1,720,967 research outputs found
Enhanced bio-production from CO<sub>2 </sub>by microbial electrosynthesis (MES) with continuous operational mode
No full textTechnologies able to convert CO2 to various feedstocks for fuels and chemicals are emerging due to the urge of reducing greenhouse gas emissions and de-fossilizing chemical production. Microbial electrosynthesis (MES) has been shown a promising technique to synthesize organic products particularly acetate using microorganisms and electrons. However, the efficiency of the system is low. In this study, we demonstrated the simple yet efficient strategy in enhancing the efficiency of MES by applying continuous feeding regime. Compared to the fed-batch system, continuous operational mode provided better control of pH and constant medium refreshment, resulting in higher acetate production rate and more diverse bio-products, when the cathodic potential of -1.0 V Ag/AgCl and dissolved CO2 were provided. It was observed that hydraulic retention time (HRT) had a direct effect on the pattern of production, acetate production rate and coulombic efficiency. At HRT of 3 days, pH was around 5.2 and acetate was the dominant product with the highest production rate of 651.8 ± 214.2 ppm per day and a significant coulombic efficiency of 90%. However at the HRT of 7 days, pH was lower at around 4.5, and lower but stable acetate production rate of 280 ppm per day and a maximum coulombic efficiency of 80% was obtained. In addition, more diverse and longer chain products, such as butyrate, isovalerate and caproate, were detected with low concentrations only at the HRT of 7 days. Although microbial community analysis showed the change in the planktonic cells communities after switching the fed-batch mode to continuous feeding regime, Acetobacterium still remained as the responsible bacteria for CO2 reduction to acetate, dominating the cathodic biofilm
Impact of applied cell voltage on the performance of a microbial electrolysis cell fully catalysed by microorganisms
No full textThe effect of the operating voltage on the performance of a microbial electrolysis cell (MEC) equipped with both a bioanode and a biocathode for hydrogen production is reported. Chronoamperometry tests ranged between 0.3 and 2.0 V were carried out after both bioelectrodes were developed. A maximum current density up to 1.6 A m−2 was recorded at 1.0 V with hydrogen production rate of nearly 6.0 ± 1.5 L m−2 cathode day−1. Trace amounts of methane, acetone and formate were detected in cathode's headspace and catholyte which followed the same trend as hydrogen production rate. Meanwhile substrate consumption in anolyte also followed the trend of hydrogen production and current density changes. The bioanode could utilise up to 95% of acetate in the tested voltage ranges, however, at a cell voltage of 2.0 V the bioanode's activity stopped due to oxygen evolution from water hydrolysis. Cyclic voltammograms revealed that the bioanode activity was vital to maintain the functionality of the whole system. The biocathode relied on the bioanode to maintain its potential during the hydrogen evolution. The overall energy efficiency recovered from both bioanode and external power in terms of hydrogen production at the cathode was determined as 29.4 ± 9.0%, within which substrate oxidation contributed up to nearly 1/3 of the total energy marking the importance of bioanode recovering energy from wastewater to reduce the external power supply
Gas diffusion electrodes modified with binary doped polyaniline for enhanced CO<sub>2</sub> conversion during microbial electrosynthesis
No full textMicrobial electrosynthesis (MES) is a promising technology to convert CO2 into value-added chemicals. Enhancing the interactions between biofilms and electrodes is the key of bioelectrochemical systems (BES). In this work, we studied the conversion of CO2 by MES in reactors equipped with novel gas diffusion electrodes (GDEs) modified with a polyaniline (PANI) polymer binary doped with H2SO4 and ammonium lauryl sulfate. The enhanced conductive and hydrophilic properties of the polymer increased the biocompatibility of the PANI-modified GDEs compared to the non-modified carbon GDEs. This increased biocompatibility resulted in faster start-up and higher bioproduction of volatile fatty acids (VFAs) such as acetate and butyrate. Up to 4400 ppm acetate was produced in PANI-modified reactors after 24 days of operation, compared to 408 ppm in reactors equipped with non-modified GDEs. A maximum acetate concentration of 7500 ppm (production rate of 554.8 ± 267.5 ppm day−1) was reached in reactors equipped with PANI-GDEs. After 60 days, apart from acetate, 245 ppm butyrate was produced in reactors equipped with the electrodes modified with PANI, while less than 60 ppm was produced with non-modified GDEs. SEM analysis revealed the development of biofilms on both modified and non-modified electrodes, but the images also suggest differences in compositions.</p
Pembangunan sel fuel mikrob untuk rawatan air sisa kilang sawit
No full textSel fuel mikrob (SFM) merupakan peranti yang menggunakan bakteria sebagai biomangkin untuk mengoksidakan bahan organik dan bukan organik bagi menjanakan arus elektrik. Tujuan utama kajian ini ialah menguji kebolehan SFM skala makmal dengan menggunakan enapcemar yang mengandungi kultur campuran yang hidup dalam air sisa buangan kilang pemprosesan sawit (POME). Kajian ini juga bertujuan membina reka bentuk SFM yang sesuai dan mengkaji keaktifan kultur campuran yang boleh menghasilkan kuasa elektrik. POME telah digunakan dalam bentuk yang dicairkan dengan kandungan COD bersamaan dengan 3750 mg-COD L-1. Prestasi penghasilan kuasa elektrik dan kecekapan rawatan yang dinilai daripada segi penyingkiran COD, nitrogen dan jumlah karbohidrat dalam SFM dwi-ruang telah dicatat dan dianalisis setiap hari selama 15 hari. Hasil padanan uji kaji dan model kekutuban adalah memuaskan dan telah menjelaskan ketumpatan kuasa elektrik yang dapat dihasilkan pada setiap hari. Ketumpatan kuasa didapati meningkat dari hari pertama 1.607 mW m-2 (3.816 mA m-2) ke nilai maksimum pada hari ketiga 1.979 mW m-2 (4.780 mA m-2) dan mula turun sehingga minimum pada hari ketujuh 1.311 mW m-2 (3.346 mA m-2). Peringkat rawatan air sisa kilang sawit oleh SFM boleh dibahagikan kepada tiga tahap yang berbeza. Kecekapan rawatan yang rendah walaupun ketumpatan kuasa meningkat pada tahap pertama, manakala pada tahap kedua kecekapan rawatan lebih tinggi dan akhirnya pada tahap ketiga penghasilan kuasa SFM mula turun. Kecekapan rawatan paling tinggi berlaku pada tahap ketiga semasa penghasilan kuasa elektrik yang terhasil agak malar. Kecekapan rawatan yang dinilaikan dalam bentuk penyingkiran COD, penggunaan nitrogen dan karbohidrat paling tinggi berlaku pada hari ke-15 dengan nilai masing-masing adalah 54.9, 100 dan 98.9%. Hubungan penghasilan kuasa elektrik dan kecekapan rawatan telah berjaya dimodelkan dalam persamaan linear matematik berdasarkan kepada tahap-tahap penghasilan kuasa elektrik ini
Bioanode as a limiting factor to biocathode performance in microbial electrolysis cells
No full textThe bioanode is important for a microbial electrolysis cell (MEC) and its robustness to maintain its catalytic activity affects the performance of the whole system. Bioanodes enriched at a potential of +0.2 V (vs. standard hydrogen electrode) were able to sustain their oxidation activity when the anode potential was varied from −0.3 up to +1.0 V. Chronoamperometric test revealed that the bioanode produced peak current density of 0.36 A/m2 and 0.37 A/m2 at applied potential 0 and +0.6 V, respectively. Meanwhile hydrogen production at the biocathode was proportional to the applied potential, in the range from −0.5 to −1.0 V. The highest production rate was 7.4 L H2/(m2 cathode area)/day at −1.0 V cathode potential. A limited current output at the bioanode could halt the biocathode capability to generate hydrogen. Therefore maximum applied potential that can be applied to the biocathode was calculated as −0.84 V without overloading the bioanode.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effects of Applied Potential and Reactants to Hydrogen-Producing Biocathode in a Microbial Electrolysis Cell
No full textUnderstanding the mechanism of electron transfer between the cathode and microorganisms in cathode biofilms in microbial electrolysis cells (MECs) for hydrogen production is important. In this study, biocathodes of MECs were successfully re-enriched and subjected to different operating parameters: applied potential, sulfate use and inorganic carbon consumption. It was hypothesized that biocathode catalytic activity would be affected by the applied potentials that initiate electron transfer. While inorganic carbon, in the form of bicarbonate, could be a main carbon source for biocathode growth, sulfate could be a terminal electron acceptor and thus reduced to elemental sulfurs. It was found that potentials more negative than −0.8 V (vs. standard hydrogen electrode) were required for hydrogen production by the biocathode. In additional, a maximum hydrogen production was observed at sulfate and bicarbonate concentrations of 288 and 610 mg/L respectively. Organic carbons were found in the cathode effluents, suggesting that microbial interactions probably happen between acetogens and sulfate reducing bacteria (SRB). The hydrogen-producing biocathode was sulfate-dependent and hydrogen production could be inhibited by excessive sulfate because more energy was directed to reduce sulfate (E° SO42-/H2S = −0.35 V) than proton (E° H+/H2 = −0.41 V). This resulted in a restriction to the hydrogen production when sulfate concentration was high. Domestic wastewaters contain low amounts of organic compounds and sulfate would be a better medium to enrich and maintain a hydrogen-producing biocathode dominated by SRB. Besides the risks of limited mass transport and precipitation caused by low potential, methane contamination in the hydrogen-rich environment was inevitable in the biocathode after long term operation due to methanogenic activities
Zinc removal and recovery from industrial wastewater with a microbial fuel cell: experimental investigation and theoretical prediction
No full textMicrobial fuel cells (MFCs) that simultaneously remove organic contaminants and recovering metals provide a potential route for industry to adopt clean technologies. In this work, two goals were set: to study the feasibility of zinc removal from industrial effluents using MFCs and to understand the removal process by using reaction rate models. The removal of Zn2+ in MFC was over 96% for synthetic and industrial samples with initial Zn2+ concentrations less than 2.0 mM after 22 h of operation. However, only 83 and 42% of the zinc recovered from synthetic and industrial samples, respectively, was attached on the cathode surface of the MFCs. The results marked the domination of electroprecipitation rather than the electrodeposition process in the industrial samples. Energy dispersive X-ray (EDX) analysis showed that the recovered compound contained not only Zn but also O, evidence that Zn(OH)2 could be formed. The removal of Zn2+ in the MFC followed a mechanism where oxygen was reduced to hydroxide before reacting with Zn2+. Nernst equations and rate law expressions were derived to understand the mechanism and used to estimate the Zn2+ concentration and removal efficiency. The zero-, first- and second-order rate equations successfully fitted the data, predicted the final Zn2+ removal efficiency, and suggested that possible mechanistic reactions occurred in the electrolysis cell (direct reduction), MFC (O2 reduction), and control (chemisorption) modes. The half-life, t1/2, of the Zn2+ removal reaction using synthetic and industrial samples was estimated to be 7.0 and 2.7 h, respectively. The t1/2 values of the controls (without the power input from the MFC bioanode) were much slower and were recorded as 21.5 and 7.3 h for synthetic and industrial samples, respectively. The study suggests that MFCs can act as a sustainable and environmentally friendly technology for heavy metal removal without electrical energy input or the addition of chemicals.</p
Multi-array tubular microbial fuel cell-based biosensor with membrane electrode assembled air-cathodes
No full textUsing microbial fuel cells (MFCs) as biosensors ensures a sustainable method for water quality detection. However, the research on MFC-based biosensors with a tubular setup is still scarce. In this study, a tubular multi-array MFC-based biosensor setup with air-cathodes was assembled under the membrane electrode assembly configuration. Three different materials, including carbon black (CB), Pt/C (PtC), and polyaniline (PANI), were synthesized and coated on the membrane-facing side of the air-cathode to demonstrate the effects of modified air-cathodes on the overall performance of the MFC-biosensors. Unmodified carbon cloths were used as anodes. Three days of startup period were required by the biosensors before producing an electrical signal output. The highest current density was obtained by the polytetrafluoroethylene (PTFE)/CB/PtC (0.31 A m−2) sample followed by PTFE/CB/PANI (0.09 A m−2), and lastly PTFE/CB (0.05 A m−2). The control (PTFE only) sample did not generate any noticeable electrical signal. The electrochemical impedance spectroscopy analysis showed that the incorporation of PtC on the PTFE/CB sample lowered the charge transfer resistance (Rct), whereas the addition of PANI increased the Rct. Despite the differences in Rct values, both PTFE/CB/PtC and PTFE/CB/PANI samples demonstrated a better current density production than the PTFE/CB sample. Thus, modified air-cathodes further elevated the biosensor's performance.</p
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