Preparation, characterization and evaluation of chitosan biguanidine hydrochloride as a novel antiscalant during membrane desalination process

Yasmine A. Maher; Mohamed E.A. Ali; Hend E. Salama; Magdy W. Sabaa

doi:10.1016/j.arabjc.2018.08.006

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Original article

13 (

); 2964-2981

doi:

10.1016/j.arabjc.2018.08.006

Preparation, characterization and evaluation of chitosan biguanidine hydrochloride as a novel antiscalant during membrane desalination process

Yasmine A. Maher^{^a}, Mohamed E.A. Ali^{^a,⁎}, Hend E. Salama^{^b}, Magdy W. Sabaa^{^b}

a Water Desalination & Treatment Unit, Hydrogeochemistry Dept., Desert Research Center, Cairo 11753, Egypt

b Chemistry Department, Faculty of Science, Cairo University, Giza 12613, Egypt

⁎Corresponding author at: Egyptian Desalination Research Center of Excellence (EDRC), Water Desalination & Treatment Unit, Hydrogeochemistry Dept., Desert Research Center, Cairo 11753, Egypt. mohamedea@edrc.gov.eg (Mohamed E.A. Ali)

Received: 2018-6-21, Accepted: 2018-8-19, Published: 2018-01-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Scale deposition is considered as one of the most critical problems leading to permeate flux decline and deterioration of membrane surface in reverse osmosis (RO) desalination plants. This study aims to preparation of novel high effective scale inhibitor, chitosan biguanidine hydrochloride (CG), to inhibit the precipitation of calcium sulfate and carbonate onto the membrane surface. The modification of Chitosan by the guanidine group was to enhance its solubility in water, because chitosan as it is dissolves only in moderately acidic solutions. CG was synthesized and characterized by FTIR, ¹³C NMR and ¹H NMR. The inhibition efficiency of our antiscalant was evaluated against CaSO₄ and CaCO₃ solutions at both static (induction time) and real application tests (cross-flow unit for 6 h). CG showed a good performance as scale inhibitor for CaSO₄ and CaCO₃ at about 10 and 15 mg·L⁻¹ with flux decline of 2.6 and 5% in feed water, respectively. In addition, the induction time of precipitation of CaSO₄ increased from 3 to 15 min with the addition of CG. SEM analysis at different magnifications for Cs and CG proved that CG strongly affects the morphology of the precipitated calcium sulfate and calcium carbonate leading to distortion of crystals.

Keywords

Reverse osmosis

Antiscalant

Calcium sulfate scale

Calcium carbonate scale

Chitosan biguanidine hydrochloride

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1 Introduction

Scaling or mineral deposition on reverse osmosis membranes (RO) is one of the most severe problems. In RO technique, sparingly soluble inorganic cations and anions like calcium, magnesium, carbonate, and sulfate may elevate resulting in concentration polarization on the surface of RO membrane. Therefore, the minerals concentration may exceed their solubility limit result in the deposition of the most common scalants onto the membrane surface such as CaSO₄, CaCO₃ and BaSO₄ (Jiang et al., 2017).

This inorganic scalants that are deposited on the membrane surface result in water flow obstructions. Dosage of antiscalant (AS) to the feed water is one of the most important techniques for controlling scale deposition and inorganic fouling by increasing the solubility limits of scaling salts. Moreover, it is considered to be the most suggested approach because of its advantages such as reducing the total operating cost and also being acceptable for the environment compared to other prevention methods.

Several factors control the inhibitory performance of the AS including the functional groups, the molecular weight, chemical formulation, concentration and the charge density of compounds. Scale inhibitors are mainly supposed to work via one of the following mechanisms such as crystal modification, threshold inhibition, dispersion, and chelation (Shemer et al., 2013). The mode of action of antiscalant seems to be attributed to the adsorption of the chemical added on the nuclei of growing crystal which impedes the growth at the suitable nucleation sites and lead to the formation of deformed, irregular crystals (Rahman, 2013). In general, antiscalants do not remove the scaling ions or its scaling capability, but they slow the initiation of crystal formation or retard the growth of crystals (Wang, 2005). Inhibition of salt deposition by antiscalants may be due to a delay in the induction time required for supersaturated salt solutions deposition (Hasson et al., 2003). As illustrated in Fig. 1, a small scale crystal begins to grow, then the antiscalant adsorbs onto the growing crystal surface. Therefore, there are three possible pathways for scale prevention that may occur (Duggirala, 2005).

A several number of scale inhibitors that delay or inhibit the formation of calcium sulfate and calcium carbonate crystals have been evaluated, such as polyelectrolytes, phosphonates, and specific types of polymers such as Polycarboxylate, polyphosphate (Li et al., 2007; Amjad, 2012; Ali et al., 2016; Xue et al., 2012; Kavitha et al., 2011; Zimmer et al., 2016 ) and also natural polymers (Popov et al., 2016; Saleah and Basta, 2008; Pervov et al., 2018 ). Lately, copolymers investigated as antiscalants since they have a great attention due to having different functional groups that is the reason for their inhibition ability and distortion of macromolecules for different types of scale (Senthilmurugan et al., 2010; Wang et al., 2009).

Chitosan (Cs) is a linear polysaccharide, it is produced by deacetylation of chitin through alkaline conditions (Hudson and Smith, 1998). Cs has interesting properties including biocompatibility, biodegradability, hydrophilicity and antibacterial effect and its degradation products are nontoxic, and noncarcinogenic which makes chitosan has wide applications in various fields such as agriculture, pharmaceuticals, cosmetics, food industries and wastewater treatment (Salama et al., 2015; Naguib et al., 2015; Abdel Aziz et al., 2015 ). Chitosan used in several applications especially in cooling water systems as it has been reported in many studies as scale inhibitor (Guo et al., 2012; Zhang et al., 2015). However, chitosan has poor solubility and limited antibacterial activity which restricts its application in certain fields (Abdel Aziz et al., 2015; Naguib et al., 2015). Chemical modification of Cs owing to the presence of hydroxyl and amino groups is helpful in improving the physicochemical characteristics and biological activity of chitosan.

Attachment of the guanidine group into chitosan can give the polymer a positive charge, which would lead to much better aqueous solubility at neutral pH and shows a powerful antimicrobial activity that may be helpful in avoiding the membrane biofouling that enhanced by antiscalants (Sweity et al., 2013). Recently, many polymers having guanidine groups that characterized by high water solubility and excellent antimicrobial activity have been investigated (Sahariah et al., 2015; Salama et al., 2017).

The main objective of this study is to use a new and ecofriendly Chitosan biguanidine hydrochloride as scale inhibitor for calcium sulfate and carbonate salts during membrane desalination process. The modification of Chitosan by the guanidine group was to enhance its solubility in water, because chitosan as it is dissolves only in moderately acidic solutions. The prepared material was characterized by using FTIR, ¹³C NMR and ¹H NMR. Evaluation of the antiscalant behavior against calcium sulfate and calcium carbonate scaling was carried out and compared with pure chitosan through measuring the normalized water flux. Detailed analyses using SEM of the membrane surfaces were obtained to examine the deposition of crystals onto the membrane surface.

2 Experimental

2.1

2.1 Materials

Calcium chloride dihydrate, anhydrous sodium sulfate, and sodium bicarbonate were of commercial grade, purchased from El-Gomhoreya Company for chemical industries, Egypt. Chitosan was obtained from Oxford laboratory, India. Its degree of deacetylation was 94%, as determined via potentiometric titration technique and the viscosity-average molecular weight was 160,000 g mol⁻¹. All the other chemical compounds used in this study were of commercial grade and used as received. A commercial thin film composite RO membrane TFC-RO (SEAPS RL4040, China) was used in our RO scaling tests.

2.2

2.2 Scaling model solutions

The scaling experiments on RO membranes were conducted using a synthetic solution of calcium sulfate as scaling feed solution noted as a solution (A), which was prepared by well mixing of CaCl₂·2H₂O and Na₂SO₄, but the feed-solution for calcium carbonate scaling test noted as a solution (B) was prepared by mixing of CaCl₂·2H₂O and NaHCO₃. The feed water composition of the scaling test solutions is shown in Table 1. The Saturation Index (SI) of saturated calcium sulfate, which describes the precipitation potential or the scaling tendency of gypsum, is defined as follows: ${SI}_{g} = L o g \frac{IAP}{K_{sp, g}}$ where IAP and K_sp,g are the ion activity product for gypsum and its solubility constant product, respectively.

Table 1 Compositions of scaling solutions used as feed water.

Parameter	Solution A (mg·L⁻¹)	Solution B (mg·L⁻¹)
Ca²⁺	1150	690
SO₄²⁻	2566	–
Na⁺	1000	200
Cl⁻	1602	1429.43
HCO₃⁻	–	213.5
TDS	6318	2426
PH	7	7.1
SI_g	0.23	–
LSI	–	0.63

The Langelier Saturation Index (LSI) (Langelier, 1936, 1946) is one of the most commonly used indices for calcium carbonate scaling tendency. This index is defined as follows: $LSI = p H - p H_{s}$ where pH and pHs are the actual pH of the solution and the pH of the solution saturated with calcium carbonate, respectively.

The permeate flux (J_w) (L/m²·h) through a semi-permeable membrane expressed in weight of the product per unit membrane area (A) in meter square was calculated as the volume (ΔV) in a liter during operation time Δt in second $J_{w} = \frac{Δ V}{A . Δ t}$

Also, the salt rejection percentage (Rs %) was recorded by measuring the electric conductivity of both permeate and feed solutions by using a conductivity meter (Jenway, UK) as follows: $R_{s} % = \frac{C_{f} {- C}_{p}}{C_{f}} \times 100$ where C_f and C_p represent the concentrations of permeate and feed water (mg/L), respectively.

2.3

2.3 Preparation of chitosan biguanidine hydrochloride (CG):

Chitosan and chitosan biguanidine hydrochloride was prepared according to previous works (Zhao et al., 2010; Salama et al., 2016; Ali, 2018; Ali et al., 2018 ). At room temperature, one gram of chitosan was dissolved in 100 ml of diluted HCl (1%) under stirring condition for 3 h; then 0.52 g of cyanoguanidine in 20 ml H₂O (with a molar ratio of 1:1 compared with a repeating unit of Cs) was wisely dropped and finally added to Cs solution. The reaction mixture was stirred at 100 °C for 3 h; then after cooling the mixture to room temperature excess methanol was added for precipitation. The obtained product filtered and dialyzed with distilled water for 24 h to remove the unreacted materials. Finally, the resulted product was dried in a vacuum for 24 h at 80 °C; the chemical reaction pathway is represented in Scheme 1.

Synthetic route of chitosan biguanidine.

2.4

2.4 Characterization and analysis

Fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical structure of Cs and CG using a Perkin Elmer B25 spectrophotometer. ¹³C NMR and ¹H NMR spectra were detected with a Bruker AC-400 in DMSO‑d₆ and DMSO‑d₆/CF3COOD as solvents. SEM images for RO membranes with and without antiscalant addition were obtained using QUANTA, FEG250 Scanning electron microscope. Membrane specimens were studied by cutting small pieces of membrane close to its middle after each test and left to dry at room temperature for the characterization by SEM to show the change in morphology and size of crystals at two different magnifications. Low magnifications are used to show a full pattern of crystallization in a wide area of the surfaces and at much higher magnification of the detailed images of each crystal at 5000× & 20,000× and 1000× & 4000× for CaCO₃ and CaSO₄, respectively.

2.5

2.5 Antiscalant performance measurement

2.5.1

2.5.1 Pre-scaling and static tests

A scaling solution of CaSO₄ with concentration of 7500 mg·L⁻¹ that prepared from mixing of CaCl₂·2H₂O and NaSO₄ was heated in a water bath of controlled-temperature at 80 °C for 120 min (Xue et al., 2012; Liu et al., 2012). To observe the crystallization of salt and the induction time (time needed for precipitation) that taken for precipitation of CaSO₄ with and without antiscalant. The induction time (time of precipitation) of the salts is the time required for supersaturated salt solutions deposition which can be determined by detecting the time until the precipitation occurs and flux decline begins in case of static tests and RO performance experiments respectively. During each experiment electrical conductivity of the solution was measured using a conductivity meter (Jenway, UK) and plotted against time (Fahiminia et al., 2007). The same experiment was repeated with CG as antiscalant at different concentrations of 6, 10, 15 mg·L⁻¹ to determine the induction time of crystallization in case of CG. At the end of the experiment, the solutions were filtered and the precipitate was dried in an oven at 50 °C to be characterized by SEM.

To elucidate the efficiency of CG as antiscalant for calcium carbonate, a simple experiment such as kinetic turbidity technique was carried out as follow; 0.0294 M of CaCl₂·2H₂O and 0.0168 M of NaHCO₃ was mixed well and heated in a water bath of controlled temperature at 60 °C for 150 min. To detect the precipitation of calcium carbonate with and without antiscalant. During each experiment turbidity of CaCO₃ solution was continuously measured using turbidity meter ORION AQ3010 (THERMO SCIENTIFIC, SINGAPORE) and plotted against time. The same experiment was carried out by the addition of different doses of CG (10, 15, and 20 mg·L⁻¹) to detect the change in turbidity during the experiments.

2.5.2

2.5.2 RO performance measurement

Membrane scaling experiments were done using a laboratory Cross-flow RO desalination unit (DDS Reverse osmosis system, model LAB-M20, manufactured by Alfa Laval Comp., Denmark) (Fig. 2). By circulating the scaling model solution (Table 1) through the membrane channel via a total recycle mode (i.e. permeate and retentate were continuously returned to the feed tank) for 6 h at trans-membrane pressure of 10 bar (Drak et al., 2000). In this study, the antiscalant efficiency was estimated based on comparison of the flux decline percent at different doses of CG with respect to control experiment.

(a) A photographic picture and (b) schematic diagram of crossflow RO laboratory desalination unit (Lab unit M20).

Water flux and salt rejection are measured continuously for the scaling test. The antiscalant was dosed into the feed solution before starting the cross-flow experiment. Evaluation of the antiscalants performance on the membrane was done by monitoring the gradual decline in membrane permeate flux (Al-Shammiri et al., 2000; Tzotzi et al., 2007). The temperature in all tests was in the range of 25–30 °C. The membrane samples were stocked with distilled water for 24 h before use. The permeate flux (J_w) through a semi-permeable membrane expressed in weight of the product per unit membrane area (A) was calculated as the volume (ΔV) in a liter during operation time Δt (L/m²·h) $J_{w} = \frac{Δ V}{A \cdot Δ t}$

Also, the salt rejection percentage (Rs %) was recorded by measuring the electric conductivity of both permeate and feed solutions by using a conductivity meter (Jenway, UK) as follows: $R_{s} % = \frac{C_{f} {- C}_{p}}{C_{f}} \times 100$ where, C_f and C_p represent the concentrations of permeate and feed water, respectively.

3 Results and discussion

3.1

3.1 Characterization of chitosan biguanidine hydrochloride

FTIR spectra of pure Cs and CG are illustrated in Fig. 3. The main characteristic bands of Cs could be assigned as follows: 3444 cm⁻¹ (—OH and —NH₂ stretching) (Guinesi and Cavalheiro, 2006), 1075 cm⁻¹ (C—O stretching), 1660 (amide I) 1597 cm⁻¹ (amide II), 2948–2866 cm⁻¹ (—CH stretching in —CH and —CH₂). In the FTIR spectrum of CG, new bands at 1532 cm⁻¹ (C⚌NH₂⁺ stretching) and 1468 cm⁻¹ (C—N stretching of the guanidinyl group) were appeared, which confirms the successful guanidinylation of Cs.

¹H NMR spectra of Cs and CG are represented in Fig. 4. All the spectra displayed the characteristic ¹H NMR pattern of Cs, i.e. the multiplet at δ 3.3–3.9 ppm due to H₃, H₄, H₅ and H₆, and two singlet at δ 2.8 ppm due to C₂ protons of the N-glucosamine and N-acetylglucosamine, and 1.9 ppm due to the N-acetyl protons of N-acetyl-glucosamine (Tian et al., 2004). The multiplets at δ 4–5.5 ppm are due to H₁ and protons of OH at C₃ and C₆. Broad singlet at 8.2 ppm is due to NH₂/NH (Rúnarsson et al., 2008). As seen from the figure, the CG possesses new signals at 7.1–7.3, 8.5 and 10.4 ppm due to the protons of guanidinium group (Zhang et al., 1999). This is consistent with the previous findings, where the structure of biguanidine consists of two imino and three amino functional groups both in the solid state and in solutions (LeBel et al., 2005). A comparison of the integral area of the C₂ protons of the N-glucosamine and N-acetylglucosamine at 2.8 ppm, and 1/3 N-acetyl proton signal at 1.9 p.m. with those of the proton integrals of amino groups of biguanidine group at 7.1–7.3 ppm gave an estimation of the degree of substitution (DS) (extent of N-substitution) of the CG from the following equation (Sajomsang et al., 2008): $DS = \frac{I_{{NH}_{2}} / 4}{(I_{H_{2}} + I_{H_{2}^{'}} - I_{NAc} / 3)}$ where “I“ is the intensity of signal, the calculated DS was found to be 0.95 with respect to amino groups of chitosan repeating units.

Fig. 5 shows ¹³C NMR spectra of Cs and CG, where the chemical shifts at 56 ppm (C₂), 59.8 ppm (C₆), 70 ppm (C₃), 75 ppm (C₅), 77.2 ppm (C₄) and 97.5 ppm (C₁) were detected in case of Cs (Fig. 5a). By comparing the ¹³C NMR spectrum of Cs with that of CG (Fig. 5b), the distinct signals at 154.4 ppm and 155.5 ppm were assigned to the carbons of biguanidine groups (He et al., 2015). The distinct signals of biguanidine group carbons appeared at 156 ppm. The results of the FTIR, ¹H NMR, and ¹³C NMR obviously supported the successful guanidinylation of chitosan.

13C NMR spectra of (a) Cs in DMSO/CF3COOD, (b) CG in DMSO.

3.2

3.2 Pre-scaling and static tests

From Fig. 6a, it is observed that the induction time of precipitation of CaSO₄ without antiscalant addition was achieved rapidly after the first 2 min, whereas as CG was added at 6, 10 and 15 mg·L⁻¹ it prolonged to 10, 15 and 8 min, respectively. Moreover, the amount of precipitation in case of 10 mg/L dose is less than the other doses with respect to the large amount of control precipitate as shown in Fig. 6b. This indicates that the CG antiscalant has influenced the crystal growth tremendously, which is evident from SEM, where the crystal morphology modified significantly, Fig. 7. Moreover, the high amount of precipitation in the absence of antiscalant reflects the positive effect of CG as scale inhibitor, Fig. 6b.

(a) Concentration of calcium sulfate solution against time. (b) Photographs shows calcium sulfate precipitation without and with different concentrations of CG antiscalant.

SEM images of calcium sulfate crystals with and without antiscalant at two magnifications 800× (left) and 2000× (right); (a, b) without antiscalant, (c, d) with 6 mg·L−1, (e, f) 10 mg·L−1, (g, h) 15 mg·L−1.

The increase in induction time of precipitation may be attributed to one of the following mechanisms: (a) The first explanation is the sequestering of the initial calcium ions by antiscalant action, thus inhibiting the formation of growing crystal (Le Gouellec and Elimelech, 2002). Moreover, results from Fig. 6 indicates that if the way of inhibition is achieved by sequestration of Ca²⁺ ions, thus the antiscalant CG has a good inhibitory effect on precipitation of CaSO₄. (b) The second explanation is adsorption of antiscalant particles and their incorporation onto the active growing sites of crystals. The effect of antiscalant molecules may be due to chemisorption on the outer surfaces of growing nuclei and thus prevented their crystallization (Liu and Nancollas, 1973).

To determine the potential impact of CG as a scale inhibitor of calcium carbonate, the Kinetic Turbidity (KT) test technique was applied (Aarag and Alnes, 2015). The turbidity profile was produced via plotting the turbidity values (NTU) against time Fig. 8. From such figure, it is obvious that the particles developed rapidly after about 15 min that identified by the sharp rise turbidity. The maximum turbidity (106 NTU) in the absence of antiscalant is shown to be decreased as CG dose increases from 10 to 20 mg·L⁻¹, and this can be attributed to the effect of antiscalant in delaying the precipitation of salts. In addition, as time of precipitation increases, the turbidity of the solutions have been shown to be increased with antiscalant concentrations with respect to the control experiment.

Turbidity of calcium carbonate solution against time.

3.3

3.3 Membrane performance without antiscalant addition

Fig. 9 shows the values of normalized flux (J/J_o) plotted against the operation time in order to evaluate the scaling formation process on the membrane performance during the desalination process without antiscalant addition. The figure illustrates that the normalized water flux is decreased from 1 to 0.883 and 0.87 as operating time increases from 30 to 360 min with a flux decline in 11.69 and 12.3% in the case of calcium sulfate and calcium carbonate, respectively. It is obvious that the induction time (time of precipitation) of the salts to form crystals onto the membrane surfaces achieved after the first three minutes. This high precipitation is due to the low solubility product of both salts (4.448 × 10⁻⁵ and 1.155 × 10⁻⁸, respectively), which result in blockage of the membrane pores and hence hinder the pathway of the water molecules. As salts precipitate, the osmotic pressure rises at the membrane surface and need an over applied pressure onto the feed solution. In addition, scale formation on the membrane surface is attributed to the phenomenon of concentration polarization of ions that may cause a concentration gradient to be formed with highest concentrations directly at the membrane. This leads to the formation of a cake layer on the surface, which produces resistance to permeate passage causing permeate flux decline (Sablani et al., 2001). However, the process of scale formation onto the membrane surface is carried out as follow; firstly, cations and anions, such as Ca²⁺, CO₃²⁻ and SO₄²⁻, could fuse to form ion pairs in solution. These ion pairs, then grow to form micro-aggregates, and some of these aggregates act as nucleation sites for crystallization. Then, more and more crystals accumulated onto the surface forming microcrystals in the feed solution which aggregates and adsorb to surfaces to grow into larger and adherent macrocrystals (Duggirala, 2005). With regard to the effect of scale formation at the membrane surface onto the salt rejection, mostly it remained constant throughout the experiments with calcium sulfate and calcium carbonate scaling tests, Fig. 9. This steady state of salt rejection may be due to that the experiment was conducted at short run using single and not the renewed solution.

Normalized permeate flux and salt rejection as a function of operating time of scaling feed solutions of calcium sulfate and calcium carbonate without antiscalant (control) at P = 10 bar.

The morphology of the membrane surface before and after scale experiment without antiscalant addition was investigated using SEM, Fig. 10. From Fig. 10(b and c) compared to the control membrane (Fig. 10a) it is clear that calcium sulfate precipitates as gypsum crystals that have a needle, rod like-shape, regular shape and compact structure (Rabizadeh et al., 2014; Shih et al., 2005). On the other hand, calcium carbonate scales are cubic crystals featuring a regular shape and compact crystal structure with large size (Fig. 10d and e).

SEM images of crystals formed on membrane surface without antiscalant. Conditions: desalination time 360 min (6 h), Pressure = 10 bar. (a) Membrane before desalination, (b, c) calcium sulfate crystals, (d, e) calcium carbonate crystals, both after desalination.

3.4

3.4 Evaluation of Cs and CG effect on calcium sulfate crystals

The effect of Cs and CG as antiscalants of calcium sulfate was studied at different doses of 6, 10 and 15 mg·L⁻¹. Fig. 11 showed that the water flux decreased by (14, 11.94, and 13.3%) with Cs and (10.17, 8.06, and 5.13%) with CG at concentrations of 6, 10 and 15 mg·L⁻¹, respectively. It can be observed that CG with 15 mg·L⁻¹ has demonstrated the a good performance compared to other concentrations. The doses were actually determined by the authors according to the results of RO experiments, where the optimum dose which represents the least flux decline with time. From previous studies, the addition of scale inhibitors extended the induction time of calcium sulfate precipitation onto the membrane surfaces (Rahman, 2013; Van der Leeden and Van Rosmalen, 1987). From Fig. 11, the induction time is considered to be the same as control test in case of Cs as antiscalant since flux begins to decline from the first 30 min with a continuous gradually decrease. On the other hand, CG with 6 mg·L⁻¹ and 10 mg·L⁻¹ extended the induction time to 60 min with slight decreases in water flux while at 15 mg·L⁻¹, the induction time was observed after 240 min. These results revealed that the membrane scaling tendency decreased as the concentration of antiscalant increases, which means that the CG has excellent effect on the membrane performance. However; the behavior of CG as antiscaling agent can be explained in a way that the positively charged chitosan molecules enhance its combination with sulfate ions because of the strong basicity of guanidinium group. These groups could be fully protonated in the neutral condition exhibited higher inhibitory performance because of interactions between the positive charge of guanidinium group and the anions in the feed solution, this is in agreement with a previous work (Ketsetzi et al., 2008). Therefore the treatment of chitosan backbone with guanidinium group could result in an increase of its cationic charges, and this is significant for the combination of CG with scalants having anionic charges on its surfaces (Salama et al., 2016; Neofotistou and Demadis, 2014). Fig. 12 shows SEM images of the membranes at different doses of Cs, where the complete deposition and aggregation of calcium sulfate crystals with full structure and spread across the whole membrane exactly similar to calcium sulfate crystals that are deposited in the control experiment in the form of needle-like shape and rod-like shape. This illustrated that Cs in its pure form without modification cannot affect the morphology of crystals or retard the crystal growth. Fig. 13 illustrates SEM images after addition of CG as antiscalant, where the crystal formation of CaSO₄ onto the membrane surface almost disappeared with all CG concentrations. This can be explained on basis that the guanidinium functional groups of CG allow the polymer to adsorb onto deposited crystals causing inhibition of mineral salt crystallization (Amjad, 1990). In addition, the little-formed crystals onto the membrane surface having irregular shapes with deformed sharp edges were observed. It was shown from SEM images that some irregular crystals appeared on the membrane surface that treated with concentrations of 6 and 10 mg·L⁻¹ and the crystal changes to smaller fragments with respect to crystals of scaling membrane. A few rods-like fragments are seen on the membrane surface that treated with CG with a concentration of 15 mg·L⁻¹ and its morphology is transformed from elongated forms to thin fragments (Ali et al., 2015).

Effect of antiscalant concentration (mg·L−1) on normalized permeate flux with calcium sulfate scaling tests (a) Cs and (b) CG.

SEM images of calcium sulfate crystals formation onto the membrane surface at different concentrations of chitosan and two magnifications of 1000× (left) and 4000× (right); (a, b) 6 mg·L−1, (c, d) 10 mg·L−1 and (e, f) 15 mg·L−1.

SEM images of calcium sulfate crystals formation onto the membrane surface at different concentrations of CG and two magnifications of 1000× (left) and 4000× (right); (a, b) 6 mg·L−1, (c, d) 10 mg·L−1 and (e, f) 15 mg·L−1.

3.5

3.5 Effect of Cs and CG on calcium carbonate crystals

The effect of Cs and CG as antiscalants was studied at different doses of 10, 15 and 20 mg·L⁻¹. From Fig. 14, it can be seen that the water flux decreased by 11.62, 17.21 and 19.90% and decreased by 2.6, 5.4% and 6.1% with Cs and CG concentrations of 10, 15, 20 mg·L⁻¹ respectively. These results show that the flux decline with Cs addition at all doses is more than that of control test. As we increase the dose of Cs, flux decline increase. Increasing dosage levels of Cs does not necessarily reduce the precipitation, which means that Cs may increase the tendency of the membrane to be scaled (Ghafour, 2003). From Fig. 14, it is observed that the induction time of CaCO₃ precipitation in case of Cs is similar to that of control test. Since flux begins to decline from the first 30 min with a continuous gradually decrease. On the other side, CG with 15 mg·L⁻¹ and 20 mg·L⁻¹ extended the induction time to 90 min with a slight decrease in water flux while at 10 mg·L⁻¹, the induction time was extended to 180 min then a constant flux is observed. SEM images (Fig. 15) with the same magnifications showing that a complete deposition of calcium carbonate crystals in case of addition of pure chitosan occurs and it’s obvious that the crystal’s size is larger than that of scaling test crystals (control) and this proved that Cs increase the scaling tendency of the membrane.

Effect of antiscalant concentration (mg·L−1) on normalized permeate flux with calcium carbonate scaling tests (a) Cs and (b) CG.

SEM images of calcium carbonate crystals formation onto the membrane surface at different concentrations of chitosan and two magnifications of 5000× (left) and 20,000× (right); (a, b) 10 mg·L−1, (c, d) 15 mg·L−1 and (e, f) 20 mg·L−1.

The morphology of the membrane surface after addition of CG as antiscalant for CaCO₃ scaling is shown in Fig. 16. For doses of 10 mg·L⁻¹ and 15 mg·L⁻¹, the number of crystals was increased, but with the small size with some cracks in the crystal structure, which indicate that the crystals were distorted and the crystallization of CaCO₃ was delayed and reduced. Meanwhile; CaCO₃ crystals formed onto RO membrane surfaces in case of CG have irregular shapes and loose structures. Also from Fig. 16(e and f), as CG dose increased to 20 mg·L⁻¹, the crystals of calcium carbonate were obviously decreased in number and size. The crystal morphology is then changed and cannot grow normally causing the crystals to be distorted (Liu et al., 2012). In general antiscalants do not exclude the scaling components or its capability; but they retard the crystallization beginning or crystal growth distortion (Antony et al., 2011).

SEM images of calcium carbonate crystals formation onto the membrane surface at different concentrations of CG and two magnifications of 5000× (left) and 20,000× (right); (a, b) 10 mg·L−1, (c, d) 15 mg·L−1 and (e, f) 20 mg·L−1.

Our results were compared with previous work (Table 2), we show that CG can be used as an effective scale inhibitor during membrane desalination process.

Table 2 Comparing CG efficiency with some antiscalants of previous works.

No.	Antiscalant	Dose	Scalant	Effect	Reference
1	PASP/Cs	8 mg/l	CaCO₃	92%	Zeng et al. (2015)
2	CM-QAOC	50 mg/l 10 mg/l	CaCO₃	98.5% 70.2%	Zhang et al. (2015)
3	AA-APEC	2 mg/l	CaSO₄	83.6%	Xue et al. (2012)
4	PAA	2 mg/l	CaSO₄	82.7%	Xue et al. (2012)
5	PAPEMP	3 mg/l	CaSO₄	79%	Xue et al. (2012)
6	AA-APEC	8 mg/l	CaCO₃	96%	Cao (2014)
7	Poly(citric acid)	25 mg/l	CaSO₄	98.8%	Zhao (2016)
8	Palm leaves extract	75 mg/l	CaCO₃	89.7%	Abd-El-Khalek (2016)
9	PAP-1	9 mg/l	CaSO₄	97.24%	Li (2006)
10	CG	6–15 mg/l	CaSO₄	95%	This study
11	CG	6–15 mg/l	CaCO₃	91%	This study

4 Conclusions

Chitosan biguanidine hydrochloride (CG) was successfully synthesized and characterized by FTIR, ¹HNMR, and ¹³C NMR spectroscopic techniques to be used as a novel antiscalant for sulfate and carbonate scale formation of calcium in reverse osmosis desalination plants. The antiscaling behavior of CG and chitosan for both scalants was successfully approached and examined by SEM and monitoring the gradual flux decline. CG showed the a good performance in retarding the scale formation with 15 mg·L⁻¹ and 10 mg·L⁻¹ in feed water for CaSO₄ and CaCO₃ respectively. SEM showed that CG has excellent antiscaling character, since in case of CaSO₄; the needle-like structure is modified and transformed into an irregular structure, while in case of CaCO₃; it is transformed from the cubic structure into cracks and distorted crystals. CG shows an effective efficiency as antiscalant in laboratory desalination unit for CaSO₄ and CaCO₃ membrane scaling.

5 Compliance with ethical standards

The authors declare that they have no conflict of interest.

References

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Sweity A., Oren Y., Ronen Z., Herzberg M., . The influence of antiscalants on biofouling of RO membranes in seawater desalination. Water Res.. 2013;47:3389-3398.
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Show Sections

[1] Aarag, I., Alnes, K.F.S., 2015. Testing of Scale Inhibitor Efficiency in a Pre-Scaled Environment.

[2] Abdel Aziz M.S., Naguib H.F., Saad G.R., . Nanocomposites based on chitosan-graft-poly(N-vinyl-2-pyrrolidone): synthesis, characterization, and biological activity. Int. J. Polym. Mater.. 2015;64:578-586.
[Google Scholar]

[3] Abdel Aziz M.S., Naguib H.F., Saad G.R., . Nanocomposites based on chitosan-graft-poly(N-vinyl-2-pyrrolidone): synthesis, characterization, and biological activity. Int. J. Polym. Mater. Polym. Biomater.. 2015;64:578-586.
[Google Scholar]

[4] Abd-El-Khalek D., . Investigation of a novel environmentally friendly inhibitor for calcium carbonate scaling in cooling water. Desalin. Water Treat.. 2016;57(7):2870-2876.
[Google Scholar]

[5] Ali M.E.A., . Synthesis and adsorption properties of chitosan-CDTA-GO nanocomposite for removal of hexavalent chromium from aqueous solutions. Arab. J. Chem.. 2018;11(7):1107-1116.
[Google Scholar]

[6] Ali M.E.A., Aboelfadl M.M.S., Selim A.M., Khalil H.F., Elkady G.M., . Chitosan nanoparticles extracted from shrimp shells, application for removal of Fe(II) and Mn(II) from aqueous phases. Sep. Sci. Technol. 2018:1-12.
[Google Scholar]

[7] Ali S.A., Kazi I., Rahman F., . Synthesis and evaluation of phosphate-free antiscalants to control CaSO4·2H2O scale formation in reverse osmosis desalination plants. Desalination. 2015;357:36-44.
[Google Scholar]

[8] Ali S.A., Haladu S.A., Mazumder M.A., Al-Muallem H.A., . Synthesis of a terpolymer and a tetrapolymer using monomers of diallylamine salts and SO2 and their application as antiscalants. Iran. Polym. J.. 2016;25:747-756.
[Google Scholar]

[9] Al-Shammiri M., Safar M., Al-Dawas M., . Evaluation of two different antiscalants in real operation at the Doha research plant. Desalination. 2000;128:1-16.
[Google Scholar]

[10] Amjad Z., . Influence of polyelectrolytes on the precipitation of amorphous calcium phosphate. Colloids Surf.. 1990;48:95-106.
[Google Scholar]

[11] Amjad Z., . Investigations on the evaluation of polymeric calcium sulfate dihydrate (gypsum) scale inhibitors in the presence of phosphonates. Desalin. Water Treat.. 2012;37:268-276.
[Google Scholar]

[12] Antony A., Low J.H., Gray S., Childress A.E., Le-Clech P., Leslie G., . Scale formation and control in high pressure membrane water treatment systems: a review. J. Membr. Sci.. 2011;383:1-16.
[Google Scholar]

[13] Cao K., . A multicarboxyl antiscalant for calcium phosphate and calcium carbonate deposits in cooling water systems. Desalin. Water Treat.. 2014;52(37–39):7258-7264.
[Google Scholar]

[14] Drak A., Glucina K., Busch M., Hasson D., Laîne J.-M., Semiat R., . Laboratory technique for predicting the scaling propensity of RO feed waters. Desalination. 2000;132:233-242.
[Google Scholar]

[15] Duggirala P.Y., . Formation of calcium carbonate scale and control strategies in continuous digesters. Concepción, Chile, Mayo: CD del II Coloquio Internacional sobre Celulosa de Eucalipto; 2005.

[16] Fahiminia, F., Watkinson, A., Epstein, N. 2007. Experiments and modelling of calcium sulphate precipitation under sensible heating conditions: initial fouling and bulk precipitation rate studies.

[17] Ghafour E.E., . Enhancing RO system performance utilizing antiscalants. Desalination. 2003;153:149-153.
[Google Scholar]

[18] Guinesi L.S., Cavalheiro É.T.G., . Influence of some reactional parameters on the substitution degree of biopolymeric Schiff bases prepared from chitosan and salicylaldehyde. Carbohydr. Polym.. 2006;65:557-561.
[Google Scholar]

[19] Guo X., Qiu F., Dong K., Zhou X., Qi J., Zhou Y., Yang D., . Preparation, characterization and scale performance of scale inhibitor copolymer modification with chitosan. J. Ind. Eng. Chem.. 2012;18:2177-2183.
[Google Scholar]

[20] Hasson D., Drak A., Semiat R., . Induction times induced in an RO system by antiscalants delaying CaSO4 precipitation. Desalination. 2003;157:193-207.
[Google Scholar]

[21] He B., Shao Y., Liang M., Li J., Cheng Y., . Biodiesel production from soybean oil by guanidinylated chitosan. Fuel. 2015;159:33-39.
[Google Scholar]

[22] Hudson S., Smith C., . Polysaccharides: chitin and chitosan: chemistry and technology of their use as structural materials. In: Biopolymers from Renewable Resources. Springer; 1998. p. :96-118.
[Google Scholar]

[23] Jiang S., Li Y., Ladewig B.P., . A review of reverse osmosis membrane fouling and control strategies. Sci. Total Environ.. 2017;595:567-583.
[Google Scholar]

[24] Kavitha A., Vasudevan T., Prabu H.G., . Evaluation of synthesized antiscalants for cooling water system application. Desalination. 2011;268:38-45.
[Google Scholar]

[25] Ketsetzi A., Stathoulopoulou A., Demadis K.D., . Being “green” in chemical water treatment technologies: issues, challenges and developments. Desalination. 2008;223:487-493.
[Google Scholar]

[26] Langelier W.F., . The analytical control of anti-corrosion water treatment. J. Am. Water Works Assoc.. 1936;28:1500-1521.
[Google Scholar]

[27] Langelier W.F., . Chemical equilibria in water treatment. J. Am. Water Works Assoc.. 1946;38:169-178.
[Google Scholar]

[28] Le Gouellec Y.A., Elimelech M., . Control of calcium sulfate (gypsum) scale in nanofiltration of saline agricultural drainage water. Environ. Eng. Sci.. 2002;19:387-397.
[Google Scholar]

[29] LeBel O., Maris T., Duval H., Wuest J.D., . A practical guide to arylbiguanides: synthesis and structural characterization. Can. J. Chem.. 2005;83:615-625.
[Google Scholar]

[30] Li H., Liu W., Qi X., . Evaluation of a novel CaSO4 scale inhibitor for a reverse osmosis system. Desalination. 2007;214:193-199.
[Google Scholar]

[31] Li H.-Y., . Inhibition of calcium and magnesium-containing scale by a new antiscalant polymer in laboratory tests and a field trial. Desalination. 2006;196(1–3):237-247.
[Google Scholar]

[32] Liu D., Dong W., Li F., Hui F., Lédion J., . Comparative performance of polyepoxysuccinic acid and polyaspartic acid on scaling inhibition by static and rapid controlled precipitation methods. Desalination. 2012;304:1-10.
[Google Scholar]

[33] Liu S.-T., Nancollas G.H., . The crystal growth of calcium sulfate dihydrate in the presence of additives. J. Colloid Interface Sci.. 1973;44:422-429.
[Google Scholar]

[34] Naguib H.F., Abdel Aziz M.S., Saad G.R., . Synthesis, characterization, and microbial activity of nanocomposites of chitosan-graft-poly (4-vinyl pyridine) copolymer/organophilic montmorillonite. Polymer-Plast. Technol. Eng.. 2015;54:1270-1279.
[Google Scholar]

[35] Naguib H.F., Abdel Aziz M.S., Saad G.R., . synthesis, characterization and microbial activity of nanocomposites of chitosan-graft-poly(4-vinyl pyridine) copolymer/organophilic montmorillonite. Polym.-Plast. Technol. Eng. 2015
[Google Scholar]

[36] Neofotistou E., Demadis K.D., . Cationic polymeric chemical inhibitors and multifunctional blends for the control of silica scale in process waters. Int. J. Corros. Scale Inhib.. 2014;3:28-34.
[Google Scholar]

[37] Pervov A.G., Andrianov A.P., Danilycheva M.N., . Preliminary evaluation of new green antiscalants for reverse osmosis water desalination. Water Sci. Technol. Water Supply. 2018;18:167-174.
[Google Scholar]

[38] Popov K., Rudakova G., Larchenko V., Tusheva M., Kamagurov S., Dikareva J., Kovaleva N., . A comparative performance evaluation of some novel “green” and traditional antiscalants in calcium sulfate scaling. Adv. Mater. Sci. Eng.. 2016;2016
[Google Scholar]

[39] Rabizadeh T., Peacock C.L., Benning L.G., . Carboxylic acids: effective inhibitors for calcium sulfate precipitation? Mineral. Mag.. 2014;78:1465-1472.
[Google Scholar]

[40] Rahman F., . Calcium sulfate precipitation studies with scale inhibitors for reverse osmosis desalination. Desalination. 2013;319:79-84.
[Google Scholar]

[41] Rúnarsson Ö.V., Malainer C., Holappa J., Sigurdsson S.T., Másson M., . tert-Butyldimethylsilyl O-protected chitosan and chitooligosaccharides: useful precursors for N-modifications in common organic solvents. Carbohydr. Res.. 2008;343:2576-2582.
[Google Scholar]

[42] Sablani S., Goosen M., Al-Belushi R., Wilf M., . Concentration polarization in ultrafiltration and reverse osmosis: a critical review. Desalination. 2001;141:269-289.
[Google Scholar]

[43] Sahariah P., Óskarsson B.M., Hjálmarsdóttir M.Á., Másson M., . Synthesis of guanidinylated chitosan with the aid of multiple protecting groups and investigation of antibacterial activity. Carbohydr. Polym.. 2015;127:407-417.
[Google Scholar]

[44] Sajomsang W., Tantayanon S., Tangpasuthadol V., Thatte M., Daly W.H., . Synthesis and characterization of N-aryl chitosan derivatives. Int. J. Biol. Macromol.. 2008;43:79-87.
[Google Scholar]

[45] Salama H.E., Saad G.R., Sabaa M.W., . Synthesis, characterization and biological activity of Schiff bases based on chitosan and arylpyrazole moiety. Int. J. Biol. Macromol.. 2015;79:996-1003.
[Google Scholar]

[46] Salama H.E., Saad G.R., Sabaa M.W., . Synthesis, characterization, and biological activity of cross-linked chitosan biguanidine loaded with silver nanoparticles. J. Biomater. Sci. Polym. Ed.. 2016;27:1880-1898.
[Google Scholar]

[47] Salama H.E., Aziz M.S.A., Saad G.R., . Thermal properties, crystallization and antimicrobial activity of chitosan biguanidine grafted poly (3-hydroxybutyrate) containing silver nanoparticles. Int. J. Biol. Macromol. 2017
[Google Scholar]

[48] Saleah A.O., Basta A.H., . Evaluation of some organic-based biopolymers as green inhibitors for calcium sulfate scales. Environmentalist. 2008;28:421-428.
[Google Scholar]

[49] Senthilmurugan B., Ghosh B., Kundu S., Haroun M., Kameshwari B., . Maleic acid based scale inhibitors for calcium sulfate scale inhibition in high temperature application. J. Petrol. Sci. Eng.. 2010;75:189-195.
[Google Scholar]

[50] Shemer, H., Hasson, D., Semiat, R., 2013. 13 Review of the State of the Art of Antiscalant Selection, Mineral Scales in Biological and Industrial Systems, p. 227.

[51] Shih W.-Y., Rahardianto A., Lee R.-W., Cohen Y., . Morphometric characterization of calcium sulfate dihydrate (gypsum) scale on reverse osmosis membranes. J. Membr. Sci.. 2005;252:253-263.
[Google Scholar]

[52] Sweity A., Oren Y., Ronen Z., Herzberg M., . The influence of antiscalants on biofouling of RO membranes in seawater desalination. Water Res.. 2013;47:3389-3398.
[Google Scholar]

[53] Tian F., Liu Y., Hu K., Zhao B., . Study of the depolymerization behavior of chitosan by hydrogen peroxide. Carbohydr. Polym.. 2004;57:31-37.
[Google Scholar]

[54] Tzotzi C., Pahiadaki T., Yiantsios S., Karabelas A., Andritsos N., . A study of CaCO3 scale formation and inhibition in RO and NF membrane processes. J. Membr. Sci.. 2007;296:171-184.
[Google Scholar]

[55] Van der Leeden M., Van Rosmalen G., . Aspects of additives in precipitation processes: performance of polycarboxylates in gypsum growth prevention. Desalination. 1987;66:185-200.
[Google Scholar]

[56] Wang Y., . Composite Fouling of Calcium Sulfate and Calcium Carbonate in a Dynamic Seawater Reverse Osmosis Unit. Australia: University of New South Wales Sydney; 2005.

[57] Wang C., Li S.-P., Li T.-D., . Calcium carbonate inhibition by a phosphonate-terminated poly (maleic-co-sulfonate) polymeric inhibitor. Desalination. 2009;249:1-4.
[Google Scholar]

[58] Xue X., Fu C., Li N., Zheng F., Yang W., Yang X., . Performance of a non-phosphorus antiscalant on inhibition of calcium-sulfate precipitation. Water Sci. Technol.. 2012;66:193-200.
[Google Scholar]

[59] Zeng D., Chen T., Zhou S., . Synthesis of polyaspartic acid/chitosan graft copolymer and evaluation of its scale inhibition and corrosion inhibition performance. Int. J. Electrochem. Sci.. 2015;10:9513-9527.
[Google Scholar]

[60] Zhang H., Cai Z., Jin X., Sun D., Wang D., Yang T., Zhang J., Han X., . Preparation of modified oligochitosan and evaluation of its scale inhibition and fluorescence properties. J. Appl. Polym. Sci.. 2015;132
[Google Scholar]

[61] Zhang Y., Jiang J., Chen Y., . Synthesis and antimicrobial activity of polymeric guanidine and biguanidine salts. Polymer. 1999;40:6189-6198.
[Google Scholar]

[62] Zhao X., Qiao Z.-Z., He J.-X., . Preparation of chitosan biguanidine hydrochloride and application in antimicrobial finish of wool fabric. J. Eng. Fibers Fabr.. 2010;5:16-24.
[Google Scholar]

[63] Zhao Y., . Inhibition of calcium sulfate scale by poly (citric acid) Desalination. 2016;392:1-7.
[Google Scholar]

[64] Zimmer K., Hater W., Icart A., Jaworski J., Kruse N., Braun G., . The performance of polycarboxylates as inhibitors for CaCO3 scaling in reverse osmosis plants. Desalin. Water Treat.. 2016;57:23162-23175.
[Google Scholar]

Preparation, characterization and evaluation of chitosan biguanidine hydrochloride as a novel antiscalant during membrane desalination process

Abstract

Keywords

Reverse osmosis

Antiscalant

Calcium sulfate scale

Calcium carbonate scale

Chitosan biguanidine hydrochloride

1 Introduction

2 Experimental

2.1 Materials

2.2 Scaling model solutions

2.3 Preparation of chitosan biguanidine hydrochloride (CG):

2.4 Characterization and analysis

2.5 Antiscalant performance measurement

2.5.1 Pre-scaling and static tests

2.5.2 RO performance measurement

3 Results and discussion

3.1 Characterization of chitosan biguanidine hydrochloride

3.2 Pre-scaling and static tests

3.3 Membrane performance without antiscalant addition

3.4 Evaluation of Cs and CG effect on calcium sulfate crystals

3.5 Effect of Cs and CG on calcium carbonate crystals

4 Conclusions

5 Compliance with ethical standards

References

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