Recovery of chromium, copper and vanadium combined with electricity generation in two-chambered microbial fuel cells.

Microbial fuel cells (MFCs) offer a promising solution towards recovery and treatment of heavy metal pollutants. In this study, two-chambered MFCs were employed for recovery of chromium, copper and vanadium (Cr (VI), Cu (II) and V (V)). One g/L concentrations of K2Cr2O7, CuCl2 and NaVO3 served as catholytes, while a mixed culture was used as anolyte. Cr (VI), Cu (II) and V (V) were reduced biologically into less toxic forms of Cr (III), Cu and V (IV) respectively. Power density and cathodic efficiency were calculated for each of the catholytes. Cr (VI) gave the maximum power density and cathodic efficiency due to its high redox potential. Current produced depended on the concentration of the catholyte. Over a period of time, biological reduction of catholytes lead to decrease in the metal concentrations, which demonstrated the application of MFC technology towards heavy metal treatment and recovery in a reasonably cost-effective manner.

Fluctuation of electrode potential based on molecular regulation induced diversity of electrogenesis behavior in multiple equilibrium microbial fuel cell.

In this study, the electrogenesis behaviors and mechanisms in multiple equilibrium microbial fuel cells (MEMFCs) which volatile fatty acids as multiple electron donors are investigated. The electrochemical property and energy recovery can be enhanced in propionic acid dominant systems (HPr-D-MEMFCs) which compares to butyric acid dominant systems (HBu-D-MEMFCs), increase power density from 0.04 to 0.43 W/m2 and energy recovery efficiency from 2.07 to 5.44%, respectively. With isotope experiment analysis, the fluctuation of electrode potentials induce diverse electrogenesis pathways that high utilization efficiencies and bioconversion efficiency of hybrid acids observed in HPr-D-MEMFCs which different with HAc-D-MEMFCs and HBu-D-MEMFCs. In addition, the electrochemical and microbial community variation of MEMFCs reveal that the direct interspecies electron transfer stimulated with higher electric double layer capacitance, and activities of exoelectrogens enhanced with high relative abundance in HPr-D-MEMFCs. The findings present an intensive study in electrogenesis, providing a promising way to promote energy recovery and further extend its application value.

In Situ Engineering of Intracellular Hemoglobin for Implantable High-Performance Biofuel Cells.

The key challenge for the broad application of implantable biofuel cells (BFCs) is to achieve inorganic-organic composite biocompatibility while improving the activity and selectivity of the catalysts. We have fabricated nanoengineered red blood cells (NERBCs) by an environmentally friendly method by using red blood cells as the raw material and hemoglobin (Hb) embedded with ultrasmall hydroxyapatite (HAP, Ca10 (PO4 )6 (OH)2 ) as the functional BFC cathode material. The NERBCs showed greatly enhanced cell performance with high electrocatalytic activity, stability, and selectivity. The NERBCs maintained the original biological properties of the natural cell, while enhancing the catalytic oxygen reduction reaction (ORR) through the interaction between -OH groups in HAP and the Hb in RBCs. They also enabled direct electron transportation, eliminating the need for an electron-transfer mediator, and showed catalytic inactivity for glucose oxidation, thus potentially enabling the development of separator-free BFCs.

Performance of trickling bed microbial fuel cell treating isopropyl alcohol vapor: Effects of shock-load and shut-down episodes.

This work investigates the enhancement in the removal efficiency of isopropyl alcohol (IPA) vapor by a hollow trickling-bed microbial fuel cell (TB-MFC) that can be achieved by certain modifications. The effects of shock load and shutdown on the performance of TB-MFC were evaluated. When organic loading (OL) of IPA was approximately 22.1-88.5 g m-3 h-1, the removal efficiency of 85.1-93.8% of the TB-MFC was achieved. With an empty bed residence time (EBRT) of 60 s and an inlet IPA concentration of 4.42 g m-3, the TB-MFC achieved its maximum EC of 150 g m-3 h-1, which was 1.7-4 times higher than reported for conventional biofiltration technology. A maximum closed-circuit voltage (CCV) of 173 mV and maximum power density (PDmax) of 53.2 mW m-3 were obtained under optimal conditions (IPA concentration = 0.73 g m-3; EBRT = 60 s). Short-term shutdown (seven days) did not cause significant changes in EC, CCV, and PDmax of the TB-MFC. This investigation establishes the feasibility of using a trickling-bed MFC to substantially increase the removal of IPA and handle shock-load and shut-down events. To increase EC and power output, this laboratory-scale TB-MFC could easily be scaled up by stacking anodes, and has great potential for future application in the field in various industries.

Optimizing the performance of organics and nutrient removal in constructed wetland-microbial fuel cell systems.

No studies have reported the operation optimization of constructed wetland-microbial fuel cell (CW-MFC) systems in terms of pollutant removal under the influence of multiple factors. Multifactor orthogonal experiment (L25(55)) was designed in this study to investigate the influence of multiple factors on the CW-MFC performance and determine the optimal operating conditions for the organics and nutrient removal. The tested factors include volume ratio of granular graphite in the substrates (A), dissolved oxygen (DO) concentration in the cathode zone (B), hydraulic retention time (HRT) (C), effluent reflux ratio (D), and external resistance (E). The results showed that the sequence and degree of the influence of the tested factors were C** > B** > E** > D* > A for chemical oxygen demand (CODCr) removal, C** > B** > D* > E > A for ammonia nitrogen (NH3-N) removal, C** > D** > B** > E* > A* for total nitrogen (TN) removal, and C** > D* > B > A > E for total phosphorus (TP) removal (* denotes significant influence (0.01 < p < 0.05) and ** denotes extremely significant influence (p ≤ 0.01)). HRT was found to be the most influential factor for pollutant removal in CW-MFCs with a contribution of over 50% for CODCr, NH3-N and TP removal, and over 45% for TN removal. The optimal operating conditions for CODCr, NH3-N, TN and TP removal in CW-MFCs were quite different from each other. Comprehensively considering the treatment efficiency of pollutant, treatment capacity of wastewater, and energy consumption from artificial aeration, the selected comprehensive optimal operating conditions for CW-MFCs were A = 20%, B = 1.5 mg/L, C = 1.5 days, D = 50%, and E ≤ 250 Ω. Moreover, incorporating the MFC significantly enhanced the organics and nitrogen removal in CWs by 8.72-11.04% CODCr and 9.78-12.04% TN.

Quick start-up and performance of microbial fuel cell enhanced with a polydiallyldimethylammonium chloride modified carbon felt anode.

It is of significant importance to simultaneously shorten the start-up time and enhance the electricity generation performance for practical application of microbial fuel cell (MFC). In this paper, the polydiallyldimethylammonium chloride (PDDA) modified carbon felt (PDDA-CF) electrode was prepared and used as the anode of PDDA-MFC. The anode significantly enhanced the start-up speed and electricity generation and dye wastewater degradation performances of the PDDA-MFC. The start-up time of PDDA-MFC is only 9 h, which is only 7.5% that of the unmodified carbon felt anode MFC (CF-MFC). The charge transfer resistance, the maximum output voltage and the maximum output power density of PDDA-MFC were 9.7 Ω, 741 mV and 537.8 mW m-2 respectively, which were 70.3% lower than, 1.7 times and 3.3 times greater than those of CF-MFC respectively. In addition, the color and chemical oxygen demand (COD) removal rates of Reactive Brilliant Red X-3B for PDDA-MFC reached 95.94% and 64.24% at 24 h respectively, which were 41.5% and 51.2% higher than those of CF-MFC respectively. Due to the electrostatic attraction of PDDA, the adhesion and metabolic mass transfer rate of exoelectrogens are accelerated, thus the PDDA-CF electrode has excellent electrochemical properties and bio-affinity. This paper provides a new idea to enhance the start-up speed and performance of MFC simultaneously.

A novel photoactive and three-dimensional stainless steel anode dramatically enhances the current density of bioelectrochemical systems.

This study reports a high-performance 3D stainless-steel photoanode (3D SS photoanode) for bioelectrochemical systems (BESs). The 3D SS photoanode consists of 3D carbon-coated SS felt bioactive side and a flat α-Fe2O3-coated SS plate photoactive side. Without light illumination, the electrode reached a current density of 26.2 ±â€¯1.9 A m-2, which was already one of the highest current densities reported thus far. Under illumination, the current density of the electrode was further increased to 46.5 ±â€¯2.9 A m-2. The mechanism of the photo-enhanced current production can be attributed to the reduced charge-transfer resistance between electrode surface and the biofilm with illumination. It was also found that long-term light illumination can enhance the biofilm formation on the 3D SS photoanode. These findings demonstrate that using the synergistic effect of photocatalysis and microbial electrocatalysis is an efficient way to boost the current production of the existing high-performance 3D anodes for BESs.

Agricultural anaerobic digestion power plants in Ireland and Germany: policy and practice.

The process of anaerobic digestion (AD) is valued as a carbon-neutral energy source, while simultaneously treating organic waste, making it safer for disposal or use as a fertilizer on agricultural land. The AD process in many European nations, such as Germany, has grown from use of small, localized digesters to the operation of large-scale treatment facilities, which contribute significantly to national renewable energy quotas. However, these large AD plants are costly to run and demand intensive farming of energy crops for feedstock. Current policy in Germany has transitioned to support funding for smaller digesters, while also limiting the use of energy crops. AD within Ireland, as a new technology, is affected by ambiguous governmental policies concerning waste and energy. A clear governmental strategy supporting on-site AD processing of agricultural waste will significantly reduce Ireland's carbon footprint, improve the safety and bioavailability of agricultural waste, and provide an indigenous renewable energy source. © 2016 Society of Chemical Industry.

Biofilm as a redox conductor: a systematic study of the moisture and temperature dependence of its electrical properties.

Some microbial biofilms are electrically conductive. However, the mechanism of electron transport remains unclear. Here, we show that µm-scale long-distance electron transport through electrode-grown Geobacter sulfurreducens biofilms occurs via redox conduction, as determined by electrical measurements performed under varied hydration states and temperatures.

Surgical Ablation of Atrial Fibrillation Using Energy Sources

ABSTRACT Surgical ablation, concomitant with other operations, is an option for treatment in patients with chronic atrial fibrillation. The aim of this study is to present a literature review on surgical ablation of atrial fibrillation in patients undergoing cardiac surgery, considering energy sources and return to sinus rhythm. A comprehensive survey was performed in the literature on surgical ablation of atrial fibrillation considering energy sources, sample size, study type, outcome (early and late), and return to sinus rhythm. Analyzing studies with immediate results (n=5), the percentage of return to sinus rhythm ranged from 73% to 96%, while those with long-term results (n=20) (from 12 months on) ranged from 62% to 97.7%. In both of them, there was subsequent clinical improvement of patients who underwent ablation, regardless of the energy source used. Surgical ablation of atrial fibrillation is essential for the treatment of this arrhythmia. With current technology, it may be minimally invasive, making it mandatory to perform a procedure in an attempt to revert to sinus rhythm in patients requiring heart surgery.

Surgical Ablation of Atrial Fibrillation Using Energy Sources.

Surgical ablation, concomitant with other operations, is an option for treatment in patients with chronic atrial fibrillation. The aim of this study is to present a literature review on surgical ablation of atrial fibrillation in patients undergoing cardiac surgery, considering energy sources and return to sinus rhythm. A comprehensive survey was performed in the literature on surgical ablation of atrial fibrillation considering energy sources, sample size, study type, outcome (early and late), and return to sinus rhythm. Analyzing studies with immediate results (n=5), the percentage of return to sinus rhythm ranged from 73% to 96%, while those with long-term results (n=20) (from 12 months on) ranged from 62% to 97.7%. In both of them, there was subsequent clinical improvement of patients who underwent ablation, regardless of the energy source used. Surgical ablation of atrial fibrillation is essential for the treatment of this arrhythmia. With current technology, it may be minimally invasive, making it mandatory to perform a procedure in an attempt to revert to sinus rhythm in patients requiring heart surgery.

Enhanced electricity generation by using algae biomass and activated sludge in microbial fuel cell.

Recently, interest is growing to explore low-cost and sustainable means of energy production. In this study, we have exploited the potential of sustainable energy production from wastes. Activated sludge and algae biomass are used as substrates in microbial fuel cell (MFC) to produce electricity. Activated sludge is used at anode as inoculum and nutrient source. Various concentrations (1-5 g/L) of dry algae biomass are tested. Among tested concentrations, 5 g/L (5000 mg COD/L) produced the highest voltage of 0.89 V and power density of 1.78 W/m(2) under 1000 Ω electric resistance. Pre-treated algae biomass and activated sludge are also used at anode. They give low power output than without pre-treatment. Spent algae biomass is tested to replace whole (before oil extraction) algae biomass as a substrate, but it gives low power output. This work has proved the concept of using algae biomass in MFC for high energy output.

MFC-cascade stacks maximise COD reduction and avoid voltage reversal under adverse conditions.

Six continuous-flow Microbial Fuel Cells (MFCs) configured as a vertical cascade and tested under different electrical connections are presented. When in parallel, stable operation and higher power and current densities than individual MFCs were observed, despite substrate imbalances. The cascading dynamic allowed for a cumulative COD reduction of >95% in approximately 5.7h, equivalent to 7.97 kg COD m(-3) d(-1). Under a series configuration, the stack exhibited considerable losses until correct fluidic/electrical insulation of the units was applied, upon which the stack also exhibited superior performance. In both electrical configurations, the 6 MFC system was systematically starved for up to 15 d, with no significant performance degradation. The results from the 14-month trials, demonstrate that cascade-stacking of small units can result in enhanced electricity production (vs single large units) and treatment rates without using expensive catalysts. It is also demonstrated that substrate imbalances and starvation do not necessarily result in cell-voltage reversal.

Improving startup performance with carbon mesh anodes in separator electrode assembly microbial fuel cells.

In a separator electrode assembly microbial fuel cell, oxygen crossover from the cathode inhibits current generation by exoelectrogenic bacteria, resulting in poor reactor startup and performance. To determine the best approach for improving startup performance, the effect of acclimation to a low set potential (-0.2V, versus standard hydrogen electrode) was compared to startup at a higher potential (+0.2 V) or no set potential, and inoculation with wastewater or pre-acclimated cultures. Anodes acclimated to -0.2 V produced the highest power of 1330±60 mW m(-2) for these different anode conditions, but unacclimated wastewater inocula produced inconsistent results despite the use of this set potential. By inoculating reactors with transferred cell suspensions, however, startup time was reduced and high power was consistently produced. These results show that pre-acclimation at -0.2 V consistently improves power production compared to use of a more positive potential or the lack of a set potential.

Glucose oxidase nanotube-based enzymatic biofuel cells with improved laccase biocathodes.

Glucose/O(2) biofuel cells (BFCs) with an improved power density and stability were developed, using glucose oxidase (GOD) nanotubes with polypyrrole (PPy)-carbon nanotubes (CNTs)-GOD layers deposited on their surface as an anode and a PPy-laccase-2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) film type cathode. The GOD nanotubes were fabricated within the nanopores of an anodized aluminum oxide membrane using a template-assisted layer-by-layer deposition method. These BFCs exhibited a higher volumetric power than the best performance reported previously; this was likely due to an increase in enzyme loading of GOD nanotubes and improved electrochemical properties of the PPy-CNTs-GOD layers. The stability of BFCs was closely related to the leakage of ABTS from the cathode. When the leakage of ABTS was suppressed, the power density of BFCs was nearly unchanged for at least 8 days under physiological conditions.

Performance of planar and cylindrical carbon electrodes at sedimentary microbial fuel cells.

This paper presents data obtained using an indigenous microbial community contained in anaerobic sediments (mud) collected from the shore of the Río de La Plata River (South America). After the sedimentary microbial fuel cells were assembled the evolution of current and power vs. time was studied. Two types of commercially available graphite materials were used as electrodes, which differ mainly in shape and size. In some experiments, an external carbon source (acetate) increased the power generation rate. The maximum power density observed in the aforementioned condition was 19.57 ± 0.35 and 8.72 ± 1.39 mW/m(2) using rod and graphite disk electrodes, respectively. The better performance of the rod electrodes can be explained, at least in part, by an enhanced rate of mass transport by radial diffusion. DGGE fingerprints were used to study the electrogenic community growing over the electrodes.

The environmental sustainability of anaerobic digestion as a biomass valorization technology.

This paper studies the environmental sustainability of anaerobic digestion from three perspectives. First, reference electricity is compared to electricity production from domestic organic waste and energy crop digestion. Second, different digester feed possibilities in an agricultural context are studied. Third, the influence of applying digestate as fertilizer is investigated. Results highlight that biomass is converted at a rational exergy (energy) efficiency ranging from 15.3% (22.6) to 33.3% (36.0). From a life cycle perspective, a saving of over 90% resources is achieved in most categories when comparing biobased electricity to conventional electricity. However, operation without heat valorization results in 32% loss of this performance while using organic waste (domestic and agricultural residues) as feedstock avoids land resources. The use of digestate as a fertilizer is beneficial from a resource perspective, but causes increased nitrogen and methane emissions, which can be reduced by 50%, making anaerobic digestion an environmentally competitive bioenergy technology.

Effect of cathode types on long-term performance and anode bacterial communities in microbial fuel cells.

Effects of cathode types on the long-term stability of microbial fuel cell (MFC) and the anodic microbial communities were studied using K(3)Fe(CN)(6) catholyte (R1), air cathode (R2) and biocathode (R3) over a testing time of 400 d. Upon 400 d of testing, the maximum power densities (P(max)) of R1 and R2 decreased by 44% and 37%, and the Coulombic efficiencies (CEs) decreased 8.4% (R1) and 2.0% (R2), respectively, using the performances on 10d as the comparison basis. Conversely, the P(max) and CE of R3 increased by 68.2% and 116.8%, respectively. The non-ohmic resistances (R(no)) in all tests were the principal contributors of cell internal resistances. Phylogenetic analyses revealed that the microbial communities on anodic surface varied with cathode types and operational history.

Performance of a continuous flow microbial electrolysis cell (MEC) fed with domestic wastewater.

In this study, MEC performance was investigated in terms of chemical oxygen demand (COD) removal, hydrogen production rate and energy consumption during continuous domestic wastewater (dWW) treatment at different organic loading rates (OLR) and applied voltages (Vapp). While the COD removal efficiency was improved at low OLRs, the electrical energy required to remove 1g of COD was significantly increased with decreasing the OLR. Hydrogen production exhibited a Monod-type trend as function of the OLR reaching a maximum production rate of 0.30 L/(Lrd). Optimal Vapp was found to be highly dependent on the strength of the dWW. The results also confirmed the fact that MEC performance can be optimized by setting Vapp at the onset potential of the diffusion control region. Although low columbic efficiencies and the occurrence of hydrogen recycling limited significantly the reactor performance, these results demonstrate that MEC can be successfully used for dWW treatment.

Improved performance of the microbial electrolysis desalination and chemical-production cell using the stack structure.

The microbial electrolysis desalination and chemical-production cell (MEDCC) is a device to desalinate seawater, and produce acid and alkali. The objective of this study was to enhance the desalination and chemical-production performance of the MEDCC using two types of stack structure. Experiments were conducted with different membrane spacings, numbers of desalination chambers and applied voltages. Results showed that the stack construction in the MEDCC enhanced the desalination and chemical-production rates. The maximal desalination rate of 0.58 ± 0.02 mmol/h, which was 43% higher than that in the MEDCC, was achieved in the four-desalination-chamber MEDCC with the AEM-CEM stack structure and the membrane spacing of 1.5mm. The maximal acid- and alkali-production rates of 0.079 ± 0.006 and 0.13 ± 0.02 mmol/h, which were 46% and 8% higher than that in the MEDCC, respectively, were achieved in the two-desalination-chamber MEDCC with the BPM-AEM-CEM stack structure and the membrane spacing of 3mm.