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Adsorption-membrane filtration process in boron removal from first stage seawater RO permeate
Desalination 241 (2009) 127 132
Adsorption-membrane filtration process in boron removal from first stage seawater RO permeate Marek Bryjaka*, Joanna Wolskaa, Iwona Sorokoa, Nalan Kabayb a
Faculty of Chemistry, Wroclaw University of Technology, Wroclaw, Poland Tel. +48 71 320 2383; email: [email protected] b Department of Chemical Engineering, Ege University, Izmir, Turkey
Received 20 August 2007; revised 28 December 2007; accepted 4 January 2008
Abstract The paper deals with evaluation of adsorption-membrane filtration (AMF) hybrid process in removal of trace amounts of boron from the first stage RO permeate. Finely ground boron selective resin, Dowex XUS 43594.00, was used as sorbent while polypropylene capillaries with pore dimension of 0.4 mm as the submerged membranes. The process combined delivery of feed and fresh resin suspension with subsequent removal of the loaded sorbent. The effects of such process variables were evaluated: diameter of resin bead, concentration of suspension, rate of suspension replacement and time of the system run. It was found that to reduce boron concentration from 2 mg/L to the WHO recommended level, 1 g/L of resin should be used. During 48 h of process, neither membranes fouling by the sorbent particles nor sedimentation of resin was observed. When resin was subjected to regeneration particle diameter was not changed after 20 alternating immersions in acidic and basic solutions. Keywords: Hybrid system; Operation parameters; Boron; Reverse osmosis
1. Introduction Boron is widely distributed element throughout lithosphere and usually appears in the form of either neutral H3BO3 or anionic borate species. Depending on natural and anthropogenic factors, its concentration in the surface water can vary from 0.1 to 10 mg/L. When *Corresponding author.
overdosed, it causes some negative effects to the living creatures. In the case of mammalians, boron induces male reproductive impediments and several teratogenic effects. Boron concentration in irrigation water, when is only slightly higher than permissible level, affects plant growth which is expressed as ‘boron poisoning effect’ * appearance of yellow spots on leaves and fruit. Boron accelerates plant decay and
Presented at the Third Membrane Science and Technology Conference of Visegrad Countries (PERMEA), Siofok, Hungary, 2–6 September 2007. 0011-9164/09/$– See front matter # 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2008.01.062
128
M. Bryjak et al. / Desalination 241 (2009) 127 132
ultimately its expiration. For this reason, the World Health Organization has recommended the acceptable level of boron in drinking and irrigative water as low as 0.3 mg B/L. Due to increasing demand for water and dramatic shortage of available resources, some water suppliers have had to search for same alternatives. Seawater, saline surface water and brackish water have appeared to be new water sources. When they are desalinated, some trace of boron contaminants can appear in the final product. Among several desalination technologies used worldwide, the interest of engineers has shifted lately to reverse osmosis process. The growth of its popularity is related to the development of new generation of highly selective RO membranes. In the case of seawater desalination plants, the new membranes can reject up to 90% of boron at the first stage of RO treatment. Nevertheless, the boron problem remains still unsolved and the obtained permeate should be subjected to the additional purification step. Literature survey points at several technologies to be useful in the lowering of boron concentration. However, most of these evaluations were conducted for feeds with elevated B concentration and their industrial applications are strongly related to that value. Some of them are listed in Table 1.
The comparison among these methods shows that ion exchange is the best for water deboronation [10]. Adsorption-membrane filtration hybrid process, a method evaluated by us lately [1113], which combines sorption on powdered boron selective resin with membrane microfiltration, seems to be an attractive alternative to the commonly used column-mode technology. The goal of the presented study is to continue investigation of the adsorption-membrane filtration system for removal of boron trace amounts from the first stage RO permeate and to check effects of some variables on the process efficiency. 2. Experimental The effect of sorbent particle diameter on boron kinetic performance was studied by contacting 1 g of Dowex (XUS 43594.00) fractions, of average particle diameter 20, 75 and 500 mm, with 100 mL of 2 mg B/L solution. The system was gently stirred and kept at room temperature. The boron concentrations were monitored in solutions during the first 10 min of sorption. In all AMF studies, finely ground Dowex XUS 43594.00 resin with average particle diameter of 20 mm served as the sorbent. Their bead size distribution is shown elsewhere [11]. Microfiltration module, equipped with capillary polypropylene membrane of ID 1.5 mm and pore
Table 1 Boron removal technologies Technology Softening Coagulation Activated carbon Reverse osmosis Ion exchange resin Two-pass RO with pH adjustment Electrodialysis Boron chelation
% Removal
Remarks
Insignificant B/28% Up to 90% 43 78% /99% Up to 90% /90% /80% /98%
Batch tests of calcite precipitation Typical removal B/10% High carbon doses needed Based on survey of eight operating RO plants pH of effluent B/4.5 for 600 BV Best removal at pH 10.5 Cost of 0.15 USD per m3 N -methyl-D-glucamine Mannitol
Refs. [1] [2] [3] [4] [5] [6] [7] [8] [9]
M. Bryjak et al. / Desalination 241 (2009) 127 132
dimension of 0.4 mm, was used to keep suspension of boron selective resin (BSR) in a circulating loop. Feed as well as suspension of fresh resin was added to the loop while suspension of boron loaded resin was subsequently removed. The setup of the used system is shown in Fig. 1. Total membrane surface was set as 24 cm2. The volume of 250 cm3 of boron solution was circulated in a loop. It contained various amounts of BSR. The fresh feed with 2.0 ppm of boron, delivered from the reservoir 2, replaced the equivalent volume of permeate in the loop. During the process two variables were evaluated: concentration of BSR and resin suspension replacement rate. The rest of the variables were kept constant*suspension was circulated with the rate of 10 mL/min and the module was placed 30 cm below the feed level. The generated hydrostatic pressure allows to obtain permeate flux of 3438 L/m2 h during the time of the system evaluation. Boron concentration in permeate was determined by the Curcumin method. The process was carried out in two short- and long-time modes: 3 and 48 h, respectively. The system was inspected after longer service to note any places where BSR particles could form the deposits. Pump 2
Pump 3
In order to check the stability of the sorbent particles, the ground resin was exposed to a cyclic contact with 5% HCl and 5% NaOH solutions, within 1 h its immersion in each solution. Distribution of particle’s diameter was evaluated by means of Mastersizer X (Melvern Instruments GmbH, Germany) and indicated as average particle diameter and diameter of 10%, 50% and 90% fraction of total particle population. These numbers were used to calculate the SPAN number ½SPAN ¼ ðd90 d10 Þ=d50 . /
3. Results and discussion The effect of BSR particle diameter on sorption kinetics is shown in Fig. 2. It is evident that to fast decrease of boron concentration from about 2 mg/L to that permissible by the WHO guideline, it is better to use small particles. After 3 min of contacting of solution with 20-mm particles, boron concentration dropped to the level that is reached after 24 h of process with the use of 500-mm beads. That observation is congruent to the previously finding that the bottlenecking phenomenon of sorption is a particle diffusion of boronate within beads [14]. Hence, it can be concluded that the smallest particles significantly improve the efficiency of separation process.
ST2
Pump 1 Suspension loop
Feed reservoir 2
Membrane module
C/Co × 100%
ST1
129
100 90 80 70 60 50 40 30 20 10 0 0
2
Permeate
Fig. 1. Set-up of the adsorption-membrane filtration system. ST1 and ST2, suspension tanks; pump 1, circulating pump; pump 2, fresh suspension delivery pump; pump 3, boron loaded suspension pump.
0.020 mm
4 6 Time (min) 0.075 mm
8
10
0.500 mm
Fig. 2. Boron sorption kinetic courses. Starting boron concentration 2 mg/L, 1 g of BSR per 1 L of solution.
M. Bryjak et al. / Desalination 241 (2009) 127 132
130
(b) B concentration (ppm)
B concentration (ppm)
(a) 2 0.25 g/L Js /Jp = 0.05 1
0 0
1
2
2 0.5 g/L Js /Jp = 0.05 1
0 0
3
1
Time (h) (c)
3
(d)
2 1.0 g/L Js /Jp = 0.05 1
0 0
1
2
3
B concentration (ppm)
B concentration (ppm)
2 Time (h)
2 0.5 g/L Js /Jp = 0.15 1
0 0
1
2
3
Time (h)
Time (h)
Fig. 3. Short-time runs of AMF system loaded with 20-mm particles of Dowex XUS resin. Concentration of resin is shown in the right corner. Js and Jp are the flows of suspension and permeate, respectively. Js/Jp ratio shows the normalized suspension delivery rate.
to use 1.0 g/L concentration of powdered Dowex resin to remove remaining amounts of boron from the RO permeate. However, it can be expected that the higher content of solids in the system can cause some unwanted effects. To check the system stability in the long-time service, the AMF hybrid was running for 48 h. To make the graphic presentation simple, the analyses are presented within the first 24 h of the process. The data are shown in Fig. 4. In all cases, the flux of permeate was kept constant at the level of 3438 L/m2 h. It is seen that the membranes are not plugged with small particles of BSR and that the process is stable for the whole time of the investigation.
Short-time evaluation of the AMF process efficiency is shown in Fig. 3. As discussed previously [12], the efficiency of boron removal depends on the relation of BSR concentration and rate of suspension exchange. After increasing suspension rate exchange, boron concentration in permeate is reduced * such effect is seen on Fig. 3(b) and (d). However, from the processing point of view, it is better to reduce rate of suspension exchange even when the resin concentration has to be increased. Additionally, the use of the more concentrated suspension protects permeate against the boron bleeding and creates some kind of buffer for the AMF system malfunctioning. For that reason, it is suggested
(b) 2
B concentration (ppm)
B concentration (ppm)
(a) 2 0.5 g/L Js /Jp = 0.05 1
0 0
6
12
18 Time (h)
24
30
1.0 g/L Js /Jp = 0.05 1
0 0
6
12
18
24
30
Time (h)
Fig. 4. Long-time runs of AMF system loaded with 20-mm particles of Dowex XUS resin for two concentrations of resins.
M. Bryjak et al. / Desalination 241 (2009) 127 132 Table 2 Bead diameter of BSR resin after 20 cycles of acid base immersion Sample
d10 (mm) d50 (mm) d90 (mm) SPAN
Before cycling 3.9 After 20 cycle 9.6
27.9 35.6
88.5 92.1
3.03 2.32
SPAN ¼ ðd90 d10 Þ=d50.
/
Additionally, the visual inspection of the AMF system did not show any deposits of resin in the system. It is foreseen however that some problems might appear when used particles are subjected to the regeneration procedure. They have to withstand cyclic changes of their volume caused by repeatable immersion in acidic and basic solutions. When the samples are prepared by mechanical grinding, it is possible that swelling stress may cause the additional disruption of the polymer matrix and lower the particle diameter. To evaluate that phenomenon, the samples of BSR resin were subjected to consecutive immersion in 5% solutions of HCl and NaOH. After simulations of 20 regeneration cycles, the bead size distribution was measured. The results are juxtaposed in Table 2. The presented data show that alternative swelling and shrinking process do not result in additional bead breaking. Hence, it was concluded that the ground resin might be used for boron separation in the AMF system. 4. Conclusions Taking into account the efficiency of adsorption-membrane filtration process, it is recommended to use boron selective resin with the small diameter. As a result of using 20-mm particles of Dowex XUS sorbent, the removal of trace amounts of boron appears within 2 3 min of the sorption. To keep the process running safety, it is suggested to use 1 g of powdered sorbent per 1 L of first stage RO
131
permeate. The ratio of suspension delivery to feed flow can be kept as low as 0.05. The AMF system can run in long cycles without any problems caused by sorbent deposition on membrane surface. The ground Dowex XUS resin can be regenerated by alternative immersion in acidic and basic solution and the resin particles do not break to smaller pieces. Acknowledgement The work was financially supported by Middle East Desalination Research Centre (MEDRC, Project No. 04-AS-004) and Wroclaw University of Technology (Grant No. 343455/Z0309). References [1] Y. Kitano, Co-precipitation of borate boron with calcium carbonate, Geochem. J., 12 (1978) 183 189. [2] Borax Consolidated Ltd, Report on Sampling at Selected Water Treatment Works to Determine the Extent of Boron Removal by Conventional Water Treatment, February 1996. [3] W.W. Choi and K.Y. Chen, Evaluation of boron removal by adsorption on solids, Environ. Sci. Technol., 13 (1979) 189 198. [4] Y. Magara, T. Aizawa, S. Kunikane, M. Itoh, M. Kohki and M. Kawasaki, The behavior of inorganic constituents and disinfection by-products in reverse osmosis water desalination processes, Water Sci. Technol., 34 (1996) 141148. [5] N. Nadav, Boron removal from seawater reverse osmosis permeate utilizing selective ion exchange resin, Desalination, 124 (1999) 131 135. [6] D. Prats, M.F. Chillon-Arias and M. RodriguezPastor, Analysis of the influence of pH and pressure on the elimination of boron in reverse osmosis, Desalination, 128 (2000) 269 273. [7] M. Turek, P. Dydo, J. Trojanowska, B. Bandura et al., Electrodialytic treatment of boron-containing wastewater, Desalination, 205 (2007) 185 192. [8] B.M. Smith, Boron removal by polymer-assisted ultrafiltration, Sep. Sci. Technol., 30 (1995) 3849 3859.
132
M. Bryjak et al. / Desalination 241 (2009) 127 132
[9] N. Geffen, R. Semiat, M.S. Eisen, Y. Balazs, I. Katz and C.G. Dosoretz, Boron removal from water by complexation to polyol compounds, J. Membr. Sci., 286 (2006) 45 51. [10] M. Simonnot, Ch. Castel, M. Nicolaie, Ch. Rosin, M. Sardin and H. Jauffret, Boron removal from drinking water with boron selective resin: is the treatment really selective? Water Res., 34 (2000) 109 116. [11] M. Bryjak, J. Wolska and N. Kabay, Removal of boron from seawater by adsorption-membrane hybrid process: implementation and challenges, Desalination, 223 (2008) 57 62.
[12] N. Kabay, I. Yilmaz, M. Bryjak and M. Yuksel, Removal of boron from aqueous solutions by ion exchange-membrane hybrid process, Desalination, 198 (2006) 74 81. [13] N. Kabay, M. Bryjak, S. Schlosser, M. Kitis, S. Avlonitis, Z. Matejka, I. Al-Mutaz and M. Yuksel, et al., Adsorption-membrane filtration hybrid process for boron removal from seawater: an overview, Desalination, 223 (2008) 38 48. [14] I. Yilmaz, N. Kabay, M. Yuksel, R. Holdich and M. Bryjak, Effect of ionic strength of solution on boron mass transfer by ion exchange separation, Sep. Sci. Technol., 42 (2007) 1013 1029.
Adsorption-membrane filtration process in boron removal from first stage seawater RO permeate Marek Bryjaka*, Joanna Wolskaa, Iwona Sorokoa, Nalan Kabayb a
Faculty of Chemistry, Wroclaw University of Technology, Wroclaw, Poland Tel. +48 71 320 2383; email: [email protected] b Department of Chemical Engineering, Ege University, Izmir, Turkey
Received 20 August 2007; revised 28 December 2007; accepted 4 January 2008
Abstract The paper deals with evaluation of adsorption-membrane filtration (AMF) hybrid process in removal of trace amounts of boron from the first stage RO permeate. Finely ground boron selective resin, Dowex XUS 43594.00, was used as sorbent while polypropylene capillaries with pore dimension of 0.4 mm as the submerged membranes. The process combined delivery of feed and fresh resin suspension with subsequent removal of the loaded sorbent. The effects of such process variables were evaluated: diameter of resin bead, concentration of suspension, rate of suspension replacement and time of the system run. It was found that to reduce boron concentration from 2 mg/L to the WHO recommended level, 1 g/L of resin should be used. During 48 h of process, neither membranes fouling by the sorbent particles nor sedimentation of resin was observed. When resin was subjected to regeneration particle diameter was not changed after 20 alternating immersions in acidic and basic solutions. Keywords: Hybrid system; Operation parameters; Boron; Reverse osmosis
1. Introduction Boron is widely distributed element throughout lithosphere and usually appears in the form of either neutral H3BO3 or anionic borate species. Depending on natural and anthropogenic factors, its concentration in the surface water can vary from 0.1 to 10 mg/L. When *Corresponding author.
overdosed, it causes some negative effects to the living creatures. In the case of mammalians, boron induces male reproductive impediments and several teratogenic effects. Boron concentration in irrigation water, when is only slightly higher than permissible level, affects plant growth which is expressed as ‘boron poisoning effect’ * appearance of yellow spots on leaves and fruit. Boron accelerates plant decay and
Presented at the Third Membrane Science and Technology Conference of Visegrad Countries (PERMEA), Siofok, Hungary, 2–6 September 2007. 0011-9164/09/$– See front matter # 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2008.01.062
128
M. Bryjak et al. / Desalination 241 (2009) 127 132
ultimately its expiration. For this reason, the World Health Organization has recommended the acceptable level of boron in drinking and irrigative water as low as 0.3 mg B/L. Due to increasing demand for water and dramatic shortage of available resources, some water suppliers have had to search for same alternatives. Seawater, saline surface water and brackish water have appeared to be new water sources. When they are desalinated, some trace of boron contaminants can appear in the final product. Among several desalination technologies used worldwide, the interest of engineers has shifted lately to reverse osmosis process. The growth of its popularity is related to the development of new generation of highly selective RO membranes. In the case of seawater desalination plants, the new membranes can reject up to 90% of boron at the first stage of RO treatment. Nevertheless, the boron problem remains still unsolved and the obtained permeate should be subjected to the additional purification step. Literature survey points at several technologies to be useful in the lowering of boron concentration. However, most of these evaluations were conducted for feeds with elevated B concentration and their industrial applications are strongly related to that value. Some of them are listed in Table 1.
The comparison among these methods shows that ion exchange is the best for water deboronation [10]. Adsorption-membrane filtration hybrid process, a method evaluated by us lately [1113], which combines sorption on powdered boron selective resin with membrane microfiltration, seems to be an attractive alternative to the commonly used column-mode technology. The goal of the presented study is to continue investigation of the adsorption-membrane filtration system for removal of boron trace amounts from the first stage RO permeate and to check effects of some variables on the process efficiency. 2. Experimental The effect of sorbent particle diameter on boron kinetic performance was studied by contacting 1 g of Dowex (XUS 43594.00) fractions, of average particle diameter 20, 75 and 500 mm, with 100 mL of 2 mg B/L solution. The system was gently stirred and kept at room temperature. The boron concentrations were monitored in solutions during the first 10 min of sorption. In all AMF studies, finely ground Dowex XUS 43594.00 resin with average particle diameter of 20 mm served as the sorbent. Their bead size distribution is shown elsewhere [11]. Microfiltration module, equipped with capillary polypropylene membrane of ID 1.5 mm and pore
Table 1 Boron removal technologies Technology Softening Coagulation Activated carbon Reverse osmosis Ion exchange resin Two-pass RO with pH adjustment Electrodialysis Boron chelation
% Removal
Remarks
Insignificant B/28% Up to 90% 43 78% /99% Up to 90% /90% /80% /98%
Batch tests of calcite precipitation Typical removal B/10% High carbon doses needed Based on survey of eight operating RO plants pH of effluent B/4.5 for 600 BV Best removal at pH 10.5 Cost of 0.15 USD per m3 N -methyl-D-glucamine Mannitol
Refs. [1] [2] [3] [4] [5] [6] [7] [8] [9]
M. Bryjak et al. / Desalination 241 (2009) 127 132
dimension of 0.4 mm, was used to keep suspension of boron selective resin (BSR) in a circulating loop. Feed as well as suspension of fresh resin was added to the loop while suspension of boron loaded resin was subsequently removed. The setup of the used system is shown in Fig. 1. Total membrane surface was set as 24 cm2. The volume of 250 cm3 of boron solution was circulated in a loop. It contained various amounts of BSR. The fresh feed with 2.0 ppm of boron, delivered from the reservoir 2, replaced the equivalent volume of permeate in the loop. During the process two variables were evaluated: concentration of BSR and resin suspension replacement rate. The rest of the variables were kept constant*suspension was circulated with the rate of 10 mL/min and the module was placed 30 cm below the feed level. The generated hydrostatic pressure allows to obtain permeate flux of 3438 L/m2 h during the time of the system evaluation. Boron concentration in permeate was determined by the Curcumin method. The process was carried out in two short- and long-time modes: 3 and 48 h, respectively. The system was inspected after longer service to note any places where BSR particles could form the deposits. Pump 2
Pump 3
In order to check the stability of the sorbent particles, the ground resin was exposed to a cyclic contact with 5% HCl and 5% NaOH solutions, within 1 h its immersion in each solution. Distribution of particle’s diameter was evaluated by means of Mastersizer X (Melvern Instruments GmbH, Germany) and indicated as average particle diameter and diameter of 10%, 50% and 90% fraction of total particle population. These numbers were used to calculate the SPAN number ½SPAN ¼ ðd90 d10 Þ=d50 . /
3. Results and discussion The effect of BSR particle diameter on sorption kinetics is shown in Fig. 2. It is evident that to fast decrease of boron concentration from about 2 mg/L to that permissible by the WHO guideline, it is better to use small particles. After 3 min of contacting of solution with 20-mm particles, boron concentration dropped to the level that is reached after 24 h of process with the use of 500-mm beads. That observation is congruent to the previously finding that the bottlenecking phenomenon of sorption is a particle diffusion of boronate within beads [14]. Hence, it can be concluded that the smallest particles significantly improve the efficiency of separation process.
ST2
Pump 1 Suspension loop
Feed reservoir 2
Membrane module
C/Co × 100%
ST1
129
100 90 80 70 60 50 40 30 20 10 0 0
2
Permeate
Fig. 1. Set-up of the adsorption-membrane filtration system. ST1 and ST2, suspension tanks; pump 1, circulating pump; pump 2, fresh suspension delivery pump; pump 3, boron loaded suspension pump.
0.020 mm
4 6 Time (min) 0.075 mm
8
10
0.500 mm
Fig. 2. Boron sorption kinetic courses. Starting boron concentration 2 mg/L, 1 g of BSR per 1 L of solution.
M. Bryjak et al. / Desalination 241 (2009) 127 132
130
(b) B concentration (ppm)
B concentration (ppm)
(a) 2 0.25 g/L Js /Jp = 0.05 1
0 0
1
2
2 0.5 g/L Js /Jp = 0.05 1
0 0
3
1
Time (h) (c)
3
(d)
2 1.0 g/L Js /Jp = 0.05 1
0 0
1
2
3
B concentration (ppm)
B concentration (ppm)
2 Time (h)
2 0.5 g/L Js /Jp = 0.15 1
0 0
1
2
3
Time (h)
Time (h)
Fig. 3. Short-time runs of AMF system loaded with 20-mm particles of Dowex XUS resin. Concentration of resin is shown in the right corner. Js and Jp are the flows of suspension and permeate, respectively. Js/Jp ratio shows the normalized suspension delivery rate.
to use 1.0 g/L concentration of powdered Dowex resin to remove remaining amounts of boron from the RO permeate. However, it can be expected that the higher content of solids in the system can cause some unwanted effects. To check the system stability in the long-time service, the AMF hybrid was running for 48 h. To make the graphic presentation simple, the analyses are presented within the first 24 h of the process. The data are shown in Fig. 4. In all cases, the flux of permeate was kept constant at the level of 3438 L/m2 h. It is seen that the membranes are not plugged with small particles of BSR and that the process is stable for the whole time of the investigation.
Short-time evaluation of the AMF process efficiency is shown in Fig. 3. As discussed previously [12], the efficiency of boron removal depends on the relation of BSR concentration and rate of suspension exchange. After increasing suspension rate exchange, boron concentration in permeate is reduced * such effect is seen on Fig. 3(b) and (d). However, from the processing point of view, it is better to reduce rate of suspension exchange even when the resin concentration has to be increased. Additionally, the use of the more concentrated suspension protects permeate against the boron bleeding and creates some kind of buffer for the AMF system malfunctioning. For that reason, it is suggested
(b) 2
B concentration (ppm)
B concentration (ppm)
(a) 2 0.5 g/L Js /Jp = 0.05 1
0 0
6
12
18 Time (h)
24
30
1.0 g/L Js /Jp = 0.05 1
0 0
6
12
18
24
30
Time (h)
Fig. 4. Long-time runs of AMF system loaded with 20-mm particles of Dowex XUS resin for two concentrations of resins.
M. Bryjak et al. / Desalination 241 (2009) 127 132 Table 2 Bead diameter of BSR resin after 20 cycles of acid base immersion Sample
d10 (mm) d50 (mm) d90 (mm) SPAN
Before cycling 3.9 After 20 cycle 9.6
27.9 35.6
88.5 92.1
3.03 2.32
SPAN ¼ ðd90 d10 Þ=d50.
/
Additionally, the visual inspection of the AMF system did not show any deposits of resin in the system. It is foreseen however that some problems might appear when used particles are subjected to the regeneration procedure. They have to withstand cyclic changes of their volume caused by repeatable immersion in acidic and basic solutions. When the samples are prepared by mechanical grinding, it is possible that swelling stress may cause the additional disruption of the polymer matrix and lower the particle diameter. To evaluate that phenomenon, the samples of BSR resin were subjected to consecutive immersion in 5% solutions of HCl and NaOH. After simulations of 20 regeneration cycles, the bead size distribution was measured. The results are juxtaposed in Table 2. The presented data show that alternative swelling and shrinking process do not result in additional bead breaking. Hence, it was concluded that the ground resin might be used for boron separation in the AMF system. 4. Conclusions Taking into account the efficiency of adsorption-membrane filtration process, it is recommended to use boron selective resin with the small diameter. As a result of using 20-mm particles of Dowex XUS sorbent, the removal of trace amounts of boron appears within 2 3 min of the sorption. To keep the process running safety, it is suggested to use 1 g of powdered sorbent per 1 L of first stage RO
131
permeate. The ratio of suspension delivery to feed flow can be kept as low as 0.05. The AMF system can run in long cycles without any problems caused by sorbent deposition on membrane surface. The ground Dowex XUS resin can be regenerated by alternative immersion in acidic and basic solution and the resin particles do not break to smaller pieces. Acknowledgement The work was financially supported by Middle East Desalination Research Centre (MEDRC, Project No. 04-AS-004) and Wroclaw University of Technology (Grant No. 343455/Z0309). References [1] Y. Kitano, Co-precipitation of borate boron with calcium carbonate, Geochem. J., 12 (1978) 183 189. [2] Borax Consolidated Ltd, Report on Sampling at Selected Water Treatment Works to Determine the Extent of Boron Removal by Conventional Water Treatment, February 1996. [3] W.W. Choi and K.Y. Chen, Evaluation of boron removal by adsorption on solids, Environ. Sci. Technol., 13 (1979) 189 198. [4] Y. Magara, T. Aizawa, S. Kunikane, M. Itoh, M. Kohki and M. Kawasaki, The behavior of inorganic constituents and disinfection by-products in reverse osmosis water desalination processes, Water Sci. Technol., 34 (1996) 141148. [5] N. Nadav, Boron removal from seawater reverse osmosis permeate utilizing selective ion exchange resin, Desalination, 124 (1999) 131 135. [6] D. Prats, M.F. Chillon-Arias and M. RodriguezPastor, Analysis of the influence of pH and pressure on the elimination of boron in reverse osmosis, Desalination, 128 (2000) 269 273. [7] M. Turek, P. Dydo, J. Trojanowska, B. Bandura et al., Electrodialytic treatment of boron-containing wastewater, Desalination, 205 (2007) 185 192. [8] B.M. Smith, Boron removal by polymer-assisted ultrafiltration, Sep. Sci. Technol., 30 (1995) 3849 3859.
132
M. Bryjak et al. / Desalination 241 (2009) 127 132
[9] N. Geffen, R. Semiat, M.S. Eisen, Y. Balazs, I. Katz and C.G. Dosoretz, Boron removal from water by complexation to polyol compounds, J. Membr. Sci., 286 (2006) 45 51. [10] M. Simonnot, Ch. Castel, M. Nicolaie, Ch. Rosin, M. Sardin and H. Jauffret, Boron removal from drinking water with boron selective resin: is the treatment really selective? Water Res., 34 (2000) 109 116. [11] M. Bryjak, J. Wolska and N. Kabay, Removal of boron from seawater by adsorption-membrane hybrid process: implementation and challenges, Desalination, 223 (2008) 57 62.
[12] N. Kabay, I. Yilmaz, M. Bryjak and M. Yuksel, Removal of boron from aqueous solutions by ion exchange-membrane hybrid process, Desalination, 198 (2006) 74 81. [13] N. Kabay, M. Bryjak, S. Schlosser, M. Kitis, S. Avlonitis, Z. Matejka, I. Al-Mutaz and M. Yuksel, et al., Adsorption-membrane filtration hybrid process for boron removal from seawater: an overview, Desalination, 223 (2008) 38 48. [14] I. Yilmaz, N. Kabay, M. Yuksel, R. Holdich and M. Bryjak, Effect of ionic strength of solution on boron mass transfer by ion exchange separation, Sep. Sci. Technol., 42 (2007) 1013 1029.