Simultaneous biopesticide wastewater treatment and bioelectricity generation in microbial fuel cell (MFC)
By the large scale use of fossil fuel, it is fast depleting. At this crucial time I have chosen microbial fuel cell (MFC) to generate alternate source of energy the electricity by using biopesticide wastewater. I conducted this project for 192 hours in batch mode on laboratory scale to understand the issues involved in electricity generation and wastewater treatment process. A maximum electricity generation of 779 mV was recorded at 102 h. Similarly, maximum COD removal efficiency of 98.79% was registered at 192 hours. By making improvement in MFC the electricity demand can be solved in the future.
All over the world fossil fuel is fast depleting alarmingly. Further, it is a major cause for climate change and environmental degradation (Levin et al., 2004; Mullai et al., 2003; Mullai et al., 2011). At this critical juncture microbial fuel cells (MFCs) have fascinated global attention over the last decade as a technology for electricity generation and wastewater treatment (Kim et al., 2008).The outcome of this work is expected to provide useful information for the development of commercially viable technology for bioelectricity production from MFC in the future. It is essential to improve MFC design to generate electricity in a commercial scale. Generation of bioelectricity in large scale by using different types of available wastewaters will facilitate all countries for economic development and for protecting the environment.
In this investigation, a dual chambered MFC was operated at 35±1°C and pH of 6.0 in batch mode with biopesticide wastewater as substrate and mangrove sediment as inoculum in anode chamber and KMnO4 as catholytic solution and graphite plates as electrodes. The maximum potential difference of 779 mV was recorded. The maximum power generation of 32.71027 mW/cm2 and current density of 0.04199 mA/cm2 were obtained at applied 100 Ω resistance. The record of maximum COD removal efficiency of 98.79% and electricity generation proved the hypotheses. The use of mangrove sediment as inoculum and biopesticide wasterwater as substrate is considered as innovative attempts. All efforts need to be taken to scale-up MFC for higher bioelectricity generation in the future.
I am S.M. Sambavi, 13 year old, living in Chidambaram, a small town in Cuddalore district of Tamil Nadu State, India. I am studying IX Standard (academic year April 2013 – March 2014) at Maharishi International Residential School located in Sunguvarchathiram, a village in Kanchipuram district, close to the Tamil Nadu State’s capital Chennai. I love reading comics, drawing pictures of natural sceneries, exploring science facts, delivering presentation of research papers and participating in environmental awareness campaign. Since my childhood (from the age of 3 years), I have been attending conferences and workshops in the fields of science and engineering along with my parents. This type of exposures made me to have passion for science and carry out experiments on science concepts. My first source of inspiration is Dr. A.P.J. Abdul Kalam, former President of India who encourages the student community to get involved in research activities. My second motivator is the late Mrs. Kalpana Chawla who created history by being the first Indian woman to travel in space shuttle and sacrificed her life in a tragic accident at the time of space expedition. I am interested in studying energy engineering with the ultimate aim of inventing new technologies in this field to energize the world. Winning is about appreciation of the knowledge and the biggest inspiration for further education. Getting prizes give pleasure and also help me to pursue subjects of my own interest and achieve my goals. It also kindles interest in achieving many laurels and credentials.
1) Will the mangrove sediments to be used as inoculum be effective ?
Since trees in the mangroves facilitate litter fall, the sediment will be highly enriched with organic matter. In turn, the organic matter will harbour a large number of microbes. Hence, it is expected that when the mangrove sediment is inoculated, it will help colonise abundant microbes in the MFC.
2) Will all the microbial species that colonise in MFC will generate electricity ?
It is expected that only some species of microbes will generate electricity.
3) Is it essential to maintain pH of the substrate ?
Microbes will thrive in all pH ranges. However, if the substrate becomes alkaline in nature it will favour the growth of methane producing methanogenic bacteria. Since they inhibit the growth of hydrogen producing acidogenic bacteria the generation of electricity will be affected. Hence it is essential to main initial pH of the substrate.
1) Biopesticide wastewater as substrate will produce more electricity and also more COD removal efficiency.
As the biopesticide wastewater contains more aliphatic organic solvents, it is purely organic in nature. The microbes to be colonized through the inoculation of mangrove sediment will consume all the organic matter and there is a possibility for more electricity generation and subsequently higher COD removal efficiency.
Even though the concept of production of bioelectricity using microbial fuel cells (MFCs) is new, considerable number of research has been carried out all over the world (Moon et al., 2005; Davis and Higson, 2007; Cheng and Logan, 2011; Masih et al., 2012). Microbial fuel cells have emerged as a promising technology to meet the dual goals of wastewater treatment and bioelectricity production in a sustainable way. Logan (2005) described the MFC as a device that converts chemical energy to electrical energy using catalytic active microorganism that oxidize soluble organic matter present in wastewater by a bioelectrochemical system (BES). Min and Logan (2004) carried out research on MFC in the production of bioelectricity from domestic wastewater. Liu et al., (2004) studied the production of electricity during wastewater treatment using a single chamber microbial fuel cell. The importance of MFC in the production of electricity has been described by Rabaey and Verstraete (2005). Extensive research on the production bioelectricity has been carried out by Venkata Mohan and his team of researchers. Venkata Mohan et al., (2008a) studied the possibility of bioelectricity generation from anaerobic chemical wastewater treatment using MFC employing selectively enriched hydrogen producing mixed culture. Yet, in another work Venkata Mohan et al., (2008b) studied the biochemical functioning of single chambered microbial fuel cell using glass wool as proton exchange membrane (PEM) operated with selectively enriched acidogenic mixed culture. Rozendal et al., (2008) in their work on bioelectrochemical wastewater treatment identified the challenges, highlighted an overview of their implications for the feasibility of bioelectrochemical wastewater treatment and explored the opportunities for future Bioelectrochemical Systems (BESs). Cheng and Logan (2011) studied the viability of MFCs and electrodes. Masih et al., (2012) carried out study on electricity generation by optimization in a dual chambered aerated membrane microbial fuel cell with E. coli as biocatalyst at different culture densities. Li and Sheng (2012) in their work reviewed the progress achieved to date in MFC technology, especially in China, and discussed the challenges and future opportunities. By scanning the available literature it is understood that no attempt has been made in the use of biopesticide wastewater in the production of electricity using MFC and mangrove sediment as inoculum. India being an agrarian country, many biopesticide industries have been established to meet the requirements. In the manufacture of biopesticides, a large quantum of wastewater is let out leading to environmental degradation. With a view to understand the viability of employing MFC in the generation of electricity and avoid degradation of the environment, the present study on batch mode was carried out on a laboratory scale. However, there is much scope to carry out research on this aspect in a commercial scale in the future by bringing out improvement in MFC in different ways and also increasing the microbial activity by gene manipulation.
Analytical grade chemicals, plastic jars, graphite plates for anode and cathode, agar salt bridge as proton exchange membrane, biopesticide wastewater as substrate, mangrove sediments, KMnO4 solution (20 mM) as cathodic solution, multimeter.
Collection of Substrate
The wastewater was collected from biopesticide manufacturing unit, Cuddalore, Tamil Nadu State. The raw wastewater collected was thoroughly mixed and the integrated sample was used for the study.
The sediment sample was collected at a depth of 100 cm from the mangroves of Pichavaram, Tamil Nadu State and heated for an hour at 110° C and used as inoculum.
A two chambered MFC was constructed using two plastic jars of 2000 ml capacity with a working volume of 1200 ml (Fig. 1). The plastic jars were perforated and connected each other by the agar salt bridge and sealed tightly to avoid leakage of solutions. Anode chamber was filled with raw biopesticide wastewater (12425 mg COD/l) and inoculated with pre-treated mangrove sediments. In the anode chamber pH was adjusted to 6.0 using 1N NaOH or 1N HCl. Potassium permanganate was used as cathodic solution (electron acceptors). The salt bridge was used for the electrolytic contact of the solutions in the two jars, where the two electrodes of the MFC were immersed. Graphite plates were used as both anode and cathode electrodes with a total surface area of 185.52 cm2 and were pretreated following the procedures of Berchmans et al., (2012). Copper wires were used to connect the cell to the external circuit. The experiments were carried out in duplicate at room temperature of 35± 1°C.
Sampling and Analysis
The sample was collected from the MFC and analyzed at once. COD concentration, pH and volatile suspended solids (VSS) were recorded daily according to standard methods (APHA, 1995). The microstructure of granules was examined using scanning electron microscope (SEM) (JEOL– JSM-5610LV, Japan).
The potential difference (V) between anode and cathode of the MFC was measured using a multimeter (Digimet, India) at 120 min intervals after stabilization of the readings. Current (I) was calculated by connecting 100 ohms as external resistance (R) using Ohm’s law, I = V/R. Power (W) was calculated using P = IV, where I is amperes (A). Power density (mW/cm2) and current density (mA/cm2) were calculated by dividing the obtained power and current with the surface area (m2) of anode.
In this experiment independent variable is time (h). The dependent variables are voltage, current, VSS concentration (biomass concentration) and COD removal efficiency. Substrate consumption was evident from the increase in biomass growth and subsequently continuous generation of electricity. As this experiment generates bioelectricity and also COD removal efficiency was higher, it could be confirmed that the experiments were carried out properly. The experiments were carried out at Pollution Control Research Laboratory of Department of Chemical Engineering, Annamalai University in Tamil Nadu State, India. Hand gloves and nose-mask were used during the conduct of the experiments.
The physicochemical characteristics of the biopesticide wastewater used in this study are given in Table 1.
Performance of MFC was evaluated by measuring voltage and current output during operation. Fig. 2 shows the voltage generated during the operation of MFC. The potential difference fluctuated between 15 mV and 779 mV. The voltage output increased with time and reached a maximum value of 779 mV at 102 h along with 7.79 mA of current generation (Fig. 3). The power density increased from 0.0121 mW/cm2 and reached 32.71 mW/cm2 at 102nd hour and declined thereafter (Fig. 4). The gradual increase in the generation of electricity could be attributed to colonization of electrogenic bacteria which could be evident from record of higher VSS concentration of 6.95 g/l when compared to lower VSS concentration of 1.5 g/l at the start of the experiment. The record of lower power density of 0.0121 mW/cm2 at the start-up of the experiment could be due to less contact time between the microorganisms on graphite plate.
COD removal efficiency
The COD removal efficiency was found to increase with increase in time (Fig. 5). The initial concentration of the substrate which was 12425 mg COD/l gradually decreased. The COD removal efficiency reached a steady state with a maximum value of 98.79% at the end of 192 hours. The record of higher COD removal efficiency could be attributed to the effective functioning of microbes found in the inoculum. Further, it is also due to highly biodegradable nature of the wastewater used.
Hydrogen ion Concentration (pH)
The mangrove sediment which was used as inoculum in the anode compartment was pretreated to inhibit the growth of methanogenic bacteria and to sustain acidogenic bacteria which produce hydrogen, essential for electricity generation. As the pH range of 5.5–6.0 was considered to be ideal to avoid both methanogenesis and solventogenesis (Venkatamohan et al., 2008a; Mullai et al., 2013), initial pH of 6.0 was maintained in the anode compartment. During the study period, pH values increased with time from 6.0 to 7.8 (Fig. 6). The increase in pH increased the activities of exoelectrogenic bacteria resulting in higher bioelectricity (Logan, 2009). Further, increase in pH from 7.8 was found to decline in the generation of electricity
Microstructure of granules
SEM image revealed that there were coci bacilli appeared in clusters with almost similar morphology (Fig. 7a). It also showed the presence of endospores, characteristics of some hydrogen-producing bacteria. Fig. 7b shows the structures for the passage of nutrients and substrates as well as the release of hydrogen.
In this research work innovative attempts have been made by using biopesticide wastewater as substrate and mangrove sediment as inoculum for the simultaneous generation of electricity and wastewater treatment. The experiment was run on batch mode for 192 hours. The maximum voltage of 779 mV was obtained at 102 h and current of 7.79 mA was recorded at 100 Ω. A maximum power generation of 32.71027 mW/cm2 at current density of 0.04199mA/cm2 was obtained under the applied external resistance of 100 Ω. A maximum COD removal efficiency of 98.79% was realized at 192 h. The hypotheses such as electricity generation and COD removal efficiency were proved.
The present study was run in batch mode. Even though morphological microstructure of microbes was studied through SEM, species identification was not done. Non-identification of colonized microbial species which are effective in the generation of electricity was limitation of the present study. Constraints of such nature would be addressed in the future work.
From the work of Oh and Logan (2005) and Yang et al., (2013) it is known that electricity generated in the present work is relatively appreciable. However, for the generation of electricity on commercial scale the MFC should be run on continuous mode with more advancement in the future.
Based on the results obtained from the present work, answer for the following question needs to be found out.
1) Will the industries be made self-sustained in meeting the energy requirements by adopting advanced MFC technology ?
2) Will each home be made self-sustained in meeting the energy requirements by adopting advanced MFC technology ?
3) Will all the nations be made self-sustained in energy sectors by following advanced MFC technology ?
4) Will our environment be protected from the industrial activities by adopting advanced MFC technology?
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The success and final outcome of this project required a lot of guidance and assistance from many people and I am extremely fortunate to have got this all along the execution of my project work. Whatever I have done is only due to such guidance and assistance and I would not forget to thank them.
I am highly indebted to Google Science Fair for having given an opportunity which made me do my best and hope for the best in this project.
I am thankful to Principal and staff members of Maharishi International Residential School, Sunguvarchathiram for their constant encouragement and support.
I take this opportunity to express my profound gratitude and deep regards to my mom Dr. P. Mullai, who is Professor of Chemical Engineering, Annamalai University, Annamalai Nagar, Chidambaram for her exemplary guidance and constant encouragement extended throughout the course of this project. The blessings and help being offered by her time to time shall carry me a long way in the journey of my life with full of research on which I am about to embark.
I also take this opportunity to express a deep sense of gratitude to my dad Dr. K. Sampath, for his cordial support, valuable information and guidance, which helped me in completing this task through various stages.
I am obliged to Ms. K. Sridevi and Ms. M. K. Yogeswari, research scholars of Chemical Engineering Department of Annamalai University, for their valuable information, help and support.
I thank the staff members of Department of Electronics and Instrumentation, Annamalai University for extending help in soldering the electrodes.
With respect I thank the authorities of the Annamalai University for allowing me to use the Pollution Control Research Laboratory, Chemical Engineering Department to do my project work and providing me with all the equipment needed.
I am beholden to my family members and friends for their constant encouragement without which this assignment would not have been possible.
Lastly, I thank the Almighty for blessing me with this golden opportunity and for my bright future career.
Lists of equipments
Hot air oven (Technico, India)
Muffle furnace (Technico, India)
Deep freezer (Blue Star, India)
Weighing balance (Shimadzu, Japan)
COD digestion unit (JSGW, India)
Hot plate (REMI, India)
pH meter (HANNA Instruments, India)
Salinity meter (ERMA , India)
Multimeter (Digimet, India)
Scanning electron microscope (SEM) (JEOL– JSM-5610LV, Japan).