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Investigation of microfiltration for treatment of emulsified oily wastewater from the processing of petroleum products
Desalination 249 (2009) 1223–1227
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Investigation of microfiltration for treatment of emulsified oily wastewater from the processing of petroleum products Yanhui Wang a,⁎, Xu Chen a, Jinchang Zhang b,c, Jingmei Yin b, Huanmei Wang d a
College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China College of Environment and Chemical Engineering, Dalian University, Dalian 116622, China School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore d Department of Petrochemical, Lanzhou Petrochemical College of Vocational Technology, Lanzhou 730060, China b c
a r t i c l e
i n f o
Article history: Accepted 28 June 2009 Available online 12 October 2009 Keywords: Microfiltration Wastewater treatment Emulsified oily wastewater
a b s t r a c t This research has investigated the possibility of using polyvinylidene fluoride (PVDF) membrane to treat the emulsified oily wastewater. Experimental results showed that the microfiltration could effectively treat the laboratory prepared emulsified oily wastewater and the fouled membrane could be recovered by using conventional cleaning methods. Similar promising results were obtained to treat factory emulsified oily wastewater by using microfiltration. In addition, different cleaning methods were investigated to recover the fouled membrane flux. Results showed that suitable interval operation of filtration and aeration could eliminate the membrane fouling under relative lower transmembrane pressure. Experimental results provided the basis for further investigation of its application in factory emulsified oily wastewater treatment. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water use has grown rapidly in modern times both because of rapid growth of humanity's actions and economics [1–4]. In most forms, water is a renewable resource since its continued flows are not affected by withdrawals or use. However, most of renewable waters have become non-renewable mainly because of contamination from human actions, which makes a significant portion of water resources unusable due to industrial and agriculture pollution and so forth [5–8]. This concern has been a main issue on the international agenda since the 1970's. The need to develop more sustainable practices for the management and efficient use of water resources, as well as the need to protect the environmental ecosystems where these resources are located, has led to fundamental shifts in awareness and public attention after that. A common understanding realizes that the disposal and treatment of sewage, and industrial effluents has become a strategy to efficiently use water resources [9,10]. The emulsified oily wastewater from the processing of petroleum products (particularly in oil exploitation) was difficult to treat by using common methods, e.g. sedimentation, centrifugation, bed filtration and so forth. In addition, those operations could produce a series of problems in applications. It would not only upset the surface equipment and potentially choke reservoir, but also produce enormous waste with the rejected wastewater containing significant amounts of crude oil and cause serious environmental pollution. A ⁎ Corresponding author. Tel.: +86 10 64416428; fax: +86 10 64423254. E-mail addresses: [email protected], [email protected] (Y. Wang). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.033
suitable method to treat this kind of oily wastewater now has become the bottleneck to improve China's oil productivity. It is well known that mechanical systems with a combination of physical, biological, and chemical processes to achieve the treatment objectives have become the preferred methods to deal with wastewaters, in which membrane filtration plays a very important role in wastewater purification [11–13]. Pozderović et al. [14] investigated the application of reverse osmosis (RO) for concentration of alcohol solutions. The effects of different types of membranes, processing pressure parameters and volume concentration with different alcohols using model solutions of alcohols, on RO operation have been studied. The gaseous effluents containing hydrophobic volatile organic compounds (VOCS) can be carried out by absorption with the use of a heavy hydrophobic solvent, while the used solvent must be regenerated to reuse it in the process of absorption. Heymes et al. [15] suggested that it could be operated using a hybrid absorption–pervaporation process, in which the pervaporation served to regenerate the solvent. Results showed that membrane operation had good ability to separate the heavy absorbent from mixture stream. The only problem was that the accumulation of absorbent could be occurring in the porous support, which could decrease the separation efficiency. Ferreira et al. [16,17] described the possibility to recover phenol from wastewater streams by membrane, which was derived from a phenolic resins production plant. González-Muñoz et al. [18] investigated the recovery of phenol from aqueous solutions by using hollow fibres, while Reis et al. [19] reported experimental results by using liquid membranes. The influence of different parameters, e.g. stripping solution, and solution concentration, on the process performance has been investigated. Sawai et al. [20] investigated the performance using a silicone rubber
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Y. Wang et al. / Desalination 249 (2009) 1223–1227
membrane on separation and recovery of 4-substituted phenol and aniline derivatives from aqueous solutions with the combination of permeation with chemical desorption (PCD) method. Results showed that phenols or anilines in aqueous solution were successfully recovered to aqueous NaOH or HCl solutions, respectively. Majewska-Nowak et al. [21] have investigated the possibility of concentrating organics in the wastewater by using ultrafiltration. Yu et al. [22] reported that the oily wastewater from an oil field could be purified by using a tubular ultrafiltration module equipped with polyvinylidene fluoride membranes, which was modified by inorganic nano-sized alumina particles. Results showed that the addition of nano-sized alumina particles improved the membrane performance of antifouling, and the flux of membrane filtration could be recovered by chemical cleaning method. Nghiem et al. [23] recently reviewed the progress of polymer inclusion membranes used for selective separation and recovery of metal ions as well as numerous organic solutes. They pointed out that the studies should not only highlight its potential in various niche applications on a practical scale but also emphasize the need for more fundamental research before any practical applications can be realized. This is particularly important for the treatment of streams containing small organic compounds as the transport mechanisms of such compounds through membranes are less well understood to date. Gray et al. [24] studied the reasons of natural organic matter (NOM) in the fouling of low-pressure membrane operation, which help to understand the methods to improve membrane performance in wastewater treatment. Ahmed and Robert [25] reviewed the research progress on membrane fouling occurring in nanofiltration operation. In addition, they also outlined the methods to clean or reduce the fouling during the membrane filtration operation. An analysis of fouling material and the effects of chemical cleaning were reported by Jung et al. [26] for a reverse osmosis membrane operation, which was used for the treatment of wastewater from a rolling mill process in the steel industry. Katsoufidou et al. [27] also provided a suitable method to recover the flux of ultrafiltration membrane operation. Based on previous studies and the feature of emulsified oily wastewater from an oil exploitation factory, we investigated the possibility to treat it by using microfiltration (MF) operation. If MF could be successfully operated, it will not only allow use of the water locally but also decrease the operational cost. This study reported MF experimental results on laboratory prepared wastewater and sample collected from an oil exploitation factory, respectively. 2 . Experimental sections 2.1 . Materials Chemically pure n-decane and analytical grade sodium dodecyl sulfate (SDS) were bought from Beijing Chemical Reagent Company. The other laboratory grade reagents used in experiments, e.g. hydrochloric acid (HCl), sulfuric acid (H2SO4), ammonium hydroxide (NH4OH), sodium hydroxide (NaOH) and so forth, were bought from Beijing Chemical Reagent Third Factory. Laboratory-made deionized water was used to prepare the emulsified oily wastewater. The local wastewater sample was kindly provided by an oil exploitation factory, China. The flat sheet membrane of polyvinylidene fluoride (PVDF) with 0.2 µm pore size was bought from Hangzhou Xidoumen Membrane Industries Co., Ltd., China. 2.2. Preparation of emulsified oily wastewater Emulsified oily wastewater was prepared by using a Nissei ACE homogenizer (Japan). The accurately weighed samples of n-decane and deionized water were heated certain temperature and then mixed together. Sodium dodecyl sulfate (SDS) was used as emulsifier
and 0.15 wt.% SDS was added. The homogenizer was operated at 3000 rpm and lasted for 20 min. 2.3. Analytical methods The laboratory prepared emulsified oily wastewater were analyzed by using the Coulter Multisizer (Beckman Coulter, America). The pH values of samples were measured with a PB-10 acid meter (Sartorius, Germany). The pH for the synthesized oily wastewater was 6.30. The concentration of organic compounds in wastewater samples was analyzed with a gas chromatography (GC4000A, Beijing East & West Analytical Instruments, Inc.) unit equipped with a flame ionization detector (FID). The removal efficiency (R) of organic compounds from the microfiltration was estimated using Eq. (1), in which Cfeed and Cpermeate are concentrations of feed and permeate, respectively. Furthermore, the surface profiles of membrane were investigated with an S-3200N Hitachi scanning electron microscope (SEM). R=
Cfeed −Cpermeate × 100 Cfeed
ð1Þ
2.4. MF operational system A diagram of the laboratory-scale operational microfiltration system is shown in Fig. 1. All experimental filtrations were carried out on membrane samples with a filtration of area of 7.4 cm2. The membrane was pretreated before the test. It was washed for 2 h with deionized water at room temperature followed by chemical washing for 10 min with 350 ppm of sodium hypochlorite solution. Thereafter the membrane was soaked in deionized water for 1 h. The filtration was performed in continuous cross-flow mode and the feed rate was about 3.0 ml min− 1. All filtration experiments were carried out at 0.2 MPa unless other stated. The filtration process commenced by supplying feed contained in the feed tank as shown in Fig. 1, and it was continuously stirred with an electric stirrer during the experiment. The permeate sample was collected in the permeate tank, shown in Fig. 1, and the retentate derived from filtration was recycled to the feed tank. Tests to recover fouled membrane flux were also investigated by using laboratory prepared cleaning solutions, which are listed in Table 1. 3. Experimental results 3.1. Synthesized emulsified oily wastewater This section firstly investigated the performance of MF on laboratory prepared emulsified oily wastewater. The wastewater sample was characterized and analyzed using a Coulter Multisizer and GC before experiments, respectively. Its mean droplet size was 2.4 µm with addition of 0.15% SDS emulsifier and the concentration of organic compound (n-decane) in wastewater was 850 ppm. Microfiltration results operated under continuous mode at room temperature are shown in Fig. 2, which showed fresh and washed membrane performance on synthesized wastewater samples. It indicated that the permeate flux of fresh membrane decreased with filtration time during the first hour of continuous filtration. After that, the permeate flux reached a stable value. GC analytical results showed that the concentration of organic compound (n-decane) in permeate was below 30 ppm. The removal efficiency of n-decane from the wastewater sample was over 95% under the experimental conditions used. In addition, fouling increased with filtration time and decreased membrane performance on treatment of the emulsified oily wastewater. The fouled membrane was cleaned by using laboratory prepared solutions followed by deionized water. The washed
Y. Wang et al. / Desalination 249 (2009) 1223–1227
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Fig. 1. A diagram of microfiltration cross-flow operation. 1—temperature controller; 2—electric stirrer; 3—pressure regulator; 4—suction pump; 5—pressure indicator; 6—flow meter; 7—purifier; 8—air pump; 9—water bath; 10—feed tank; 11—gas diffuser; 12—membrane reactor; 13—flat membrane; 14—membrane module; 15—permeate tank.
Operational parameters, mainly temperature and transmembrane pressure, have influence on MF performance for wastewater treatment. Increasing pressure implies that the operation would consume more energy, which normally is not preferred in the industry. However, the temperature of wastewater stream might be varied with different factory operational conditions. Hereby, the effects of temperature variation on MF performance were investigated. Results are shown in Fig. 3 and indicated that the permeate flux slightly increased with increasing operation temperature. GC analytical results showed that the removal efficiency of organic compounds has not changed very much. This experimental result showed that MF operation could be operated at relative flexible conditions, which was useful for it to be applied in industries.
the permeate flux reached to a stable value, which was lower than that of the experimental results with laboratory prepared emulsified oily wastewater. GC analytical results showed that the concentration of total organic compounds in the permeate water sample was below 75.0 ppm, which implied that the removal efficiency for total organic compounds was over 94.0%. This is close to the experimental results obtained by using laboratory prepared emulsified oily wastewater. The concentrated stream derived from the retentate could be used as fuel or other products through further treatment, and the water collected from the permeate flux could be reinjected if it is used in the practical operation. A series of cleaning experiments using laboratory prepared washing solutions were carried out and results (Fig. 4) showed that the regenerated membrane could not completely recover its permeate flux as a fresh membrane. This was probably because the factory emulsified oily wastewater contained more small particles, which could deposit in the membrane pores under continuous filtration and could not easily be removed from the membrane pores. However, MF operation combined with economic method of powdered activated carbons (PACs) or other pretreatment methods might improve its performance on the factory emulsified oily wastewater treatment according to previous studies [10].
3.3. Experiments on factory's emulsified oily wastewater
3.4. Membrane cleaning test with interval aeration
Based on MF performance for the laboratory synthesized oily wastewater, experiments using the wastewater sample of oil exploitation factory were conducted on an MF operation. The wastewater sample was characterized and analyzed using Coulter Multisizer and GC before the experiments, respectively. GC results showed that the concentration of total organic compounds in the wastewater was 1450 ppm. The analytical results by using Coulter Multisizer showed that the distributions of emulsified oily particles were a bit different from the laboratory prepared sample. The compositions of the former wastewater sample were as follows: emulsified particle sizes below 1.8 µm, 1.8–2.4 µm, 2.4–3.0 µm, and over 3.0 µm are 10.0%, 55.0%, 21.0%, 14.0%, respectively. Microfiltration results under continuous mode at room temperature are shown in Fig. 4. Similarly, it indicated that the permeate flux decreased with continuous filtration time. After about 1 h of filtration,
It has been known that the operation using interval filtration and aeration under suitable transmembrane pressure (TMP) in membrane bioreactor (MBR) could effectively alleviate membrane fouling and thus improve its performance. Tests with 10 min of filtration under
membrane performance on wastewater sample treatment was also shown in Fig. 2. It indicated that the fouling membrane could be recovered using conventional cleaning methods. The cleaned membrane had almost the same removal efficiency for n-decane as a fresh membrane. 3.2. Effects of temperature on permeate flux
Table 1 Laboratory prepared solutions for cleaning membrane. Solutions
Concentration (M)
pH
Sodium dodecylbenzenesulfate Sodium hydroxide Hydrochloric acid Citric acid
0.05 0.50 0.20 0.15
7.97 13.2 0.92 1.95
Fig. 2. MF performance on treatment of laboratory-made emulsified oily wastewater.
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Fig. 3. Operational temperature effects of MF performance on treatment of laboratorymade emulsified oily wastewater.
Fig. 5. Membrane performance by combination of filtration with interval aeration.
0.12 MPa and intervals of 2-minute aeration with air were investigated in this study. The aeration rate was 3.0 ml min− 1. During the flux tests, recordings were taken with four or five minute intervals lasting for 2 h, which was carried out twice in the daily time. Results are shown in Fig. 5 and indicated that the membrane flux could be maintained in a stable value with a combination of aeration. SEM characterized surface textures of operated membrane for 10 days did not show much difference to the fresh membrane (Fig. 6). It indicated that this operation could be a promising method to improve membrane performance on the treatment of a factory's emulsified oily wastewater. This research provides a basis for further investigation to test its possibility to be used in this process.
emulsified oily wastewater was that the MF membrane could not be fully regenerated by using conventional cleaning methods. However, experimental results showed that the combination of filtration with interval aeration under suitable operational pressure could effectively alleviate membrane fouling and thus improve membrane performance, which provides the basis for further investigation of its application in factory emulsified oily wastewater treatment.
4. Conclusions This study showed that the MF operation using PVDF membrane could effectively remove the laboratory simulated emulsified oily wastewater. The removal efficiency of organic compounds from the wastewater sample is over 95% under the experimental conditions used. Experimental results indicated that the fouled membrane could be recovered by using conventional cleaning methods. Further experiments to treat the factory wastewater sample were also carried out using MF operation. Similar results were obtained compared to the filtration on laboratory prepared emulsified oily wastewater. For fresh membranes, higher removal efficiency and stable permeate flux were obtained. The problem observed in the treatment of the factory
Fig. 4. MF performance on treatment of factory locale emulsified oily wastewater.
Fig. 6. SEM surface photograph of fresh and used membranes. (a) Fresh membrane; (b) dense membrane contacted to wastewater sample.
Y. Wang et al. / Desalination 249 (2009) 1223–1227
Acknowledgement This research was supported by the CNPC foundation. References [1] A.F. Viero, T.M. de Melo, A.P.R. Torres, et al., The effects of long-term feeding of high organic loading in a submerged membrane bioreactor treating oil refinery wastewater, J. Membr. Sci. 319 (2008) 223–230. [2] X.L. Qiao, Z.J. Zhang, J.L. Yu, X.F. Ye, Performance characteristics of a hybrid membrane pilot-scale plant for oilfield-produced wastewater, Desalination 225 (2008) 113–122. [3] G. Libralato, A. Volpi Ghirardini, F. Avezzù, Evaporation and air-stripping to assess and reduce ethanolamines toxicity in oily wastewater, J. Hazard. Mater. 153 (2008) 928–936. [4] M. Perez, R. Rodriguez-Cano, L.I. Romero, D. Sales, Performance of anaerobic thermophilic fluidized bed in the treatment of cutting-oil wastewater, Bioresour. Technol. 98 (2007) 3456–3463. [5] Y.H. Wang, J.L. Zhu, C.G. Zhao, J.C. Zhang, Removal of trace organic compounds from wastewater by ultrasonic enhancement on adsorption, Desalination 186 (2005) 89–96. [6] M. Kriipsalu, M. Marques, D.R. Nammari, W. Hogland, Bio-treatment of oily sludge: the contribution of amendment material to the content of target contaminants, and the biodegradation dynamics, J. Hazard. Mater. 148 (2007) 616–622. [7] Y.B. Zeng, C.Z. Yang, J.D. Zhang, W.H. Pu, Feasibility investigation of oily wastewater treatment by combination of zinc and PAM in coagulation/ flocculation, J. Hazard. Mater. 147 (2007) 991–996. [8] C.T. Carmen, D.K. Marie, A.S. Henry, C.S. Jan, Evaluation of secondary refinery effluent treatment using ultrafiltration membranes, Water Res. 33 (1999) 2172–2180. [9] X.Y. Li, H.P. Chu, Membrane bioreactor for the drinking water treatment of polluted surface water supplies, Water Res. 37 (2003) 4781–4791. [10] J.C. Zhang, Y.H. Wang, L.F. Song, J.Y. Hu, S.L. Ong, W.J. Ng, L.Y. Lee, Feasibility investigation of refinery wastewater treatment by combination of PACs and coagulant with ultrafiltration, Desalination 174 (3) (2005) 247–256. [11] M. Bodzek, K. Konieczny, Comparison of various membrane types and module configurations in the treatment of natural water by means of low-pressure membrane methods, Sep. Purif. Technol. 14 (1998) 69–78. [12] M. Thanuttamavong, K. Yamamoto, J.I. Oh, K.H. Choo, S.J. Choi, Rejection characteristics of organic and inorganic pollutants by ultra low-pressure nanofiltration of surface water for drinking water treatment, Desalination 145 (2002) 257–264.
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[13] P. Linke, A. Kokossis, Advanced process systems design technology for pollution prevention and waste treatment, Adv. Environ. Res. 8 (2004) 229–245. [14] A. Pozderović, T. Moslavac, A. Pichler, Concentration of aqueous solutions of organic components by reverse osmosis: II. Influence of transmembrane pressure and membrane type on concentration of different alcohol solutions by reverse osmosis, J. Food Eng. 77 (2006) 810–817. [15] F. Heymes, P. Manno Demoustier, F. Charbit, J.L. Fanlo, P. Moulin, Recovery of toluene from high temperature boiling absorbents by pervaporation, J. Membr. Sci. 284 (2006) 145–154. [16] F.C. Ferreira, L.G. Peeva, A. Boam, S.F. Zhang, A.G. Livingston, Pilot scale application of the Membrane Aromatic Recovery System (MARS) for recovery of phenol from resin production condensates, J. Membr. Sci. 257 (2005) 120–133. [17] F.C. Ferreira, L.G. Peeva, A.G. Livingston, Mass transfer enhancement in the membrane aromatic recovery system (MARS): experimental results and comparison with theory, Chem. Eng. Sci. 60 (2005) 1029–1042. [18] M.J. González-Muñoz, S. Luque, J.R. Álvarez, J. Coca, Recovery of phenol from aqueous solutions using hollow fibre contactors, J. Membr. Sci. 213 (2003) 181–193. [19] M. Teresa, A. Reis, O.M.F. de Freitas, M. Rosinda, C. Ismael, J.M.R. Carvalho, Recovery of phenol from aqueous solutions using liquid membranes with Cyanex 923, J. Membr. Sci. 305 (2007) 313–324. [20] J. Sawai, N. Ito, T. Minami, M. Kikuchi, Separation of low volatile organic compounds, phenol and aniline derivatives, from aqueous solution using silicone rubber membrane, J. Membr. Sci. 252 (2005) 1–7. [21] K. Majewska-Nowak, M. Kabsch-Korbutowicz, T. Winnicki, Concentration of organic contaminants by ultrafiltration, Desalination 221 (2008) 358–369. [22] S.L. Yu, Y. Yan, B.X. Chai, J.H. Liu, Treatment of oily wastewater by organic– inorganic composite tubular ultrafiltration (UF) membranes, Desalination 196 (2006) 76–83. [23] L.D. Nghiem, P. Mornane, I.D. Potter, J.M. Perera, R.W. Cattrall, S.D. Kolev, Extraction and transport of metal ions and small organic compounds using polymer inclusion membranes (PIMs), J. Membr. Sci. 281 (2006) 7–41. [24] S.R. Gray, C.B. Ritchie, T. Tran, B.A. Bolto, P. Greenwood, F. Busetti, B. Allpike, Effect of membrane character and solution chemistry on microfiltration performance, Water Res. 42 (2008) 743–753. [25] A.A. Ahmed, W.L. Robert, Fouling strategies and the cleaning system of NF membranes and factors affecting cleaning efficiency, J. Membr. Sci. 303 (2007) 4–28. [26] Y.J. Jung, Y. Kiso, T. Yamada, T. Shibata, T.G. Lee, Chemical cleaning of reverse osmosis membranes used for treating wastewater from a rolling mill process, Desalination 190 (2006) 181–188. [27] K. Katsoufidou, S.G. Yiantsios, A.J. Karabelas, An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery, Desalination 220 (2008) 214–227.
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Investigation of microfiltration for treatment of emulsified oily wastewater from the processing of petroleum products Yanhui Wang a,⁎, Xu Chen a, Jinchang Zhang b,c, Jingmei Yin b, Huanmei Wang d a
College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China College of Environment and Chemical Engineering, Dalian University, Dalian 116622, China School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore d Department of Petrochemical, Lanzhou Petrochemical College of Vocational Technology, Lanzhou 730060, China b c
a r t i c l e
i n f o
Article history: Accepted 28 June 2009 Available online 12 October 2009 Keywords: Microfiltration Wastewater treatment Emulsified oily wastewater
a b s t r a c t This research has investigated the possibility of using polyvinylidene fluoride (PVDF) membrane to treat the emulsified oily wastewater. Experimental results showed that the microfiltration could effectively treat the laboratory prepared emulsified oily wastewater and the fouled membrane could be recovered by using conventional cleaning methods. Similar promising results were obtained to treat factory emulsified oily wastewater by using microfiltration. In addition, different cleaning methods were investigated to recover the fouled membrane flux. Results showed that suitable interval operation of filtration and aeration could eliminate the membrane fouling under relative lower transmembrane pressure. Experimental results provided the basis for further investigation of its application in factory emulsified oily wastewater treatment. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water use has grown rapidly in modern times both because of rapid growth of humanity's actions and economics [1–4]. In most forms, water is a renewable resource since its continued flows are not affected by withdrawals or use. However, most of renewable waters have become non-renewable mainly because of contamination from human actions, which makes a significant portion of water resources unusable due to industrial and agriculture pollution and so forth [5–8]. This concern has been a main issue on the international agenda since the 1970's. The need to develop more sustainable practices for the management and efficient use of water resources, as well as the need to protect the environmental ecosystems where these resources are located, has led to fundamental shifts in awareness and public attention after that. A common understanding realizes that the disposal and treatment of sewage, and industrial effluents has become a strategy to efficiently use water resources [9,10]. The emulsified oily wastewater from the processing of petroleum products (particularly in oil exploitation) was difficult to treat by using common methods, e.g. sedimentation, centrifugation, bed filtration and so forth. In addition, those operations could produce a series of problems in applications. It would not only upset the surface equipment and potentially choke reservoir, but also produce enormous waste with the rejected wastewater containing significant amounts of crude oil and cause serious environmental pollution. A ⁎ Corresponding author. Tel.: +86 10 64416428; fax: +86 10 64423254. E-mail addresses: [email protected], [email protected] (Y. Wang). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.033
suitable method to treat this kind of oily wastewater now has become the bottleneck to improve China's oil productivity. It is well known that mechanical systems with a combination of physical, biological, and chemical processes to achieve the treatment objectives have become the preferred methods to deal with wastewaters, in which membrane filtration plays a very important role in wastewater purification [11–13]. Pozderović et al. [14] investigated the application of reverse osmosis (RO) for concentration of alcohol solutions. The effects of different types of membranes, processing pressure parameters and volume concentration with different alcohols using model solutions of alcohols, on RO operation have been studied. The gaseous effluents containing hydrophobic volatile organic compounds (VOCS) can be carried out by absorption with the use of a heavy hydrophobic solvent, while the used solvent must be regenerated to reuse it in the process of absorption. Heymes et al. [15] suggested that it could be operated using a hybrid absorption–pervaporation process, in which the pervaporation served to regenerate the solvent. Results showed that membrane operation had good ability to separate the heavy absorbent from mixture stream. The only problem was that the accumulation of absorbent could be occurring in the porous support, which could decrease the separation efficiency. Ferreira et al. [16,17] described the possibility to recover phenol from wastewater streams by membrane, which was derived from a phenolic resins production plant. González-Muñoz et al. [18] investigated the recovery of phenol from aqueous solutions by using hollow fibres, while Reis et al. [19] reported experimental results by using liquid membranes. The influence of different parameters, e.g. stripping solution, and solution concentration, on the process performance has been investigated. Sawai et al. [20] investigated the performance using a silicone rubber
1224
Y. Wang et al. / Desalination 249 (2009) 1223–1227
membrane on separation and recovery of 4-substituted phenol and aniline derivatives from aqueous solutions with the combination of permeation with chemical desorption (PCD) method. Results showed that phenols or anilines in aqueous solution were successfully recovered to aqueous NaOH or HCl solutions, respectively. Majewska-Nowak et al. [21] have investigated the possibility of concentrating organics in the wastewater by using ultrafiltration. Yu et al. [22] reported that the oily wastewater from an oil field could be purified by using a tubular ultrafiltration module equipped with polyvinylidene fluoride membranes, which was modified by inorganic nano-sized alumina particles. Results showed that the addition of nano-sized alumina particles improved the membrane performance of antifouling, and the flux of membrane filtration could be recovered by chemical cleaning method. Nghiem et al. [23] recently reviewed the progress of polymer inclusion membranes used for selective separation and recovery of metal ions as well as numerous organic solutes. They pointed out that the studies should not only highlight its potential in various niche applications on a practical scale but also emphasize the need for more fundamental research before any practical applications can be realized. This is particularly important for the treatment of streams containing small organic compounds as the transport mechanisms of such compounds through membranes are less well understood to date. Gray et al. [24] studied the reasons of natural organic matter (NOM) in the fouling of low-pressure membrane operation, which help to understand the methods to improve membrane performance in wastewater treatment. Ahmed and Robert [25] reviewed the research progress on membrane fouling occurring in nanofiltration operation. In addition, they also outlined the methods to clean or reduce the fouling during the membrane filtration operation. An analysis of fouling material and the effects of chemical cleaning were reported by Jung et al. [26] for a reverse osmosis membrane operation, which was used for the treatment of wastewater from a rolling mill process in the steel industry. Katsoufidou et al. [27] also provided a suitable method to recover the flux of ultrafiltration membrane operation. Based on previous studies and the feature of emulsified oily wastewater from an oil exploitation factory, we investigated the possibility to treat it by using microfiltration (MF) operation. If MF could be successfully operated, it will not only allow use of the water locally but also decrease the operational cost. This study reported MF experimental results on laboratory prepared wastewater and sample collected from an oil exploitation factory, respectively. 2 . Experimental sections 2.1 . Materials Chemically pure n-decane and analytical grade sodium dodecyl sulfate (SDS) were bought from Beijing Chemical Reagent Company. The other laboratory grade reagents used in experiments, e.g. hydrochloric acid (HCl), sulfuric acid (H2SO4), ammonium hydroxide (NH4OH), sodium hydroxide (NaOH) and so forth, were bought from Beijing Chemical Reagent Third Factory. Laboratory-made deionized water was used to prepare the emulsified oily wastewater. The local wastewater sample was kindly provided by an oil exploitation factory, China. The flat sheet membrane of polyvinylidene fluoride (PVDF) with 0.2 µm pore size was bought from Hangzhou Xidoumen Membrane Industries Co., Ltd., China. 2.2. Preparation of emulsified oily wastewater Emulsified oily wastewater was prepared by using a Nissei ACE homogenizer (Japan). The accurately weighed samples of n-decane and deionized water were heated certain temperature and then mixed together. Sodium dodecyl sulfate (SDS) was used as emulsifier
and 0.15 wt.% SDS was added. The homogenizer was operated at 3000 rpm and lasted for 20 min. 2.3. Analytical methods The laboratory prepared emulsified oily wastewater were analyzed by using the Coulter Multisizer (Beckman Coulter, America). The pH values of samples were measured with a PB-10 acid meter (Sartorius, Germany). The pH for the synthesized oily wastewater was 6.30. The concentration of organic compounds in wastewater samples was analyzed with a gas chromatography (GC4000A, Beijing East & West Analytical Instruments, Inc.) unit equipped with a flame ionization detector (FID). The removal efficiency (R) of organic compounds from the microfiltration was estimated using Eq. (1), in which Cfeed and Cpermeate are concentrations of feed and permeate, respectively. Furthermore, the surface profiles of membrane were investigated with an S-3200N Hitachi scanning electron microscope (SEM). R=
Cfeed −Cpermeate × 100 Cfeed
ð1Þ
2.4. MF operational system A diagram of the laboratory-scale operational microfiltration system is shown in Fig. 1. All experimental filtrations were carried out on membrane samples with a filtration of area of 7.4 cm2. The membrane was pretreated before the test. It was washed for 2 h with deionized water at room temperature followed by chemical washing for 10 min with 350 ppm of sodium hypochlorite solution. Thereafter the membrane was soaked in deionized water for 1 h. The filtration was performed in continuous cross-flow mode and the feed rate was about 3.0 ml min− 1. All filtration experiments were carried out at 0.2 MPa unless other stated. The filtration process commenced by supplying feed contained in the feed tank as shown in Fig. 1, and it was continuously stirred with an electric stirrer during the experiment. The permeate sample was collected in the permeate tank, shown in Fig. 1, and the retentate derived from filtration was recycled to the feed tank. Tests to recover fouled membrane flux were also investigated by using laboratory prepared cleaning solutions, which are listed in Table 1. 3. Experimental results 3.1. Synthesized emulsified oily wastewater This section firstly investigated the performance of MF on laboratory prepared emulsified oily wastewater. The wastewater sample was characterized and analyzed using a Coulter Multisizer and GC before experiments, respectively. Its mean droplet size was 2.4 µm with addition of 0.15% SDS emulsifier and the concentration of organic compound (n-decane) in wastewater was 850 ppm. Microfiltration results operated under continuous mode at room temperature are shown in Fig. 2, which showed fresh and washed membrane performance on synthesized wastewater samples. It indicated that the permeate flux of fresh membrane decreased with filtration time during the first hour of continuous filtration. After that, the permeate flux reached a stable value. GC analytical results showed that the concentration of organic compound (n-decane) in permeate was below 30 ppm. The removal efficiency of n-decane from the wastewater sample was over 95% under the experimental conditions used. In addition, fouling increased with filtration time and decreased membrane performance on treatment of the emulsified oily wastewater. The fouled membrane was cleaned by using laboratory prepared solutions followed by deionized water. The washed
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Fig. 1. A diagram of microfiltration cross-flow operation. 1—temperature controller; 2—electric stirrer; 3—pressure regulator; 4—suction pump; 5—pressure indicator; 6—flow meter; 7—purifier; 8—air pump; 9—water bath; 10—feed tank; 11—gas diffuser; 12—membrane reactor; 13—flat membrane; 14—membrane module; 15—permeate tank.
Operational parameters, mainly temperature and transmembrane pressure, have influence on MF performance for wastewater treatment. Increasing pressure implies that the operation would consume more energy, which normally is not preferred in the industry. However, the temperature of wastewater stream might be varied with different factory operational conditions. Hereby, the effects of temperature variation on MF performance were investigated. Results are shown in Fig. 3 and indicated that the permeate flux slightly increased with increasing operation temperature. GC analytical results showed that the removal efficiency of organic compounds has not changed very much. This experimental result showed that MF operation could be operated at relative flexible conditions, which was useful for it to be applied in industries.
the permeate flux reached to a stable value, which was lower than that of the experimental results with laboratory prepared emulsified oily wastewater. GC analytical results showed that the concentration of total organic compounds in the permeate water sample was below 75.0 ppm, which implied that the removal efficiency for total organic compounds was over 94.0%. This is close to the experimental results obtained by using laboratory prepared emulsified oily wastewater. The concentrated stream derived from the retentate could be used as fuel or other products through further treatment, and the water collected from the permeate flux could be reinjected if it is used in the practical operation. A series of cleaning experiments using laboratory prepared washing solutions were carried out and results (Fig. 4) showed that the regenerated membrane could not completely recover its permeate flux as a fresh membrane. This was probably because the factory emulsified oily wastewater contained more small particles, which could deposit in the membrane pores under continuous filtration and could not easily be removed from the membrane pores. However, MF operation combined with economic method of powdered activated carbons (PACs) or other pretreatment methods might improve its performance on the factory emulsified oily wastewater treatment according to previous studies [10].
3.3. Experiments on factory's emulsified oily wastewater
3.4. Membrane cleaning test with interval aeration
Based on MF performance for the laboratory synthesized oily wastewater, experiments using the wastewater sample of oil exploitation factory were conducted on an MF operation. The wastewater sample was characterized and analyzed using Coulter Multisizer and GC before the experiments, respectively. GC results showed that the concentration of total organic compounds in the wastewater was 1450 ppm. The analytical results by using Coulter Multisizer showed that the distributions of emulsified oily particles were a bit different from the laboratory prepared sample. The compositions of the former wastewater sample were as follows: emulsified particle sizes below 1.8 µm, 1.8–2.4 µm, 2.4–3.0 µm, and over 3.0 µm are 10.0%, 55.0%, 21.0%, 14.0%, respectively. Microfiltration results under continuous mode at room temperature are shown in Fig. 4. Similarly, it indicated that the permeate flux decreased with continuous filtration time. After about 1 h of filtration,
It has been known that the operation using interval filtration and aeration under suitable transmembrane pressure (TMP) in membrane bioreactor (MBR) could effectively alleviate membrane fouling and thus improve its performance. Tests with 10 min of filtration under
membrane performance on wastewater sample treatment was also shown in Fig. 2. It indicated that the fouling membrane could be recovered using conventional cleaning methods. The cleaned membrane had almost the same removal efficiency for n-decane as a fresh membrane. 3.2. Effects of temperature on permeate flux
Table 1 Laboratory prepared solutions for cleaning membrane. Solutions
Concentration (M)
pH
Sodium dodecylbenzenesulfate Sodium hydroxide Hydrochloric acid Citric acid
0.05 0.50 0.20 0.15
7.97 13.2 0.92 1.95
Fig. 2. MF performance on treatment of laboratory-made emulsified oily wastewater.
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Fig. 3. Operational temperature effects of MF performance on treatment of laboratorymade emulsified oily wastewater.
Fig. 5. Membrane performance by combination of filtration with interval aeration.
0.12 MPa and intervals of 2-minute aeration with air were investigated in this study. The aeration rate was 3.0 ml min− 1. During the flux tests, recordings were taken with four or five minute intervals lasting for 2 h, which was carried out twice in the daily time. Results are shown in Fig. 5 and indicated that the membrane flux could be maintained in a stable value with a combination of aeration. SEM characterized surface textures of operated membrane for 10 days did not show much difference to the fresh membrane (Fig. 6). It indicated that this operation could be a promising method to improve membrane performance on the treatment of a factory's emulsified oily wastewater. This research provides a basis for further investigation to test its possibility to be used in this process.
emulsified oily wastewater was that the MF membrane could not be fully regenerated by using conventional cleaning methods. However, experimental results showed that the combination of filtration with interval aeration under suitable operational pressure could effectively alleviate membrane fouling and thus improve membrane performance, which provides the basis for further investigation of its application in factory emulsified oily wastewater treatment.
4. Conclusions This study showed that the MF operation using PVDF membrane could effectively remove the laboratory simulated emulsified oily wastewater. The removal efficiency of organic compounds from the wastewater sample is over 95% under the experimental conditions used. Experimental results indicated that the fouled membrane could be recovered by using conventional cleaning methods. Further experiments to treat the factory wastewater sample were also carried out using MF operation. Similar results were obtained compared to the filtration on laboratory prepared emulsified oily wastewater. For fresh membranes, higher removal efficiency and stable permeate flux were obtained. The problem observed in the treatment of the factory
Fig. 4. MF performance on treatment of factory locale emulsified oily wastewater.
Fig. 6. SEM surface photograph of fresh and used membranes. (a) Fresh membrane; (b) dense membrane contacted to wastewater sample.
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