A Cascade of Miniature Microbial Fuel Cells Coupled with an Electrochemical Reactor for Energy Harvesting
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This work reports the use of the Microbial Fuel Cell (MFC) technology, in combination with an electrochemical reactor, for the generation of electricity while removing Chlorella vulgaris microalgae contained in wastewater. In particular, Chlorella vulgaris algae was pre-treated by using an electrolytic cell. To this aim, a fixed bed reactor with 3D electrodes was employed. The pre-treated wastewater was used as feedstock for a 3D printed miniature air-cathode MFCs arranged in cascade for further algal removal and energy production. The performance of the system was studied by measuring the chemical oxygen demand, the optical density and the recorded voltage in all the experiments. Results show that the efficiency of the system, in terms of output energy recovery and water treatment, increases when a higher number of MFCs is used in the cascade.Keywords:
Chlorella vulgaris
Chemical energy
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The start-up procedures, the degradation efficiency of organics at the anode and the removal efficiency of Cu2+ at the cathode of the cell were studied, based on which the performance of MFC (microbial fuel cell) in electricity generation and wastewater treatment was evaluated. A simple two-chamber microbial fuel cell was established with simulated molasses wastewater as substrate at the anode and simulated electroplating wastewater as an electron acceptor at the cathode. The results from a batch of experiments showed that the highest voltage output of 417.00 mV was obtained at an external resistance of 800 Omega, and that the maximum power density of 44.17 mW x m(-2) was obtained with an internal resistance of 293 Omega based on the polarization curve. In addition, COD removal rate reached its highest value (47.31%) in the fifth cycle, and the maximum removal rate (59.76%) for Cu2+ was recorded in the fourth cycle. In summary, the application of MFC in the treatment of organic wastewater and electroplating wastewater is feasible.
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Chemical energy
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Microbial fuel cells (MFCs) are bioelectrochemical systems which enable the conversion of chemical energy directly into electrical energy with microorganism. Studies focused on using organic materials of waste to increase power production performance. In this study, two different MFC reactors were investigated to produce electricity using domestic wastewater. The highest current and power density were 1385 mA/m 2 and 16 mW/m 2 at Ti-TiO2/Nafion combination with 78% COD removal. Ti-TiO2/CMI7000 assemblies generated 750 mA/m2 of current densities and 5 mW/m2 of power density and HRT of 1 day was found favorable for MFC system.
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The ultimate goal of this thesis was to investigate and produce an MFC with self-sustainable cathode so it could be implemented in real world applications. Using methods previously employed [polarisation curve experiments, power output measurements, chemical assays for determining COD in wastewater and other elements present in anolyte or catholyte, biomass assessments] and with a focus on the cathode, experiments were conducted to compare and contrast different designs, materials and nutrient input to microbial fuel cells with appropriate experimental control systems.
Results from these experiments show that: Firstly, the choice of polymeric PEM membrane showed that the most effective materials in terms of power performance were cation exchange membranes. In terms of cost effectiveness the most promising was CM-I, which was the preferred separator for later experiments.
Secondly, a completely biotic MFC with the algal cathode was shown to produce higher power output (7.00 mW/m2) than the abiotic control (1.52 mW/m2). At the scale of the experimental system, the reservoir of algal culture produced sufficient dissolved oxygen to serve the MFCs in light or dark conditions. To demonstrate usable power, 16 algal cathode-designed MFCs were used to power a dc pump as a practical application.
It has been presented that the more power the MFC generates, the more algal biomass will be harvested in the connected photoreactor. The biomass grown was demonstrated to be a suitable carbon-energy resource for the same MFC units in a closed loop scenario, whereby the only energy into the system was light.
In the open to air cathode configuration various modifications to the carbon electrode materials including Microporous Layer (MPL) and Activated Carbon (AC) showed catholyte synthesis directly on the surface of the electrode and elemental extraction such as Na, K, Mg, from wastewater in a power dependent manner. Cathode flooding has been identified as an important and beneficial factor for the first time in MFCs, and has been demonstrated as a carbon capture system through wet scrubbing of carbon dioxide from the atmosphere. The captures carbon dioxide was mineralised into carbonate and bicarbonate of soda (trona). The novel inverted, tubular MFC configuration integrates design and operational simplicity showing significantly improved performance rendering the MFC system feasible for electricity recovery from waste. The improved power (2.58 mW) from an individual MFC was increased by 5-fold compared to the control unit, and 2-fold to similar sized tubular systems reported in the literature; moreover it was able to continuously power a LED light, charge a mobile phone and run a windmill motor, which was not possible before.
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Chlorella vulgaris
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Microbial fuel cell (MFC) is a new proposed technology reported to generate renewable energy while simultaneously treating wastewater. Membraneless microbial fuel cell (ML-MFC) system was developed to eliminate the requirement of membrane which is expensive and prone to clogging while enhancing electricity generation and wastewater treatment efficiency. For this purpose, a reactor was designed in two chambers and connected via three pipes (1 cm in diameter) to enhance fluid diffusion. Influent flowrate was maintained by adjusting peristaltic pump at the base of anaerobic chamber. Carbon cloth (235 cm2) was used as anode and paired with gas diffusion layer (GDL) carbon-Pt as cathode. Anaerobic sludge was filtered and used as starter feed for the anaerobic chamber. The experiment was carried out by feeding synthetic wastewater to anaerobic chamber; while current response and potential were recorded. Performance of reactor was evaluated in terms of chemical oxygen demand (COD). Electroactive microbe was inoculated from anaerobic sludge and showed current response (0.55-0.65 mA) at 0,35 V, range of diameter 1.5-2 µm. The result of microscopics can showed three different species. The microbial performance was increased by adding ferric oxide 1 mM addition as acceptor electron. The reactor was able to generate current, voltage, and electricity power of 0.36 mA, 110 mV, and 40 mWatt (1.5 Watt/m2), respectively, while reaching COD removal and maximum coulomb efficiency (EC) of 16% and 10.18%, respectively.
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The photosynthesis microbial fuel cell was constructed using separated Chlorella vulgaris.Electricity production and mechanism of the cell were preliminarily studied.By analyzing the cell voltage measured by the acquisition system, it was proved that the photosynthetic microbial fuel cell was feasible.Microbial electricity generation was mainly attributed to the electrochemically and biologically active cells attached to the electrode, and the suspended algae in the solution were not involved.The illumination was one of main influential factors on the voltage of MFC.By adding Fe3+ to the cathode chamber, electron transfer driving force was generated in coupling of Fe3+ reduction to Fe2+ on the cathode.The Fe2+ cations were subsequently oxidized by O2 in air.For this Fe3+ circular effect,the electron transfer and oxidation-reduction efficiency were enhanced.The output power density of MFC was up to 11.82 mV/m2, and the removal rate of COD reached 40%.This kind of MFC could produce electricity and treat the wastewater simultaneously.
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