Design of a microbial fuel cell and its transition to microbial electrolytic cell for hydrogen production by electrohydrogenesis

Transcription

1 Indian Journal of Experimental Biology Vol. 51, October 2013, pp Design of a microbial fuel cell and its transition to microbial electrolytic cell for hydrogen production by electrohydrogenesis Pratima Gupta *, Piyush Parkhey, Komal Joshi & Anjali Mahilkar Department of Biotechnology, National Institute of Technology, Raipur, Chhattisgarh , India Received 8 November 2012; revised 10 July 2013 Anaerobic bacteria were isolated from industrial wastewater and soil samples and tested for exoelectrogenic activity by current production in double chambered microbial fuel cell (MFC), which was further transitioned into a single chambered microbial electrolytic cell to test hydrogen production by electrohydrogenesis. Of all the cultures, the isolate from industrial water sample showed the maximum values for current = ma, current density = ma/m 2 and power density = mw/m 2 with graphite electrode. Maximum voltage across the cell, however, was reported by the isolate from sewage water sample (506 mv) with copper as electrode. Tap water with KMnO 4 was the best cathodic electrolyte as the highest values for all the measured MFC parameters were reported with it. Once the exoelectrogenic activity of the isolates was confirmed by current production, these were tested for hydrogen production in a single chambered microbial electrolytic cell (MEC) modified from the MFC. Hydrogen production was reported positive from co-culture of isolates of both the water samples and co-culture of one soil and one water sample. The maximum rate and yield of hydrogen production was 0.18 m 3 H 2 /m 3 /d and 3.2 mol H 2 /mol glucose respectively with total hydrogen production of 42.4 ml and energy recovery of 57.4%. Cumulative hydrogen production for a five day cycle of MEC operation was 0.16 m 3 H 2 /m 3 /d. Keywords: Exoelectrogenic activity, Hydrogen gas, Microbial Electrolytic Cell, Microbial Fuel Cell. Hydrogen, as a fuel has attracted much attention in recent years from global scientific community. Its properties of high calorific value, zero carbon content and easy availability of substrates for its production make it an ideal replacement option for fossil fuels. It has highest gravimetric energy density than any known fuel 1-4 and can be used for energy conversion either by electrochemical or combustion processes. These features make it a promising alternate for fossil fuels and confer it several technical, socio-economic and environmental benefits 5,6. Hydrogen can be produced by thermochemical methods such as steam reformation of natural gas, coal gasification, and splitting water with electricity or by biological methods such as fermentation (using biomass as substrate) and biophotolysis of water 7,8. However, the industrial methods are highly energy intensive and release carbon dioxide and other greenhouse gases and pollutants as byproducts, while biological methods suffer from the drawbacks of lower production rates and yields. These disadvantages economically limit the usage of these methods for industrial level hydrogen production. * Correspondent author Mobile: prati_biotech@yahoo.co.in Recently, electrohydrogenesis has attracted much attention as another potential technology for achieving higher hydrogen yield in a more cost effective manner Electrohydrogenesis is essentially a biocatalysed electrolysis procedure, wherein hydrogen gas is produced by organic matter being degraded by bacteria in microbial electrolytic cells (MECs) 9. Exoelectron generating bacteria or exoelectrogens are key players in either MECs or microbial fuel cells (MFCs) 12,13. These are the bacteria which utilize organic rich matter as carbon source, oxidise them and release the electrons outside the cell. In a MFC, exoelectrogenic bacteria oxidize organic matter and transfer electrons to an anode which in turn travel through an external circuit to cathode where they combine with protons and oxygen to form water. Such exoelectron generators can effectively also be used for production of hydrogen gas. In electrohydrogenesis, electrons released by exoelectrogenic bacteria in specially designed reactors (based on modifying microbial fuel cells) reduce the protons (released simultaneously during metabolism) to form hydrogen gas when a small voltage (~0.8V) is applied through the circuit. Such modified microbial fuel cells are essentially called as microbial electrolysis cells or MEC s. These can be effectively

2 GUPTA et al: MICROBIAL FUEL CELL & HYDROGEN PRODUCTION 861 used to achieve complete substrate conversion and thereby increase the total yield of hydrogen per molecule of substrate In this communication, design of a microbial fuel cell and measurement of exoelectrogenic activity of bacteria isolated from different industrial waste water and soil samples is reported. The exoelectrogens were further used in a single chambered microbial electrolytic cell modified from constructed microbial fuel cell for hydrogen production. Hydrogen production was confirmed by gas chromatography. Rate, yield and total volumetric hydrogen production was also determined along with energy efficiency of the process. Materials and Methods Sampling and isolation Samples of soil and wastewater were collected from different sources in area around Raipur (21.14 N, E), India to isolate electrochemically active bacteria. Soil samples were collected from iron-ore based industries in Urla, Raipur. The wastewater samples were collected from industrial wastewater line and sewage tank. The samples were serially diluted and inoculated in an enrichment media containing (gl -1 ) peptone: 15, yeast extract: 5, D-glucose: 5.5, NaCl: 2.5, Cysteine hydrochloride: 0.5, and agar: Cysteine hydrochloride was added to reduce the redox potential of the medium required for the growth of anaerobes. Agar was added to increase the viscosity of the medium and thus to decrease the diffusion of atmospheric oxygen into it. The autoclaved culture tubes were flushed with nitrogen beforehand and a 2 cm layer of autoclaved oil was applied on top of medium and sealed to ensure anaerobic conditions. Isolation of amaerobic bacteria A total of four anaerobic bacteria, two from soil and two from wastewater were isolated from the collected samples. Each bacterial isolate was given a separate code as Soil Sample from Mahamaya Ispat industry - SS2, Soil Sample from Abhishek Industry - SS4, Wastewater sample from Amleshwar industrial region WS1 and Wastewater sample from Urla industrial region WS2. The isolates SS2 and WS2 were found to be Gram positive, whereas isolates SS4 and WS1 were Gram negative. All the isolates showed negative result for catalase test. Construction of microbial fuel cell (MFC) MFCs was constructed using two glass test tubes (35 ml capacity) connected with a salt bridge (5 mm diameter). Salt bridge was constructed using plastic U-tube filled with KNO 3 (saturated) and agar (20 g/l). Graphite rods (surface area sq. cm) and copper plates (surface area sq. cm) were used as electrodes. The electrodes were soaked in phosphate buffer (50 mm) before placing in MFC. Copper wires (resistance Ω/m) were used for connecting circuits. Different cathodic electrolytes were used to study the effect of reduction potential of catholyte on MFC performance. The cathodic electrolytes used were tap water, NaCl (10g/L) with tap water, and KMnO 4 (0.2 g/l) with tap water. The anodic compartments were inoculated with enriched culture and soil samples (Fig. 1). Current and voltage measurements were recorded using a digital multimeter (Mastech, M-830BZ, Taipei, Taiwan) after 48 h incubation. Calculations Current density of MFC was calculated using i (ma/m 2 ) = I/A, where I is the current measured (ma) and A is the geometric surface area of anode (m 2 ). The power density of the MFC was calculated using formula: P (mw/m 2 ) = IV, where I is the current density and V is the voltage measured (mv). Construction of microbial electrolytic cell (MEC) Single chambered MEC s modified from MFC was constructed using airtight plastic bottles of working volume 250 ml. Graphite rods of surface area sq. cm were used as electrodes and connecting wires were same as the ones used in MFC. The electrodes were connected to an external power source which supplied a constant DC voltage of 0.8V. A gas collection unit was attached to the top of the Fig.1 Schematic of setup of double chambered microbial fuel cell (MFC), where cathodic chamber (A) containing 48 h grown bacterial culture is connected to air tight anodic chamber (B) through a salt bridge (C). Graphite electrodes (D) and (E) are immersed in catholyte and anolyte respectively. A multimeter (F) is connected across the cell to measure the MFC parameters.

3 862 INDIAN J EXP BIOL, OCTOBER 2013 cell for sampling gas at regular intervals for detection and analysis. Initially three MECs were operated with different mixed cultures, (1) with mixed culture of one isolate of water sample (WS 1) with one isolate of soil sample (SS4), (2) with mixed culture of all isolates from water sample (WS1+WS2), and (3) with mixed culture of all isolates from soil sample (SS2 + SS4). Sodium thioglycolate (0.5 g/l) and sodium acetate (1.5 g/l) was added in addition to all other media components as in MFC. While sodium thioglycolate acts as oxygen scavenger, sodium acetate aids in better electron transfer. Schematic set up the three MEC s which were run simultaneously is given in Fig. 2. Based on results of hydrogen production from the mix cultures, isolates of water sample WS1 and WS2 were later also used individually to run two different MECs (Fig. 3). To determine the rate, yield and volumetric hydrogen production, the gas outlet from MEC s were connected to tube filled with water which was again connected to a measuring cylinder. The schematic diagram of the setup is shown in Fig. 4. Hydrogen gas produced in MEC reactor entered the falcon tube, where being insoluble in water, it displaced water into the measuring cylinder. The displaced volume of water in the measuring cylinder gave the volumetric production of H 2 gas. Hydrogen yield (Y H2 ) was calculated as number of moles of hydrogen gas produced (n H2 ) per mole of glucose (n S ) consumed. Hydrogen production rate (Q H2 ) was calculated as volume of gas produced (m 3 ) per unit volume of reactor (m 3 ) per day, i.e. (m 3 H 2 /m 3 /d). Energy recovery (η) of the whole process was calculated as ratio of energy produced in the form of hydrogen (W H2 ) to the energy input in form of glucose as substrate (W S ), where W H2 = n H2 H H2, and Ws = n S H S where n H2 and n S are number of moles of hydrogen gas produced and number of moles of glucose consumed respectively, and H H2 and H S are heat of combustion of hydrogen gas ( kj/mol) and substrate (2805 kj/mol, for glucose) respectively. Gas chromatography The gas produced was analysed by Gas chromatography (Thomas Scientific, Ceres 800 Plus, Chemito instruments, Fig. 2 Schematic setup of three microbial electrolytic cells, MEC (A) mixed culture of WS1 and SS4, MEC (B) mixed culture of WS1 and WS2, and MEC (C) mixed culture of SS2 and SS4. The MECs are connected in parallel to a 0.8 V supply and hydrogen produced in the three reactors was collected in D1, D2 and D3 respectively. Fig. 3 Setup of microbial electrolytic cell with wastewater isolates, WS1 and WS2 in monocultures. Fig. 4 Schematic set up microbial electrolytic cell (MEC) for determination of rate and yield of hydrogen gas production. Single chambered MEC (A) with graphite electrodes is connected to external power supply of 0.8 V. Gas produced in MEC gets collected into an air tight chamber (B) filled with water via saline tube (C). Hydrogen being insoluble in water pushes it through another saline tube (D) into a measuring cylinder (E). Water collected in measuring cylinder is equal to hydrogen gas collected on top of chamber B. Fresh media inoculation and gas sampling for gas chromatography can be done from ports F and G respectively.

4 GUPTA et al: MICROBIAL FUEL CELL & HYDROGEN PRODUCTION 863 Mumbai, India) fitted with a thermal conductivity detector (TCD) using Nitrogen (N 2 ) as carrier gas and Porapak Q column. The oven temperature during GC run was kept at 50 C, while injector and detector temperatures were maintained at 80 C and 100 C respectively. Pure hydrogen gas was test run through the column for standard. Results and Discussion Determination of exoelectrogenic activity in MFC The exoelectrogenic activity of the isolated anaerobes was confirmed by current generation in constructed MFC. For all the isolates current and power density were measured along with current and voltage for each different catholyte and electrode separately (Table 1). In each case maximum values of all parameters for all isolates tested across all catholyte combinations were reported using graphite rods, except with WS2, where maximum voltage of 506 mv was reported with copper electrode. The overall maximum power and current density of mw/m 2 and ma/m 2 respectively were obtained when WS1 was used in MFC using graphite electrodes. Using copper electrode the maximum power and current density was mw/m 2 and ma/m 2 respectively reported in WS2. This study thus suggests that graphite electrodes are more efficient than copper electrodes for current generation in MFC. Continuous operation of MFC leads to the development of overpotential between electrodes, which reduces cell voltage (You et al 22 ). KMnO 4, being an excellent antioxidant reduces this overpotential and thus increases the efficiency of MFC. This is evident from the results of this study as maximum values for all the parameters studied were reported when KMnO 4 was used as catholyte. These are comparable to the results of Jadhav and Ganghrekar 23 where they also reported higher power densities using KMnO 4 solution as catholyte. This communication deals with current generation in a double chambered MFC using glucose as substrate. However, current generation using MFCs of different designs with different substrates such as glucose 24, waste water 25, and organic acids 26 has been reported. The results from these reports indicate that MFCs operating on organic acids substrates such as acetate and butyrate are more efficient that those operating on pure carbohydrates or wastewaters. This suggests that other than pure substrates, end products from fermentation reactions, constituting mainly of organic acids such as acetate and butyrate can also be used for current generation in MFC. Hydrogen production using MEC Hydrogen production by the exoelectrogens was carried out in constructed single chambered MECs. Three MECs were run simultaneously, first with mixed culture of one isolate of water sample (WS 1) with one isolate of soil sample (SS4), second with mixed culture of both the isolates from water sample, and third with mixed culture of both isolates from soil sample. The first and second MEC reactors i.e. the reactor with co-culture of one soil and one wastewater isolate and the reactor with mixed culture of both wastewater isolates showed positive hydrogen production as detected by gas chromatography. No hydrogen production was detected in reactor with mixed culture of both soil isolates and therefore they were not tested Table 1 Characterisation of microbial fuel cell for current generation operated with different bacterial isolates. Isolate SS2 SS4 WS1 WS2 Cathodic electrolyte Voltage (mv) Current (ma) Current density (ma/m 2 ) Power density (mw/m 2 ) Graphite Copper Graphite Copper Graphite Copper Graphite Copper Tap water Tap water with NaCl Tap water with KMnO Tap water Tap water with NaCl Tap water with KMnO Tap water Tap water with NaCl Tap water with KMnO Tap water Tap water with NaCl Tap water with

5 864 INDIAN J EXP BIOL, OCTOBER 2013 individually for hydrogen production. Each wastewater isolate, i.e. WS1 and WS2 were inoculated as monocultures in MEC reactor to check hydrogen production and both WS1 and WS2 showed positive hydrogen production. Reactors inoculated with WS1 and WS2 showed hydrogen production for five and four days respectively, as shown by displacement of water from centrifuge tube after which the hydrogen production stopped. Figures 5 and 6 depict the rate and yield of hydrogen production from WS1 and WS2 respectively. As can be seen, WS1 is efficient hydrogen producer than WS2 as rate and yield of hydrogen production for WS1 is higher than WS2. Thus, by using a single chamber MEC, it was possible to produce hydrogen by exoelectrogens Fig. 5 Comparative assessment of yield and rate of hydrogen production of the two isolates. WS1 showed no hydrogen production after 120 h, while in WS2, hydrogen production stopped after 96 h of operation. Fig. 6 Volumetric hydrogen production and energy efficiency of the isolates WS1 and WS2 for hydrogen production over a 5 day cycle. Vol WS1 and Vol WS2 show the volumetric hydrogen production while E EF WS1 and E EF WS2 show the energy efficiency for WS1 and WS2 respectively. isolated from industrial waste water samples. While the yield of hydrogen gas reported in this communication is comparable to the previously published reports, the rate of hydrogen production is relatively less The most probable reason for the lower rate of hydrogen production is large MEC volume/electrode ratio. If the size of MEC would be decreased similar to electrode size, substantial increase in rate of hydrogen production can be achieved. Decreasing the distance between electrodes is another option which can result in higher rates of hydrogen production. Although the setup discussed in the current communication confirms production of hydrogen gas using exoelectrogenic bacteria. Alteration in design of MEC setup can be done to significantly escalate the rate and yield of hydrogen production, thereby increasing the overall efficiency of the process. Conclusion Exoelectrogens were successfully isolated from the soil and waste water samples. Their exoelectrogenic activity was characterised using the designed double chambered microbial fuel cell. The MFC inoculated with the exoelectrogens was characterised for parameters such as voltage and current production, along with current and power density using copper and graphite electrodes and different catholytes. The exoelectrogens were tested for hydrogen production in monocultures and in mixed cultures in designed single chambered microbial electrolytic cell. The isolates from the wastewater samples showed positive hydrogen production while the soil isolates showed no hydrogen evolution. The total volumetric hydrogen production, along with rate and yield of hydrogen production and energy efficiency of the whole process was also evaluated for both wastewater isolates. The MFC and MEC were designed at basic lab scale and can further be optimized for enhanced current production and subsequent hydrogen production respectively. References 1 Das D & Veziroglu T N, Hydrogen production by biological processes: A survey of literature, Int J Hydrogen Energy, 26 (2001) Lee H S, Vermaas W F J & Rittmann BE, Biological hydrogen production: Prospects and challenges, Trends Biotechnol, 28 (2010) Li C & Fang H H P, Fermentative hydrogen production from wastewater and solid wastes by mixed cultures, Crit Rev Environ Sci Technol, 37 (2007) 1.

6 GUPTA et al: MICROBIAL FUEL CELL & HYDROGEN PRODUCTION Selembo P A, Perez J M, Lloyd W A & Logan B E, High hydrogen production from glycerol or glucose by electrohydrogenesis using microbial electrolysis cells, Int J Hydrogen Energy, 34 (2001) Das D, Advances in biohydrogen production processes: An approach towards commercialization, Int J Hydrogen Energy 34, (2009) Su H, Cheng J, Zhou J, Song W & Cen K, Improving hydrogen production from cassava starch by combination of dark and photo fermentation, Int J Hydrogen Energy, 34 (2009) Argun H & Kargi F, Photo-fermentative hydrogen gas production from dark fermentation effluent of ground wheat solution: Effects of light source and light intensity, Int J Hydrogen Energy, 35 (2010) Barbosa M J, Rocha J, Tramper J & Wijffels R H, Acetate as a carbon source for hydrogen production by photosynthetic bacteria, J biotechnol, 85 (2001) Cheng S & Logan B E, Sustainable and efficient biohydrogen production via electrohydrogenesis, Proc Nat Acad Sci, 104 (2007) Wrana N, Sparling R, Cicek N & Levin D B, Hydrogen gas production in a microbial electrolysis cell by electrohydrogenesis, J Clean Prod, 18 (1) (2010) S Logan B E, Call D, Cheng S, Hamelers H V M, Sleutels T H J A, Jeremiasse A W & Rozendal RE, Microbial electrolysis cells for high yield hydrogen gas production from organic matter, Environ Sci Technol, 42 (23) (2008) Logan B E & Regan J M, Electricity-producing bacterial communities in microbial fuel cells, Trends Microbiol, 14, (2006) Logan B E & Regan J M, Microbial fuel cells-challenges and applications, Environ Sci Technol, 40 (2006) Lalaurette E, Thammannagowda S, Mohagheghi A, Maness P C & Logan B E, Hydrogen production from cellulose in a two-stage process combining fermentation and electrohydrogenesis, Int J Hydrogen Energy, 34 (2009) Hallenbeck P C & Ghosh D, Advances in fermentative biohydrogen production: the way forward, Trends Biotechnol, 27(5) (2008) Sinha P & Pandey A, An evaluative report and challenges for fermentative biohydrogen production, Int J Hydrogen Energy, 36 (2011) Fan Y T, Zhang Y H, Zhang S F, Hou H W & Ren B Z, Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost, Bioresour Technol, 97 (2006) Kotsopoulos T A, Zeng R J & Angelidaki I, Biohydrogen production in granular up-flow anaerobic sludge blanket (UASB) reactors with mixed cultures under hyperthermophilic Temperature (70 C), Biotechnol Bioengg, 94 (2), (2006) Kotsopoulos T A, Fotidis I A, Tsolakis N & Martzopoulos G G, Biohydrogen production from pig slurry in a CSTR reactor system with mixed cultures under hyper-thermophillic temperature (70 C), Biomass Bioenergy, 33 (2009) Chen C C, Lin C Y & Chang J S, Kinetics of hydrogen production with continuous anaerobic cultures utilizing sucrose as limiting substrate. Appl Microbiol Biotechnol, 57 (2001) Mu Y, Wang G & Yu H Q, Kinetic modeling of batch hydrogen production process by mixed anaerobic cultures, Bioresource Technol, 97 (2006). 22 You S, Zhao Q, Zhang J, Jiang J & Zhao S, A microbial fuel cell using permanganate as the cathodic electron acceptor, J Power Sources, 162 (2006) Jadhav G S & Ghangrekar M M, Improving performance of MFC by design alteration and adding cathodic electrolytes, Appl biochem biotech, 151, (2008). 24 Chaudhuri S K & Lovley D R, Electricity generation by direct oxidation of glucose in mediator less microbial fuel cells, Nat Biotechnol, 21 (2003) Moon H, Chang I S & Kim B H, Continuous electricity production from artificial wastewater using a mediator-less microbial fuel cell, Bioresour Technol, 97 (2006) Liu H, Cheng S & Logan B E, Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell, Environ Sci Technol, 39 (2005) Call D & Logan B E, Hydrogen production in a single chamber microbial electrolysis cell lacking a membrane, Environ Sci Technol, 42 (2008). 28 Hu H, Fan Y & Liu H, Hydrogen production using singlechamber membrane-free microbial electrolysis cells, Water Res, 42 (2008) Lee H S, & Rittmann B E, Significance of biological hydrogen oxidation in a continuous single-chamber microbial electrolysis cell, Environ Sci Technol, 44 (2009) 948.