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

微生物电解电池可以同时处理废水，并以氢气等增值产品的形式回收能量。该系统利用了阳极上的生物膜，该生物膜由电生微生物组成，当施加0.14V的外部电压时，电生微生物将有机物厌氧分解成电子和H+， H+在阴极上反应产生氢气。该技术在实验室规模上的性能已经得到证实，然而，试点研究表明，要实现其在能量回收和处理性能、系统可变性和成本等领域的商业应用，还需要克服主要的限制。该研究项目旨在优化这些障碍的性能，并使该技术能够在更大范围内严格评估其作为能源中性或积极的废水处理资产的可行性。迄今为止，很少有试点试验能够产生足够的氢气来实现净正能源性能，据报道电回收效率低至3%2。这归因于阴极室2-4中清除氢的微生物。因此，本研究项目将研究MEC内的灭菌模式（如H2O2生成）和电解质再循环，以抑制微生物竞争，并评估其对制氢和能源效率的好处。此外，将考虑在使用真实废水的中试MEC上进行输入电压优化实验，以评估不同电压对更大规模氢气回收率和体积处理率的影响。这里的新颖之处在于，输入电压只在实验室规模上进行了优化，在实验室规模上的研究使用了合成废水，而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，以优化性能，使用现有的计算流动力学（CFD）模型测试的场景。因此，将使用Howdon污水处理厂的试点MEC或BEWISE MEC设施（Northumbrian Water Ltd/Newcastle University）来研究缩小通道宽度对电流、H2产量和处理率的实际影响，BEWISE MEC设施允许调整电极盒。污泥回流液将作为MEC应用的途径进一步探索，因为它们提供足够的COD，以最大限度地减少对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。在一系列试验中，已经观察到试点mec的性能变化，这就对其产生一致的氢- 2-4的能力提出了质疑。因此，本研究的另一个期望将侧重于减少这种可变性，首先通过验证生物膜发育差异、细胞内部抗性差异或两者的差异来确定其在MEC系统中的起源。这将通过在相同条件下运行大量的复制反应器，并使用微生物分析和电化学阻抗谱（EIS）来了解性能良好和性能较差的反应器之间的差异来进行测试。在此之后，将制定启动期间播种反应堆和重新播种失败反应堆的策略。CostsAiken等人强调阳极和集流器材料成本需要降低90%，以及其他目标，以使mec在经济上可行5。因此，本研究旨在通过监测废水中的材料降解和处理性能，在更大范围内测试使用低成本再生碳纤维作为阳极材料的实用性。这与处理和可变性优化一起，将能够对MEC进行全面的市场分析。

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.