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Prussian blue non-woven filter for cesium removal from drinking water
Accepted Manuscript Prussian blue non-woven filter for cesium removal from drinking water Guan-Ru Chen, Yin-Ru Chang, Xiang Liu, Tohru Kawamoto, Hisashi Tanaka, Durga Parajuli, Man-Li Chen, Yu-Kuo Lo, Zhongfang Lei, Duu-Jong Lee PII: DOI: Reference:
S1383-5866(15)30164-7 http://dx.doi.org/10.1016/j.seppur.2015.08.029 SEPPUR 12516
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
22 April 2015 15 July 2015 16 August 2015
Please cite this article as: G-R. Chen, Y-R. Chang, X. Liu, T. Kawamoto, H. Tanaka, D. Parajuli, M-L. Chen, Y-K. Lo, Z. Lei, D-J. Lee, Prussian blue non-woven filter for cesium removal from drinking water, Separation and Purification Technology (2015), doi: http://dx.doi.org/10.1016/j.seppur.2015.08.029
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Prussian blue non-woven filter for cesium removal from drinking water Guan-Ru Chen1, Yin-Ru Chang2, Xiang Liu2,3, Tohru Kawamoto4, Hisashi Tanaka4, Durga Parajuli4, Man-Li Chen5, Yu-Kuo Lo5, Zhongfang Lei6, Duu-Jong Lee1,2,* 1
Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan; 2Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan; 3Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China; 4National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan; 5Taipei Water Department, Taipei City Government, Taipei 106, Taiwan; 6Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan * Corresponding author: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan, Tel: +886-2-33663028; Fax: +886-2-23623040; Email: [email protected] ABSTRACT Cesium (Cs) removal from tap waters is an emerging issue after the Fukushima Daiichi Nuclear Power Plant Disaster. Adsorbents highly specific to Cs in the presence of other alkali and alkali earth metals are desired to supply safe drinking waters to residents near the contaminated area. This work for the first time used Prussian blue (PB) nanoparticles implemented non-woven fabric as an efficient adsorbent for Cs removal. Adsorption isotherms were obtained using Langmuir equation at 288, 298 and 308 K, from which the maximum adsorption capacities were estimated as 216, 241, 260 mg/g. The studied PB-Cs adsorption was endothermic process while its capacity was lower in acid than in alkaline solutions. The column tests with synthetic raw water and pilot plant column with low and high-turbidity real raw waters revealed almost complete removal of Cs by sufficiently long contact time. All PB treatments had no noticeable effects on water quality while the produced water had no biological acute toxicities. Use of PB non-woven fabric for decontaminating Cs pollution in drinking water was discussed. Keywords: Cesium, tap water, Prussian blue,
1
1. INTRODUCTION The East Japan Earthquake seriously damaged Fukushima Daiichi Nuclear Power Plant, leading to release of 630000−770000 terabecquerels of radioactive nuclides to environment (NRA, 2013). Japanese soils had been contaminated by the 2011; 2013; Murakami et al., 2014). The half live for
137
137
Cs fallout (Yasunari et al.,
Cs is much longer than
131
I
(Thammawong et al., 2013), hence left residual radioactivity to local residents at 1.8×1016 Bq 134Cs and 1.5×1016 Bq 137Cs one year after the Fukushima Disaster (Parajuli et al., 2013). Radioactive fallout can lead to contaminated surface water and/or groundwater, eventually pollute the drinking water production chain (Smith et al., 2001). At two years after the Fukushima Disaster trace of radiocesium was still found in drinking water of many cities in Japan (NRA, 2013). Conventional
coagulation-sedimentation
processes
can
effectively
remove
particle-bound cesium but can hardly remove soluble cesium ions from waters. Cs behaves similarly with K and Na, hence leading to low removal efficiency by conventional drinking water treatment processes such as coagulation-sedimentation and sand filtration (Morton and Straub, 1956; Goossens et al., 1989; Gafvert et al., 2002; Baeza et al., 2012). Brown et al. (2008)
commented
that
removal
efficiencies
of
Cs
in
raw
waters
in
coagulation-sedimentation and sand filtration stage ranged 10–40%. The best available technologies and the small system compliance technologies by Radionuclides Final Rule (Dec. 7, 2000) by US Environmental Protection Agency for beta particle removal in drinking water are ionic exchange (IC) and reverse osmosis (RO). Hamasaki et al. (2014) reviewed the methods proposed for Cs removal. Adsorption efficiencies of Cs from waters using natural adsorbents are generally low (Liang and Hsu, 1993; Dyer et al., 1999; Bayulken et al., 2011; Kim et al., 2013; Pangeni et al., 2014; Yakout and Hassan, 2014; Liu and Lee, 2014a). Expensive synthetic 2
adsorbents are proposed to remove Cs from waters (Chitrakar et al., 2013; Ararem et al., 2013; Du et al., 2013; Ding et al., 2013; 2014; Han et al., 2012; Tasdelen et al., 2013). Prussian blue (PB) is a pigment of dark blue color with chemical formula Fe7(CN)18, which has a simple face-centered crystal structure with eight water molecules forming a unit cell. PB crystal has a cage size similar to the hydration radius of Cs+ (3.25 Å), which are smaller than those for Na+ (3.6 Å), Ca2+ (4.1 Å) and Mg2+ (4.25 Å) (Thammawong et al., 2013). Owing to the size screening effects, pharmaceutical-grade PB has been utilized for assisting Cs removal from patient body after the Chernobyl disaster. Ishizakiet al. (2013) revealed that synthesized PB nanoparticles (Fe4(Fe(CN)6)3 with hydrophilic defect sites has supreme Cs adsorption capability and proposed that the Cs+ ions were adsorbed via the defect sites of nanoparticles by proton-elimination reaction from the coordinated waters. The small size of PB nanoparticles provides them very large specific surface area for enhancing adsorption capability. The PB nanoparticles can effectively uptake Cs ions, however, their recovery after adsorption is an obstacle to field applications of these adsorbents (Namiki et al., 2012; Thammawong et al., 2013). The concept of using nanocomposites containing PB-type nanoparticles covalently linked to a matrix appears to be a promising route to the decontamination of cesium ions (Delchet et al., 2012). Kitajima et al. (2012) adopted the ion-exchange technique (Na+ to K+) for immobilizing PB nanoparticles onto the cotton matrices, and applied the so-produced PB-matrices to adsorb Cs+ from water at a decontamination factor of order of 106. Yasutaka et al. (2013a) applied PB impregnated nonwoven fabric to remove
134
Cs and
137
Cs from water streams. These authors noted that the
radioactive cesium in water samples could be concentrated within 20–60 min by passing the sample through 10–12 columns, connected in series to recover 100–108% of isotopes. This method was used to concentrate the radionuclides in water samples in short period of time. Yasutaka et al. (2013b) adopted the cartridges with PB impregnated fabric to remove water 3
with 0.005–5 Bq/L of Cs. The recovery of Cs ranged 83–98% when the water was passed through the cartridge. On the other hand, polymeric binder was commonly adopted to immobilize functional particles for specific applications. Vipin et al. (2013) encapsulated Prussian blue in calcium/alginate beads and the beads were reinforced by carbon nanotubes. The so-yielded beads were used to adsorb cesium and revealed high affinity over wide range of pH and concentrations of potassium and sodium ions. These authors also demonstrated the use of these beads in large columns for large-scale water treatment. However, after adsorption of radioactive cesium, radiation heating may deteriorate the durability of polymeric matrix thus produced. Kawamoto et al. (2012) filed the patent on the use of inorganic binder to form Cs-granules as adsorbent, which was used later by Chen et al. (2015) for Cs removal from waters. Hu et al. (2012) developed a spongiform adsorbent that contains PB for adsorbing cesium. This adsorbent was a quaternary (polyurethane/carbon nanotubes/diatomite/PB) composites. The caged PB after being permanently immobilized in polyurethane spongy showed a 167 mg/g capability for absorbing cesium. This study applied the PB-non-woven fabric in batch and in column tests to remove soluble Cs+ from waters. The cesium barriers applicable to waterworks have to be of high efficiency, cost-effective, stable in storage and compatible to the existing treatment processes. Additionally, impurities in drinking waters such as humic substances, residual coagulants (Al or Fe salts) and residual chlorine (if any) may interfere with Cs removal efficiency. Most existing literature works on Cs removal handled wastewaters or natural waters for non-potable purpose. As per our best knowledge, this is the first paper reporting the feasibility of using PB fabrics in waterworks for Cs removal from contaminated waters.
2. EXPERIMENTAL 2.1 PB adsorbent 4
The PB-immobilized nonwoven adsorbents used in the previous paper were prepared (Yasutaka et al., 2013a, Kitajima et al., 2014) (Fig. S1b). The PB density in the adsorbent is 3–6 wt%, depending on the Lot. No. The fabric was filled up the testing column of diameter 6.7 cm and height 10 cm and columns of diameter 35 cm and height 120 cm for lab test and field test, respectively.
2.2 Non-woven fabric tests In lab tests columns of diameter 6.7 cm and length 10 cm were packed with the PB non-woven fabric (100 mm10 m) with 3% w/w PB. Tap water with 30 ppb dosed Cs and 0.40 NTU, pH 7.0 and 102 μS cm-1 was fed continuously at column bottom with flow rate controlled for contact time up to 400 s. The effluent samples were collected after 25 liters of water had flowed through the column at each contact time. The filtered effluent was measured in its residual Cs concentration in the filtrate being measured using inductively coupled plasma mass spectroscopy (model 7700 series ICP-MS, Agilent Technologies). In filed test, four identical columns (35 cm123 cm) were packed with 3% w/w PB non-woven fabric and were installed at Zhitan Waterworks, New Taipei City, Taiwan, which produces three millions metric tons of potable water per day (Fig. S1). Raw water received by the Zhitan Waterworks at the distribution wells was fed into the pilot plant facility, which had identical processes by the full-scale production chain. In brief, the raw water was first dosed with 30 ppb Cs+ at receiving tank and then was dosed with polyaluminum chloride (PACl) as coagulant at rapid mixing basin, followed by a flocculation basin, sedimentation basin and a rapid filtration basin. (Note: The concentration chosen is to fit the detection limit of the applied ICP-MS (0.1 ppb) in water samples. Although in real scenario the radioactive Cs should be at much lower concentration, we believe the tests herein conducted provide a reference on the potential of applying the current fabrics in tap water treatment.) Flow rates 5
into the four columns were controlled so the contact times of water to the PB fabric were initially at 100, 150, 200 and 375 s, respectively. Experiments were conducted in the period with a hit of a tropical typhoon with heavy shower and high turbidity of raw waters to demonstrate the effects of rapid change in raw water quality on cesium removal from waters. Water samples were collected at 2-h intervals after each process unit with their properties being measured.
2.3 Other analysis The water samples were collected and filtered through 0.45 μm filters. The residual Cs concentrations (Ce) in the filtrate were measured using inductively coupled plasma mass spectroscopy (model 7700 series ICP-MS, Agilent Technologies), from which the adsorbed quantity on PB was evaluated (qe). All tests were conducted in triplicate to assure data quality. Zeta potential measurement of particles in suspensions was carried out in a Zetasizer (Nano-ZS, Malvern Co., UK). The cell repeated flushing by DI water and ethanol several times before the measurement. The pH of the samples was measured using a calibrated pH meter (WTW pH-315, Weilheim, Germany). The TOC data of water samples were analyzed by Aurora Model 1030 TOC analyzer (OI Analytical, Co., College Station, USA). The non-purgable dissolved organic carbon (NPDOC) is an index of organic composition concentration. The DOC data were averaged over triplicate analysis. Water quality were measured
based
on
standard
methods
by
Taiwan
EPA
(http://www.niea.gov.tw/analysis/method/ListMethod.asp?methodtype=WATER). Biological acute tests with Cyprinus carpio and Daphnia pulex for collected water samples were performed using Standard methods by Taiwan EPA NIEA B904.13B and NIEA B901.14B, respectively. 6
3. RESULTS AND DISCUSSION 3.1 Batch adsorption 3.1.1 Adsorption equilibrium The adsorption isotherms for PB nonwoven fabric in Cs+ solution at 288, 298 and 308K were shown in Fig. 1. At Ce<2000 μg/L, the distribution coefficient (adsorbed amount (qe) in μg/g PB to Ce in μg/ml solution can be greater than 4104. At Ce=30000 μg/L, the distribution coefficient is still greater than 20. Hence, the studied PB non-woven fabric is highly efficient Cs adsorbent at room temperatures. The amount of adsorbed Cs+ was increased with temperature, suggesting that the present adsorption process in endothermic. Langmuir isotherm model (q e=qmax(KdCe/(1+KdCe)) was used to fit the data (figures not shown), leading to the best-fit parameters at r2>0.99 for non-woven filters as follows: Kad=97400, 150000, and 260000 L/mole, and qmax=216, 241, 260 mg/g at 288, 298, 308 K, respectively. Satisfactory fitting with Langmuir model indicated that cesium ions were captured by the sites of PB, each cesium ion corresponds to a site for adsorption, like a monolayer adsorption mechanism. The van't Hoff equation (ln(Kd)=-ΔH/RT+ΔS/R), where ΔH and ΔS are the enthalpy and entropy changes of the adsorption process, respectively, is widely used to estimate the thermodynamic parameters for the adsorption processes. Although being challenged by literature work (Ramesh et al., 2005; Liu and Lee, 2014b), the thermodynamic parameters were still estimated at r2>0.98 as a reference for comparison: (ΔH, ΔS)=(36.4 kJ/mol and 220 J/mol-K) for non-woven fabric. Since these values were evaluated from a single correlation hence cannot be regarded justified.
3.1.2 Effects of solution pH, competing ions and NaOCl 7
Table 1 lists the influence of pH and competing ions on the adsorbed quantities of cesium (qe). The value of qe peaked at pH 7. At low pH, excess H+ ions compete with cesium ions on the adsorption sites via ion-exchange mechanism. At alkaline pH, the qe was kept unchanged with pH. The Ca2+ and K+ ions decreased the value of qe. However, even in the presence of 145 mg l-1 Ca2+, the qe with feed of 30 μg l-1 Cs+ was decreased from 640 mg g-1 to 395 mg g-1. Residue chloride exists in drinking water. The adsorption capacities of cesium ions by PB non-woven filter were not affected by up to 10 mg/L NaOCl (Table 1). This observation was favorable for water decontamination with residual chlorine. However, trace of iron ions were noted with high dosage of NaOCl (Table 1). The OCl- could attack the PB lattice to release Fe from the matrix, although only less than 2 ppb iron ions were released at 1 mg/L NaOCl dosage.
3.2 The PB column tests The contact time need to remove 99% Cs+ is about 30 s, which was much shorter than the data (420 s) reported by Liu et al. (2014). This observation should be attributable to the higher PB loading (3% w/w) for the present fabric than that used by Liu et al. (1.5% w/w). The column permeability was estimated using Darcy’s law by passing through water at constant head (1 m H2O) as 9.6106 Pa-s/m2. Using the permeability data the correlation between bed height, flow rate and pressure drop can be established. Over a period of 24-h testing, water samples were collected each hour and the ranges of pH, concentration of cations, turbidity, and electric conductivity were listed on Table 2. PB column treatment did not affect the water quality. In applications, the water head available for the column and the volumetric flow rate are the constraints while the column size can be designed with a given volume loading and water 8
head provided by the plant as follows: L=(∆Ptc)/k)0.5 and A=Q(ktc/∆P)0.5, where L, A, Q, ∆P, tc and k are the height (m), cross-sectional area of column (m2), volumetric flow rate (m3/s), water head loss (Pa), contact time (s) and permeability (Pa-s/m2), respectively. For instance, taking the tested column as example, at Q=10000 CMD and ∆P=1 m H2O, 30 s contact time acquires a column of thickness of 17.5 cm and cross-sectional area of about 20 m2, or a circle of radius of 2.5 m (Fig. 2), not a big column for supply 10,000 CMD water to the public.
3.3 Pilot plant test Typhoon Usagi formed in the east of the Philippines, swept over the southern part of Taiwan on Sept. 20 and 22, 2013. This typhoon led to heavy showers over the entire Taiwan, and high turbidity of raw water to the Zhitan Waterworks. Figure S2a shows the turbidity of raw water during Sept. 20, 0900 and Sept. 23 02:00, 2013. The raw water turbidity peaked at 11:00, Sept. 21, 2013, reaching 1,720 NTU, which then declined gradually back to low turbidity (<10 NTU) at 10:00, Sept. 22. The corresponding pH ranged 7.37–7.90, while the corresponding conductivity remained almost constant (Fig. S2b). The high-turbidity raw water corresponded to a weakly alkaline pH (7.90). Figure S3a shows the turbidity of raw water received by the pilot plant. Certain turbidity was removed in the distribution well of full-scale plant so the turbidity of raw water to the pilot plant peaked at 11:00, Sept. 21, 2013 to 500 NTU. The corresponding PACl dosing amount at the pilot plant was also shown as a reference. Figure S3b shows the zeta potential data for the coagulated water samples. Except for a period of time on Sept. 22, most particles were neutralized in charge by the dosed PACl. This observation suggested that the coagulation control of the studied site worked well under low and high turbidity regimes. Concentrations of cations were not changed by the treatment process (Figs. S3c and S3d). Figure 3 shows the cesium concentrations of water samples collected at different units in 9
the treatment process. Over the 65-h testing period, the concentrations of cesium were almost the same for water samples collected at the same time (considering the lag phase of processing time) from different units. This observation showed that the traditional treatment process has no removal capacity of dissolved cesium. During h 24–45 with high-turbidity raw water, up to 66% of dosed cesium was removed by the process. This observation suggests that the particles in the raw water could adsorb dissolved cesium, which was then removed in the subsequent units (or the membrane filtration step before the ICP-MASS measurement). The cesium removals by the PB filter columns in pilot plant all reached >99.99% at contact time >150 s (Fig. 4). We cannot quantitatively measure the real cesium removal rate since all readings are not detectable by the applied ICP-MASS, suggesting that the residual cesium concentrations were all lower than 0.01 ppb. At 100 s contact time, the removal rate was around 67% when treating the first three tons of water. Then the removal rate increased to over 95% after treatment of 5 tons of water. Figure S4a–d shows the data of turbidity, total dissolved solids, conductivity and pH for water samples before and after the PB columns. Table 3 lists the water quality data for the water samples after PB columns. At different contact times, the PB adsorption did not affect the water characteristics while the produced water quality fits the drinking water standards of Taiwan. Biological acute tests revealed that the biological acute toxicities for both Carp and Daphnia were all <1.0 (TUa) (or LC50>100%). The filtration flux data versus testing time (not shown) revealed that the turbidity in feed water would lead to blockage of fine pores in the PB columns hence reducing the filtration flux. After filtering for 10 h, the filtration flux reached a steady state with no significant flux decline.
3.4 Discussion 10
The tested PB implemented non-woven fabric revealed satisfactory Cs adsorption capability (216–260 mg/g) at room temperatures with a Langmuir isotherm (Fig. 1), which was reversible adsorption onto the PB site with minimal interference by the competing ions or residual chlorine (Table 1). The lab column tests showed that 30 s contact time was sufficient to remove 99% Cs+ with no noticeable influences on the water quality. Pilot plant tests at Zhitan Waterworks with real raw water during the hit of typhoon Usagi during Sept. 20-22, 2013 demonstrated that the tested PB columns worked well under low or high turbidity environments, providing >99.99% Cs removal at >150 s contact time. Comprehensive water quality measurements showed that the produced water fit all water quality standards except for the concentration of iron ions. Two concerns are worthy of further discussion. The tested columns had flux decline during filtration. In application backwashing mechanism should be added if the columns are to be operated in a long period of time. In case of emergent water supply for decontaminated drinking water to radiocesium affected area with a short period of time, blockage problem may be ignored in the present study. Another concern is the release of Fe-containing fragments from non-woven fabric that were detected in the present batch tests, lab column tests and pilot plant column tests. Biological acute tests revealed no biological acute toxicities for the produced water to both Carp and Daphnia, hence the decontaminated water should be safe to drink. Proposal to have an ion-exchange column following the PB columns to remove all released PB fragments is proposed and under testing in the lab. This action, however, will increase the fixed and operational costs of the decontamination system. The addition of NaOCl would attack the PB matrix so pre-chlorination stage should be prevented and post-chlorination should be applied after the PB columns in practice.
11
4. CONCLUSIONS This study tested the cesium adsorption capacities of PB implemented non-woven fabric at room temperatures. In batch tests, endothermic adsorption isotherms at pH 7 following qe=qmax(KdCe/(1+KdCe)) with Kad=97400, 150000, and 260000 L/mole, and qmax=216, 241, 260 mg/g at 288, 298, 308 K, respectively, were obtained. The adsorption capacity became lower at acidic environment; while the presence of competing ions (Na +, K+, Ca2+ and Mg2+) or residual chlorine had no effects on the PB adsorption capacity. The laboratory column (6.7 cm10 cm) tests reached 99% removal of Cs at 30 s contact time. The pilot plant columns (35 cm123 cm) tests had 99.99% removal of Cs at >150 s contact time. Column flux was declined owing to particle clogging in the packing fabric. All PB treatments had no noticeable effects on water quality except for the increment of iron ion concentrations. Although leading to no biological acute effects, the release of PB fragments from the non-woven fabric can be minimized by preventing chlorination stage before the PB units or application of an effective ion-exchange unit following the PB columns.
5. ACKNOWLEDGEMENT Financial supports from Taipei Water Department, Taipei City Government are highly appreciated.
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from an aqueous solution, Chemical Engineering Research and Design, http://dx.doi.org/10.1016/j.cherd.2013.07.020. Liang, T., Hsu, C. 1993. Sorption of cesium and strontium on natural mordenite. Radiochimica Acta, 61, 105–108. Liu, X., Lee, D.J. 2014a. Biosorption studies on bioremediation and biorecovery. Journal of the Taiwan Institute of Chemical Engineers 45, 1863–1864. Liu, X., Lee, D.J. 2014b. Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters. Bioresource Technology 160, 24–31. Kawamoto, T., Tanaka, H., Kurihara, M., Sakamoto, M., Yamada, M. 2010. Ultrafine particles of Prussian blue-type metal complex, dispersion liquid thereof and their production methods. National Institute of Advanced Industrial Science and Technology, March 16, 2010. US patent 07678188. Kawamoto, T., Tanaka, H., Watanabe, H., Sugiyama, Y., Hattori, T., Matsuzaki, S., Shibaba, M. 2012. Granular adsorbent for r-Cs with inorganic binder. Patent JPA 2012-250904. Kitajima, A., Tanaka, H., Minami, N., Yoshino, K., Kawamoto, T. 2012. Efficient cesium adsorbent using Prussian blue nanoparticles immobilized on cotton matrices. Chemistry Letters 41(11), 1473–1474. Kitajima, A., Ogawa, H., Kobayashi, T., Kawasaki, T., Kawatsu, Y., Kawamoto, T., and Tanaka, H, 2014. Monitoring low-radioactivity caesium in Fukushima waters Environmental Science: Processes & Impacts, 16, 28–32. Morton, R.J., Straub, C.P. 1956. Removal of radionuclides from water by water treatment processes. Journal of American Water Works Association 48, 545–558. Murakami, M., Ohte, N., Suzuki, T., Ishii, N., Igarashi, Y., Tanoi, K. 2014. Biological proliferation of cesium-137 through the detrital food chain in a forest ecosystem in Japan. Scientific Reports 4, Art 3599. Doi:10.1038/srep03599. 15
Namiki, Y., Nakimi, T., Ishii, Y., Koido, S., Nagase, Y., Tsubota, A., Tada, N., Kitamoto, Y. 2012. Inorganic-organic magnetic nanocomposites for use in preventive medicine: A rapid and reliable elimination system for cesium. Pharmaceutical Research 29, 1404–1418. NRA (Nuclear Regulation Authority, Japan) 2013. Readings of radioactivity in drinking water by prefecture. July-September, 2013. Pangeni, B., Paudyal, H., Inoue, K., Ohto, K., Kawakita, H., Alam, S. 2014. Preparation of natural cation exchanger from persimmon waste and its application for the removal of cesium from water. Chemical Engineering Journal 242, 109–116. Parajuli, D., Tanaka, H., Hakuta, Y., Minami, K., Fukuda, S., Umeoka, K.,Kamimura, R., Hayashi, Y., Ouchi, M., Kawamoto, T. 2013. Dealing with the aftermath of Fukushima Daiichi Nuclear Accident: decontamination of radioactive cesium enriched ash. Environmental Science & Technology 47, 3800–3806. Ramesh, A., Lee, D.J., Wong, J.W.C. 2005. Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters with low-cost adsorbents. Journal of Colloid and Interface Science 291, 588–291. Smith, J.T., Voitsekhovitch, O.V., Hakanson, L., Hilton, J. 2001. A critical review of measures to reduce radioactive doses from drinking water and consumption of freshwater foodstuffs. Journal of Environmental Radioactivity 56, 11–32. Szabo, J., Minamyer, S. 2014. Decontamination of radiological agents from drinking water infrastructure; A literature review and summary. Environmental International 72, 129–132. Tasdelen, B., Osmanlioglu, A.E., Kam, E. 2013. The adsorption behavior of cesiumon poly(N-isopropylacrylamide/itaconic acid) copolymeric hydrogels. Polymer Bulletin 70, 3041–3053. Thammawong, C., Opaprakasit, P., Tangboriboonrat, P., Sreearunothai, P. 2013.Prussian 16
blue-coated magnetic nanoparticles for removal of cesium from contaminated environment. Journal of Nanoparticle Research In press. doi:10.1007/s11051-013-1689-z. Vipin, A.K., Hu, B., Fugetsu, B. 2013. Prussian blue caged in alginate/calcium beads as adsorbents for removal of cesium ions from contaminated water. Journal of Hazardous Materials 258, 93–101. Yakout, S.M., Elsherif, E. 2010. Batch kinetics, isotherm and thermodynamic studies of adsorption of strontium from aqueous solutions onto low cost rice-straw based carbons. Carbon - Science and Technology, 3, 144–153 Yakout, S.M., Hassan, H.S. 2014. Adsorption characteristics of sol-gel-derived zirconia for cesium ions from aqueous solutions. Molecules 19, 9160–9172. Yasunari, T.J., Stohl, A., Hayano, R.S., Burkhart, J.F., Eckhardt, S., Yasunari, T. Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident. Proceedings of National Academy of Sciences, 2011, 108, 19530–19534. Yasunari, T.J., Stohl, A., Hayano, R.S., Burkhart, J.F., Eckhardt, S., Yasunari, T. Correction for Yasunari et al., Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident. Proceedings of National Academy of Sciences, 2013, 110 7525–7528. Yasutaka, T., Kawamoto, T., Kawabe, Y., Sato, T., Sato, M., Suzuki, Y., Nakamura, K.,Komai, T. 2013a. Rapid measurement of radiocesium in water using a Prussian blue impregnated nonwoven fabric: Fukushima NPP Accident Related. Journal of Nuclear Science and Technology 50, 674–681. Yasutaka, T., Tsuji, H., Kondo, Y., Suzuki, Y. 2013b, Development of Rapid Monitoring for Dissolved Radioactive Cesium with a Cartridge Type of Prussian Blue-Impregnated Nonwoven Fabric. Bunseki Kagaku 62, 499–506.
17
Table 1. Batch tests at different pH, competing ions and NaOCl. Remarks pH
5
6
7
8
9
0.95 mg/L non-woven fabric
qe (μg/g)
1365±42
1441±52
1522±64
1518±38
1531±46
Initial Cs=3000 ppb.
Competing ions
NA
160 mg/L Na+
200 mg/L K+
100 mg/L Mg2+
145 mg/L Ca2+
qe (μg/g)
935±15
924±7
920±17
924±8
921±14
0.383 g/L non-woven fabric Initial Cs=3000 ppb.
NaOCl
NA
1 mg/L
10 mg/L
0.383 g/L non-woven fabric
qe (μg/g)
895±12
907±17
902±14
Initial Cs=3000 ppb.
Iron (ng/g)
16±2
18±1
122±8
18
Table 2. pH, cation, turbidity and conductivity for water samples in lab column test. Before column After column pH 7.28 7.23–7.34 Cation Ca: 9.6 mg/L Ca: 8.8–9.6 mg/L K: 2 mg/L K: 1.6–1.8 mg/L Mg: 3.1 mg/L Mg: 3–3.2 mg/L Na: 6.8 mg/L Na: 6–6.8 mg/L Fe: 0 mg/L Fe: 0.12–0.15 mg/L Turbidity 0.75 NTU 0.55 NTU Conductivity 99 μS/cm 96 μS/cm
19
Contact time Filtered water amount (ton) Temperature (oC) Turbidity (NTU) Colour (unit) pH Chloride (mg/L) Sulfate (mg/L) Fluoride (mg/L) Ammonia (mg/L) Nitrite-nitrogen (mg/L) Nitrate-nitrogen (mg/L) Total dissolved solids (mg/L) Hardness (mg/L) Calcium (mg/L) Magnesium (mg/L) Total organic carbon (mg/L) UV254 Fluorescence Iron (mg/L) Manganese (mg/L) Lead (mg/L) Aluminum (mg/L) Zinc (mg/L)
Table 3. Quality for filtered water from PB columns at different contact times. standard* 100 s 150 s 200 s 5 10 15 30 10 20 10 18 26.3 26.6 25.0 25.8 25.0 25.9 25.2 25.8 2 0.50 0.85 0.75 0.60 0.70 0.65 0.60 0.65 5 4 4 5 5 5 4 4 5 6–8.5 7.2 7.2 7.0 7.1 7.1 7.1 7.0 7.1 250 5.06 5.22 5.34 7.39 5.38 7.60 5.26 250 10.9 9.99 12.4 10.3 13.2 10.2 11.7 10.3 0.8 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.1 ND ND ND ND ND ND ND ND 0.1 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 10 0.36 0.36 0.35 0.46 0.36 0.46 0.42 0.45 500 61 58 66 58 69 57 64 58 300 39.3 33.5 36.3 36.1 41.3 35.3 36.1 35.3 10.6 8.9 9.2 8.8 9.4 8.6 9.6 9.2 3.1 2.7 3.3 3.5 4.3 3.4 3.0 3.0 0.8 0.9 0.8 0.8 1.1 0.6 0.9 1.0 0.0294 0.0280 0.0255 0.0256 0.0334 0.0200 0.0296 0.0312 ND ND ND ND ND ND ND ND 0.3 0.524 0.479 0.420 0.422 0.636 0.306 0.535 0.702 0.05 <0.001 <0.001 0.001 <0.001 ND 0.001 <0.001 ND 0.01 ND 0.0011 ND ND ND ND ND ND 0.4 0.052 0.042 0.062 0.028 0.018 0.028 0.035 0.024 5 ND ND ND ND ND ND ND ND
*
375 s 10 25.9 0.70 5 6.9 6.12 9.07 0.04 ND <0.01 0.48 54 34.9 8.7 3.2 1.2 0.0308 ND 0.709 ND ND 0.060 ND
Drinking water quality standards, Taiwan; Revisions to Article 3 promulgated by Environmental Protection Administration Order Huan-Shu-Tu-Tzu No.1030001229 on January 9, 2014. http://law.moj.gov.tw/Eng/LawClass/LawContent.aspx?PCODE=O0040019
20
15 25.8 0.60 4 7.1 5.34 10.2 0.04 ND <0.01 0.46 58 36.9 8.7 3.7 0.8 0.0255 ND 0.473 <0.001 ND 0.050 ND
3e+5
qe (μ g/g)
2e+5 288 K 298 K 308 K 1e+5
0 0
10000
20000
30000
40000
Ce (ppb)
Figure 1. Adsorption isotherms for Cs+ adsorption on PB non-woven fabric. pH 7.4, Contact time 24 h. Adsorption amount has been calculated based on impregnated PB (3% w/w).
21
25
L (cm), A (m2)
20
15 L (cm) A (m2) 10
5
0 0
5
10
15
20
25
30
contact time (s)
Figure 2. The PB non-woven column design (Q=10000 CMD; ∆P= 1 m H2O).
22
40 Raw Water Mix Water Precipitate Water Filtration Water Tap Water
Concentration (ppb)
30
20
10
0 0
5
10
15
20
25
30
35
40
45
50
55
60
Time (hr)
Figure 3. Concentrations of cesium in water samples collected at different units in the treatment process. Sept. 20, 0900 to Sept. 23 02:00, 2013.
23
65
100
Removal ratio (%)
80
tc= 100 sec tc= 150 sec tc= 200 sec tc= 375 sec
60
40
20
0 0
5
10
15
20
25
30
Total volume of filtered (ton)
Figure 4. Cesium removals by PB columns at different contact time.
24
Highlights >Cesium removal from tap waters using Prussian blue non-woven fabric was studied. >The maximum adsorption capacities of cesium with fabric were estimated. >The column tests with high-turbidity real raw waters were conducted. >All PB treatments led to quality tap water with high cesium removals.
25
S1383-5866(15)30164-7 http://dx.doi.org/10.1016/j.seppur.2015.08.029 SEPPUR 12516
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
22 April 2015 15 July 2015 16 August 2015
Please cite this article as: G-R. Chen, Y-R. Chang, X. Liu, T. Kawamoto, H. Tanaka, D. Parajuli, M-L. Chen, Y-K. Lo, Z. Lei, D-J. Lee, Prussian blue non-woven filter for cesium removal from drinking water, Separation and Purification Technology (2015), doi: http://dx.doi.org/10.1016/j.seppur.2015.08.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Prussian blue non-woven filter for cesium removal from drinking water Guan-Ru Chen1, Yin-Ru Chang2, Xiang Liu2,3, Tohru Kawamoto4, Hisashi Tanaka4, Durga Parajuli4, Man-Li Chen5, Yu-Kuo Lo5, Zhongfang Lei6, Duu-Jong Lee1,2,* 1
Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan; 2Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan; 3Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China; 4National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan; 5Taipei Water Department, Taipei City Government, Taipei 106, Taiwan; 6Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan * Corresponding author: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan, Tel: +886-2-33663028; Fax: +886-2-23623040; Email: [email protected] ABSTRACT Cesium (Cs) removal from tap waters is an emerging issue after the Fukushima Daiichi Nuclear Power Plant Disaster. Adsorbents highly specific to Cs in the presence of other alkali and alkali earth metals are desired to supply safe drinking waters to residents near the contaminated area. This work for the first time used Prussian blue (PB) nanoparticles implemented non-woven fabric as an efficient adsorbent for Cs removal. Adsorption isotherms were obtained using Langmuir equation at 288, 298 and 308 K, from which the maximum adsorption capacities were estimated as 216, 241, 260 mg/g. The studied PB-Cs adsorption was endothermic process while its capacity was lower in acid than in alkaline solutions. The column tests with synthetic raw water and pilot plant column with low and high-turbidity real raw waters revealed almost complete removal of Cs by sufficiently long contact time. All PB treatments had no noticeable effects on water quality while the produced water had no biological acute toxicities. Use of PB non-woven fabric for decontaminating Cs pollution in drinking water was discussed. Keywords: Cesium, tap water, Prussian blue,
1
1. INTRODUCTION The East Japan Earthquake seriously damaged Fukushima Daiichi Nuclear Power Plant, leading to release of 630000−770000 terabecquerels of radioactive nuclides to environment (NRA, 2013). Japanese soils had been contaminated by the 2011; 2013; Murakami et al., 2014). The half live for
137
137
Cs fallout (Yasunari et al.,
Cs is much longer than
131
I
(Thammawong et al., 2013), hence left residual radioactivity to local residents at 1.8×1016 Bq 134Cs and 1.5×1016 Bq 137Cs one year after the Fukushima Disaster (Parajuli et al., 2013). Radioactive fallout can lead to contaminated surface water and/or groundwater, eventually pollute the drinking water production chain (Smith et al., 2001). At two years after the Fukushima Disaster trace of radiocesium was still found in drinking water of many cities in Japan (NRA, 2013). Conventional
coagulation-sedimentation
processes
can
effectively
remove
particle-bound cesium but can hardly remove soluble cesium ions from waters. Cs behaves similarly with K and Na, hence leading to low removal efficiency by conventional drinking water treatment processes such as coagulation-sedimentation and sand filtration (Morton and Straub, 1956; Goossens et al., 1989; Gafvert et al., 2002; Baeza et al., 2012). Brown et al. (2008)
commented
that
removal
efficiencies
of
Cs
in
raw
waters
in
coagulation-sedimentation and sand filtration stage ranged 10–40%. The best available technologies and the small system compliance technologies by Radionuclides Final Rule (Dec. 7, 2000) by US Environmental Protection Agency for beta particle removal in drinking water are ionic exchange (IC) and reverse osmosis (RO). Hamasaki et al. (2014) reviewed the methods proposed for Cs removal. Adsorption efficiencies of Cs from waters using natural adsorbents are generally low (Liang and Hsu, 1993; Dyer et al., 1999; Bayulken et al., 2011; Kim et al., 2013; Pangeni et al., 2014; Yakout and Hassan, 2014; Liu and Lee, 2014a). Expensive synthetic 2
adsorbents are proposed to remove Cs from waters (Chitrakar et al., 2013; Ararem et al., 2013; Du et al., 2013; Ding et al., 2013; 2014; Han et al., 2012; Tasdelen et al., 2013). Prussian blue (PB) is a pigment of dark blue color with chemical formula Fe7(CN)18, which has a simple face-centered crystal structure with eight water molecules forming a unit cell. PB crystal has a cage size similar to the hydration radius of Cs+ (3.25 Å), which are smaller than those for Na+ (3.6 Å), Ca2+ (4.1 Å) and Mg2+ (4.25 Å) (Thammawong et al., 2013). Owing to the size screening effects, pharmaceutical-grade PB has been utilized for assisting Cs removal from patient body after the Chernobyl disaster. Ishizakiet al. (2013) revealed that synthesized PB nanoparticles (Fe4(Fe(CN)6)3 with hydrophilic defect sites has supreme Cs adsorption capability and proposed that the Cs+ ions were adsorbed via the defect sites of nanoparticles by proton-elimination reaction from the coordinated waters. The small size of PB nanoparticles provides them very large specific surface area for enhancing adsorption capability. The PB nanoparticles can effectively uptake Cs ions, however, their recovery after adsorption is an obstacle to field applications of these adsorbents (Namiki et al., 2012; Thammawong et al., 2013). The concept of using nanocomposites containing PB-type nanoparticles covalently linked to a matrix appears to be a promising route to the decontamination of cesium ions (Delchet et al., 2012). Kitajima et al. (2012) adopted the ion-exchange technique (Na+ to K+) for immobilizing PB nanoparticles onto the cotton matrices, and applied the so-produced PB-matrices to adsorb Cs+ from water at a decontamination factor of order of 106. Yasutaka et al. (2013a) applied PB impregnated nonwoven fabric to remove
134
Cs and
137
Cs from water streams. These authors noted that the
radioactive cesium in water samples could be concentrated within 20–60 min by passing the sample through 10–12 columns, connected in series to recover 100–108% of isotopes. This method was used to concentrate the radionuclides in water samples in short period of time. Yasutaka et al. (2013b) adopted the cartridges with PB impregnated fabric to remove water 3
with 0.005–5 Bq/L of Cs. The recovery of Cs ranged 83–98% when the water was passed through the cartridge. On the other hand, polymeric binder was commonly adopted to immobilize functional particles for specific applications. Vipin et al. (2013) encapsulated Prussian blue in calcium/alginate beads and the beads were reinforced by carbon nanotubes. The so-yielded beads were used to adsorb cesium and revealed high affinity over wide range of pH and concentrations of potassium and sodium ions. These authors also demonstrated the use of these beads in large columns for large-scale water treatment. However, after adsorption of radioactive cesium, radiation heating may deteriorate the durability of polymeric matrix thus produced. Kawamoto et al. (2012) filed the patent on the use of inorganic binder to form Cs-granules as adsorbent, which was used later by Chen et al. (2015) for Cs removal from waters. Hu et al. (2012) developed a spongiform adsorbent that contains PB for adsorbing cesium. This adsorbent was a quaternary (polyurethane/carbon nanotubes/diatomite/PB) composites. The caged PB after being permanently immobilized in polyurethane spongy showed a 167 mg/g capability for absorbing cesium. This study applied the PB-non-woven fabric in batch and in column tests to remove soluble Cs+ from waters. The cesium barriers applicable to waterworks have to be of high efficiency, cost-effective, stable in storage and compatible to the existing treatment processes. Additionally, impurities in drinking waters such as humic substances, residual coagulants (Al or Fe salts) and residual chlorine (if any) may interfere with Cs removal efficiency. Most existing literature works on Cs removal handled wastewaters or natural waters for non-potable purpose. As per our best knowledge, this is the first paper reporting the feasibility of using PB fabrics in waterworks for Cs removal from contaminated waters.
2. EXPERIMENTAL 2.1 PB adsorbent 4
The PB-immobilized nonwoven adsorbents used in the previous paper were prepared (Yasutaka et al., 2013a, Kitajima et al., 2014) (Fig. S1b). The PB density in the adsorbent is 3–6 wt%, depending on the Lot. No. The fabric was filled up the testing column of diameter 6.7 cm and height 10 cm and columns of diameter 35 cm and height 120 cm for lab test and field test, respectively.
2.2 Non-woven fabric tests In lab tests columns of diameter 6.7 cm and length 10 cm were packed with the PB non-woven fabric (100 mm10 m) with 3% w/w PB. Tap water with 30 ppb dosed Cs and 0.40 NTU, pH 7.0 and 102 μS cm-1 was fed continuously at column bottom with flow rate controlled for contact time up to 400 s. The effluent samples were collected after 25 liters of water had flowed through the column at each contact time. The filtered effluent was measured in its residual Cs concentration in the filtrate being measured using inductively coupled plasma mass spectroscopy (model 7700 series ICP-MS, Agilent Technologies). In filed test, four identical columns (35 cm123 cm) were packed with 3% w/w PB non-woven fabric and were installed at Zhitan Waterworks, New Taipei City, Taiwan, which produces three millions metric tons of potable water per day (Fig. S1). Raw water received by the Zhitan Waterworks at the distribution wells was fed into the pilot plant facility, which had identical processes by the full-scale production chain. In brief, the raw water was first dosed with 30 ppb Cs+ at receiving tank and then was dosed with polyaluminum chloride (PACl) as coagulant at rapid mixing basin, followed by a flocculation basin, sedimentation basin and a rapid filtration basin. (Note: The concentration chosen is to fit the detection limit of the applied ICP-MS (0.1 ppb) in water samples. Although in real scenario the radioactive Cs should be at much lower concentration, we believe the tests herein conducted provide a reference on the potential of applying the current fabrics in tap water treatment.) Flow rates 5
into the four columns were controlled so the contact times of water to the PB fabric were initially at 100, 150, 200 and 375 s, respectively. Experiments were conducted in the period with a hit of a tropical typhoon with heavy shower and high turbidity of raw waters to demonstrate the effects of rapid change in raw water quality on cesium removal from waters. Water samples were collected at 2-h intervals after each process unit with their properties being measured.
2.3 Other analysis The water samples were collected and filtered through 0.45 μm filters. The residual Cs concentrations (Ce) in the filtrate were measured using inductively coupled plasma mass spectroscopy (model 7700 series ICP-MS, Agilent Technologies), from which the adsorbed quantity on PB was evaluated (qe). All tests were conducted in triplicate to assure data quality. Zeta potential measurement of particles in suspensions was carried out in a Zetasizer (Nano-ZS, Malvern Co., UK). The cell repeated flushing by DI water and ethanol several times before the measurement. The pH of the samples was measured using a calibrated pH meter (WTW pH-315, Weilheim, Germany). The TOC data of water samples were analyzed by Aurora Model 1030 TOC analyzer (OI Analytical, Co., College Station, USA). The non-purgable dissolved organic carbon (NPDOC) is an index of organic composition concentration. The DOC data were averaged over triplicate analysis. Water quality were measured
based
on
standard
methods
by
Taiwan
EPA
(http://www.niea.gov.tw/analysis/method/ListMethod.asp?methodtype=WATER). Biological acute tests with Cyprinus carpio and Daphnia pulex for collected water samples were performed using Standard methods by Taiwan EPA NIEA B904.13B and NIEA B901.14B, respectively. 6
3. RESULTS AND DISCUSSION 3.1 Batch adsorption 3.1.1 Adsorption equilibrium The adsorption isotherms for PB nonwoven fabric in Cs+ solution at 288, 298 and 308K were shown in Fig. 1. At Ce<2000 μg/L, the distribution coefficient (adsorbed amount (qe) in μg/g PB to Ce in μg/ml solution can be greater than 4104. At Ce=30000 μg/L, the distribution coefficient is still greater than 20. Hence, the studied PB non-woven fabric is highly efficient Cs adsorbent at room temperatures. The amount of adsorbed Cs+ was increased with temperature, suggesting that the present adsorption process in endothermic. Langmuir isotherm model (q e=qmax(KdCe/(1+KdCe)) was used to fit the data (figures not shown), leading to the best-fit parameters at r2>0.99 for non-woven filters as follows: Kad=97400, 150000, and 260000 L/mole, and qmax=216, 241, 260 mg/g at 288, 298, 308 K, respectively. Satisfactory fitting with Langmuir model indicated that cesium ions were captured by the sites of PB, each cesium ion corresponds to a site for adsorption, like a monolayer adsorption mechanism. The van't Hoff equation (ln(Kd)=-ΔH/RT+ΔS/R), where ΔH and ΔS are the enthalpy and entropy changes of the adsorption process, respectively, is widely used to estimate the thermodynamic parameters for the adsorption processes. Although being challenged by literature work (Ramesh et al., 2005; Liu and Lee, 2014b), the thermodynamic parameters were still estimated at r2>0.98 as a reference for comparison: (ΔH, ΔS)=(36.4 kJ/mol and 220 J/mol-K) for non-woven fabric. Since these values were evaluated from a single correlation hence cannot be regarded justified.
3.1.2 Effects of solution pH, competing ions and NaOCl 7
Table 1 lists the influence of pH and competing ions on the adsorbed quantities of cesium (qe). The value of qe peaked at pH 7. At low pH, excess H+ ions compete with cesium ions on the adsorption sites via ion-exchange mechanism. At alkaline pH, the qe was kept unchanged with pH. The Ca2+ and K+ ions decreased the value of qe. However, even in the presence of 145 mg l-1 Ca2+, the qe with feed of 30 μg l-1 Cs+ was decreased from 640 mg g-1 to 395 mg g-1. Residue chloride exists in drinking water. The adsorption capacities of cesium ions by PB non-woven filter were not affected by up to 10 mg/L NaOCl (Table 1). This observation was favorable for water decontamination with residual chlorine. However, trace of iron ions were noted with high dosage of NaOCl (Table 1). The OCl- could attack the PB lattice to release Fe from the matrix, although only less than 2 ppb iron ions were released at 1 mg/L NaOCl dosage.
3.2 The PB column tests The contact time need to remove 99% Cs+ is about 30 s, which was much shorter than the data (420 s) reported by Liu et al. (2014). This observation should be attributable to the higher PB loading (3% w/w) for the present fabric than that used by Liu et al. (1.5% w/w). The column permeability was estimated using Darcy’s law by passing through water at constant head (1 m H2O) as 9.6106 Pa-s/m2. Using the permeability data the correlation between bed height, flow rate and pressure drop can be established. Over a period of 24-h testing, water samples were collected each hour and the ranges of pH, concentration of cations, turbidity, and electric conductivity were listed on Table 2. PB column treatment did not affect the water quality. In applications, the water head available for the column and the volumetric flow rate are the constraints while the column size can be designed with a given volume loading and water 8
head provided by the plant as follows: L=(∆Ptc)/k)0.5 and A=Q(ktc/∆P)0.5, where L, A, Q, ∆P, tc and k are the height (m), cross-sectional area of column (m2), volumetric flow rate (m3/s), water head loss (Pa), contact time (s) and permeability (Pa-s/m2), respectively. For instance, taking the tested column as example, at Q=10000 CMD and ∆P=1 m H2O, 30 s contact time acquires a column of thickness of 17.5 cm and cross-sectional area of about 20 m2, or a circle of radius of 2.5 m (Fig. 2), not a big column for supply 10,000 CMD water to the public.
3.3 Pilot plant test Typhoon Usagi formed in the east of the Philippines, swept over the southern part of Taiwan on Sept. 20 and 22, 2013. This typhoon led to heavy showers over the entire Taiwan, and high turbidity of raw water to the Zhitan Waterworks. Figure S2a shows the turbidity of raw water during Sept. 20, 0900 and Sept. 23 02:00, 2013. The raw water turbidity peaked at 11:00, Sept. 21, 2013, reaching 1,720 NTU, which then declined gradually back to low turbidity (<10 NTU) at 10:00, Sept. 22. The corresponding pH ranged 7.37–7.90, while the corresponding conductivity remained almost constant (Fig. S2b). The high-turbidity raw water corresponded to a weakly alkaline pH (7.90). Figure S3a shows the turbidity of raw water received by the pilot plant. Certain turbidity was removed in the distribution well of full-scale plant so the turbidity of raw water to the pilot plant peaked at 11:00, Sept. 21, 2013 to 500 NTU. The corresponding PACl dosing amount at the pilot plant was also shown as a reference. Figure S3b shows the zeta potential data for the coagulated water samples. Except for a period of time on Sept. 22, most particles were neutralized in charge by the dosed PACl. This observation suggested that the coagulation control of the studied site worked well under low and high turbidity regimes. Concentrations of cations were not changed by the treatment process (Figs. S3c and S3d). Figure 3 shows the cesium concentrations of water samples collected at different units in 9
the treatment process. Over the 65-h testing period, the concentrations of cesium were almost the same for water samples collected at the same time (considering the lag phase of processing time) from different units. This observation showed that the traditional treatment process has no removal capacity of dissolved cesium. During h 24–45 with high-turbidity raw water, up to 66% of dosed cesium was removed by the process. This observation suggests that the particles in the raw water could adsorb dissolved cesium, which was then removed in the subsequent units (or the membrane filtration step before the ICP-MASS measurement). The cesium removals by the PB filter columns in pilot plant all reached >99.99% at contact time >150 s (Fig. 4). We cannot quantitatively measure the real cesium removal rate since all readings are not detectable by the applied ICP-MASS, suggesting that the residual cesium concentrations were all lower than 0.01 ppb. At 100 s contact time, the removal rate was around 67% when treating the first three tons of water. Then the removal rate increased to over 95% after treatment of 5 tons of water. Figure S4a–d shows the data of turbidity, total dissolved solids, conductivity and pH for water samples before and after the PB columns. Table 3 lists the water quality data for the water samples after PB columns. At different contact times, the PB adsorption did not affect the water characteristics while the produced water quality fits the drinking water standards of Taiwan. Biological acute tests revealed that the biological acute toxicities for both Carp and Daphnia were all <1.0 (TUa) (or LC50>100%). The filtration flux data versus testing time (not shown) revealed that the turbidity in feed water would lead to blockage of fine pores in the PB columns hence reducing the filtration flux. After filtering for 10 h, the filtration flux reached a steady state with no significant flux decline.
3.4 Discussion 10
The tested PB implemented non-woven fabric revealed satisfactory Cs adsorption capability (216–260 mg/g) at room temperatures with a Langmuir isotherm (Fig. 1), which was reversible adsorption onto the PB site with minimal interference by the competing ions or residual chlorine (Table 1). The lab column tests showed that 30 s contact time was sufficient to remove 99% Cs+ with no noticeable influences on the water quality. Pilot plant tests at Zhitan Waterworks with real raw water during the hit of typhoon Usagi during Sept. 20-22, 2013 demonstrated that the tested PB columns worked well under low or high turbidity environments, providing >99.99% Cs removal at >150 s contact time. Comprehensive water quality measurements showed that the produced water fit all water quality standards except for the concentration of iron ions. Two concerns are worthy of further discussion. The tested columns had flux decline during filtration. In application backwashing mechanism should be added if the columns are to be operated in a long period of time. In case of emergent water supply for decontaminated drinking water to radiocesium affected area with a short period of time, blockage problem may be ignored in the present study. Another concern is the release of Fe-containing fragments from non-woven fabric that were detected in the present batch tests, lab column tests and pilot plant column tests. Biological acute tests revealed no biological acute toxicities for the produced water to both Carp and Daphnia, hence the decontaminated water should be safe to drink. Proposal to have an ion-exchange column following the PB columns to remove all released PB fragments is proposed and under testing in the lab. This action, however, will increase the fixed and operational costs of the decontamination system. The addition of NaOCl would attack the PB matrix so pre-chlorination stage should be prevented and post-chlorination should be applied after the PB columns in practice.
11
4. CONCLUSIONS This study tested the cesium adsorption capacities of PB implemented non-woven fabric at room temperatures. In batch tests, endothermic adsorption isotherms at pH 7 following qe=qmax(KdCe/(1+KdCe)) with Kad=97400, 150000, and 260000 L/mole, and qmax=216, 241, 260 mg/g at 288, 298, 308 K, respectively, were obtained. The adsorption capacity became lower at acidic environment; while the presence of competing ions (Na +, K+, Ca2+ and Mg2+) or residual chlorine had no effects on the PB adsorption capacity. The laboratory column (6.7 cm10 cm) tests reached 99% removal of Cs at 30 s contact time. The pilot plant columns (35 cm123 cm) tests had 99.99% removal of Cs at >150 s contact time. Column flux was declined owing to particle clogging in the packing fabric. All PB treatments had no noticeable effects on water quality except for the increment of iron ion concentrations. Although leading to no biological acute effects, the release of PB fragments from the non-woven fabric can be minimized by preventing chlorination stage before the PB units or application of an effective ion-exchange unit following the PB columns.
5. ACKNOWLEDGEMENT Financial supports from Taipei Water Department, Taipei City Government are highly appreciated.
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from an aqueous solution, Chemical Engineering Research and Design, http://dx.doi.org/10.1016/j.cherd.2013.07.020. Liang, T., Hsu, C. 1993. Sorption of cesium and strontium on natural mordenite. Radiochimica Acta, 61, 105–108. Liu, X., Lee, D.J. 2014a. Biosorption studies on bioremediation and biorecovery. Journal of the Taiwan Institute of Chemical Engineers 45, 1863–1864. Liu, X., Lee, D.J. 2014b. Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters. Bioresource Technology 160, 24–31. Kawamoto, T., Tanaka, H., Kurihara, M., Sakamoto, M., Yamada, M. 2010. Ultrafine particles of Prussian blue-type metal complex, dispersion liquid thereof and their production methods. National Institute of Advanced Industrial Science and Technology, March 16, 2010. US patent 07678188. Kawamoto, T., Tanaka, H., Watanabe, H., Sugiyama, Y., Hattori, T., Matsuzaki, S., Shibaba, M. 2012. Granular adsorbent for r-Cs with inorganic binder. Patent JPA 2012-250904. Kitajima, A., Tanaka, H., Minami, N., Yoshino, K., Kawamoto, T. 2012. Efficient cesium adsorbent using Prussian blue nanoparticles immobilized on cotton matrices. Chemistry Letters 41(11), 1473–1474. Kitajima, A., Ogawa, H., Kobayashi, T., Kawasaki, T., Kawatsu, Y., Kawamoto, T., and Tanaka, H, 2014. Monitoring low-radioactivity caesium in Fukushima waters Environmental Science: Processes & Impacts, 16, 28–32. Morton, R.J., Straub, C.P. 1956. Removal of radionuclides from water by water treatment processes. Journal of American Water Works Association 48, 545–558. Murakami, M., Ohte, N., Suzuki, T., Ishii, N., Igarashi, Y., Tanoi, K. 2014. Biological proliferation of cesium-137 through the detrital food chain in a forest ecosystem in Japan. Scientific Reports 4, Art 3599. Doi:10.1038/srep03599. 15
Namiki, Y., Nakimi, T., Ishii, Y., Koido, S., Nagase, Y., Tsubota, A., Tada, N., Kitamoto, Y. 2012. Inorganic-organic magnetic nanocomposites for use in preventive medicine: A rapid and reliable elimination system for cesium. Pharmaceutical Research 29, 1404–1418. NRA (Nuclear Regulation Authority, Japan) 2013. Readings of radioactivity in drinking water by prefecture. July-September, 2013. Pangeni, B., Paudyal, H., Inoue, K., Ohto, K., Kawakita, H., Alam, S. 2014. Preparation of natural cation exchanger from persimmon waste and its application for the removal of cesium from water. Chemical Engineering Journal 242, 109–116. Parajuli, D., Tanaka, H., Hakuta, Y., Minami, K., Fukuda, S., Umeoka, K.,Kamimura, R., Hayashi, Y., Ouchi, M., Kawamoto, T. 2013. Dealing with the aftermath of Fukushima Daiichi Nuclear Accident: decontamination of radioactive cesium enriched ash. Environmental Science & Technology 47, 3800–3806. Ramesh, A., Lee, D.J., Wong, J.W.C. 2005. Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters with low-cost adsorbents. Journal of Colloid and Interface Science 291, 588–291. Smith, J.T., Voitsekhovitch, O.V., Hakanson, L., Hilton, J. 2001. A critical review of measures to reduce radioactive doses from drinking water and consumption of freshwater foodstuffs. Journal of Environmental Radioactivity 56, 11–32. Szabo, J., Minamyer, S. 2014. Decontamination of radiological agents from drinking water infrastructure; A literature review and summary. Environmental International 72, 129–132. Tasdelen, B., Osmanlioglu, A.E., Kam, E. 2013. The adsorption behavior of cesiumon poly(N-isopropylacrylamide/itaconic acid) copolymeric hydrogels. Polymer Bulletin 70, 3041–3053. Thammawong, C., Opaprakasit, P., Tangboriboonrat, P., Sreearunothai, P. 2013.Prussian 16
blue-coated magnetic nanoparticles for removal of cesium from contaminated environment. Journal of Nanoparticle Research In press. doi:10.1007/s11051-013-1689-z. Vipin, A.K., Hu, B., Fugetsu, B. 2013. Prussian blue caged in alginate/calcium beads as adsorbents for removal of cesium ions from contaminated water. Journal of Hazardous Materials 258, 93–101. Yakout, S.M., Elsherif, E. 2010. Batch kinetics, isotherm and thermodynamic studies of adsorption of strontium from aqueous solutions onto low cost rice-straw based carbons. Carbon - Science and Technology, 3, 144–153 Yakout, S.M., Hassan, H.S. 2014. Adsorption characteristics of sol-gel-derived zirconia for cesium ions from aqueous solutions. Molecules 19, 9160–9172. Yasunari, T.J., Stohl, A., Hayano, R.S., Burkhart, J.F., Eckhardt, S., Yasunari, T. Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident. Proceedings of National Academy of Sciences, 2011, 108, 19530–19534. Yasunari, T.J., Stohl, A., Hayano, R.S., Burkhart, J.F., Eckhardt, S., Yasunari, T. Correction for Yasunari et al., Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident. Proceedings of National Academy of Sciences, 2013, 110 7525–7528. Yasutaka, T., Kawamoto, T., Kawabe, Y., Sato, T., Sato, M., Suzuki, Y., Nakamura, K.,Komai, T. 2013a. Rapid measurement of radiocesium in water using a Prussian blue impregnated nonwoven fabric: Fukushima NPP Accident Related. Journal of Nuclear Science and Technology 50, 674–681. Yasutaka, T., Tsuji, H., Kondo, Y., Suzuki, Y. 2013b, Development of Rapid Monitoring for Dissolved Radioactive Cesium with a Cartridge Type of Prussian Blue-Impregnated Nonwoven Fabric. Bunseki Kagaku 62, 499–506.
17
Table 1. Batch tests at different pH, competing ions and NaOCl. Remarks pH
5
6
7
8
9
0.95 mg/L non-woven fabric
qe (μg/g)
1365±42
1441±52
1522±64
1518±38
1531±46
Initial Cs=3000 ppb.
Competing ions
NA
160 mg/L Na+
200 mg/L K+
100 mg/L Mg2+
145 mg/L Ca2+
qe (μg/g)
935±15
924±7
920±17
924±8
921±14
0.383 g/L non-woven fabric Initial Cs=3000 ppb.
NaOCl
NA
1 mg/L
10 mg/L
0.383 g/L non-woven fabric
qe (μg/g)
895±12
907±17
902±14
Initial Cs=3000 ppb.
Iron (ng/g)
16±2
18±1
122±8
18
Table 2. pH, cation, turbidity and conductivity for water samples in lab column test. Before column After column pH 7.28 7.23–7.34 Cation Ca: 9.6 mg/L Ca: 8.8–9.6 mg/L K: 2 mg/L K: 1.6–1.8 mg/L Mg: 3.1 mg/L Mg: 3–3.2 mg/L Na: 6.8 mg/L Na: 6–6.8 mg/L Fe: 0 mg/L Fe: 0.12–0.15 mg/L Turbidity 0.75 NTU 0.55 NTU Conductivity 99 μS/cm 96 μS/cm
19
Contact time Filtered water amount (ton) Temperature (oC) Turbidity (NTU) Colour (unit) pH Chloride (mg/L) Sulfate (mg/L) Fluoride (mg/L) Ammonia (mg/L) Nitrite-nitrogen (mg/L) Nitrate-nitrogen (mg/L) Total dissolved solids (mg/L) Hardness (mg/L) Calcium (mg/L) Magnesium (mg/L) Total organic carbon (mg/L) UV254 Fluorescence Iron (mg/L) Manganese (mg/L) Lead (mg/L) Aluminum (mg/L) Zinc (mg/L)
Table 3. Quality for filtered water from PB columns at different contact times. standard* 100 s 150 s 200 s 5 10 15 30 10 20 10 18 26.3 26.6 25.0 25.8 25.0 25.9 25.2 25.8 2 0.50 0.85 0.75 0.60 0.70 0.65 0.60 0.65 5 4 4 5 5 5 4 4 5 6–8.5 7.2 7.2 7.0 7.1 7.1 7.1 7.0 7.1 250 5.06 5.22 5.34 7.39 5.38 7.60 5.26 250 10.9 9.99 12.4 10.3 13.2 10.2 11.7 10.3 0.8 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.1 ND ND ND ND ND ND ND ND 0.1 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 10 0.36 0.36 0.35 0.46 0.36 0.46 0.42 0.45 500 61 58 66 58 69 57 64 58 300 39.3 33.5 36.3 36.1 41.3 35.3 36.1 35.3 10.6 8.9 9.2 8.8 9.4 8.6 9.6 9.2 3.1 2.7 3.3 3.5 4.3 3.4 3.0 3.0 0.8 0.9 0.8 0.8 1.1 0.6 0.9 1.0 0.0294 0.0280 0.0255 0.0256 0.0334 0.0200 0.0296 0.0312 ND ND ND ND ND ND ND ND 0.3 0.524 0.479 0.420 0.422 0.636 0.306 0.535 0.702 0.05 <0.001 <0.001 0.001 <0.001 ND 0.001 <0.001 ND 0.01 ND 0.0011 ND ND ND ND ND ND 0.4 0.052 0.042 0.062 0.028 0.018 0.028 0.035 0.024 5 ND ND ND ND ND ND ND ND
*
375 s 10 25.9 0.70 5 6.9 6.12 9.07 0.04 ND <0.01 0.48 54 34.9 8.7 3.2 1.2 0.0308 ND 0.709 ND ND 0.060 ND
Drinking water quality standards, Taiwan; Revisions to Article 3 promulgated by Environmental Protection Administration Order Huan-Shu-Tu-Tzu No.1030001229 on January 9, 2014. http://law.moj.gov.tw/Eng/LawClass/LawContent.aspx?PCODE=O0040019
20
15 25.8 0.60 4 7.1 5.34 10.2 0.04 ND <0.01 0.46 58 36.9 8.7 3.7 0.8 0.0255 ND 0.473 <0.001 ND 0.050 ND
3e+5
qe (μ g/g)
2e+5 288 K 298 K 308 K 1e+5
0 0
10000
20000
30000
40000
Ce (ppb)
Figure 1. Adsorption isotherms for Cs+ adsorption on PB non-woven fabric. pH 7.4, Contact time 24 h. Adsorption amount has been calculated based on impregnated PB (3% w/w).
21
25
L (cm), A (m2)
20
15 L (cm) A (m2) 10
5
0 0
5
10
15
20
25
30
contact time (s)
Figure 2. The PB non-woven column design (Q=10000 CMD; ∆P= 1 m H2O).
22
40 Raw Water Mix Water Precipitate Water Filtration Water Tap Water
Concentration (ppb)
30
20
10
0 0
5
10
15
20
25
30
35
40
45
50
55
60
Time (hr)
Figure 3. Concentrations of cesium in water samples collected at different units in the treatment process. Sept. 20, 0900 to Sept. 23 02:00, 2013.
23
65
100
Removal ratio (%)
80
tc= 100 sec tc= 150 sec tc= 200 sec tc= 375 sec
60
40
20
0 0
5
10
15
20
25
30
Total volume of filtered (ton)
Figure 4. Cesium removals by PB columns at different contact time.
24
Highlights >Cesium removal from tap waters using Prussian blue non-woven fabric was studied. >The maximum adsorption capacities of cesium with fabric were estimated. >The column tests with high-turbidity real raw waters were conducted. >All PB treatments led to quality tap water with high cesium removals.
25