Surface modification of PVDF membrane by radiation-induced graft polymerization for novel membrane bioreactor

https://doi.org/10.1016/j.jiec.2016.10.020Get rights and content

Highlights

  • PVDF membrane was successfully modified by radiation induced graft polymerization.

  • Roughness of membranes was decreased with GMA concentration.

  • Physical characteristics of modified membrane were influenced by GMA concentration.

  • Modified membrane exhibited higher ammonia mass flux than that of CEM.

Abstract

PVDF (poly vinylidene fluoride) membrane was modified with glycidyl methacrylate (GMA) and sodium sulfite using a radiation-induced graft polymerization technique for unique ammonia removal process. Ion exchange capacities (IECs) of unmodified PVDF membrane, modified PVDF membrane and commercial cation exchange membrane (CEM) were investigated. The IEC value increased as the concentration of GMA increased. Batch experiments were carried out to evaluate the ion transport via the modified membrane. The mass flux of ammonia via the CEM and modified membrane at the initial ammonia concentration of 2000 mg/L were 1.16 mg-NH4+/m2 s and 2.89 mg-NH4+/m2 s, respectively.

Introduction

Membrane bioreactors have been widely used to remove suspended solid and nutrients in wastewater treatment plants (WWTPs). Among the nutrients, the ammonia is a critical pollutant in aquatic environments because it can cause eutrophication and can be toxic. The US EPA (Environmental Protection Agency) reported that ammonia can act as a toxicant [1]. Therefore, most wastewater treatment plants incorporate the facilities to remove ammonia in wastewaters. For example, in the nitrification process, ammonia is oxidized to nitrate using oxygen as an electron acceptor by AOBs (ammonia oxidizing bacteria). However, this oxidizing reaction occurs when organic matter is below an inhibition level [2], [3]. As a result, the organic matter should be oxidized before nitrification and series of treatment processes is needed to remove nitrogen in wastewaters. However, the operation cost and time are increased by installation of a series of treatment processes.

Conventional processes such as A/A/O (anaerobic/anoxic/aerobic) and A/O (anoxic/aerobic) processes which control the aerobic and anoxic environments have been used to remove ammonia nitrogen. However, these processes require a long hydraulic retention time because oxidation reactions and recycling for denitrification are time consuming. Therefore, recent research has been focused on the simultaneous removal of nitrogen and organics in a single reactor [4], [5], [6]. The whole wastewater treatment process can be simplified when the simultaneous removal of organics and nitrogen is achieved in a single system. Especially, a sequential batch reactor (SBR) is the system to achieve the simplification. The aerobic and anoxic phases can be separately applied in a sequential batch reactor to control the aeration time [7], [8]. Simultaneous nitrification and denitrification (SND) processes under lower oxygen conditions is a new technique to remove nitrogen and organics from the wastewater [9]. However, it is very sensitive to maintain the simultaneous removal of nitrogen and organics because the basic reactions are autotrophic ammonia oxidation and heterotrophic denitrification. In general, ammonia oxidation bacteria have a much lower growth rate than heterotrophic bacteria. Because of these different growth rates, it is difficult to control simultaneous nitrification and denitrification. To solve the problem, researchers become interested in an ion exchange membrane bioreactor throughout separating the aerobic and anoxic conditions in a single reactor [10], [11], [12]. The performance of an ion exchange membrane bioreactor is mainly determined by the ion exchange capacity of the membrane [13].

Membrane surface modification is an option used to enhance the ion exchange performance in an ion exchange membrane bioreactor. Khodabakhshi et al. [14] reported that the ion exchange capacity of a modified membrane could be adjusted by modification of conditions with a blending method for membrane coating. Hosseini et al. [15] successfully modified a cation exchange PVC membrane using nanoparticles. However, these methods make it difficult to control the modification reaction. Moreover, the functionalized membrane surface by coating method is decayed by the elapsed operation time [16]. Grafting polymerization is a common and well-established method for chemical modification of membrane surface. Initiation of grafting process can be achieved using several techniques such as UV photo irradiation, plasma, high energy irradiation and “living” controlled polymerization, which could develop the water flux recovery and hydrophilicity of PVDF membrane [17]. However, UV photo irradiation has lower penetration ability to modify the inner membrane surface than gamma rays. Chemical living polymerization is hard to control the polymerization than radiation-induced polymerization. In addition, plasma grafting technique has a distinct disadvantage: the chemical and physical modification reactions can only occur on the membrane surface [18].

Radiation-induced graft polymerization is a good method to modify a membrane surface, and has unique advantages for this purpose. The advantages are homogenous reaction, absence of chemical initiators, high penetration ability, and reduction of the quantity of monomer required to modify the membrane surface [19], [20]. Chakrabarty et al. [21] reported that the radiation-induced cross-linked ion exchange membrane showed a higher ion transport capacity than thermal cross-linked ion exchange membrane. However, most applied ion exchange membrane is non-porous membrane.

In this study, the porous PVDF membrane was modified using radiation-induced graft polymerization and functionalized by sulfide groups to transport ammonia in a novel membrane bioreactor. In addition, the effects of the monomer concentration on radiation-induced graft polymerization were also investigated. The modified porous PVDF membranes were characterized for ammonia transport performance in comparison with a commercial cation exchange membrane.

Section snippets

Materials and chemicals

A hydrophobic PVDF porous membrane (average pore size: 0.2 μm, thickness: 100 μm) was purchased from Millipore Co. (Middlesex, UK). A cation exchange membrane (CEM) was purchased from ASTOM Co. (Tokyo, Japan). Glycidyl methacrylate (GMA), methanol, isopropanol, and sodium sulfite from Sigma–Aldrich Co. (St. Louis, USA) were used for radiation-induced grafting polymerization and sulfonation. Isobutanol and sodium hydroxide (NaOH) were purchased from Merck (Darmstadt, Germany). Deionized (DI) water

Grafting and conversions of epoxy group

The radiation-induced graft polymerization was influenced by monomer concentrations in the monomer solution. When the monomer concentration or irradiation dose increased, the degree of grafting was also influenced [23]. To confirm this, the effects of monomer concentration were investigated to determine the optimal grafting conditions. The initial monomer concentrations for radiation graft polymerization were set as 0.05, 0.1, 0.25, 0.5, and 0.75%, respectively. Fig. 2 and Table 1 show the

Conclusions

In this study, the surface modification of PVDF membrane by radiation modification technique was investigated to evaluate the ammonia transport in novel membrane bioreactor. The results from ATR-FTIR, SEM-EDS, AFM and IEC illustrate that a porous PVDF membrane for a novel membrane bioreactor was successfully modified by radiation-induced graft polymerization. The modified porous PVDF membranes have lower roughness and higher IEC values than that of unmodified porous PVDF membranes. The

Conflict of interest

The authors declare no actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations.

Acknowledgments

This research was supported by the nuclear R&D program and basic science research program through the national research foundation of Korea (NRF), funded by the Ministry of Science, ICT and Future Planning.

References (38)

  • Q.-L. Zhang et al.

    Bioresour. Technol.

    (2012)
  • D. Kulikowska et al.

    Bioresour. Technol.

    (2010)
  • Y.-C. Chiu et al.

    Int. Biodeterior. Biodegrad.

    (2007)
  • M. Reza et al.

    J. Environ. Chem. Eng.

    (2016)
  • D. Wei et al.

    Bioresour. Technol.

    (2014)
  • W. Jia et al.

    Bioresour. Technol.

    (2013)
  • A. Hussain et al.

    J. Environ. Manag.

    (2016)
  • W. Park et al.

    Water Res.

    (2009)
  • S.J. Lim et al.

    Bioresour. Technol.

    (2012)
  • A. Khodabakhshi et al.

    Sep. Purif. Technol.

    (2012)
  • S. Hosseini et al.

    Desalination

    (2012)
  • F. Tang et al.

    Corros. Sci.

    (2012)
  • G. Botelho et al.

    Polym. Test.

    (2008)
  • T. Yamaguchi et al.

    J. Membr. Sci.

    (1994)
  • S.D. Poynton et al.

    Solid State Ionics

    (2015)
  • D.W. O’Connell et al.

    Bioresour. Technol.

    (2008)
  • T. Chakrabarty et al.

    Radiat. Phys. Chem.

    (2011)
  • A. Taeger et al.

    React. Funct. Polym.

    (2003)
  • G. Estrada-Villegas et al.

    Radiat. Phys. Chem.

    (2013)
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