Dipak A. Jadhav

Comparison of oxygen and hypochlorite as cathodic electron acceptor in microbial fuel cells.

Effect of oxygen and sodium hypochlorite (NaOCl) as cathodic electron acceptors on performance of a clayware microbial fuel cell (MFC) was evaluated in this study. Maximum power density of 6.57 W/m(3) was obtained with NaOCl as catholyte, which is about 9 times higher than oxygen being used as an electron acceptor. Voltammetry and Tafel analysis further supported the faster reduction kinetics lead to increase in power output and reduction in internal resistance of MFC operated with NaOCl as an electron acceptor. Using NaOCl as catholyte, higher exchange current density of 10.91 and 11.52 mA/m(2) and lower charge transfer resistance of 0.58 and 0.56 kΩ m(2) was observed for anode and cathode, respectively. Higher organic matter removal of about 90% with 25% Coulombic efficiency was achieved using NaOCl as catholyte. Higher internal resistance, lower cathode potential and slow reduction kinetics deteriorated performance of MFC using oxygen as cathodic electron acceptor.

Simultaneous organic matter removal and disinfection of wastewater with enhanced power generation in microbial fuel cell

Presence of pathogenic microorganism in anodic effluent of microbial fuel cell (MFC) makes it unfit for reuse. In this study, performance of dual chamber MFC was evaluated in terms of organic matter removal, power generation and disinfection in cathodic chamber. Anodic effluent was treated further in cathodic chamber for achieving disinfection with different doses of sodium hypochlorite (NaOCl) with available chlorine varying from 0.67, 1.32, 2, 3 and 4 g/L. Addition of different doses of NaOCl resulted in satisfactory disinfection along with removal of nitrogenous compounds. Power output of MFC improved up to 3g/L of available chlorine (6.5 W/m(3)); however, further increase in chlorine concentration decreased the power. Voltammetric and impedance analysis showed higher and faster electron reduction and decrease in polarization resistance at 3g/L dose. Higher organic matter removal from wastewater and complete elimination of microorganism, along with improved power output, demonstrates effectiveness of hypochlorite as catholyte.

Enhancing waste activated sludge digestion and power production using hypochlorite as catholyte in clayware microbial fuel cell

Waste activated sludge was digested in anodic compartment of dual chambered clayware microbial fuel cell (MFC). Performance of MFC was evaluated using oxygen (MFC-1) and hypochlorite (MFC-2) as cathodic electron acceptors. Power production of 8.7 W/m(3) was achieved using hypochlorite as catholyte, which was two times higher than using oxygen (4.2 W/m(3)). Total chemical oxygen demand of sludge was reduced by 65.4% and 84.7% in MFC-1 and MFC-2, respectively. Total and volatile suspended solids reductions were higher in MFC-2 (75.8% and 80.2%, respectively) as compared to MFC-1 (66.7% and 76.4%, respectively). Use of hypochlorite demonstrated 3.8 times higher Coulombic efficiency (13.8%) than oxygen. Voltammetric and impedance analysis revealed increase in reduction peak (from 8 to 24 mA) and decreased polarization resistance (from 42.6 to 26.5 Ω). Hypochlorite proved to be better cathodic electron acceptor, supporting rapid sludge digestion within 8 days of retention time and improved power production in MFC.

Improving performance of microbial fuel cell while controlling methanogenesis by Chaetoceros pretreatment of anodic inoculum

Loss of substrate due to methanogenesis reduces Coulombic efficiency (CE) of the microbial fuel cell (MFC) significantly. Hexadecatrienoic acid present in the marine algae Chaetoceros inhibits the growth of methanogenic archaea. Influence of Chaetoceros pre-treated mixed anaerobic sludge on the electrogenic activity of MFC was evaluated. A MFC inoculated with Chaetoceros pre-treated mixed anaerobic sludge demonstrated maximum CE of 45.18%, with volumetric power density of 21.43W/m(3) and current density of 93A/m(3). Cyclic voltammetry indicated higher electron discharge on the anode surface due to suppression of methanogenesis. Tafel analysis also showed a higher exchange current density and a lower Tafel slope and charge transfer resistance, indicating advantage of this pre-treatment method in reducing the cell internal losses. A 60% reduction in specific methanogenic activity was observed in anaerobic sludge pre-treated with Chaetoceros; emphasizing significance of this pretreatment for suppressing methanogenesis and its utility for enhancing electricity generation in MFC.

Effective ammonium removal by anaerobic oxidation in microbial fuel cells

Dual-chamber microbial fuel cells (MFCs), made of clayware cylinder, were operated at different chemical oxygen demands: ammonium-nitrogen (COD:) ratio (1:1, 10:1 and 5:1) under batch mode for simultaneous removal of ammonia and organic matter from wastewater. Ammonium-N removal efficiencies of 63–32.66% were obtained for COD: ratio of 1:10, respectively. Average COD removal efficiencies demonstrated by these MFCs were about 88%; indicating effective use of MFCs for treatment of wastewater containing organic matter and high ammonia concentration. MFCs operated with COD: ratio of 10:1 produced highest volumetric power density of 752.88 mW/m3. The ammonium-N removal slightly increased when microbes were exposed to only ammonium as a source of electron when organic source was not supplemented. When this MFC was operated with imposed potential on cathode and without aeration in the cathode chamber, oxidation of ammonium ions at a faster rate confirmed anaerobic oxidation. During the non-turnover condition of cyclic voltammetry, MFC operated with COD: ratio of 10:1 gave higher oxidative and reductive currents than MFC operated with COD: ratio of 1:1 due to higher redox species. Successful application of such an anammox process for ammonium oxidation in MFCs will be useful for treatment of wastewater containing higher ammonium concentration and harvesting energy in the form of electricity.

Enhancing the power generation in microbial fuel cells with effective utilization of goethite recovered from mining mud as anodic catalyst.

Catalytic effect of goethite recovered from iron-ore mining mud was studied in microbial fuel cells (MFCs). Characterization of material recovered from mining mud confirms the recovery of iron oxide as goethite. Heat treated goethite (550 °C) and untreated raw goethite were coated on stainless-steel anode of MFC-1 and MFC-2, respectively; whereas, unmodified stainless-steel anode was used in MFC-3 (control). Fivefold increment in power was obtained in MFC-1 (17.1 W/m(3) at 20 Ω) than MFC-3 (3.5 W/m(3)). MFC with raw goethite coated anode also showed enhanced power (11 W/m(3)). Higher Coulombic efficiency (34%) was achieved in MFC-1 than control MFC-3 (13%). Decrease in mass-transport losses and higher redox current during electrochemical analyses support improved electron transfer with the use of goethite on anode. Cheaper goethite coating kinetically accelerates the electron transfer between bacteria and anode, proving to be a novel approach for enhancing the electricity generation along with organic matter removal in MFC.

Enhancing the performance of single-chambered microbial fuel cell using manganese/palladium and zirconium/palladium composite cathode catalysts

Application of ZrO2, MnO2, palladium, palladium-substituted-zirconium oxide (Zr0.98Pd0.02O2) and palladium-substituted-manganese oxide (Mn0.98Pd0.02O2) cathode catalysts in a single-chambered microbial fuel cell (MFC) was explored. The highest power generation (1.28W/m3) was achieved in MFC with Mn0.98Pd0.02O2 catalyst, which was higher than that with MnO2 (0.58W/m3) alone; whereas, MFC having Zr0.98Pd0.02O2 catalyzed cathode and non-catalyzed cathode produced powers of 1.02 and 0.23W/m3, respectively. Also, low-cost zirconium-palladium-composite showed better catalytic activity and capacitance over ZrO2 with 20A/m3 current production and demonstrated its suitability for MFC applications. Cyclic voltammetry analyses showed higher well-defined redox peaks in composite catalysts (Mn/Zr-Pd-C) over other catalyzed MFCs containing MnO2 or ZrO2. Electrochemical behaviour of composite catalysts on cathode showed higher availability of adsorption sites for oxygen reduction and, hence, enhanced the rate of cathodic reactions. Thus, Mn/Zr-Pd-C-based composite catalysts exhibited superior cathodic performance and could be proposed as alternatives to costly Pd-catalyst for field applications.

Recent Progress Towards Scaling Up of MFCs

Microbial fuel cell (MFC) is an advanced bioelectrochemical system for treatment of wastewater which transforms chemical energy available in the organic matter present in wastewater directly into electrical output using electrochemical active bacteria (EAB) as a biocatalyst without causing any harmful effects (Logan 2008). At the anode in anodic chamber, EAB convert biologically oxidizable organic matter into carbon dioxide, protons and electrons (Fig. 23.1a). Electrons (e−) are travelled to the anode electrode and further passed to the cathode through an electrical circuit. Protons (H+) are exchanged from anodic chamber to cathodic chamber through a CEM by cation exchange capacity of membrane. In cathodic chamber, the protons and electrons combine with oxygen to form water as an end product during reduction reaction.

Architectural adaptations of microbial fuel cells

Conventional wastewater treatment consumes a large amount of money worldwide for removal of pollutants prior to its discharge into water body or facilitating reuse. Decreasing energy expenditure during wastewater treatment and rather recovering some value-added products while treating wastewater is an important goal for researchers. Microbial fuel cells (MFCs) are representative bioelectrochemical systems, which offer energy-efficient wastewater treatment. MFCs convert chemical energy of organic matter into electrical energy by using biocatalytic activities. Although MFCs are not truly commercialized, they have potential to make energy-gaining wastewater treatment technologies and represent their capabilities successfully. Over the last decade, MFCs have developed remarkably in almost every dimension including wastewater treatment capabilities, power output, and cost optimization; however, its architectural design is an important consideration for scaling up. Here, we review various architectural advancements and technology up-gradation MFCs have experienced during its journey, to take this technology step forward for commercialization.