Sanath Kondaveeti

Bacterial communities in a bioelectrochemical denitrification system: The effects of supplemental electron acceptors

Electrochemical treatment of nitrate (NO3(-)), nitrite (NO2(-)) and mixtures of nitrate and nitrite was evaluated with microbial catalysts on a cathode in three different bioelectrochemical denitrification systems (BEDS). The removal rates and removal percentage of nitrogen (N) compounds varied during biotic and abiotic operations. The biotic cathode using NO3(-)-N as an electron acceptor showed enhanced removal percentages (88%) compared to the operation with NO2(-)-N (85%). The simultaneous reduction of NO3(-)-N and NO2(-)-N occurred in the operation with a mixture of N compounds. The bacterial diversity from the initial inoculum (return sludge) changed at the end of bioelectrochemical denitrification operation after 55 days. The microbial community composition was different depending on the type of electron acceptor. BEDS operation with NO3(-)-N and NO2(-)-N was enriched with Proteobacteria and Firmicutes respectively. BEDS with a mixture of N electron acceptors showed enrichment with Proteobacteria. There was no clear, distinct microbial community between the cathode biofilm and suspended biomass.

Microalgae Scenedesmus obliquus as renewable biomass feedstock for electricity generation in microbial fuel cells （MFCs）

Renewable algae biomass, Scenedesmus obliquus, was used as substrate for generating electricity in two chamber microbial fuel cells (MFCs). From polarization test, maximum power density with pretreated algal biomass was 102 mW·m−2 (951 mW·m−3) at current generation of 276 mA·m−2. The individual electrode potential as a function of current generation suggested that anodic oxidation process of algae substrate had limitation for high current generation in MFC. Total chemical oxygen demand (TCOD) reduction of 74% was obtained when initial TCOD concentration was 534 mg ·L−1 for 150 h of operation. The main organic compounds of algae oriented biomass were lactate and acetate, which were mainly used for electricity generation. Other byproducts such as propionate and butyrate were formed at a negligible amount. Electrochemical Impedance Spectroscopy (EIS) analysis pinpointed the charge transfer resistance (112 Ω) of anode electrode, and the exchange current density of anode electrode was 1214 nA·cm−2.

Bioelectrochemical reduction of volatile fatty acids in anaerobic digestion effluent for the production of biofuels

This study proves for the first time the feasibility of biofuel production from anaerobic digestion effluent via bioelectrochemical cell operation at various applied cell voltages (1.0, 1.5 and 2.0 V). An increase in cell voltage from 1 to 2 V resulted in more reduction current generation (-0.48 to -0.78 mA) at a lowered cathode potential (-0.45 to -0.84 mV vs Ag/AgCl). Various alcohols were produced depending on applied cell voltages, and the main products were butanol, ethanol, and propanol. Hydrogen and methane production were also observed in the headspace of the cell. A large amount of lactic acid was unexpectedly formed at all conditions, which might be the primary cause of the limited biofuel production. The addition of neutral red (NR) to the system could increase the cathodic reduction current, and thus more biofuels were produced with an enhanced alcohol formation compared to without a mediator.

Minimum interspatial electrode spacing to optimize air-cathode microbial fuel cell operation with a membrane electrode assembly

An optimum electrode spacing of less than 1cm was determined for an air cathode microbial fuel cell (MFC) with a membrane electrode assembly (MEA) system. The lag period decreased as the electrode spacing increased and the voltage generation increased. Stable power density increased from 93 mW/m(2) to 248 mW/m(2) when the electrode distance increased from 0mm to 9 mm. In the polarization test, a maximum power density (400 mW/m(2)) was obtained at a distance of 6mm. The oxygen mass transfer coefficient (KO=4.60×10(-5) cm/s) with a 0mm spacing was five times higher than that at a 9 mm spacing (0.89×10(-5) cm/s). Long-term operation of the MFC exhibited relatively stable anode potentials of -285±25 (0 mm) and -517±20 mV (3, 6, and 9 mm) and a gradual decrease in cathode potential for all distances, especially with 0-mm spacing. The performance of air cathode MFCs can be improved using minimum electrode spacing rather than no spacing.

Bioelectrochemical methane (CH4) production in anaerobic digestion at different supplemental voltages

Microbial electrolysis cells (MECs) at various cell voltages (0.5, 0.7 1.0 and 1.5V) were operated in anaerobic fermentation. During the start-up period, the cathode potential decreased from -0.63 to -1.01V, and CH4 generation increased from 168 to 199ml. At an applied voltage of 1.0V, the highest methane yields of 408.3ml CH4/g COD glucose was obtained, which was 30.3% higher than in the control tests (313.4ml CH4/g COD glucose). The average current of 5.1mA was generated at 1.0V at which the maximum methane yield was obtained. The other average currents were 1.42, 3.02, 0.53mA at 0.5, 0.7, and 1.5V, respectively. Cyclic voltammetry and EIS analysis revealed that enhanced reduction currents were present at all cell voltages with biocatalyzed cathode electrodes (no reduction without biofilm), and the highest value was obtained with 1V external voltage.

The performance and long-term stability of low-cost separators in single-chamber bottle-type microbial fuel cells

ABSTRACT This study evaluates long-term stability of low-cost separators in single-chamber bottle-type microbial fuel cells with domestic wastewater. Low-cost separators tested in this study were nonwoven fabrics (NWF) of polypropylene (PP80, PP100), textile fabrics of polyphenylene sulfide (PPS), sulfonated polyphenylene sulfide (SPPS), and cellulose esters. NWF PP80 separator generated the highest power density of 280 mW/m2, which was higher than with ion-exchange membranes (cation exchange membrane; CEM = 271 mW/m2, cation exchange membrane; CMI = 196 mW/m2, Nafion = 260 mW/m2). MFC operations with other size-selective separators such as SPPS, PPS, and cellulose esters exhibited power densities of 261, 231, and 250 mW/m2, respectively. During a 280-day operation, initial power density of PP80 (278 mW/m2) was decreased to 257 mW/m2, but this decrease was smaller than with others (Nafion: 265–230 mW/m2; PP100: 220–126 mW/m2). The anode potential of around −430 mV did not change much with all separators in the long-term operation, but the initial cathode potential gradually decreased. Fouling analysis suggested that the presence of carbonaceous substance on Nafion and PP80 after 280 days of operation and Nafion was subject to be more biofouling.

Anodic Electron Transfer Mechanism in Bioelectrochemical Systems

The reality of bacteria in transporting electron beyond their cell wall and ability to electrically interact with electrode has been nearly over a century (Potter 1911). Microbial fuel cells are growing bioelectrochemical systems that use bacteria as a catalyst and generate bioelectricity using organic matter. The bacteria act as powerhouse at the anode of MFC and oxidize organic matter to CO2 by generating electrons and protons (Kondaveeti 2014). These electrons move from anode to cathode and get reduced as water by using oxygen as an electron acceptor. The generated electrons from bacteria can be transferred to anode by direct contact with biofilm or by using mediators, which can be either exogenic or endogenic (Kondaveeti and Min 2015). The natural mediators such as flavins which are secreted by bacteria or other active complexes such as c-type chromosomes present on outer cell membranes can shuttle electrons. Up to date the metal reducing bacterial species such as Geobacter and Shewanella have been widely noticed in MFC technology, due to their external electron transfer mechanism and for synthesis of natural mediators (riboflavins), which can be a rival for other exoelectrogens (Logan 2008). The external insoluble shuttles such as neutral red, and methyl viologen etc. were used in microbial fuel cells for electron transfer from the bacterial cell wall to electrodes. The initial studies in addition of exogenous mediators to MFC were pursued (Cohen 1931; Schroder 2007). In this study low current generation in MFC might be due to lack of electromotive oxidation and reductive force. These were resurfaced in 1980 by Bennetto and coworkers and it was further investigated by many other researchers. In the present chapter, the electron transfer mechanisms such as direct electron transfer, mediated electron transfer and interspecies electron transfer mechanisms with electroactive anode bacteria are discussed.

Physicochemical Parameters Governing Microbial Fuel Cell Performance

Microbial fuel cell (MFC) performance has been dramatically improved by optimizing physicochemical parameters, especially in the early period of MFC research, for MFC practical applications. The enhancement in power output of MFC can be dependent on several physical and chemical parameters such as electrode material and morphology, catalyst on electrode, reactor design, membrane/separator, temperature, pH, electrolyte conductivity, and types of oxidants and substrates (fuels). The optimized conditions of physical and chemical parameters can enhance performance of MFC by decreasing internal resistance which is the sum of over potentials at the anode and cathode chambers and the separator part, and by increasing Columbic efficiencies. The effects of these parameters on MFC performance are discussed below in details.