Sunil A. Patil

Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber.

Feasibility of using chocolate industry wastewater as a substrate for electricity generation using activated sludge as a source of microorganisms was investigated in two-chambered microbial fuel cell. The maximum current generated with membrane and salt bridge MFCs was 3.02 and 2.3 A/m(2), respectively, at 100 ohms external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m(2). The use of chocolate industry wastewater in cathode chamber was promising with 4.1 mA current output. Significant reduction in COD, BOD, total solids and total dissolved solids of wastewater by 75%, 65%, 68%, 50%, respectively, indicated effective wastewater treatment in batch experiments. The 16S rDNA analysis of anode biofilm and suspended cells revealed predominance of beta-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), alpha-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and gamma-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.

Electroactive mixed culture derived biofilms in microbial bioelectrochemical systems: the role of pH on biofilm formation, performance and composition.

The pH-value played a crucial role for the development and current production of anodic microbial electroactive biofilms. It was demonstrated that only a narrow pH-window, ranging from pH 6 to 9, was suitable for growth and operation of biofilms derived from pH-neutral wastewater. Any stronger deviation from pH neutral conditions led to a substantial decrease in the biofilm performance. Thus, average current densities of 151, 821 and 730 μA cm(-2) were measured for anode biofilms grown and operated at pH 6, 7 and 9 respectively. The microbial diversity of the anode chamber community during the biofilm selection process was studied using the low cost method flow-cytometry. Thereby, it was demonstrated that the pH value as well as the microbial inocula had an impact on the resulting anode community structure. As shown by cyclic voltammetry the electron transfer thermodynamics of the biofilms was strongly depending on the solutions pH-value.

In Situ Spectroelectrochemical Investigation of Electrocatalytic Microbial Biofilms by Surface‐Enhanced Resonance Raman Spectroscopy

Metal-reducing bacteria not only play a key role in geochemical redox cycles, but also attract increasing attention in view of their relevance for microbial bioelectrochemical systems, a seminal sustainable technology. This growing research interest is triggered by the bacteria s capability to oxidize substrates such as acetate and to transfer the released electrons to an insoluble terminal electron acceptor, for example, iron-containing minerals in nature or a fuel cell anode in bioelectrochemical applications. The underlying electron-transfer (ET) mechanisms between the bacteria and the terminal electron acceptor may occur by different mechanisms, including direct and mediated electron transfer denoted as DET and MET, respectively. In the case of DET, the electrons are transferred from the respiratory chain in the cell to extracellular inorganic material via a complex architecture involving several outer membrane cytochromes (OMCs). These cytochromes are multiheme proteins whose function and number of heme groups may vary largely within the same family. Although several studies investigated the behavior of these proteins embedded in microbial biofilms of wild-type and mutant Geobacter sulfurreducens, the archetype bacteria family employing DET, the role of these cytochromes in the heterogeneous ET across the biofilm/electrode interface is far from clearly understood. This is particularly true since structural data are currently only known for two OMCs, namely, OmcF and OmcZ. 11] In this respect, spectroscopic techniques that can be applied to biofilms in situ may provide important structural information about the OMCs involved in the DET. To date, only two spectroscopic studies were devoted to the investigation of OMCs embedded in the cellular membrane. 13] The spectroscopic measurements of these works were carried out with washed and re-suspended cells, but did not refer to intact biofilms grown on an electrode. Herein, we present for the first time in situ spectroscopic characterization of OMCs in a catalytically active microbial biofilm. By measuring the electrochemical and spectroscopic properties of microbial cells embedded in their natural biofilm habitat, a more realistic picture on the natural electron transfer will be provided. Therefore, we have employed surface-enhanced resonance Raman (SERR) spectroscopy in combination with cyclic voltammetry (CV). SERR spectroscopy exploits the combination of the molecular resonance Raman (RR) and the surface-enhanced Raman (SER) effect to probe selectively the heme groups solely of the proteins in proximity of the electrode surface. 14] This powerful technique, in our case performed under strict electrochemical control, reveals the redox, coordination and spin states of the heme iron as well as the nature of its axial ligand, thereby providing important structural information that may complement the interpretation of electrochemical data obtained by CV. 16] The biofilms were grown at a constant potential on roughened (i.e. SER-active) silver electrodes using 10 mm acetate as substrate (see the Supporting Information for experimental details). These biofilms produced a maximum chronoamperometric current density of 600 mAcm 2 (Figure SI2 in the Supporting Information), which is in good agreement with previous studies using graphite anodes. The voltammetric behavior of the biofilms was monitored under turnover (Figure SI3) and nonturnover conditions [that is, with and without the substrate (e.g. acetate), respectively]. Figure 1 shows the CV behavior of such a biofilm for nonturnover conditions. The two redox couples that are proposed to be involved in the DET, Ef,1 and Ef,2, are centered at formal potentials of 282 mV and 363 mV, respectively (all potentials are reported versus the Ag/AgCl (3.0m KCl) reference electrode). The main overall shape and peak positions of the cyclic voltammogram shown in Figure 1 are very similar to those obtained on graphite electrodes in parallel experiments and in previous studies, showing that biofilm formation is not affected by the nature of the electrode material. The similarity between these CV traces and those obtained solely from biofilms of Geobacter sulfurreducens indicates that the biofilm is highly dominated [*] Dr. D. Millo, H. K. Ly, Prof. Dr. P. Hildebrandt Institut f r Chemie, Sekr. PC14, Technische Universit t Berlin Strasse des 17. Juni 135, 10623 Berlin (Germany) Fax: (+ 49)30-3142-1122 E-mail: diego.millo@tu-berlin.de

A logical data representation framework for electricity-driven bioproduction processes☆☆☆

Microbial electrosynthesis (MES) is a process that uses electricity as an energy source for driving the production of chemicals and fuels using microorganisms and CO2 or organics as carbon sources. The development of this highly interdisciplinary technology on the interface between biotechnology and electrochemistry requires knowledge and expertise in a variety of scientific and technical areas. The rational development and commercialization of MES can be achieved at a faster pace if the research data and findings are reported in appropriate and uniformly accepted ways. Here we provide a framework for reporting on MES research and propose several pivotal performance indicators to describe these processes. Linked to this study is an online tool to perform necessary calculations and identify data gaps. A key consideration is the calculation of effective energy expenditure per unit product in a manner enabling cross comparison of studies irrespective of reactor design. We anticipate that the information provided here on different aspects of MES ranging from reactor and process parameters to chemical, electrochemical, and microbial functionality indicators will assist researchers in data presentation and ease data interpretation. Furthermore, a discussion on secondary MES aspects such as downstream processing, process economics and life cycle analysis is included.

Electroactive mixed culture biofilms in microbial bioelectrochemical systems: the role of temperature for biofilm formation and performance.

In this paper we investigate the temperature dependence and temperature limits of waste water derived anodic microbial biofilms. We demonstrate that these biofilms are active in a temperature range between 5°C and 45°C. Elevated temperatures during initial biofilm growth not only accelerate the biofilm formation process, they also influence the bioelectrocatalytic performance of these biofilms when measured at identical operation temperatures. For example, the time required for biofilm formation decreases from above 40 days at 15°C to 3.5 days at 35°C. Biofilms grown at elevated temperatures are more electrochemically active at these temperatures than those grown at lower incubation temperature. Thus, at 30°C current densities of 520 μA cm(-2) and 881 μA cm(-2) are achieved by biofilms grown at 22°C and 35°C, respectively. Vice versa, and of great practical relevance for waste water treatment plants in areas of moderate climate, at low operation temperatures, biofilms grown at lower temperatures outperform those grown at higher temperatures. We further demonstrate that all biofilms possess similar lower (0°C) and upper (50°C) temperature limits--defining the operational limits of a respective microbial fuel cell or microbial biosensor--as well as similar electrochemical electron transfer characteristics.

Selective enrichment establishes a stable performing community for microbial electrosynthesis of acetate from CO2

The advent of renewable energy conversion systems exacerbates the existing issue of intermittent excess power. Microbial electrosynthesis can use this power to capture CO2 and produce multicarbon compounds as a form of energy storage. As catalysts, microbial populations can be used, provided side reactions such as methanogenesis are avoided. Here a simple but effective approach is presented based on enrichment of a robust microbial community via several culture transfers with H2:CO2 conditions. This culture produced acetate at a concentration of 1.29 ± 0.15 g L(-1) (maximum up to 1.5 g L(-1); 25 mM) from CO2 at a fixed current of -5 Am(-2) in fed-batch bioelectrochemical reactors at high N2:CO2 flow rates. Continuous supply of reducing equivalents enabled acetate production at a rate of 19 ± 2 gm(-2)d(-1) (projected cathode area) in several independent experiments. This is a considerably high rate compared with other unmodified carbon-based cathodes. 58 ± 5% of the electrons was recovered in acetate, whereas 30 ± 10% of the electrons was recovered in H2 as a secondary product. The bioproduction was most likely H2 based; however, electrochemical, confocal microscopy, and community analyses of the cathodes suggested the possible involvement of the cathodic biofilm. Together, the enrichment approach and galvanostatic operation enabled instant start-up of the electrosynthesis process and reproducible acetate production profiles.

Engineering electrodes for microbial electrocatalysis

Microbial electrocatalysis refers to the use of microorganisms to catalyze electrode reactions. Many processes have been developed on this principle, ranging from power generation to CO2 conversion using bioelectrochemical systems. The nature of the interface between the microorganisms and the electrodes determines the functioning and efficiency of these systems. This interface can be manipulated in terms of chemical and topographical features to better understand the interaction at nanometer and micrometer scales. Here we discuss how the electrode surface topography and chemistry impact the microorganism-electrode interaction both for direct and indirect electron transfer mechanisms. It appears that composite materials that combine high conductivity with excellent biocompatibility are most attractive towards application. In most cases this implies a combination of a metallic backbone with a carbon coating with a defined topography and chemistry.

Flame oxidation of stainless steel felt enhances anodic biofilm formation and current output in bioelectrochemical systems

Stainless steel (SS) can be an attractive material to create large electrodes for microbial bioelectrochemical systems (BESs), due to its low cost and high conductivity. However, poor biocompatibility limits its successful application today. Here we report a simple and effective method to make SS electrodes biocompatible by means of flame oxidation. Physicochemical characterization of electrode surface indicated that iron oxide nanoparticles (IONPs) were generated in situ on an SS felt surface by flame oxidation. IONPs-coating dramatically enhanced the biocompatibility of SS felt and consequently resulted in a robust electroactive biofilm formation at its surface in BESs. The maximum current densities reached at IONPs-coated SS felt electrodes were 16.5 times and 4.8 times higher than the untreated SS felts and carbon felts, respectively. Furthermore, the maximum current density achieved with the IONPs-coated SS felt (1.92 mA/cm(2), 27.42 mA/cm(3)) is one of the highest current densities reported thus far. These results demonstrate for the first time that flame oxidized SS felts could be a good alternative to carbon-based electrodes for achieving high current densities in BESs. Most importantly, high conductivity, excellent mechanical strength, strong chemical stability, large specific surface area, and comparatively low cost of flame oxidized SS felts offer exciting opportunities for scaling-up of the anodes for BESs.

Toxicity Response of Electroactive Microbial Biofilms—A Decisive Feature for Potential Biosensor and Power Source Applications

Herein, we investigate the effect of exemplary biocides on wastewater-derived electroactive microbial biofilms. We show that the current response of these biofilms as a measure of their bioelectrocatalytic performance is not affected by the presence of antimicrobial compounds such as the sulfonamide-based antibiotics sulfamethaxozole and sulfadiazin, the disinfectant chloramine B and the metal ions Cu(2+), Ag(+), Pb(2+), and Hg(2+), even at concentrations an order of magnitude higher than average concentrations of these compounds in wastewaters. In contrast to the electroactive biofilms, planktonic cells of the same origin, studied in a mediator-based microbial fuel cell, are massively affected by the presence of the antimicrobial agents.

Revealing the electrochemically driven selection in natural community derived microbial biofilms using flow-cytometry

In this communication we demonstrate that electrochemically active microbial biofilms and their enrichment at the anode of a microbial bioelectrochemical system (BES) can be quantitatively and easily characterized by flow-cytometry. This analysis revealed that the anodic biofilm of a BES, formed from a highly diverse microbial community and fed with single substrate artificial wastewater, was dominated by only one phylotype.