M. Lenin Babu

Microbial catalyzed electrochemical systems: A bio-factory with multi-facet applications

Microbial catalyzed electrochemical systems (MCES) have been intensively pursued in both basic and applied research as a futuristic and sustainable platform specifically in harnessing energy and generating value added bio-products. MCES have documented multiple/diverse applications which include microbial fuel cell (for harnessing bioelectricity), bioelectrochemical treatment system (waste remediation), bioelectrochemical system (bio-electrosynthesis of various value added products) and microbial electrolytic cell (H2 production at lower applied potential). Microorganisms function as biocatalyst in these fuel cell systems and the resulting electron flux from metabolism plays pivotal role in bio-electrogenesis. Exo-electron transfer machineries and strategies that regulate metabolic flux towards exo-electron transport were delineated. This review addresses the contemporary progress and advances made in MCES, focusing on its application towards value addition and waste remediation.

Potential of mixed microalgae to harness biodiesel from ecological water-bodies with simultaneous treatment.

Biodiesel as an eco-friendly fuel is gaining much acceptance in recent years. This communication provides an overview on the possibility of using mixed microalgae existing in ecological water-bodies for harnessing biodiesel. Microalgal cultures from five water-bodies are cultivated in domestic wastewater in open-ponds and the harvested algal-biomass was processed through acid-catalyzed transesterification. Experiments evidenced the potential of using mixed microalgae for harnessing biodiesel. Presence of palmitic acid (C16:0) in higher fraction and physical properties of algal oil correlated well with the biodiesel properties. Functional characteristics of water-bodies showed to influence both species diversity and lipid accumulation. Microalgae from stagnant water-bodies receiving domestic discharges documented higher lipid accumulation. Algal-oil showed to consist 33 types of saturated and unsaturated fatty acids having wide food and fuel characteristics. Simultaneous wastewater treatment was also noticed due to the syntrophic association in the water-body microenvironment. Diversity studies visualized the composition of algae species known to accumulate higher lipids.

Bio-electrolytic conversion of acidogenic effluents to biohydrogen: An integration strategy for higher substrate conversion and product recovery

Feasibility of integrating Microbial electrolysis cell (MEC) process with dark-fermentation process for additional hydrogen recovery as well as substrate degradation was demonstrated in the present study. MEC was employed in order to utilize the residual organic fraction present in the acidogenic effluents of dark fermentation process as substrate for hydrogen production with input of small electric current. MEC was operated at volatile fatty acids (VFA) concentration of 3000 mg/l under different poised potentials (0.2, 0.5, 0.6, 0.8 and 1.0 V) using anaerobic consortia as biocatalyst. Maximum hydrogen production rate (HPR), cumulative hydrogen production (CHP) (0.53 mmol/h and 3.6 mmol), dehydrogenase activity (1.65 μg/ml) and VFA utilization (49.8%) was recorded at 0.6 V. Bio-electrochemical behavior of mixed consortia was evaluated using cyclic voltammetry and by Tafel slope analysis. Microbial diversity analysis using denaturing gradient gel electrophoresis confirmed the presence of γ-proteobacteria (50%), Bacilli (25%) and Clostridia (25%).

Dehydrogenase activity in association with poised potential during biohydrogen production in single chamber microbial electrolysis cell

Variation in the dehydrogenase (DH) activity and its simultaneous influence on hydrogen (H2) production, substrate degradation rate (SDR) and volatile fatty acid (VFA) generation was investigated with respect to varying poised potential in single chambered membrane-less microbial electrolysis cell (MEC) using anaerobic consortia as biocatalyst. Poised potential showed significant influence on H2 production and DH activity. Maximum H2 production was observed at 1.0V whereas the control system showed least H2 production among the experimental variations studied. DH activity was observed maximum at 0.6V followed by 0.8, 0.9 and 1.0V, suggests the influence of poised potential on the microbial metabolism. Almost complete degradation of substrate was observed in all the experimental conditions studied irrespective of the applied potential. Experimental data was also analysed employing multiple regression analysis and 3D-surface plots to find out the best theoretical poised potential for maximum H2 production and DH activity.

Insight into the dehydrogenase catalyzed redox reactions and electron discharge pattern during fermentative hydrogen production

Dehydrogenase (DH) activity associated with bio-electrochemical behavior was analyzed for the first time to understand the redox reactions involved in fermentative hydrogen (H(2)) production process in concurrence with proton (H(+)) shuttling and electron (e(-)) discharge (ED) pattern. DH facilitates the availability of H(+) through redox reactions to make H(2). We have designed a comprehensive experimental study to evaluate the DH activity (H(+) shuttling) and ED to understand the biochemical process with the function of pH (5, 6, 7 and 8) and metabolic microenvironment [anaerobic, anoxic and aerobic (control)]. DH activity was observed to be higher during anaerobic operation suggesting the higher availability of H(+) and e(-) due to the inter-conversion of metabolites and the same was reflected in the voltammetry analysis. Higher H(2) production under anaerobic operation corroborated well with these findings. The DH activity associated with H(+) shuttling and ED was also correlated with the substrate degradation pattern.

Influence of graphite flake addition to sediment on electrogenesis in a sediment-type fuel cell.

Graphite flakes at levels of 5%, 15%, 20% and 40% (weight per sediment volume) were added to lake bed sediment and electrogenesis in a sediment-type fuel cell was evaluated. Addition of graphite flakes by 20% to the sediment showed higher electrogenic activity of the fuel cell (578mV; 0.37mW) compared to control (304mV; 0.26mW). Further increment in the graphite loading showed a negative influence on the fuel cell behavior. A higher energy and capacitance were recorded with 20% addition of graphite flakes compared to the control. Increase in the exchange current density and decrease in the Tafel slope and electron transfer coefficient was observed with addition of graphite flakes. Apparent surface coverage analysis also supported the higher performance upon addition of 20% graphite flakes. The relative increase in the conductivity of bed due to addition of graphite flakes might be the reason for observed electrogenic activity. Marginal variation in the substrate utilization ( [Formula: see text] 50-55%) was observed with the addition of graphite flakes. By adding an optimum level of graphite flakes to sediment influences the fuel cell performance.

Microbial Fuel Cells for Sustainable Bioenergy Generation: Principles and Perspective Applications

The energy gain in microbes is driven by oxidizing an electron donor and reducing an electron acceptor. Variation in the electron acceptor conditions creates a feasibility to harness energy. In order to support the microbial respiration, electrons will transfer to the exocellular medium toward the available electron acceptor, especially in the absence of oxygen. The microbes can use a wide range of electron acceptors such as metals, nutrients, minerals, etc., including solid electrodes. When the microbes use the solid electrode as electron acceptors, the setup is called microbial fuel cell (MFC) and the electrons can be harvested and used for different applications. MFC can be defined as a microbially catalyzed electrochemical system which can facilitate the direct conversion of substrate to electricity through a cascade of redox reactions, especially in the absence of oxygen. Linking the microbial metabolism to anode and then transmitting the electrons to cathode generates a net electrical power from the degradation of available electron donor. This concept of MFC operation has expanded considerable interest in the recent research due to its application in the energy recovery from wastewater. Microbes in MFC can also use variety of organic or inorganic electron donors as well as acceptors to produce a surfeit of desirable biofuels or biochemicals which is termed as microbial electrosynthesis. Apart from the electrogensis, the applications of MFC are widespread in different fields including waste/wastewater remediation, toxic pollutants/xenobiotics removal, recovery of commercially viable products, sequestration of CO2, harvesting the energy stored in marine sediments, desalination, etc. In this chapter, an attempt was made to bring out all the existing applications of MFC into one platform to make a comprehensive understanding on the inherent potential of microbial metabolism, when the designated electron acceptor is present.

Microbial Electrolysis of Synthetic Acids for Biohydrogen Production: Influence of Biocatalyst Pretreatment and pH with the Function of Applied Potential

Bioelectrolysis of synthetic acids (acetate, butyrate and propionate) was evaluated in a single chamber Microbial Electrolysis Cell (MEC) to produce biohydrogen (H2). The influence of culture pretreatment (untreated and acid pretreated) and pH (6 and 7) conditions on electrolytic process were studied. MEC was operated at three optimized potentials viz., 0.2, 0.6 and 1.0 V along with control operated without any applied potential. Maximum Hydrogen Production Rate (HPR), Cumulative Hydrogen Production (CHP) and Specific Hydrogen Yield (SHY) were registered at 0.6 V followed by 1.0 and 0.2 V operations under all the experimental conditions studied. Culture pretreatment and pH variation showed influence on the MEC process. Pretreatment (PTr) operation at pH 7 showed good process performance than pH 6. MEC with untreated (UTr) at pH 6 and 7 showed lower performance compared to PTr operations. About 53% removal of synthetic acids was registered during the process which is a good sign for MEC as a wastewater treatment unit. Electrokinetic evaluation through Tafel slope showed that MEC operations with PTr and UTr at pH 6 recorded lower redox slopes and lower polarization resistance (Rp) at 0.2 V and 0.6 V whereas pH 7 recorded lower redox slopes and Rp at 0.6 V and 1.0 V.