Investigating the specific role of external load on the performance versus stability trade-off in microbial fuel cells

The performance and behavior of microbial fuel cells (MFCs) are influenced by among others the external load (Rext). In this study, the anode-surface biofilm formation in MFCs operated under different Rext selection/tracking-strategies was assessed. MFCs were characterized by electrochemical (voltage/current generation, polarization tests, EIS), molecular biological (microbial consortium analysis) and bioinformatics (principal component analysis) tools. The results indicated that the MFC with dynamic Rext adjustment (as a function of the actual MFC internal resistance) achieved notably higher performance but relatively lower operational stability, mainly due to the acidification of the biofilm. The opposite (lower performance, increased stability) could be observed with the static (low or high) Rext application (or OCV) strategies, where adaptive microbial processes were assumed. These possible adaptation phenomena were outlined by a theoretical framework and the significant impact of Rext on the anode colonization process and energy recovery with MFCs was concluded

Comparison of anaerobic degradation processes for bioenergy generation from liquid fraction of pressed solid waste

A novel substrate (obtained from biofraction of municipal solid waste by pressing and called LPW) rich in organic substances was used in three anaerobic degradation processes (biogas, biohydrogen fermentation and microbial fuel cells) to comparatively assess their feasibility for energy recovery. It has turned out that all the processes have successfully degraded that substrate and produced energy carriers (methane and hydrogen) as well as bioelectricity. The maximum energy yields (J g-1 CODremoved day-1) and associated COD removal capacities were 255, 200, 2.8 and 46, 52 and 72 % for biohydrogen, biogas and microbial fuel cell, respectively. The outcomes suggested the prominence of biohydrogen process for simultaneous waste treatment and energy recovery from LPWunder the test conditions ensured. © Springer Science+Business Media Dordrecht 2015

Bioelectrochemical treatment of municipal waste liquor in microbial fuel cells for energy valorization

Microbial fuel cells (MFCs) are recognized as promising applications to produce bioelectricity by utilizing various waste materials. In this study, dual-chamber microbial fuel cells were employed for energy valorization of an untested substrate, the liquid fraction of pressed municipal solid waste (LPW). This by-product is potentially applicable as a substrate in MFCs because of its high organic matter content. In the course of the experiments, the anodic biofilm response and energy production efficiency have been investigated by experimental design approach, taking substrate and fresh inoculum - mesophilic anaerobic sludge (MAS) - addition into account as factors. It was observed that reinoculation could result in a negative effect on the energy production, especially at low substrate (LPW) dosing levels. However, when the LPW to fresh MAS ratio in the anode chamber exceeded a particular value, the biofilm-associated electrical utilization dominated against the degradation in the bulk phase. Furthermore, the results indicated that the highest energy yields (8-9Jg-1δCODd-1) could be attained at the lowest input COD concentrations. The maximal and average COD removal efficiencies were 94% and 87%, respectively, which indicate the excellent biodegradability of LPW. As for COD removal rate, 1.2-1.9kgCODm-3d-1 could be reached. © 2015 Elsevier Ltd

Municipal waste liquor treatment via bioelectrochemical and fermentation (H2 + CH4) processes: Assessment of various technological sequences

In this paper, the anaerobic treatment of a high organic-strength wastewater-type feedstoc®k, referred as the liquid fraction of pressed municipal solid waste (LPW) was studied for energy recovery and organic matter removal. The processes investigated were (i) dark fermentation to produce biohydrogen, (ii) anaerobic digestion for biogas formation and (iii) microbial fuel cells for electrical energy generation. To find a feasible alternative for LPW treatment (meeting the two-fold aims given above), various one- as well as multi-stage processes were tested. The applications were evaluated based on their (i) COD removal efficiencies and (ii) specific energy gain. As a result, considering the former aspect, the single-stage processes could be ranked as: microbial fuel cell (92.4 %)> anaerobic digestion (50.2 %)> hydrogen fermentation (8.8 %). From the latter standpoint, an order of hydrogen fermentation (2277 J g-1 CODremoved d-1)> anaerobic digestion (205 J g-1 CODremoved d-1)> microbial fuel cell (0.43 J g-1 CODremoved d-1) was attained. The assessment showed that combined, multi-step treatment was necessary to simultaneously achieve efficient organic matter removal and energy recovery from LPW. Therefore, a three-stage system (hydrogen fermentation-biomethanation-bioelectrochemical cell in sequence) was suggested. The different approaches were characterized via the estimation of COD balance, as well

Feasibility of quaternary ammonium and 1,4-diazabicyclo[2.2.2]octane-functionalized anion-exchange membranes for biohydrogen production in microbial electrolysis cells

In this work, two commercialized anion-exchange membranes (AEMs), AMI-7001 and AF49R27, were applied in microbial electrolysis cells (MECs) and compared with a novel AEM (PSEBS CM DBC, functionalized with 1,4-diazabicyclo[2.2.2]octane) to produce biohydrogen. The evaluation regarding the effect of using different AEMs was carried out using simple (acetate) and complex (mixture of acetate, butyrate and propionate to mimic dark fermentation effluent) substrates. The MECs equipped with various AEMs were assessed based on their electrochemical efficiencies, H2 generation capacities and the composition of anodic biofilm communities. pH imbalances, ionic losses and cathodic overpotentials were taken into consideration together with changes to substantial AEM properties (particularly ion-exchange capacity, ionic conductivity, area- and specific resistances) before and after AEMs were applied in the process to describe their potential impact on the behavior of MECs. It was concluded that the MECs which employed the PSEBS CM DBC membrane provided the highest H2 yield and lowest internal losses compared to the two other separators. Therefore, it has the potential to improve MECs

Enzyme kinetics approach to assess biocatalyst inhibition and deactivation caused by [bmim][Cl] ionic liquid during cellulose hydrolysis

The aim of this work was to study the inhibition and deactivation of commercial enzyme cocktail (Cellic® Htec2) in the presence of [bmim][Cl] ionic liquid employing model cellulosic substrate, carboxymethyl cellulose (CMC). It turned out from the experiements – relying on enzyme kinetics appproach – that [bmim][Cl] could act as a competitive inhibitor. Furthermore, depending on the process conditions i.e. contact of enzyme solution with high concentration [bmim][Cl], severe biocatalyst inactivation should be also taken into account as a potential risk during the enzymatic cellulose hydrolysis even in as short process times as few minutes

On the efficiency of dual-chamber biocatalytic electrochemical cells applying membrane separators prepared with imidazolium-type ionic liquids containing [NTf2]− and [PF6]− anions

In this study, the dependency of energy recovery on separator characteristics applied in microbial fuel cells (MFCs) was sought by testing an emerging class of membranes (supported ionic liquid membranes (SILMs), prepared with [hmim][PF6] and [bmim][NTf2] ionic liquids) comparatively with well-known proton exchange (Nafion N115) and microfiltration (PVDF) counterparts. Crucial membrane features such as O2 and substrate (acetate as the sole carbon source) crossovers were assessed and as a result, mass transfer as well as diffusivity coefficients of these compounds (kO, kA, DO, DA, respectively) were determined. The experiments showed that SILM-operated MFCs could work in a reliable way and among them, the [bmim][NTf2]-based one produced higher specific energy yield (YS = 9.78 kJ g−1CODin m−2) than the Nafion-MFC (YS = 8.25 kJ g−1CODin m−2) used as an important reference. This outcome was found to be associated with the membrane-cross oxygen shuttle properties of the membranes (kO = 1.25 cm s−1 and 1.31 cm s−1, respectively). As for the two SILMs, significant differences in terms of the energy yield, mass transfer and diffusion coefficients were noted, however, it has appeared from cell polarization measurements that the internal resistances of the SILM-MFCs were nearly the same. The evaluation of the SILM-operated MFCs’ power production was complemented by measuring the dielectric traits of ionic liquids that can be related with the ion conductivity of these materials. It turned out that the [hmim][PF6] IL had an order of magnitude lower ionic conductivity

Performance evaluation of microbial electrochemical systems operated with Nafion and supported ionic liquid membranes

In this work, the performance of dual-chamber microbial fuel cells (MFCs) constructed either with commonly used Nafion® proton exchange membrane or supported ionic liquid membranes (SILMs) was assessed. The behavior of MFCs was followed and analyzed by taking the polarization curves and besides, their efficiency was characterized by measuring the electricity generation using various substrates such as acetate and glucose. By using the SILMs containing either [C6mim][PF6] or [Bmim][NTf2] ionic liquids, the energy production of these MFCs from glucose was comparable to that obtained with the MFC employing polymeric Nafion® and the same substrate. Furthermore, the MFC operated with [Bmim][NTf2]-based SILM demonstrated higher energy yield in case of low acetate loading (80.1 J g−1 CODin m−2 h−1) than the one with the polymeric Nafion® N115 (59 J g−1 CODin m−2 h−1). Significant difference was observed between the two SILM-MFCs, however, the characteristics of the system was similar based on the cell polarization measurements. The results suggest that membrane-engineering applying ionic liquids can be an interesting subject field for bioelectrochemical system research