Developing large scale microbial electrolysis cells (MECs) for the treatment of sludge return liquors

微生物电解池可以同时处理废水和回收能源的形式增值产品，如氢气。该系统利用阳极上的生物膜，该生物膜由产电微生物组成，当施加>0.14V的外部电压时，该产电微生物厌氧地将有机物质分解成电子和H+，其在阴极处反应以产生氢气1。该技术在实验室规模上的性能已经得到证明，但是，试点研究表明，要使其在能源回收和处理性能、系统可变性和成本等领域的商业应用能够克服主要局限性。该研究项目旨在针对这些障碍优化性能，并将该技术置于重要位置，以评估其作为更大规模的能源中性或积极废水处理资产的可行性。能源回收和处理性能迄今为止，很少有试点试验产生足够的氢气以实现净正能量性能，据报道电回收效率低至3%2。这归因于阴极室中的氢清除微生物2 -4。因此，本研究项目将研究MEC内的灭菌（例如H2 O2生成）和电解质再循环模式，以抑制微生物竞争，并评估其对制氢和能源效率的益处。此外，将考虑在使用真实的废水的中试MEC上进行输入电压优化实验，以评估在更大规模下不同电压对氢气回收率和体积处理率的影响。这里的新奇在于，输入电压仅在实验室规模上进行了优化，其中研究使用了合成废水，忽略了在规模上增加过电位对性能的挑战。将探索反应器设计，以使用现有计算流体动力学（CFD）模型测试的场景来优化性能。因此，将使用Howdon污水处理厂的中试MEC或BEWISE MEC设施（Northumbrian Water Ltd/纽卡斯尔大学）研究变窄通道宽度对电流、H2产量和处理速率的真实的影响，该设施允许调整电极盒。将进一步探索污泥回流液作为MEC应用的途径，因为它们提供足够的COD，以最大限度地减少电流和氢气生产的浓度限制。MEC和活性污泥处理液线之间的成本节约也将与正在进行的反应器优化进行比较。在许多试验中观察到中试MEC的性能变化，这引起了对其生产一致氢气的能力的质疑2 -4。因此，这项研究的另一个期望将集中在减少这种变异性，首先通过验证生物膜发育的差异，这将通过在相同条件下操作大量复制反应器并使用微生物分析和电化学阻抗谱（EIS）进行测试来理解好的和坏的反应堆之间的区别。在此之后，将制定在启动期间向反应堆播种和重新播种失败的反应堆的策略。CostsAiken等人强调，阳极和集电器材料成本需要降低90%沿着其他目标，以使MEC在财务上可行5。因此，本研究旨在通过监测废水中的材料降解和较大规模的处理性能来测试使用低成本回收碳纤维作为阳极材料的实用性。沿着治疗和变异性优化，这将使对MEC进行全面的市场分析成为可能。

Microbial electrolysis cells can simultaneously treat wastewater and recover energy in the form of value-added products such as hydrogen. The system utilises a biofilm on an anode consisting of electrogenic microbes which anaerobically break down organic matter into electrons and H+ which react at a cathode to produce hydrogen when an external voltage of >0.14V is applied1. The technology's performance at lab-scale has been proven, however, pilot-studies have demonstrated major limitations that need to be overcome to enable its commercial application in the areas of energy recovery and treatment performance, system variability and costs. This research project aims to optimize performance against these barriers and move the technology into position to critically assess its feasibility as an energy neutral or positive wastewater treatment asset at a larger scale.Energy recovery and treatment performanceTo date, few of the pilot-trials have produced sufficient hydrogen to achieve net-positive energy performance, with electrical recovery efficiencies reported to be as low as 3%2. This has been attributed to hydrogen scavenging microbes in the cathode compartment2-4. Hence, this research project will investigate modes of sterilization (e.g H2O2 generation) and electrolyte recirculation within the MEC to inhibit microbial competition and assess their benefits on hydrogen generation and energy efficiency. Additionally, an input voltage optimization experiment on a pilot MEC using real wastewater will be considered to assess the influence of varying voltage on hydrogen recovery and volumetric treatment rates at a larger scale. The novelty here is that input voltages have only been optimized at lab-scale, where studies have used synthetic wastewater and neglect the challenges of increasing overpotentials on performance at scale.Reactor design will be explored to optimize performance using scenarios tested by an existing computational flow dynamics (CFD) model. Hence, the real effect of narrowing channel width on current, H2 production and treatment rates will be investigated using the pilot MEC at Howdon Sewage Treatment works or the BEWISE MEC facility (Northumbrian Water Ltd/Newcastle University) which allows for electrode cassettes to be adjusted. Sludge return liquors will be further explored as an avenue for MEC application as they provide sufficient COD to minimize concentration limitations on current and hydrogen production. Cost savings between MEC and activated sludge treatment of the liquor line will also be compared with ongoing reactor optimization. System Variability Performance variability within pilot-MECs has been observed in a number of trials which raises questions about its ability to produce consistent hydrogen2-4. Hence, another expect of this research will focus on reducing this variability by first identifying its origins in the MEC system by verifying if differences in biofilm development, cell internal resistance or both causes it. This will be tested by operating a high number of replica reactors under identical conditions and using microbial analysis and electrochemical impedance spectroscopy (EIS) to understand the differences between good and bad performing reactors. Following this, strategies for seeding reactors during start up and re-seeding those that fail will be developed. CostsAiken et al highlighted anode and current collector material costs need to be reduced by 90% along with other targets to make MECs financially viable5. Therefore, this research will aim to test the practicalities of using low-cost recycled carbon fibre as an anode material by monitoring material degradation in wastewater and treatment performance overtime at larger scales. This, along with the treatment and variability optimizations, will enable a full market analysis to be undertaken for the MEC.