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Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic concentrations
JES-01075; No of Pages 9 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S X X (2 0 1 7 ) XX X–XXX
Available online at www.sciencedirect.com
ScienceDirect www.elsevier.com/locate/jes
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Yan Wu1 , Yun Kang1 , Liqiu Zhang, Dan Qu, Xiang Cheng, Li Feng⁎
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Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic concentrations
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Beijing Key Lab for Source Control Technology of Water Pollution, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China. E-mails: [email protected], [email protected]
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Article history:
In this study, direct contact membrane distillation (DCMD) was used for treating 16
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Received 5 July 2016
fermentation wastewater with high organic concentrations. DCMD performance character- 17
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Revised 20 December 2016
istics including permeate flux, permeate water quality as well as membrane fouling were 18
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Accepted 23 January 2017
investigated systematically. Experimental results showed that, after 12 hr DCMD, the feed 19
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Available online xxxx
wastewater was concentrated by about a factor of 3.7 on a volumetric basis, with the 20
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Keywords:
membrane fouling; the protein concentration in the feed wastewater was increased by 22
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Fermentation wastewater
about 3.5 times and achieved a value of 6178 mg/L, which is suitable for reutilization. 23
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Direct contact membrane distillation
Although COD and TOC in permeate water increased continuously due to the transfer of 24
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Membrane fouling
volatile components from wastewater, organic rejection of over 95% was achieved in 25
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permeate flux decreasing from the initial 8.7 L/m2/hr to the final 4.3 L/m2/hr due to 21
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wastewater. GC–MS results suggested that the fermentation wastewater contained 128 26
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kinds of organics, in which 14 organics dominated. After 12 hr DCMD, not only volatile 27 organics including trimethyl pyrazine, 2-acetyl pyrrole, phenethyl alcohol and phenylacetic 28
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acid, but also non-volatile dibutyl phthalate was detected in permeate water due to 29 membrane wetting. FT-IR and SEM–EDS results indicated that the deposits formed on the 30
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membrane inner surface mainly consisted of Ca, Mg, and amine, carboxylic acid and 31 aromatic groups. The fouled membrane could be recovered, as most of the deposits could be 32 © 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. 34
Introduction
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In recent years, an increasing amount of fermentation wastewater has been generated with the rapid industrial development in China. In general, fermentation wastewater is dark in color and has a high chemical oxygen demand (COD) value ranging from 1 × 105 to 6 × 105 mg/L (Zeng et al., 2009).
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removed using a HCl/NaOH chemical cleaning method.
Published by Elsevier B.V. 35
The highly-concentrated non-biodegradable organics, especially metabolites, make fermentation wastewater difficult to biodegrade, so a treatment method is needed to prevent the environmental problems caused by its discharge. Multi-effect distillation (MED) and activated sludge treatment are the main methods developed to treat fermentation wastewater. However, MED requires too much energy, and activated sludge treatment
⁎ Corresponding author. E-mail: [email protected] (Li Feng). 1 The authors contributed equally to this work.
http://dx.doi.org/10.1016/j.jes.2017.01.015 1001-0742/© 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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The fermentation wastewater samples were obtained from a yeast factory in Harbin, China. Before DCMD treatment, all the samples were preserved in a refrigerator. COD, TOC and protein concentrations of the fermentation wastewater were characterized as 54,900, 20,900 and 1765 mg/L, respectively. For solutions without inorganics, the value of COD (mg O2/L)/ TOC (mg carbon/L) is generally 2.66 and varies with water quality (e.g., between 2.0 to 5.0 for municipal wastewater). Therefore, although COD was much higher than TOC in the studied wastewater, the value of COD/TOC (calculated as 2.63) is in the normal range. The pH value of the fermentation wastewater was 6.0–7.0. Analyzed by gas chromatography– mass spectrometry (GC–MS), fourteen major organic compounds (area percentage > 1%) including isoamyl, 2-methyl butyric acid, 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole, 2-pyrrolidinone, phenethyl alcohol, benzoic acid, phenylacetic acid, 4-ethenyl-2-methoxyphenol, o-hydroxybenzoic acid, p-hydroxyphenyl ethanol, p-hydroxyphenylcyanide, 4-hydroxy3-methoxyphenethyl alcohol and butyl phthalate were found in the fermentation wastewater.
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1.2. DCMD set-up and running conditions
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The schematic diagram of the DCMD set-up used in this study for fermentation wastewater treatment is shown in Fig. 1. The membrane module in the DCMD set-up was a self-made polyester tube combined with two unplasticized polyvinyl chloride T-tubes. The outside diameter, inside diameter and effective length of the module were 20, 15 and 225 mm, respectively. Sixteen pieces of commercial hollow fiber polypropylene (PP) membranes (ACCUREL PP Q3/2, Membrana, Germany) with a total effective membrane area of 0.023 m2 were packed in the module. The basic membrane properties are as following: pore average diameter 0.46 μm, outer diameter/inner diameter is 2.5 mm/2.0 mm, thickness 0.25 mm, porosity 80%, liquid entrance pressure (LEP) 400 kPa. DCMD was operated to run for 12 hr to treat fermentation wastewater. With an initial volume of 1 L, the feed fermentation wastewater was pumped continuously into the tube side after being heated by a heater (DK-98-IIA, Tianjing Taisite Technology, China), and the permeate water with an initial volume of 1 L was pumped into the shell side after cooling by a cooler (SDC-6, Nanjing Xinzhi Biotechnology, China). To prevent the feed wastewater being overly concentrated, wastewater of the same properties was supplemented continuously to the feed tank at a rate of 115 mL/hr. Limited by the low power of the cooler, the permeate temperature was
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1.1. Characteristics of fermentation wastewater
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1. Materials and methods
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well-designed DCMD configuration with a self-made membrane module was used as a pretreatment for treating fermentation wastewater with high organic concentrations from a yeast factory. DCMD performance characteristics such as permeate flux, permeate water quality, as well as membrane fouling mechanism and recovery methods were investigated systematically.
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wastes recyclable resource like protein in wastewater; thus, an appropriate treatment method for fermentation wastewater is urgently required to protect the environment and recover valuable resources in the meantime. Membrane distillation (MD) is a membrane separation process driven thermally by the temperature difference between the feed side and the permeate side of the membrane. Theoretically, an MD system has the capability of producing pure water from natural water because only water vapor molecules can transfer through the porous hydrophobic membrane during the separation process (El-Bourawi et al., 2006). For MD systems there are four different configurations, namely: direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), and vacuum membrane distillation (VMD). Based on the characteristics of hydrophobic membranes, these MD configurations have been studied for seawater desalination, solute recovery and wastewater treatment (Hou et al., 2010; Khayet et al., 2004, 2005; Qu et al., 2009; Shirazi et al., 2014; Zarebska et al., 2014). As the easiest and simplest configuration among them all, DCMD is the most widely studied (Drioli et al., 2015). To enhance water desalination, Cath et al. (2004) designed and investigated a new MD configuration and a new membrane module. Their research results showed that salt rejection in vacuum-enhanced DCMD could be greater than 99.9% in almost all cases. Al-Obaidani et al. (2008) developed an extensive analysis of DCMD performance and made an economic evaluation that the estimated water cost for DCMD with heat recovery was $1.17/m3. With the advantage of a lower fouling tendency, DCMD has been applied in treating various kinds of complex wastewater in recent research. El-Abbassi et al. (2009, 2013) applied DMCD in treating olive mill wastewater (OMW); their study results showed that the OMW concentration factor for the membrane TF200 was 1.72 after 9 hr DCMD operation, and an integrated microfiltration/DCMD system could be used to obtain clean water and a phenolic-rich concentrate from OMW. In the studies of Jacob et al. (2015), DCMD showed a reasonable flux of 2.09 L/m2/hr and high rejections of ammonia and COD of up to 89.6%–96.3% and 97.8%–99.9%, respectively, when treating anaerobic effluent. Wijekoon et al. (2014) investigated the feasibility of DCMD for removing trace organic compounds (TrOCs) during water and wastewater treatment, and the results of their experiments suggested that DCMD could be used as a promising post-treatment in conjunction with thermophilic membrane bioreactor for TrOC removal. Khayet (2013) used surface-modified membranes to process low and intermediate radioactive liquid wastes by DCMD, and their experimental results indicated that DCMD with surfacemodified membranes has potential for application in nuclear technology. Although DCMD has been proved applicable for wastewater treatment in many studies, its feasibility and performance in treating fermentation wastewater have rarely been studied. For a yeast factory, the highly-concentrated fermentation wastewater generated from the centrifugal filter unit generally has poor biodegradability, owing to the high concentration of organics (10,000–90,000 mg/L COD) it contains, therefore an efficient pretreatment is needed to remove a large part of the organics before further advanced treatment. In this study, a
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Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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To investigate the DCMD performance in treating fermentation wastewater, the volume of permeate water was measured every hour during the DCMD process, and the feed and permeate water were collected every hour for the testing of COD, TOC and protein, as well as organic compound identification. The permeate flux ( J, L/m2/hr) was calculated by Eq. (1):
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1.3. Evaluation of DCMD performance in treating fermentation 191 wastewater 192
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maintained at 30°C, and the feed temperature was controlled in the range of 55–60°C to satisfy the temperature difference requirement (5–20°C in general) of the MD process. Both the feed and the permeate water were recycled at the same flow rate of 2.0 L/min to their tanks concurrently via two magnetic pumps. For concentration of the proteins in fermentation wastewater, the DCMD process was applied under similar operating conditions to those used for wastewater treatment, whereas the initial 1 L feed wastewater was first concentrated for one hour before being supplemented by supplementary wastewater samples continuously. Before wastewater treatment, the pure water flux of the commercial PP membranes was tested under the same DCMD conditions as the wastewater treatment. Fig. 2 shows the variation of membrane pure water flux with time. The relatively high water flux (>15 L/m2/hr) indicated the feasibility of using PP membranes in the DCMD process.
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Fig. 1 – The schematic diagram of direct contact membrane distillation (DCMD) set-up in this work (1. feed tank; 2. heater; 3. magnetic pump; 4. flow meter; 5. membrane module; 6. cooler; 7. overflow permeate circle bulk; 8. permeate collecting tank).
J¼
V A∙Δt
C f0 −Cpt C f0
Fig. 2 – Pure water flux of the commercial polypropylene (PP) membrane in direct contact membrane distillation (DCMD) under the same conditions as the fermentation wastewater treatment.
C ft C f0
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ð2Þ
where Cf0 (mg/L) is the contaminant concentration in the original feed wastewater, and Cpt (mg/L) is the contaminant concentration in the permeate water collected at time t. The concentration multiple (CM) of contaminants was calculated by Eq. (3): CM ¼
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ð1Þ
where V (L) is the volume of permeate water, A (m2) is the total effective membrane area in module, and Δt (hr) is DCMD running time. The values of COD and TOC in the feed wastewater and the permeate water were tested with a fast COD analyzer (5B-3B (V8), Lianhua, China) and a TOC/TC analyzer (Multi N/C 3100, Jena, Germany), respectively. The protein concentration was measured by the Bradford Method with an UV spectrophotometer. The rejection (R) of contaminants (COD, TOC and protein) was calculated by Eq. (2): R¼
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ð3Þ
where Cft (mg/L) is the contaminant concentration in the feed wastewater at time t, and Cf0 (mg/L) is the contaminant concentration in original feed wastewater. To identify the organic compounds in both the feed wastewater and the permeate water, samples of the feed wastewater and the permeate water collected after 5, 10, and 12 hr DCMD operation were analyzed using a GC–MS analyzer (7890A–5975C, Agilent, USA) after being extracted to dichloromethane and
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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2. Results and discussion
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2.1. Performance of DCMD in treating fermentation wastewater
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2.1.1. Variation of COD and TOC in the feed fermentation wastewater and the permeate water during DCMD
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Fig. 3 presents the COD and TOC variations in the feed wastewater and the permeate water during the 12 hr DCMD process. As shown in Fig. 3, both COD and TOC concentrations in the feed wastewater and the permeate water increased approximately linearly with DCMD running time. In addition, the concentration variations of TOC were in accordance with those of COD. In detail, after the 12 hr DCMD process, the permeate volume had an increase of 1.19 L, and the feed wastewater was measured to be 640 mL; the feed and the permeate COD concentrations reached 170,050 and 2558 mg/L, respectively; the feed and the permeate TOC concentrations reached 71,900 and 900 mg/L, respectively; the rejections of COD and TOC were 95.3% and 95.7%, respectively; the CMs of COD and TOC were 3.5 and 3.4, respectively. The increase of permeate COD and TOC indicated that part of the contaminants in the feed wastewater passed through the membrane. This may due to the volatile compounds in the feed wastewater preferentially transferring through membrane. In addition, the partial wetting phenomenon of membrane
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To investigate membrane fouling as well as recovery methods, scanning electron microscopy (SEM, S3400N, Hitachi, Japan)– energy dispersive spectrometry (EDS, S3400N, Hitachi, Japan) and field emission scanning electron microscopy (FESEM, MERLIN, Carl Zeiss, Germany) were used to characterize the inner surface and the cross-section of virgin membrane, fouled membrane after the 12 hr DCMD process and recovered membranes, using two different methods. To obtain crosssectional morphologies, all the membrane samples were rinsed with water gently and subsequently freeze-fractured in liquid nitrogen, and before being characterized with SEM–EDS and FESEM, all the membrane samples were dried at room temperature and sputtered with gold afterward. Fourier transform infrared spectroscopy (FT-IR, Perkin-Elmer Spectrum GX, BRUKER, USA) was also used for fouling analysis. The FT-IR spectra were recorded in the mid-IR region 4000–400/cm with resolution of 4/cm and 16 scans. All measurements and operations were performed in a dry atmosphere at 20 ± 5°C. The two different membrane recovery methods in this study were pure water rinsing and chemical cleaning, respectively. For the pure water rinsing method, fouled membrane was rinsed with pure water for 60 min; for the chemical cleaning method, fouled membrane was first rinsed with pure water for 10 min, and then washed sequentially with HCl aqueous solution (0.5 mol/L), NaOH aqueous solution (0.5 mol/L) and pure water for 20, 20 and 10 min, respectively.
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concentrated by a rotary evaporator (RE-52AA, Shanghai Yarong, China).
Fig. 3 – Concentration variations of COD and TOC in the feed Q1 wastewater and the permeate water during the 12 hr direct contact membrane distillation (DCMD) process. COD: chemical oxygen demand.
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pores in the MD process would also contribute to the organic contaminants being transferred through the membrane pores (Gryta, 2012). In MD, the LEP (MPa) of the membrane has a relationship with the hydrophobicity of the membrane, and the equation can be expressed as Eq. (4) (El-Bourawi et al., 2006): LEP ¼
2∙γL ∙ cosθ r
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where γL (N/m) is the surface tension of liquid, θ (°) is the contact angle of the feed liquid with the membrane surface, and r (μm) is the radius of membrane pore. According to Eq. (4), it is easier for liquid to enter membrane pores having larger r and lower LEP, thus leading to membrane wetting. The partially wetted membrane pores allow not only volatile components, but also contaminants in the feed wastewater to transfer to the permeate side. Although COD and TOC in the permeate water increased continuously, membrane wetting was not extensive enough to deteriorate the permeate water quality to a great extent in this study.
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2.1.2. Identification of organic compounds in the permeate water 304 The GC–MS results for the permeate water collected after 5, 10 and 12 hr of the DCMD process are shown in Table 1. In total five kinds of organic compounds were detected in the permeate water.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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t1:3
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Table 1 – Gas chromatography–mass spectrometry (GC–MS) results for the permeate water collected after 5, 10 and 12 hr DCMD process. No.
Detected organic compound
Area percentage in permeate water
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5 hr
10 hr
12 hr
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2,3,5-Trimethyl pyrazine
4.48%
24.39%
7.04%
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II
2-Acetyl pyrrole
12.62%
26.92%
12.56%
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Phenethyl alcohol
72.16%
19.72%
9.65%
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Phenylacetic acid
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5.13%
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Dibutyl phthalate
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Organic compound structure
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After 5 hr of the DCMD process, only 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole and phenethyl alcohol were detected in the permeate water. These are all volatile compounds which can transfer through membrane pores easily as vapor molecules. At ten hours, another organic compound, phenylacetic acid, was detected. The delayed appearance of phenylacetic acid compared to the former three organic compounds was due to its complex structure. It should be noticed that dibutyl phthalate, which is not a volatile compound, was found in the permeate water collected at 12 hr. As discussed before, membrane wetting might occur in DCMD and result in non-volatile organics being transferred through the membrane pores to the permeate water. The appearance of dibutyl phthalate in permeate water could be evidence of membrane wetting. In addition, the GC–MS results would also contribute to explaining the increase of permeate COD and TOC as discussed in Section 2.1.1.
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DCMD: direct contact membrane distillation.
The rapid increase of protein concentration may be due to the presence of non-volatile proteins in the feed wastewater. The protein concentration in the permeate water showed slight fluctuations around 20 mg/L. This might have resulted from the transfer of some portion of protein through the aforementioned wetting of pores. After the 12 hr DCMD process, the CM and the rejection of protein in the feed wastewater reached 3.5% and 98.9%, respectively, indicating good DCMD performance in concentrating protein during fermentation wastewater treatment.
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2.1.3. Concentration variations of protein in the feed wastewater and the permeate water during DCMD In fermentation wastewater, protein is a valuable resource to be concentrated for reutilization. Fig. 4 presents the concentration variations of protein concentration in the feed wastewater and the permeate water during the 12 hr DCMD process. As shown in Fig. 4, the protein concentration in the feed wastewater increased rapidly from 1765 to 4517 mg/L within the first hour before achieving a value of 6178 mg/L at 12 hr.
Fig. 4 – Concentration variations of protein in the feed wastewater and the permeate water within the 12 hr direct contact membrane distillation (DCMD) process.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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Figs. 6, 7 and Table 2 are inner surface SEM, cross-section FESEM images and EDS analytical results for the virgin membrane, fouled membrane, fouled membrane after pure water rinsing and fouled membrane after chemical cleaning. In Fig. 7, the observed foulants are circled with dashed yellow lines. As shown in Figs. 6 and 7, almost the whole inner surface of the fouled membrane (Figs. 6b, 7b) was covered by an amorphous deposited fouling layer compared with the virgin membrane (Figs. 6a, 7a), owing to the highly-concentrated organics in the feed wastewater. The EDS results in Table 2 showed that besides the C and O elements that the virgin membrane mainly consisted of, other elements such as N (13.10 wt.%), Mg, Si, P, S, Cl, K, Ca, Fe and Zn were also found on the inner surface of the fouled membrane. This may due to the combined effect of salt deposition and organic adsorption on the membrane surface during DCMD, indicating that there might be both inorganic fouling and organic fouling. After pure water rinsing, the content of elements such as K, Ca and Zn decreased significantly, while large amounts of N
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2.2.1. Variation of membrane permeate flux
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Fig. 5 shows the permeate flux variation with time during DCMD. After 12 hr, permeate flux decreased by 50.5%, from 8.7 to 4.3 L/m2/hr. The decrease of permeate flux was mainly caused by membrane fouling and polarization effects. Organic and inorganic matters in the feed wastewater may deposit on the membrane inner surface and block membrane pores, thus
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Fig. 5 – Permeate flux of the polypropylene (PP) membrane within direct contact membrane distillation (DCMD) process before and after cleaned by pure water.
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hindering the transfer of water molecules. In addition, the vapor pressure of water also declined with the increase of solute concentration in the feed wastewater. Since water molecule transfer through the membrane was driven by the vapor pressure gradient, the decline of vapor pressure was another reason for the permeate flux decline in this study (Ding et al., 2003). After the fouled membrane was cleaned by pure water, the permeate flux recovered to 7.6 L/m2/hr, which is 87.8% of the virgin membrane permeate flux.
Fig. 6 – Inner surface scanning electron microscopy (SEM) images of membrane samples (a. virgin membrane; b. fouled membrane after 12 hr direct contact membrane distillation process; c. fouled membrane after pure water rinsing; d. fouled membrane after chemical cleaning). Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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2.2.3. FT-IR analysis
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Fig. 8 shows the FT-IR spectra of a virgin membrane, fouled membrane after 12 hr DCMD process, fouled membrane after pure water rinsing and fouled membrane after chemical cleaning. As shown in Fig. 8, the virgin PP membrane spectrum has peaks typical of \CH2\ and \CH3 functional groups at 2840– 2950/cm and 1380/cm (Andreassen, 1999), as well as aromatic
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t2:6
Table 2 – Energy dispersive spectrometry (EDS) analysis of virgin membrane (a), fouled membrane (b), fouled membrane after pure water rinsing (c), and fouled membrane after chemical cleaning (d). Elements
t2:7 t2:8 t2:9 t2:10 t2:11 t2:12 t2:13 t2:14 t2:15 t2:16 t2:17 t2:18 t2:19 t2:20 t2:21
C N O Na Mg Si P S Cl K Ca Fe Zn Total
Element mass fraction of different membrane samples (wt.%)
a
b
c
d
92.18 0 7.70 0.12 0 0 0 0 0.09 0 0 0 0 100.00
33.15 13.10 28.28 0.56 1.42 5.11 7.96 1.47 0.46 0.91 4.10 1.42 2.51 100.00
41.254 8.99 25.19 0.13 1.18 4.93 5.94 0.51 0 0.08 2.63 1.52 1.66 100.00
89.31 0 7.81 0.14 0.17 1.01 0 0.10 0.10 0 0.07 0.29 1.01 100
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and O elements remained on the fouled membrane surface (Figs. 6c, 7c and Column (c) in Table 2). In contrast, most of the foulants, especially N-containing compounds, were flushed off by chemical cleaning (Figs. 6d, 7d and Column (d) in Table 2). The SEM–EDS and FESEM results in this study revealed that water rinsing could only remove a part of the membrane foulants, while the chemical cleaning method was much more effective for the recovery of fouled membranes.
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Fig. 7 – Cross-sectional field emission scanning electron microscope (FESEM) images of membrane samples (a. virgin membrane; b. fouled membrane after 12 hr direct contact membrane distillation process; c. fouled membrane after pure water rinsing; d. fouled membrane after chemical cleaning), foulants are circled with dashed yellow lines. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 8 – Fourier transform infrared spectroscopy (FT-IR) spectra for membrane samples (line a: virgin membrane; line b: fouled membrane after 12 hr direct contact membrane distillation process; line c: fouled membrane after pure water rinsing; line d: fouled membrane after chemical cleaning).
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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3. Conclusions
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In this study, the performance of DCMD in treating fermentation wastewater with high organic concentrations was investigated for the first time. The results showed that after the 12 hr DCMD process, the volume of the feed wastewater, COD, TOC and protein in the feed fermentation wastewater were concentrated by 3.7, 3.5, 3.4 and 3.5 times, respectively. Meanwhile, over 95% COD, TOC and protein were rejected, indicating the good performance and prospects of DCMD in treating fermentation wastewater.
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Acknowledgments
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Membrane fouling in the MD process contains mainly three aspects; inorganic scaling, particulate and colloidal fouling, as well as biofouling (Warsinger et al., 2015). Based on the SEM– EDS, FESEM characterization and FT-IR analysis of foulants, it can be concluded that there was no crystallization observed in this study, and the foulants were made up of organic matters and inorganic ions. The feed fermentation wastewater contained a lot of organic acids, alcohols and proteins. These organic components contained both hydrophilic functional groups like carboxyl, and hydrophobic functional groups like hydrocarbon chains. The amphiprotic property of these organic components provided them with the ability to be adsorbed onto the hydrophobic surface of PP membrane. The increasing amount of the element N as well as the detection of amine functional groups in the fouled membrane confirmed the assumption that foulants were adsorbed on the membrane surface. In addition, the hydrophilic functional groups in these organics changed the membrane morphology and made the membrane surface hydrophilic, which might contribute to the initiation of fouling and hydrophilization of the membrane surface (Naidu et al., 2014). The initial fouling layer formed on the membrane made the hydrophilic organics in wastewater adhere much more easily to it and accelerated membrane fouling as a result (Tijing et al., 2015). According to the SEM–EDS results, although no crystallization was found on the membrane surface under SEM scanning, the inorganic elements like Ca and Mg contained in the foulants could strengthen the structure of the deposits and make the fouling layer more compact (Meng et al., 2015).
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This work was supported by the Special S&T Project 476 on Treatment and Control of Water Pollution (No. 477 2013ZX07201007-003). 478
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Five organic compounds including 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole, phenethyl alcohol, phenylacetic acid and dibutyl phthalate were detected in the permeate water. The permeate flux decreased 50.5% within 12 hr DCMD due to the foulants formed on the membrane inner surface facing the feed wastewater. The deposited foulants were mainly made up of organic components combined with inorganics. They were hard to flush off by water rinsing, while most of them could be removed by the combination of HCl solution (0.5 mol/L) and NaOH solution (0.5 mol/L). In conclusion, DCMD is a promising process for treating fermentation wastewater with high organic concentrations, due to its good performance in organic rejection and valuable resource recovery. Furthermore, as membrane fouling is still an obstacle to DCMD development, further studies on membrane fouling control are needed when applying DCMD in fermentation wastewater treatment.
REFERENCES
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hydrocarbons at 1600/cm and 1453/cm (Mahapatra et al., 2012). In the spectrum of the fouled membrane, the wide single peak at 3300/cm and twin peak near 1600/cm, which could normally be identified as the functional groups of amine and carboxylic acid, are characteristic of protein deposits. The spectrum of the fouled membrane after pure water rinsing (line c in Fig. 8) shows that the twin peak near 1600/cm in the fouled membrane (line b in Fig. 8) shifted to become a single peak near 1600/cm, which is assigned to aromatic hydrocarbons; the weak peak appearing at 1100/cm is attributed to the presence of sulfate radical. In contrast, the spectrum of the fouled membrane after chemical cleaning was quite similar to that of the virgin membrane, indicating the effective recovery of the fouled membrane via chemical cleaning in this study.
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Al-Obaidani, S., Curcio, E., Macedonio, F., Di Profio, G., Al-Hinai, H., Drioli, E., 2008. Potential of membrane distillation in seawater desalination: thermal efficiency, sensitivity study and cost estimation. J. Membr. Sci. 323, 85–98. Andreassen, E., 1999. Infrared and Raman spectroscopy of polypropylene. In: Karger-Kocsis, J. (Ed.), Polypropylene: An A–Z Reference. Springer Netherlands, Dordrecht, pp. 320–328. Cath, T.Y., Adams, V.D., Childress, A.E., 2004. Experimental study of desalination using direct contact membrane distillation: a new approach to flux enhancement. J. Membr. Sci. 228, 5–16. Ding, Z., Ma, R., Fane, A.G., 2003. A new model for mass transfer in direct contact membrane distillation. Desalination 151, 217–227. Drioli, E., Ali, A., Macedonio, F., 2015. Membrane distillation: recent developments and perspectives. Desalination 356, 56–84. El-Abbassi, A., Hafidi, A., García-Payo, M.C., Khayet, M., 2009. Concentration of olive mill wastewater by membrane distillation for polyphenols recovery. Desalination 245, 670–674. El-Abbassi, A., Hafidi, A., Khayet, M., García-Payo, M.C., 2013. Integrated direct contact membrane distillation for olive mill wastewater treatment. Desalination 323, 31–38. El-Bourawi, M.S., Ding, Z., Ma, R., Khayet, M., 2006. A framework for better understanding membrane distillation separation process. J. Membr. Sci. 285, 4–29. Gryta, M., 2012. Wettability of polypropylene capillary membranes during the membrane distillation process. Chem. Pap. 66, 92–98. Hou, D., Wang, J., Zhao, C., Wang, B., Luan, Z., Sun, X., 2010. Fluoride removal from brackish groundwater by direct contact membrane distillation. J. Environ. Sci. 22, 1860–1867. Jacob, P., Phungsai, P., Fukushi, K., Visvanathan, C., 2015. Direct contact membrane distillation for anaerobic effluent treatment. J. Membr. Sci. 475, 330–339. Khayet, M., 2013. Treatment of radioactive wastewater solutions by direct contact membrane distillation using surface modified membranes. Desalination 321, 60–66.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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membrane distillation. Chem. Eng. Process. Process Intensif. 76, 16–25. Tijing, L.D., Woo, Y.C., Choi, J.S., Lee, S., Kim, S.-H., Shon, H.K., 2015. Fouling and its control in membrane distillation—a review. J. Membr. Sci. 475, 215–244. Warsinger, D.M., Swaminathan, J., Guillen-Burrieza, E., Arafat, H.A., Lienhard, V.J.H., 2015. Scaling and fouling in membrane distillation for desalination applications: a review. Desalination 356, 294–313. Wijekoon, K.C., Hai, F.I., Kang, J., Price, W.E., Cath, T.Y., Nghiem, L.D., 2014. Rejection and fate of trace organic compounds (TrOCs) during membrane distillation. J. Membr. Sci. 453, 636–642. Zarebska, A., Nieto, D.R., Christensen, K.V., Norddahl, B., 2014. Ammonia recovery from agricultural wastes by membrane distillation: fouling characterization and mechanism. Water Res. 56, 1–10. Zeng, Y.-F., Liu, Z.-L., Qin, Z.-Z., 2009. Decolorization of molasses fermentation wastewater by SnO2-catalyzed ozonation. J. Hazard. Mater. 162, 682–687.
O
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Khayet, M., Matsuura, T., Mengual, J.I., 2005. Porous hydrophobic/ hydrophilic composite membranes: estimation of the hydrophobic-layer thickness. J. Membr. Sci. 266, 68–79. Khayet, M., Velázquez, A., Mengual, J.I., 2004. Direct contact membrane distillation of humic acid solutions. J. Membr. Sci. 240, 123–128. Mahapatra, K., Ramteke, D.S., Paliwal, L.J., 2012. Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal. J. Anal. Appl. Pyrolysis 95, 79–86. Meng, S., Ye, Y., Mansouri, J., Chen, V., 2015. Crystallization behavior of salts during membrane distillation with hydrophobic and superhydrophobic capillary membranes. J. Membr. Sci. 473, 165–176. Naidu, G., Jeong, S., Kim, S.J., Kim, I.S., Vigneswaran, S., 2014. Organic fouling behavior in direct contact membrane distillation. Desalination 347, 230–239. Qu, D., Wang, J., Fan, B., Luan, Z., Hou, D., 2009. Study on concentrating primary reverse osmosis retentate by direct contact membrane distillation. Desalination 247, 540–550. Shirazi, M.M.A., Kargari, A., Tabatabaei, M., 2014. Evaluation of commercial PTFE membranes in desalination by direct contact
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Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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Available online at www.sciencedirect.com
ScienceDirect www.elsevier.com/locate/jes
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Yan Wu1 , Yun Kang1 , Liqiu Zhang, Dan Qu, Xiang Cheng, Li Feng⁎
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Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic concentrations
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Beijing Key Lab for Source Control Technology of Water Pollution, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China. E-mails: [email protected], [email protected]
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Article history:
In this study, direct contact membrane distillation (DCMD) was used for treating 16
12
Received 5 July 2016
fermentation wastewater with high organic concentrations. DCMD performance character- 17
13
Revised 20 December 2016
istics including permeate flux, permeate water quality as well as membrane fouling were 18
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Accepted 23 January 2017
investigated systematically. Experimental results showed that, after 12 hr DCMD, the feed 19
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Available online xxxx
wastewater was concentrated by about a factor of 3.7 on a volumetric basis, with the 20
36
Keywords:
membrane fouling; the protein concentration in the feed wastewater was increased by 22
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Fermentation wastewater
about 3.5 times and achieved a value of 6178 mg/L, which is suitable for reutilization. 23
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Direct contact membrane distillation
Although COD and TOC in permeate water increased continuously due to the transfer of 24
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Membrane fouling
volatile components from wastewater, organic rejection of over 95% was achieved in 25
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permeate flux decreasing from the initial 8.7 L/m2/hr to the final 4.3 L/m2/hr due to 21
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wastewater. GC–MS results suggested that the fermentation wastewater contained 128 26
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kinds of organics, in which 14 organics dominated. After 12 hr DCMD, not only volatile 27 organics including trimethyl pyrazine, 2-acetyl pyrrole, phenethyl alcohol and phenylacetic 28
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acid, but also non-volatile dibutyl phthalate was detected in permeate water due to 29 membrane wetting. FT-IR and SEM–EDS results indicated that the deposits formed on the 30
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membrane inner surface mainly consisted of Ca, Mg, and amine, carboxylic acid and 31 aromatic groups. The fouled membrane could be recovered, as most of the deposits could be 32 © 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. 34
Introduction
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In recent years, an increasing amount of fermentation wastewater has been generated with the rapid industrial development in China. In general, fermentation wastewater is dark in color and has a high chemical oxygen demand (COD) value ranging from 1 × 105 to 6 × 105 mg/L (Zeng et al., 2009).
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removed using a HCl/NaOH chemical cleaning method.
Published by Elsevier B.V. 35
The highly-concentrated non-biodegradable organics, especially metabolites, make fermentation wastewater difficult to biodegrade, so a treatment method is needed to prevent the environmental problems caused by its discharge. Multi-effect distillation (MED) and activated sludge treatment are the main methods developed to treat fermentation wastewater. However, MED requires too much energy, and activated sludge treatment
⁎ Corresponding author. E-mail: [email protected] (Li Feng). 1 The authors contributed equally to this work.
http://dx.doi.org/10.1016/j.jes.2017.01.015 1001-0742/© 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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The fermentation wastewater samples were obtained from a yeast factory in Harbin, China. Before DCMD treatment, all the samples were preserved in a refrigerator. COD, TOC and protein concentrations of the fermentation wastewater were characterized as 54,900, 20,900 and 1765 mg/L, respectively. For solutions without inorganics, the value of COD (mg O2/L)/ TOC (mg carbon/L) is generally 2.66 and varies with water quality (e.g., between 2.0 to 5.0 for municipal wastewater). Therefore, although COD was much higher than TOC in the studied wastewater, the value of COD/TOC (calculated as 2.63) is in the normal range. The pH value of the fermentation wastewater was 6.0–7.0. Analyzed by gas chromatography– mass spectrometry (GC–MS), fourteen major organic compounds (area percentage > 1%) including isoamyl, 2-methyl butyric acid, 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole, 2-pyrrolidinone, phenethyl alcohol, benzoic acid, phenylacetic acid, 4-ethenyl-2-methoxyphenol, o-hydroxybenzoic acid, p-hydroxyphenyl ethanol, p-hydroxyphenylcyanide, 4-hydroxy3-methoxyphenethyl alcohol and butyl phthalate were found in the fermentation wastewater.
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1.2. DCMD set-up and running conditions
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The schematic diagram of the DCMD set-up used in this study for fermentation wastewater treatment is shown in Fig. 1. The membrane module in the DCMD set-up was a self-made polyester tube combined with two unplasticized polyvinyl chloride T-tubes. The outside diameter, inside diameter and effective length of the module were 20, 15 and 225 mm, respectively. Sixteen pieces of commercial hollow fiber polypropylene (PP) membranes (ACCUREL PP Q3/2, Membrana, Germany) with a total effective membrane area of 0.023 m2 were packed in the module. The basic membrane properties are as following: pore average diameter 0.46 μm, outer diameter/inner diameter is 2.5 mm/2.0 mm, thickness 0.25 mm, porosity 80%, liquid entrance pressure (LEP) 400 kPa. DCMD was operated to run for 12 hr to treat fermentation wastewater. With an initial volume of 1 L, the feed fermentation wastewater was pumped continuously into the tube side after being heated by a heater (DK-98-IIA, Tianjing Taisite Technology, China), and the permeate water with an initial volume of 1 L was pumped into the shell side after cooling by a cooler (SDC-6, Nanjing Xinzhi Biotechnology, China). To prevent the feed wastewater being overly concentrated, wastewater of the same properties was supplemented continuously to the feed tank at a rate of 115 mL/hr. Limited by the low power of the cooler, the permeate temperature was
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well-designed DCMD configuration with a self-made membrane module was used as a pretreatment for treating fermentation wastewater with high organic concentrations from a yeast factory. DCMD performance characteristics such as permeate flux, permeate water quality, as well as membrane fouling mechanism and recovery methods were investigated systematically.
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wastes recyclable resource like protein in wastewater; thus, an appropriate treatment method for fermentation wastewater is urgently required to protect the environment and recover valuable resources in the meantime. Membrane distillation (MD) is a membrane separation process driven thermally by the temperature difference between the feed side and the permeate side of the membrane. Theoretically, an MD system has the capability of producing pure water from natural water because only water vapor molecules can transfer through the porous hydrophobic membrane during the separation process (El-Bourawi et al., 2006). For MD systems there are four different configurations, namely: direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), and vacuum membrane distillation (VMD). Based on the characteristics of hydrophobic membranes, these MD configurations have been studied for seawater desalination, solute recovery and wastewater treatment (Hou et al., 2010; Khayet et al., 2004, 2005; Qu et al., 2009; Shirazi et al., 2014; Zarebska et al., 2014). As the easiest and simplest configuration among them all, DCMD is the most widely studied (Drioli et al., 2015). To enhance water desalination, Cath et al. (2004) designed and investigated a new MD configuration and a new membrane module. Their research results showed that salt rejection in vacuum-enhanced DCMD could be greater than 99.9% in almost all cases. Al-Obaidani et al. (2008) developed an extensive analysis of DCMD performance and made an economic evaluation that the estimated water cost for DCMD with heat recovery was $1.17/m3. With the advantage of a lower fouling tendency, DCMD has been applied in treating various kinds of complex wastewater in recent research. El-Abbassi et al. (2009, 2013) applied DMCD in treating olive mill wastewater (OMW); their study results showed that the OMW concentration factor for the membrane TF200 was 1.72 after 9 hr DCMD operation, and an integrated microfiltration/DCMD system could be used to obtain clean water and a phenolic-rich concentrate from OMW. In the studies of Jacob et al. (2015), DCMD showed a reasonable flux of 2.09 L/m2/hr and high rejections of ammonia and COD of up to 89.6%–96.3% and 97.8%–99.9%, respectively, when treating anaerobic effluent. Wijekoon et al. (2014) investigated the feasibility of DCMD for removing trace organic compounds (TrOCs) during water and wastewater treatment, and the results of their experiments suggested that DCMD could be used as a promising post-treatment in conjunction with thermophilic membrane bioreactor for TrOC removal. Khayet (2013) used surface-modified membranes to process low and intermediate radioactive liquid wastes by DCMD, and their experimental results indicated that DCMD with surfacemodified membranes has potential for application in nuclear technology. Although DCMD has been proved applicable for wastewater treatment in many studies, its feasibility and performance in treating fermentation wastewater have rarely been studied. For a yeast factory, the highly-concentrated fermentation wastewater generated from the centrifugal filter unit generally has poor biodegradability, owing to the high concentration of organics (10,000–90,000 mg/L COD) it contains, therefore an efficient pretreatment is needed to remove a large part of the organics before further advanced treatment. In this study, a
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Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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To investigate the DCMD performance in treating fermentation wastewater, the volume of permeate water was measured every hour during the DCMD process, and the feed and permeate water were collected every hour for the testing of COD, TOC and protein, as well as organic compound identification. The permeate flux ( J, L/m2/hr) was calculated by Eq. (1):
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maintained at 30°C, and the feed temperature was controlled in the range of 55–60°C to satisfy the temperature difference requirement (5–20°C in general) of the MD process. Both the feed and the permeate water were recycled at the same flow rate of 2.0 L/min to their tanks concurrently via two magnetic pumps. For concentration of the proteins in fermentation wastewater, the DCMD process was applied under similar operating conditions to those used for wastewater treatment, whereas the initial 1 L feed wastewater was first concentrated for one hour before being supplemented by supplementary wastewater samples continuously. Before wastewater treatment, the pure water flux of the commercial PP membranes was tested under the same DCMD conditions as the wastewater treatment. Fig. 2 shows the variation of membrane pure water flux with time. The relatively high water flux (>15 L/m2/hr) indicated the feasibility of using PP membranes in the DCMD process.
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Fig. 1 – The schematic diagram of direct contact membrane distillation (DCMD) set-up in this work (1. feed tank; 2. heater; 3. magnetic pump; 4. flow meter; 5. membrane module; 6. cooler; 7. overflow permeate circle bulk; 8. permeate collecting tank).
J¼
V A∙Δt
C f0 −Cpt C f0
Fig. 2 – Pure water flux of the commercial polypropylene (PP) membrane in direct contact membrane distillation (DCMD) under the same conditions as the fermentation wastewater treatment.
C ft C f0
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ð2Þ
where Cf0 (mg/L) is the contaminant concentration in the original feed wastewater, and Cpt (mg/L) is the contaminant concentration in the permeate water collected at time t. The concentration multiple (CM) of contaminants was calculated by Eq. (3): CM ¼
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ð1Þ
where V (L) is the volume of permeate water, A (m2) is the total effective membrane area in module, and Δt (hr) is DCMD running time. The values of COD and TOC in the feed wastewater and the permeate water were tested with a fast COD analyzer (5B-3B (V8), Lianhua, China) and a TOC/TC analyzer (Multi N/C 3100, Jena, Germany), respectively. The protein concentration was measured by the Bradford Method with an UV spectrophotometer. The rejection (R) of contaminants (COD, TOC and protein) was calculated by Eq. (2): R¼
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ð3Þ
where Cft (mg/L) is the contaminant concentration in the feed wastewater at time t, and Cf0 (mg/L) is the contaminant concentration in original feed wastewater. To identify the organic compounds in both the feed wastewater and the permeate water, samples of the feed wastewater and the permeate water collected after 5, 10, and 12 hr DCMD operation were analyzed using a GC–MS analyzer (7890A–5975C, Agilent, USA) after being extracted to dichloromethane and
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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2. Results and discussion
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2.1. Performance of DCMD in treating fermentation wastewater
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2.1.1. Variation of COD and TOC in the feed fermentation wastewater and the permeate water during DCMD
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Fig. 3 presents the COD and TOC variations in the feed wastewater and the permeate water during the 12 hr DCMD process. As shown in Fig. 3, both COD and TOC concentrations in the feed wastewater and the permeate water increased approximately linearly with DCMD running time. In addition, the concentration variations of TOC were in accordance with those of COD. In detail, after the 12 hr DCMD process, the permeate volume had an increase of 1.19 L, and the feed wastewater was measured to be 640 mL; the feed and the permeate COD concentrations reached 170,050 and 2558 mg/L, respectively; the feed and the permeate TOC concentrations reached 71,900 and 900 mg/L, respectively; the rejections of COD and TOC were 95.3% and 95.7%, respectively; the CMs of COD and TOC were 3.5 and 3.4, respectively. The increase of permeate COD and TOC indicated that part of the contaminants in the feed wastewater passed through the membrane. This may due to the volatile compounds in the feed wastewater preferentially transferring through membrane. In addition, the partial wetting phenomenon of membrane
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To investigate membrane fouling as well as recovery methods, scanning electron microscopy (SEM, S3400N, Hitachi, Japan)– energy dispersive spectrometry (EDS, S3400N, Hitachi, Japan) and field emission scanning electron microscopy (FESEM, MERLIN, Carl Zeiss, Germany) were used to characterize the inner surface and the cross-section of virgin membrane, fouled membrane after the 12 hr DCMD process and recovered membranes, using two different methods. To obtain crosssectional morphologies, all the membrane samples were rinsed with water gently and subsequently freeze-fractured in liquid nitrogen, and before being characterized with SEM–EDS and FESEM, all the membrane samples were dried at room temperature and sputtered with gold afterward. Fourier transform infrared spectroscopy (FT-IR, Perkin-Elmer Spectrum GX, BRUKER, USA) was also used for fouling analysis. The FT-IR spectra were recorded in the mid-IR region 4000–400/cm with resolution of 4/cm and 16 scans. All measurements and operations were performed in a dry atmosphere at 20 ± 5°C. The two different membrane recovery methods in this study were pure water rinsing and chemical cleaning, respectively. For the pure water rinsing method, fouled membrane was rinsed with pure water for 60 min; for the chemical cleaning method, fouled membrane was first rinsed with pure water for 10 min, and then washed sequentially with HCl aqueous solution (0.5 mol/L), NaOH aqueous solution (0.5 mol/L) and pure water for 20, 20 and 10 min, respectively.
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concentrated by a rotary evaporator (RE-52AA, Shanghai Yarong, China).
Fig. 3 – Concentration variations of COD and TOC in the feed Q1 wastewater and the permeate water during the 12 hr direct contact membrane distillation (DCMD) process. COD: chemical oxygen demand.
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pores in the MD process would also contribute to the organic contaminants being transferred through the membrane pores (Gryta, 2012). In MD, the LEP (MPa) of the membrane has a relationship with the hydrophobicity of the membrane, and the equation can be expressed as Eq. (4) (El-Bourawi et al., 2006): LEP ¼
2∙γL ∙ cosθ r
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where γL (N/m) is the surface tension of liquid, θ (°) is the contact angle of the feed liquid with the membrane surface, and r (μm) is the radius of membrane pore. According to Eq. (4), it is easier for liquid to enter membrane pores having larger r and lower LEP, thus leading to membrane wetting. The partially wetted membrane pores allow not only volatile components, but also contaminants in the feed wastewater to transfer to the permeate side. Although COD and TOC in the permeate water increased continuously, membrane wetting was not extensive enough to deteriorate the permeate water quality to a great extent in this study.
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2.1.2. Identification of organic compounds in the permeate water 304 The GC–MS results for the permeate water collected after 5, 10 and 12 hr of the DCMD process are shown in Table 1. In total five kinds of organic compounds were detected in the permeate water.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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t1:3
t1:4
Table 1 – Gas chromatography–mass spectrometry (GC–MS) results for the permeate water collected after 5, 10 and 12 hr DCMD process. No.
Detected organic compound
Area percentage in permeate water
t1:5
5 hr
10 hr
12 hr
I
2,3,5-Trimethyl pyrazine
4.48%
24.39%
7.04%
t1:7
II
2-Acetyl pyrrole
12.62%
26.92%
12.56%
t1:8
III
Phenethyl alcohol
72.16%
19.72%
9.65%
t1:9
IV
Phenylacetic acid
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5.13%
t1:10
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Dibutyl phthalate
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Organic compound structure
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After 5 hr of the DCMD process, only 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole and phenethyl alcohol were detected in the permeate water. These are all volatile compounds which can transfer through membrane pores easily as vapor molecules. At ten hours, another organic compound, phenylacetic acid, was detected. The delayed appearance of phenylacetic acid compared to the former three organic compounds was due to its complex structure. It should be noticed that dibutyl phthalate, which is not a volatile compound, was found in the permeate water collected at 12 hr. As discussed before, membrane wetting might occur in DCMD and result in non-volatile organics being transferred through the membrane pores to the permeate water. The appearance of dibutyl phthalate in permeate water could be evidence of membrane wetting. In addition, the GC–MS results would also contribute to explaining the increase of permeate COD and TOC as discussed in Section 2.1.1.
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DCMD: direct contact membrane distillation.
The rapid increase of protein concentration may be due to the presence of non-volatile proteins in the feed wastewater. The protein concentration in the permeate water showed slight fluctuations around 20 mg/L. This might have resulted from the transfer of some portion of protein through the aforementioned wetting of pores. After the 12 hr DCMD process, the CM and the rejection of protein in the feed wastewater reached 3.5% and 98.9%, respectively, indicating good DCMD performance in concentrating protein during fermentation wastewater treatment.
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2.1.3. Concentration variations of protein in the feed wastewater and the permeate water during DCMD In fermentation wastewater, protein is a valuable resource to be concentrated for reutilization. Fig. 4 presents the concentration variations of protein concentration in the feed wastewater and the permeate water during the 12 hr DCMD process. As shown in Fig. 4, the protein concentration in the feed wastewater increased rapidly from 1765 to 4517 mg/L within the first hour before achieving a value of 6178 mg/L at 12 hr.
Fig. 4 – Concentration variations of protein in the feed wastewater and the permeate water within the 12 hr direct contact membrane distillation (DCMD) process.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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Figs. 6, 7 and Table 2 are inner surface SEM, cross-section FESEM images and EDS analytical results for the virgin membrane, fouled membrane, fouled membrane after pure water rinsing and fouled membrane after chemical cleaning. In Fig. 7, the observed foulants are circled with dashed yellow lines. As shown in Figs. 6 and 7, almost the whole inner surface of the fouled membrane (Figs. 6b, 7b) was covered by an amorphous deposited fouling layer compared with the virgin membrane (Figs. 6a, 7a), owing to the highly-concentrated organics in the feed wastewater. The EDS results in Table 2 showed that besides the C and O elements that the virgin membrane mainly consisted of, other elements such as N (13.10 wt.%), Mg, Si, P, S, Cl, K, Ca, Fe and Zn were also found on the inner surface of the fouled membrane. This may due to the combined effect of salt deposition and organic adsorption on the membrane surface during DCMD, indicating that there might be both inorganic fouling and organic fouling. After pure water rinsing, the content of elements such as K, Ca and Zn decreased significantly, while large amounts of N
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Fig. 5 shows the permeate flux variation with time during DCMD. After 12 hr, permeate flux decreased by 50.5%, from 8.7 to 4.3 L/m2/hr. The decrease of permeate flux was mainly caused by membrane fouling and polarization effects. Organic and inorganic matters in the feed wastewater may deposit on the membrane inner surface and block membrane pores, thus
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Fig. 5 – Permeate flux of the polypropylene (PP) membrane within direct contact membrane distillation (DCMD) process before and after cleaned by pure water.
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hindering the transfer of water molecules. In addition, the vapor pressure of water also declined with the increase of solute concentration in the feed wastewater. Since water molecule transfer through the membrane was driven by the vapor pressure gradient, the decline of vapor pressure was another reason for the permeate flux decline in this study (Ding et al., 2003). After the fouled membrane was cleaned by pure water, the permeate flux recovered to 7.6 L/m2/hr, which is 87.8% of the virgin membrane permeate flux.
Fig. 6 – Inner surface scanning electron microscopy (SEM) images of membrane samples (a. virgin membrane; b. fouled membrane after 12 hr direct contact membrane distillation process; c. fouled membrane after pure water rinsing; d. fouled membrane after chemical cleaning). Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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Fig. 8 shows the FT-IR spectra of a virgin membrane, fouled membrane after 12 hr DCMD process, fouled membrane after pure water rinsing and fouled membrane after chemical cleaning. As shown in Fig. 8, the virgin PP membrane spectrum has peaks typical of \CH2\ and \CH3 functional groups at 2840– 2950/cm and 1380/cm (Andreassen, 1999), as well as aromatic
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Table 2 – Energy dispersive spectrometry (EDS) analysis of virgin membrane (a), fouled membrane (b), fouled membrane after pure water rinsing (c), and fouled membrane after chemical cleaning (d). Elements
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C N O Na Mg Si P S Cl K Ca Fe Zn Total
Element mass fraction of different membrane samples (wt.%)
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92.18 0 7.70 0.12 0 0 0 0 0.09 0 0 0 0 100.00
33.15 13.10 28.28 0.56 1.42 5.11 7.96 1.47 0.46 0.91 4.10 1.42 2.51 100.00
41.254 8.99 25.19 0.13 1.18 4.93 5.94 0.51 0 0.08 2.63 1.52 1.66 100.00
89.31 0 7.81 0.14 0.17 1.01 0 0.10 0.10 0 0.07 0.29 1.01 100
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and O elements remained on the fouled membrane surface (Figs. 6c, 7c and Column (c) in Table 2). In contrast, most of the foulants, especially N-containing compounds, were flushed off by chemical cleaning (Figs. 6d, 7d and Column (d) in Table 2). The SEM–EDS and FESEM results in this study revealed that water rinsing could only remove a part of the membrane foulants, while the chemical cleaning method was much more effective for the recovery of fouled membranes.
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Fig. 7 – Cross-sectional field emission scanning electron microscope (FESEM) images of membrane samples (a. virgin membrane; b. fouled membrane after 12 hr direct contact membrane distillation process; c. fouled membrane after pure water rinsing; d. fouled membrane after chemical cleaning), foulants are circled with dashed yellow lines. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 8 – Fourier transform infrared spectroscopy (FT-IR) spectra for membrane samples (line a: virgin membrane; line b: fouled membrane after 12 hr direct contact membrane distillation process; line c: fouled membrane after pure water rinsing; line d: fouled membrane after chemical cleaning).
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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3. Conclusions
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In this study, the performance of DCMD in treating fermentation wastewater with high organic concentrations was investigated for the first time. The results showed that after the 12 hr DCMD process, the volume of the feed wastewater, COD, TOC and protein in the feed fermentation wastewater were concentrated by 3.7, 3.5, 3.4 and 3.5 times, respectively. Meanwhile, over 95% COD, TOC and protein were rejected, indicating the good performance and prospects of DCMD in treating fermentation wastewater.
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Acknowledgments
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Membrane fouling in the MD process contains mainly three aspects; inorganic scaling, particulate and colloidal fouling, as well as biofouling (Warsinger et al., 2015). Based on the SEM– EDS, FESEM characterization and FT-IR analysis of foulants, it can be concluded that there was no crystallization observed in this study, and the foulants were made up of organic matters and inorganic ions. The feed fermentation wastewater contained a lot of organic acids, alcohols and proteins. These organic components contained both hydrophilic functional groups like carboxyl, and hydrophobic functional groups like hydrocarbon chains. The amphiprotic property of these organic components provided them with the ability to be adsorbed onto the hydrophobic surface of PP membrane. The increasing amount of the element N as well as the detection of amine functional groups in the fouled membrane confirmed the assumption that foulants were adsorbed on the membrane surface. In addition, the hydrophilic functional groups in these organics changed the membrane morphology and made the membrane surface hydrophilic, which might contribute to the initiation of fouling and hydrophilization of the membrane surface (Naidu et al., 2014). The initial fouling layer formed on the membrane made the hydrophilic organics in wastewater adhere much more easily to it and accelerated membrane fouling as a result (Tijing et al., 2015). According to the SEM–EDS results, although no crystallization was found on the membrane surface under SEM scanning, the inorganic elements like Ca and Mg contained in the foulants could strengthen the structure of the deposits and make the fouling layer more compact (Meng et al., 2015).
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This work was supported by the Special S&T Project 476 on Treatment and Control of Water Pollution (No. 477 2013ZX07201007-003). 478
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Five organic compounds including 2,3,5-trimethyl pyrazine, 2-acetyl pyrrole, phenethyl alcohol, phenylacetic acid and dibutyl phthalate were detected in the permeate water. The permeate flux decreased 50.5% within 12 hr DCMD due to the foulants formed on the membrane inner surface facing the feed wastewater. The deposited foulants were mainly made up of organic components combined with inorganics. They were hard to flush off by water rinsing, while most of them could be removed by the combination of HCl solution (0.5 mol/L) and NaOH solution (0.5 mol/L). In conclusion, DCMD is a promising process for treating fermentation wastewater with high organic concentrations, due to its good performance in organic rejection and valuable resource recovery. Furthermore, as membrane fouling is still an obstacle to DCMD development, further studies on membrane fouling control are needed when applying DCMD in fermentation wastewater treatment.
REFERENCES
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hydrocarbons at 1600/cm and 1453/cm (Mahapatra et al., 2012). In the spectrum of the fouled membrane, the wide single peak at 3300/cm and twin peak near 1600/cm, which could normally be identified as the functional groups of amine and carboxylic acid, are characteristic of protein deposits. The spectrum of the fouled membrane after pure water rinsing (line c in Fig. 8) shows that the twin peak near 1600/cm in the fouled membrane (line b in Fig. 8) shifted to become a single peak near 1600/cm, which is assigned to aromatic hydrocarbons; the weak peak appearing at 1100/cm is attributed to the presence of sulfate radical. In contrast, the spectrum of the fouled membrane after chemical cleaning was quite similar to that of the virgin membrane, indicating the effective recovery of the fouled membrane via chemical cleaning in this study.
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Al-Obaidani, S., Curcio, E., Macedonio, F., Di Profio, G., Al-Hinai, H., Drioli, E., 2008. Potential of membrane distillation in seawater desalination: thermal efficiency, sensitivity study and cost estimation. J. Membr. Sci. 323, 85–98. Andreassen, E., 1999. Infrared and Raman spectroscopy of polypropylene. In: Karger-Kocsis, J. (Ed.), Polypropylene: An A–Z Reference. Springer Netherlands, Dordrecht, pp. 320–328. Cath, T.Y., Adams, V.D., Childress, A.E., 2004. Experimental study of desalination using direct contact membrane distillation: a new approach to flux enhancement. J. Membr. Sci. 228, 5–16. Ding, Z., Ma, R., Fane, A.G., 2003. A new model for mass transfer in direct contact membrane distillation. Desalination 151, 217–227. Drioli, E., Ali, A., Macedonio, F., 2015. Membrane distillation: recent developments and perspectives. Desalination 356, 56–84. El-Abbassi, A., Hafidi, A., García-Payo, M.C., Khayet, M., 2009. Concentration of olive mill wastewater by membrane distillation for polyphenols recovery. Desalination 245, 670–674. El-Abbassi, A., Hafidi, A., Khayet, M., García-Payo, M.C., 2013. Integrated direct contact membrane distillation for olive mill wastewater treatment. Desalination 323, 31–38. El-Bourawi, M.S., Ding, Z., Ma, R., Khayet, M., 2006. A framework for better understanding membrane distillation separation process. J. Membr. Sci. 285, 4–29. Gryta, M., 2012. Wettability of polypropylene capillary membranes during the membrane distillation process. Chem. Pap. 66, 92–98. Hou, D., Wang, J., Zhao, C., Wang, B., Luan, Z., Sun, X., 2010. Fluoride removal from brackish groundwater by direct contact membrane distillation. J. Environ. Sci. 22, 1860–1867. Jacob, P., Phungsai, P., Fukushi, K., Visvanathan, C., 2015. Direct contact membrane distillation for anaerobic effluent treatment. J. Membr. Sci. 475, 330–339. Khayet, M., 2013. Treatment of radioactive wastewater solutions by direct contact membrane distillation using surface modified membranes. Desalination 321, 60–66.
Please cite this article as: Wu, Y., et al., Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic..., J. Environ. Sci. (2017), http://dx.doi.org/10.1016/j.jes.2017.01.015
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membrane distillation. Chem. Eng. Process. Process Intensif. 76, 16–25. Tijing, L.D., Woo, Y.C., Choi, J.S., Lee, S., Kim, S.-H., Shon, H.K., 2015. Fouling and its control in membrane distillation—a review. J. Membr. Sci. 475, 215–244. Warsinger, D.M., Swaminathan, J., Guillen-Burrieza, E., Arafat, H.A., Lienhard, V.J.H., 2015. Scaling and fouling in membrane distillation for desalination applications: a review. Desalination 356, 294–313. Wijekoon, K.C., Hai, F.I., Kang, J., Price, W.E., Cath, T.Y., Nghiem, L.D., 2014. Rejection and fate of trace organic compounds (TrOCs) during membrane distillation. J. Membr. Sci. 453, 636–642. Zarebska, A., Nieto, D.R., Christensen, K.V., Norddahl, B., 2014. Ammonia recovery from agricultural wastes by membrane distillation: fouling characterization and mechanism. Water Res. 56, 1–10. Zeng, Y.-F., Liu, Z.-L., Qin, Z.-Z., 2009. Decolorization of molasses fermentation wastewater by SnO2-catalyzed ozonation. J. Hazard. Mater. 162, 682–687.
O
F
Khayet, M., Matsuura, T., Mengual, J.I., 2005. Porous hydrophobic/ hydrophilic composite membranes: estimation of the hydrophobic-layer thickness. J. Membr. Sci. 266, 68–79. Khayet, M., Velázquez, A., Mengual, J.I., 2004. Direct contact membrane distillation of humic acid solutions. J. Membr. Sci. 240, 123–128. Mahapatra, K., Ramteke, D.S., Paliwal, L.J., 2012. Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal. J. Anal. Appl. Pyrolysis 95, 79–86. Meng, S., Ye, Y., Mansouri, J., Chen, V., 2015. Crystallization behavior of salts during membrane distillation with hydrophobic and superhydrophobic capillary membranes. J. Membr. Sci. 473, 165–176. Naidu, G., Jeong, S., Kim, S.J., Kim, I.S., Vigneswaran, S., 2014. Organic fouling behavior in direct contact membrane distillation. Desalination 347, 230–239. Qu, D., Wang, J., Fan, B., Luan, Z., Hou, D., 2009. Study on concentrating primary reverse osmosis retentate by direct contact membrane distillation. Desalination 247, 540–550. Shirazi, M.M.A., Kargari, A., Tabatabaei, M., 2014. Evaluation of commercial PTFE membranes in desalination by direct contact
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