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Journal of Desalination and Water Purification 0128-2387 © Ababil Publishers www.ababilpub.com/jdwp http://dx.doi.org/xx

Research Article

Regeneration of fouled nanofiltration membrane used in dye-house wastewater treatment 1,

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Mona A. Abdel-Fatah *, Omar E. Abdel-Salam , Radwa Z. Abdel-Maoty 1

Chemical Engineering Dept, National Research Center (NRC), Cairo, Egypt Chemical Engineering Dept, Faculty of Engineering, Cairo University, Cairo, Egypt 3 Egyptian Environmental Affairs Agency (EEAA), Ministry of Environmental Affairs, Cairo, Egypt *Corresponding author. Tel.: +201223732428; Fax: +233371615; Email: [email protected] (Mona A. Abdel-Fatah). 2

GRAPHICAL ABSTRACT

HIGHLIGHTS • • • • •

The aim of this study is the regeneration of fouled nanofiltration membrane. It is used in dying process of textile wastewater treatment. The goal is to increase its lifetime and therefore reduce the expenses. The regeneration of fouled membrane is carried out by chemical treatment. The influence of the chemicals on the used membrane's surface is studied.

Nanofiltration membrane KEYWORDS

ABSTRACT

Textile dye-house Nanofiltration membrane Fouling membrane Regeneration Chemical methods Cleaning agents

Textile dye-house industrial processing is considered a major source of considerable chemical pollution as it includes: pretreatment, dyeing, printing, and finishing. This type of industries needs the advanced treatment technology. Nanofiltration membrane is considered one of the most effective technologies. The aim of this study was the regeneration of fouled nanofiltration membrane used in dying process of textile wastewater treatment for increasing its lifetime and therefore reducing the expenses. The regeneration process for the fouled membrane was carried out using chemical treatment method. Different concentrations of sulfuric acid, acetic acid, sodium hydroxide, and EDTA were used for that purpose. The time and temperature varied in each case. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) were used to investigate the influence of the chemicals on the used membrane's surface. Complete analysis proceeded to identify the best type of chemical cleaning. The factors affect the success of the cleaning process such as the nature of the foulant, type of cleaning agents, temperature, pH, concentration of the cleaning chemicals, and contact time were also investigated. The characteristics of the cleaned nanofiltration membrane were compared with the virgin and fouled membranes. © 2017 Ababil Publishers. All rights reserved.

ARTICLE HISTORY JDWP-2017003 Received 18 May 2017 Received revision 28 June 2017 Accepted 29 June 2017 Available online 30 June 2017

1. Introduction Fouling is a major disadvantage of the membrane treatment; it is an excessively complicated phenomenon that has not been exactly determined. Generally, the term fouling is applied to explain the unwanted deposits which accumulated on the membrane surface area. This phenomenon occurs when discarded particulate matters are not transferred from the membrane surface back to the bulk stream [1-2]. In industries using the membrane separation process, cleaning of membrane is one of the most significant concerns from the economic and scientific point of view. Cleaning membrane may be via several techniques: physical, chemical and physical-chemical methods. Practically, the most common process applied to the membrane cleaning is the physical cleaning methods followed by chemical cleaning methods. [3].

It is very important to study the characteristics of the foulant deposited on the membrane so as to choose an effective cleaning procedure. The best method of foulant identification is membrane autopsy after fouling, which is considered as an off-line method for fouling characterization. However, this is a destructive and expensive method that may be considered to enhance system performance when fouling is complex, when cleaning fails to restore membrane performance [3,4], and when membranes will be damaged after the cleaning process. Membrane autopsies are characterized by using techniques that are able to identify both inorganic and organic materials which may be found on the membrane surface: • Scanning Electron Microscope (SEM) and Scanning Electron Microscope coupled with Energy Dispersed X-ray (SEM-EDX) to determinate inorganic foulant elemental composition.

Copyright © 2017 Ababil Publishers. All rights reserved. http://ababilpub.com/download/jdwp7-3/ Journal of Desalination and Water Purification, 7:14-22, 2017

Abdel-Fatah et al./ Regeneration of fouled nanofiltration membrane used in dye-house wastewater treatment

• Fourier Transform Infrared Spectroscopy (FTIR) to identify organic compounds. • Targeted Energy Dispersive X-Ray Analysis (T-EDXA) as an indication of inorganic compounds. According to the variety of membrane types, the fouling mechanisms and types of foulant many research papers have been done for identifying the most suitable reagent for each single case. The chemical nature and fouling mechanism, the reactants can be divided into several groups as follow [5]: • • • • • •

Alkali (NaOH, KOH, NH4OH); Acids (HCl, H2SO4, HNO3, H3PO4, citric acid, oxalic acid); Salts (NaCl, KCl, NaNO2, NaNO3, Na2SO4, NH4Cl); Surfactants (SDS – anionic, CTAB – cationic); Chelating agents: ethylenediaminetetraacetic acid (EDTA); Sodium salt of ethylene diamine tetraacetic acid (Na2EDTA, Na4EDTA); • Enzymes (peptidases, proteolytic, hydrolytic); and • Disinfectants (oxidants) NaClO, H2O2, KMnO4. In general, alkaline cleaning recovers the flux, while the introduction of alkaline chelating agent further increases the flux. Liikanen et al. [6] reported using alkaline chelating such as EDTA which increased the flux more than plain alkaline cleaning (NaOH) due to membrane charge increase in EDTA alkaline environment. Liikanen et al. concluded that alkaline and chelating cleaning agents increase the membrane flux; on the other hand, they reduced the ion retention, whereas acidic cleaning could be used in order to recover membrane ion retention in a recent study. Mona et al. [7] noticed that combined simultaneous process of NaOH with sodium dodecyl sulfate (SDS) demonstrated greater cleaning power and cleaning efficiency by about more than 100% compared to that of single cleaning with each of NaOH or SDS alone. This is also true when two-step method in which SDS cleaning step was performed after caustic treatment [8]. Ahmed et al. [9] reported that hydrochloric acid cleaning showed better results than citric acid in the removal of the iron deposition on the membrane surface [10]. Jacques et al. [11-12] reported that sequential use of both caustic and acid cleaning was more effective, in terms of high flux recovery, than caustic or acid alone in removing both acidic and basic fractions of NOM. Also, the same author reported that the caustic cleaning was found to be more effective than the acid cleaning in removing NOM foulant. Which may be attributed to the presence of hydroxyl ions in caustic solutions; which could promote disruption of the foulant layer using the following mechanisms: (i) increasing ionic strength, (ii) increasing solubility of NOM foulant, (iii) increasing pH value should result in an increasingly negative charge of NOM, because of deprotonation of the carboxyl and phenolic groups. Conversely, decreasing the negative charge of NOM was observed as a result of adsorption of sodium ions to NOM during cleaning [11,13].

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EDTA and SDS were also used as effective cleaning agents in order to remove virtually or all of the NOM foulant material [12,14]. The acid cleaning is effective in the removal of precipitated salts (scaling) from the membrane surface and also from the pores [15]. The polyamide thin film membrane (TFM) is very sensitive to disruption by the oxidizing agent. Powerful oxidation agents have not been used in order to regenerate membrane performance because of oxidizing agent typically causes irreversible damage to these membranes. However, there is a procedure based on a patented chemical cleaning using NaOCl where a known concentration is prepared and recirculated through the membrane cells for 20 min at pH >10, while chlorine oxidation effects were almost negligible [16-17]. One of the problems of textile industry, which influences the usage of filtration membranes, is the membrane fouling. In this industry, fouling is caused by the high concentration of salts used in dyeing. Furthermore, the high concentration of salt causes an osmotic pressure difference, which lowers the flux. The selection of nanofiltration depends on many factors as the characteristics of the dye type [18,19]. Generally, the cleaning cycle consists of subsequent steps such as; removal of the product followed by water washing, cleaning more than one times, and finally repeats the water washing. Higher velocity cross-flow and lower pressure than those used during the normal operation should be used in order to obtain a good cleaning effect results chemical cleaning operation is influenced by a number of factors like temperature, chemical concentration, pH, pressure, flow, and time. Increasing temperature to the maximum temperature membrane limits will cause increasing the cleaning efficiency [20,21]. While, cross flow velocity appears to be ineffective for the cleaning process. However, increasing trans-membrane pressure possibly affects and lowering cleaning efficiency, so trans-membrane pressure should not be applied to reach the maximum efficiency of removing deposits. The time required to attain high cleaning efficiency depends on the foulant type and cleaning process. For example; cleaning agent Sodium hydroxide (NaOH) solutions, chelating agents, and surfactants remove colloidal [22-24]. For chemically cleaning nanofiltration membrane, there are many types of chemical cleaning agents could be used, which are divided into six classes; alkalis, acids, metal chelating agents, surfactants, oxidizing agents, and enzymes. For example, salts deposits such as; CaCO3 removed by using the convenient acid cleaning agent whereas alkaline cleaning is used to remove adsorbed organics [25, 6]. The aim was to study the possibility of regeneration of fouled nanofiltration membrane used in textile wastewater treatment. The study was based on solving the high degradation of nanofiltration membrane used during the treatment of wastewater, and to increase the lifetime in membrane and therefore reducing the cost.

Journal of Desalination and Water Purification, 7:14-22, 2017

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2. Tools and methodology 2.1 Cleaning chemicals Five concentrations of the used cleaning chemicals were prepared with the concentration range from 1 to 5% and at times ½, 1, 1½ 2, 2½ hr. The chemicals used in the cleaning process are listed below: • • • •

Sulfuric acid (H2SO4) of concentration (98%). Acetic acid (CH3COOH) of concentration (96%). Sodium hydroxide (NaOH) pellets of concentration (99%). Ethylene diamine tetraacetic acid (EDTA) manufactured by Fluka chemika Company. • Ethylene diamine tetraacetic acid (EDTA) and sulfuric acid (H2SO4), EDTA used at the concentration range of 1-5%, mixed with 3% H2SO4.

Parameters Volume (ml) Time (min) Temperature (ºC)

H2SO4 1-5 30 15

Fig. 1 Preparing samples for regeneration. The previously prepared EDTA solution of all concentration with the contact time of 2½ hr was mixed with

Table 1 Experimental information. Cleaning agents CH3COOH NaOH EDTA 1-5 1-5 1-5 60 120 150 19 27 27

2.2 Methods Three methods were used to evaluate cleaning efficiency of regenerated membrane as follows.

EDTA & H2SO4 1-5 180 27

3% H2SO4 and left for 1½ hr at 27°C. Table 1 shows the experiment timetable; for each cleaning agent 30 experiments were done. 3. Results and discussion

i. Scanning electron microscopy (SEM) 3.1 Membrane fouling results Deposits on a membrane surface before and after cleaning was analyzed using Scanning Electron Microscopy (SEM) is a technique used to examine surface precipitates. ii. Energy dispersive X-ray (EDX) Energy dispersive X-ray (EDX) was used to identify the chemical composition of surface deposits.

3.1.1 SEM membrane during filtration process Regeneration of the membrane was studied using different cleaning agents namely H2SO4, Acetic acid, NaOH, EDTA, and finally (H2SO4+EDTA). From the results of SEM images, it was found that particles of dye solution have adhered to the surface of the membrane as shown in Fig. 2.

iii. Fourier transform infrared spectroscopy (FTIR) Fourier transform infrared spectroscopy (FTIR) is a technique used to discover the inter-atomic bonds (single, double, and triple) of organic compounds structural formulas. Different types of bonds will absorb different intensities at varying frequencies. 2.3 Experimental work The fouled membrane was divided into equal small samples (parts), each of area 1cm2 as shown in Fig. 1, which were precipitate in flasks under the following operating conditions: • • •

Fig. 2 SEM images of the inner membrane surface. 3.1.2 EDX membrane during filtration process

Concentration: 1, 2, 3, 4 and 5 %. Cleaning Temperature: 15°C, 19°C, and 27°C. Contact time: ½,1, 1½ ,2, and 2½ hr.

Examination of surface deposits using SEM at high resolution with energy dispersive X-ray (EDX) revealed that the surface deposits are illustrated in Fig. 3; while the results of


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elemental analysis of these deposits are shown in Table 2. Table 2 EDX elements analysis during filtration*. Element

Weight %

Atomic %

Element

Weight %

Atomic %

C 36.90 47.20 S 6.64 3.18 O 46.30 44.47 Cl 0.35 0.15 Na 3.60 2.40 Ca 3.68 1.41 Mg 0.51 0.32 Fe 0.11 0.03 Al 0.44 0.25 Cu 0.39 0.09 Si 0.62 0.34 Zn 0.33 0.08 P 0.14 0.07 Totals 100.0 100.0 *Spectrum processing. Processing option: all elements analyzed (normalized). Number of iterations = 7.

3.2.1 Sulfuric acid (H2SO4) cleaning agent a. Scanning electron microscopy (SEM) Testing of regenerated NF samples using SEM images showed the inner membrane surface after cleaning with H2SO4. Also, Table 3 and Fig. 6 show the results of elementals analysis and the EDX of washed membrane.

Fig. 5 SEM image after cleaning with H2SO4 with scale 1000x. b. Energy dispersive X-ray (EDX)

Fig. 3 EDX analysis of elements during filtration.

Table 3 and Fig. 6 show the EDX elements analysis. Table 3 EDX elements analysis after cleaning with H2SO4.

3.1.3 Fourier transforms infrared spectroscopy (FTIR) Fig. 4 illustrates the results of FTIR of the fouled nanofiltration membrane. As shown in the figure different numbers were shaded with different colors.

Element C O Al S

Weight% 46.19 37.31 0.27 16.24

Atomic% 57.45 34.84 0.15 7.57

Net Int. 9.01 13.69 0.7 44.95

Error% 13.26 13.33 67.31 3.26

Fig. 6 EDX analysis of elements after cleaning with H2SO4. Fig. 4 FTIR of fouled nanofiltration membrane. c. Fourier transforms infrared spectroscopy (FTIR) 3.2 Membrane regeneration results The regenerated NF samples were studied using the SEM images of the inner membrane surface, and EDX analysis of elements. The samples were prepared as shown in Fig. 5.

The regenerated membrane using H2SO4 examined by FTIR and the results are shown in Fig.7 from which different elements are shaded with different colors.



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Fig. 9 EDX analysis of elements after cleaning with CH3COOH. 3.2.3 Sodium hydroxide (NaOH) as cleaning agent Fig. 7 FTIR of the membrane regenerated with H2SO4. 3.2.2 Acetic acid (CH3COOH) as cleaning agent a. Scanning electron microscopy (SEM) Acetic acid was used with the previously mentioned concentrations it is clear from the SEM images shown in Fig. 8 with different scales that the deposits still exist.

Fig. 8 SEM image after using CH3COOH with scale 1000x.

a. Scanning electron microscopy (SEM) Trying sodium hydroxide as cleaning agent then testing of the membrane by SEM, EDX, and FTIR showed the removal of different scales of some deposits but the membrane is still fouled as shown in Figs. 11-13 and Table 5.

Fig. 10 FTIR of membrane regenerated with CH3COOH.

b. Energy dispersive X-ray (EDX) Table 4 and Fig. 9 show the EDX elements analysis.

Table 4 EDX elements analysis by cleaning with CH3COOH. Element % C O Na Si S Cl

Weight 59.53 26.25 3.31 0.67 9.38 0.85

Atomic % 69.99 23.17 2.03 0.34 4.13 0.34

Net Int. 15.52 8.48 4.12 2.08 26.35 2.01

Error 11.4 14.86 16.9 27.8 4.38 29.68 Fig. 11 SEM image after using NaOH with scale 1000x.

c. Fourier transform infrared spectroscopy (FTIR) Fig. 10 shows the FTIR of nanofiltration membrane cleaned with CH3COOH.

b. Energy dispersive X-ray (EDX) Table 5 and Fig. 12 show the EDX elements analysis.


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Table 5 EDX elements analysis after cleaning with NaOH. Element% Weight Atomic % Net Int. Error C 50.28 61.52 9.68 12.24 O 29.55 27.15 8.34 14.48 Na 11.33 7.24 10.73 11.14 Si 0.65 0.34 1.38 35.37 S 8.2 3.76 16.57 5.53

with EDTA.

Fig. 14 SEM image after using EDTA with scale 1000x.

Fig. 12 EDX analysis of elements after cleaning with NaOH. c. Fourier Transform Infrared Spectroscopy (FTIR) Fig. 13 shows the FTIR of NF membrane cleaned with NaOH.

Table 6 EDX elements analysis after cleaning with EDTA. Element% Weight Atomic % Net Int. Error C

52.91

63.98

12.19

11.94

O

29.34

26.64

9.66

14.34

Na

7.5

4.74

8.59

12.15

S

10.25

4.64

26.12

4.21

Fig. 15 EDX analysis of elements after cleaning with EDTA.

Fig. 13 FTIR of membrane regenerated with NaOH. 3.2.4 EDTA as cleaning agent a. Scanning electron microscopy (SEM) Using different concentrations of EDTA as the cleaning agent for the membrane then examination with SEM, EDX, and FTIR showed the removal of the deposits and partially cleaning the membrane surface as it is clear in Figs 14-16 and Table 6. b. Energy dispersive X-ray (EDX) Table 6 and Fig. 15 show the EDX elements analysis. c. Fourier Transform Infrared Spectroscopy (FTIR) Fig. 16 shows the FTIR of nanofiltration membrane cleaned

Fig. 16 FTIR of membrane regenerated with EDTA.


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3.2.5 Mixture of EDTA+H2SO4 as cleaning agent a. Scanning electron microscopy (SEM) Using the mixture of (EDTA with H2SO4); for washing the membrane then test using SEM, EDX, and FTIR. As shown from the results of the previous test: Figs 17-19 and Table 7 gave the best results due to the removal of the deposits and cleaning the membrane.

green indicate the possible compounds of the membrane and regeneration agent on membrane surface as shown in tables. Fig. 19 shows that fouling layers totally covers the membrane; however in the later figures and tables of FTIR results which mentioned previously shows the cleaning progress; the worst results of acetic acid in Fig. 10 and Table 4, the mild results of sulfuric acid and sodium hydroxide that shown in Figs. 7 and 13 respectively and Tables 3 and 5 respectively, and the best results of EDTA only and EDTA with sulfuric acid solution as shown in Figs. 16 and 19, respectively and Tables 6 and 7, respectively.

Fig. 17 SEM image after using EDTA+ H2SO4 with scale 1000x. Fig. 18 EDX analysis of elements by cleaning (EDTA + H2SO4).

b. Energy dispersive X-ray (EDX) Table 7 and Fig. 18 show the EDX elements analysis. Table 7 EDX elements analysis by cleaning (EDTA+ H2SO4). Element % Weight Atomic % Net Int. Error C 17.02 24.62 1.5 22.99 O 54.62 59.32 20.04 11.56 Na 3.2 2.42 2.15 23.3 S 25.17 13.64 44.77 3.57 c. Fourier Transform Infrared Spectroscopy (FTIR) Fig. 19 shows the FTIR of nanofiltration membrane cleaned with EDTA. Summarizing the results of FTIR: The shaded numbers with yellow indicate the possible compounds in fouled and regenerated membrane as shown in figures above; and the shaded numbers with violate indicate the possible compounds of the fouled layer. On the other hand, the shaded numbers with

Fig. 19 FTIR of membrane regenerated with EDTA+ H2SO4.

Table 8 Summarizing of EDX results of all membrane cases. Regeneration agent (atomic %) Element C O Na Mg Si S Cl Al

Standard membrane 74.43 23.04 2.53 -

Fouled membrane 53.68 32.2 3.06 0.58 0.77 5.98 0.29 0.35

H2SO4

CH3COOH

NaOH

EDTA

EDTA+H2SO4

57.45 34.84 7.57 0.15

69.99 23.17 2.03 0.34 4.13 0.34 -

61.52 27.15 7.24 0.34 3.76 -

63.98 26.64 4.74 4.64 -

24.62 59.32 2.42 13.64 -



3.3 Analysis of EDX Results (virgin – fouled – washed) Table 8 shows the comparison between EDX analysis results of the basic elements of the membrane at the different cases of the membrane; standard, fouled, and regenerated membrane with various regeneration agents. For C, O, and S, the basic elements of membrane, carbon decreased in fouled membrane due to presence of fouling layer on membrane surface. Then, it was increased due to regeneration according to efficiency of each regeneration agent, while oxygen and sulfur increased due to the presence of fouling layer which contains salts, organic precipitate and metal oxides. Then, it was decreased due to regeneration according to efficiency of each regeneration agent, except the case of using EDTA+ H2SO4 regeneration solution, while carbon decreased but oxygen and sulfur increased. The case of using mixture regeneration solution the results of EDX and SEM shows a damage in membrane due to another fouling materials which not detected by the used techniques. For other elements, it is clear that the worst results are obtained upon using acetic acid and sulfuric acid while the best results were obtained upon using EDTA and (EDTA+ H2SO4) respectively. 4. Conclusions The study investigated the possibility of the regeneration of fouled nanofiltration membrane used in dying process of textile industry. Fouled nanofiltration membrane can be cleaned and regenerated by chemical treatment. Cleaning of fouled membrane was carried out using H2SO4 at concentration of 98% utilized at 15°C, CH3COOH at concentration of 96% utilized at 19°C, NaOH pellets of concentration of 99% used at 27°C, EDTA utilized at 27°C and mixture EDTA with H2SO4. Three techniques were used to assess and evaluate cleaning efficiency of regenerated membrane namely; scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). Comparing obtained results of the three cases of namely; virgin membrane, fouled membrane and cleaned membrane shows that cleaning by using acetic acid and H2SO4 gives the worst results while using EDTA separately or as a mixture with H2SO4 gives the best results. References [1] Al-Amoudi A, Lowitt RW. Fouling strategies and the cleaning system of NF membranes and factors affecting cleaning efficiency. Journal of Membrane Science 2007;303:4-28. [2] Field R. Fundamentals of Fouling, Membranes for Water Treatment: vol. 4. Peinemann KV, Nunes SP Eds. WILEY-VCH, Germany; 2010. [3] Tran-Ha MH, Wiley DE. The relationship between membrane cleaning efficiency and water quality. Journal of Membrane Science 1998;145:99-110. [4] Murthy GS, Sridhar S, Sunder MS, Shankaraiah B, Ramakrishna M. Concentration of xylose reaction liquor by nanofiltration for the production of xylitol sugar alcohol. Seperation and Purification Technology 2005;44:205-211.

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[23] Arnal JM, García-Fayos B, Sancho M. Membrane Cleaning, Expanding Issues in Desalination. Ning RY Eds. Intech Croatia; 2011. [24] Rashidi HR, Sulaiman NMN, Hashim NA, Hassan CRC, Ramli MR. Synthetic reactive dye wastewater treatment by using nano-membrane filtration. Faculty of Engineering, University of Malaya, Malaysia, 2014. [25] Abdel-Fatah MA, Sherif HO, Agour F, Hawash SI, Textile wastewater treatment by chemical coagulation technology. Global Journal of Advanced Engineering Technologies and Sciences. 2015;2(12):20-28. [26] Arnal JM, Garcia-Fayos B, Sancho M, Verdu G. Cleaning ultrafiltration membranes by different chemical solutions with air bubbles. Desalination and Water Treatment 2009;10(1-3):198-205. Appendix

Fig. A1 Regeneration process of membrane. To cite this article: Abdel-Fatah MA, Abdel-Salam OE, Abdel-Maoty RZ. Regeneration of fouled nanofiltration membrane used in dye-house wastewater treatment. Journal of Desalination and Water Purification 2017;7:14-22. To link this article: http://ababilpub.com/download/jdwp7-3/
