Seawater Desalination Using Microbial Desalination Cell Based on Bio-Catalytic Devices Modication.

Microbial desalination cell (MDC) built on bio-catalytic devices modication has been studied for sea water desalination using Saccharomyces cerevisiae as biocatalyst. Here we focussed the modication of anode and this study has been conrmed that bio-catalytic devices maintenance could contribute to the long-term MDC perform during desalination process. The goal of this study is to provide and develop a sea water desalination system without requiring an energy support by applying modication of anode as electron acceptor, and the different potential charges that occur between anode and cathode can plays as driving force for electro dialysis of sea water desalination. Several types of bio-catalytic devices modication have been conducted, i.e. by immobilization of mediator, immobilization of biocatalyst or a combination of both. The optimization of each device has been characterized by cyclic voltammetry, Chronoamperometry, and applied in Microbial fuel cell prior observed in MDC. The concentrations of ion salt migration have been determined by Ion Exchange Chromatography. The proles of surface device have been detected by Scanning electron microscope and Energy Dispersive X-ray spectroscopy. Results shows that the modication of anode could be a promising method for bioelectricity generation delivered from MDC which as simultaneously produce an electricity and sea water desalination and provide a green chemistry technology.


Introduction
As a newly-developed technology, Microbial desalination cell (MDC) is an electricity energy production system and assimilated with Microbial Fuel Cell (MFC) and electrodialysis process. Recently, owing to environmental approachable and free energy requirement create MDC received extensive attention for waste water treatment and desalination. In the continuation of their perform, MDC could be used as stand-alone process or can be shared with other desalination process such as electrodialysis or reverse osmosis (RO) [1]. As mention in previous, that MDC technology is an extension of MFC where as shown in Fig. 1a, the MFC unit is consist of anode, cathode, and each chamber was separated with cationselective membrane, and also the external wire. Meanwhile, the MDC unit ( Fig. 1b) has adapted with MFC as well, the present of anode and cathode chamber is require and there is the addition of desalination chamber as known as dilute and concentrate chamber, respectively. The MDC con guration, the desalination chamber put in the middle designed by inserting cation-exchange membrane (CEM) and anion-exchange membrane (AEM) on either side [2][3][4][5]. The aerobic and anaerobic conditions have been conserved, in anode and cathode chamber, respectively. In our last work, MFC based Saccharomyces cerevisiae as known as bakery's yeast has been delivered and the electron transfer has facilitated by the present of mediator as seen in Fig 1a. Neutral red was appropriated as redox mediator for migration of electron to the anode surface [6][7]. However, some MFCs operate with or without a mediator, the activity of microbes was oxidizing of organic matter realizing protons and electrons [8][9]. In direct electron transfer the available bacteria are proliferated and produce a thick cell aggregate in anode surface which called bio lm [8]- [11]. As mentioned, in MDC construction, the anode plays and responsible for organic degradation route and deliver an electricity generation, cathode chamber nalizes the electrical loop, meanwhile the salt removal from sea water has been held liable by the middle chamber [12].
A simple of desalination process in MDC occur and initiation as follow: the organic mechanism has been done in anode chamber as product of the bacteria activity oxidize the organic matter. CO 2 and proton loosed into anolyte, then the electron streams into the cathode through an external circuit and a current across the cell is recognized. Meanwhile in cathode chamber, the external electron acceptor and oxygen in catholyte consumes these electrons to reduction process and produce a water [13][14]. This situation causes a potential gradient transversely the anode and cathode chamber and in direction to preserve electro-neutrality. In the meantime, the anion such as chloride ion migrate from dilute chamber contain of seawater across the AEM into concentrate chamber and sodium ion ow across CEM to the cathode chamber. This route known as desalination and be able to eliminate more than 99% of the salt from saline water and at the equal time harvest more energy and does not requiring an external energy supply because they can operate the system use they own energy [4,[15][16].
During perform, the desalination rate (DR) is one of the most essential parameters of the MDC action, and signi cantly dependent on the salt concentration of the seawater. Normally, MDC is well considered to be proper for desalinating highly concentrated saltwater. The higher salt concentration would cause reduction of the ohmic resistance and resulting in a high current density across the circuit and upgrade the DR value [17]. Besides that, the salt concentration in the dilute chamber ideally should be higher than the electrolyte in concentrate chamber is due to the lower concentration could effect to the decreasing of DR value as dialysis happened by the reverse concentration gradient between concentrate and dilute chamber which contain an electrolyte solution [17][18].
However, there also some great opportunities that must be pointed out for further expansion, despite the abundant interest and development in MDC technology. The possibility enhancement of MDC perform should be done and exploit more. First, compared with the conventional desalination technology the low rate of desalination process of MDC should be maintained. This condition has been con rmed that related to the limitation of current density delivered from bio-anode or desalinating process has been occurred in low-salinity water [14]. Second, the cost operational of MDC manufacturing is still high and is related to the material cost such as electrode, catalyst or membrane. The waste water treatment and desalination application generated from MDC should be well addressed. As mentioned, the waste water treatment and desalination is the main point and also give a bene t for MDC technology. With appropriate assessment of MDC both of waste water treatment and saline water desalination could be delivered from MDC. In fact, currently the scaling-up of MDC have been demonstrated and resulted a good application [19]. However, the construction and operation associated with the bio-anode performance is require to investigated more.
Recently, MDC has been advanced as a low-energy desalination technology. In the past century, the technology of MDC has been developed signi cantly is due to their capability providing the sustainability of fresh water through salt water desalination. A new desalination technology as known as MDC has successfully demonstrated that saline water could be desalinated without the present of energy supply.
Moreover, this process could also simultaneously integrated with waste water treatment and energy production [3,[20][21]. During desalination process, ion salt will have removed from saline water through conductive solution in concentrate chamber and this situation will cause the salinity increases in the concentrate and cathode chambers, respectively. While this addition of ion is generally acceptable for waste water treatment and supports with the conductivity conditioning [22]. In our con guration study, yeast has been worked as biocatalyst for provide the present of electron from its activities in organic degradation. This work has been motivated that some microorganisms i.e direct electron transfer have been observed, however the possibility of such new method using yeast as biocatalyst for MDC application has never been demonstrated. A glucose solution has been added during MDC perform. Meanwhile in cathode solution a ferricyanide has been selected as catholythe as observed in previous study [7]. The most usually selected as catholyte next to oxygen is ferricyanide or hexacyanoferrate (III) which value of standard potential is 0.361V/NHE. the advantages by using them are they have greatly soluble in water and does not needed a costly metal on cathode like Pt. Results con rmed that test with ferricyanide delivered greater power generation than applying with oxygen. A little polarization of the cathode has been responsible for this reason so that cathode potential reached is relatively close to that calculated for standard condition [23][24].
Beside anode, cathode plays an important element also in MDC. The cathode has a prodigious in uence on the electricity typical generation. Some studies has been focused in the nature and type of the electrode and the catalyst on the electrode [25], [26]. The designated of cathode material is one of the critical factor for biofuel cell includes MDC. The oxygen reduction process normally needs a fourelectrons transfer, but this situation may not be reached. It also probable that another molecule could be conducted as hydrogen peroxide production and this reaction only require two-electron transfer reaction. The present of H 2 O 2 is unexpected and causes a problem, is due to their strong oxidizer characterization.
They could damage the surface of membrane or cathode itself. However, they could also act as disinfectant for maintenance the cathode surface or to prevent the bio lm formation.
As mention above, the application of MDC as a new approach for desalination have been conducted both in reactor designs or operational conditions. Several patterns of MDC, from two-chamber up ow tubular to three-chamber or multi-chamber have been investigated and included the system performance [14,20,[27][28]. The MDC performance can also be enhanced using multiple pair of ion-exchange membranes (IEMs), placed in between the anode and chatode chambers. This condition has been done on the grounds that the charge transfer e ciency would improve and may impact to signi cantly enlargement the quantity of salt ion removal from saline water [29]. In the other hand, the utilization of some microorganisms in MDC have been observed [30]. In previous work, the use of yeast as biocatalyst has been studied and results con rmed that it could effect to MFC performs [31][32][33], but the wider application for MDC is require to be observed more.
With this perspective in mind in order to improve the electricity generation during MDC process, we propose surface modi cation. Anode modi cation has been done by biocatalyst-mediator immobilization and electropolymerization of NR at the surface of anode [6,7]. Previous study of biocatalyst immobilization reported that as a promising method and new strategy for enhancement longer working lifetime than free cell [34]. Moreover, this situation can be adapted in MDC operation. Cell immobilization can be categorized refers to the technique delivered, such as physical entrapment within porous matrix, encapsulation or chemical-cross linking attachment [35] The principle of immobilization entrapped method is based on the cell localization within a polymer matrix or membrane and this method is commonly and preferable used in cell immobilization. Several advantages have been obtained from this method such as easy to operate, has a great loading capacity and decreased cell leakage [36]. In addition, this method could be applied in wide variety of polymer material including synthetic and natural polymers. In our work, a natural polymer i.e calcium alginate has been chosen is due to the mostly used for cell immobilization and has good stability [37][38][39]. For successfully immobilization, the polymer support must be conductive to allow the viability of cell as well as have a good permeability to permit of oxygen transport, supply of nutrient, and su cient diffusion. Nevertheless, by applying physicochemical immobilization between mediator and cell as simultaneously is suitable to overcome a problem, because the present of mediator in solution can make an environmental problem if processed without proper treatment. Besides for sustainable green energy production, the enlargement of system operational with electron carrier powerfully immobilized at biodevice is being desirable. Mediator immobilization has been conducted using a several procedures, such as direct covalent attachment through the formation of lm deposited electrochemically on the surface of electrode [40], mediator electropolymerization of the electrode surface [41,42] or just only adding and mixing into carbon pasta. The advantages of this technique are has large catalytic response and longterm perform stability [42].
Meanwhile, Poly-Neutral Red (PNR) has been synthesized and characterized electrochemically as redox polymer to provide electron transfer in biosensor [6,[43][44][45]. The formation of PNR has been carried out from electropolymerization procedure by allowing the monomer to be oxidizing for 20-30 cycles of polymerization on the electrode material. The resulting lm (PNR) will play as electrons carrier during MDC performance. Challenges for designing cost-e cient MDC systems can be addopted from experience gained from MFC based anode modi cation. Nowadays, the enlargement of MDC concept based desalination has been resulted but deployed yeast as biocatalyst concurrently with bio-catalytic devices modi cation is a new application. Yeast fuel cell has an attractive potential as a low cost desalination process with signi cant environmental pro t. Therefore, the challenge to employ yeast and anode modi cation should be investigated more to enhance the desalination perform and resulting a signi cant number of ion salt migration. The bio-catalytic devices modi cation have been foccused to development of anode modi cation. We have been demonstrated the potency of yeast and the effect of bio-catalytic devices modi cation for practical application of sea water desalination as a sustanable method for desalination.

Cell preparation
A slurry of yeast have been prepared refers to previously reported [32] and should be cultivated in 30 0 C for 24 h. It was composed of 2 g of dried yeast mixed with 1.8 g pepton (Sigma-Aldrich, France); 1.5 g dextrose (Sigma-Aldrich, France); 1 g malt extract (Sigma-Aldrich, France) and dissolved in 50 mL of phosphate buffer (PB) pH 7. The cells were centrifugated at 5000 rpm for 5 min, harvested then washed twice in PB pH 7. Re-suspended cell have been conducted in PB pH 7. Prior used, the cell have been activated at 40 0 C for 5 min and stored at 4 0 C as a storage temperature.

Bio-catalytic devices modi cation
Carbon felt (CF) (Alfa-Caesar, 7 cm x 1.5 cm x 0.5cm) and nickel (Alfa-Caesar, 7 cm x 1.5cm) have been selected as anode and cathode then connected externally by a copper wire. The electrodes were cleaned from trash material successively using 1 M HCl for 48 h, rinsed with ultra pure water. A mixture of 1:1 of ethanol-water solution has been used to soak the electrodes for a few minutes then followed by sonication in ultrapure water subsequently dried in the oven at 100 0 C for 15 min [32]. Meanwhile neutral red (NR) has been selected as redox mediator to facilitate the electron transport to anode.
A protocol of anode modi cation has been adopted based on our previous studies where the immobilization of yeast-mediator [7] and polymerization of neutral red (PNR) [6] have been conducted to create a several types of anode modi cation design. Na-Alginate (Sigma-Aldrich, Fraance) has been applied as polymer matrix in immobilization method. As seen in Fig 2, a three-kind of bio-catalytic devices modi cation have been deployed as anode and successfully showed an excellent bioelectrocatalytic activity and current generation. There were CF/Immob yeast-NR (yeast-NR entrapped in Na-alginate immobilized on CF); CF/PNR (PNR polymerized on CF); CF/PNR-Immob yeast (PNR layer covered by yeast entrapped in Na-alginate immobilized on CF), respectively. The third bio-device is combination from the rst and the second of modi cation method, as displayed in Figure 2a.
The electrochemical characterization has been controlled by chronoamperometric and tested in 0.1 M glucose (Sigma-Aldrich, France) using 0.3 V / SCE as potential applied where CF modi ed as working electrode (WE), SCE as reference electrode (RE) and platinum as counter electrode (CE). The observation of anode surface has been performed by Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray spectroscopy (EDX) from Hitachi S-4800 and Hitachi S-4500, respectively.

MDC construction and process.
A four-chambers of MDC have been designed, compose of anode, concentrate, dilute, and cathode chambers, with cation exchange membrane (CEM) placed next to anode, followed by anion exchange membrane (AEM) separating the concentrate and dilute chamber and CEM located close to cathode chamber. Each chamber has volume capasity of 80 mL. As a membrane, CEM and AEM have been prepared using CMX (CMI-7000) and AMX-SB (AMI-7001) (Tokuyama Soda-Japan) and diameter size of membrane was 3 cm. 0.1M glucose in PB pH 7 has made as the carbon source in the anode chamber, meanwhile concentrate and dilute chamber have been lled with 0.5 M KNO 3 (Sigma-Aldrich, France) and seawater, then 0.02 M K 3 Fe(CN) 6 (PF) (Sigma-Aldrich, France) in PB pH7 acts as electron acceptor in cathode chamber. Prior used, all membranes have treated by soaked in 0.1 M HNO 3 for 1 h then washed with ultrapure water. Bio-catalytic devices modi ed have been applied as anode, meanwhile nickel plate plays as cathode. Figure 2b explained the scheme design of MDC modi cation, the aim of this section is to observe the best con guration for MDC design. As preliminary, the MDC experimental has been set up refers to model 1, but here the arrangement of the concentrate and dilute chamber location has been changed and called as model 2. The composition of the solutions used consists of 0.1 M KNO3 and 0.1 M NaCl in concentrate and dilute chamber, respectively.
All desalination performs have been operated at ambient temperature (25+1 o C). Digital multimeter Volcraft (model VC 850) was employed to investigate the potential (E) generated and current was calculated according to the equation I =E/R with an external resistance xed at 1 kΩ. The monitoring of ion salt removal from dilute and concentrate chambers have been measured by ion exchange chromatography (DIONEX ICS 900 for cation and DIONEX ICS 1000 for anion). Meanwhile, the percentage of ion salt removal was calculated using Eq 1.
C and Co is concentration in mg.L -1 , where C is ion concentration at time measurement and Co is initial concentration.

The bio-catalytic devices modi cation characterization and its electrocatalytic activities.
The surface images of anode modi cation by immobilization of yeast within alginate polymer and PNR layer on the anode surface have been observed by SEM and EDX as displayed in Fig. 3.
Images found that there are several spherical shapes around 4 nm, spread homogenous within the alginate polymer lm and it was con rmed as yeast cells. The thickness of alginate polymer lm was varied from 4 to 16 nm and has a good roughness is due to the presence of yeast inside and ready to be used for electro-catalytic process. Fig 3c and 3d shows the morphology of the PNR lm deposited on the CF support refers from EDX spectrum. Results found that 5.04% of N has been contained in CF modi ed and it was con rmed that the PNR has been presented at the CF surface. The present of C and N atoms was completed expected since they come from NR and CF, meanwhile potassium and oxygen atoms from KNO 3 solution which used as the supported electrolyte solution during the synthesis of polymer and sodium could delivered from phosphate buffer as supporting pH solution.
The observation of current density delivered from bio-devices modi cation has been recorded and All the experiments result as seen in Fig 4. The chronoamperometry observation has been performed, electrodes were polarized at 0.3 V/SCE to ensure glucose oxidation. All surface modi cations have been tested as working electrode and Pt as counter electrode. Results repot that CF/PNR has the highest current density delivered compared with others. Meanwhile CF without modi cation has been examined also using 2 % of yeast and 10 mM NR in PB pH 6 solution. Fig 4 a reports that compared with conventional method, by employing surface modi cation through the formation of PNR layer gives the best performance delivered 64% of current density value against to CF/Y-NR in solution. While, CF/Immob Y-NR and CF/PNR-Immob have been resulted enhancement 43% and 35% of current density value compared with conventional method i.e anode without modi cation. Besides that, CF/Immob-Y without involving NR has been act as base line of measurement. All current density values generated have been monitored during 2 hours after a 30 minutes of stabilization time.
The next electro-catalytic observation was continued through MFC and dual-chambers of MFC have been prepared. All the surface modi cation electrodes have been applied as anode, there were CF/Immob Y-NR; CF/PNR; CF/PNR-Immob Y. However, a conventional MFC has been carried out also using yeast and NR in solution where CF without modi cation plays as anode. The power density produced from MFC has been recorded using digital multimeter voltcraft (VC 850) and 1 kΩ of load has been xed. Results con rmed that the utilization of PNR as surface modi cation method provides good effectiveness of MFC process during 10 days of observation as displayed in Fig. 4b. According to the results, PNR de nitely leads to a higher power density followed with CF/Immob Y-NR then CF/PNR-Immob Y if we compare the results with applying conventional MFC. In our case, after 10 days of experimental observation, the maximum power density delivered from CF/PNR was 5.02 + 0,25 W m -2 . It is di cult to compare this value with previous research that has been studied, because MFC operate under a large variety conditions such as temperature, pH, the availability of mediator, material electrode, size of reactor and time of operation. However, the maintenance of pH is important to provide the optimum operation conditions. In this present study, the measurement have been done at pH 7 as a good alternative to get high performance of MFC [32] Meanwhile, the scheme of electron transfers from glucose to the electrode has been explained in Fig. 4c. MFCs working with surface modi cation shows a good stability of current especially stable by using NR as mediator entrapped within surface of anode. During perform as anode in MFC, the biological activity of yeast within glucose oxidation has been facilitated by PNR. The PNR oxidized form captures electrons generated and PNR reduced form will directly transfer electron to anode. The recycling of NaDH to NAD + is important to keep the sustainability the glycolysis process in fermentation pathways. The use of redox mediator, substituting between oxidized state (PNR ox ) and reduced state (PNR red ) is obligatory in order to touch the electron transfer chain which is found at the mitochondria within cytoplasm [46].

Microbial desalination cell Characterization.
As preliminary work, the determination of the best con guration has been done using bio-devices non modi cation. The composition of each chamber compose of, 2% of yeast in 0.1 M glucose; 0.1 M KNO3; 0.1 M NaCl and 0.02 M PF as solution in anode, concentrate, dilute and cathode chambers, respectively.
The observation of current density has been recorded during 10 days delivered from each variation of con guration model design and results can be seen in Fig 5a.   Fig 5a illustrations that from model 2, the % transport of salt ion was lower than model 1. Refers to model 1, 31% of salt ion has successfully migrated from dilute to concentrate chamber, meanwhile 20% of NaCl have been removed from initial concentration. Clhas migrated from dilute to anode and passing AEM, in contrast Na + has moved to concentrate chamber after passing through CEM. Moreover, the measurement of pH on anolyte has been investigated also, the results was obtained the fact that the pH of anolyte has decreased from 6.88 as initially to 4.78. It was assumed that protons could not pass through the AEM membrane, so they remain in anode chamber. In the same time, the present of Clion will react with proton and produced HCl. The evolution of pH value on anolyte could affect the stability of biocatalyst performance, then for the next MDC appearance, model 2 is no longer recommended for used.
In addition, Fig 5b describes the diffusion process during MDC where the concentration gradient across to ion exchange membrane (IEM) can also induce ion diffusion processes. In our study, this phenomenon has been monitored refers to model 1 of MDC during 14 days operation and without the presence of yeast in anode. Results con rm that 9.3 % of Clion concentration has been decrease from dilute compartment. This can be interpreted that diffusion can contribute to the MDC process. Meanwhile, as seen in Fig 5c, the conductivity from dilute and concentrate chamber have been observed also and result mention that there has been an increase the conductivity value from concentrate chamber up to 9% from the initial 50.8 mS s -1 into 55.2 mS s -1 respectively. The concentration gradient across to IEM also induce the osmotic water transport. It was suggested that the osmotic water transport has been delivered from cathode and compartment chamber to dilute chamber. During diffusion process, 8.4 mL of water has been moved into dilute chamber for 14 days of MDC perform and resulting up to 9.3% of reduction of salinity (initially 3.5 g L -1 NaCl).
In the meantime, the electrodialysis process has been monitored using Chronopotentiometry by current employing of 50 µA, refers to the average value of the current generated from model 1 . Fig 5d. reports that Clions have been migrated from dilute to concentrate chamber during electrodialysis and produced 16% of ion transport during 14 days of electrodialysis process. However, it should be noted that the most important as driving force in MDC is the electric current generated by exoelectrogenic microbes.
3.3 Microbial desalination cell using bio-devices modi cation.
First MDC observation has been made by employing bio-devices non modi cation, 43% of NaCl transport and 73.3 mA m -2 of maximum current density have been obtained from 30 days of running. The observation of salt ion concentration has been measured from dilute chamber. The maintenance of all MDCs perform have been conducted by the addition of 1 g glucose in anolyte and refreshing of 0.02 M PF in catholyte every 13 th day of perform. As described in Fig 6d. initially the currents generated were an increase then gradually decreased until 13 th days, but after refreshment of anolyte and catholyte composition, the improvement of the current value does not appear until at the end of perform. It can be assumed that the lifetime of yeast has been reached.
Hereinafter, studies were performed by varying the bio-devices modi cation as anode to understand the effect of modi cation and its MDC behavior on desalination process during 30 days perform and bioelectricity generation. CF/Immob Y-NR has been tested in MDC and resulted the 83 mA m -2 of max current density and 55% of NaCl transport. As seen in Fig 6a at 11 th day of running, the current has been decrease slightly and at 20 th day, there has been declined until the end of process. Then, the CF/PNR electro-kinetic behavior has been investigated and delivered 92.5 of max current density and 61 % of NaCl transport. Compared with others, this value is highest both for current density and % of NaCl transport.
The reduction of electrochemical signal has been occurred at 12 th day and slightly becomes drop from 19 th day until completed the process as reported in Fig 6b. It was suggested that the presence of PNR layer has been successfully plays as redox mediator at surface of anode and provides the effectiveness of electron transport process.
Moreover, at the end of investigation the CF/PNR-Immob Y has been used as anode. According to the results in Fig 6c. The evolution of current density has been delivered 80.2 mA m -2 of maximum current density and 51.53% of NaCl transport. After 11 th day although glucose and PF have been added, it seems there was no signi cantly affect to the signal produced. It was assumed that the existence of alginate layer inhibits for glucose to penetrate within yeast alginate layer and this condition causes the slightly decrease current generated until MDC accomplishment. All experiments result can be seen in Fig 6d. Prior used, the composition of sea water has been determined and the large concentration was coming from sodium and chloride ( i.e 12.14 g L -1 and 22.85 g L -1 ). While the other ions such as nitrate (1.35 g L -1 ); nitrite (0.99 g L -1 ); sulfate (6.30 g L -1 ) potassium (2.05 g L -1 ); calcium (3.05 g L -1 ); magnesium (2.05 g L -1 ) and phosphate (0.98 g L -1 ). During MDC process, the electrical potential gradient was created by the electrode reactions, and commonly responsible for the salt ion migration. Besides that, the IEM junction potential and water transport could affect also to the desalination rate. In a four-chamber MDC, these factors work can play also as additional driving forces for desalination.
The current e ciency from this experiment has been measured refers to eq 2 [47].
The current e ciency (η i ) is the amount of ion divided by the amount of electrons transferred at the biodevices modi cation. Where ∆c is reduction of salt water concentration, V is the volume desalinated, N cp is the number of cell pairs and i is the current. All the current e ciency values are displayed in Table 1. However, the current e ciency is also dependent on the existence of mediator in anolyte, because the electron transport has been facilitated by mediator. Tabel 1 also describe the e ciency of bio-devices modi cation expressed per availability mass of mediator from each bio-devices. Table 1 explains that the highest e ciency value was obtained from CF/PNR followed with CF/ImmobY-NR and CF/PNR-Immob Y. It was assumed that the manifestation of PNR layer at the anode surface is more effective than the monomer (NR) entrapped in yeast immobilization layer. Hence, the thickness of the alginate layer can also be one of the obstacles in the process of entry of glucose into the surface of layer, where the electricity generated mostly dependent of glucose oxidation.
We can estimate the amount of PNR deposited on surface refers to Equation 3: where b is the number of electrons exchanged per mole involved in the redox couple of PNR (b=2); w (g) is the weight of PNR; F is Faraday constant (96.500 C) ; M is NR molecular weight ; and v represents the scan rate. According to equation 3, the amount of PNR is 14.2 µg cm -2 from 10.2 cm 2 of surface area.

Conclusion
Many challenges for designing cost-e cient MDC systems have been demonstrated by employing biodevices modi cation as anode in MDC, and that are just beginning to be developed. We have presented a simple method of bio-devices modi cation to be applied in MDC with simple design of construction.
Result founded that CF/PNR generated the highly signi cant performance shown by maximum of current e ciency, bio-devices e ciency, current density and also value of % NaCl transport. However, the ndings demonstrated in this present study are greatly substantial to be exploit more and for future challenges in industry application. However, MDC will have unique challenges for development compared to other systems and the integration of MFC based yeast into MDC has delivered a great opportunity for wider application.
Declarations lm electrodes, and application as sensors for hydrogen peroxide.   The observation of MDC performs: (A) Current density and % NaCl Transport produced from variation of MDC design; (B) % NaCl transport generated from diffusion process; (C) Conductivity value of dilute and concentrate chambers generated from diffusion process; (D) Cl-ion concentration delivered from electrodiaysis process.