- Email: [email protected]
Separation of cesium from wastewater with copper hexacyanoferrate film in an electrochemical system driven by microbial fuel cells
Bioresource Technology 278 (2019) 456–459
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Separation of cesium from wastewater with copper hexacyanoferrate film in an electrochemical system driven by microbial fuel cells
T
Qinqin Taoa,b, Xu Zhangb, Krishnamoorthy Prabaharana, Ying Daia,
⁎
a b
State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, Jiangxi, China School of Civil Engineer and Architecture, East China Jiaotong University, Nanchang 330013, Jiangxi, China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Electrochemical Adsorption Copper hexacyanoferrate Cesium Microbial fuel cell
A electrochemical adsorption system driven by microbial fuel cell (MFC-adsorption) was developed based on copper(II) hexacyanoferrate(III) (CuHCF) film for cesium (Cs) removal from wastewater. Cs uptake and elution can be simply controlled by regulating the redox states of the CuHCF films. Chemical oxygen demand (COD) removal showed little difference as MFC was connected to adsorption system. Meanwhile, power density and coulombic efficiency of MFC were dramatically reduced. The efficiencies of Cs adsorption and desorption were undesirable. MFC-adsorption technology used for actual nuclear wastewater treatment still has far to go.
1. Introduction With the development of nuclear industry, a lot of radioactive wastes have been generated. The contamination of wastewater by radioactive isotopes has become a major concern due to their risks to both human health and environment (Little et al., 2017). 137Cs is the principal ingredient of the radioactive waste has the following features: (1) A strong gamma emitter (Kim et al., 2017). (2) Having a long halflife (Zheng et al., 2017). (3) Highly mobile in aqueous media (Chen et al., 2013). Technologies such as extraction (Awual, 2016), ⁎
precipitation (He, 2016), adsorption (Yang et al., 2016a), and ion exchange (Yang et al., 2016b; Hasan et al., 2007) have been applied for Cs removal from wastewater. Among them, ion exchange appears to be a superior technology (Chen et al., 2013; Hasan et al., 2007). Transition metal hexacyanoferrates (MHCF) were preferred to be competitive Cs ion exchanges over other materials due to their selectivity and high capacity (Nilchi et al., 2003). Copper(II) hexacyanoferrate(III) (CuHCF) is often selected as the agent in practical analysis for Cs removal because it can be readily prepared, and chemically stable in a large pH range (Milonji et al., 2002). However, small
Corresponding author. E-mail address: [email protected] (Y. Dai).
https://doi.org/10.1016/j.biortech.2019.01.093 Received 27 November 2018; Received in revised form 20 January 2019; Accepted 22 January 2019 Available online 23 January 2019 0960-8524/ © 2019 Published by Elsevier Ltd.
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
sized CuHCF particles will result in second contamination to water and shorten powdery CuHCF’s service life. For this reason, electrochemically switched ion exchange (ESIX) as a Cs separation technique has been developed (Sun et al., 2012). In ESIX system, a low constant potential was provided (e.g. 0.4 V (Chen et al., 2015), 1.0 V (Henrik and Gregory, 1999), 1.3 V (Chen et al., 2013)), MHCF films were electro- or chemical deposited on electrode (Henrik and Gregory, 1999; Steen et al., 2002). Microbial fuel cell (MFC) is a kind of device convert the chemical energy to electrical energy with the help of bacteria (Ndayisenga et al., 2018; Zhong et al., 2018). Due to the internal losses, a MFC always produce an open circuit voltage (OCV) less than 0.8 V (Liu et al., 2005), and a working voltage of ∼0.5 V. However, desired current or voltage would be obtained by combining the appropriate number of series and parallel connected MFCs (Aelterman et al., 2006), which means MFC may be used to drive the electrochemical system for Cs removal. The relevant reactions, referring to Cs adsorption and desorption, were proposed as follows:
Cu3 [Fe III (CN )6]2 + 2e + 2Cs+
Cs2 Cu3 [Fe II (CN )6]2
adsorption. CuHCF modified graphite was dipped into the Cs containing wastewater. (4) MFC-CuHCF adsorption. 133CsNO3 solution was used to simulate radioactive Cs containing wastewater (initial Cs concentration = 20 mg/L, volume = 130 ml). Regeneration study was carried out in 1 M KCl solution by regulating the redox states of CuHCF modified electrode. Adsorption and regeneration tests were operated as the output voltage from MFC was about the maximum value. Solution in adsorption system was low-speed stirred with a magnetic stirrer. Cs concentration was measured by flame atomic absorption spectroscopy (AA240FS, Varian, AU). 2.4. Analysis CuHCF film was characterized using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS, EVO LS10, Car Zeiss, UK). X-ray powder diffractometry (XRD, Ultima X, Rigaku, Japan) was carried out to determine the crystalline structures. The electrochemical response of the electrodes was determined by cyclic voltammetry (CV) with CHI 660C (Chenhua Instruments Co., Ltd., Shanghai, China). CV was performed in a three-electrode cell, in which the working, reference and counter electrodes were respectively, a CuHCF modified graphite sheet, Hg/Hg2Cl2 electrode and a platinum wire electrode.
(1)
Herein, a technology (MFC-adsorption) of electrochemically remove Cs driven by MFC was proposed. Working electrode in adsorption system was modified with CuHCF film by chemical deposition. This study explores the possibility of MFC-adsorption technology used for Cs removal without extra energy and chemical addition.
3. Results and discussion
2. Experimental
3.1. Characterization of CuHCF film
2.1. MFC configuration and operation
XRD patterns show the film on the electrode was cubic CuHCF crystal mixed with a small amount of CuHCF analogue, such as KCu[Fe (CN)6]. SEM image indicates the film were well dispersed heterogeneous nanoparticles. E-Supplementary data for the works above can be found in e-version of this paper online. The EDS results were illustrated in Table 1, elements of Fe, Cu, C and N, can be named as CuHCF. The atom ration of Cu:Fe is 3.06:2.22, which is differ subtly from the stoichiometric proportion of elemental composition in Cu3[Fe(CN)6]2 (3:2). This again means that the film was a mixture of compounds, such as Cu3[Fe(CN)6]2, KCu[Fe(CN)6] and non-reacted reactants. Cs signals detected referring to the Cs loading on the film. The maximum loading of CuHCF film was 0.26 Cs/Fe which was much higher than the results from powdery CuHCF (0.073) (Ayrault et al., 1998), but half of the results from Chen et al. (2013) (0.52). Compared with the study of Chen et al. (2013), CuHCF film in our study is easier to be obtained, the cost is lower and the operation more simple.
The MFC used was single-chamber MFC, similar to the singlechamber MFC in a published paper (Tao et al., 2015). The anode and cathode were both carbon cloth with ∼7 cm2 (3.8 cm diameter) projected area. The cathode was modified as previously described (Tao et al., 2015). The anode was rolled up tightly like a burrito with titanium wire, and the distance between two electrodes was ∼0.5 cm. With the exception of adsorption system loading, a 1000 Ω resistor was connected in the circuit. The MFC was inoculated with mixed anaerobic sludge and aerobic sludge (v/v = 2:1) from domestic sewage treatment plant. The MFC was operated in fed-batch mode with synthetic wastewater (NaC2H3O2 1.00 g/L, NH4Cl 0.31 g/L, NaHCO3 3.13 g/L, NaH2PO4 0.75 g/L, KCl 0.13 g/L, metals and trace minerals) at 30 ± 0.5 °C. After MFC achieved 3 cycles of stable voltage outputs, experiments were carried out. Synthetic wastewater was fed into the MFC when the voltage less than 50 mV. The output voltage (V) and current (I) were monitored using a data acquisition system (M2700, Keithley, USA). Power was calculated according to P = IV. Power density was calculated by dividing P by the net cathode area. Coulombic efficiency (CE) was calculated as previously described (Liu et al., 2005). Chemical oxygen demand (COD) concentration was measured according to the Standard Methods (APHA, 2005).
3.2. Cyclic voltammetric response of the CuHCF modified electrode CuHCF coating made a pronounced change on electrode’s cyclic voltammetry (Fig. 1a). The current through the electrodes increased clearly. Two oxidation peaks and two reduction peaks appeared. The voltammetric features might be attributed to the reactions of Cu3[Fe (CN)6]2 and KCu[Fe(CN)6]: Reduction reactions:
2.2. Fabrication of a CuHCF modified electrode Cs adsorption system was a two-electrode cell. Two electrodes were both graphite sheet with the same size (1.5 mm × 20 mm × 20 mm). CuHCF was deposited on the working electrode by chemical deposition process (Henrik and Gregory, 1999).
Table 1 Chemical composition on the surface of CuHCF film after Cs adsorption.
2.3. Adsorption and regeneration study Adsorption tests were carried out in four groups: (1) Bare graphite adsorption. Graphite sheet was dipped into the Cs containing wastewater. (2) MFC-bare graphite adsorption. No CuHCF coated on electrode with MFC-adsorption technology. (3) CuHCF modified graphite 457
Element
Weight (%)
Atoms (%)
CK NK OK Fe L Cu L Cs L
20.58 15.34 5.27 18.40 28.84 11.56
42.75 27.33 8.21 8.22 11.32 2.17
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
Fig. 1. Comparison of cyclic voltammetric data for bare graphite and CuHCF modified electrode (a), CuHCF modified graphite electrode before exposure to Cs and regeneration after loading with Cs (b). Electrodes were in 1 M KCl, the voltammogram recorded after 25 scans, scan rate 25 mV/s.
KCu [Fe III (CN )6] + e + K+
Cu3
[Fe III (CN )
6 ]2
+ 2e +
(2)
K2 CuFe II (CN )6
2K+
K2 Cu3
[Fe II (CN )
6 ]2
electrode, which was in concordance with the low release rate of Cs. The reduction in Cs adsorption capacity of the regenerated electrode partly attributed to the exfoliation of CuHCF nanoparticles from the electrode.
(3)
Oxidation reactions
K2 CuFe II (CN )6
e
K2 Cu3 [Fe II (CN )6 ]2
K+ 2e
KCu [Fe III (CN )6] 2K+
Cu3 [Fe III (CN )6 ]2
(4)
3.4. The effects of Cs separation on MFC performance
(5)
The output voltage increased as MFC and adsorption system were connected (Fig. 3a). High internal resistance of the adsorption system may be the reason for increasing output voltage. Low ionic strength of the solution in the adsorption system could lead to high internal resistance. In spite of more output voltage, a far lower power density was obtained from MFC as connected to adsorption system. This is also thought to be a result of high internal resistance of adsorption system. Adsorption system loading has little effect on COD removal in MFC (Fig. 3b). However, the average CE was decreased from 30% to 12% as the MFC was loaded to adsorption system. The CE was calculated as Eq. (6):
The peaks were absent for bare graphite sheet. Similar results were mentioned in the literature (Henrik and Gregory, 1999). 3.3. Electrochemical adsorption and regeneration The results in Fig. 2a indicate that multiple factors affecting Cs adsorption extend the time to attain absorption equilibrium. The removal efficiency of Cs at equilibrium in MFC-CuHCF absorption test was significantly higher than the other three absorption tests. The results suggest that Cs was removed by the synergies of graphite matrix adsorption, ion exchange of CuHCF film and electrochemical adsorption, in which electrochemical adsorption was the dominant factor for Cs adsorption speed and removal efficiency. The removal rate of Cs in this study was unfavorable, low potential provided by the MFC maybe the reason. The maximum Cs release rate of MFC-CuHCF technology was about 28% (Fig. 2b). The cause for this were: ① Oxidation potential provided by MFC was insufficient to drive more adsorbed Cs exchange with K and then release from CuHCF modified electrode. ② CuHCF modified electrode has better selectivity toward Cs compared with other alkali metal ions. The intensity of the voltammetric peaks of regenerated CuHCF modified electrode were lower (Fig. 2b). The results indicated the reduction of absorption capacity of the regenerated CuHCF modified
CE =
CP × 100% CTi
(6)
where Cp, is the total coulombs calculated by integrating the current over time. CTi is the theoretical amount of coulombs that can be produced from sodium acetate. Similar average COD removal efficiency indicates similar CTi. Evaluating CE of MFC before and after connecting the adsorption system can be achieved by comparing the CP value. CP was calculated as Eq. (7): n
CP =
Ii ti i=1
(7)
where Ii is the current over time, which can be calculated as I = V/R
Fig. 2. Cs adsorption (a) and deintercalation (b) with contact time. 458
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
Fig. 3. Output voltages and power density curves (a), COD removal efficiency and coulombic efficiency (b) of the MFC before and after connecting the adsorption system.
according to Ohm’s Law. On account of this we can find that adsorption system with high internal resistance would decrease the current I, which in turn lead to the low CE of MFC.
wastewater using copper hexacyanoferrate nanofilms in an electrochemical system. Electrochim. Acta 87, 119–125. Chen, R., Asai, M., Fukushima, C., Ishizaki, M., Kurihara, M., Arisaka, M., Nankawa, T., Watanabe, M., Kawamoto, T., Tanaka, H., 2015. Column study on electrochemical separation of cesium ions from wastewater using copper hexacyanoferrate film. J. Radioanal. Nucl. Chem. 303, 1491–1495. He, J., 2016. An integrated device for coprecipitation and filtration of radiocesium in seawater. J. Environ. Radioact. 165, 35–38. Hasan, S., Ghosh, T.K., Viswanath, D.S., Loyalka, S.K., Sengupta, B., 2007. Preparation and evaluation of fullers earth beads for removal of cesium from waste streams. Sep. Sci. Technol. 42 (4), 717–738. Henrik, G., Gregory, V., 1999. Separation of cesium from high ionic strength solutions using a cobalt hexacyanoferrate-modified graphite electrode. Environ. Sci. Technol. 33 (15), 2633–2637. Kim, Y., Kim, Y.K., Kim, S., Harbottle, D., Lee, J.W., 2017. Nanostructured potassium copper hexacyanoferrate-cellulose hydrogel for selective and rapid cesium adsorption. Chem. Eng. J. 313, 1042–1050. Little, I., Seaton, K., Alorkpa, E., Vasiliev, A., 2017. Adsorption of cesium on bound porous materials containing embedded phosphotungstic acid. Adsorption 23 (6), 809–819. Liu, H., Cheng, S.A., Logan, B.E., 2005. Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell. Environ. Sci. Technol. 39, 658–662. Milonji, S., Bispo, I., Fedoroff, M., Loos-Neskovic, C., Vidal-Madjar, C., 2002. Sorption of cesium on copper hexacyanoferrate/polymer/silica composites in batch and dynamic conditions. J. Radioanal. Nucl. Chem. 252 (3), 497–501. Nilchi, A., Malek, B., Maragheh, M.G., Khanchi, A., 2003. Exchange properties of cyanide complexes. J. Radioanal. Nucl. Chem. 258 (3), 457–462. Ndayisenga, F., Yu, Z., Yu, Y., Lay, C., Zhou, D., 2018. Bioelectricity generation using microalgal biomass as electron donor in a bio-anode microbial fuel cell. Bioresour. Technol. 270, 286–293. Sun, B., Hao, X., Wang, Z., Zhang, Z., Liu, S., Guan, G., 2012. Continuous separation of cesium based on NiHCF/PTCF electrode by electrochemically switched ion exchange. Chin. J. Chem. Eng. 20 (5), 837–842. Steen, W.A., Jeerage, K.M., Schwartz, D.T., 2002. Raman spectroscopy of redox activity in cathodically electrodeposited nickel hexacyanoferrate thin films. Appl. Spectrosc. 56 (8), 1021–1029. Tao, Q., Zhou, S., Luo, J., Yuan, J., 2015. Nutrient removal and electricity production from wastewater using microbial fuel cell technique. Desalination 365, 92–98. Yang, H.M., Jang, S.C., Hong, S.B., Lee, K.W., Roh, C., Huh, Y.S., Seo, B.K., 2016a. Prussian blue-functionalized magnetic nanoclusters for the removal of radioactive cesium from water. J. Alloys Compd. 657, 387–393. Yang, H.J., Luo, M., Luo, L.L., Wang, H.X., Hu, D.D., Lin, J., Wang, X., Wang, Y.L., Wang, S., Bu, X.H., Feng, P.Y., Wu, T., 2016b. Highly selective and rapid uptake of radionuclide cesium based on robust zeolitic chalcogenide via stepwise ion-exchange strategy. Chem. Mater. 28, 8774–8780. Zheng, Y., Qiao, J., Yuan, J., Shen, J., Wang, A., Niu, L., 2017. Electrochemical removal of radioactive cesium from nuclear waste using the dendritic copper hexacyanoferrate/ carbon nanotube hybrids. Electrochim. Acta 257, 172–180. Zhong, D., Liao, X., Liu, Y., Zhong, N., Xu, Y., 2018. Enhanced electricity generation performance and dye wastewater degradation of microbial fuel cell by using a petaline NiO@ polyaniline-carbon felt anode. Bioresour. Technol. 258, 125–134.
4. Conclusion By use of MFC-adsorption technology, Cs was removed by the synergies of multiple factors, in which electrochemical adsorption was the dominant factor for Cs adsorption speed and removal efficiency. CuHCF film can be regenerated by switching the potential between electrodes. Low efficiency in electricity generation of MFC and high internal resistance of adsorption system were two major causes for Cs removal, CuHCF film regeneration, output voltage, power density and CE. Acknowledgements Financial supports from National Natural Science Foundation of China (Nos. 11705060, 11605027), Natural Science Foundation of Jiangxi Province (No. 20161BAB213086), and the Project of the Jiangxi Provincial Department of Education (No. GJJ170400) are gratefully acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.biortech.2019.01.093. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, 19th ed. American Public Health Association, Washington, DC, USA. Awual, M.R., 2016. Ring size dependent crown ether based mesoporous adsorbent for high cesium adsorption from wastewater. Chem. Eng. J. 303, 539–546. Aelterman, P., Rabaey, K., Pham, H.T., Boon, N., Verstraete, W., 2006. Continuous electricity generation at high voltages and currents using stacked microbial fuel cells. Environ. Sci. Technol. 40 (10), 3388–3394. Ayrault, S., Jimenez, B., Garnier, E., Fedoroff, M., Jones, D.J., Loos-Neskovic, C., 1998. Sorption mechanisms of cesium on CuII2FeII(CN)6 and CuII3[FeIII(CN)6]2 hexacyanoferrates and their relation to the crystalline structure. J. Solid State Chem. 475–485. Chen, R., Tanaka, H., Kawamoto, T., Asai, M., Fukushima, C., Na, H., Kurihara, M., Watanabe, M., Arisaka, M., Nankawa, T., 2013. Selective removal of cesium ions from
459
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Separation of cesium from wastewater with copper hexacyanoferrate film in an electrochemical system driven by microbial fuel cells
T
Qinqin Taoa,b, Xu Zhangb, Krishnamoorthy Prabaharana, Ying Daia,
⁎
a b
State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, Jiangxi, China School of Civil Engineer and Architecture, East China Jiaotong University, Nanchang 330013, Jiangxi, China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Electrochemical Adsorption Copper hexacyanoferrate Cesium Microbial fuel cell
A electrochemical adsorption system driven by microbial fuel cell (MFC-adsorption) was developed based on copper(II) hexacyanoferrate(III) (CuHCF) film for cesium (Cs) removal from wastewater. Cs uptake and elution can be simply controlled by regulating the redox states of the CuHCF films. Chemical oxygen demand (COD) removal showed little difference as MFC was connected to adsorption system. Meanwhile, power density and coulombic efficiency of MFC were dramatically reduced. The efficiencies of Cs adsorption and desorption were undesirable. MFC-adsorption technology used for actual nuclear wastewater treatment still has far to go.
1. Introduction With the development of nuclear industry, a lot of radioactive wastes have been generated. The contamination of wastewater by radioactive isotopes has become a major concern due to their risks to both human health and environment (Little et al., 2017). 137Cs is the principal ingredient of the radioactive waste has the following features: (1) A strong gamma emitter (Kim et al., 2017). (2) Having a long halflife (Zheng et al., 2017). (3) Highly mobile in aqueous media (Chen et al., 2013). Technologies such as extraction (Awual, 2016), ⁎
precipitation (He, 2016), adsorption (Yang et al., 2016a), and ion exchange (Yang et al., 2016b; Hasan et al., 2007) have been applied for Cs removal from wastewater. Among them, ion exchange appears to be a superior technology (Chen et al., 2013; Hasan et al., 2007). Transition metal hexacyanoferrates (MHCF) were preferred to be competitive Cs ion exchanges over other materials due to their selectivity and high capacity (Nilchi et al., 2003). Copper(II) hexacyanoferrate(III) (CuHCF) is often selected as the agent in practical analysis for Cs removal because it can be readily prepared, and chemically stable in a large pH range (Milonji et al., 2002). However, small
Corresponding author. E-mail address: [email protected] (Y. Dai).
https://doi.org/10.1016/j.biortech.2019.01.093 Received 27 November 2018; Received in revised form 20 January 2019; Accepted 22 January 2019 Available online 23 January 2019 0960-8524/ © 2019 Published by Elsevier Ltd.
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
sized CuHCF particles will result in second contamination to water and shorten powdery CuHCF’s service life. For this reason, electrochemically switched ion exchange (ESIX) as a Cs separation technique has been developed (Sun et al., 2012). In ESIX system, a low constant potential was provided (e.g. 0.4 V (Chen et al., 2015), 1.0 V (Henrik and Gregory, 1999), 1.3 V (Chen et al., 2013)), MHCF films were electro- or chemical deposited on electrode (Henrik and Gregory, 1999; Steen et al., 2002). Microbial fuel cell (MFC) is a kind of device convert the chemical energy to electrical energy with the help of bacteria (Ndayisenga et al., 2018; Zhong et al., 2018). Due to the internal losses, a MFC always produce an open circuit voltage (OCV) less than 0.8 V (Liu et al., 2005), and a working voltage of ∼0.5 V. However, desired current or voltage would be obtained by combining the appropriate number of series and parallel connected MFCs (Aelterman et al., 2006), which means MFC may be used to drive the electrochemical system for Cs removal. The relevant reactions, referring to Cs adsorption and desorption, were proposed as follows:
Cu3 [Fe III (CN )6]2 + 2e + 2Cs+
Cs2 Cu3 [Fe II (CN )6]2
adsorption. CuHCF modified graphite was dipped into the Cs containing wastewater. (4) MFC-CuHCF adsorption. 133CsNO3 solution was used to simulate radioactive Cs containing wastewater (initial Cs concentration = 20 mg/L, volume = 130 ml). Regeneration study was carried out in 1 M KCl solution by regulating the redox states of CuHCF modified electrode. Adsorption and regeneration tests were operated as the output voltage from MFC was about the maximum value. Solution in adsorption system was low-speed stirred with a magnetic stirrer. Cs concentration was measured by flame atomic absorption spectroscopy (AA240FS, Varian, AU). 2.4. Analysis CuHCF film was characterized using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS, EVO LS10, Car Zeiss, UK). X-ray powder diffractometry (XRD, Ultima X, Rigaku, Japan) was carried out to determine the crystalline structures. The electrochemical response of the electrodes was determined by cyclic voltammetry (CV) with CHI 660C (Chenhua Instruments Co., Ltd., Shanghai, China). CV was performed in a three-electrode cell, in which the working, reference and counter electrodes were respectively, a CuHCF modified graphite sheet, Hg/Hg2Cl2 electrode and a platinum wire electrode.
(1)
Herein, a technology (MFC-adsorption) of electrochemically remove Cs driven by MFC was proposed. Working electrode in adsorption system was modified with CuHCF film by chemical deposition. This study explores the possibility of MFC-adsorption technology used for Cs removal without extra energy and chemical addition.
3. Results and discussion
2. Experimental
3.1. Characterization of CuHCF film
2.1. MFC configuration and operation
XRD patterns show the film on the electrode was cubic CuHCF crystal mixed with a small amount of CuHCF analogue, such as KCu[Fe (CN)6]. SEM image indicates the film were well dispersed heterogeneous nanoparticles. E-Supplementary data for the works above can be found in e-version of this paper online. The EDS results were illustrated in Table 1, elements of Fe, Cu, C and N, can be named as CuHCF. The atom ration of Cu:Fe is 3.06:2.22, which is differ subtly from the stoichiometric proportion of elemental composition in Cu3[Fe(CN)6]2 (3:2). This again means that the film was a mixture of compounds, such as Cu3[Fe(CN)6]2, KCu[Fe(CN)6] and non-reacted reactants. Cs signals detected referring to the Cs loading on the film. The maximum loading of CuHCF film was 0.26 Cs/Fe which was much higher than the results from powdery CuHCF (0.073) (Ayrault et al., 1998), but half of the results from Chen et al. (2013) (0.52). Compared with the study of Chen et al. (2013), CuHCF film in our study is easier to be obtained, the cost is lower and the operation more simple.
The MFC used was single-chamber MFC, similar to the singlechamber MFC in a published paper (Tao et al., 2015). The anode and cathode were both carbon cloth with ∼7 cm2 (3.8 cm diameter) projected area. The cathode was modified as previously described (Tao et al., 2015). The anode was rolled up tightly like a burrito with titanium wire, and the distance between two electrodes was ∼0.5 cm. With the exception of adsorption system loading, a 1000 Ω resistor was connected in the circuit. The MFC was inoculated with mixed anaerobic sludge and aerobic sludge (v/v = 2:1) from domestic sewage treatment plant. The MFC was operated in fed-batch mode with synthetic wastewater (NaC2H3O2 1.00 g/L, NH4Cl 0.31 g/L, NaHCO3 3.13 g/L, NaH2PO4 0.75 g/L, KCl 0.13 g/L, metals and trace minerals) at 30 ± 0.5 °C. After MFC achieved 3 cycles of stable voltage outputs, experiments were carried out. Synthetic wastewater was fed into the MFC when the voltage less than 50 mV. The output voltage (V) and current (I) were monitored using a data acquisition system (M2700, Keithley, USA). Power was calculated according to P = IV. Power density was calculated by dividing P by the net cathode area. Coulombic efficiency (CE) was calculated as previously described (Liu et al., 2005). Chemical oxygen demand (COD) concentration was measured according to the Standard Methods (APHA, 2005).
3.2. Cyclic voltammetric response of the CuHCF modified electrode CuHCF coating made a pronounced change on electrode’s cyclic voltammetry (Fig. 1a). The current through the electrodes increased clearly. Two oxidation peaks and two reduction peaks appeared. The voltammetric features might be attributed to the reactions of Cu3[Fe (CN)6]2 and KCu[Fe(CN)6]: Reduction reactions:
2.2. Fabrication of a CuHCF modified electrode Cs adsorption system was a two-electrode cell. Two electrodes were both graphite sheet with the same size (1.5 mm × 20 mm × 20 mm). CuHCF was deposited on the working electrode by chemical deposition process (Henrik and Gregory, 1999).
Table 1 Chemical composition on the surface of CuHCF film after Cs adsorption.
2.3. Adsorption and regeneration study Adsorption tests were carried out in four groups: (1) Bare graphite adsorption. Graphite sheet was dipped into the Cs containing wastewater. (2) MFC-bare graphite adsorption. No CuHCF coated on electrode with MFC-adsorption technology. (3) CuHCF modified graphite 457
Element
Weight (%)
Atoms (%)
CK NK OK Fe L Cu L Cs L
20.58 15.34 5.27 18.40 28.84 11.56
42.75 27.33 8.21 8.22 11.32 2.17
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
Fig. 1. Comparison of cyclic voltammetric data for bare graphite and CuHCF modified electrode (a), CuHCF modified graphite electrode before exposure to Cs and regeneration after loading with Cs (b). Electrodes were in 1 M KCl, the voltammogram recorded after 25 scans, scan rate 25 mV/s.
KCu [Fe III (CN )6] + e + K+
Cu3
[Fe III (CN )
6 ]2
+ 2e +
(2)
K2 CuFe II (CN )6
2K+
K2 Cu3
[Fe II (CN )
6 ]2
electrode, which was in concordance with the low release rate of Cs. The reduction in Cs adsorption capacity of the regenerated electrode partly attributed to the exfoliation of CuHCF nanoparticles from the electrode.
(3)
Oxidation reactions
K2 CuFe II (CN )6
e
K2 Cu3 [Fe II (CN )6 ]2
K+ 2e
KCu [Fe III (CN )6] 2K+
Cu3 [Fe III (CN )6 ]2
(4)
3.4. The effects of Cs separation on MFC performance
(5)
The output voltage increased as MFC and adsorption system were connected (Fig. 3a). High internal resistance of the adsorption system may be the reason for increasing output voltage. Low ionic strength of the solution in the adsorption system could lead to high internal resistance. In spite of more output voltage, a far lower power density was obtained from MFC as connected to adsorption system. This is also thought to be a result of high internal resistance of adsorption system. Adsorption system loading has little effect on COD removal in MFC (Fig. 3b). However, the average CE was decreased from 30% to 12% as the MFC was loaded to adsorption system. The CE was calculated as Eq. (6):
The peaks were absent for bare graphite sheet. Similar results were mentioned in the literature (Henrik and Gregory, 1999). 3.3. Electrochemical adsorption and regeneration The results in Fig. 2a indicate that multiple factors affecting Cs adsorption extend the time to attain absorption equilibrium. The removal efficiency of Cs at equilibrium in MFC-CuHCF absorption test was significantly higher than the other three absorption tests. The results suggest that Cs was removed by the synergies of graphite matrix adsorption, ion exchange of CuHCF film and electrochemical adsorption, in which electrochemical adsorption was the dominant factor for Cs adsorption speed and removal efficiency. The removal rate of Cs in this study was unfavorable, low potential provided by the MFC maybe the reason. The maximum Cs release rate of MFC-CuHCF technology was about 28% (Fig. 2b). The cause for this were: ① Oxidation potential provided by MFC was insufficient to drive more adsorbed Cs exchange with K and then release from CuHCF modified electrode. ② CuHCF modified electrode has better selectivity toward Cs compared with other alkali metal ions. The intensity of the voltammetric peaks of regenerated CuHCF modified electrode were lower (Fig. 2b). The results indicated the reduction of absorption capacity of the regenerated CuHCF modified
CE =
CP × 100% CTi
(6)
where Cp, is the total coulombs calculated by integrating the current over time. CTi is the theoretical amount of coulombs that can be produced from sodium acetate. Similar average COD removal efficiency indicates similar CTi. Evaluating CE of MFC before and after connecting the adsorption system can be achieved by comparing the CP value. CP was calculated as Eq. (7): n
CP =
Ii ti i=1
(7)
where Ii is the current over time, which can be calculated as I = V/R
Fig. 2. Cs adsorption (a) and deintercalation (b) with contact time. 458
Bioresource Technology 278 (2019) 456–459
Q. Tao et al.
Fig. 3. Output voltages and power density curves (a), COD removal efficiency and coulombic efficiency (b) of the MFC before and after connecting the adsorption system.
according to Ohm’s Law. On account of this we can find that adsorption system with high internal resistance would decrease the current I, which in turn lead to the low CE of MFC.
wastewater using copper hexacyanoferrate nanofilms in an electrochemical system. Electrochim. Acta 87, 119–125. Chen, R., Asai, M., Fukushima, C., Ishizaki, M., Kurihara, M., Arisaka, M., Nankawa, T., Watanabe, M., Kawamoto, T., Tanaka, H., 2015. Column study on electrochemical separation of cesium ions from wastewater using copper hexacyanoferrate film. J. Radioanal. Nucl. Chem. 303, 1491–1495. He, J., 2016. An integrated device for coprecipitation and filtration of radiocesium in seawater. J. Environ. Radioact. 165, 35–38. Hasan, S., Ghosh, T.K., Viswanath, D.S., Loyalka, S.K., Sengupta, B., 2007. Preparation and evaluation of fullers earth beads for removal of cesium from waste streams. Sep. Sci. Technol. 42 (4), 717–738. Henrik, G., Gregory, V., 1999. Separation of cesium from high ionic strength solutions using a cobalt hexacyanoferrate-modified graphite electrode. Environ. Sci. Technol. 33 (15), 2633–2637. Kim, Y., Kim, Y.K., Kim, S., Harbottle, D., Lee, J.W., 2017. Nanostructured potassium copper hexacyanoferrate-cellulose hydrogel for selective and rapid cesium adsorption. Chem. Eng. J. 313, 1042–1050. Little, I., Seaton, K., Alorkpa, E., Vasiliev, A., 2017. Adsorption of cesium on bound porous materials containing embedded phosphotungstic acid. Adsorption 23 (6), 809–819. Liu, H., Cheng, S.A., Logan, B.E., 2005. Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell. Environ. Sci. Technol. 39, 658–662. Milonji, S., Bispo, I., Fedoroff, M., Loos-Neskovic, C., Vidal-Madjar, C., 2002. Sorption of cesium on copper hexacyanoferrate/polymer/silica composites in batch and dynamic conditions. J. Radioanal. Nucl. Chem. 252 (3), 497–501. Nilchi, A., Malek, B., Maragheh, M.G., Khanchi, A., 2003. Exchange properties of cyanide complexes. J. Radioanal. Nucl. Chem. 258 (3), 457–462. Ndayisenga, F., Yu, Z., Yu, Y., Lay, C., Zhou, D., 2018. Bioelectricity generation using microalgal biomass as electron donor in a bio-anode microbial fuel cell. Bioresour. Technol. 270, 286–293. Sun, B., Hao, X., Wang, Z., Zhang, Z., Liu, S., Guan, G., 2012. Continuous separation of cesium based on NiHCF/PTCF electrode by electrochemically switched ion exchange. Chin. J. Chem. Eng. 20 (5), 837–842. Steen, W.A., Jeerage, K.M., Schwartz, D.T., 2002. Raman spectroscopy of redox activity in cathodically electrodeposited nickel hexacyanoferrate thin films. Appl. Spectrosc. 56 (8), 1021–1029. Tao, Q., Zhou, S., Luo, J., Yuan, J., 2015. Nutrient removal and electricity production from wastewater using microbial fuel cell technique. Desalination 365, 92–98. Yang, H.M., Jang, S.C., Hong, S.B., Lee, K.W., Roh, C., Huh, Y.S., Seo, B.K., 2016a. Prussian blue-functionalized magnetic nanoclusters for the removal of radioactive cesium from water. J. Alloys Compd. 657, 387–393. Yang, H.J., Luo, M., Luo, L.L., Wang, H.X., Hu, D.D., Lin, J., Wang, X., Wang, Y.L., Wang, S., Bu, X.H., Feng, P.Y., Wu, T., 2016b. Highly selective and rapid uptake of radionuclide cesium based on robust zeolitic chalcogenide via stepwise ion-exchange strategy. Chem. Mater. 28, 8774–8780. Zheng, Y., Qiao, J., Yuan, J., Shen, J., Wang, A., Niu, L., 2017. Electrochemical removal of radioactive cesium from nuclear waste using the dendritic copper hexacyanoferrate/ carbon nanotube hybrids. Electrochim. Acta 257, 172–180. Zhong, D., Liao, X., Liu, Y., Zhong, N., Xu, Y., 2018. Enhanced electricity generation performance and dye wastewater degradation of microbial fuel cell by using a petaline NiO@ polyaniline-carbon felt anode. Bioresour. Technol. 258, 125–134.
4. Conclusion By use of MFC-adsorption technology, Cs was removed by the synergies of multiple factors, in which electrochemical adsorption was the dominant factor for Cs adsorption speed and removal efficiency. CuHCF film can be regenerated by switching the potential between electrodes. Low efficiency in electricity generation of MFC and high internal resistance of adsorption system were two major causes for Cs removal, CuHCF film regeneration, output voltage, power density and CE. Acknowledgements Financial supports from National Natural Science Foundation of China (Nos. 11705060, 11605027), Natural Science Foundation of Jiangxi Province (No. 20161BAB213086), and the Project of the Jiangxi Provincial Department of Education (No. GJJ170400) are gratefully acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.biortech.2019.01.093. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, 19th ed. American Public Health Association, Washington, DC, USA. Awual, M.R., 2016. Ring size dependent crown ether based mesoporous adsorbent for high cesium adsorption from wastewater. Chem. Eng. J. 303, 539–546. Aelterman, P., Rabaey, K., Pham, H.T., Boon, N., Verstraete, W., 2006. Continuous electricity generation at high voltages and currents using stacked microbial fuel cells. Environ. Sci. Technol. 40 (10), 3388–3394. Ayrault, S., Jimenez, B., Garnier, E., Fedoroff, M., Jones, D.J., Loos-Neskovic, C., 1998. Sorption mechanisms of cesium on CuII2FeII(CN)6 and CuII3[FeIII(CN)6]2 hexacyanoferrates and their relation to the crystalline structure. J. Solid State Chem. 475–485. Chen, R., Tanaka, H., Kawamoto, T., Asai, M., Fukushima, C., Na, H., Kurihara, M., Watanabe, M., Arisaka, M., Nankawa, T., 2013. Selective removal of cesium ions from
459