A continuous method for arsenic removal from groundwater using hybrid biopolymer‐iron‐nanoaggregates: improvement through factorial designs

About: This article is published in Journal of Chemical Technology & Biotechnology.The article was published on 2021-04-01 and is currently open access. It has received None citations till now. The article focuses on the topics: Factorial experiment.

Summary

1. Introduction

• Arsenic (As) in water represents a global problem, affecting low- and high-income countries1.
• About 50% of the population in rural areas is exposed to As poisoning, including several clinical manifestations such as cancer, hypertension, diabetes, and hyperpigmentation9.
• Biosorption is a novel method that has demonstrated a high capacity to remove several contaminants14-17, mainly when applied in continuous flow systems16,18.
• This has been reported previously in the literature20-22.
• The aim of this work was the synthesis of a new material based on chitosan and iron derived nanopartiples (CIN) and its use in continuous treatment of natural contaminated groundwater.

2.1 Analytical methods

• Groundwater natural samples were obtained from Piamonte Town, Santa Fe, Argentina.
• Arsenic concentration was increased until 1.0 mg/L in column experiments in order to work with a value within the concentration range found in natural groundwater of the area under study.
• All the reagents for the current research were of analytical grade.
• As(V) quantification in aqueous solutions was performed applying a self-made modification of molybdenum blue method16.

2.2 Chitosan Iron Nanoaggegates synthesis (CIN)

• Iron nanoparticles synthesis and stabilization was achieved from a stock solution containing 1:2 molar ratio ferrous: ferric species, which was slowly poured (drop-wise) into an alkali source, composed of sodium hydroxide, under vigorous stirring and nitrogen sparging.
• Core-shell magnetic crystals (Feº core - magnetite and / or maghemite shell) formed and precipitated.
• CIN was prepared by mixing a water-based suspension of iron nanoaggregates, functionalized with starch to promote interaction and linking to chitosan, incorporated as a powder.
• 20 w/w iron/chitosan) was stirred to achieve homogenization, also known as The mixture (1.
• Then it was allowed to settle, supernatant water was eliminated, and the material was dried at 60 °C for 72 hours.

2.3 CIN stability and total iron quantification

• The filtered supernatant was analyzed to measure the presence of iron using ICP-MS.
• Quantification of total iron was carried out by disaggregation of samples, and iron in aquous phase were measured by ICP-MS.

2.4 pH zero-point charge (pHZPC) determination

• After that, 1.0 g of CIN was added to each solution and stirring for 24 hours at room temperature (25°C).
• The final pH (pHf) was measured and the ΔpH was calculated.
• The intersection point on the x-axis in the ΔpH vs pH0 graph indicates the pHZPC14.

2.5 Sorbent composition effect on the As(V) sorption

• Batch experiments were carried out using chitosan, iron nanoaggregates, and CIN individually.
• Arsenic concentration was raised up to 20 mg/L in order to magnified differences between the three materials.
• Groundwater was divided into three equal parts, and each one was placed in a beaker with constant stirring.
• At the end of the reaction time, solutions were filtered under reduced pressure using cellulose nitrate filters (0.45 µm pore size).

2.6 FT-IR, XRD and TGA

• FT-IR spectroscopy (Perkin Elmer FT-IR Spectrum One spectrophotometer) was performed to identify the chemical functional groups present on CIN.
• TGA was performed in Thermogravimetric equipment DTG-60H, Shimadzu, made in Japan.

2.7 SEM and EDAX

• Iron nanoaggregates size and morphology were analyzed in a Zeiss Supra 40VP fieldemission scanning electron microscope (SEM).
• A SEM Philips 515 with EDS probe focused on individual agglomerates was used to assess the composition of nanoparticles.

2.8 Continuous Up-Flow Fixed-Bed Column Sorption Experiments

• Polypropylene columns of 2.0 cm internal diameter and 9.5 cm long were used for sorption experiments.
• CIN sorbent was hydrated in 100 mL of Milli-Q water (pH 4.5) at room temperature with constant agitation.
• Groundwater containing 1.0 mg L-1 of As(V) was pumped through the bed column with a peristaltic pump (Gilson This article is protected by copyright.
• Volumetric flow-rate and pH were periodically controlled.
• Finally, As(V) removal percentage (%R) can be obtained from min and mout, through Eq. 2: %R = 𝑚𝑚𝑖𝑖𝑖𝑖−𝑚𝑚𝑜𝑜𝑜𝑜𝑜𝑜 𝑚𝑚𝑖𝑖𝑖𝑖 x 100 Eq. 2 Desorption studies was performed employing 0.10 M solution of NaOH eluent and an upward flow of 8.5 mL min-1.

2.9 Statistical, mathematical modeling of experimental column data

• Different mathematical models are used to describe the sorption process behavior.
• These models include Thomas23, Yoon−Nelson24, and Modified Dose Response25.
• After preliminary tests, a central composite design (CCD) was selected for As(V) removal improvement.
• Table I presents the range and levels of independent variables: volumetric flow-rate (Q) and column bed height (H). Insert Table I here For RSM, experimental conditions were: pH = 4.5, packing density = 270 kg / m3, [As(V)]0 = 1.0 mg / L. Evaluated factors were: H and Q. All rights reserved.
• The study of the adjustment of experimental data to the mathematical model was carried out through Analysis of the Variance .

3.1 pHzpc determination

• An increase in the pHZPC of CIN (8.6) compared to chitosan (6.3)15 can be explained by the presence of iron oxides/hydroxides, which give a higher positive charge density on its surface27.
• At pH 4.5, CIN has a positive surface charge, which favors As(V) sorption, because it is present predominantly as H2AsO4- see Figure S228.
• Under these conditions, As(V) could form the ferric arsenate species according to the following reaction29: Fe(OH)2+ + H2AsO4- = FeAsO4 + 2H2O.
• The formation of this specie explains that, in addition to physical sorption, chemical sorption can also take place.

3.2. Effect of pH and iron content

• At this pH there is a favorable electrostatic attraction between As(V) and CIN, allowing efficient removal of arsenate ions.
• Table II details the batch experiment results, carried out with solutions of As(V) and: a) CIN, b) iron nanoaggregates, and c) chitosan.
• It can be seen that the CIN material has a higher retention capacity of As(V).
• The more surface area exposed implies more binding sites available and a higher retention capacity.
• Insert Table II here Elution profiles of columns filled with chitosan and CIN are compared in Figure 2.

3.3 FTIR, XRD and TGA characterization

• In the spectra shown below , the characteristic signals of chitosan and CIN after being exposed to arsenate ions are observed.
• In the CIN-As diffractogram, a marked decrease in the intensity of the peaks mentioned above is observed, so it can be affirmed that the sorption of arsenate ions breaks the semi-crystallinity state of the polymeric portion of the material and iron oxides present in it.

3.5 Improvement of the contaminant sorption process in fixed bed columns

• Values for each factor generated by the CCD and the responses obtained are shown in Table III.
• An acceptable tb indicates the column effluent must have an As(V) concentration of 0.05 mg L-1 according to the Argentine drinking water standards12.
• Both responses (tb and Vol) were optimized, generating the desirability function.
• The results of these analyses are detailed below.

3.6. tb improvement

• ANOVA analysis for this model is shown in Table S2.
• The lack of adjustment is not significant and indicates that the model has a good correlation with the experimental values.
• Statistical parameters of the model prediction are shown in Table S3.
• The response Surface obtained, Figure S6, showed that tb increase when H increases and decrease when Q increases.
• All rights reserved. of As(V) is entering the column in less time, which causes saturation of the active sorption sites.

3.7. Vol improvement

• The quadratic model for Vol response was significant (Table S4) Values of R2predicted and R2-adjusted did not show significant differences (Table S5), discarding block effects, and the presence of outliers, Figure S7.
• The signal-to-noise ratio (adequate accuracy), is greater than 4.
• The lack of adjustment is not significant, indicating the model has a good correlation with experimental values.
• The graph of the response surface, Figure S8, showed that increasing H increases the Vol of purified water due to a more significant number of active sites of the sorbent and therefore the amount of As(V) retained will be higher.

3.8 Desirability Function

• When a simple response is being analyzed, the model analysis indicates areas in the design region where the system is likely to give desirable results.
• Two responses were simultaneously optimized: minimizes tb and maximizes Vol are desirable.
• The breakthrough curve for this experimental condition and the adjustment to experimental data made by Thomas32, Yoon Nelson33, and Dose-Response34 models are shown in Figure S9 and Table S6.
• Thus, it can be said that the desirability function validates the objective of optimizing both responses studied satisfactorily.
• The percentage (%) of As(V) desorption was 75% in the second cycle and breakthrough time (tb) decreased to 35 min in the second cycle (over 40 % loss of removal capacity).

4. Conclusions

• Continuous sorption of As(V) in groundwater was studied using a hybrid material as sorbent: CIN.
• SEM, EDS, TGA, XRD and FTIR spectroscopic techniques were applied to characterize the sorbent.
• FTIR spectra of As and the decrease in the degree of crystallinity by XRD confirm As(V) sorption.
• The use of the experimental design in fixed bed column studies was successfully applied.
• Having a multi-response model allowed the generation of the desirability function by optimizing the process for the two responses studied: tb and Vol.

Figures

Figure 1

Figure 2

Figure 5

Table II. As(V) removal. b

Table I. Coded levels for independent factors used in the experimental design.

Table III. Values for each factor generated by the CCD and the responses obtained.

Figure 4

Figure 3

Full text

This article has been accepted for publication and undergone full peer review but has not
been through the copyediting, typesetting, pagination and proofreading process which
may lead to differences between this version and the Version of Record. Please cite this
article as doi: 10.1002/jctb.6600
A continuous method for arsenic removal from groundwater using hybrid
biopolymer-iron-nanoaggregates: improvement through factorial designs
Marianela Batistelli
2
, Bárbara Pérez Mora
1
, Florencia Mangiameli
1,2
, Nadia Mamana
3
,
Gerardo Lopez
4
, María F. Goddio
4
, Sebastián Bellú *
1,2
and Juan C. González*
1,2
1
Área Química General e Inorgánica, Departamento de Química-Física, Facultad de
Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha
531, S2002LRK Rosario, Santa Fe, Argentina
2
Instituto de Química de Rosario-CONICET (IQUIR), Suipacha 570, S2002LRK
Rosario, Santa Fe, Argentina
3
Laboratorio de Materiales Cerámicos IFIR, CONICET, FCEIA, UNR, Bv. 27 de
Febrero 210 Bis, 2000 Rosario, Argentina.
4
NANOTEK SA, Parque Tecnológico Litoral Centro - Ruta Nacional 168, Argentina.
∗Corresponding author: Universidad Nacional de Rosario, Facultad de Ciencias
Bioquímicas y Farmacéuticas, Suipacha 531, S2002LRK Rosario, Santa Fe, Argentina.
Tel.: +54 341 4350214; e-mail addresses: gonzalez@iquir-conicet.gov.ar (Juan C.
González); bellu@iquir-conicet.gov.ar (Sebastián Bellú)
Abstract
This article is protected by copyright. All rights reserved.

Background: Due to a variety of toxicological problems, the presence of As(V) in
aquifers is a significant problem. Sorption using chitosan doped with iron
nanoaggregates results in green and cheap methodology for its elimination.
Results: The hybrid sorbent was characterized by SEM, EDS, TGA, XRD, and FTIR
spectroscopy. Its stability against pH and time was determined by ICP-MS, while
conventional analytical techniques verified its Fe content. The sum of an individual
As(V) removal capacity by chitosan and iron nanoaggregates, was smaller than that of
the hybrid sorbent, indicating the existence of synergy.
Conclusion: This study demonstrates the great capacity of the hybrid sorbent to
eliminate As(V) working with a continuous system (columns). The additional use of a
factorial design allows determining optimal operating values to optimize two responses.
In other words, in this multi-response system, column service time (tb) was minimized
and, at the same time, maximized the volumes of purified water obtained ([As(V)]
<0.05 m L
-1
) using desirability function.
Keywords: ARSENIC; IRON-NANOPARTICLE; GROUNDWATER;
IMPROVEMENT
1. Introduction
Arsenic (As) in water represents a global problem, affecting low- and high-income
countries
1
. More than 226 million people are exposed
2
through the ingestion of
contaminated drinking water and food
3
. Compounds containing As can be found in
This article is protected by copyright. All rights reserved.

soils, rocks and natural waters
4
. Both organic and inorganic forms are naturally found,
being the last the most toxic
5
. In natural waters, it is present with two predominant
oxidation states, As(III) and As(V)
6
.
Argentina is one of the most affected countries in Latin America
7
. In the Chaco-
Pampean plain areas, As concentrations vary in a wide range (0.005 - 5 mg L
-1
)
8
. About
50% of the population in rural areas is exposed to As poisoning, including several
clinical manifestations such as cancer, hypertension, diabetes, and hyperpigmentation
9
.
About 30% of the people exposed to As develop cancer, especially of skin and internal
organs
10
.
The guideline value of As in drinking water is 0.01 mg/L recommended by the World
Health Organization
11
, whereas the value of 0,05 mg/L, is valid for the Argentine
drinking water standards
12
.
For this reason, it is essential to develop a simple, economical, and sustainable As
removal technology. Most of the current methods to remove As include
oxidation/reduction, coagulation, precipitation, sorption, ionic exchange, membrane
technologies, and bioremediation
13
. However, some of these methods are expensive
and/or unfriendly to the environment. Biosorption is a novel method that has
demonstrated a high capacity to remove several contaminants
14-17
, mainly when applied
in continuous flow systems
16,18
. Our previous work showed chitosan capacity to remove
As from water and groundwater
16,19
. Chitosan doped with iron derived nanoparticles can
increase the adsorption properties of the material. This has been reported previously in
the literature
20-22
. Nanoparticles have high removal capacity and fast reaction kinetics
This article is protected by copyright. All rights reserved.

against contaminants due to their high surface/volume ratio. A combination of iron
nanoparticles and biopolymers increase the system stability, creating a synergy for As
removal
23
. The aim of this work was the synthesis of a new material based on chitosan
and iron derived nanopartiples (CIN) and its use in continuous treatment of natural
contaminated groundwater. The use of a factorial design allowed the determination of
the operating values to optimize two responses at the same time: minimum columns
service time (tb) and maximum purified water volume (Vol).
2. Experimental
2.1 Analytical methods
Groundwater natural samples were obtained from Piamonte Town, Santa Fe, Argentina.
Groundwater characterization was analized by standard methods and the results are
showed in Table S1. Water samples were supplemented by the addition of sodium
arsenate (Na
2
HAsO·7H
2
O) solution until 1.0 mg/L As(V). Arsenic concentration was
increased until 1.0 mg/L in column experiments in order to work with a value within the
concentration range found in natural groundwater of the area under study. All the
reagents for the current research were of analytical grade. As(V) quantification in
aqueous solutions was performed applying a self-made modification of molybdenum
blue method
16
. Detection Limit (DL) and Quantification Limit (QL) were 0.0043 mg L
-1
and 0.013 mg L
-1
, respectively. The molar extinction coefficient (ε) obtained in the
experimental linear range (0.0050-0.50 mg L
-1
) was (19150 ± 150) M
-1
cm
-1
.
2.2 Chitosan Iron Nanoaggegates synthesis (CIN)
This article is protected by copyright. All rights reserved.

Iron nanoparticles synthesis and stabilization was achieved from a stock solution
containing 1:2 molar ratio ferrous: ferric species, which was slowly poured (drop-wise)
into an alkali source, composed of sodium hydroxide, under vigorous stirring and
nitrogen sparging. Core-shell magnetic crystals (Feº core - magnetite and / or
maghemite shell) formed and precipitated. CIN was prepared by mixing a water-based
suspension of iron nanoaggregates, functionalized with starch to promote interaction
and linking to chitosan, incorporated as a powder. The mixture (1:20 w/w iron/chitosan)
was stirred to achieve homogenization. Then it was allowed to settle, supernatant water
was eliminated, and the material was dried at 60 °C for 72 hours. The resultant solid
was then ground to obtain a suitable powder.
Chitosan used for the CIN's synthesis was previously characterized (molecular weight
and deacetylation degree) by our group
15,19
.
2.3 CIN stability and total iron quantification
CIN stability was determined as follow: 1.0 g of CIN were mixed with 60.0 mL of acid
solution (pH 4.5 given by H
2
SO
4
) and stirred at 350 rpm for 4.5 h. The filtered
supernatant was analyzed to measure the presence of iron using ICP-MS. Quantification
of total iron was carried out by disaggregation of samples, and iron in aquous phase
were measured by ICP-MS.
2.4 pH zero-point charge (pH
ZPC
) determination
This article is protected by copyright. All rights reserved.

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This article is protected by copyright. This study demonstrates the great capacity of the hybrid sorbent to eliminate As ( V ) working with a continuous system ( columns ).