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Possibilities for the use of membrane processes for the pre-treatment of wastewater from the production of dried potato purée
Desalination 249 (2009) 135–138
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
Possibilities for the use of membrane processes for the pre-treatment of wastewater from the production of dried potato purée Evžen Šárka ⁎, Vladimír Pour, Anežka Veselá, Zdeněk Bubník Department of Carbohydrate Chemistry and Technology, ICT Prague, Technicka 5, 166 28 Prague 6, Czech Republic
a r t i c l e
i n f o
Article history: Accepted 2 October 2008 Available online 29 September 2009 Keywords: Starch wastewater Membrane filtration Potato purée
a b s t r a c t Our research focused on the membrane separation of wastewater resulting from the production of dried potato purée. Our aim was to investigate possibilities for recycling obtained retentate back to the actual production process, and, consequently, for reducing wastewater pollution. This paper describes trials of MF and RO membrane filtration of starch wastewater. The treated water contained starch, in either granulated or gelatinized form, and solids (fine pieces of potato skins). The trials were conducted in either one or two stages. We used a pilot plant equipped with a ceramic membrane with a filtration area of 0.35 m2 and pore sizes of 500 and 100 nm. We also tested an organic RO membrane (7410) in the laboratory. High permeate flux above 100 l/(m2 h) was measured for the 100 nm membrane, but with considerable fouling. Filtration through this membrane resulted in high COD and BOD5 rejection (approximately 60%), an effect which was increased by the subsequent RO filtration. The content of soluble carbohydrate, 0.011% in permeate (with 0.44% dry substance), was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The aim of the study was to investigate the membrane separation of wastewater resulting from the production of dried potato purée, with the purpose of recycling obtained retentate back to the actual production process and, consequently, of reducing wastewater pollution. Such water belongs to the group of starch wastewaters, separation of which is known to be difficult. Considerable technological problems are involved in the operation of anaerobic and aerobic systems in wastewater treatment plants specifically designed for starch waters. And membrane separation itself is not a simple process because of the considerable fouling associated with it. Membrane filtration is a modern method used for particle separation by membrane pores of various sizes and shapes. One of the basic parameters used to describe membrane processes is permeate flux; namely, permeate flow divided by membrane area. An understanding of the way in which process parameters influence permeate flux helps in the design of the process unit. The most problematic aspect of membrane filtration is the reduction in permeate flux over time, the scale of which significantly affects investment costs. It is therefore vital to minimize membrane fouling by
⁎ Corresponding author. Tel.: +420 22044 3115; fax: +420 220 445 130. E-mail address: [email protected] (E. Šárka). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2008.10.026
using back-flushing, surfactants or enzymes, or a combination of these approaches [1]. The quality of the separating process (selectivity) can be evaluated using the rejection R (%) defined as:
R = 1−
CP 100; CF ⋅
ð1Þ
where CP is the concentration of the analyzed component in the permeate, and CF is the concentration of the analyzed component in the feed. There are no literature data concerning wastewater coming from this technology so that we compared the experimental data of membrane filtered wastewater with similar ones — wastewaters from potato and starch technologies. The difference between these materials however can be in chemical composition of wastewaters and in starch state. Cancino et al. [2] conducted a pilot test for the treatment of corn starch wastewater using membrane technologies. During microfiltration (250 kPa, 0.2 μm), they achieved permeate flux of approximately 0.0108 l/m2 h; which seems very low. The permeate obtained from the subsequent reverse osmosis (3 MPa) showed a flux of 59 l/m2 h, with a suspended solids content of 10 ppm and a BOD5 of 31.2 mg O2/l, 0.2% of the original wastewater BOD5. According to very low solids content the main separation effect was during microfiltration. According to the authors, their results indicate that a combination of microfiltration and
E. Šárka et al. / Desalination 249 (2009) 135–138
136
reverse osmosis is suitable for the treatment of wastewater resulting from the production of corn starch. Rüffer et al. [3] used a pilot-scale RO filtration unit to filter potato fruit water originating from the overflow of centrifuges used to separate protein and other solubles from potato starch after rasping. RO membranes, made of cellulose acetate, ran with a permeate flux of approximately 20 l/m2 h (during 20 h) and at an average pressure of 4 MPa, with a pressure drop of 500 kPa from module inlet to outlet. CODrejection and dry substance rejection both exceeded 99%. Reimann and Yeo [4] dealt with the practical use of various membranes for potato washing water. A 50 nm SiC mineral membrane (200 kPa) achieved a permeate flux of approximately 100 l/(m2 h), but COD-rejection increased as pressure on the inorganic membrane increased (from 20 to 84%). The permeate flux of the 50 nm SiC membrane was higher than that of the 100 nm A1203 membrane, and CODrejection correspondingly lower. Therefore, the concentration polarization at the feed side of the membranes by concentration was very high. Permeate flux decreased as the concentration of COD increased [5]. 2. Materials and methods The treated water, which was a mixture of warm and cold waters coming from various points in a Czech factory producing dried potato purée, contained starch, in granulated or gelatinized form, proteins and solids (fine pieces of potato skins). Pollution of the water was high; COD measuring more than 11,000 mg O2/l, and BOD5 exceeding 8000 mg O2/l. Prior to membrane filtration the water was leaked through a sieve mesh (0.75 mm). We used a pilot plant (T.I.A.Bollene) dedicated to research and/or industrial experiments (see Fig. 1). The process module P37-30 was equipped with ceramic membranes (Membralox) with a filtration area of 0.35 m2 and pore sizes of 500 (alumina) and 100 nm (zirconia). The module channels had profile area of 261 mm2. Retentate flowed from the membrane module back to the supply tank. The temperature was kept in the range of 40–50 °C, and a constant transmembrane pressure of 100 kPa was maintained. Feed flow was 11 m3/h; volume concentration factor defined VCR = V0 = VR ;
ð2Þ
where V0 is initial volume and VR is volume of retentate equal to 8.3. In addition, employing a similar technological arrangement in the laboratory, we used an ARNO 600 separation test unit (Mikropur, s.r.o., Hradec Králové) to test the organic RO membrane 7410 (Nitto Denko Corporation, Osaka). In this case, the temperature was maintained at around 30 °C, and the transmembrane pressure adjusted to 2 MPa. The
Fig. 1. Scheme of the filtration unit (T.I.A.Bollene).
channel had profile area of 44 mm2. Feed flow was 0.6 m3/h; volume concentration factor was 4.2. During our tests, the temperature, the pressures before and after membrane separation, and the permeate flux were all regularly recorded. Three arrangements of membrane modules were evaluated: a) wastewater separation through the 500 nm membrane, b) wastewater separation through the 100 nm membrane, c) second stage separation of the permeate resulting from b) through the 7410 membrane. Samples were taken at the end of each experiment to determine the COD and BOD5 concentrations, as well as the content of dry substance (evaporation residue). In this case it was more acceptable to analyze the content of dry substance than analyzing only solids because from the technological view some important impurities were present in the solution (e.g. gelatinized starch) and, furthermore the classical filtration of the samples was difficult and time-consuming. Because we assumed a higher concentration of proteins [3,6], the dry substance was analyzed while drying the wastewater for 4 h at 105 °C [7]. We then used Eq. (1) to calculate the rejection coefficient for the components observed. The content of soluble carbohydrate in permeate was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection. Separation was performed in a single 30 min run using a Dionex CarboPac PA 1 column (mobile phase 16 mM NaOH, flow 0.25 ml/min, temperature 25 °C, injected sample volume 10 μl). Peak identification was realized using standard solutions. 3. Results and discussion 3.1. Permeate flux Fig. 2 plots the results for the test conducted using the 500 nm MF membrane with wastewater resulting from the production of dried potato purée. After 40 min, permeate flux had fallen from initial 1200 l/ (m2 h) to about 20 l/(m2 h), as a result of which the experiment was stopped. The low permeability of the 500 nm membrane can be explained by the clogging of its pores by bigger particles, and the consequent fouling (see chap. Separation effects). Despite an overall decrease of 80%, permeate flux through the 100 nm MF membrane (Fig. 3) was unexpectedly high. Therefore we stopped our experiments after 9 min because of empty supply tank. The permeate flow above 100 l/(m2 h) was more than 7 times the rate achieved in arrangement a). This permeate flow is comparable with data of Reimann and Yeo [4] processing potato washing water by 50 nm SiC mineral membrane (200 kPa). Gelatinized starch in wastewater from the production of dried potato purée caused higher fouling, and lower pressure should be not used to have appropriate flux. Membranes with pores 20–50 nm could be tested.
Fig. 2. Permeate flux I (-♦- ) vs. time (arrangement a — 500 nm), -■- temperature.
E. Šárka et al. / Desalination 249 (2009) 135–138
137
Table 1 Separation using the 500 nm and 100 nm membranes. Sample
Dry substance (%)
COD (mgO2/l)
BOD5 (mgO2/l)
F R500 P500 R (%) R100 P100 R (%)
0.67 0.96 0.41 38.2 1.70 0.44 34.1
11,840 14,310 7890 33.4 27,170 4400 62.8
8670 9410 5900 31.9 14,470 3620 58.2
F — feed, P — permeate, R — retentate.
Table 2 Second stage separation using the 7410 membrane. Fig. 3. Permeate flux I (-♦- ) vs. time (arrangement b — 100 nm), -■- temperature.
Permeate flux through the organic RO membrane (7410) is shown in Fig. 4. The feed used in this experiment was the permeate from our experiments with the 100 nm membrane. The flow rates measured were similar to those obtained by Cancino et al. [2]. As usual the RO membrane produced lower flux rates in comparison with MF membranes despite the higher pressure difference. Conversely, permeate flux was constant without any drop in the rate, and after 4 h we hadn't observed any fouling. The results indicate that a combination of microfiltration and reverse osmosis is a suitable treatment for wastewater from the production of dried potato purée. 3.2. Separation effects The analytical results for feed, permeate and retentate for both the 500 nm and 100 nm membrane samples are displayed in Table 1. Rejection was high in both cases. For the 500 nm membrane, rejection of dry substance was around 38%, with COD and BOD5 rejection being approximately 32–33%. When balancing measured data it confirmed the creation of solid starch layer on the surface of the module. For the 100 nm membrane, rejection of dry substance was approximately 34%, with COD and BOD5 rejection being around 60%, comparable with data of Reimann and Yeo [4] for potato washing water. The 100 nm permeate contained 0.034 g/l of monosaccharides, and 0.074 g/l of disaccharides. When balancing the measured data in Table 1, it results that the substances bonding oxygen are more liable to fouling. Rejections for the second stage separation using the 7410 RO membrane were very different for the separate components (Table 2). Rejection of dry substance was approximately 59%, while COD and BOD5 rejection were 14% and 29% respectively. The permeate COD concentration 3770 mg O2/l is not extremely high when compared with the data of
Sample
Dry substance (%)
COD (mgO2/l)
BOD5 (mgO2/l)
Fnanof/P100 Rnanof Pnanof R (%)
0.44 0.45 0.18 58.6
4400 8420 3770 14.3
3620 5090 2570 29.0
F — feed, P — permeate, R — retentate.
Ray et al. [8] who used RO as a preconcentration step prior to conventional corn steepwater evaporation reported a COD of 7000 to 9800 mg/l. On the other hand results BOD5 of Cancino et al. [2] for wastewater from corn starch production were much lower. The measured combined effect for both stages was around 70%. 4. Conclusions We used membrane separation to pre-treat wastewater from the production of dried potato purée, with the purpose of assessing possibilities for recycling obtained retentate back to the actual production process and, consequently, for the reduction of wastewater pollution. This paper describes trials, conducted in either one or two stages, of MF and RO membrane filtration of starch wastewater. The low permeability of the 500 nm membrane can be explained by the clogging of its pores by bigger sticky particles, and the consequent fouling. High permeate flux over 100 l/(m2 h) was measured for the 100 nm membrane. COD and BOD5 rejection was high (approximately 60%) for filtration through the 100 nm membrane, an effect that was increased by the subsequent RO filtration. Because of high permeate flux, low fouling and a high separation effect, filtration through RO membranes appears to be promising for wastewater treatment by factory production of dried potato purée. From these data we can draw partial conclusions about the technological steps that might be taken to increase permeate flux and, in this way, to improve the capacity of separation units. Because of possible concentration polarization it would probably be appropriate to test lower membrane pore size (e.g. 20 nm). Also, RO filtration in the second stage should be tested using higher pressures. Therefore, at this time it is necessary to conduct further research and obtain more measurements in order to accurately identify a wider range of the required process parameters. Acknowledgements This research was supported by the Research Proposal, “Theoretical Fundamentals of Food and Biochemical Technologies” of MSMT CR, No. MSM 6046137305.
References Fig. 4. Permeate flux I (-♦- ) vs. time (arrangement c — Nitto Denko 7410), -■- temperature.
[1] P. Mikulášek and J. Šír, Tlakové membránové separační procesy a zařízení, Procesní inženýrství, Praha, 1994.
138 [2] [3] [4] [5] [6]
E. Šárka et al. / Desalination 249 (2009) 135–138 B. Cancino, F. Rossier, C. Orellana, Desalination 200 (2006) 750–751. H. Rüffer, U. Kremser, M. Seekamp, Starch/Stärke 49 (1997) 354–359. W. Reimann, I. Yeo, Desalination 109 (1997) 263–267. W. Reimann, Desalination 109 (1997) 51–55. D. Knorr, J. Food Technol. 12 (1977) 563–580.
[7] S. Zelenka, E. Pexiederová and I. Bohačenko, Cvičení z technologie sacharidů, Návod k technologickým cvičením z krmivářství a škrobárenství, SNTL, Praha, 1977. [8] R.J. Ray, J.K. Gienger, S. Retzlaff, Membrane-based hybrid processes for energy-efficient waste-water treatment, J. Membr. Sci. 28 (1986) 87–106.
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
Possibilities for the use of membrane processes for the pre-treatment of wastewater from the production of dried potato purée Evžen Šárka ⁎, Vladimír Pour, Anežka Veselá, Zdeněk Bubník Department of Carbohydrate Chemistry and Technology, ICT Prague, Technicka 5, 166 28 Prague 6, Czech Republic
a r t i c l e
i n f o
Article history: Accepted 2 October 2008 Available online 29 September 2009 Keywords: Starch wastewater Membrane filtration Potato purée
a b s t r a c t Our research focused on the membrane separation of wastewater resulting from the production of dried potato purée. Our aim was to investigate possibilities for recycling obtained retentate back to the actual production process, and, consequently, for reducing wastewater pollution. This paper describes trials of MF and RO membrane filtration of starch wastewater. The treated water contained starch, in either granulated or gelatinized form, and solids (fine pieces of potato skins). The trials were conducted in either one or two stages. We used a pilot plant equipped with a ceramic membrane with a filtration area of 0.35 m2 and pore sizes of 500 and 100 nm. We also tested an organic RO membrane (7410) in the laboratory. High permeate flux above 100 l/(m2 h) was measured for the 100 nm membrane, but with considerable fouling. Filtration through this membrane resulted in high COD and BOD5 rejection (approximately 60%), an effect which was increased by the subsequent RO filtration. The content of soluble carbohydrate, 0.011% in permeate (with 0.44% dry substance), was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The aim of the study was to investigate the membrane separation of wastewater resulting from the production of dried potato purée, with the purpose of recycling obtained retentate back to the actual production process and, consequently, of reducing wastewater pollution. Such water belongs to the group of starch wastewaters, separation of which is known to be difficult. Considerable technological problems are involved in the operation of anaerobic and aerobic systems in wastewater treatment plants specifically designed for starch waters. And membrane separation itself is not a simple process because of the considerable fouling associated with it. Membrane filtration is a modern method used for particle separation by membrane pores of various sizes and shapes. One of the basic parameters used to describe membrane processes is permeate flux; namely, permeate flow divided by membrane area. An understanding of the way in which process parameters influence permeate flux helps in the design of the process unit. The most problematic aspect of membrane filtration is the reduction in permeate flux over time, the scale of which significantly affects investment costs. It is therefore vital to minimize membrane fouling by
⁎ Corresponding author. Tel.: +420 22044 3115; fax: +420 220 445 130. E-mail address: [email protected] (E. Šárka). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2008.10.026
using back-flushing, surfactants or enzymes, or a combination of these approaches [1]. The quality of the separating process (selectivity) can be evaluated using the rejection R (%) defined as:
R = 1−
CP 100; CF ⋅
ð1Þ
where CP is the concentration of the analyzed component in the permeate, and CF is the concentration of the analyzed component in the feed. There are no literature data concerning wastewater coming from this technology so that we compared the experimental data of membrane filtered wastewater with similar ones — wastewaters from potato and starch technologies. The difference between these materials however can be in chemical composition of wastewaters and in starch state. Cancino et al. [2] conducted a pilot test for the treatment of corn starch wastewater using membrane technologies. During microfiltration (250 kPa, 0.2 μm), they achieved permeate flux of approximately 0.0108 l/m2 h; which seems very low. The permeate obtained from the subsequent reverse osmosis (3 MPa) showed a flux of 59 l/m2 h, with a suspended solids content of 10 ppm and a BOD5 of 31.2 mg O2/l, 0.2% of the original wastewater BOD5. According to very low solids content the main separation effect was during microfiltration. According to the authors, their results indicate that a combination of microfiltration and
E. Šárka et al. / Desalination 249 (2009) 135–138
136
reverse osmosis is suitable for the treatment of wastewater resulting from the production of corn starch. Rüffer et al. [3] used a pilot-scale RO filtration unit to filter potato fruit water originating from the overflow of centrifuges used to separate protein and other solubles from potato starch after rasping. RO membranes, made of cellulose acetate, ran with a permeate flux of approximately 20 l/m2 h (during 20 h) and at an average pressure of 4 MPa, with a pressure drop of 500 kPa from module inlet to outlet. CODrejection and dry substance rejection both exceeded 99%. Reimann and Yeo [4] dealt with the practical use of various membranes for potato washing water. A 50 nm SiC mineral membrane (200 kPa) achieved a permeate flux of approximately 100 l/(m2 h), but COD-rejection increased as pressure on the inorganic membrane increased (from 20 to 84%). The permeate flux of the 50 nm SiC membrane was higher than that of the 100 nm A1203 membrane, and CODrejection correspondingly lower. Therefore, the concentration polarization at the feed side of the membranes by concentration was very high. Permeate flux decreased as the concentration of COD increased [5]. 2. Materials and methods The treated water, which was a mixture of warm and cold waters coming from various points in a Czech factory producing dried potato purée, contained starch, in granulated or gelatinized form, proteins and solids (fine pieces of potato skins). Pollution of the water was high; COD measuring more than 11,000 mg O2/l, and BOD5 exceeding 8000 mg O2/l. Prior to membrane filtration the water was leaked through a sieve mesh (0.75 mm). We used a pilot plant (T.I.A.Bollene) dedicated to research and/or industrial experiments (see Fig. 1). The process module P37-30 was equipped with ceramic membranes (Membralox) with a filtration area of 0.35 m2 and pore sizes of 500 (alumina) and 100 nm (zirconia). The module channels had profile area of 261 mm2. Retentate flowed from the membrane module back to the supply tank. The temperature was kept in the range of 40–50 °C, and a constant transmembrane pressure of 100 kPa was maintained. Feed flow was 11 m3/h; volume concentration factor defined VCR = V0 = VR ;
ð2Þ
where V0 is initial volume and VR is volume of retentate equal to 8.3. In addition, employing a similar technological arrangement in the laboratory, we used an ARNO 600 separation test unit (Mikropur, s.r.o., Hradec Králové) to test the organic RO membrane 7410 (Nitto Denko Corporation, Osaka). In this case, the temperature was maintained at around 30 °C, and the transmembrane pressure adjusted to 2 MPa. The
Fig. 1. Scheme of the filtration unit (T.I.A.Bollene).
channel had profile area of 44 mm2. Feed flow was 0.6 m3/h; volume concentration factor was 4.2. During our tests, the temperature, the pressures before and after membrane separation, and the permeate flux were all regularly recorded. Three arrangements of membrane modules were evaluated: a) wastewater separation through the 500 nm membrane, b) wastewater separation through the 100 nm membrane, c) second stage separation of the permeate resulting from b) through the 7410 membrane. Samples were taken at the end of each experiment to determine the COD and BOD5 concentrations, as well as the content of dry substance (evaporation residue). In this case it was more acceptable to analyze the content of dry substance than analyzing only solids because from the technological view some important impurities were present in the solution (e.g. gelatinized starch) and, furthermore the classical filtration of the samples was difficult and time-consuming. Because we assumed a higher concentration of proteins [3,6], the dry substance was analyzed while drying the wastewater for 4 h at 105 °C [7]. We then used Eq. (1) to calculate the rejection coefficient for the components observed. The content of soluble carbohydrate in permeate was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection. Separation was performed in a single 30 min run using a Dionex CarboPac PA 1 column (mobile phase 16 mM NaOH, flow 0.25 ml/min, temperature 25 °C, injected sample volume 10 μl). Peak identification was realized using standard solutions. 3. Results and discussion 3.1. Permeate flux Fig. 2 plots the results for the test conducted using the 500 nm MF membrane with wastewater resulting from the production of dried potato purée. After 40 min, permeate flux had fallen from initial 1200 l/ (m2 h) to about 20 l/(m2 h), as a result of which the experiment was stopped. The low permeability of the 500 nm membrane can be explained by the clogging of its pores by bigger particles, and the consequent fouling (see chap. Separation effects). Despite an overall decrease of 80%, permeate flux through the 100 nm MF membrane (Fig. 3) was unexpectedly high. Therefore we stopped our experiments after 9 min because of empty supply tank. The permeate flow above 100 l/(m2 h) was more than 7 times the rate achieved in arrangement a). This permeate flow is comparable with data of Reimann and Yeo [4] processing potato washing water by 50 nm SiC mineral membrane (200 kPa). Gelatinized starch in wastewater from the production of dried potato purée caused higher fouling, and lower pressure should be not used to have appropriate flux. Membranes with pores 20–50 nm could be tested.
Fig. 2. Permeate flux I (-♦- ) vs. time (arrangement a — 500 nm), -■- temperature.
E. Šárka et al. / Desalination 249 (2009) 135–138
137
Table 1 Separation using the 500 nm and 100 nm membranes. Sample
Dry substance (%)
COD (mgO2/l)
BOD5 (mgO2/l)
F R500 P500 R (%) R100 P100 R (%)
0.67 0.96 0.41 38.2 1.70 0.44 34.1
11,840 14,310 7890 33.4 27,170 4400 62.8
8670 9410 5900 31.9 14,470 3620 58.2
F — feed, P — permeate, R — retentate.
Table 2 Second stage separation using the 7410 membrane. Fig. 3. Permeate flux I (-♦- ) vs. time (arrangement b — 100 nm), -■- temperature.
Permeate flux through the organic RO membrane (7410) is shown in Fig. 4. The feed used in this experiment was the permeate from our experiments with the 100 nm membrane. The flow rates measured were similar to those obtained by Cancino et al. [2]. As usual the RO membrane produced lower flux rates in comparison with MF membranes despite the higher pressure difference. Conversely, permeate flux was constant without any drop in the rate, and after 4 h we hadn't observed any fouling. The results indicate that a combination of microfiltration and reverse osmosis is a suitable treatment for wastewater from the production of dried potato purée. 3.2. Separation effects The analytical results for feed, permeate and retentate for both the 500 nm and 100 nm membrane samples are displayed in Table 1. Rejection was high in both cases. For the 500 nm membrane, rejection of dry substance was around 38%, with COD and BOD5 rejection being approximately 32–33%. When balancing measured data it confirmed the creation of solid starch layer on the surface of the module. For the 100 nm membrane, rejection of dry substance was approximately 34%, with COD and BOD5 rejection being around 60%, comparable with data of Reimann and Yeo [4] for potato washing water. The 100 nm permeate contained 0.034 g/l of monosaccharides, and 0.074 g/l of disaccharides. When balancing the measured data in Table 1, it results that the substances bonding oxygen are more liable to fouling. Rejections for the second stage separation using the 7410 RO membrane were very different for the separate components (Table 2). Rejection of dry substance was approximately 59%, while COD and BOD5 rejection were 14% and 29% respectively. The permeate COD concentration 3770 mg O2/l is not extremely high when compared with the data of
Sample
Dry substance (%)
COD (mgO2/l)
BOD5 (mgO2/l)
Fnanof/P100 Rnanof Pnanof R (%)
0.44 0.45 0.18 58.6
4400 8420 3770 14.3
3620 5090 2570 29.0
F — feed, P — permeate, R — retentate.
Ray et al. [8] who used RO as a preconcentration step prior to conventional corn steepwater evaporation reported a COD of 7000 to 9800 mg/l. On the other hand results BOD5 of Cancino et al. [2] for wastewater from corn starch production were much lower. The measured combined effect for both stages was around 70%. 4. Conclusions We used membrane separation to pre-treat wastewater from the production of dried potato purée, with the purpose of assessing possibilities for recycling obtained retentate back to the actual production process and, consequently, for the reduction of wastewater pollution. This paper describes trials, conducted in either one or two stages, of MF and RO membrane filtration of starch wastewater. The low permeability of the 500 nm membrane can be explained by the clogging of its pores by bigger sticky particles, and the consequent fouling. High permeate flux over 100 l/(m2 h) was measured for the 100 nm membrane. COD and BOD5 rejection was high (approximately 60%) for filtration through the 100 nm membrane, an effect that was increased by the subsequent RO filtration. Because of high permeate flux, low fouling and a high separation effect, filtration through RO membranes appears to be promising for wastewater treatment by factory production of dried potato purée. From these data we can draw partial conclusions about the technological steps that might be taken to increase permeate flux and, in this way, to improve the capacity of separation units. Because of possible concentration polarization it would probably be appropriate to test lower membrane pore size (e.g. 20 nm). Also, RO filtration in the second stage should be tested using higher pressures. Therefore, at this time it is necessary to conduct further research and obtain more measurements in order to accurately identify a wider range of the required process parameters. Acknowledgements This research was supported by the Research Proposal, “Theoretical Fundamentals of Food and Biochemical Technologies” of MSMT CR, No. MSM 6046137305.
References Fig. 4. Permeate flux I (-♦- ) vs. time (arrangement c — Nitto Denko 7410), -■- temperature.
[1] P. Mikulášek and J. Šír, Tlakové membránové separační procesy a zařízení, Procesní inženýrství, Praha, 1994.
138 [2] [3] [4] [5] [6]
E. Šárka et al. / Desalination 249 (2009) 135–138 B. Cancino, F. Rossier, C. Orellana, Desalination 200 (2006) 750–751. H. Rüffer, U. Kremser, M. Seekamp, Starch/Stärke 49 (1997) 354–359. W. Reimann, I. Yeo, Desalination 109 (1997) 263–267. W. Reimann, Desalination 109 (1997) 51–55. D. Knorr, J. Food Technol. 12 (1977) 563–580.
[7] S. Zelenka, E. Pexiederová and I. Bohačenko, Cvičení z technologie sacharidů, Návod k technologickým cvičením z krmivářství a škrobárenství, SNTL, Praha, 1977. [8] R.J. Ray, J.K. Gienger, S. Retzlaff, Membrane-based hybrid processes for energy-efficient waste-water treatment, J. Membr. Sci. 28 (1986) 87–106.