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Sci.Int.(Lahore),25(1),57-61,2013

ISSN 1013-5316; CODEN: SINTE

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ELECTRICITY GENERATION FROM SEWAGE SLUDGE USING ENVIRONMENT-FRIENDLY DOUBLE CHAMBER MICROBIAL FUEL CELL Shaheen Aziz, Abdul Rehman Memon*, Syed Feroz Shah, Suhail A. Soomro, Anand Parkash, Abdul Sattar. Jatoi * Corresponding author e-mail: [email protected] Department of Chemical Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan

ABSTRACT: The recurring increase in the energy demand, coupled with the over- consumption of nonrenewable sources of energy has led to the exploration and use of renewable and cost effective energy resources. In this context, present study deals with the utilization of sewage sludge, which contains high levels of readily biodegradable organics and is also one of the major sources of environmental pollution, as substrate in a microbial fuel cell (MFC). Saccharomyces cerverciae sp. as a mediator and potassium ferricyanide as an oxidizing agent were used for the conversion of sewage organics into electric current and power generation using lab-scale double chamber MFC. The cells were connected in series with the anodic and cathodic solutions being introduced in batch and continuous modes. A maximum voltage of 830mV (3.3 mA) was obtained per liter of the sludge with the anode in batch- feed and cathode in continuous modes of operation under optimum conditions of the operating parameters of oxygen flow rate, pH and substrate concentration. Keywords: Electrical Energy, Microbial fuel cell, Saccharomyce cerevisiae sp., Sewage sludge INTRODUCTION The increased energy consumption along with unbalanced energy management the world over has called for serious attention to the use of renewable energy sources, of which reutilization of the waste materials is at the forefront nowadays [1-3]. Due to this renewed interest in the business of renewable energy sources and their utilization, fuel cell technology has gained much importance. This is reflected from the current amount of research done in this regard, by which many microorganisms have been tested to be promising agents for the process of electricity generation. The concept of using microorganism as catalyst in fuel cell technology was first explored in the 1970s [4, 5]. When microbes respire, the electrons received from sugars are denoted to metals or other elements. This metabolic activity of microorganisms can be used to retrieve electrons which when coupled in a circuit, can give electric current [6-11]. Producing electricity from organic matter using microbial fuel cells (MFCs) is a concept that dates back to 100 years [4]. MFC has great potential as a wastewater treatment process since organic contaminants are converted into electricity with the concomitant reduction of the excess sludge production [12]. The growing concern of scientists and environmentalists to generate alternative sources of energy that are sustainable, eco-friendly and economical opens the way for operation of MFCs. An MFC is a bio battery and environmentally safe process capable of harvesting electricity using various species of microbes, which are generally metal reducing [13-18]. MFCs are capable of converting energy, available as a bio-convertible substrate, directly into electricity with the help of bacteria [19]. These bacteria switch from natural electron acceptor, such as oxygen or nitrogen, to an insoluble acceptor, such as MFC anode. This transfer can either occur by membraneassociated components or by soluble electron shuttles. The electrons then flow through a resistor to a cathode, at which

the electron acceptor is reduced. In contrast to anaerobic digestion, an MFC creates electrical current and releases an off-gas containing mainly carbon dioxide instead of an energy-rich gas such as methane or hydrogen [20]. Industrial or domestic wastewaters are generally regarded as conducive substrates to the phenomenon of bioconversion in a bioreactor, whereby highly concentrated organic wastewaters contain higher chemical energy per unit volume as compared to that present in lowly concentrated organic wastewaters. Therefore, highly concentrated organic wastewaters like sewage sludge are deemed as a suitable fuel for microbial fuel cell operation in terms of electricity production [21]. In addition, domestic or municipal wastewater (sewage), which contains multitude of organic compounds, could be used as the substrate in MFCs without actively feeding air into a cathode chamber [22, 23]. Most of the current research performed on MFCs is concerned with increasing the power density of the system with respect to peripheral anode surface area. Whereas, substantial amount of research should be devoted to determining the effects of various fuel cell components on voltage output like oxygen flow rate, substrate concentration and pH. Towards this direction, the aim of this research is to harness the inner contents of waste material such as sewage sludge utilizing environment-friendly technique of MFCs in relation to its operational parameters as a means of renewable energy production in the form of electricity generation. MATERIALS AND METHODS Microorganisms Pure strain of Saccharomyce Cerevisiae was used as a biocatalyst [24]. Like yeasts, this type of strain is also known to exhibit high coulomb efficiency and is capable of transferring the majority of electrons gained from the carbon sources such as acetate or glucose to the electrode [25, 26]. This implied towards viability of the selected strain in terms

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of higher electron transfer efficiency given the favorable conditions of operational parameters in the MFC. This is regardless of the energy transfer phenomenon during the course of microbial function, which is dependent on the product of current and potential of the system. Fabrication and Operation of double chamber MFC Double chamber MFC, as shown in Fig.1, contains two chambers: one is anode and the other is cathode chamber. The two chambers of the MFC are represented by two plastic bottles with height of 8″ and a diameter of 3″. A hole was made on to the bottles so that a PVC pipe could be inserted to connect the two bottles. In addition, a small hole was also drilled in the lid so that copper wire could be entered. The cell was run in both batch and continuous modes. Methylene blue was added as a mediator in the anodic chamber. Equal volumes of culture broth, sewage sludge and nutrients were added in the MFC. Salt Bridge Salt bridge was constructed with the following items: 10 g of agar (at concentration of 100 g/L), 10 g NaCl and 200 ml of distilled water (DW), which was heated in a beaker at maximum temperature of 100°C followed by the addition of agar in the boiling water. Salt was added to the mixture while it was still hot and the mixture was continuously stirred. Then the mixture was poured via the PVC pipe while it was warm before it began to thicken. Afterwards, the agar/salt mixture was allowed to cool to the room temperature in order to solidify. The PVC pipe was placed to one of the holes of the two bottles and was then connected to the other bottle with the connection being secured via the application of epoxy. Anode and Cathode Two copper rods were taken that served as the electrodes of the MFC. These copper rods had a length of 6″ each. In assembling the circuit, the material used was: copper wires, two copper rods, four alligator clips, and two multitesters. The black copper wire was for the anode and the red copper wire was for the cathode. The black wire was inserted into the hole in one bottle lid and was connected to a copper rod while the other end was connected to a multitester using an alligator clip. The same procedure was applied to the red wire. The lids were sealed with epoxy Assembling the Fuel Cell The sample of sewage sludge was put to the cathode bottle and the bottle lid was joined with the copper electrode. On the cathode chamber, 400 ml of H2SO4 was prepared in a beaker and was transferred to the cathode bottle. The copper electrode connected to the lid was inserted. As the microbes in the negative chamber digest the cellulose, electrons are released and protons are created, which move into the positive (cathode) chamber from the negative (anode) chamber through a salt bridge. The electrical current is created by this movement of protons, along with the movement of electrons across the resistor and wire. The multitester was set to voltmeter mode to measure the output of the fuel cell. Electrical parameters and measurements Electrical power, which was produced during experiments, was measured with a digital multitester connected to the line

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between the anode and cathode in the open and closed circuit configuration. The corresponding voltages and power currents across the resistor terminals were recorded with the timer and the electrical outputs were estimated. All the readings were recorded after every 20 min for three times for a maximum of 200 min and presented as the mean results with a hint of standard deviation. All the experiments were performed at room temperature.

Fig. 1: Double Chamber Microbial Fuel Cell. RESULTS AND DISCUSSION All the experiments were carried out in double chamber microbial fuel cell (MFC). The power output from MFC was controlled by a number of factors, apart from the efficiency of electron transfer from micro organisms to electrode surface area, resistance of the chamber. The anodic chamber solution was in batch-fed mode and the cathode solution was in continuous mode of operation. For the generation of electricity, three liters of sewage sludge were fed into the MFC, which yielded a total voltage of 2.5 V (830 mV per liter) after 200 minutes of run time. Fig. 2 clearly demonstrates that the two-chamber MFC can generate electricity from sewage sludge. The maximum voltage was achieved after 140 min of operation whereas afterwards it showed gradual decrease during the next 60 min. This decline in voltage production after 140 min of operation probably occurred due to the substrate limitation. This implied that maximum current generation was related to the amount of substrate added meaning that the substrate concentration determines the amount of electricity generation from it [20]. These results also suggested that the selected strain of microorganism was able to readily convert the organics present in the sewage sludge at their optimum efficiency resulting in the transfer of maximum no. of electrons leading to concomitant voltage generation.

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the ionic form of the active sites, which would further change the enzymatic activity leading to the variation in the reaction rate as well [25]. The results also suggested that at pH 6 and below, electrochemical and cellulosic activities would likely be lower when compared to the results obtained at higher pH. This might be due to the denaturation of celluloses, proteins or active sites under acidic conditions. This finding was in agreement with that reported by Z. He et al. who observed that neutral pH was suitable for cellulose degraders, as acidic conditions tend to inhibit the growth of the majority of cellulose degrading yeasts [14].

Fig. 2: Voltage generation from sewage sludge versus time. Factors affecting electricity generation Effect of oxygen flow rate on electricity generation Effect of oxygen flow rate on power production during the running of MFC was studied using different oxygen flow rates from 20 to 200 ml/min yielding in power production between 220 and 995 mV per litre of the sewage treatment, respectively (Fig 3). These results suggested that power production increased as the air flow rate was increased and reached the maximum of around 1V at oxygen flow rate of 150 ml/min before showing decline afterwards. This indicates that at the higher air flow rate, power generation capacity of MFC was substantially reduced due to the higher rate of oxygen in the air diffused down to the vicinity of anode, which probably disturbed the anaerobic microbes living on the surface of the anode.

Fig. 3: Effect of oxygen flow rate on power generation. Effect of pH on electricity generation pH is a major factor affecting the activity of most prokaryotes. At optimum PH, microbes perform biological activities of growth and metabolism at the maximum rate. Fig. 4 highlights the point that the highest yield of power was obtained at pH 8.5, when perhaps the enzymes secreted by the microbes would have been in a conducive form of ionic groups on their active sites to function properly. Reportedly, variation in the pH would result in changes in

Fig. 4: Influence of pH on power generation. Effect of substrate concentration on electricity generation Power production was observed to increase with the increase in the substrate concentration (Fig. 5). Starting from about 10% concentration of the substrate, the power obtained at this substrate concentration was 0.725V. At the substrate concentration of 70% power generation was increased by 2.5V. Further increases in the concentration up to 100 % resulted in the decrease in power production by more than 100% when it reached the value of 1V. This was probably due to the reduction in the activity of the enzymes owing to various factors such as pH. This also indicates that higher concentration of the substrate could actually affect the anode performance significantly resulting in simultaneous lesser power production.

Fig. 5: Effect of substrate concentration on power generation.

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CONCLUSIONS Double chamber microbial fuel cell (MFC) using Saccharomyce cerevisiae was tested for its performance and process optimization. With the anode maintained in batchfed mode and cathode chamber maintained at continuous mode, maximum voltage of 830mV (3.3 mA) was obtained per litre of sewage processed. This meant that, overall, MFC operation yielded in an open-circuit voltage of 2.5V. Our results have indicated towards the specificity in mediatormicroorganism combination and the importance of developing a dual chamber MFC in this regard. Further work is suggested for improvements in MFC performance with respect to varying operational conditions and MFC capability to handle waste discharges with higher organic loadings. ACKNOWLEDGEMENTS The authors wish to express their sincere thanks for the lab facilities provided for this work in the Department of Chemical Engineering Mehran University of Engineering & Technology, Jamshoro. REFERENCES [1] Chang I. S., Kim B. H., Lovitt R. W. and J. S. Bang, Effect of CO partial pressure on cell-recycled continuous CO fermentation by Eubacterium limosum KIST612, Process Biochemistry, 37: 411(2001). [2] Chang I. S., Jang J. K., Gil G. C., Kim M., Kim H. J., Cho B. W. and B. H. Kim, Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor, Biosensors and Bioelectronics, 19: 607–613(2004). [3] Chang I. S, Moon H., Jang J. K. and B. H. Kim, Improvement of a microbial fuel cell performance as a BOD sensor using respiratory inhibitors, Biosensors and Bioelectronics, 20: 1856-1859(2005). [4] Cheng X., Shi Z., Glass N., Zhang L., Zhang J., Song D., Liu Z-S, Wang H. and J. Shen, A review of PEM hydrogen fuel cell contamination: impacts, mechanisms, and mitigation, Journal of Power Sources, 305: 1280–1283(2004). [5] Gong M., Liu X., Trembly J. and C. Johnson, Sulfurtolerant anode materials for solid oxide fuel cell application, Journal of Power Sources, 168: 289– 298(2007). [6] Kim I. S., Chae K-J, Choi M-J and W. Verstraete, Microbial fuel cells: recent advances, bacterial communities and application beyond electricity generation, Environmental Engineering Research, 13 (2): 51–65(2008). [7] Kim J. R., Min B. and B. E. Logan, Evaluation of procedures to acclimate a microbial fuel cell for electricity generation, Applied Microbiology Biotechnology, 68: 23–30(2005). [8] Lee J., Phung N. T., Chang I. S., Kim B. H. and H. C. Sung, Use of acetate for enrichment of electrochemically active microorganisms and their 16S rDNA analyses, FEMS Microbiology Letters, 223: 185–191(2003).

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[22] Sung T. O., Jung R. K., Giuliano C. P., Tae H. L., Changwon K. and W. T. Sloan, Sustainable wastewater treatment: How might microbial fuel cells contribute, Biotechnology Advances, 28: 871–881(2010). [23] Zhuwei D., Haoran L. and Tingyue G., A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy, Biotechnology Advances, 25: 464–482(2007). [24] Zhao F., Harnisch F. and U. Schroder, Application of pyrolyzed iron (II) phthalocyanine and CoTMPP based oxygen reduction catalysts as cathode materials in microbial fuel cells. Biotechnology Letters, 30: 1771– 1776(2006).

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