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A novel electrochemical ion exchange system and its application in water treatment

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A novel electrochemical ion exchange system with porous cylinder electrodes is proposed for treatment of wastewater. This system can be used for desalination without the costly ion-exchange membrane and extra chemical reagents. Since the electrodes
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  Journal of Environmental Sciences 2011, 23(Supplement) S14–S17 A novel electrochemical ion exchange system and its application in watertreatment Yansheng Li 1, ∗ , Yongbin Li 1 , Zhigang Liu 1 , Tao Wu 2 , Ying Tian 1 1. College of Environmental and Chemical Engineering, Dalian Jiaotong University and Liaoning Key Laboratory for Environmental Science and Technology, Dalian 116028, China. E-mail: hjx@djtu.edu.cn2. Dalian Development Centre of Environmental Technology, Dalian 116024, China Abstract A novel electrochemical ion exchange system with porous cylinder electrodes is proposed for treatment of wastewater. This systemcanbeusedfordesalinationwithoutthecostlyion-exchangemembraneandextrachemicalreagents.Sincetheelectrodesarecompletelyuniform and no ion-exchange membrane was used in this system, it can be operated by switching anodes and cathodes flexibly foreliminating the scaling on the surface of electrodes. The strong base ion-exchange resin grains placed among the anode and cathodehave played as supporting electrolyte, which is capable for the treatment of wastewater with low conductivity. The concentrated andneutralized anolyte containing chlorine is e ff  ective for disinfection and contaminants removal. Under the experimental conditions,the removal percentage of total dissolved salts was 83% and the removal percentage of chemical oxygen demand was 92% withoutconsumption of extra chemical reagents. Keywords : flow-through;novelelectrochemicalionexchangesystem;titanicporousfiltercylinderelectrode,desalination,disinfection Introduction Electrochemical ion exchange (EIX) is an advancedion-exchange process for removing metal ions fromwastewater (Janssen and Koene, 2002). In this system, ionexchange media is incorporated into the electrodialysisstack, forming an integrated membrane  /  electrode sand-wich structure, in which the ion exchange resin grains areplaced in the central part of the system (Andrew, 1996;Manosso and Forbicini, 2009). The advantage of EIX overthe traditional ion-exchange is the use of electrons as theonly reagent, thus reducing the waste volumes. However,ion exchange membranes used in EIX are very costlywhich limit its extensive application. The e ffi ciency of EIX process is not satisfactory because of concentrationpolarization and electrode scaling (Konstantinos and Kon-stantinos, 2008).To overcome these problems, we proposed a new elec-trochemical ion exchange system (NEIXS) by introducingporous cylinder electrodes (PCF) as the electroosmot-ic unit. In new EIX system, anolyte and catholyte areselectively flow from PFC, thus avoiding the use of ion-exchange membranes. Polarity of the electrodes can beflexibly switched, thus eliminating the electrodes scalingfor long-time operation. The proposed system utilizeselectrochemical redox and ion-exchange simultaneouslyto obtain the neutralized electrolyzed oxidizing water,desalted water and a side-product of hydrogen. * Corresponding author. E-mail: hjx@djtu.edu.cn 1 Materials and methods 1.1 Titanic porous filter cylinder electrode and elec-troosmotic unit The properties of the porous filter cylinder are shown inTable 1.The electroosmotic unit was constructed with threeanodes and cathodes (area 0.0113 m 2 ) in hexagon withinan insulated polymethyl methacrylate shell. The distanceof anode and cathode is 25 mm. The electrolyzed oxidizingwater (containing gases) and electrolyzed reducing waterwere pressed to flow out of the anode and cathode,respectively (Fig. 1). The strong basic anion exchangeresin grains were packed among the electrodes. The fluxof the simulated wastewater is 7.5 L  /  hr. The voltage of the NEIXS is controlled at 25 V. The ratio of electrolyzedoxidizing water and electrolyzed reducing water is 1:1.COD was determined by bichromate method. Concentra-tion of Cl − was determined by titration with silver nitratesolution. A power supply (WSA-H 100V  /  30A, ShenzhenLeteac Technology Co., Ltd., China.) was used to maintainconstant DC voltage. Conductivities were measured by aconductometer (DDS-IIA, Shanghai San-xin Instrumen-tation Inc., China). PH of water was measured by anacidimeter (DELTA320, Meltler-Toledo Instruments Co.,Ltd., China). Temperature was held at room temperatureduring all experiments.  Supplement A novel electrochemical ion exchange system and its application in water treatment S15 Table 1  Properties of the porous filter cylinderSpeciality Dimension Porous Porosity Penetrability of Compression Most pressure(mm) dimension ( µ m) factor (%) gas (L  /  (cm 2 · min · Pa)) resistance (MPa) di ff  erence (MPa)Value  Φ 12 × 100 30–50 28–50 0.02–20 0.5–1.5 0.6 H+O 2 ←H 2 O OutflowOutflow→Na +  InflowOCl –  CO 2 ←Contaminant←Cl – →Na +   Na + →H 2 O→ H 2  OH –  Cl 2 ←Cl –  ←Cl – ←Cl –  Na + →    A  n  o   d  e      N   A  -   F  o  r  m   D   1   1   3      D   W   C  a   t   h  o   d  e    H  -   F  o  r  m   D   1   1   3      N   E   O   W Fig. 1  Schematic representation of the new electrochemical ion ex-change system. NEOW: neutralized electrolyzed oxidizing water; DW:desalted water. 1.2 Cationexchangetreatmentofelectrolyzedoxidizingand electrolyzed reducing water The electrolyzed oxidizing water out of anode waspumped into Na-form D113 bed (Table 2). The elec-trolyzed reducing water out of cathode was pumped intoH-form D113 bed. 2 Results and discussion 2.1 Treatment of the simulated wastewater The properties of water samples, including the feed,electrolyzed oxidizing water, electrolyzed reducing waterand the desalted water are shown in Table 3. The removalpercentage of total dissolved solid for the desalted water is83% and the removal percentage of COD for the desaltedwater is 92%. This result demonstrates that the novel EIXcan remove contaminants e ff  ectively without chemicalreagents.Figure 2 shows pH variation for neutralized electrolyzedoxidizing water, desalted water from NEIXS versus time.It can be seen that pH of neutralized electrolyzed oxidizingwater gradually decreased, while pH of desalted watergradually increased with time. The change of pH canprovide information about ion exchanger transformingdegree for switching polarity operation periodically.Figure 3 shows bacteria concentration in the feed anddesalted water samples. It can be observed that there aregroups of bacteria in the feed sample. When water passesthrough the electrode, the bacteria can be perished bydirectly touching the electrodes. As a result, no bacteriaexist in culture dish. 2.2 Mechanism of ions migration and COD removal The strong base anion exchange resins placed betweenanode and cathode have played an important role forgathering anions, adjusting ions migration and being assupporting electrolyte. There are three routes for anionsmigration: (1) ions migrate alternatively through solutionor ion-exchange resins, (2) ions migrate through ion-exchange resin grains, (3) ions migrate in solution (Yeonet al., 2003). However, there is only one route for cationsmigration, that is, through solution. Furthermore, the di ff  u-sion coe ffi cient for ions migration in ion-exchange resinsis much higher than that in solution. As a result, theamount of anions in anode a ffi nity is much higher than thecations in cathode a ffi nity. Chlorine ions thus gathered inanode district and formed concentrated chlorine water. Therelevant reactions are shown as follows:2Cl − − 2e − −→  Cl 2  (1)H 2 O + Cl 2  −→  H + + Cl − + HClO (2)H 2 O − 2e − −→  H + +  12O 2  (3)Organic matter - ne  −→  Intermediate + CO 2  (4)The organic substances around the anode were oxidizeddirectly or indirectly into carbon dioxide or intermediate.The hydroxide ions were concentrated and passed throughthefiltercylindercathode.Hydrogenformedbywaterelec-trolysis penetrated into the inner part of PCF by the forceof electric fields and flow fields. In this case, concentration Table 2  Properties of D113 weak acid cation exchangerGroup Exchange capacity Diameter Water Density Expansibility Upper limit of pH(mmol  /  mL) (mm) content (%) (g  /  mL) (%) temperature (°C)–COO −  10 0.35–0.55 45–52 1.15–1.20 ( H → Ca) 20–30 100 5–14 Table 3  Properties of the feed and the electrolyzed oxidizing and electrolyzed reducing waterCl − concentration pH Conductivity COD(mg  /  L) ( µ S  /  cm) (mg  /  L)Simulated wastewater 689 7.28 2100 426Electrolyzed oxidizing water 2899.10 2.24Electrolyzed reducing water 120.00 12.36 4500Desalted water 4.16 350 32.6  S16 Journal of Environmental Sciences 2011, 23(Supplement) S14–S17  /  Yansheng Li et al. Vol. 23 0 5 10 15 20 25 30 35 40 45 50 55 60 651234567   p   H Time (min)0 10 20 30 40 50 602004006008001000120014001600180020002200 Conductivity pHTime (min)    C  o  n   d  u  c   t   i  v   i   t  y   (  µ   S   /  c  m   ) 23456789   p   H DW NEOW Fig. 2  pH of NEOW, DW versus time by the new electrochemical ion exchange system (NEIXS).  Feed DW  Fig. 3  Comparison of bacteria concentration in the feed and the desalted water.  +eContaminantCO 2  Na +  Na + HOH - -eH 2 OO 2 H+-eCl - Cl 2  Na +  Na +  Na +  Na + H 2 OOH-H 2  H 2 OH - OH-H 2   H 2 OH - H 2 OO 2 H + O 2 O 2   O 2 H + H + H + Cl - Cl - Cl - Cl 2 Cl 2 ClCl 2 CO 2 COCO 2 COContaminantContaminantContaminantContaminantCl - H 2 OH 2 O H 2 O H 2 OH 2 O H 2 OH 2 O Fig. 4  Mechanisms of ions migration process. and ohm resistance can be reduced remarkably. Hydrogenevolution from water electrolysis is shown as follows:2H 2 O + Na + + 2e − −→  H 2  + Na + + 2OH – (5)H + + 2e – −→  H 2  (6)Figure 4 shows the ions migration from bulk solution tothe inner part of PCF during the electroosmosis process.The pH of NEOW and DW can be controlled by adjustingoperation time. The gases generated by electrode reactionswere brought into the inner part of PCF with water flow,avoiding concentration polarization and decreasing ohmresistance.Asaresult,currente ffi ciencycanbesignificant-ly improved. 2.3 Mechanism of ion exchange The neutralization reaction between the electrolyzedreducing water and the H-form D113 resin is as follows:R-COOH + Na + + OH − −→  R-COONa + H 2 O (7)Na + was adsorbed on ion-exchange resin, realizing todesalt from the feeds. The Na-form D113 ion-exchangeresin was regenerated into H-form D113 with the elec-  Supplement A novel electrochemical ion exchange system and its application in water treatment S17 Feed DW  NEOW 50% H 2 O 50% H 2 O17% NaCl 8% COD83% NaCl 92% COD Fig. 5  Schematic representation of material equilibrium. trolyzed oxidizing water for reusing. The reaction is shownas follows:R-COONa + H + −→  R-COOH + Na + (8)Since the electrodes are completely uniform and no ion-exchange membrance was used in this system, this NEIXScan be operated by switching anodes and cathodes flexibly,eliminating the scaling on the surface of electrodes. 2.4 Material equilibrium The material equilibrium of this NEIXS was calculatedaccording to the ratio of electrolyzed oxidizing waterand electrolyzed reducing water as shown in Fig. 5. Asmentioned in Section 2.2, NaCl were concentrated inanode district to reaching 83% (mass ratio) with the help of strong base ion-exchange resin and electric fields. Organiccontaminants were oxidized in anode with COD removalpercentage of 92%. 3 Conclusion and expectation We proposed a NEIXS with porous cylinder electrodesinstead of 2-dimensional plane electrodes in conventionalEIX system. This system can be used for desalinationwithout the costly ion-exchange membrane and extrachemical reagents. The mechanism of desalination is theingenious combination of the electrolyzed reducing waterand neutralization reaction with H-form D113. Since theelectrodes are completely uniform and no ion-exchangemembrane was used in this system, it can be operatedby switching anodes and cathodes flexibly for the elim-inating the scaling from the surface of electrodes. Thestrong base ion-exchange resin grains placed among theanode and cathode have played as supporting electrolyte,which is capable for the treatment of wastewater with lowconductivity. The concentrated anolyte containing chlorineis e ff  ective for disinfection and contaminants removal. References Andrew T, 1996. Electrochemical ion exchange.  Membane Tech-nology , 75: 6–9.Janssen L J, Koene L, 2002. The role of electrochemistry andelectrochemical technology in environmental protection. Chemical Engineering Journal , 85: 137–146.Konstantinos D, Konstantinos O, 2008. Continuous capacitivedeionization-electrodialysis reversal through electrostaticshielding for desalination and deionization of water.  Elec-trochimica Acta , 53: 7123–7130.ManossoHC,ForbiciniCALGdeO,2009.Treatmentofwastescontaining cesium ions by electrochemical ion-exchange(EIX).  Journal of Radioanalytical and Nuclear Chemistry ,279(2): 417–422.Yeon K H, Seong J H, Rengaraj S, Moon S H, 2003. Electro-chemical characterization of ion-exchange resin beds andremoval of cobalt by electrodeionization for high purity wa-ter production.  Separation Science and Technology , 38(2):443–462.
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