Biotechnlogy - Microbial Fuel Cell - Lab Report Example

Third experiment 22/11/13-2/12/13 Plan Electri generation using the dual chambered MFCs in the presence of cation exchange membrane and fluorescent Pseudomonas trivialis as biocatalyst. Preparations: 22/11/13 Materials Synthetic wastewater, sucrose solution, LB broth was prepared and autoclaved in the first experiment except PSB buffer, which was prepared again, since it was finished during the second experiment. BUFFER PREPARATION FOR CATHODE CHAMBERS: It was prepared at PH: 7, concentration of 50 mM and volume of 2 litres. Based on sodium phosphate dibasic hepta-hydrate’s (HNa2O4P) molecular weight (268.07 g/mol) 16.298 g of this component was added to 5.395 g of sodium phosphate monobasic monohydrate with 137.99 g/mol molecular weight. Calculation: Sodium phosphate dibasic hepta-hydrate (HNa2O4P) 268.07 (mM) * 0.0608 M = 16.298 g Sodium phosphate monobasic monohydrate (H2NaO4P) 137.99 (mM) * 0.0391 M = 5.395 g After weighting the components, they were added into 2 litres of distilled water. All conditions, materials and also quantity of materials were kept the same as the first and second experiments except the type of microorganism, which in this case was Pseudomonas trivialis. Cultivation and activation of Pseudomonas trivialis 22/11/13 Pseudomonas trivialis was sub-cultured on LB media and incubated at 37 0C under an aerobic condition at 150 rpm (incubator). The bacterial culture were revived and grown over night, before transferring to the anode chambers. Design and set-up The MFCs used in this experiment were constructed by using double chamber as their anode and cathode compartments. Each two chambers were separated by CEM and assembled using external metal clips, two washers. Graphite plates were used as anode and cathode electrodes. The anode was placed in the centre of the anodic chamber and it was connected to the cathode via wire. An external resistance (1000Ω) was conducted to control the electron flow through the wire from anode to cathode chamber. Four double chamber MFCs were constructed, two for test MFCs and two for control MFCs. One of the control MFCs was control water and the other one was control open circuit voltage MFC. Carbon cloth and platinum clothed carbon cloth were applied on the anode and cathode as their electrodes, respectively. Anode chambers contained 180 ml of synthetic wastewater, 20 ml of Pseudomonas trivialis culture and 4ml of sucrose solution. The anode chambers were purged and deoxygenated with nitrogen gas. Cathode chambers were provided with 200 ml of PBS buffer and aerated with air. The MFCs were kept at 30 0C from 25/11/13 to 2/12/13. Progress and summary: Second experiment was done precisely. The results met my expectations. Third experiment was constructed. Materials were autoclaved and applied on the MFCs. The computer program was instructed in order to record the voltage. From last two experiments, I thoroughly analysed my mistakes, made conclusions and took lessons for my onward experiments. For example in the first experiment, the water MFC was contaminated, but from second experiment, the procedures were done accurately to avoid contamination. In order to do so, the syringe, which was used for sampling from four anodes, was rinsed with distilled water and dried before taking samples from each anode chamber. Also, the electrodes on the anode compartments were shaken every day to remove dead microorganisms, in order to improve the efficiency of voltage generation. However, samples had to be taken every day and kept in the fridge for GC Chromatography and COD test. GC had to be booked on the 2/12/13. Also, manual voltage reading had to be done on Thursday. Results: Voltage was recorded on the 29th/11/13. Digital multimeter and 20 different external resistances were exploited. Resistance (Ω) Voltage (mV) current (V/R) (mA) current density (I/area) (mA/m2) Power (V2/R) (mW) Power density (P/area) (mW/m2) test1 10 1.6 0.16 0.695652174 0.256 1.113043478 20 3.7 0.185 0.804347826 0.6845 2.976086957 50 7.8 0.156 0.67826087 1.2168 5.290434783 100 16.3 0.163 0.708695652 2.6569 11.55173913 200 34.9 0.1745 0.758695652 6.09005 26.47847826 500 69.7 0.1394 0.606086957 9.71618 42.24426087 700 96.7 0.138142857 0.600621118 13.35841429 58.08006211 1000 131 0.131 0.569565217 17.161 74.61304348 2000 221.5 0.11075 0.481521739 24.531125 106.6570652 4700 338 0.071914894 0.312673451 24.30723404 105.6836263 6800 387 0.056911765 0.247442455 22.02485294 95.76023018 10000 438 0.0438 0.190434783 19.1844 83.41043478 22000 518 0.023545455 0.102371542 12.19654545 53.0284585 47000 565 0.012021277 0.05226642 6.792021277 29.53052729 67000 594 0.008865672 0.038546398 5.266208955 22.89656067 100000 612 0.00612 0.026608696 3.74544 16.28452174 220000 627 0.00285 0.012391304 1.78695 7.769347826 470000 636 0.001353191 0.005883441 0.860629787 3.74186864 680000 639 0.000939706 0.004085678 0.600472059 2.610748082 1000000 641 0.000641 0.002786957 0.410881 1.78643913 Table1. Resistances (Ω) were applied to record voltage (mV), when Pseudomonas trivialis was grown on the anode on the Test 1 MFC. Followed, current density mA/m2) and power density were calculated based on generated voltage. The dimension of electrode on the anode on the test1 MFC was used to calculate power density (mW/m2) and current density (mA/m2): Width: 4.5 cm Length: 5.1 cm Area = 5.1 * 4.5 = 0.23 m2 Resistance (Ω) Voltage (mV) current (V/R) (mA) current density (I/area) (mA/m2) Power (V2/R) (mW) Power density (P/area) (mW/m2) 10 1.1 0.11 0.458333333 0.121 0.504166667 20 2.5 0.125 0.520833333 0.3125 1.302083333 50 5.5 0.11 0.458333333 0.605 2.520833333 100 11.7 0.117 0.4875 1.3689 5.70375 200 24.8 0.124 0.516666667 3.0752 12.81333333 500 50 0.1 0.416666667 5 20.83333333 700 70.4 0.100571429 0.419047619 7.080228571 29.50095238 1000 97.5 0.0975 0.40625 9.50625 39.609375 2000 179.7 0.08985 0.374375 16.146045 67.2751875 4700 286 0.060851064 0.253546099 17.40340426 72.5141844 6800 339 0.049852941 0.207720588 16.90014706 70.41727941 10000 393 0.0393 0.16375 15.4449 64.35375 22000 476 0.021636364 0.090151515 10.29890909 42.91212121 47000 528 0.011234043 0.046808511 5.931574468 24.71489362 67000 553 0.008253731 0.034390547 4.564313433 19.01797264 100000 571 0.00571 0.023791667 3.26041 13.58504167 220000 590 0.002681818 0.011174242 1.582272727 6.59280303 470000 601 0.001278723 0.005328014 0.768512766 3.202136525 680000 605 0.000889706 0.003707108 0.538272059 2.242800245 1000000 608 0.000608 0.002533333 0.369664 1.540266667 Table2. Resistances (Ω) were applied to record voltage (mV), when Pseudomonas trivialis was grown on the anode on the Test 2 MFC. Followed, current density mA/m2) and power density (mW/m2) were calculated based on generated voltage. The dimensions of the electrode on the anode chamber in the test 2 MFC: Width: 4.7 cm Length: 5 cm Area = 4.7 * 5 = 0.235 m2 = 0.24 m2 Resistance (Ω) Voltage (mV) current (V/R) (mA) current density (I/area) (mA/m2) Power (V2/R) (mW) Power density (P/area) (mW/m2) 10 0 0 0 0 0 20 0.1 0.005 0.022727273 0.0005 0.002272727 50 0 0 0 0 0 100 0.4 0.004 0.018181818 0.0016 0.007272727 200 1 0.005 0.022727273 0.005 0.022727273 500 1.8 0.0036 0.016363636 0.00648 0.029454545 700 2.7 0.003857143 0.017532468 0.010414286 0.047337662 1000 3.8 0.0038 0.017272727 0.01444 0.065636364 2000 7.9 0.00395 0.017954545 0.031205 0.141840909 4700 16.5 0.003510638 0.015957447 0.057925532 0.263297872 6800 23.5 0.003455882 0.015708556 0.081213235 0.36915107 10000 33.7 0.00337 0.015318182 0.113569 0.516222727 22000 59.5 0.002704545 0.012293388 0.160920455 0.731456612 47000 100.5 0.002138298 0.009719536 0.214898936 0.976813346 67000 141.9 0.00211791 0.009626866 0.300531493 1.366052239 100000 155.5 0.001555 0.007068182 0.2418025 1.099102273 220000 177.5 0.000806818 0.003667355 0.143210227 0.650955579 470000 211 0.000448936 0.002040619 0.094725532 0.4305706 680000 236 0.000347059 0.00157754 0.081905882 0.372299465 1000000 254 0.000254 0.001154545 0.064516 0.293254545 Table3. Resistances (Ω) were applied to record voltage (mV), when Pseudomonas trivialis was grown on the anode on the control water MFC. Followed, current density mA/m2) and power density (mW/m2) were calculated based on generated voltage. The dimension of electrode on the anode chamber in the C.W MFC: Width: 4.3 cm Length: 5.2 cm Area = 4.3 * 5.2 = 0.22 m2 Figure1. Polarization curves indicated power density (mW/m2) against current density (mA/m2), based on table 1, 2, 3. As depicted by figure 1, the catalytic action of Pseudomonas trivialis caused the oxidation of organic compounds in the LB medium. The polarization curves showed a slight difference between test1 and test2 MFCs. The variance was a consequence of uneven aeration on the cathode chambers. Proper aeration was necessary for the cathode to be effective (Ghangrekar & Shinde 2003; Park & Zeikus 2002). Aeration was faster on the T.1 MFC than on T.2 MFC. However, the C.W in this case was effective because there was no polarization observed for the C. W. That was as expected because there was no microorganism in the control to generate any current. Moreover, the proportion of porous on the electrode might precipitate the differences. They could be more on the electrode on the T.1 MFC than the T.2 MFC. The position of the anode electrodes in the MFCs could change the values. One of the most important factors that possibly had great effect on the performance and also voltage generation was the electrodes. They had not been replaced from first experiment; the previous electrodes were washed and used again. Since they were washed and used three times their efficiency was bound to reduce. Oxygen could diffuse into the anode chambers and interrupt the metabolic activity of microorganisms. Oxygen could enter to the anode compartments via spits, narrow cracks and the pipe, which the samples were taken. However, the highest power density generated by Pseudomonas trivialis was 106.65 (mW/m2) when current density and voltage were 0.481 (mA/m2) and 221.5 mV, respectively, at 2000Ω. Water Control MFC had the lowest voltage generation, since there were no microorganisms to generate voltage and consequently current. P. trivialis was the lowest voltage producer because the conditions present in the MFCs were not the optimum for its growth. For example, it is not a good utilize of sucrose as a n energy source as illustrated by a study by Behrendt, Ulrich and Schumann (2003). Figure1. The graphs illustrated the polarization curves of E. coli, Pseudomonas trivialis and Shewanella oneidensis. The average voltage between Test 1 and Test 2 MFCs were determined for each microorganism. Average power density (T1+T2)/2 Ecoli Average current density (T.1+T.2)/2 Ecoli Average power density (T.1+T.2)/2 Pseudomonas Average current Density (T.1+T.2)/2 Pseudomonas Average power Density(T.1+T.2)/2 Shewanella Average current density (T.1+T.2)/2 Shewanella 4.091213768 1.319746377 0.808605072 0.576992754 4.990151515 1.32197 10.43872283 1.49048913 2.139085145 0.66259058 9.440056818 1.326705 18.6563587 1.260326087 3.905634058 0.568297101 21.66920455 1.242045 41.47115942 1.328623188 8.627744565 0.598097826 46.04793561 1.287689 87.48041667 1.364583333 19.6459058 0.637681159 93.01768939 1.301326 123.4043406 1.025036232 31.5387971 0.511376812 127.2672235 0.975492 160.4769203 0.987914079 43.79050725 0.509834369 146.7931061 0.898755 192.8870435 0.906086957 57.11120924 0.487907609 160.2741345 0.795133 235.238587 0.707336957 86.96612636 0.42794837 201.6845568 0.64108 179.2950779 0.402848443 89.09890533 0.283109775 156.4032882 0.373549 150.5571052 0.306945332 83.0887548 0.227581522 133.4909481 0.288408 119.3097464 0.225344203 73.88209239 0.177092391 107.2392424 0.214129 65.08115942 0.112220026 47.97028986 0.096261528 60.82085916 0.109237 33.3157416 0.054933703 27.12271045 0.049537465 32.64937137 0.054908 24.11273929 0.039142602 20.95726666 0.036468473 24.18625905 0.039617 16.47177446 0.026480978 14.9347817 0.025200181 16.74244697 0.026992 7.645344203 0.012163208 7.181075428 0.011782773 7.896837982 0.012501 3.607648589 0.005716351 3.472002582 0.005605728 3.773794326 0.005913 2.497585118 0.003954204 2.426774163 0.003896393 2.629161932 0.004103 1.703739855 0.002693116 1.663352899 0.002660145 1.799169697 0.002799 Table4. The table indicates average power density (mW/m2) and current density (mA/m2). Results from T.1 and T.2 MFCs added together and divided to two for each microorganism. From figure1, it was observed that E. coli generated the maximum power density of 235.32 (mW/m2), among three microorganisms. This was followed by Shewanella and Pseudomonas with power densities of 201.684 (mW/m2) and 89.098 (mW/m2) respectively. A similar trend was witnessed in the power densities of all the microorganisms, i.e. the graphs indicated a gradual increase in power densities reaching peaks that gradually decreased. The difference between the three graphs might be caused by the rate of electron transfer to the anode, which was more significant in the second experiment as a result of metabolic activity of E. coli when using 0.98 g/l sucrose as substrate on the anodes. It seemed that E. coli had greater ability to degrade sucrose than other microorganisms. Furthermore, the physiology of the bacteria probably caused the differences. For example, the presence of a great amount of cytochrome in Shewanella could justify its performance in voltage generation in compared to Pseudomonas (Logan & Regan 2006). In addition, it was likely that Pseudomonas trivialis were suited to living in aerobic conditions rather than anaerobic conditions. Therefore, they did not multiply as well as E. coli and Shewanella under the anaerobic conditions of the anode in the MFC. The metabolic activity of might be more on the aerobic condition than anaerobic. Also, the applied temperature was another considerable factor, which could affect metabolic activity of the microorganisms, for example, Pseudomonas were more active at 21 0C. It was possible that oxygen to be diffused into anode chambers and affect on the anode condition, which could interrupt the microorganisms’ performance. Voltage was recorded on the computer over 8 days: Figure2. The graphs illustrated the voltage generation, when Pseudomonas trivialis was grown on the MFCs. Test1, test2, control water and control open circuit voltage MFCs were shown. OCV MFC recorded the highest voltage showing that the MFCs were in good working condition. Therefore, the voltage generated by P. trivialis could be compared and determined. Of the two tests, test 1 had the highest voltage followed by test 2. The difference in the voltages between the two cells was probably because T.2 was less aerated than T.1 thereby affecting the metabolism of the microorganisms. However, there were some unnecessary changes in the graph that had nothing to do with the metabolism of Pseudomonas trivialis. There were significant fluctuations in the voltage in test 1 especially around the 5th day. Those fluctuations could be attributed to disturbances in the MFCs especially in the power supply units and the connections. It was likely that some loose connections developed in the wires since they had been made manually. Motion or movement in the laboratory around that time probably disturbed the components of the MFC necessitating more time to settle. In addition, external interference could have arisen from devices such as mobile phones that emitted unwanted signals. Such disturbances could be avoided in the future by carrying out such experiments in a secluded section of the laboratory that is less prone to disturbances. The C.W MFC displayed the least voltage. This observation was what was expected because the addition of sodium azide solved the problem of contamination by eliminating any microorganisms in the control water MFC. Figure3. The average voltage generation between T.1 and T.2 MFCs for each microorganism Based on figure3 all three microorganisms were able to generate voltage by using sucrose as the carbon and energy source. The most significant voltage generation belonged to E. coli. The metabolic activity of E. coli revealed greater voltage generation than the other two biocatalysts over the eight days. E. coli generated the highest voltage because it exhibits good utilization of sucrose as a source of energy under anaerobic conditions (Rohan et al. 2013). In addition, the temperature and pH was also favoured the multiplication of E. coli hence the generation of voltage. There was a gradual reduction in the voltage generated as the days progressed. This was because of accumulation of metabolites on the anodic compartment over time. Some of these metabolites were acidic in nature (such as acetic acid and butyric acid). As a result, they changed the pH of the medium by lowering it causing the decrease in voltage (Finch et al. 2011). Another reason for the decline in voltage was a reduction in the availability of carbon source (sucrose) as the initially available sucrose was used up in the initial stages of growth of microorganisms. COD results: Five samples of each anode were taken from 25/11/13 to 02/12/13. The Chemical Oxygen Demand test was done in order to show the amount of carbon sources that were not oxidized by Pseudomonas trivialis. The procedures used were similar to those utilized in the first and second experiments. Titration results 25/11/2013 26/11/2013 27/11/2013 28/11/2013 02/12/2013 T.1 2.5 2.55 2.5 2.7 2.7 T.2 2.3 2.4 2.7 2.65 3 C.W 2.6 2.7 2.65 2.75 2.75 C.OCV 2.5 2.7 2.7 2.75 2.8 It was realized that a relatively higher amount of ferrous ammonium sulphate was required to react with the excess amount of potassium dichromate on the fifth day than on the first four days. That was because more potassium dichromate remained unoxidised, which also meant that less carbon dioxide was needed to oxidise the organic matter. COD they are calculated the same way as the first and second experiments 25/11/2013 26/11/2013 27/11/2013 28/11/2013 02/12/2013 T.1 7500 6000 7500 1500 1500 T.2 13500 10500 1500 3000 -7500 C.W 4500 1500 3000 0 0 C.OCV 7500 1500 -1500 0 -1500 It was noted that the COD removal reduced as the days progressed. That was because the number of microorganisms multiplied and increased in number thereby consuming most of the carbon sources that were present in the MFCs. However, it was interesting to note that in the control MFC with water, there was no microorganism added and yet the COD removal was recorded was zero by the third day. That could be attributed to contamination of the control by a mixture of different microorganisms whose rate of consumption of carbon sources was significantly higher than that of Pseudomonas trivialis. In T.1, the COD on 26/11/2013 was 6000 while a value of 7500 was recorded on 27/11/2013. The value recorded on 27th was erroneous since it was expected that it should be less than 6000. The probable reason for that recording could be errors in the readings during titration. A similar error was also recorded for T.2 on 27/11/2013 and on 28/11/2013. It was expected that the values on 27th should be between 3000 and 10500 and yet the value that was recorded was less than 3000. For C.W, the COD value on the 26/11/2013 and 27/11/2013 were contrary to the expectations. It was expected that the COD removal value on the 27th would be between 0 and 1500 and yet it was found to be 3000. For the C.OCV, an erroneous value was also recorded on 27/11/2013 and 28/11/2013. A COD removal value of 0 was to be recorded before recording the negative value. It was not a mere coincidence that all the errors occurred on the same day (27/11/2013). There was a probability that certain changes in the experimental conditions affected the results on that particular day. It was likely that there was chloride interference from the oxidising agent (potassium dichromate), which subsequently affected the COD removal values that were obtained. According to the Environmental Agency (2007), COD tests were likely to be affected by oxidation due to chlorides. Ammonia in the samples caused exaggerated positive results when they reacted with chlorides to yield chloramines (Environmental Agency 2007). In addition, the establishment of COD is usually experimental. Various experiments reveal that slight changes in the strength of reagents, temperature as well as other conditions cause immense disparities in results that are obtained. These changes may take place during the digestion stages or even during titration. Temperature, for example, influences the rates of reaction, oxidisation capability as well as volatilisation potential (Environmental Agency 2007). It was highly likely that changes in temperature and chloride interference were responsible for the inconsistency of the results especially on 27/11/2013. In addition, some methods of determining COD use spectrophotometry to establish the ultimate COD of a sample. Spectrophotometry tends to give precise results if proper calibration is done with the proper standards. However, in all these three experiments, the ultimate COD was established from calculations using the amounts of ferrous ammonium sulphate that reacted with excess potassium dichromate solution. As earlier stated, the end points were not identical with equivalence points, and colour changes of indicators were not instant. The procedures in the three experiments did not factor in the effects of the matrix such as turbidity. These were some of the factors that led to the inconsistencies in the COD removal values. A comparison between the three experiments revealed that E. coli was the greatest consumer of carbon of the three microorganisms. After eight days, they were -10500 mg/l in T.2 MFC in the second experiment (E. coli), 13500 mg/l in T.1 MFC in the first experiment (Shewanella oneidensis) and -7500 mg/l in the third experiment (Pseudomonas trivialis). Those results had three possible implications. The first implication was that S. oneidensis was the most economical microbial species to be used as a biocatalyst since it required little carbon compounds to generate energy. E. coli, on the other hand, was found to be the most uneconomical microbial species of the three in terms of carbon consumption. The inclusion of carbon sources in MFCs is one of the factors that make usage of bacteria for generation of power not feasible by increasing production costs. However, taking into consideration both the carbon consumption and generation of power capabilities, S. oneidensis is still the most economical species followed by E. coli and finally P. trivialis. Despite requiring more carbon sources than P. trivialis, E. coli generates a significantly large amount of current than the former species, which in a way compensates for its carbon consumption. This problem could be solved by including cheap carbon sources. The Coulombic Efficiency 25/11/2013 26/11/2013 27/11/2013 28/11/2013 02/12/2013 T.1 44.44444444 55.55555556 66.66666667 100 111.1111111 T.2 0 22.22222222 88.88888889 77.77777778 155.5555556 C.W 66.66666667 88.88888889 77.77777778 100 100 C.OCV 44.44444444 88.88888889 111.1111111 100 111.1111111 Coulombic efficiency (CE) depicts the efficacy of the movement of charges in a system which subsequently leads to an electrochemical reaction. Charges may be lost in electrochemical cells when electrons get wasted. This wastage may be in the form of heat in addition to the formation of chemical products. Coulombic efficiency is usually computed by establishing the ratio between the quantities of charge output to charge input. It is the proportion of electrons extracted for conversion into electricity compared to the total number of electrons in the starting organic material. It is calculated by determining the substrate removal efficiency using COD. The above table shows that in T.1 MFC the CE increased gradually from 44 on 25/11/2013 to 111.111 on 02/12/2013. The increasing trend was as was expected. However, it is known that even the most efficient battery can never have a CE of 100% because of losses of charge in the form of heat or other chemical components. Despite this, it was observed that the values of CE in all the samples on 02/11/2013 were 100% and above. These observations could be attributed to the negative values of CODs, which were used in the computation of the CE values. On comparing the coulombic efficiency values in experiment two and three, it was realized that a similar trend was obtained in both experiments as the CE values increased gradually as time progressed. It was also noted that on the final days of both experiments the coulombic efficiencies reached and surpassed 100% in the test samples and the controls thereby implying that a small element of contamination was present in both experiments. GC Chromatography results: GC was carried out to establish the components present in the products of microbial degradation and their compositions. Based on the standard samples, butyric acid was obtained when the retention time in minutes was approximately 12.680. On the other hand, a retention time of about 11.24 minutes signified the presence of acetic acid, whereas a retention time of approximately 13.020 minutes implied the presence of alcohol. However, due to errors in the injection process, the results were not reproducible when the test samples were used. Therefore, approximations of the retention times were used to determine the presence of the three compounds (acetic acid, alcohol and butyric acid), whereas the area under the peaks was used to determine the concentration of the substances. Retention time (min) Peak Area (mV*min) Ethanol Concentration (mg/l)on the test samples T.1 3.021 4.6733 5778.5 T.2 3.211 3.3725 4152.5 C.W 3.093 3.5351 4355.75 C.OCV 2.999 3.7458 4619.125 Retention time (min) Peak Area (mV*min) Acetic acid Concentration (mg/l) on the test samples T.1 11.214 0.496 612 T.2 11.219 0.4027 495.375 C.W 11.217 0.3343 409.875 C.OCV 11.228 0.2249 273.125 Retention time (min) Peak Area (mV*min) Butyric acid Concentration (mg/l) on the test samples T.1 12.646 0.4984 32.15789474 T.2 12.655 0.2872 -79 C.W 12.658 0.5933 82.10526316 C.OCV 12.666 0.1946 -127.7368421 It was shown that T.1 had the highest concentration of acetic acid at 612 mg/ml, whereas T.2 had an acetic acid concentration of 495.375 mg/ml. The chromatograph showed that there were many other peaks implying the presence of several other components. However, it was not possible to identify all the other components and their concentrations because their standards were unknown. The major components whose retention times were known were ethanol, acetic acid and butyric acid just like in the first two experiments. It was noted that ethanol was the major component in the MFCs with 5778.5 mg/l in T.1 and 4152.5 mg/l in T.2. The water control had 4355.75 mg/l while the open circuit control had 4619.125 mg/l of ethanol. The slight differences in the concentrations ethanol between T.1 and T.2 could be attributed to the fact that there were differences in the aeration in the MFCs which consequently affected the activity of the microorganism by slowing it down. Acetic acid was the second largest in concentration with a concentration of 612 mg/l in T.1, 495 mg/l in T.2, 409.875 mg/l in C. W and 273.125 mg/l in O.CW. Butyric acid had the least concentration in the MFCs with Pseudomonas trivialis as the biocatalyst with only 32.15 mg/l being generated on T.2 MFC. It was realized that C.W despite being the control without any microorganism generated more butyric acid (82.10mg/l) than T.2. The fact that C.W had significant amounts of acetic acid, butyric acid and ethanol proves the presence of contamination in the control because if no microorganism had been present there would be no formation of these products since they are by-products of microbial metabolism. In the exploitation of Shewanella oneidensis in the generation of biofuel (first experiment), it was realized that ethanol was the major product of the MFC reactions followed by acetic acid and finally butyric acid had the least concentration. Test 1 had the highest concentration of butyric acid at was 499.526316 mg/l. On the other hand, the concentration of butyric acid on the control open circuit MFC was -186.6842 mg/l. The retention time retention time guaranteed that there was butyric acid on the solution because a tiny peak was present at that point. However, the amount of butyric acid was below zero. Acetic acid concentration was 1175.625 mg/l on T.2 MFC, whereas the concentration was 650.75 on T.1 MFC. This was a two-fold reduction in the amount of acetic acid that was generated on T.2. Those differences could be attributed to the state of Shewanella, which was in turn determined by the aeration of the anode and acclimatization of the bacteria to their environment. The bacteria in T.2 adapted well and faster to the condition of the MFC hence resulting in the observed concentration of acetic acid. C.W had a concentration of 191.75 mg/l acetic acid while C.OCV had 481 mg/l acetic acid generated. The presence of acetic acid on the controls indicated the presence of contaminating microorganisms. These metabolites are referred to as renewable substrates because they further be used as energy sources although the efficiency of the utilization depends on the microorganism. The accumulation of acetic acid and butyric acid lead to a decrease in pH causing the microorganisms to begin a solventogenic growth phase (Finch et al. 2011). In this phase, acetic acid is converted into acetone, whereas butyric acid is changed to butanol (Finch et al. 2011). In these new forms, the metabolites can be used as carbon sources by the microorganisms. The highest ethanol concentration in the three experiments was generated by Shewanella oneidensis (8400.25 mg/l) on T.1 MFC followed by P. trivialis with 5778.5 mg/l and finally E. coli with 2893.875 mg/l. The highest concentration of acetic acid was produced by S. oneidensis at 1175.625 mg/l followed by E. coli at 901.375 mg/l while P. trivialis produced 612 mg/l. Butyric acid was highly generated by S. oneidensis on T.1 at a concentration of 499.526316 mg/l followed by P. trivialis with a concentration of 32.15 mg/l and finally E. coli, which had a concentration of less than 100 mg/l as was portrayed by the negative concentration. These results implied that butyric acid was the least generated metabolic product by microbial cells in MFCs while ethanol was the highly produced metabolic product. Ethanol was the most abundantly produced metabolite because it undergoes further metabolism easily to energy. Butyric acid was produced in the least quantities because for it to be further utilized it first needs to be converted into butanol. Acetic acid is also converted to acetone before further use. However, the conversion of acetic acid into acetone for further use requires less energy than the conversion of butyric acid to butanol. These results indicated that it was economically viable to combine microbial fuel cells for power generation with ethanol generating bioreactors so as to reap double benefits from the same process. Conclusion The three experiments proved that indeed microorganisms had the capability to be used as biocatalysts in the generation of electricity. That was evident in the amounts of currents obtained when all the three microorganisms were used to generate current from synthetic wastewater. However, it was also evident that the ability to generate current varied among the three microbial species. It was observed that E. coli generated the maximum power density of 235.32 (mW/m2) followed by Shewanella and Pseudomonas with power densities of 201.684 (mW/m2) and 89.098 (mW/m2) respectively. The morphological and physiological traits of S. oneidensis were thought to play a significant role in its current generation capabilities. Through genetic engineering, it is possible to create transgenic microorganisms by introducing the useful or desirable traits of Shewanella oneidensis to E. coli to improve their ability to generate electricity. Consequently, the maximum potential of generating current using microorganisms as biocatalysts can be attained. It was realized that some of the experiments did not behave as was expected due to the presence of contaminating microorganisms. That was a significant challenge in the experiment considering the stringent measures that were observed during the experimental procedures (autoclaving and sterilization of surfaces, equipment and media). There was a likelihood that some of these contaminants affected the accuracy of the results. Sodium azide was added to the control water MFC, which did not contain any microorganism, to kill all bacteria. However, the same chemical cannot be added to the other MFCs as it would kill even the required bacteria. Consequently, there is a need to carry out further research on ways of minimizing contamination of other microorganisms. One such way could be through carrying out trials that involve the inclusion of antibiotics in the MFCs that would only allow the bacteria of interest to replicate while inhibiting the growth of unwanted bacteria. Perhaps that would give an accurate representation of the capabilities of various bacteria to generate electricity. To improve the amount of current, it also recommended that MFCs with larger plate surface areas are used since the amount of charge is usually directly proportional to the surface area of the electrodes. References Behrendt, U., Ulrich, A., & Schumann, P 2003, “Fluorescent pseudomonads associated with the phyllosphere of grasses; Pseudomonas trivialis sp. nov., Pseudomonas poae sp. nov. and Pseudomonas congelanssp. nov,” International Journal of Systematic and Evolutionary Microbiology, vol.53 no. 203, pp. 1461–1469. Environmental Agency 2007, The determination of chemical oxygen demand in waters and effluents, viewed 25 January 2014, http://www.environment-agency.gov.uk/static/documents/Research/COD-215nov.pdf Finch, A. S., Mackie, T. D., Sund, C. J., & Sumner, J. J 2011, “Metabolite analysis of Clostridium acetobutylicum: fermentation in a microbial fuel cell,” Bioresource Technology, vol.102 no.1, pp. 312-315. Ghangrekar, M. M. & Shinde, V.B 2003, Microbial fuel cell: a new approach of wastewater treatment with power generation, viewed 25 January 2014, . Kim, B. H & Chang, I. S., & Gadd, G. M 2007, “Challenges in microbial fuel cell development and operation,” Appl Microbiol Biotechnol, vol. 2007 no. 76, pp. 485–494. Odio, C 2013, Shewanella oneidensis MR-1: background and applications, viewed 25 January 2014, . Park, D. H. & Zekus, J. 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