Removal of nitrate from aqueous solution using nanocrystalline cellulose
Parisa Azadbakht1, Hamidreza Pourzamani2, Seyed Rahman Jafari Petroudy3, Bijan Bina2
1 Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan; Student Research Committee, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan; Environment Research Center, Research Institute for Primordial Prevention of Non-communicable disease, Isfahan University of Medical Sciences, Isfahan, Iran
3 Department of Cellulose and Paper Technology, Faculty of Energy and New Technologies Engineering, Zirab Scientific and Research Campus, Shahid Beheshti University, Tehran, Iran
|Date of Web Publication||15-Sep-2016|
Prof. Bijan Bina
Department of Environment Health Engineering, School of Health, Isfahan University of Medical Sciences, Hezar Jerib Avenue, Isfahan
Source of Support: None, Conflict of Interest: None
Aims: In this study, the removal of nitrate was investigated using nanocrystalline cellulose (NCC) extracted from sugarcane bagasse.
Materials and Methods: NCC was extracted by acid hydrolysis of bagasse at 40°C for 45 min and then used as an absorbent for the removal of nitrate. The properties of absorbent were evaluated by atomic force microscopy and dynamic light scattering. The effect of various parameters including pH, initial concentration of nitrate, adsorbent dose, and exposure time was investigated on the removal of nitrate.
Results: NCC was obtained in a diameter and length of <14.7 and 500 nm, respectively. Optimal conditions for removal of nitrate were determined in the initial nitrate concentration, adsorbent dose, pH, and exposure time of 100 mg/L, 6, 3 g/L, and 100 min, respectively. In optimal conditions, the maximum adsorption of nitrate was 8.33 mg/g.
Conclusion: The highest efficiency of nitrate removal at pH, 6 was obtained as 25%. The results showed that the NCC, extracted from bagasse, could be used as a very effective adsorbent to remove nitrate from water and wastewater resources.
Keywords: Adsorbent, cellulose nanocrystal, NCC, nitrate, sugarcane bagasse
|How to cite this article:|
Azadbakht P, Pourzamani H, Petroudy SR, Bina B. Removal of nitrate from aqueous solution using nanocrystalline cellulose. Int J Env Health Eng 2016;5:17
|How to cite this URL:|
Azadbakht P, Pourzamani H, Petroudy SR, Bina B. Removal of nitrate from aqueous solution using nanocrystalline cellulose. Int J Env Health Eng [serial online] 2016 [cited 2020 Dec 4];5:17. Available from: https://www.ijehe.org/text.asp?2016/5/1/17/190643
| Introduction|| |
The use of nitrogen fertilizers and improper treatment of industrial wastewater cause many environmental problems including increase of nitrogen-rich compounds in surface water and groundwater.  One of the most common forms of nitrogen-rich compounds is nitrate ion (NO 3− ).  Concentration of nitrate higher than the permissible exposure limit has potential risk to the environment and public health.  United States Environmental Protection Agency has announced that the maximum permissible levels of nitrate in drinking water is 10 mg/L NO 3− − N.  In Iran, according to standard number 1053 of Industrial Research Institute of Standard, the maximum permissible concentration of nitrate in drinking water is 50 mg/L NO 3− - NO 3− .  High concentration of nitrate (over permissible exposure limit) in drinking water leads to methemoglobinemia, and disorders such as hypertension, increased infant mortality, gastric cancer, thyroid disorders, cytogenetic defects, meningitis, and Parkinson's disease. ,, The commonly used treatment methods for nitrate removal include ion exchange,  electrochemical reduction,  reverse osmosis,  catalytic,  biological denitrification,  and adsorption.  These methods are often expensive and ineffective, and produce by-product.  Among the method of removing contaminants, biosorption is the best compared to other methods in terms of initial cost, simplicity, and low cost.  Hence, cellulose is considered as the most abundant biopolymer because of the cheap, renewable, and biodegradability properties.  Cellulose is converted to the nanoscale particles through the special mechanical, chemical, physical, and biological processes.  The prepared nanocellulose is classified into three subcategories according to the methods and conditions of production, which are microfibrillated cellulose, nanocrystalline cellulose (NCC), and the bacterial nanocellulose.  The structure of cellulose contains amorphous and crystalline parts; during the reaction with sulfuric acid, amorphous (disordered) parts were hydrolyzed, and the crystalline parts (regular) remained, which the obtained nanocellulose is called as NCC.  NCC has been formed from rod-shaped particles with a width of 5-70 nm, and a length of 100 nm to a few micrometers.  NCC contains unique properties such as nontoxic, low density, high surface area, biodegradability, and surface properties which can be modified.  NCC is applicable for a wide range of purposes including electronics,  pharmaceuticals,  cosmetic, paper, and cardboard industries, food industry, medicine, and nanocomposites;  nevertheless, its consumption as adsorbent of pollutants, colors, etc., has not been studied extensively. 
In 2015, Samiey and Tehrani studied the removal of methylene blue (MB) and Janus green B dyes using NCC extracted from cotton linters.  In 2013, He et al. investigated the removal of MB dye using monolith, and NCC produced from MCC. 
Further researches showed that the extracted NCC through acidic hydrolysis of bagasse has not been used to remove nitrate ions. Therefore, herein, we studied the nitrate removal using NCC extracted from bagasse. In this study, NCC was obtained through acidic hydrolysis of sugarcane pulp (bagasse), and then, it was used as adsorbents for the removal of nitrate from aqueous solution. Subsequently, the effect of contact time, pH, initial concentration of nitrate, and adsorbent dosage were studied on the adsorption efficiency of NCC. The number of test for the interaction of these variables at different values was attained via Design of Experiments Software (DOE 6) [State University of New York at Buffalo Department of Civil].
| Materials and Methods|| |
To extract NCC, bagasse was purchased from Shahid Beheshti University, Faculty of Energy, and New Technologies Engineering. Other chemicals were prepared from Sigma-Aldrich Company, which include KNO 3 (≥98%), KOH (≥85%), NaOH (≥98%), Acetic acid (≥99.7%), HCl (37%), and H 2 SO 4 (≥95%).
Preparation of nanocrystalline cellulose
Initially, the alkali treatment of bagasse was accomplished according to the method of Gong et al.,  using a solution of potassium hydroxide (6%) and acetic acid, and then acidic hydrolysis was performed in the presence of sulfuric acid 64% (the ratio of acid: Pulp was 13:1) at 40°C for 45 min. Then, the hydrolysis was stopped by adding 10-fold distilled water in suspension. In the next step, the mixture was washed with distilled water using a centrifuge (model Remi, India) with 10000 rpm for 15 min to separate acid residues, and consequently, acidity of suspension reached to neutral pH. Afterward, the suspension was treated with ultrasonic homogenizer (BANDELIN Electronic, UW 3200, Germany) for 10 min with the power of 150 W.
The process of nitrate removal
The stock solution of nitrate was prepared by dissolving an appropriate amount of KNO 3 in distilled water. Then, the concentrations of 30, 50, 100, and 150 mg/L were prepared from the stock solution. The nitrate removal process using NCC was scanned in doses of 1, 3, 5, and 10 g/L; reaction time of 50, 100, 150, and 200 min; and pH: 5, 6, 7, and 8. the pH of samples was adjusted with HCl and NaOH (0.1 M) and was determined using a pH meter (Cyberscan pH 1500, The Netherlands). Samples were centrifuged) CLEMENTS 20000) for 15 min at a speed of 3500 rpm, and then filtered (0.22 CA). Finally, adsorption amount of nitrate ions was determined for all samples by a spectrophotometer (DR5000, HACH-LANGE, USA) at 220 and 275 nm. The amount of adsorbed nitrate on adsorbent (q e ) and removals (%R) were evaluated through equations (1) and (2):
Where, C0, and Ce are the initial, and the equilibrium concentrations of nitrate (mg/L), while m and V are the weight of the adsorbent (g), and the volume of the solution (L).
Analysis of data
To determine the relation between the factors and optimized condition, Design of Experiments software (DOE 6) was used. The Taguchi orthogonal array plan was applied by four factors at four levels [Table 1], and accordingly, 16 runs were carried out for 3 times, and consequently, a total number of 48 samples were analyzed.
Characterization of nanocrystalline cellulose
To characterize the morphology of the adsorbent particles, atomic force microscopy (AFM) image was obtained by AFM (JPK Instruments, Berlin, Germany).
The size distribution and zeta potential of prepared nanocrystals were determined through dynamic light scattering (DLS) method under the following conditions: Refractive index of 1.50, temperature of 25°C, viscosity of 0.8872 cP, the absorption coefficient 0.3, and the refractive index of water 1.33 using a DLS (DLS, version 5.00, Malvern) instrument.
| Results|| |
Characterization of adsorbent
AFM image of the extracted NCC is shown in [Figure 1]. DLS diagram and zeta potential of NCC are shown in [Figure 2] and [Figure 3], respectively.
|Figure 1: Atomic force microscopic image of nanocrystals cellulose (hydrolyzed in 40°C, 45 min)|
Click here to view
Determination of optimum conditions of nitrate removal
The effect of factors and the interaction among them are summarized in [Table 2]. One-way ANOVA displayed a significant correlation between the different variables, and the nitrate removal (P < 0.05). According to the [Figure 4], with the change of pH from 5 to 6, the nitrate removal efficiency was increased, and when the pH was changed from 6 to 7, removal efficiency decreased. To investigate the effects of initial concentration of nitrate on its adsorption by the absorbent, the experiment was accomplished in a nitrate concentration range of 30-150 mg/L. [Figure 5] shows the effect of the initial concentration of nitrate on its adsorption using NCC. The results on the effect of contact time and adsorbent dosage on nitrate removal are shown in [Figure 6] and [Figure 7], respectively.
|Table 2: Effects of the factors and interactions obtained by fractional factorial design |
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| Discussion|| |
The AFM image and DLS graph NCC are shown in [Figure 1], [Figure 2], [Figure 3], respectively. Based on AFM image, the extracted NCC are rod-shaped materials with a length, and diameter <500, and 14.7 nm, respectively, which is in accordance with the results of Jin et al.,  DLS diagram and zeta potential of NCC are shown in [Figure 2] and [Figure 3], respectively. The results of DLS showed that all the particles (100%) have a diameter < 14.7 nm. Nanocrystals of sugarcane bagasse in the study of Mandal and Chakrabarty,  which was produced by acidic hydrolysis had a diameter in the range of 40 nm. In a study conducted by Farasati et al., nanoparticles of Phragmites australis with a diameter of <327.5 nm were obtained using a ball mill.  Average zeta potential of adsorbent at pH 5, 6, 7, and 8 was −45.4, −14.8, −61.9, and −45.8 mV, respectively.
Based on the statistical analysis shown in [Table 2], the Fvalue test exhibited that the initial concentration of nitrate had the maximum effect over absorption performance (50.76%). In addition, the contact time and concentrations of NCC have the minimum effect on the absorption performance due to their Fvalue (8.79, and 5.56, respectively). Priority of factors affecting nitrate removal is as follows:
Initial nitrate concentration > pH > interaction AB > contact time > concentration of NCC.
The nitrate removal by the NCC could be represented as equation 3:
Considering the results of zeta potential of the adsorbent [Figure 3], it is obvious that at pH = 6, the negative charge of surface is less than that at other pHs, and thus, the efficiency of the nitrate removal at pH = 6 was increased. The highest efficiency of nitrate removal at pH, 6 was obtained as 25%. In a study conducted by Farasati et al. On nitrate removal using the modified nanoparticles of cane, the highest nitrate removal was achieved at pH = 6.  Due to the negative charge of the surface at pH = 7 which leads to electrostatic repulsion between adsorbent and absorbing nitrate, removal rate was decreased. At higher pH values, removal of nitrate is reduced because of the competition of OH− ions with nitrate ions for the active sites. 
The most efficiency of nitrate removal was obtained in a concentration of 100 mg/L of nitrate ions [Figure 5]. With an increase of initial nitrate concentration, the efficiency of nitrate removal is decreased which is in accordance with the results of Malakootian et al. studies.  It is probably because of the saturation of adsorption sites by the nitrate ions in high concentrations. Increasing the initial concentration of nitrate leads to increase of the electrostatic interactions which consequently causes to formation of sites with lower affinity to interact with nitrate ions.  As shown in [Table 2], among different parameters, initial concentration of nitrate ion has the maximum effect on the efficiency of nitrate removal.
As shown in [Figure 6], the maximum amount of nitrate removal is occurred at 100 min after beginning of the reaction, and nitrate removal rate decreases with increasing the contact time. This is probably because of the saturation of the adsorption sites over the time.  To investigate the effect of adsorbent dosage on the nitrate removal, the experiment was accomplished in different dosage values of adsorbent including 1, 3, 5, and 10 g/L. The effect of adsorbent dosage on the removal of nitrate is shown in [Figure 7]. Increasing the absorption dosage from 1 to 3 g/L cause to increase of the nitrate removal which is because of the large surface area, and more availability of adsorption sites. , With an increase of the adsorbent dosage from 3 to 10 g/L, the efficiency of removal is decreased which is in accordance with the results of Hsu et al.'s study. It is possibly due to the enhancement of the adsorbent dosage and contact time between the joined particles and particles of adsorbent, and subsequently, removal efficiency is increased. ,
| Conclusions|| |
In this study, NCC was extracted from sugarcane bagasse by acidic hydrolysis. AFM image analysis and DLS results showed that the dimensions of the extracted cellulose crystals are in nanoscale range. Initial nitrate concentration has the greatest effect among the examined factors, and contact time has the least impact on nitrate adsorption by the nanocrystals. However, due to the total negative charge of nanocrystalline and negative charge of nitrate, there was not a very high adsorption, but because the negative charge of nanocrystals at pH = 6 is less than the others, the maximum adsorption was obtained. The effect of the interaction of initial nitrate concentration with adsorbent dosage could also be an effective factor on nitrate removal. Based on the obtained results, NCC prepared from bagasse by acid hydrolysis, can be relatively an effective adsorbent in nitrate removal from contaminated water and wastewater.
This article is part of a Master's thesis with the code of 393506. The financial support from the Deputy of Research, and Technology, Isfahan University of Medical Sciences, the cooperation of Cellulose, and Paper Technology Department, Faculty of Engineering, and New Technologies, Shahid Beheshti University in Tehran, and other colleagues involved in this research would be appreciated.
Financial support and sponsorship
Isfahan University of Medical Sciences, Isfahan, Iran.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2]