| dc.description.abstract | Microbial fuel cell (MFC) technology has been attracting great attention recently due to its potential for simultaneously harvesting electric energy, removing pollutants and monitoring organic matter concentration at wastewater. To date, the air cathode has been the bottleneck for MFC development. To deepen the understanding and improve the performance of air-cathode MFC, the study was conducted through 3 aspects of air cathode: surface and structural modification, practical application and numerical modelling.
In a surface modification study, it was found that sufficient catalyst (38 mg/cm2) was critical to generate high power density and coulombic efficiency (CE) and maintain good performance at long-term operation. As to blended material, Ti-blended reactors obtained slightly higher performance than carbon black (CB)-blended MFCs in terms of power density, CE and long-term stability. Over short-term operation (1 month), Cu-blended reactors showed the worst performance due to copper ion inhibition over anode biofilm. However, Cu-blended reactors achieved the best performance over long-term operation (4.5 months). High pressure and temperature (HPT) treated by autoclave was a convenient and efficient method to modify cathode. With this method, the power density increased regardless of the blended material. HPT modification could also remove the short-term inhibition of Cu and generate much higher maximum power density over CB and Ti. In terms of the separator, Denim fabric (DF) had a similar short-term performance to that of glass fibre (GF). After the 5-months of operation, DF achieved much higher CE than GF due to its stability and anti-microbial growth.
In terms of structural modification, a novel 3D cathode which could significantly increase MFC?s cathode specific surface area (CSSA) was developed and tested. The maximum power density was improved from 23 ? 2 W/m3 to 46 ? 1 W/m3 when the flat cathode ? a common cathode widely used in MFCs - was changed to the 3D cathode. The significant improvement (increased by 248%) was also obtained when further increased the CSSA to 219 m2/m3. The 3D cathode also increased CE by 28% due to the advantages of full organic matter consumption and cathode biofilm inhibition. COD removal rate showed good agreement with first-order degradation kinetic regardless of the CSSA difference. Over long-term operation, the MFC with the low CSSA (41 m2/m3) demonstrated a very high stability while the power of MFCs with high CSSA (104-509 m2/m3) showed a reversible change, which was due to the mass oxygen crossover.
Then the 3D cathode was employed to construct the configuration of cathode surrounding anode (CSA) with large volume. In practical application of dairy wastewater, CSA with 3D cathodes obtained high power generation (4.7 ? 0.2 W/m3) and 88.0%- COD and 93.9%-TN removal, respectively. In addition, the 3D cathode could reduce the NH3 emission significantly. It was also found that the current density rather than the total current played a key role in NH3 emission. The 3D cathode blended with Cu particles could further improve the power generation performance, reduce the NH3 emission and enhance the total nitrogen (TN) removal.
In addition to treating real wastewater, MFC was also developed as a sensor to selectively test urine glucose. The novel structure of self-cleaning sensor (SCS), obtained quick response (6.7 ? 0.4 minutes), large detection range (0.3-2 mM) and excellent linear relationship (R2 higher than 0.98) between glucose concentration and peak currents. More importantly, SCS obtained up to the 5 months of stable operation, around 100% longer than traditional flat MFCs. In addition to peak current, the current increase rate was an alternative parameter to indicate the glucose concentration with quicker response (100 s) and larger detection range (0.3-5 mM). The selectivity of SCS was validated by using both synthetic and real diabetes-negative urine samples. In terms of accuracy, SCS showed a good agreement compared to a commercial glucose analyser (recovery ranged from 93.6 % to 127.9 %) when the diabetes-positive urine samples were tested. Due to the multiple advantages (high stability, low cost and high sensitivity and selectivity) over urine test strip, SCS provides a novel and reliable approach for continuous monitoring of urine glucose, which will greatly benefit diabetes assessment and control.
Finally, a robust 3D model was developed to investigate the potential optimum configuration. The numerical results showed that most of the areas of cylindrical cathodes are active during the reaction, which reveals the reason for the high efficiency of the CSA configuration. In terms of cathode area, the study showed that 90 m2/m3-CSSA was the optimum value to maximize current generation, organic matter removal while keeping oxygen crossover down to an innocuous level. As for the control of oxygen crossover, growing a biofilm on the cathode was demonstrated to be a fast and zero-cost method to curb DO crossover. Finally, it was found that the ideal design is to fabricate the Cu-blended 3D cathode as a helical hollowed shape surrounding the anode. | en |
