-0696), which confirmed the presence of nZVI. The results also showed other peaks, which correspond to the calcium alginate beads reported by Kim et al.22 XRD for a biofilm on nZVI−C−A beads (Figure 4B) indicates the high-intensity peak at 47.43°, which corresponds to the (110) phase of the BCC of iron (JCPDS no. 00-0060696). The results obtained from XRD showed that the presence of nZVI in a biofilm on nZVI−C−A beads and a few other 2θ peaks at 35.68° correspond to the iron oxide layer on nZVI, bacterial cells, and calcium alginate beads.41 The XRD patterns for nZVI−C−A beads and a biofilm on nZVI−C−A beads after interaction with Cr(VI) (Figure 4C,D) indicate the presence of Fe2O3 (2θ = 35.68° and 55.62°), Fe3O4 (2θ = 35.45° and 65.76°), and Cr2FeO4 (2θ = 35.50°).42 The appearance of Fe(II), Fe(III), and Cr(III) in nZVI−C−A beads and a biofilm on nZVI−C−A beads after reaction demonstrated the occurrence of redox reactions between Fe(0) and Cr(VI), where nZVI particles were acting as reductants, which is an agreement with the previous literature.43 Figure 5 shows SEM images of nZVI−C−A beads and a biofilm on the nZVI−C−A beads. The average sizes of nZVI− C−A wet and dry beads (Figure 5A) were found to be 2 ± 0.2 and 1 ± 0.5 mm, respectively. The rough surface was observed in nZVI−C−A beads (Figure 5B). After interacting with Cr(VI), the nZVI−C−A wet and dry beads (Figure 5C) were observed to be similar, but there was a change in the surface. The surface of the nZVI−C−A beads was found to be smooth (Figure 5D); this is due to the adsorption of Cr ions onto the surface of the nZVI−C−A beads. According to the SEM image, the size of a dry biofilm on nZVI−C−A beads was in the range of 1 ± 0.7 mm (Figure 5E), whereas the average wet bead size was found to be 2 ± 0.5 mm. The surface of a biofilm on nZVI−C−A beads was observed to F


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Figure 6. FTIR spectra of (A) nZVI−C−A beads, (B) Cr(VI)interacted nZVI−C−A beads, (C) a biofilm on nZVI−C−A beads, and (D) a Cr(VI)-interacted biofilm on nZVI−C−A beads.

Figure 5. SEM images of (A) nZVI−C−A beads and (B) surface, (C) Cr(VI)-interacted nZVI−C−A beads and (D) surface, (E) a biofilm on nZVI−C−A beads and (F) surface, and (G) a Cr(VI)-interacted biofilm on nZVI−C−A beads and (H) surface. EDX results of (I) nZVI−C−A beads, (J) Cr(VI)-interacted nZVI−C−A beads, (K) a biofilm on nZVI−C−A beads, and (L) a Cr(VI)-interacted biofilm on nZVI−C−A beads.

decreases in the peaks at 3316 cm−1 (hydroxyl), 1479 cm−1 (carbonyl), and 1621 cm−1 (carboxyl) are noted. The decrease in the adsorption peak intensity (% T) was due to the electrostatic attraction between the Cr(VI) ions and the beads.13,26 Further, the intensity (% T) of the peak at 1039 cm−1 was observed to be decreased, which is due to the complexation of Cr ions.44 In addition to this, the adsorption peak appeared at 796 cm−1 after interaction with Cr(VI) representing Cr−O vibrations (Figure 6B), as reported by Dhal et al.45 and Samuel et al.27 Similarly, the adsorption peaks were observed for a biofilm on nZVI−C−A beads (Figure 6C) and a Cr(VI)-interacted biofilm on nZVI−C−A beads (Figure 6D). After interaction of a biofilm on nZVI−C−A beads with Cr(VI), the intensities (% T) of the peaks at 3320, 1464, and 1027 cm−1 were decreased.23 The peak intensities (% T) at 2369 and 1620 cm−1 were observed to be increased and decreased, respectively. Moreover, a new absorption peak corresponding to Cr−O vibrations at 762 cm−1 was observed.45 The Cr−O peaks at 796 cm−1 of nZVI−C−A beads and 762 cm−1 in a biofilm on nZVI−C−A beads confirm the presence of Cr ion on the sorbent surface. Determination of Cr(VI) concentrations in the influent and effluent Cr(VI) from the continuous-flow studies showed that effluent Cr(VI) was lower than influent Cr(VI) (Figure 7). To investigate whether a part of Cr(VI) was reduced to Cr(III) and remained in the dissolved phase, the concentration of dissolved Cr(III) was determined using the following equation:23

be rough (Figure 5F); this is due to the presence of bacterial consortia (biofilm). The average thickness of a biofilm on nZVI−C−A beads was observed to be 0.3 ± 0.08 mm. After interaction with Cr(VI) in the column, there was a slight decrease in the bead size (Figure 5G), and the presence of biofilm cells was observed on nZVI−C−A beads (Figure 5H). The elemental composition of nZVI−C−A beads (Figure 5I) and a biofilm on nZVI−C−A beads (Figure 5J) were analyzed by EDX spectroscopy. EDX results showed the presence of C, O, Na, Cl, Ca, and Fe elements in nZVI−C−A beads and a biofilm on nZVI−C−A beads. After exposure to Cr(VI), the presence of a Cr ion was observed in nZVI−C−A beads and a biofilm on nZVI−C−A beads (Figure 5K,L). The weight percentages of Cr ions present on the surface of nZVI−C−A beads and a biofilm on nZVI−C−A beads were found to be 1.11 and 2.87 wt %, respectively. The weight percentage of Cr ion on the surface of a biofilm on nZVI−C−A beads was found to be high compared with that of nZVI−C−A beads. It may be due to adsorption of Cr(VI) by the biofilm cells. Thus, the EDX result confirmed that nZVI and a biofilm were involved in the Cr(VI) removal process. Figure 6 shows the FTIR spectra of nZVI−C−A beads (Figure 6A), the respective functional groups of which take part in the adsorption process. Significant changes of the adsorption bands were observed in the functional groups before and after interactions with Cr(VI) (Figure 6B). The broad absorption peaks at 3316 and 3325 cm−1 suggested that the presence of a hydroxyl group (−OH), and the adsorption peaks at 2341 and 2349 cm−1 were due to a C−H stretching band present in sodium alginate.13 The adsorption peaks at 1634 and 1420 cm−1 denoted the presence of carboxyl (asymmetric stretching) and C−O (stretching vibration) groups, respectively.26 The resulting FTIR spectra were recorded for nZVI−C−A beads before and after interaction with Cr(VI) (Figure 6A,B), and

Cr(III) in an effluent = total Cr in an effluent (AAS) − Cr(VI) in an effluent (DPC)

(8)

Figure 7A shows that there was more reduction in Cr(VI) during the removal process using nZVI−C−A beads compared with the results of a biofilm on nZVI−C−A beads (Figure 7B). For Cr(VI) removal using a biofilm on nZVI−C−A beads, the experimental results showed that there was less reduction and G


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different natural water samples because it does not show much difference in the Cr(VI) removal percentage compared with distilled water.

4. CONCLUSIONS The removal of Cr(VI) using nZVI−C−A beads and biofilmcoated nZVI−C−A beads in fixed-bed column modes was investigated as a function of the different flow rates, initial Cr(VI) concentrations, and bed heights. The results demonstrated that the removal percentage and removal capacity of Cr(VI) were enhanced in the presence of a biofilm on nZVI− C−A beads compared with bare nZVI−C−A beads. Mathematically, the breakthrough data presented a good match with the Thomas and Yoon−Nelson models. The efficiency of metal removal in Cr(VI)-spiked GW and lake water was also studied to determine the applicability of the sorbent in real conditions. The developed sorbents were successfully employed for Cr(VI) removal in Cr(VI)-spiked environmental water.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b01006. Cr(VI) removal using different concentrations of nZVI, nZVI−C−A beads, and a biofilm on nZVI−C−A beads and parameters for the Adams−Bohart, Thomas, and Yoon−Nelson models (PDF)

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Figure 7. Concentration of dissolved chromium species in influent and effluent solutions for removal of Cr(VI) using (A) nZVI−C−A beads and (B) a biofilm on nZVI−C−A beads.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected] or [email protected]. Tel.: +91 416 220 2620.

more adsorption of Cr(VI). These results revealed that, in nZVI−C−A beads, the removal of Cr(VI) was mainly in the reduction process by nZVI. In the case of a biofilm on nZVI− C−A beads, a Cr(VI) removal process was performed through both adsorption by biofilm cells and reduction by nZVI. 3.5. Cr(VI) Removal in Environmental Water Matrixes. To the collected natural water was added 10 mg/L Cr(VI), and an experiment was performed to remove Cr(VI) in the column for estimating the potential application of the two sorbents. For Cr(VI)-spiked lake water, the removal percentage and removal capacity were experimentally found to be 85.42 ± 2.01% and 259.94 ± 2.34 mg/g, respectively, whereas for GW, the values were 80.91 ± 1.12% and 264.53 ± 4.2 mg/g using nZVI−C−A beads. The breakthrough curve was found to be 216 min for lake water and 222 min for GW. Using a biofilm on nZVI−C−A beads, the Cr(VI) removal percentage and removal capacity were experimentally found to be 83.13 ± 2.3% and 339.95 ± 5.25 mg/g in Cr(VI)-spiked lake water and 87.43 ± 1.85% and 387.89 ± 5.13 mg/g in Cr(VI)spiked GW, respectively. The breakthrough curves for Cr(VI)spiked samples were found to be 360 min for lake water and 440 min for GW. Compared to Cr(VI) removal using sorbents in distilled deionized water, the removal percentage was decreased by 10− 15% in Cr(VI)-spiked environmental water samples. The presence of natural colloids in the environmental water samples could be a reason for the reduced removal percentage and removal capacity.23 The experimental results suggest that the developed sorbents could be employed in Cr(VI) removal from

Notes

In this study, neither human participants nor animals were involved. The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the Department of Science and Technology− Science and Engineering Research Board (Grant SB/S3/ME/ 0019/13), Government of India, for providing a grant throughout this research work.

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REFERENCES

(1) Talreja, N.; Kumar, D.; Verma, N. Removal of hexavalent chromium from water using Fe-grown carbon nanofibers containing porous carbon microbeads. J. Water Process Eng. 2014, 3, 34−45. (2) Oze, C.; Bird, D. K.; Fendorf, S. Genesis of hexavalent chromium from natural sources in soil and groundwater. Proc. Natl. Acad. Sci. U. S. A. 2007, 104 (16), 6544−6549. (3) Agarwal, G.; Bhuptawat, H. K.; Chaudhari, S. Biosorption of aqueous chromium (VI) by Tamarindus indica seeds. Bioresour. Technol. 2006, 97 (7), 949−956. (4) Lin, Y.-H.; Wu, C.-L.; Li, H.-L.; Hsu, C.-H. Verification of model for adsorption and reduction of chromium (VI) by Escherichia coli 33456 using chitosan bead as a supporting medium. Appl. Math. Model. 2011, 35 (6), 2736−2751. (5) Kokare, C.; Chakraborty, S.; Khopade, A.; Mahadik, K. Biofilm: Importance and applications. Indian J. Biotechnol. 2009, 8 (2), 159− 168. (6) Comte, S.; Guibaud, G.; Baudu, M. Biosorption properties of extracellular polymeric substances (EPS) resulting from activated

H


Article

Industrial & Engineering Chemistry Research sludge according to their type: soluble or bound. Process Biochem. 2006, 41 (4), 815−823. (7) Yan, F.-F.; Wu, C.; Cheng, Y.-Y.; He, Y.-R.; Li, W.-W.; Yu, H.-Q. Carbon nanotubes promote Cr (VI) reduction by alginateimmobilized Shewanella oneidensis MR-1. Biochem. Eng. J. 2013, 77, 183−189. (8) Pang, Y.; Zeng, G.-M.; Tang, L.; Zhang, Y.; Liu, Y.-Y.; Lei, X.-X.; Wu, M.-S.; Li, Z.; Liu, C. Cr (VI) reduction by Pseudomonas aeruginosa immobilized in a polyvinyl alcohol/sodium alginate matrix containing multi-walled carbon nanotubes. Bioresour. Technol. 2011, 102 (22), 10733−10736. (9) Quintelas, C.; Rocha, Z.; Silva, B.; Fonseca, B.; Figueiredo, H.; Tavares, T. Removal of Cd (II), Cr (VI), Fe (III) and Ni (II) from aqueous solutions by an E. coli biofilm supported on kaolin. Chem. Eng. J. 2009, 149 (1), 319−324. (10) Gabr, R. M.; Gad-Elrab, S. M.; Abskharon, R. N.; Hassan, S. H.; Shoreit, A. A. Biosorption of hexavalent chromium using biofilm of E. coli supported on granulated activated carbon. World J. Microbiol. Biotechnol. 2009, 25 (10), 1695−1703. (11) Silva, B.; Figueiredo, H.; Quintelas, C.; Neves, I. C.; Tavares, T. Zeolites as supports for the biorecovery of hexavalent and trivalent chromium. Microporous Mesoporous Mater. 2008, 116 (1), 555−560. (12) Chirwa, E. M.; Wang, Y.-T. Hexavalent chromium reduction by Bacillus sp. in a packed-bed bioreactor. Environ. Sci. Technol. 1997, 31 (5), 1446−1451. (13) Samuel, J.; Pulimi, M.; Paul, M. L.; Maurya, A.; Chandrasekaran, N.; Mukherjee, A. Batch and continuous flow studies of adsorptive removal of Cr (VI) by adapted bacterial consortia immobilized in alginate beads. Bioresour. Technol. 2013, 128, 423−430. (14) Li, X.-q.; Elliott, D. W.; Zhang, W.-x. Zero-valent iron nanoparticles for abatement of environmental pollutants: materials and engineering aspects. Crit. Rev. Solid State Mater. Sci. 2006, 31 (4), 111−122. (15) Geranio, L. Review of zero valent iron and apatite as reactive materials for permeable reactive barrier. Term Paper, 2007, Vol. 7. (16) Loyaux-Lawniczak, S.; Refait, P.; Ehrhardt, J.-J.; Lecomte, P.; Génin, J.-M. R. Trapping of Cr by formation of ferrihydrite during the reduction of chromate ions by Fe (II)-Fe (III) hydroxysalt green rusts. Environ. Sci. Technol. 2000, 34 (3), 438−443. (17) Nahuel Montesinos, V.; Quici, N.; Beatriz Halac, E.; Leyva, A. G.; Custo, G.; Bengio, S.; Zampieri, G.; Litter, M. I. Highly efficient removal of Cr (VI) from water with nanoparticulated zerovalent iron: Understanding the Fe (III)−Cr (III) passive outer layer structure. Chem. Eng. J. 2014, 244, 569−575. (18) Mueller, N. C.; Braun, J.; Bruns, J.; Č erník, M.; Rissing, P.; Rickerby, D.; Nowack, B. Application of nanoscale zero valent iron (NZVI) for groundwater remediation in Europe. Environ. Sci. Pollut. Res. 2012, 19 (2), 550−558. (19) Singh, R.; Misra, V.; Singh, R. P. Synthesis, characterization and role of zero-valent iron nanoparticle in removal of hexavalent chromium from chromium-spiked soil. J. Nanopart. Res. 2011, 13 (9), 4063−4073. (20) Ramazanpour Esfahani, A.; Hojati, S.; Azimi, A.; Farzadian, M.; Khataee, A. Enhanced hexavalent chromium removal from aqueous solution using a sepiolite-stabilized zero-valent iron nanocomposite: Impact of operational parameters and artificial neural network modeling. J. Taiwan Inst. Chem. Eng. 2015, 49, 172−182. (21) Bezbaruah, A. N.; Krajangpan, S.; Chisholm, B. J.; Khan, E.; Elorza Bermudez, J. J. E. Entrapment of iron nanoparticles in calcium alginate beads for groundwater remediation applications. J. Hazard. Mater. 2009, 166 (2), 1339−1343. (22) Kim, H.; Hong, H.-J.; Jung, J.; Kim, S.-H.; Yang, J.-W. Degradation of trichloroethylene (TCE) by nanoscale zero-valent iron (nZVI) immobilized in alginate bead. J. Hazard. Mater. 2010, 176 (1), 1038−1043. (23) Ravikumar, K.; Kumar, D.; Rajeshwari, A.; Madhu, G.; Mrudula, P.; Chandrasekaran, N.; Mukherjee, A. A comparative study with biologically and chemically synthesized nZVI: applications in Cr (VI) removal and ecotoxicity assessment using indigenous microorganisms

from chromium-contaminated site. Environ. Sci. Pollut. Res. 2016, 23 (3), 2613−2627. (24) Yang, L.; Shi, J.; Zhou, X.; Cao, S. Hierarchically organization of biomineralized alginate beads for dual stimuli-responsive drug delivery. Int. J. Biol. Macromol. 2015, 73, 1−8. (25) Karthik, R.; Meenakshi, S. Removal of Cr (VI) ions by adsorption onto sodium alginate-polyaniline nanofibers. Int. J. Biol. Macromol. 2015, 72, 711−717. (26) Gopalakannan, V.; Viswanathan, N. Synthesis of magnetic alginate hybrid beads for efficient chromium (VI) removal. Int. J. Biol. Macromol. 2015, 72, 862−867. (27) Samuel, J.; Paul, M. L.; Pulimi, M.; Nirmala, M. J.; Chandrasekaran, N.; Mukherjee, A. Hexavalent chromium bioremoval through adaptation and consortia development from Sukinda chromite mine isolates. Ind. Eng. Chem. Res. 2012, 51 (9), 3740−3749. (28) Córdoba, A.; Vargas, P.; Dussan, J. Chromate reduction by Arthrobacter CR47 in biofilm packed bed reactors. J. Hazard. Mater. 2008, 151 (1), 274−279. (29) Gokhale, S.; Jyoti, K.; Lele, S. Modeling of chromium (VI) biosorption by immobilized Spirulina platensis in packed column. J. Hazard. Mater. 2009, 170 (2), 735−743. (30) Jakopec, S.; Dubravcic, K.; Polanc, S.; Kosmrlj, J.; Osmak, M. Diazene JK-279 induces apoptosis-like cell death in human cervical carcinoma cells. Toxicol. In Vitro 2006, 20 (2), 217−226. (31) Bohart, G.; Adams, E. Some aspects of the behavior of charcoal with respect to chlorine. 1. J. Am. Chem. Soc. 1920, 42 (3), 523−544. (32) Thomas, H. C. Heterogeneous ion exchange in a flowing system. J. Am. Chem. Soc. 1944, 66 (10), 1664−1666. (33) Yoon, Y. H.; NELSON, J. H. Application of gas adsorption kinetics I. A theoretical model for respirator cartridge service life. Am. Ind. Hyg. Assoc. J. 1984, 45 (8), 509−516. (34) Ševců, A.; El-Temsah, Y. S.; Joner, E. J.; Č erník, M. Oxidative stress induced in microorganisms by zero-valent iron nanoparticles. Microbes Environ. 2011, 26 (4), 271−281. (35) Charumathi, D.; Das, N. Packed bed column studies for the removal of synthetic dyes from textile wastewater using immobilised dead C. tropicalis. Desalination 2012, 285, 22−30. (36) Noreen, S.; Bhatti, H. N.; Nausheen, S.; Sadaf, S.; Ashfaq, M. Batch and fixed bed adsorption study for the removal of Drimarine Black CL-B dye from aqueous solution using a lignocellulosic waste: A cost affective adsorbent. Ind. Crops Prod. 2013, 50, 568−579. (37) Sharma, R.; Singh, B. Removal of Ni (II) ions from aqueous solutions using modified rice straw in a fixed bed column. Bioresour. Technol. 2013, 146, 519−524. (38) Kathiravan, M. N.; Karthiga Rani, R.; Karthick, R.; Muthukumar, K. Mass transfer studies on the reduction of Cr (VI) using calcium alginate immobilized Bacillus sp. in packed bed reactor. Bioresour. Technol. 2010, 101 (3), 853−858. (39) Karimi, M.; Shojaei, A.; Nematollahzadeh, A.; Abdekhodaie, M. J. Column study of Cr (VI) adsorption onto modified silica− polyacrylamide microspheres composite. Chem. Eng. J. 2012, 210, 280−288. (40) Yahaya, N.; Abustan, I.; Latiff, M.; Bello, O. S.; Ahmad, M. A. Fixed-bed column study for Cu(II) removal from aqueous solutions using rice husk based activated carbon. Int. J. Eng. Technol. 2011, 11 (1), 248−252. (41) Fakhri, A.; Adami, S. Response surface methodology for adsorption of fluoride ion using nanoparticle of zero valent iron from aqueous solution. J. Chem. Eng. Process Technol. 2013, 4, XXX. (42) Blowes, D. W.; Ptacek, C. J.; Jambor, J. L. In-situ remediation of Cr (VI)-contaminated groundwater using permeable reactive walls: laboratory studies. Environ. Sci. Technol. 1997, 31 (12), 3348−3357. (43) Ponder, S. M.; Darab, J. G.; Mallouk, T. E. Remediation of Cr (VI) and Pb (II) aqueous solutions using supported, nanoscale zerovalent iron. Environ. Sci. Technol. 2000, 34 (12), 2564−2569. (44) Tytłak, A.; Oleszczuk, P.; Dobrowolski, R. Sorption and desorption of Cr (VI) ions from water by biochars in different environmental conditions. Environ. Sci. Pollut. Res. 2015, 22 (8), 5985−5994. I


Article

Industrial & Engineering Chemistry Research (45) Dhal, B.; Thatoi, H.; Das, N.; Pandey, B. D. Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product. J. Chem. Technol. Biotechnol. 2010, 85 (11), 1471−1479. (46) Liu, T.; Wang, Z.-L.; Zhao, L.; Yang, X. Enhanced chitosan/Fe 0-nanoparticles beads for hexavalent chromium removal from wastewater. Chem. Eng. J. 2012, 189, 196−202. (47) Li, X.; Ai, L.; Jiang, J. Nanoscale zerovalent iron decorated on graphene nanosheets for Cr (VI) removal from aqueous solution: Surface corrosion retard induced the enhanced performance. Chem. Eng. J. 2016, 288, 789−797.

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Enhanced Cr(VI) Removal by Nanozerovalent Iron-Immobilized

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