Understanding the Effects of Kinetic Limitations on Degradation Rates for Different Substrates in MFCs and the Impact on Trophic Layers on these Rates

全球对清洁能源和水的需求不断增加，最近引发了人们对微生物燃料电池(MFC)的兴趣。尽管过去25年来在改进这项技术方面取得了重大进展，但对MFC内发生的过程，如复杂有机化合物的降解率，仍然缺乏了解。关于现实条件下这些比率的有限文献阻碍了这项技术的优化。这个研究项目的第一阶段旨在通过研究不同底物(醋酸盐、葡萄糖和淀粉)在动力学和非动力学限制系统中以及在不同温度下的降解率来帮助填补这一研究空白。先前的研究表明，使用较简单的化合物(醋酸酯)时的功率输出比使用复杂化合物(淀粉)时要高得多，因为醋酸酯不需要通过发酵来分解，这表明在这些系统中，水解是速度限制步骤。然而，这是在充分搅拌的条件下进行的。在现实中，许多MFC以间歇模式运行，而那些连续的MFC具有如此低的流速，以至于湍流不会产生完全搅拌的条件。如果要将MFC用于真正的废水处理，则需要充分了解其降解率和局限性。为了有效地模拟和设计MFC反应器，需要这样的速率。为了确定系统是否受到动力学限制，将使用两种实验室规模的反应器配置；一种是完全搅拌的，允许确定主要降解路径的基本限制；另一种是不搅拌的，表明系统内的过程是在大块液体中进行还是在生物膜上进行。搅拌和非搅拌条件将被用来确定MFC内的传质限制，并最终帮助设计反应器和操作条件，使其最大限度地提高其处理复杂废物的效率。该研究项目的第二阶段将涉及重复这些初始实验，但使用更大的MFC配置来模拟分散处理规模。这将允许测试更现实的条件。由于废水由高度多样化的底物组成，因此需要优化复杂化合物的分解。这个问题的一个潜在解决方案是将植物和基于土壤的介质结合到MFC系统中。植物MFC(P-MFC)是MFC的一种改进型，近年来出现，并在MFC性能方面显示出良好的效果。研究表明，以植物为基础的MFC是成功的。然而，要提高这些系统在冬季月份的产量，仍需做一些工作。人们希望，将土壤和植物引入MFC系统将进一步提高新陈代谢食物网内的营养水平。将植物连接到阴极的土壤中将充满蠕虫等生物和许多不同的微生物区系，所有这些都可能有助于这些系统中的消化/降解途径，并最终提高它们的性能以及随后的废水处理和能量回收。几项研究已经证明了在家庭和大规模使用蠕虫处理和转化废水、污水和湿污泥的有效性。因此，本研究项目的最后阶段将调查营养层对L规模的MFC降解速率的影响。反应堆将设计和安装一式三份，并将在不同条件下进行初步测试。最初，测试将在实验室进行，最终将在外部进行测试，以使我们能够确定这项技术是否可行，以及是否可以将其应用于现实生活中的设置。

Increasing global demand for clean energy and water has sparked recent interest in Microbial Fuel Cells (MFCs). Despite significant progress in improving this technology over the last 25 years, there remains a lack of understanding of the processes occurring within MFCs, such as degradation rates of complex organic compounds. Limited literature on what these rates are under realistic conditions hinders this technology's optimisation. This first phase of this research project aims to help fill this research gap by investigating the degradation rates of different substrates (acetate, glucose and starch) in kinetic and non-kinetic limited systems and at varying temperatures.Previous research has shown that power outputs when using simpler compounds (acetate) are significantly higher when compared to complex compounds (starch) due to acetate not needing to be broken down by fermentation, indicating hydrolysis is the rate-limiting step in these systems. However, this was under fully stirred conditions. In reality, many MFCs operate in batch mode, and those which are continuous, have such low flow rates that turbulence does not create fully stirred conditions. If MFCs are to be used for real wastewater treatment, the degradation rates and limitations need to be fully understood. Such rates are needed to model and engineer MFC reactors effectively.To determine whether the systems are kinetically limited, two bench-scale reactor configurations will be used; one that is fully stirred, allowing the basic limitations of the main degradation pathways to be determined; and one that is not stirred, giving an indication as to whether the processes within the system are taking place in the bulk liquid or on the biofilm. Stirring and non-stirring conditions will be used to determine the mass transfer limitations within the MFCs, and ultimately help design reactors and operational conditions which maximise their efficacy for treating complex wastes.The second phase of this research project will involve repeating these initial experiments but with larger MFC configurations that simulate decentralised treatment scales. This will allow for more realistic conditions to be tested. Since wastewater is comprised of highly multifarious substrates, the breakdown of complex compounds needs to be optimised. A potential solution to this is problem is the incorporation of plants as well as a soil based medium to the MFC system. Plant MFCs (P-MFCs), a modification of MFCs, have recently emerged and show promising results for MFC performance. Studies have demonstrated that plant based MFCs are successful. However, work still needs to be done to improve the output of these systems in winter months. It is the hope that the introduction of soil and plants to an MFC system will give the further benefit of trophic levels within the metabolic food web. The soil connecting the plants to the cathode will be full of organisms such as worms and many different microbiota, all of which could possibly aid the digestion/degradation pathways within these systems and ultimately increase their performance and subsequent wastewater treatment and energy recovery. Several studies have demonstrated the effectiveness of using worms to treat and transform wastewater, sewage, and wet sludge at both household and large-scale.The final phase of this research project will therefore investigate the impact of trophic layers on the rates of degradation in L-scale MFCs. The reactors will be designed and built-in triplicate and will undergo preliminary tests under variable conditions. Initially, tests will be carried out in the laboratory, and eventually will be tested outside to enable us to determine if this technology is viable and if it can be implemented into real life set ups.