Facile preparation of antifouling nanofiltration membrane by grafting zwitterions for reuse of shale gas wastewater

https://doi.org/10.1016/j.seppur.2021.119310Get rights and content

Highlights

  • Zwitterion was grafted on NF membrane via surface-initiated ARGET-ATRP.

  • Modified NF membranes were applied for SGW treatment following coagulation and UF.

  • The modified membrane had excellent protein antifouling property.

  • NF fouling mechanism by SGW were investigated using XDLVO theory.

  • Fluorescence EEM was used to analyze the removal of dissolved organics by NF.

Abstract

Complex organic matter causes severe fouling when membranes are applied for shale gas wastewater (SGW) treatment. This study reports the grafting of a zwitterionic polymer brush consisting of poly (sulfobetaine methacrylate) (PSBMA) onto the surface of a commercial nanofiltration (NF) membrane via electron transfer-atom transfer radical polymerization (ARGET-ATRP) to achieve anti-fouling property, especially against organic foulants. Compared to the pristine NF membranes, the PSBMA-grafted NF membrane showed high performance when challenged by SGW as a feed stream: (1) The flux stability was significantly improved during long-term operation, with a 64.28% increase in flux normalization at 50% recovery rate of SGW, while maintaining a suitable initial flux and near constant ion removal rate; (2) Based on excitation-emission-matrix spectra integrated in the fluorescence region, the removal of protein-like organic matters and humus-like organic matters increased by 34% and 16.5%, respectively; (3) The XDLVO theory supports the hypothesis that the hydrophobic interactions between the membrane surface and organic foulants were reduced by enhancing the Lewis acid-base interaction energy. The proposed anti-fouling zwitterionic membranes has potential in industrial application for the on-site reuse of SGW.

Introduction

The “shale gas revolution” was first successfully practiced in the USA to ensure energy security. China is currently accelerating the pace of shale gas development and exploration [1], [2]. According to evaluations made by the Chinese government, China has 25.08 × 1012 m3 of technically recoverable shale gas reserves, positioning it as one of the most promising countries in the world for shale gas development [3], [4]. However, the shale gas exploration process consumes large amounts of freshwater resources and generates significant quantities of shale gas wastewater (SGW) [5], [6]. In the Sichuan Basin, China, the average freshwater demand of a shale gas well is 23,650–34,000 m3, and 8–70% of the shale gas flowback and produced water is returned to the ground [7], [8], [9].

SGW in the Sichuan Basin contains low to moderate salinity, complex and heterogeneous organic compounds, and its treatment to safe standard is costly and challenging [10]. Currently, most SGW both in China and USA are reused for fracturing in new wells, since the recycling of the fracturing fluid can achieve both cost savings and environmental pollution reduction [11], [12], [13]. The effective removal of divalent ions is critical for SGW reuse to avoid scaling on production equipment and in the shale formation [14], [15], [16]. Based on the salinity and composition of the Sichuan Basin SGW, nanofiltration (NF) membrane technology is a suitable and promising candidate for purification with the aim to remove divalent ions and maintain a stable production of shale gas [9], [17], [18]. However, membrane fouling is a key drawback that restricts the application of NF membranes and can lead to increased energy consumption, alongside increased frequency of chemical cleaning and shortened membrane life [19], [20], [21]. In general, membrane fouling is the result of a complex series of physicochemical interactions between the surface of membrane and the fouling agents [21], [22], [23], [24]. The complex organic mixture in SGW is arguably the main cause of NF membrane fouling in this application [25]. Effective pretreatments are often used to improve the NF performance and ensure its sustainable operation [13], [26]. The combination of coagulation [27], adsorption [28], ozone pre-oxidation [29], or biological treatment technology [30] with UF has been applied for pre-treatment. However, NF fouling is still inevitable and few studies have investigatedthe properties of the NF membrane itself to improve their resistance to toux from SGW foulants.

The synthesis of new antifouling membranes through surface modification is an ideal approach to control fouling [22], and direct modification of the membrane surface is ideal for large-scale processing applications [31], [32], [33]. Antifouling membrane modification materials are mainly polymers, and the introduction of hydrophilic monomers or polar groups can significantly improve the membrane antifouling performance [34], [35]. Commonly used modifiers include: poly(vinyl alcohol) (PVA) [36], polyethylene glycol (PEG) [37], MXene [38], polydopamine (PDA) [39], and polyurethane [40]. Compared to other hydrophilic materials, zwitterionic polymer brushes (e.g., sulfobetaine methacrylate, SBMA) comprising both anionic and cationic end groups exhibit excellent antifouling performance at high salt concentrations [41], because of their overall electrical neutrality and strong hydration ability. SBMA is able to form a tightly hydrated layer on the surface of membrane materials, which weaken the interaction force between organic pollutants and the membrane surface [21], [31], [41], [42], [43], [44], [45], [46], [47], [48]. In particular, this mechanism is effective against hydrophobic organic substances, such as protein-like and humic-like matter, which accounts for a relatively high proportion of the organics in SGW and which can easily adhere to the membrane surface and cause membrane fouling [28], [29], [35], [49]. Typical modification methods include chemical grafting, physical coating, and polymer modification, where chemical grafting regulates the separation mechanism of the membrane by grafting specific groups to the surface, which not only achieves specific selectivity of the membrane, but also is an effective way to minimize fouling [44], [45], [47]. Modification through activators regenerated by electron transfer–atom transfer radical polymerization (ARGET-ATRP) is suitable to modify the membrane surface at large scale under routine industrial conditions in an easy and quick way, because it only requires a low dosage of copper catalyst and has high tolerance to oxygen [50], [51]. Our previous study used ARGET-ATRP method to graft [2-(methacryloyloxy) ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide (DMAPS) on the surface of self-made green ultrafiltration membranes showing highly promising results also for other membrane processes and applications [52].

In this work, we tune and apply this procedure to fabricate a high-performance NF membrane deployed to treat SGW with the goal of reuse. The relationship between membrane surface modification and improved antifouling performance is investigated upon grafting a zwitterionic polymer brush PSBMA onto the surface of a commercial NF membranes via an ARGET-ATRP method. The water flux decline rate is analyzed and evaluated in the light of the membrane surface characteristics and the degree of organic deposition. The effect of membrane fouling is discussed using the XDLVO theory. The purpose of this paper is to provide valuable information on ways to reduce NF membrane fouling by designing NF membranes suitable for shale gas wastewater treatment.

Section snippets

Pretreatment of the SGW

The SGW utilized in this experiment was acquired from a reservoir of the Weiyuan shale gas sites, Sichuan, China. The water characteristics and preceding steps in nanofiltration have been thoroughly summarized in our previous study [13]. In short, the ideal experimental condition for coagulation involved addition of 900 mg/L ferric chloride hexahydrate (FeCl3·6H2O) followed by 30 min settling. The supernatant was then fed to the tank of an ultrafiltration system comprising a hollow fiber poly

Membrane surface properties

Membrane surface characteristics, such as charge and roughness, hydrophobicity and chemical composition determine the selective separation properties and the anti-fouling performance of the membrane [42], [58]. Fig. 1A presents that the ATR-FTIR spectra determined between 500 cm−1 and 4000 cm−1 for the pristine NF90 and VNF1 membranes, the BiBB-initiation-PDA mobilized membranes (NF90-PDA, VNF1-PDA), and the PDA-g-PSBMA modified NF membranes (NF90-PSBMA, VNF1-PSBMA). The stretching vibration

Conclusion

Zwitterionic polymer brushes SBMA were grafted onto the surface of commercial NF membranes, greatly improving the membrane antifouling ability and organics removal while retaining high values of water permeability and only slightly decreasing the rejection rate of conventional monovalent and divalent ions. The VNF1-PSBMA membrane displayed extremely high performance with a pure water flux of 86.3 LMH, sodium sulfate removal rate of 95.67%, and with the J/J0 ratio upon fouling 73.5% higher than

CRediT authorship contribution statement

Minli Hu: Methodology, Data curation, Formal analysis, Validation, Visualization, Writing – original draft. Qidong Wu: Validation, Formal analysis, Investigation. Chen Chen: Writing - review & editing. Songmiao Liang: Writing - review & editing. Yuanhui Liu: Writing - review & editing. Yuhua Bai: Writing - review & editing. Alberto Tiraferri: Formal analysis, Writing - review & editing. Baicang Liu: Conceptualization, Supervision, Formal analysis, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (52070134, 51678377), Sichuan University and Yibin City People's Government strategic cooperation project (2019CDYB-25), and Xinglin Environment Project (2020CDYB-H02). We would like to thank the Institute of New Energy and Low-Carbon Technology, Sichuan University, for AFM and SEM, and the Analytical & Testing Center of Sichuan University for XPS work and we would be grateful to Suilin Liu for his help of XPS analysis.

References (71)

  • S. Jiang et al.

    A review of reverse osmosis membrane fouling and control strategies

    Sci. Total Environ.

    (2017)
  • E. Mohammad-Pajooh et al.

    On-site treatment of flowback and produced water from shale gas hydraulic fracturing: a review and economic evaluation

    Chemosphere

    (2018)
  • W. Yu et al.

    Ultrafiltration and nanofiltration membrane fouling by natural organic matter: mechanisms and mitigation by pre-ozonation and pH

    Water Res.

    (2018)
  • F.-X. Kong et al.

    Application of coagulation-UF hybrid process for shale gas fracturing flowback water recycling: Performance and fouling analysis

    J. Membr. Sci.

    (2017)
  • Y. Liu et al.

    Green aerogel adsorbent for removal of organic compounds in shale gas wastewater: high-performance tuning and adsorption mechanism

    Chem. Eng. J.

    (2021)
  • P. Tang et al.

    Sustainable reuse of shale gas wastewater by pre-ozonation with ultrafiltration-reverse osmosis

    Chem. Eng. J.

    (2020)
  • P. Tang et al.

    Organics removal from shale gas wastewater by pre-oxidation combined with biologically active filtration

    Water Res.

    (2021)
  • Y.-C. Chiang et al.

    A facile zwitterionization in the interfacial modification of low bio-fouling nanofiltration membranes

    J. Membr. Sci.

    (2012)
  • T. Sun et al.

    Magnetic field assisted arrangement of photocatalytic TiO2 particles on membrane surface to enhance membrane antifouling performance for water treatment

    J. Colloid Interface Sci.

    (2020)
  • M. He et al.

    Zwitterionic materials for antifouling membrane surface construction

    Acta Biomater.

    (2016)
  • F.-X. Kong et al.

    Desalination and fouling of NF/low pressure RO membrane for shale gas fracturing flowback water treatment

    Sep. Purif. Technol.

    (2018)
  • C. Zhao et al.

    Fabrication of a charged PDA/PEI/Al2O3 composite nanofiltration membrane for desalination at high temperatures

    Sep. Purif. Technol.

    (2021)
  • P. Kanagaraj et al.

    Membrane fouling mitigation for enhanced water flux and high separation of humic acid and copper ion using hydrophilic polyurethane modified cellulose acetate ultrafiltration membranes

    React. Funct. Polym.

    (2020)
  • H. Liu et al.

    Facile preparation of structured zwitterionic polymer substrate via sub-surface initiated atom transfer radical polymerization and its synergistic marine antifouling investigation

    Eur. Polym. J.

    (2019)
  • Q. Li et al.

    A facile surface modification strategy for improving the separation, antifouling and antimicrobial performances of the reverse osmosis membrane by hydrophilic and Schiff-base functionalizations

    Colloids Surf., A

    (2020)
  • D. Saeki et al.

    Anti-biofouling of polyamide reverse osmosis membranes using phosphorylcholine polymer grafted by surface-initiated atom transfer radical polymerization

    Desalination

    (2014)
  • J. Wang et al.

    Improving the water flux and bio-fouling resistance of reverse osmosis (RO) membrane through surface modification by zwitterionic polymer

    J. Membr. Sci.

    (2015)
  • W.-W. Yue et al.

    Grafting of zwitterion from polysulfone membrane via surface-initiated ATRP with enhanced antifouling property and biocompatibility

    J. Membr. Sci.

    (2013)
  • H. Chang et al.

    Smart ultrafiltration membrane fouling control as desalination pretreatment of shale gas fracturing wastewater: the effects of backwash water

    Environ. Int.

    (2019)
  • W. Xie et al.

    Green and sustainable method of manufacturing anti-fouling zwitterionic polymers-modified poly(vinyl chloride) ultrafiltration membranes

    J. Colloid Interface Sci.

    (2021)
  • M. He et al.

    Performance improvement for thin-film composite nanofiltration membranes prepared on PSf/PSf-g-PEG blended substrates

    Sep. Purif. Technol.

    (2020)
  • S. Hong et al.

    Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes

    J. Membr. Sci.

    (1997)
  • W. Wu et al.

    Stability versus flocculation of particle suspensions in water—correlation with the extended DLVO approach for aqueous systems, compared with classical DLVO theory

    Colloids Surf., B

    (1999)
  • F. Zhao et al.

    Combined effects of organic matter and calcium on biofouling of nanofiltration membranes

    J. Membr. Sci.

    (2015)
  • Z. Bai et al.

    Membrane fouling behaviors of ceramic hollow fiber microfiltration (MF) membranes by typical organic matters

    Sep. Purif. Technol.

    (2021)
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