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Removal of heavy metals from wastewater by membrane processes: a comparative study
DESALINATION ELSEVIER
Desalination 164 (2004) 105-110
www.elscvier.com/1oca&deaa l
Removal of heavy metals from wastewater by membrane processes: a comparative study Hani Abu Qdais a* , Hassan Moussab 'Department of Civil Engineering, Department of Chemical Engineering, Jordan University of Science and Technology, PO Box 3030, Irbid 22110, Jordan Tel . +962 (2) 709-5111 ; Fax +962 (2) 709-5018 ; email : [email protected]
Received 28 October 2002 ; accepted 14 August 2003
Abstract Wastewater containing copper and cadmium can be produced by several industries . The application of both reverse osmosis (RO) and nanofiltration (NF) technologies for the treatment of wastewater containing copper and cadmium ions to reduce fresh water consumption and environmental degradation was investigated . Synthetic wastewater samples containing Cu" and Cd2+ ions at various concentrations were prepared and subjected to treatment by RO and NF in the laboratory . The results showed that high removal efficiency of the heavy metals could be achieved by RO process (98% and 99% for copper and cadmium, respectively) . NF, however, was capable of removing more than 90% of the copper ions existing in the feed water . The effectiveness of RO and NF membranes in treating wastewater containing more than one heavy metal was also investigated . The results showed that the RO membrane was capable of treating wastewater with an initial concentration of 500 ppm and reducing the ion concentration to about 3 ppm (99 .4% removal), while the average removal efficiency of NF was 97% . The low level of the heavy metals concentration in the permeate implies that water with good quality could be reclaimed for further reuse . Keywords : Heavy metals ; Reverse osmosis ; Nanofiltration ; Removal efficiency ; Industrial wastewater
1 . Introduction Reverse osmosis (RO) and nanofiltration (NF) are relatively new processes, which were initially developed for the production of potable water from saline and brackish water . However, the development of these processes has been
*Corresponding author .
accelerated in recent years and has begun to find applications in the treatment of industrial wastewater . Recent research indicates that wastewater reclamation by RO offers great promise for a sustainable reduction in cost, conserving natural resources, as well as marked improvements of pollutant removal efficiency . Wilf and Alt [1] applied RO for the reclamation of municipal wastewater . They found
0011-9164/04/$- See front matter © 2004 Elsevier B .V . All rights reserved P11 :SOO11-9164(04)00169-9
1 06
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
that RO was capable of treating secondary effluents. Ujang and Anderson [2] illustrated the feasibility of using a low- pressure RO process for the removal of Zn2' and Cu z+ from wastewater in the presence of EDTA as a chelating agent . Steenkamp et al . [3] manu-factured a tubular alumina/chitosan composite membrane and used it to remove Cu" ions . An effluent of Cu" ions below 1 mg/l was achieved . Durham et al . [4] applied microfiltration prior to using RO to treat municipal wastewater to reduce capital and operating costs of the RO treatment process . Redondo [5] presented trends for using RO to treat low-quality feed water . He discussed the various benefits and problems encountered in using RO for treating wastewater . Padilla and Tavani [6] studied the removal of trivalent chromium from tanning wastewater using RO . The study revealed effective removal of the chromium from wastewater . Okazaki et al . [7] demonstrated that the use of the RO process in combination with a microfiltration system removed cadmium from wastewater produced by electronic microchip manufacturing to below detectable levels (i .e ., <0 .01 mg/l) . Berg et al . [8] applied NF to remove pesticides and other micropollutants . Their study revealed that at neutral pH values complete rejection of polar organics is possible with NF . Tang and Chen [9] applied NF for the treatment of textile wastewater . The investigation showed that 98% dye rejection was achieved at an applied pressure of 500 kPa. Koyuncu [10] investigated the effect of cross flow velocity and feed concentration on the removal of reactive dyes using NF . His study showed a removal greater than 99% can be achieved by NF mem-branes containing vinylsulphone dyes . Del Re and Giacomo [11] coupled NF and supercritical water oxidation to remove and destroy toxic micropolluting organic compounds from wastewater. They claimed that such coupling reduces both the investment and the operating costs of
removing toxic and dangerous micropollutants present in the wastewater and produces water of high level of purity . Schafer et al . [12], Hong and Elimelech [13] and Cho et al . [14] applied NF for the removal of natural organic matter and studied NF membranes fouling behavior by its presence . Heavy metals are considered as one of the serious environmental contaminants because of their high toxicity . Wastewater containing copper and cadmium can be produced by a variety of industries such as metal finishing, batteries manufacturing, electrical cables and electronic microchip manufacturing, and the mining industry . Legal requirements oblige industries to install effective wastewater treatment systems . Since the price of the noble materials such as heavy metals is constantly increasing, interesting processes are those capable, in addition to wastewater purification, of recovering metals . RO and NF may be such processes . Membrane separation processes are increasingly used as an alternative to conventional industrial wastewater treatment . There are several advantages of using membranes in water and wastewater treatment [15] . Reuse of water from industrial processes is an important business goal, especially when the industry is using large amounts of water . This goal can be achieved through industrial wastewater treatment by membrane processes . Using these processes will also enable the industry to comply with the effluent standard limits imposed by environmental regulations [16] . The conventional and most commonly used method for the treatment of industrial wastewater containing heavy metals is the chemical precipitation method [17] . However, this process requires a large amount of treatment chemicals to decrease the heavy metals to levels imposed by the regulations . In addition, the sludge produced from the precipitation process has to be subjected to dewatering and disposal into landfills, which adds an additional cost to the treatment process .
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
Therefore, it is important to recover the valuable materials (metals and water) and prevent environmental degradation . The purpose of this study is to evaluate the performance of the RO and NF processes in removing heavy metals from industrial wastewater .
2. Materials and methods Synthetic samples of wastewater were prepared by adding different amounts of copper and cadmium as cupric and cadmium sulfates to distilled water . To monitor the performance of the RO and NF processes, the total dissolved solids (TDS) concentration was used as an indicator of performance . Several solutions were prepared with different concentrations of copper and cadmium sulfates . The TDS was measured each time at 19°C, and the calibration curve between the added concentration and TDS was prepared . Figs . 1 and 2 show good correlation between the added concentration of copper and cadmium and TDS (R2 is 0 .984 and 0 .995 for copper and cadmium, respectively) . The high correlation obtained suggests that TDS is a good indicator for measuring the concentration of the heavy metals in the solution .
107
The initial concentration of the metal sulfates used in the experiments ranged from 25 to 200 ppm for both CuSO 4 and CdSO 4 . A benchscale membrane unit was used to carry out the experiments consisting of a module containing two tubular spiral-wound membranes arranged in series . The system is fed by a plunger pump, which provides high pressure . The experimental set-up is shown in Fig. 3, and the membrane characteristics are presented in Table 1 . Initially the experiments were conducted using cupric and cadmium sulfates separately . After that, a mixture with various ratios of CuSO 4 :CdSO4 (1 :3, 1 :1 and 3 :1) were subjected to treatment by both RO and NF processes .
160
Fig . 2 . Calibration curve using TDS as an indicator to measure CdSO 4 concentration.
MEMBRANE ASSEMBLY
Pressure gauge
0
0 .5 Tank
Initial concentration, mM
Fig . 1 . Calibration curve using TDS as an indicator to measure CuSO4 concentration.
Fig . 3 . Schematic diagram of the membrane unit .
H.A . Qdais, H. Moussa /Desalination 164 (2004) 1 05-110
108 Table 1
Membrane specifications used in the experiments Characteristics
RO membrane
NF membrane
Membrane material Membrane configuration
Polyamide
Polyamide
Spiral wound
Spiral wound
Membrane surface area, m 2
2 .5
2 .5
Allowable operating pH range
4-11
2 .5-11
Maximum operating temperature, °C
45 1
45
Maximum feed turbidity, NTU Maximum feed SDI, 15 min
1 5
5
3. Results and discussion The efficiency of RO and NF processes in removing Cu+2 and Cd2+ from wastewater is presented in Figs . 4 and 5 . As shown from Fig . 4, Cu" ions were successfully removed from the wastewater by both RO and NF . The concentration of Cu" in the product water (permeate) for RO was reduced to an average value 3 .5± 1 .7 ppm with an average removal efficiency of 97% . On the other hand, the removal efficiency of Cue{ by NF ranged from 84% to 96% for an initial feed concentration of 25 and 200 ppm, respectively . The same result can be observed for Cd2+ ions (see Fig . 5) where its concentration in the permeate from RO was reduced to 1 .77±
0.11 ppm with average removal efficiency of 98.5%, while the cadmium removal efficiency of the NF ranged from 82 to 97% . This implies that membrane techniques such as RO and NF are efficient processes for removing heavy metals from wastewater, so as to reclaim this water for further uses. The results obtained also show that Cd2+ ions were removed at a slightly higher efficiency compared to Cu e+ . This might be due to the fact that the size of the Cd2+ is larger than that of Cu e+ . A somewhat similar result was found by Ujang and Anderson [2], who reported that Zn 2+ ions can be removed at a slightly higher efficiency compared to Cu e+ . This was also confirmed by the higher removal of cadmium than the copper under the same pressure by RO, as shown in Fig . 6 .
10
10
• RO O NF 0
O
0
0
0
• RO
0
ONF
E CL
O
O 0
•
•
0
•
•
•
•
•
0 f-
•
•
2
O
0
0
0
0
•
0 0
50
100
150
200
250
Initial concentration, ppm
0
50
100
150
200
Initial concentration, ppm
Fig . 4 . Concentration of CuSO4 in the permeate from RO
Fig . 5 . Concentration of CdSO4 in the permeate from RO
and NF for different feed concentrations .
and NF for different feed concentrations
H.A . Qdais, H. Moussa /Desalination 164 (2004) 1 05 -110
109
Table 2 RO efficiency in treating the mixture of copper and cadmium salts Solution
Concentration of CuSO4 , ppm
Concentration of CdSO4, ppm
TDS in the feed to the RO, ppm
Permeate
no . 1
125
375
500
3 .09
2
250
250
500
3 .20
3
375
125
500
3 .34
concentration, ppm
Table 3 NF efficiency in treating the mixture of copper and cadmium salts Solution
Concentration
Concentration of
of CuSO 4, ppm
CdSO4 , ppm
TDS in the feed to the RO, ppm
Permeate
no .
concentration, ppm
1
125
375
500
12 .34
2
250
250
500
13 .16
3
375
125
500
13 .58
The effectiveness of RO and NF membranes in treating wastewater containing mixed heavy metals was tested. Three different solutions were prepared which contained concentrations of CuSO4 and CdSO4 with different ratios so as to achieve a solution with TDS of 500 ppm . The ratios of CuSO 4 and CdSO4 concentrations in the solutions are given in Tables 2 and 3 . The concentration of the ions in the permeate from the RO was found to be about 3 ppm (99 .4% removal efficiency), whereas it was 13 ppm from the NF experiment (97 .4% removal efficiency) . This is a clear indication that RO and NF are also capable of treating wastewater containing more than one heavy metal . The results also show that RO is more effective than NF in obtaining water with lower heavy metal concentration as obtained in the single heavy metal cases . The local Jordanian standards of industrial wastewater discharges (JS 202/1991) require that the concentration of Cu 2T and Cd2+ in discharge water should not exceed I and 0 .01 ppm, respectively . Slightly higher values were obtained in the experiments performed . The concentration of the above ions can still be lowered by further treating
E CL CL
EL
s
d Q
0 5
7
9
11
13
15
Applied pressure (bar) Fig . 6 . Effect of the applied pressure on permeate concentration for both cadmium and copper by RO (feed concentration 500 ppm) .
the permeate in another RO unit or increasing the operating pressure . Fig . 6 shows the effect of the applied pressure on the concentration of the ions in the permeate from RO . The results confirm that lower concentration can be achieved by increasing the applied pressure . It can also be seen from this figure that the removal of Cd +2 is always higher than Cu +2 for the same pressure and
110
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
initial concentration . The results obtained in this study are of great importance for a country like Jordan where water is scarce, and it is necessary to investigate all means to prevent water resources degradation and to conserve freshwater for domestic use .
4. Conclusions Wastewater containing copper and cadmium is produced by several industries . Environmental regulations oblige industries to treat the wastewater containing heavy metals to reduce their concentration to acceptable levels . The present study suggests that membrane processes are very successful techniques for the removal of heavy metals such as Cu" and Cd 2+ from wastewater streams . They are capable of reducing the heavy metal concentration in the effluent stream to low levels that are accepted and recommended by local Jordanian standards for industrial wastewater discharge . Reuse of industrial wastewater containing heavy metals after treatment by RO and NF is feasible and can contribute in alleviating the pressure on conventional water resources. This is especially important in a country like Jordan, which suffers from a chronic water shortage . Membrane process should be explored further for the possibility of heavy metals recovery .
References [1] M. Wilf and S . Alt, Desalination, 132 (2000) 11-19 . [2] Z . Ujang and G .K . Anderson, Water Sci . Technol., 34 (1996) 247-253 . [3] G.C . Steenkamp, K . Keizer, W .H .J .P . Neomagus and H.M. Krieg, J . Membr. Sci ., 197 (2002) 147-156 . [4] B . Durham, M.M . Bourbigot and T . Pankratz, Desalination, 138 (2001) 83-90 . [5] J.A . Redondo, Desalination, 138 (2002) 29 . [6] A.P . Padilla and E .L . Tavani, Desalination, 126 (1999) 219-226 . [7 ] M . Okazaki, M . Uraki, M . Kunio and T . Nishida, Proc. Conference on Membranes in Drinking and Industrial Water Production, Paris, Vol . 1, 2000, pp . 97-105 . [8] P. Berg, G . Hagmeyer and R . Gimble, Desalination, 113 (1997) 205-208 . [9] C . Tang and V . Chen, Desalination, 143 (2002) 1120 . [10] I . Koyuncu, Desalination, 143 (2003) 243-253 . [11] G . Del Re and G . Di Giacomo, Desalination, 138 (2001) 61-64 . [12] A .1 . Schafer, A.G. Fane and T .D . Waite, Desalination, 118 (1998) 109-122 . [13] S . Hong and M. Elimelech, J . Membr. Sci., 132 (1997) 159-181 . [14] J . Cho, G . Amy, J . Pellegrino and Y . Yoon, Desalination, 118 (1998) 101-108. [15] J. Agustin Suarez and J .M. Veza, Desalination, 127 (2000)47-58 . [16] D. Paul and S .K. Sikdar, Clean Products Proc ., 1 (1998) 39-48 . [17] X .J. Yang, A.G . Fane and S . MacNaughton, Water Sci . Technol ., 43 (2001) 341-348 .
Desalination 164 (2004) 105-110
www.elscvier.com/1oca&deaa l
Removal of heavy metals from wastewater by membrane processes: a comparative study Hani Abu Qdais a* , Hassan Moussab 'Department of Civil Engineering, Department of Chemical Engineering, Jordan University of Science and Technology, PO Box 3030, Irbid 22110, Jordan Tel . +962 (2) 709-5111 ; Fax +962 (2) 709-5018 ; email : [email protected]
Received 28 October 2002 ; accepted 14 August 2003
Abstract Wastewater containing copper and cadmium can be produced by several industries . The application of both reverse osmosis (RO) and nanofiltration (NF) technologies for the treatment of wastewater containing copper and cadmium ions to reduce fresh water consumption and environmental degradation was investigated . Synthetic wastewater samples containing Cu" and Cd2+ ions at various concentrations were prepared and subjected to treatment by RO and NF in the laboratory . The results showed that high removal efficiency of the heavy metals could be achieved by RO process (98% and 99% for copper and cadmium, respectively) . NF, however, was capable of removing more than 90% of the copper ions existing in the feed water . The effectiveness of RO and NF membranes in treating wastewater containing more than one heavy metal was also investigated . The results showed that the RO membrane was capable of treating wastewater with an initial concentration of 500 ppm and reducing the ion concentration to about 3 ppm (99 .4% removal), while the average removal efficiency of NF was 97% . The low level of the heavy metals concentration in the permeate implies that water with good quality could be reclaimed for further reuse . Keywords : Heavy metals ; Reverse osmosis ; Nanofiltration ; Removal efficiency ; Industrial wastewater
1 . Introduction Reverse osmosis (RO) and nanofiltration (NF) are relatively new processes, which were initially developed for the production of potable water from saline and brackish water . However, the development of these processes has been
*Corresponding author .
accelerated in recent years and has begun to find applications in the treatment of industrial wastewater . Recent research indicates that wastewater reclamation by RO offers great promise for a sustainable reduction in cost, conserving natural resources, as well as marked improvements of pollutant removal efficiency . Wilf and Alt [1] applied RO for the reclamation of municipal wastewater . They found
0011-9164/04/$- See front matter © 2004 Elsevier B .V . All rights reserved P11 :SOO11-9164(04)00169-9
1 06
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
that RO was capable of treating secondary effluents. Ujang and Anderson [2] illustrated the feasibility of using a low- pressure RO process for the removal of Zn2' and Cu z+ from wastewater in the presence of EDTA as a chelating agent . Steenkamp et al . [3] manu-factured a tubular alumina/chitosan composite membrane and used it to remove Cu" ions . An effluent of Cu" ions below 1 mg/l was achieved . Durham et al . [4] applied microfiltration prior to using RO to treat municipal wastewater to reduce capital and operating costs of the RO treatment process . Redondo [5] presented trends for using RO to treat low-quality feed water . He discussed the various benefits and problems encountered in using RO for treating wastewater . Padilla and Tavani [6] studied the removal of trivalent chromium from tanning wastewater using RO . The study revealed effective removal of the chromium from wastewater . Okazaki et al . [7] demonstrated that the use of the RO process in combination with a microfiltration system removed cadmium from wastewater produced by electronic microchip manufacturing to below detectable levels (i .e ., <0 .01 mg/l) . Berg et al . [8] applied NF to remove pesticides and other micropollutants . Their study revealed that at neutral pH values complete rejection of polar organics is possible with NF . Tang and Chen [9] applied NF for the treatment of textile wastewater . The investigation showed that 98% dye rejection was achieved at an applied pressure of 500 kPa. Koyuncu [10] investigated the effect of cross flow velocity and feed concentration on the removal of reactive dyes using NF . His study showed a removal greater than 99% can be achieved by NF mem-branes containing vinylsulphone dyes . Del Re and Giacomo [11] coupled NF and supercritical water oxidation to remove and destroy toxic micropolluting organic compounds from wastewater. They claimed that such coupling reduces both the investment and the operating costs of
removing toxic and dangerous micropollutants present in the wastewater and produces water of high level of purity . Schafer et al . [12], Hong and Elimelech [13] and Cho et al . [14] applied NF for the removal of natural organic matter and studied NF membranes fouling behavior by its presence . Heavy metals are considered as one of the serious environmental contaminants because of their high toxicity . Wastewater containing copper and cadmium can be produced by a variety of industries such as metal finishing, batteries manufacturing, electrical cables and electronic microchip manufacturing, and the mining industry . Legal requirements oblige industries to install effective wastewater treatment systems . Since the price of the noble materials such as heavy metals is constantly increasing, interesting processes are those capable, in addition to wastewater purification, of recovering metals . RO and NF may be such processes . Membrane separation processes are increasingly used as an alternative to conventional industrial wastewater treatment . There are several advantages of using membranes in water and wastewater treatment [15] . Reuse of water from industrial processes is an important business goal, especially when the industry is using large amounts of water . This goal can be achieved through industrial wastewater treatment by membrane processes . Using these processes will also enable the industry to comply with the effluent standard limits imposed by environmental regulations [16] . The conventional and most commonly used method for the treatment of industrial wastewater containing heavy metals is the chemical precipitation method [17] . However, this process requires a large amount of treatment chemicals to decrease the heavy metals to levels imposed by the regulations . In addition, the sludge produced from the precipitation process has to be subjected to dewatering and disposal into landfills, which adds an additional cost to the treatment process .
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
Therefore, it is important to recover the valuable materials (metals and water) and prevent environmental degradation . The purpose of this study is to evaluate the performance of the RO and NF processes in removing heavy metals from industrial wastewater .
2. Materials and methods Synthetic samples of wastewater were prepared by adding different amounts of copper and cadmium as cupric and cadmium sulfates to distilled water . To monitor the performance of the RO and NF processes, the total dissolved solids (TDS) concentration was used as an indicator of performance . Several solutions were prepared with different concentrations of copper and cadmium sulfates . The TDS was measured each time at 19°C, and the calibration curve between the added concentration and TDS was prepared . Figs . 1 and 2 show good correlation between the added concentration of copper and cadmium and TDS (R2 is 0 .984 and 0 .995 for copper and cadmium, respectively) . The high correlation obtained suggests that TDS is a good indicator for measuring the concentration of the heavy metals in the solution .
107
The initial concentration of the metal sulfates used in the experiments ranged from 25 to 200 ppm for both CuSO 4 and CdSO 4 . A benchscale membrane unit was used to carry out the experiments consisting of a module containing two tubular spiral-wound membranes arranged in series . The system is fed by a plunger pump, which provides high pressure . The experimental set-up is shown in Fig. 3, and the membrane characteristics are presented in Table 1 . Initially the experiments were conducted using cupric and cadmium sulfates separately . After that, a mixture with various ratios of CuSO 4 :CdSO4 (1 :3, 1 :1 and 3 :1) were subjected to treatment by both RO and NF processes .
160
Fig . 2 . Calibration curve using TDS as an indicator to measure CdSO 4 concentration.
MEMBRANE ASSEMBLY
Pressure gauge
0
0 .5 Tank
Initial concentration, mM
Fig . 1 . Calibration curve using TDS as an indicator to measure CuSO4 concentration.
Fig . 3 . Schematic diagram of the membrane unit .
H.A . Qdais, H. Moussa /Desalination 164 (2004) 1 05-110
108 Table 1
Membrane specifications used in the experiments Characteristics
RO membrane
NF membrane
Membrane material Membrane configuration
Polyamide
Polyamide
Spiral wound
Spiral wound
Membrane surface area, m 2
2 .5
2 .5
Allowable operating pH range
4-11
2 .5-11
Maximum operating temperature, °C
45 1
45
Maximum feed turbidity, NTU Maximum feed SDI, 15 min
1 5
5
3. Results and discussion The efficiency of RO and NF processes in removing Cu+2 and Cd2+ from wastewater is presented in Figs . 4 and 5 . As shown from Fig . 4, Cu" ions were successfully removed from the wastewater by both RO and NF . The concentration of Cu" in the product water (permeate) for RO was reduced to an average value 3 .5± 1 .7 ppm with an average removal efficiency of 97% . On the other hand, the removal efficiency of Cue{ by NF ranged from 84% to 96% for an initial feed concentration of 25 and 200 ppm, respectively . The same result can be observed for Cd2+ ions (see Fig . 5) where its concentration in the permeate from RO was reduced to 1 .77±
0.11 ppm with average removal efficiency of 98.5%, while the cadmium removal efficiency of the NF ranged from 82 to 97% . This implies that membrane techniques such as RO and NF are efficient processes for removing heavy metals from wastewater, so as to reclaim this water for further uses. The results obtained also show that Cd2+ ions were removed at a slightly higher efficiency compared to Cu e+ . This might be due to the fact that the size of the Cd2+ is larger than that of Cu e+ . A somewhat similar result was found by Ujang and Anderson [2], who reported that Zn 2+ ions can be removed at a slightly higher efficiency compared to Cu e+ . This was also confirmed by the higher removal of cadmium than the copper under the same pressure by RO, as shown in Fig . 6 .
10
10
• RO O NF 0
O
0
0
0
• RO
0
ONF
E CL
O
O 0
•
•
0
•
•
•
•
•
0 f-
•
•
2
O
0
0
0
0
•
0 0
50
100
150
200
250
Initial concentration, ppm
0
50
100
150
200
Initial concentration, ppm
Fig . 4 . Concentration of CuSO4 in the permeate from RO
Fig . 5 . Concentration of CdSO4 in the permeate from RO
and NF for different feed concentrations .
and NF for different feed concentrations
H.A . Qdais, H. Moussa /Desalination 164 (2004) 1 05 -110
109
Table 2 RO efficiency in treating the mixture of copper and cadmium salts Solution
Concentration of CuSO4 , ppm
Concentration of CdSO4, ppm
TDS in the feed to the RO, ppm
Permeate
no . 1
125
375
500
3 .09
2
250
250
500
3 .20
3
375
125
500
3 .34
concentration, ppm
Table 3 NF efficiency in treating the mixture of copper and cadmium salts Solution
Concentration
Concentration of
of CuSO 4, ppm
CdSO4 , ppm
TDS in the feed to the RO, ppm
Permeate
no .
concentration, ppm
1
125
375
500
12 .34
2
250
250
500
13 .16
3
375
125
500
13 .58
The effectiveness of RO and NF membranes in treating wastewater containing mixed heavy metals was tested. Three different solutions were prepared which contained concentrations of CuSO4 and CdSO4 with different ratios so as to achieve a solution with TDS of 500 ppm . The ratios of CuSO 4 and CdSO4 concentrations in the solutions are given in Tables 2 and 3 . The concentration of the ions in the permeate from the RO was found to be about 3 ppm (99 .4% removal efficiency), whereas it was 13 ppm from the NF experiment (97 .4% removal efficiency) . This is a clear indication that RO and NF are also capable of treating wastewater containing more than one heavy metal . The results also show that RO is more effective than NF in obtaining water with lower heavy metal concentration as obtained in the single heavy metal cases . The local Jordanian standards of industrial wastewater discharges (JS 202/1991) require that the concentration of Cu 2T and Cd2+ in discharge water should not exceed I and 0 .01 ppm, respectively . Slightly higher values were obtained in the experiments performed . The concentration of the above ions can still be lowered by further treating
E CL CL
EL
s
d Q
0 5
7
9
11
13
15
Applied pressure (bar) Fig . 6 . Effect of the applied pressure on permeate concentration for both cadmium and copper by RO (feed concentration 500 ppm) .
the permeate in another RO unit or increasing the operating pressure . Fig . 6 shows the effect of the applied pressure on the concentration of the ions in the permeate from RO . The results confirm that lower concentration can be achieved by increasing the applied pressure . It can also be seen from this figure that the removal of Cd +2 is always higher than Cu +2 for the same pressure and
110
H.A . Qdais, H. Moussa /Desalination 164 (2004) 105-110
initial concentration . The results obtained in this study are of great importance for a country like Jordan where water is scarce, and it is necessary to investigate all means to prevent water resources degradation and to conserve freshwater for domestic use .
4. Conclusions Wastewater containing copper and cadmium is produced by several industries . Environmental regulations oblige industries to treat the wastewater containing heavy metals to reduce their concentration to acceptable levels . The present study suggests that membrane processes are very successful techniques for the removal of heavy metals such as Cu" and Cd 2+ from wastewater streams . They are capable of reducing the heavy metal concentration in the effluent stream to low levels that are accepted and recommended by local Jordanian standards for industrial wastewater discharge . Reuse of industrial wastewater containing heavy metals after treatment by RO and NF is feasible and can contribute in alleviating the pressure on conventional water resources. This is especially important in a country like Jordan, which suffers from a chronic water shortage . Membrane process should be explored further for the possibility of heavy metals recovery .
References [1] M. Wilf and S . Alt, Desalination, 132 (2000) 11-19 . [2] Z . Ujang and G .K . Anderson, Water Sci . Technol., 34 (1996) 247-253 . [3] G.C . Steenkamp, K . Keizer, W .H .J .P . Neomagus and H.M. Krieg, J . Membr. Sci ., 197 (2002) 147-156 . [4] B . Durham, M.M . Bourbigot and T . Pankratz, Desalination, 138 (2001) 83-90 . [5] J.A . Redondo, Desalination, 138 (2002) 29 . [6] A.P . Padilla and E .L . Tavani, Desalination, 126 (1999) 219-226 . [7 ] M . Okazaki, M . Uraki, M . Kunio and T . Nishida, Proc. Conference on Membranes in Drinking and Industrial Water Production, Paris, Vol . 1, 2000, pp . 97-105 . [8] P. Berg, G . Hagmeyer and R . Gimble, Desalination, 113 (1997) 205-208 . [9] C . Tang and V . Chen, Desalination, 143 (2002) 1120 . [10] I . Koyuncu, Desalination, 143 (2003) 243-253 . [11] G . Del Re and G . Di Giacomo, Desalination, 138 (2001) 61-64 . [12] A .1 . Schafer, A.G. Fane and T .D . Waite, Desalination, 118 (1998) 109-122 . [13] S . Hong and M. Elimelech, J . Membr. Sci., 132 (1997) 159-181 . [14] J . Cho, G . Amy, J . Pellegrino and Y . Yoon, Desalination, 118 (1998) 101-108. [15] J. Agustin Suarez and J .M. Veza, Desalination, 127 (2000)47-58 . [16] D. Paul and S .K. Sikdar, Clean Products Proc ., 1 (1998) 39-48 . [17] X .J. Yang, A.G . Fane and S . MacNaughton, Water Sci . Technol ., 43 (2001) 341-348 .