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Optimisation of the removal of toxic mono-valent anions from water supplies in the ion exchange membrane bioreactor
Desalination 199 (2006) 322–324
Optimisation of the removal of toxic mono-valent anions from water supplies in the ion exchange membrane bioreactor Cristina T. Matos*, Raquel Fortunato, Svetlozar Velizarov, Maria A. M. Reis, João G. Crespo REQUIMTE/CQFB, Department of Chemistry, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal email: [email protected] Received 26 October 2005; accepted 2 March 2006
1. Introduction The ion exchange membrane bioreactor (IEMB) concept arose from the necessity of finding a technology for drinking water treatment that would be able to selectively remove ionic pollutants such as nitrate, perchlorate and bromate, which have strong negative effect on human health even at small doses, to values below the recommended levels (25 ppm of NO3– by the EU, 24.5 ppb of ClO4– by the US EPA and 25 ppb of BrO3– by the WHO). The proposed concept [1] is an integrated process that combines the transport of the charged pollutants through a dense ion exchange membrane with their simultaneous biodegradation to harmless products, by a suitable microbial culture in a separated compartment. A schematic diagram of anion transport and bio-reduction in the IEMB is shown in Fig. 1. The membrane used is positively charged and allows the transport of the target anions *Corresponding author.
from the water stream to a biocompartment, where they are reduced to harmless products. The target anions transport is governed by the Donnan equilibrium principle and, therefore, it is possible to maximise it by using a driving counter-ion (chloride) added in excess to the biocompartment. The main advantage of the IEMB process is the possibility to avoid not only the secondary contamination of the treated water, since the membrane used is nonporous, but also the formation of an anion-polluted waste stream, because after their transport the pollutants are reduced biologically. Additionally, unlike what happens in the traditional biological removal processes, the water treatment rate does not depend on the pollutant biodegradation rate but rather on the transport rate of the target ion through the membrane. As a result, the quality of the treated water is not affected even if the system is operated under extreme conditions, such as prolonged periods of carbon source limitation [2].
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.076
C.T. Matos et al. / Desalination 199 (2006) 322–324
Biocompartment Na
+
CO2 + N2
Na NO3–
NO3–
ClO4–
ClO4–
CO2 + Cl–
BrO3–
BrO3–
Cl–
Cl– CO2 + Br–
+
Cl–
Cl–
Ethanol + Nutrients – + Excess of Cl
Water Compartment
Br–-
Br–
Nutrients Membrane Biofilm
Fig. 1. Schematic diagram of anion transport and bioreduction in the ion exchange membrane bioreactor.
323
perchlorate concentrations to values below 0.5 ppm and 4 ppb, respectively, while preserving the water composition in respect to other ions. The removal efficiency of the IE-B membrane was slightly lower, although the nitrate and perchlorate concentrations in the treated water were still below the recommended limits (25 ppm for NO3– and 24.5 ppb for ClO4–). Preliminary results on bromate removal showed that the IEMB, operating with the Neosepta ACS membrane, removes bromate from artificially contaminated tap water with 200 ppb of bromate to values below 18 ppb.
2. Results and discussion 3. Conclusions
100
ClO4– ACS NO3– ACS NO3– IE-B ClO4– IE-B
80 60
ClO4– Flux (µg/m2.h) NO3– Flux (mg/m2.h)
Considering the actual recommended limits for NO3–, ClO4– and BrO3–, it can be concluded that the IEMB process can efficiently treat water streams contaminated with these ions. Lower pollutant levels are even possible to obtain by adjusting the water flow rate per membrane area (F/A). On-going research is
Concentration of ClO4– (µg/L) Concentration of NO3– (mg/L)
The membrane used in the IEMB must allow high pollutant ions fluxes during long-term operation, avoiding flux decline, and at the same time must be an effective barrier against transport of nutrients and metabolic by-products from the biocompartment to the treated water. The IEMB process operated under continuous conditions and at a water flow rate per membrane area (F/A) of 3.1 L/(m2h) (HRT = 8.3 h) proved to remove effectively perchlorate and nitrate from artificially contaminated tap water with 100 ppb of ClO4– and 60 ppm of NO3– using the membrane Neosepta ACS, manufactured by Tokuyama Soda (Japan) [2]. With the objective of reaching a compromise between system efficiency and membrane cost, other membranes are being also tested. Fig. 2 depicts the results obtained when the IEMB system was operated using the Neosepta ACS and a non commercial lower cost ion exchange membrane, hereby named IE-B, to treat contaminated tap water (as mentioned earlier). The two identical systems (except for the membrane used) were operated for more than one month without any observed flux decline. Additionally, it was possible with the ACS membrane to reduce the outlet nitrate and
0.32 0.24 0.16 0.08 0.00
40
0
4
8 12 16 20 24 28 32 36 Time (days)
16 8 0 0
4
8
12
16 20 24 Time (days)
28
32
36
Fig. 2. Treated water concentrations and fluxes of nitrate and perchlorate for the IEMB operation using the EI-B (open symbols) and the ACS membrane (closed symbols).
324
C.T. Matos et al. / Desalination 199 (2006) 322–324
focused on the use of different system configurations and spacers in the water compartment with the objective of improving the drinking water production rate.
FCT for the PhD scholarship SFRH/BD/9087/ 2002. References [1]
Acknowledgements The financial support by Fundação para a Ciência e a Tecnologia (FCT), Portugal through Project POCTI/EQU/39482/2001 is gratefully acknowledged. Cristina Matos acknowledges
[2]
J.G. Crespo and M.A.M. Reis, Treatment of aqueous media containing electrically charged compounds, Eur. Patent 1,246,778, 2003. C.T. Matos, S. Velizarov, J.G. Crespo and M.A.M Reis, Simultaneous Removal of perchlorate and nitrate from drinking water in an ion exchange membrane bioreactor, Water Research, in press.
Optimisation of the removal of toxic mono-valent anions from water supplies in the ion exchange membrane bioreactor Cristina T. Matos*, Raquel Fortunato, Svetlozar Velizarov, Maria A. M. Reis, João G. Crespo REQUIMTE/CQFB, Department of Chemistry, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal email: [email protected] Received 26 October 2005; accepted 2 March 2006
1. Introduction The ion exchange membrane bioreactor (IEMB) concept arose from the necessity of finding a technology for drinking water treatment that would be able to selectively remove ionic pollutants such as nitrate, perchlorate and bromate, which have strong negative effect on human health even at small doses, to values below the recommended levels (25 ppm of NO3– by the EU, 24.5 ppb of ClO4– by the US EPA and 25 ppb of BrO3– by the WHO). The proposed concept [1] is an integrated process that combines the transport of the charged pollutants through a dense ion exchange membrane with their simultaneous biodegradation to harmless products, by a suitable microbial culture in a separated compartment. A schematic diagram of anion transport and bio-reduction in the IEMB is shown in Fig. 1. The membrane used is positively charged and allows the transport of the target anions *Corresponding author.
from the water stream to a biocompartment, where they are reduced to harmless products. The target anions transport is governed by the Donnan equilibrium principle and, therefore, it is possible to maximise it by using a driving counter-ion (chloride) added in excess to the biocompartment. The main advantage of the IEMB process is the possibility to avoid not only the secondary contamination of the treated water, since the membrane used is nonporous, but also the formation of an anion-polluted waste stream, because after their transport the pollutants are reduced biologically. Additionally, unlike what happens in the traditional biological removal processes, the water treatment rate does not depend on the pollutant biodegradation rate but rather on the transport rate of the target ion through the membrane. As a result, the quality of the treated water is not affected even if the system is operated under extreme conditions, such as prolonged periods of carbon source limitation [2].
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.076
C.T. Matos et al. / Desalination 199 (2006) 322–324
Biocompartment Na
+
CO2 + N2
Na NO3–
NO3–
ClO4–
ClO4–
CO2 + Cl–
BrO3–
BrO3–
Cl–
Cl– CO2 + Br–
+
Cl–
Cl–
Ethanol + Nutrients – + Excess of Cl
Water Compartment
Br–-
Br–
Nutrients Membrane Biofilm
Fig. 1. Schematic diagram of anion transport and bioreduction in the ion exchange membrane bioreactor.
323
perchlorate concentrations to values below 0.5 ppm and 4 ppb, respectively, while preserving the water composition in respect to other ions. The removal efficiency of the IE-B membrane was slightly lower, although the nitrate and perchlorate concentrations in the treated water were still below the recommended limits (25 ppm for NO3– and 24.5 ppb for ClO4–). Preliminary results on bromate removal showed that the IEMB, operating with the Neosepta ACS membrane, removes bromate from artificially contaminated tap water with 200 ppb of bromate to values below 18 ppb.
2. Results and discussion 3. Conclusions
100
ClO4– ACS NO3– ACS NO3– IE-B ClO4– IE-B
80 60
ClO4– Flux (µg/m2.h) NO3– Flux (mg/m2.h)
Considering the actual recommended limits for NO3–, ClO4– and BrO3–, it can be concluded that the IEMB process can efficiently treat water streams contaminated with these ions. Lower pollutant levels are even possible to obtain by adjusting the water flow rate per membrane area (F/A). On-going research is
Concentration of ClO4– (µg/L) Concentration of NO3– (mg/L)
The membrane used in the IEMB must allow high pollutant ions fluxes during long-term operation, avoiding flux decline, and at the same time must be an effective barrier against transport of nutrients and metabolic by-products from the biocompartment to the treated water. The IEMB process operated under continuous conditions and at a water flow rate per membrane area (F/A) of 3.1 L/(m2h) (HRT = 8.3 h) proved to remove effectively perchlorate and nitrate from artificially contaminated tap water with 100 ppb of ClO4– and 60 ppm of NO3– using the membrane Neosepta ACS, manufactured by Tokuyama Soda (Japan) [2]. With the objective of reaching a compromise between system efficiency and membrane cost, other membranes are being also tested. Fig. 2 depicts the results obtained when the IEMB system was operated using the Neosepta ACS and a non commercial lower cost ion exchange membrane, hereby named IE-B, to treat contaminated tap water (as mentioned earlier). The two identical systems (except for the membrane used) were operated for more than one month without any observed flux decline. Additionally, it was possible with the ACS membrane to reduce the outlet nitrate and
0.32 0.24 0.16 0.08 0.00
40
0
4
8 12 16 20 24 28 32 36 Time (days)
16 8 0 0
4
8
12
16 20 24 Time (days)
28
32
36
Fig. 2. Treated water concentrations and fluxes of nitrate and perchlorate for the IEMB operation using the EI-B (open symbols) and the ACS membrane (closed symbols).
324
C.T. Matos et al. / Desalination 199 (2006) 322–324
focused on the use of different system configurations and spacers in the water compartment with the objective of improving the drinking water production rate.
FCT for the PhD scholarship SFRH/BD/9087/ 2002. References [1]
Acknowledgements The financial support by Fundação para a Ciência e a Tecnologia (FCT), Portugal through Project POCTI/EQU/39482/2001 is gratefully acknowledged. Cristina Matos acknowledges
[2]
J.G. Crespo and M.A.M. Reis, Treatment of aqueous media containing electrically charged compounds, Eur. Patent 1,246,778, 2003. C.T. Matos, S. Velizarov, J.G. Crespo and M.A.M Reis, Simultaneous Removal of perchlorate and nitrate from drinking water in an ion exchange membrane bioreactor, Water Research, in press.