EAGER: Coupling of Gas-Liquid Plasma Chemical Reactors with Bioengineered Microbes

非热等离子体是由高压放电产生的低温、大气压电离气体。当这些等离子体与液态水接触时，形成自由基，有效地分解有毒化合物或将有机废物转化为增值产品。虽然单独使用非热等离子体可以将目标污染物完全降解为矿化产物，但所需的总电力可能使该过程在经济上不可行的。另一方面，生物处理过程可以完全转化一些化学废物，大大降低了电力需求。然而，这些方法仅限于可生物降解的化合物，并且可能需要较长的处理时间。该研究小组先前的工作表明，使用等离子体反应器启动废物化合物的分解，然后使用生物反应器完成该过程的顺序组合可以显著节省能源。然而，研究还发现，较慢的生物反应器动力学导致时间尺度上的不匹配，最终导致非常大的反应器系统。为了克服这个问题，在这项研究中，微生物细胞将通过基因工程实现：a)在与非热等离子体接触的液态水中存活；b)增加酶的产生，使生物反应途径的速率与等离子体的速率相比较。这两个过程时间尺度的匹配将使设计和运行集成、紧凑和节能的等离子体生物反应器系统成为可能，用于降解废水流中的有害和有毒化合物或从废物中生产有用的化合物。关于非生物（非生物）系统（如非热等离子体反应器）与细菌细胞代谢的耦合的基础知识也将通过这项工作产生。本项目旨在开发非热等离子体气液生物反应器，将等离子体化学和化学反应工程与生物工程相结合。等离子体反应在不到1秒的时间尺度上发生，而传统的生物反应器通常在数小时、数天甚至数周的时间尺度上运行。这些时间尺度上的巨大差异表明，通过将非热等离子体与含有用于等离子体抗性和特定代谢任务的生物工程微生物的生物反应器耦合，可能获得更高的效率和反应过程协同作用。这项工作的总体目标是验证这样一种假设，即对等离子体产生的氧化性化合物具有抗性的微生物可以通过基因工程改造，在气液非热等离子体反应器的反应环境中进行其他有用的生化转化。血浆抗性大肠杆菌将被改造以增强其固有的代谢羧酸的能力，特别是乙醇酸、甲酸和草酸。同样，等离子体反应器将被设计成促进细胞与气液等离子体环境之间的有效接触。该提议的具体假设是：1)新开发的细胞将能够在暴露于等离子体时发挥作用，2)将这些细胞纳入等离子体反应器将导致目标有机化合物的更快的整体矿化。在这项工作中要研究的第一个实际应用涉及处理有毒和难以生物降解的有机化合物。可以在高度氧化的等离子体环境中创造微生物来进行有用的化学转化的演示将构成在化学处理中有效利用电能的新例子。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-thermal plasmas are low-temperature, atmospheric-pressure ionized gases that are generated by high-voltage electric discharges. When these plasmas are in contact with liquid water, free radical species are formed that effectively decompose toxic compounds or transform organic waste into value-added products. While non-thermal plasmas alone can be used to completely degrade target pollutants into mineralized products, the total electrical power required may make the process economically nonviable. Biological treatment processes, on the other hand, can completely transform some chemical waste species with greatly reduced power demands. However, these processes are limited to biodegradable compounds and may require lengthy processing times. Previous work by this research team demonstrated that the sequential combination of using a plasma reactor to initiate the breakdown of waste compounds followed by a bioreactor to complete the process can lead to significant energy savings. It was also found, however, that the slower bioreactor dynamics results in a mismatch in time scales that ultimately led to very large reactor systems. To overcome this problem, in this study microbial cells will be genetically engineered to: a) survive in the liquid water contacting the non-thermal plasma, and b) increase enzyme production so that the rates of the biological reaction pathways compare to those of the plasma. This matching of the two process time scales will make possible the design and operation of integrated, compact, and energy efficient plasma-bioreactor systems for degrading hazardous and toxic compounds from wastewater streams or to produce useful compounds from waste materials. Fundamental knowledge on coupling a non-biological (abiotic) system such as the non-thermal plasma reactor with the cellular metabolism of a bacterium also will be generated by this work.This project seeks to develop non-thermal plasma gas-liquid bioreactors, research that couples plasma chemistry and chemical reaction engineering with bioengineering. Plasma reactions occur over time scales of less than 1 second while conventional bioreactors often operate on time scales of hours to days to weeks. These large differences in time scales suggest that it may be possible to attain greater efficiency and reaction process synergy by coupling non-thermal plasma to bioreactors containing microbes bioengineered for both plasma resistance and specific metabolic tasks. The overall goal of the proposed work is to test the hypothesis that microbes resistant to the plasma-produced oxidizing compounds can be genetically engineered to perform other useful biochemical transformations within the reactive environment of gas-liquid non-thermal plasma reactors. Plasma resistant E. coli will be engineered to enhance their inherent capacity to metabolize carboxylic acids, specifically glycolic, formic and oxalic acids. Likewise, the plasma reactor will be engineered to promote effective contact between the cells and the gas-liquid plasma environment. The specific hypotheses of this proposal are: 1) that the newly developed cells will be able to function while exposed to the plasma, and 2) the incorporation of these cells in the plasma reactor will lead to a faster overall mineralization of a target organic compound. The first practical applications to be investigated in this work involve treatment of toxic and difficult to biodegrade organic compounds. The demonstration that microbes can be created to perform useful chemical transformation within the highly oxidizing plasma environment will constitute a novel example of the effective use of electrical energy in chemical processing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.