A critical revisit of the key parameters used to describe microbial electrochemical systems

Electro-stimulated microbial factory for value added product synthesis

Interplay of charge between bacteria and electrode has led to emergence of bioelectrochemical systems which leads to applications such as production of electricity, wastewater treatment, bioremediation and production of value added products. Many electroactive bacteria have been identified that have unique external electron transport systems. Coupling of electron transport with carbon metabolism has opened a new approach of carbon dioxide sequestration. The electron transport mechanism involves various cellular and sub cellular molecules. The outer membrane cytochromes, Mtr-complex and Ech-complex are few key molecules involved in electron transport in many electrogenic bacteria. Few cytochrome independent acetogenic electroactive bacteria were also discovered using Rnf complex to transport electrons. For improved productivity, an efficient bioreactor design is mandatory. It should encompass all certain critical issues such as microbial cell retention, charge dissipation, separators and simultaneous product recovery.

Cathodic bacterial community structure applying the different co-substrates for reductive decolorization of Alizarin Yellow R

Selective enrichment of cathodic bacterial community was investigated during reductive decolorization of AYR fedding with glucose or acetate as co-substrates in biocathode. A clear distinction of phylotype structures were observed between glucose-fed and acetate-fed biocathodes. In glucose-fed biocathode, Citrobacter (29.2%), Enterococcus (14.7%) and Alkaliflexus (9.2%) were predominant, and while, in acetate-fed biocathode, Acinetobacter (17.8%) and Achromobacter (6.4%) were dominant. Some electroactive or reductive decolorization genera, like Pseudomonas, Delftia and Dechloromonas were commonly enriched. Both of the higher AYR decolorization rate (k(AYR)=0.46) and p-phenylenediamine (PPD) generation rate (k(PPD)=0.38) were obtained fed with glucose than acetate (k(AYR)=0.18; k(PPD)=0.16). The electrochemical behavior analysis represented a total resistance in glucose-fed condition was about 73.2% lower than acetate-fed condition. The different co-substrate types, resulted in alteration of structure, richness and composition of bacterial communities, which significantly impacted the performances and electrochemical behaviors during reductive decolorization of azo dyes in biocathode.

Carbon Material Optimized Biocathode for Improving Microbial Fuel Cell Performance

To improve the performance of microbial fuel cells (MFCs), the biocathode electrode material of double-chamber was optimized. Alongside the basic carbon fiber brush, three carbon materials namely graphite granules, activated carbon granules (ACG) and activated carbon powder, were added to the cathode-chambers to improve power generation. The result shows that the addition of carbon materials increased the amount of available electroactive microbes on the electrode surface and thus promote oxygen reduction rate, which improved the generation performance of the MFCs. The Output current (external resistance = 1000 Ω) greatly increased after addition of the three carbon materials and maximum power densities in current stable phase increased by 47.4, 166.1, and 33.5%, respectively. Additionally, coulombic efficiencies of the MFC increased by 16.3, 64.3, and 20.1%, respectively. These results show that MFC when optimized with ACG show better power generation, higher chemical oxygen demands removal rate and coulombic efficiency.

A comparative evaluation of different types of microbial electrolysis desalination cells for malic acid production

The aim of this study was to investigate different microbial electrolysis desalination cells for malic acid production. The systems included microbial electrolysis desalination and chemical-production cell (MEDCC), microbial electrolysis desalination cell (MEDC) with bipolar membrane and anion exchange membrane (BP-A MEDC), MEDC with bipolar membrane and cation exchange membrane (BP-C MEDC), and modified microbial desalination cell (M-MDC). The microbial electrolysis desalination cells performed differently in terms of malic acid production and energy consumption. The MEDCC performed best with the highest malic acid production rate (18.4 ± 0.6 mmol/Lh) and the lowest energy consumption (0.35 ± 0.14 kWh/kg). The best performance of MEDCC was attributable to the neutral pH condition in the anode chamber, the lowest internal resistance, and the highest Geobacter percentage of the anode biofilm population among all the reactors.

Development of exoelectrogenic bioanode and study on feasibility of hydrogen production using abiotic VITO-CoRE™ and VITO-CASE™ electrodes in a single chamber microbial electrolysis cell (MEC) at low current densities

Single chamber membrane-free microbial electrolysis cell (MEC) was operated for the assessment of exoelectrogenic bacteria (EB) growth at carbon felt anode and resultant hydrogen (H2) production at abiotic cathodes, made using cold rolling (VITO-CoRE™) and casting (VITO-CASE™) methods. Progressive enrichment of EB was observed on anode during 70 days of operation at an applied potential of +0.2V vs Ag/AgCl, and a maximum current density (CD) of 330.59 mA/m(2) (1.38 mA) was recorded. H2 production at selected abiotic cathodes was observed, when the enriched bioanode was coupled to them in galvanostat mode between 0.1 and 1.0 mA current range for 10 min each. Higher H2 production of 114.46±3.75 mL/m(2) was documented with VITO-CoRE™ at 0.6 mA, while 102.76±3.75 mL/m(2) was recorded with VITO-CASE™ at 0.8 mA of current application. This study demonstrates the feasibility of H2 production on abiotic cathodes using enriched bioanode at low current densities.

Carbon dioxide reduction by mixed and pure cultures in microbial electrosynthesis using an assembly of graphite felt and stainless steel as a cathode

Carbon dioxide (CO2) reduction to multi-carbon compounds at the cathode using chemolithoautotrophs is an emerging application of microbial electrosynthesis (MES). In this study, CO2 reduction in MES was investigated at hydrogen evolving potentials, separately by a mixed culture and Clostridium ljungdahlii, using a graphite felt and stainless steel assembly as cathode. The mixed culture reactor produced acetate at the maximum rate of 1.3 mM d(-1), along with methane and hydrogen at -1.1 V/Ag/AgCl. Over 160 days of run-time in four fed-batches, 26% of bicarbonate was converted to acetate between day 28 and 41, whereas in the late batches, methane production prevailed. Out of 45 days of run-time in the C. ljungdahlii reactor, 2.4 mM d(-1) acetate production was achieved at -0.9 V/Ag/AgCl in Batch 1. Simultaneous product degradation occurred when the mixed culture was not selectively enriched. Hydrogen evolution is potentially the rapid way of transferring electrons to the biocatalysts for higher bioproduction rates.

Adaptively Evolving Bacterial Communities for Complete and Selective Reduction of Cr(VI), Cu(II), and Cd(II) in Biocathode Bioelectrochemical Systems

Bioelectrochemical systems (BESs) have been shown to be useful in removing individual metals from solutions, but effective treatment of electroplating and mining wastewaters requires simultaneous removal of several metals in a single system. To develop multiple-reactor BESs for metals removal, biocathodes were first individually acclimated to three different metals using microbial fuel cells with Cr(VI) or Cu(II) as these metals have relatively high redox potentials, and microbial electrolysis cells for reducing Cd(II) as this metal has a more negative redox potential. The BESs were then acclimated to low concentrations of a mixture of metals, followed by more elevated concentrations. This procedure resulted in complete and selective metal reduction at rates of 1.24 ± 0.01 mg/L-h for Cr(VI), 1.07 ± 0.01 mg/L-h for Cu(II), and 0.98 ± 0.01 mg/L-h for Cd(II). These reduction rates were larger than the no adaptive controls by factors of 2.5 for Cr(VI), 2.9 for Cu(II), and 3.6 for Cd(II). This adaptive procedure produced less diverse microbial communities and changes in the microbial communities at the phylum and genus levels. These results demonstrated that bacterial communities can adaptively evolve to utilize solutions containing mixtures of metals, providing a strategy for remediating wastewaters containing Cr(VI), Cu(II), and Cd(II).

Electrifying white biotechnology: engineering and economic potential of electricity-driven bio-production

The production of fuels and chemicals by electricity-driven bio-production (i.e., using electric energy to drive biosynthesis) holds great promises. However, this electrification of white biotechnology is particularly challenging to achieve because of the different optimal operating conditions of electrochemical and biochemical reactions. In this article, we address the technical parameters and obstacles to be taken into account when engineering microbial bioelectrochemical systems (BES) for bio-production. In addition, BES-based bio-production processes reported in the literature are compared against industrial needs showing that a still large gap has to be closed. Finally, the feasibility of BES bio-production is analysed based on bulk electricity prices. Using the example of lysine production from sucrose, we demonstrate that there is a realistic market potential as cost savings of 8.4 % (in EU) and 18.0 % (in US) could be anticipated, if the necessary yields can be obtained.

Bio-electro degradation of azo-dye in a combined anaerobic–aerobic process along with energy recovery

Complete removal of reactive orange 16 in a microbial fuel cell coupled aerobic post-treatment process along with energy recovery.

Optimization of electrochemical parameters for sulfate-reducing bacteria (SRB) based biocathode

This study focuses on the effect of operational and physiochemical factors on a stable sulfate reducing bacteria biocathode and their effect on the electrochemical response thereof.

Evaluating the effects of scaling up on the performance of bioelectrochemical systems using a technical scale microbial electrolysis cell

This study focuses on the challenges of the scaling up process of bioelectrochemical systems on the example of a technical scale microbial electrolysis cell referred to as the "prototype". Anodically treating real wastewater and operated in continuous mode at a hydraulic retention time of 1.23 d with an average chemical oxygen demand (COD)-loading rate of 0.5 g O2 d(-1) L Reactor(-1) the prototype on average showed COD removal efficiency of 67% with effluent concentrations of 210 mg O2 L(-1) and an ammonium elimination rate of 17.8 ± 3.9 mg Nd(-1) L Reactor(-1) resulting in effluent concentrations of 30.7 ± 3.7 mg NL(-1) with a removal efficiency of 40% at a current generation of 72 μA cm(-2) and Coulomb efficiency of 11%. A model is described as a method for comparing conventional and BES based technology using the above mentioned criteria and balancing them against the respective loading rates.