Enhanced separation performance of coal-based carbon membranes coupled with an electric field for oily wastewater treatment

https://doi.org/10.1016/j.seppur.2016.05.020Get rights and content

Highlights

  • Coal-based carbon membrane coupled with an electric field is designed.

  • The electric field has a positive effectiveness on suppressing membrane fouling.

  • Improved separation properties are achieved due to anodic oxidation.

  • Carbon membrane possess good fouling resistance to oil droplets under acidic condition.

  • Fouling analysis confirms enhanced antifouling ability by applying an electric field.

Abstract

Coal-based carbon membrane coupled with an electric field is designed to achieve enhanced separation performance for oily wastewater treatment in this study. Effect of electric field intensity, concentration and pH of oily wastewater, rotate speed of peristaltic pump, electrolyte concentration, and electrode distance on separation performance of carbon membrane are investigated. The morphologies of carbon membranes are examined using scanning electron microscope (SEM). Fouling analysis is also carried out for further evaluating the antifouling ability of coal-based carbon membrane. The results demonstrate that coal-based carbon membranes integrated with an electric field show improved permeate flux and removal efficiency for oily wastewater treatment due to anodic oxidation. No obvious oil foulants are observed on carbon membrane by SEM images. Low total fouling ratio (TFR) and high flux recovery (FR) imply that exerting an electric field can significantly improve antifouling ability of carbon membrane. Acidic condition is benefit for carbon membrane to possess good fouling resistance to oil droplets. An decrease in electrode distance improves the separation performance of the treatment system. The optimum operation conditions of 0.31 V/cm electric field intensity, 7.5 r/min pump rotate speed, and 5 g/L electrolyte concentration are recommended. After cleaning, carbon membrane coupled with an electric field still demonstrates great potential in oily wastewater treatment.

Introduction

Nowadays, large quantities of oily wastewater are generated from various industries including petrochemical, steel, leather, textile, and transportation, etc., which are considered as the major threat to aquatic environment [1], [2], [3], [4]. This ecologically hazardous oily wastewater must be treated before being discharged according to related environmental regulations [5], [6], [7]. Up to date, several conventional techniques, including gravity separation, air flotation, chemical de-emulsification, coagulation, flocculation, and biological treatment, etc., have been used for oily wastewater treatment [8]. However, these techniques have several limitations such as more time consumption, low efficiency, high operation costs, and not effective on treating tiny oil droplets. These disadvantages prompt many researchers to turn to develop novel treatment technology for oily wastewater [9], [10].

Among large numbers of emerging methods on oily wastewater treatment, membrane separation gets extensive concern as a promising technology due to the advantages of compact design, small space occupancy, simple operation process, low energy consuming, high retention ratio and easy control of membrane properties [11], [12]. Also, another important reason to choose the technology is that it can purify the oily wastewater containing oil droplets smaller than 20 μm with acceptable discharge quality [13]. To my knowledge, investigation on the treatment of oily wastewaters using membrane separation processes has been started since 1976 [14]. After that, a lot of related works using various membranes processes, such as nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF), etc., are reported [15], [16], [17]. These studies reveal membrane separation technology possesses high oil removal efficiency compared to conventional treatment methods. However, as approved by many researchers, membrane separation performance is often deteriorated by membrane fouling, resulting from deposition or adsorption of foulants on membrane surface and/or inside pores during filtration, which has become one of the major obstacles greatly limiting the commercialization of membrane technology [18].

To minimize membrane fouling, various approaches have been adopted in previous literatures, which were classified into four categories: boundary layer (or velocity) control; turbulence inducers/generators; membrane modification and materials, and combined (external) fields [19], [20], [21]. Among them, applying an electric field to reduce membrane fouling is found to be quite effective due to the electrophoretic forces induced by the electric field can prevent foulants from depositing on the membrane [22], [23]. Moreover, some adsorbed substances may be electrochemically degraded. The idea inspires many researchers to use an external electric field to improve separation efficiency during membrane process. In their previous works, two different configurations have been reported. One is that an electric field is applied across the membrane. This configuration usually suffers from low efficiency due to the placement of an anode and a cathode located on opposite sides of the membrane. Also, extra electrodes will increase commercial implementation and reactor volume. The other is that the electric field is applied between the membrane (as an electrode) and another electrode. The configuration thus requires less energy in order to obtain the same electric field intensity. Therefore, developing novel materials which not only behave as membranes but also will have the ability to conduct electricity will favor the successful application of the electric field enhanced antifouling technology. Huotari et al. used a carbon fiber-carbon composite membrane as a cathode to treat oily wastewater, and demonstrates significant improvement in flux and permeate quality [24]. Dudchenko et al. synthesized a conductive thin film made of cross-linked poly (vinylalcohol) and carboxylated multi-walled carbon nanotubes as a cathode to treat alginic acid. Significant fouling inhibition was observed due to electrostatic repulsion, which prevented alginic acid from interacting with the membrane surface [25]. Akamatsu et al. developed a novel membrane-carbon cloth assembly for submerged MBRs by applying an electric field intermittently to suppress fouling, in which low cost carbon cloth was adopted as electrodes [26]. These studies demonstrate that carbon materials have great potential as electrodes on electric field enhanced antifouling system due to their electrical conductivities.

Carbon membranes are novel porous inorganic membranes, which are usually prepared by pyrolysis of carbonaceous materials, such as polyimide and derivatives, polyacrylonitrile (PAN), phenol formaldehyde (PF), and poly(furfuryl alcohol) (PFA) [27]. In our previous work, we developed novel carbon membrane derived from coal, which exhibit great potential on wastewater treatment [28], [29], [30]. Moreover, coal-based carbon membrane possesses good electrical conductivity, which makes it be a good candidate as electrode materials on the antifouling system for wastewater treatment. In this work, we design an antifouling treatment system, where coal-based carbon membrane is adopted as the anode and coupled with an electric field for oily wastewater treatment. The influence of an electric field on the improved separation performance of carbon membrane is studied in detail. Fouling analysis is also carried out to further approve the enhanced antifouling ability of carbon membrane under the electric field. Moreover, other operating conditions such as concentration and pH of oily wastewater, rotate speed of peristaltic pump and electrolyte concentration are investigated and optimized.

Section snippets

Properties of coal-based carbon membrane

Tubular coal-based carbon membrane with average pore diameter of 0.382 μm and porosity of 49.56% is used in this study. The inner diameter and membrane area are 8.5 mm and 0.0024 m2, respectively. The preparation process of coal-based carbon membrane refers to our previous literatures [29].

Treatment of oily wastewater

Oily wastewater is obtained by mixing 180# fuel oil, distillated water and surfactant (sodium dodecylbenzene sulfonate (SDS)) for 8 h at a speed of 5000 rpm using a homogenizer. Sodium sulfate (Na2SO4) is added

Effects of electric field intensity

In order to investigate the enhanced separation performance of coal-based carbon membrane coupled with an electric field, the electric field intensities of 0.15 V/cm, 0.23 V/cm, 0.31 V/cm, 0.38 V/cm, and 0.42 V/cm are exerted on the treatment system. For comparison, the treatment of oily wastewater using carbon membrane without an electric field is also performed at the same procedure. Fig. 2a illustrates that electric field intensity has a great influence on permeate flux. Without an electric field,

Conclusions

In summary, coal-based carbon membranes coupled with an electric field are successfully employed for the treatment of oily wastewater in this study. As expected, the electric field exerted on carbon membranes has a positive effectiveness on suppressing membrane fouling, and the optimal separation performance of carbon membrane is observed at the electric field intensity of 0.31 V/cm. The color and chemical oxygen demand (COD) removal are also more efficient when the electric field is exerted.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21276035, 21476034), the Scientific Research Project of Education Department of Liaoning Province (L2013203), the Natural Science Foundation of Liaoning Province (2014025014) and the Science and Technology Foundation for Overseas Chinese Scholars, Ministry of Human Resources and Social Security of China.

References (56)

  • Y. Zhu et al.

    PH-Induced non-fouling membrane for effective separation of oil-in-water emulsion

    J. Membr. Sci.

    (2015)
  • M. Masuelli et al.

    SPC/PVDF membranes for emulsified oily wastewater treatment

    J. Membr. Sci.

    (2009)
  • A. Salahi et al.

    Asymmetric polyethersulfone ultrafiltration membranes for oily wastewater treatment: synthesis, characterization, ANFIS modeling, and performance

    J. Environ. Chem. Eng.

    (2015)
  • J. Zhong et al.

    Treatment of oily wastewater produced from refinery processes using flocculation and ceramic membrane filtration

    Sep. Purif. Technol.

    (2003)
  • L. Qin et al.

    A submerged membrane bioreactor with pendulum type oscillation (PTO) for oily wastewater treatment: membrane permeability and fouling control

    Bioresource Technol.

    (2015)
  • C.S. Ong et al.

    Investigation of submerged membrane photocatalytic reactor (sMPR) operating parameters during oily wastewater treatment process

    Desalination

    (2014)
  • A. Salahi et al.

    Experimental performance evaluation of polymeric membranes for treatment of an industrial oily wastewater

    Desalination

    (2010)
  • Y. Weng et al.

    Removal of humic substances (HS) from water by electro-microfiltration (EMF)

    Water Res.

    (2006)
  • B. Sarkar et al.

    A study of electric field enhanced ultrafiltration of synthetic fruit juice and optical quantification of gel deposition

    J. Membr. Sci.

    (2008)
  • H.M. Huotari et al.

    Electrically enhanced cross-flow membrane filtration of oily waste water using the membrane as a cathode

    J. Membr. Sci.

    (1999)
  • A.V. Dudchenko et al.

    Organic fouling inhibition on electrically conducting carbon nanotube–polyvinyl alcohol composite ultrafiltration membranes

    J. Membr. Sci.

    (2014)
  • K. Akamatsu et al.

    Development of a membrane–carbon cloth assembly for submerged membrane bioreactors to apply an intermittent electric field for fouling suppression

    Sep. Purif. Technol.

    (2012)
  • A.F. Ismail et al.

    A review on the latest development of carbon membranes for gas separation

    J. Membr. Sci.

    (2001)
  • L. Li et al.

    Preparation and gas separation performance of supported carbon membranes with ordered mesoporous carbon interlayer

    J. Membr. Sci.

    (2014)
  • C. Song et al.

    Preparation of coal-based microfiltration carbon membrane and application in oily wastewater treatment

    Sep. Purif. Technol.

    (2006)
  • G. Han et al.

    Water reclamation from emulsified oily wastewater via effective forward osmosis hollow fiber membranes under the PRO mode

    Water Res.

    (2015)
  • S. Zhang et al.

    Sustainable water recovery from oily wastewater via forward osmo-sis-membrane distillation (FO-MD) forward osmosis hollow fiber membranes under the PRO mode

    Water Res.

    (2014)
  • M. Ahsani et al.

    Study on the fouling behavior of silica nanocomposite modified polypropylene membrane in purification of collagen protein

    Chem. Eng. Res. Des.

    (2015)
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