The urgent need for sustainable energy solutions driven by climate change has catalysed the development of groundbreaking technologies poised to transform the energy landscape. Amongst these innovations, soil microbial fuel cells (SMFCs) stand as a promising source of renewable energy, leveraging electroactive microorganisms in soil to produce clean electricity. Despite their potential, a limited understanding of operational fundamentals and thermodynamic constraints hinders their power density, and market viability. This thesis tackles these challenges by aiming to optimise and scale the SMFC technology, striving for performance levels suitable for low-power applications. To do so, the life cycle of conventional flat-plate SMFCs was closely monitored and assessed, revealing four critical stages in their evolution. It took 42 days for the anodes and cathodes to enrich in catalytic biofilms, and for the SMFCs to reach peak power densities of 28mWm-2. To increase the power output, a variety of SMFC reactor designs were tested. The optimal reactor featured a horizontally placed cathode, and three vertically submerged anodes, resulting in a 50% increase in power density, and a more stable voltage over the course of two months. Moreover, connecting multiple fuel cells in parallel proved effective in linearly scaling the power output. This approach was applied in field trials in the North-East of Brazil, where an array of 64 parallelly stacked SMFCs powered an electrochemical water treatment reactor. Field generated data matched the laboratory results, proving the concept and treating 3L of water per day. To address performance instability issues highlighted during the field studies, a custom power management system (PMS) was developed. The PMS utilised a model-based power estimation strategy, tailored to the voltage dynamics of the soil-based fuel cells. A perturb and observe algorithm actively tracked any performance shifts, maximising harnessing efficiency, by maintaining the performance near the maximum power point. Finally, minimum voltage thresholds were embedded to sustain long term performance, as evidenced through a 25-day long battery charge test. Overall, these results underscore the importance of comprehensive optimisation, emphasizing the critical role of fine-tuning all components of a system (SMFCs, PMS and the load), to achieve optimal performance. This insight is crucial for future research endeavours, to bring the SMFC technology closer to commercial readiness.
Development of innovative soil microbial fuel cells for remote energy harvesting. : (Alternative Format Thesis)
Dziegielowski, J. (Author). 22 May 2024
Student thesis: Doctoral Thesis › PhD