Synthesis of low-cost hydrophilic ceramic–polymeric composite membrane for treatment of oily wastewater Piyush Mittal, Somen Jana, Kaustubha Mohanty ⁎ Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, India abstract article info Article history: Received 30 May 2011 Received in revised form 28 June 2011 Accepted 29 June 2011 Available online 23 July 2011 Keywords: Ceramic membrane Composite membrane Dip-coating Oil–water emulsion Wastewater treatment A low-cost, hydrophilic ceramic–polymeric composite membrane was prepared from clay (collected from the bank of river Ganges), kaolin and small amount of binding materials. The support was prepared by paste casting whereas the composite membrane was prepared by dip coating with 10% cellulose acetate (CA) solution in acetone (w/v) with 60 s dipping time. The ceramic support was characterized by TGA, SEM, XRD, water permeability test and acid–base treatment and the composite membrane was characterized using SEM and pure water flux. A novel theoretical method was proposed for determination of the porosity and average pore size of the polymeric layer. Mass of the CA film, thickness of the polymeric layer, hydraulic permeabilities of the support and composite membrane were used for the theoretical derivation. The porosity and effective pore size of the composite membrane were found to be 0.56 and 28 nm. The prepared composite membrane was used to treat an oil-in-water emulsion containing 50, 100 and 200 mg L -1 oil. For all the initial oil concentrations, rejection increased with time whereas rejection was higher for high oil concentrations. Maximum rejection observed was 93% with a permeate oil concentration of 14 mg L -1 at 138 kPa. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Recently the use of composite membranes is gaining huge interest due to their higher selectivity, permeation rate, and chemical and thermal stability comparing to the polymeric membrane [1]. In recent years, various ceramic–polymeric composite membranes were syn- thesized with very good structural integrity, fouling resistance and high selectivity. These membranes are composed of different types of thin polymeric layers like polysulfone [2] or of styrene acrylonitrile [3] with the ceramic supports of pore sizes around 0.2 μm made from alumina [2] or from kaolin, ball clay and quartz [3]. Both microfiltra- tion (MF) and ultrafiltration (UF) range ceramic–polymeric composite membranes have been synthesized and tested for various applications [4–6]. However, use of these membranes in industrial applications was limited mainly due to the high cost of ceramic support which varies between 500 $/m 2 to 1000 $/m 2 [7]. There is a need to look for alternative low-cost materials for preparing the ceramic support so as to make the composite membrane commercially competitive. To prepare the polymeric top layer over the ceramic support, many techniques were reported such as spray coating [3], grafting [8], spin coating [9], self assembly [10], dip coating [11] and vapor deposition [12]. Among these methods, dip coating is simple, inexpensive, thus most desirable choice for industrial purpose. Many articles were published using dip-coating technique for the preparation of polymer– ceramic composite membranes. Matsumoto et al. have fabricated an UF range sulfonated polysulfone–ceramic composite membrane [2]. The composite membrane showed a high pure water flux of 39.5 × 10 -6 m 3 m -2 s -1 at an applied pressure of 100 kPa and a molecular weight cut-off of 20,000 Da. Nandi et al. have prepared cellulose acetate–ceramic composite membranes using dip coating with a wide range of pore sizes (485–25 nm) which was used for both microfiltration (MF) and UF ranges [5]. Similarly, Hong and Hong [4], Xiangli et al. [11], Aranda et al. [6], Rezac and Koros [13] prepared different polymer–ceramic composite membranes using their indi- vidual polymer precursors and commercial ceramic supports for preparing membranes to suit UF and pervaporation (PV) applications. UF membranes can remove higher molecular-weight substances, colloidal materials, and organic–inorganic polymeric molecules. As a novel and green technology, UF process has gradually becoming a powerful technology for oil/water separation also. Since, the size of the oil droplets are usually in the range of 0.1–10 μm, most of the oil droplets can efficiently be removed by UF [14]. The wastewater from different process industries like metallurgical, transportation, food processing and petroleum refineries contains large amount (50– 1000 mg L -1 ) of oil-in-water (o/w) or water-in-oil (w/o) emulsions [15]. The industrial oily wastewater exists in three broad categories: free-floating oil, unstable oil/water emulsion and stable oil/water emulsion [16]. Conventional methods like electroflotation can remove the free-floating oil or unstable oily wastewater [17]. But this process doesn't work for stable wastewater as the submicron sized oil droplets take very long residence time to rise to the top surface of the emulsion. Other techniques like thermal demulsification or biological treatment Desalination 282 (2011) 54–62 ⁎ Corresponding author. Tel.: +91 361 2582267; fax: +91 361 2582291. E-mail address: kmohanty@iitg.ernet.in (K. Mohanty). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.06.071 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal