Treatment of biodiesel production wastes with simultaneous electricity generation using a single-chamber microbial fuel cell

Biodiesel production through transesterification of lipids generates large quantity of biodiesel waste (BW) containing mainly glycerin. BW can be treated in various ways including distillation to produce glycerin, use as substrate for fermentative propanediol production and discharge as wastes. This study examined microbial fuel cells (MFCs) to treat BW with simultaneous electricity generation. The maximum power density using BW was 487 ± 28 mW/m² cathode (1.5 A/m² cathode) with 50 mM phosphate buffer solution (PBS) as the electrolyte, which was comparable with 533 ± 14 mW/m² cathode obtained from MFCs fed with glycerin medium (COD 1400 mg/L). The power density increased from 778 ± 67 mW/m² cathode using carbon cloth to 1310 ± 15 mW/m² cathode using carbon brush as anode in 200 mM PBS electrolyte. The power density was further increased to 2110 ± 68 mW/m² cathode using the heat-treated carbon brush anode. Coulombic efficiencies (CEs) increased from 8.8 ± 0.6% with carbon cloth anode to 10.4 ± 0.9% and 18.7 ± 0.9% with carbon brush anode and heat-treated carbon brush anode, respectively.     

Application of Co-naphthalocyanine (CoNPc) as alternative cathode catalyst and support structure for microbial fuel cells

Co-naphthalocyanine (CoNPc) was prepared by heat treatment for cathode catalysts to be used in microbial fuel cells (MFCs). Four different catalysts (Carbon black, NPc/C, CoNPc/C, Pt/C) were compared and characterized using XPS, EDAX and TEM. The electrochemical characteristics of oxygen reduction reaction (ORR) were compared by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The Co-macrocyclic complex improves the catalyst dispersion and oxygen reduction reaction of CoNPc/C. The maximum power of CoNPc/C was 64.7 mW/m² at 0.25 mA as compared with 81.3 mW/m² of Pt/C, 29.7 mW/m² of NPc/C and 9.3 mW/m² of carbon black when the cathodes were implemented in H-type MFCs. The steady state cell, cathode and anode potential of MFC with using CoNPc/C were comparable to those of Pt/C.     

Improved performance of membrane free single-chamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes

Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened by 45% and 51%, respectively as compared to that for MFC-AT equipped with an unmodified anode. Moreover, the power output of MFCs with modified anodes was significantly improved. In comparison with MFC-AT which had a maximum power density of 1304 mW/m², the MFC-N achieved a maximum power density of 1641 mW/m². The nitric acid-treated anode in MFC-A increased the power density by 58% reaching 2066 mW/m². XPS analysis of the treated and untreated anode materials indicated that the power enhancement was attributable to the changes of surface functional groups.     

Growth of <Emphasis Type="Italic">Salinispora tropica</Emphasis> strains CNB440, CNB476, and NPS21184 in nonsaline,low-sodium media

Effective wastewater treatment using microbial fuel cells (MFCs) will require a better understanding of how operational parameters and solution chemistry affect treatment efficiency, but few studies have examined power generation using actual wastewaters. The efficiency of wastewater treatment of a beer brewery wastewater was examined here in terms of maximum power densities, Coulombic efficiencies (CEs), and chemical oxygen demand (COD) removal as a function of temperature and wastewater strength. Decreasing the temperature from 30°C to 20°C reduced the maximum power density from 205 mW/m² (5.1 W/m³, 0.76 A/m²; 30°C) to 170 mW/m² (20°C). COD removals (R _COD) and CEs decreased only slightly with temperature. The buffering capacity strongly affected reactor performance. The addition of a 50-mM phosphate buffer increased power output by 136% to 438 mW/m², and 200 mM buffer increased power by 158% to 528 mW/m². In the absence of salts (NaCl), maximum power output varied linearly with wastewater strength (84 to 2,240 mg COD/L) from 29 to 205 mW/m². When NaCl was added to increase conductivity, power output followed a Monod-like relationship with wastewater strength. The maximum power (P _max) increased in proportion to the solution conductivity, but the half-saturation constant was relatively unaffected and showed no correlation to solution conductivity. These results show that brewery wastewater can be effectively treated using MFCs, but that achievable power densities will depend on wastewater strength, solution conductivity, and buffering capacity.     

Effects on capacitance by overexpression of membrane proteins

Functional Channelrhodopsin-2 (ChR2) overexpression of about 10⁴ channels/μm² in the plasma membrane of HEK293 cells was studied by patch-clamp and freeze-fracture electron microscopy. Simultaneous electrorotation measurements revealed that ChR2 expression was accompanied by a marked increase of the area-specific membrane capacitance (C_m). The C_m increase apparently resulted partly from an enlargement of the size and/or number of microvilli. This is suggested by a relatively large C_m of 1.15 ± 0.08 μF/cm² in ChR2-expressing cells measured under isotonic conditions. This value was much higher than that of the control HEK293 cells (0.79 ± 0.02 μF/cm²). However, even after complete loss of microvilli under strong hypoosmolar conditions (100 mOsm), the ChR2-expressing cells still exhibited a significantly larger C_m (0.85 ± 0.07 μF/cm²) as compared to non-expressing control cells (0.70 ± 0.03 μF/cm²). Therefore, a second mechanism of capacitance increase may involve changes in the membrane permittivity and/or thickness due to the embedded ChR2 proteins.     

Effect of nitrogen addition on the performance of microbial fuel cell anodes

Carbon cloth anodes were modified with 4(N,N-dimethylamino)benzene diazonium tetrafluoroborate to increase nitrogen-containing functional groups at the anode surface in order to test whether the performance of microbial fuel cells (MFCs) could be improved by controllably modifying the anode surface chemistry. Anodes with the lowest extent of functionalization, based on a nitrogen/carbon ratio of 0.7 as measured by XPS, achieved the highest power density of 938 mW/m². This power density was 24% greater than an untreated anode, and similar to that obtained with an ammonia gas treatment previously shown to increase power. Increasing the nitrogen/carbon ratio to 3.8, however, decreased the power density to 707 mW/m². These results demonstrate that a small amount of nitrogen functionalization on the carbon cloth material is sufficient to enhance MFC performance, likely as a result of promoting bacterial adhesion to the surface without adversely affecting microbial viability or electron transfer to the surface.     

Performance of microbial fuel cell in response to change in sludge loading rate at different anodic feed pH

Performance of two dual chambered mediator-less microbial fuel cells (MFCs) was evaluated at different sludge loading rate (SLR) and feed pH. Optimum performance in terms of organic matter removal and power production was obtained at the SLR of 0.75 kg COD kg VSS⁻¹ d⁻¹. Maximum power density of 158 mW/m² and 600 mW/m² was obtained in MFC-1 (feed pH 6.0) and MFC-2 (feed pH 8.0), respectively. Internal resistance of the cell decreased with increase in SLR. When operated only with biofilm on anode, the maximum power density was 109.5 mW/m² in MFC-1 and 459 mW/m² in MFC-2, which was, respectively, 30% and 23.5% less than the value obtained in MFC-1 and MFC-2 at SLR of 0.75 kg COD kg VSS⁻¹ d⁻¹. Maximum volumetric power of 15.51 W/m³ and 36.72 W/m³ was obtained in MFC-1 and MFC-2, respectively, when permanganate was added as catholyte. Higher feed pH (8.0) favoured higher power production.     

Factors affecting current production in microbial fuel cells using different industrial wastewaters

This study evaluated how different types of industrial wastewaters (bakery, brewery, paper and dairy) affect the performance of identical microbial fuel cells (MFCs); and the microbial composition and electrochemistry of MFC anodes. MFCs fed with paper wastewater produced the highest current density (125 ± 2 mA/m²) at least five times higher than dairy (25 ± 1 mA/m²), brewery and bakery wastewaters (10 ± 1 mA/m²). Such high current production was independent of substrate degradability. A comprehensive study was conducted to determine the factor driving current production when using the paper effluent. The microbial composition of anodic biofilms differed according to the type of wastewater used, and only MFC anodes fed with paper wastewater showed redox activity at −134 ± 5 mV vs NHE. Electrochemical analysis of this redox activity indicated that anodic bacteria produced a putative electron shuttling compound that increased the electron transfer rate through diffusion, and as a result the overall MFC performance.     

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/m², respectively, at 100 Ω external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m². 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 β-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), α-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and γ-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.     

Electricity generation and modeling of microbial fuel cell from continuous beer brewery wastewater

Electricity production and modeling of microbial fuel cell (MFC) from continuous beer brewery wastewater was studied in this paper. A single air-cathode MFC was constructed, carbon fiber was used as anode and diluted brewery wastewater (COD = 626.58 mg/L) as substrate. The MFC displayed an open-circuit voltage of 0.578 V and a maximum power density of 9.52 W/m³ (264 mW/m²). Using the model based on polarization curve, various voltage losses were quantified. At current density of 1.79 A/m², reaction kinetic loss and mass transport loss both achieved to 0.248 V; while ohmic loss was 0.046 V. Results demonstrated that it was feasible and stable for producing bioelectricity from brewery wastewater; while the most important factors which influenced the performance of the MFC are reaction kinetic loss and mass transport loss.     

Production,partial purification and characterization of organic solvent tolerant lipase from Burkholderia multivorans V2 and its application for ester synthesis

Burkholderia multivorans V2 (BMV2) isolated from soil was found to produce an extracellular solvent tolerant lipase (6.477 U/mL). This lipase exhibited maximum stability in n-hexane retaining about 97.8% activity for 24 h. After performing statistical optimization of medium components for lipase production, a 2.2-fold (14 U/mL) enhancement in the lipase production was observed. The crude lipase from BMV2 was partially purified by ultrafiltration and gel permeation chromatography with 24.64-fold purification. The K_m and V_max values for partially purified BMV2 lipase were found to be 1.56 mM and 5.62 μmoles/mg min. The metal ions Ca²⁺, Mg²⁺ and Mn²⁺ had stimulatory effect on lipase activity, whereas Cu²⁺, Fe²⁺ and Zn²⁺ strongly inhibited the lipase activity. EDTA and PMSF at 10 mM concentration strongly inhibited the lipase activity. Non-ionic and anionic surfactants stimulated the lipase activity. BMV2 lipase was proved to be efficient in synthesis of ethyl butyrate ester under non-aqueous environment.     

The role of riboflavin in decolourisation of Congo red and bioelectricity production using <Emphasis Type="Italic">Shewanella oneidensis</Emphasis>-MR1 under MFC and non-MFC conditions

Dissimilatory metal reducing bacteria can exchange electrons extracellularly and hold great promise for their use in simultaneous wastewater treatment and electricity production. This study investigated the role of riboflavin, an electron carrier, in the decolourisation of Congo red in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 as a model organism. The contribution of the membrane-bound protein MtrC to the decolourisation process was also investigated. Within the range of riboflavin concentrations tested, 20 µM was found to be the best with >95% of the dye (initial concentration 200 mg/L) decolourised in MFCs within 50 h compared to 90% in the case where no riboflavin was added. The corresponding maximum power density was 45 mW/m². There was no significant difference in the overall decolourisation efficiencies of Shewanela oneidensis MR-1 ΔMtrC mutants compared to the wild type. However, in terms of power production the mutant produced more power (P_max 76 mW/m²) compared to the wild type (P_max 46 mW/m²) which was attributed to higher levels of riboflavin secreted in solution. Decolourisation efficiencies in non-MFC systems (anaerobic bottles) were similar to those under MFC systems indicating that electricity generation in MFCs does not impair dye decolourisation efficiencies. The results suggest that riboflavin enhances both decolourisation of dyes and simultaneous electricity production in MFCs.     

Antifeedant activity of ethanolic extract from Flourensia oolepis and isolation of pinocembrin as its active principle compound

The ethanolic extract from Flourensia oolepis aerial parts showed strong antifeedant activity against the pest larvae, Epilachna paenulata, with an antifeedant index (AI%) of 99.1% at 100 μg/cm². Based on chromatographic fractionation of the extract, guided by bioassays on E. paenulata, the flavanone pinocembrin (1) was isolated as the most active principle. In a choice assay, compound 1 showed strong antifeedant activity against E. paenulata, Xanthogaleruca luteola and Spodoptera frugiperda with an AI% of 90, 94 and 91% (p < 0.01) respectively, at 50 μg/cm². The dosages necessary for 50% feeding inhibition of the insects (ED₅₀) were 7.98, 6.13 and 8.86 μg/cm², respectively. The feeding inhibitory activity of 1 against E. paenulata was compared with the activity of other structurally related flavonoids like naringenin, which was inactive up to 100 μg/cm², catechin which was nearly 6 times less active than 1, and quercetin which was equally active as 1. The effect of these on the feeding behavior of E. paenulata was also studied.     

Performance of electron acceptors in catholyte of a two-chambered microbial fuel cell using anion exchange membrane

The performance of the cathodic electron acceptors (CEA) used in the two-chambered microbial fuel cell (MFC) was in the following order: potassium permanganate (1.11 V; 116.2 mW/m²) > potassium persulfate (1.10 V; 101.7 mW/m²) > potassium dichromate, K₂Cr₂O₇ (0.76 V; 45.9 mW/m²) > potassium ferricyanide (0.78 V; 40.6 mW/m²). Different operational parameters were considered to find out the performance of the MFC like initial pH in aqueous solutions, concentrations of the electron acceptors, phosphate buffer and aeration. Potassium persulfate was found to be more suitable out of the four electron acceptors which had a higher open circuit potential (OCP) but sustained the voltage for a much longer period than permanganate. Chemical oxygen demand (COD) reduction of 59% was achieved using 10 mM persulfate in a batch process. RALEX™ AEM-PES, an anion exchange membrane (AEM), performed better in terms of power density and OCP in comparison to Nafion®117 Cation Exchange Membrane (CEM).     

Relationship of rapid light curves of variable fluorescence to photoacclimation and non-photochemical quenching in a benthic diatom

The response of rapid light–response curves (RLCs) of variable fluorescence to changes in short- and long-term photoacclimation status was studied in an estuarine benthic diatom. The diatom Nitzschia palea was grown under low- (LL, 20 μmol m⁻² s⁻¹) and high-light (HL, 400 μmol m⁻² s⁻¹) conditions, with the purpose of characterising the effects of long-term photoacclimation on (i) steady-state light–response curves (LC) of relative electron transport rate, rETR, (ii) the response of RLCs to changes in ambient irradiance (E, the irradiance to which the sample is acclimated to immediately before the RLCs), (iii) the relationship of RLCs to LC parameters and non-photochemical quenching (NPQ). Photoacclimation to LL and HL conditions induced distinct light–response patterns of rETR and NPQ. Higher growth light resulted in rETR vs. E curves with lower initial slopes (α, 0.591 μmol⁻¹ m² s vs. 0.661 μmol⁻¹ m² s, for HL and LL, respectively) and markedly higher maximum rates (rETR_m, 95.9 vs. 29.3), reached under higher E levels (higher light-saturation coefficient, E_k: 162.4 μmol m⁻² s⁻¹ vs. 44.3 μmol m⁻² s⁻¹). Acclimation to HL induced bi-phasic NPQ vs. E curves, with minimum values reached under low E levels (15–25 μmol m⁻² s⁻¹) and not on dark-acclimated samples. The response of RLCs to changes in ambient irradiance varied with the long-term photoacclimation status of the samples. The initial slope, α_RLC, decreased monotonically with E in LL cultures, from 0.68 to 0.25 μmol⁻¹ m² s, while varied bi-phasically in HL-acclimated samples. Typically, α_RLC of HL cultures increased under low E, reaching a maximum of 0.61 μmol⁻¹ m² s under 25–55 μmol m⁻² s⁻¹, and decreased gradually under higher E levels to 0.25 μmol⁻¹ m² s. RLC maximum rETR, rETR_m,RLC, and saturation coefficient E_k,RLC, increased with E following a saturation-like pattern, with the HL cultures presenting markedly higher values for all the E range (maximum rETR_m,RLC values were 108.6 and 33.4 for HL and LL cultures, respectively). An inverse relationship was consistently found between α_RLC and NPQ, both on LL and HL cultures, causing strong correlations (P < 0.001 in all cases) between NPQ and the high light-induced decrease of α_RLC, Δα_RLC. RLCs were confirmed to also provide information on the long-term photoacclimation status, as significant correlations (P < 0.001 both for HL and LL cultures) were verified between E_k and an index based on RLC parameters, Ê_k, both for LL and HL cultures. These results reinforce the usefulness of RLCs as a tool for inferring on the short- and long-term photoacclimation status of samples with different long-term light histories, through the estimation of LC parameters and the monitoring of NPQ levels.     

A membrane-free baffled microbial fuel cell for cathodic reduction of Cu(II) with electricity generation

A membrane-free baffled microbial fuel cell (MFC) was developed to treat synthetic Cu(II) sulfate containing wastewater in cathode chamber and synthetic glucose-containing wastewater fed to anode chamber. Maximum power density of 314 mW/m³ with columbic efficiency of 5.3% was obtained using initial Cu²⁺ concentration of 6400 mg/L. Higher current density favored the cathodic reduction of Cu²⁺, and removal of Cu²⁺ by 70% was observed within 144 h using initial concentration of 500 mg/L. Powder X-ray diffraction (XRD) analysis indicated that the Cu²⁺ was reduced to Cu₂O or Cu₂O plus Cu which deposited on the cathode, and the deficient cathodic reducibility resulted in the formation of Cu₄(OH)₆SO₄ at high initial Cu²⁺ concentration (500-6400 mg/L). This study suggested a novel low-cost approach to remove and recover Cu(II) from Cu²⁺-containing wastewater using MFC-type reactor.     

Long-term cathode performance and the microbial communities that develop in microbial fuel cells fed different fermentation endproducts

To better understand how cathode performance and substrates affected communities that evolved in these reactors over long periods of time, microbial fuel cells were operated for more than 1 year with individual endproducts of lignocellulose fermentation (acetic acid, formic acid, lactic acid, succinic acid, or ethanol). Large variations in reactor performance were primarily due to the specific substrates, with power densities ranging from 835 ± 21 to 62 ± 1 mW/m³. Cathodes performance degraded over time, as shown by an increase in power of up to 26% when the cathode biofilm was removed, and 118% using new cathodes. Communities that developed on the anodes included exoelectrogenic families, such as Rhodobacteraceae, Geobacteraceae, and Peptococcaceae, with the Deltaproteobacteria dominating most reactors. Pelobacter propionicus was the predominant member in reactors fed acetic acid, and it was abundant in several other MFCs. These results provide valuable insights into the effects of long-term MFC operation on reactor performance.     

Treatment of phenolics containing synthetic wastewater in an internal loop airlift bioreactor (ILALR) using indigenous mixed strain of Pseudomonas sp. under continuous mode of operation

The scope of this study is to evaluate the performance of internal loop airlift bioreactor (ILALR) in treating synthetic wastewater containing phenol and m-cresol, in single and multi component systems. The microbe utilized in the process was an indigenous mixed strain of Pseudomonas sp. isolated from a wastewater treatment plant. The reactor was operated at both lower and higher hydraulic retention times (HRTs) i.e., 4.1 and 8.3 h, respectively, by providing an inlet feed flow rate of 5 and 10 mL/min. Shock loading experiments were also performed up to a maximum concentration of 800 mg/L for phenol at 8.3 h HRT and 500 mg/L for m-cresol at 4.1 h HRT. The study showed complete degradation of both phenol and m-cresol, when they were degraded individually at a HRT of 8.3 h. Experiments with both phenol and m-cresol present as mixtures were performed based on the 2² full factorial design of experiments.     

Endothelium-independent vasorelaxation effects of 16-O-acetyldihydroisosteviol on isolated rat thoracic aorta

Aims

The aim of this study is to investigate the vasorelaxant effect of 16-O-acetyldihydroisosteviol (ADIS) and its underlying mechanisms in isolated rat aorta.

Main methods

Rat aortic rings were isolated, suspended in organ baths containing Kreb's solution, maintained at 37 °C, and mounted on tungsten wire and continuously bubbled with a mixture of 95% O₂ and 5% CO₂ under a resting tension of 1 g. The vasorelaxant effects of ADIS were investigated by means of isometric tension recording experiment.

Key findings

ADIS (0.1 μM–3 mM) induced relaxation of aortic rings pre-contracted by phenylephrine (PE, 10 μM) and KCl (80 mM) with intact-endothelium (E_max = 79.26 ± 3.74 and 79.88 ± 3.79, respectively) or denuded-endothelium (E_max = 88.05 ± 3.69 and 78.22 ± 6.86, respectively). In depolarization Ca²⁺-free solution, ADIS inhibits calcium chloride (CaCl₂)-induced contraction in endothelium-denuded rings in a concentration-dependent manner. In addition, ADIS attenuates transient contractions in Ca²⁺-free medium containing EGTA (1 mM) induced by PE (10 μM) and caffeine (20 mM). By contrast, relaxation was not affected by tetraethylammonium (TEA, 5 mM), 4-aminopyridine (4-AP, 1 mM), glibenclamide (10 μM), barium chloride (BaCl₂, 1 mM), and 1H-[1,2,3]oxadiazolo[4,3-α]quinoxalin-1-one (ODQ, 1 μM).

Significance

These findings reveal the vasorelaxant effect of ADIS, through endothelium-independent pathway. It acts as a Ca^2 + channel blocker through both intracellular and extracellular Ca^2 + release.     

Activity and stability of pyrolyzed iron ethylenediaminetetraacetic acid as cathode catalyst in microbial fuel cells

A low-cost and effective iron-chelated catalyst was developed as an electrocatalyst for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). The catalyst was prepared by pyrolyzing carbon mixed iron-chelated ethylenediaminetetraacetic acid (PFeEDTA/C) in an argon atmosphere. Cyclic voltammetry measurements showed that PFeEDTA/C had a high catalytic activity for ORR. The MFC with a PFeEDTA/C cathode produced a maximum power density of 1122 mW/m², which was close to that with a Pt/C cathode (1166 mW/m²). The PFeEDTA/C was stable during an operation period of 31 days. Based on X-ray diffraction and X-ray photoelectron spectroscopy measurements, quaternary-N modified with iron might be the active site for the oxygen reduction reaction. The total cost of a PFeEDTA/C catalyst was much lower than that of a Pt catalyst. Thus, PFeEDTA/C can be a good alternative to Pt in MFC practical applications.