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Abstract Economically harvesting energy from a microbial fuel cell (MFC), increasing its electrical power production, and developing its role as a practical energy supply, needs a low-cost and high-performance design of the MFC compartments. According to this strategy, a novel monolithic membrane electrode assembly (MEA) was fabricated and evaluated as an air–cathode in a single-chamber MFC (SCMFC). The MEA was made of bacterial cellulose (BC), conductive multi-walled carbon nanotubes (CNT), and nano-zycosil (NZ). BC, as a nano-celluloses with oxygen barrier property, can maintain anaerobic conditions for the anode compartment. Binder-less CNT coating on BC avoids costly binders such as poly-tetra fluoro ethylene (PTFE) and Nafion and decreases the MEA charge transfer resistance. NZ, as a very cheap modifier, not only prevents the anolyte leakage but also provides more MEA’s active sites for the oxygen reduction reaction (ORR). The electrochemical performance of the MEA was compared to a PTFE- based gas diffusion electrode (GDE) in the SCMFC. The MEA cell provided a pulse power density of 1790 mW/m2, roughly twice as high as the pulse power density of GDE (920 mW/m2). SCMFC’s internal resistance decreased from 1.84 KΩ (with GDE) to 0.8 KΩ (with MEA). Also, the cell’s columbic efficiency increased from 4.2% (with GDE) to11.7% (with MEA). Additionally, the capacitance of the MEA (65 mF) was much higher than the value for GDE (0.73 mF). Thus, the MEA compared to the GDE showed higher performance in the SCMFC for electricity generation and wastewater treatment at a lower cost.

Abstract The almost two-dimensional steady-state rates of heat loss from arrays of uniformly-spaced vertical rectangular fins, extending upwards—in otherwise stagnant air—from horizontal heated bases, have been measured. (The vertical air gaps between the fins were closed at their sides, by insulated vertical end-barriers.) The effects of various combinations of height, thickness and spacing of the fins, for different base temperatures (in the range 40 to 100°C), have been studied. For the configuration considered, in a normal ambient environment (∼ 20°C), there is an optimal fin spacing (⋍ 16 mm) corresponding to the greatest steady-state rate of free convective/conductive heat loss through the air from the finned system, and this is almost independent of the temperature of the heat exchanger base (in the range 40–100°C). At this optimal spacing for base temperatures not greater than 50°C, the convective/conductive heat transfer rate from the array increases with the fin height up to about 60 mm, so that it would be uneconomic to employ taller fins if convection/conduction is dominant compared with radiation. If the radiation contribution is also considered, then the optimal spacing corresponding to the maximum total steady-state rate of heat loss through the air is somewhat less than the optimal spacing for which, under the same temperature conditions, the maximum steady-state rate of convective/conductive heat leak occurs. The greater the emissivity of the heat exchanger surfaces, the narrower the optimal uniform gaps between the fins. A two-dimensional finite-difference computer program has been composed to predict the temperature distribution throughout the heat exchanger for a stipulated ambient environmental temperature and experimentally-determined distribution of the heat transfer coefficient over the surfaces of the exchanger. This enables, for instance, any hot spots to be located prior to a proposed design being built.

In-situ biomethanisation reduces the CO2 in biogas to CH4 via direct H2 injection into an anaerobic digester, but volumetric methane production (VMP) is limited by organic loading. Ex-situ biomethanisation, where gaseous substrates are fed to pure or mixed cultures of hydrogenotrophic methanogens, offers higher VMP but requires an additional reactor and supply of essential nutrients. This work combined the two approaches in a novel hybrid application achieving simultaneous in-situ and ex-situ biomethanisation within an organically-loaded anaerobic digester receiving supplementary biogas. Conventional stirred-tank digesters were first acclimated to H2 addition, increasing biogas methane content from 50% to 95% and VMP from 0.86 to 1.51 L L-1 day-1 at a moderate loading rate of 3 g organic chemical oxygen demand per L per day (g CODorg L-1 day-1). Externally-produced biogas was then added to demonstrate simultaneous biomethanisation of endogenous and imported CO2. This further increased VMP to 2.76 L L-1 day-1 without affecting organic substrate degradation. In-situ CO2 reduction can alter digester pH by reducing bicarbonate buffering: the combined process operated stably at around pH 8.0 with 3-5% CO2 in the headspace. Microbial community analysis indicated the process was mediated by bacterial syntrophic acetate oxidation and highly enriched hydrogenotrophic methanogenic archaea (up to 97% of the archaeal population). This approach presents the opportunity to retrofit a single digester for H2 injection to convert and upgrade biogas from several others, minimising capital and operating costs by utilising both existing infrastructure and waste-derived feedstock nutrients for simultaneous biogas upgrading and power-to-methane.

Abstract Many organizations in the world are interested in waste management problems and their potential solutions. In order to solve these problems, a Japanese venture company has developed an innovative thermal decomposer for organic wastes called ERCM (Earth-Resource-Ceramic-Machine). The ERCM reactor employs electron injected air to promote the thermal decomposition reaction, while the effect of electron injection into air has not yet been clarified. An experimental work was performed using a fixed bed reactor to explore the effects of different parameters of electron injection into air, the reaction temperature and different feedstock on the syngas generation. The main purpose of this study is to clarify the phenomena occurring in the ERCM reactor where a direct current electric field is produced in the flame reaction zone to enhance the thermal decomposition of wastes. In this regard, a mathematical model for simulating the thermal decomposition of solid waste in the presence of an electric field have been developed. The equations of aero-thermochemistry are coupled to the balance equations for densities of charged species, and the Poisson equation for the electrical potential is solved. The model was validated by the experimental data and showed a good agreement. The results showed that the electric field significantly improves the stabilization of the flame. From the release behavior of CO and CO2, it is noted that the electron injection would affect the char combustion process significantly. Finally the effect of the flame reaction zone generated by the field induced ion wind on the thermal decomposition was investigated.

Abstract The preparation of a Pt–Co/C electrocatalyst for the oxygen reduction reaction in PEM fuel cells was achieved via a combined process of impregnation and seeding. The effects of initial pH of the precursor solution and Pt loading were all found to have a significant effect on both the electrocatalyst morphology and the cell performance when tested in a single PEM fuel cell. The optimum condition found for preparing the Pt–Co/C electrocatalyst was from an initial precursor solution pH of 2 at the metal loading of 23.6–30.3% (w/w). The Pt–Co/C electrocatalysts, formed under these optimal conditions, tested in a single PEM fuel cell with the carbon sub-layer, gave a cell performance of 772 mA/cm2 or 460 mW/cm2 at 0.6 V in a H2/O2 system. An electron pathway of oxygen reduction on the prepared Pt–Co/C electrocatalyst was also determined using a rotating disk electrode.

Abstract Considerable effort has been directed at improving the power conversion efficiency of organic photovoltaics, using oxide/metal/oxide multilayers as transparent electrodes, because of their numerous advantages including lower sheet resistance, higher transmittance, and higher flexibility in comparison to typical indium tin oxides. However, to date, most organic photovoltaics based on oxide/metal/oxide electrodes exhibit a lower conversion efficiency than indium tin oxide-based organic photovoltaics, without any clarification. In this investigation, we identify crucial factors that influence the power conversion efficiency of oxide/metal/oxide-based organic photovoltaics to fully exploit the potential of these devices, based on the correlation between the optical cavity and the transmittance. For this purpose, we fabricate five sets of inverted organic photovoltaics using poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) and [6,6]-Phenyl C71 butyric acid methyl ester-based active layers and ZnO/Ag/ZnO electrodes with top ZnO layers of varying thicknesses, with reference organic photovoltaics using indium tin oxides, on both rigid and flexible substrates. The highest power conversion efficiency of 8.71% and 7.53% is obtained from single-junction organic photovoltaics with 40/9/8-nm-thick ZnO/Ag/ZnO electrodes on each substrate, due to strong micro-cavity effects between the top and bottom Ag layers, despite the relatively low transmittance of the electrode. This result is supported by the relation between the electric-field intensity and the transmittance curves of the ZnO/Ag/ZnO/solution-based ZnO/active bulk optical stacks based on simulation results. Furthermore, flexible organic photovoltaics with the ZnO/Ag/ZnO electrodes demonstrate much better performance in mechanical bending tests in comparison to the performance of standard indium tin oxide-based organic photovoltaics, and the previously reported oxide/metal/oxide-based organic photovoltaics.

Abstract Microalgae have reported to be one of the most promising feedstock for biofuel production. However, microalgal cultivation for biofuel production is a costly process due to the large amounts of water, inorganic nutrients (mainly N and phosphate (P)), and CO2 needed. In this study, we evaluated whether the nutrient-rich ash and flue gas generated in biomass power plants could serve as a nutrient source for Chlorella sp. C2 cultivation to produce biolipids in a cost-efficient manner. When ash was incorporated in the culture medium and photosynthesis was enhanced by CO2 from flue gas, Chlorella cultures produced a lipid productivity of 99.11 mg L−1 d−1 and a biomass productivity of 0.31 g L−1 d−1, which are 39% and 35% more than the control cultures grown in BG11 medium. Additionally, the cultures reduced the nitrogen oxide (NOx) present in the flue gas and sequestered CO2, with a maximum ash denutrition rate of 13.33 g L−1 d−1, a NOx reduction (DeNOx) efficiency of ∼ 100%, and a CO2 sequestration rate of 0.46 g L−1 d−1. The residual medium was almost nutrient-free and suitable for recycling for continuous microalgal cultivation or farmland watering, or safely disposed off. Based on these results, we propose a technical strategy for biomass power plants in which the industrial wastes released during power generation nourish the microorganisms used to produce biofuel. Implementation of this strategy would enable carbon negative bioenergy production and impart significant environmental benefits.

Abstract In-situ CO2 biomethanisation offers a means to combine biogas upgrading with increased methane productivity, but its potential contribution to power-to-gas is often ignored due to concerns over process stability and control. The research presents an equation derived from fundamental chemical equilibria which predicts the relationship between partial CO2 pressure and digester pH, and allows estimation of the maximum achievable biogas methane content compatible with stable operation. A rapid experimental determination was also developed to support these predictions. The results were validated by long-term experiments using synthetic feedstock with different ammonia concentrations (2 and 3 g N L-1). Further trials carried out using food waste and sewage sludge as substrates showed stable operation at biogas methane contents of 92 and 90% CH4 and pH 8.5 and 7.9, respectively. CO2 biomethanisation was successfully demonstrated in a food waste digester with a total ammoniacal nitrogen of 4.8 g N L-1 with volumetric methane production enhanced by more than 2 times, from 2.29 to 5.01 L CH4 per L digester per day. The predictive approach used is applicable to digesters fed on different feedstocks and to hybrid systems with biomethanisation of both endogenous and exogenous CO2; and offers a basis for both process design guidelines and operational control. The output from the work thus provides engineers, operators and plant designers with a valuable tool for the successful implementation of in-situ biomethanisation in anaerobic digesters.