VALORIZATION OF SOLID DIGESTATE THROUGH AUTOTHERMAL HYDROTHERMAL LIQUEFACTION

该项目探索了解决日益严重的湿废物问题的新方法，这些湿废物包括农场产生的动物粪便，以及食品工业中加工水果和蔬菜的废水。湿废物通常比固体废物含有更多的水，因此无法在堆填区正常运输和储存或通过燃烧处理。相反，通常采用生物过程来处理湿废物，但这些过程很慢，并且经常留下需要特殊处理的大量固体残留物。本项目探索水热液化（HTL）过程，这是一种高温高压的过程，将氧气溶解到湿废物中，将废物转化为液体燃料，而不需要外部能源驱动该过程。通过将废物转化为液体燃料，这一过程既消除了废物，又产生了有价值的产品。如果成功，该项目将为扩大HTL工艺规模提供新的途径，使其更广泛地使用，从而加强国家的能源安全，同时减少农业和其他食品工业的废物量。该项目还将培训博士后研究人员和研究生，通过使用由首席研究员指导的分层指导方法，在未来的工程工作中有效地指导他们自己的学生。该项目的目标是通过直接耦合自热操作来强化水热液化（HTL）。这种操作将克服为该过程提供能量的传热瓶颈，并允许扩大到商业用途。爱荷华州立大学先前的研究表明，通过向反应器中引入少量空气，快速热解装置可以实现自热运行。与传统（非氧化）热解相比，氧气的增加使产量增加了三倍，而生物油生产的损失最小。本研究提出了HTL反应器的类似自热操作，通过部分氧化液化的一些低价值水相产品为该过程提供焓。据推测，氧将优先溶解在HTL产品的水馏分中，在那里它很容易与溶解的有机物发生反应。相比之下，更有价值的生物原油，一种悬浮在水溶液中的乳液，与溶解氧的接触要少得多，不会被氧化。该项目的方法是开发一种量热HTL反应器，该反应器将允许在动物粪便厌氧消化固体消化物的HTL过程中确定能量流动以及产品组成。在惰性和氧化环境下进行的实验将确定液化焓可以通过对不太有价值的液化产物进行部分氧化来提供的程度。除了在大气条件下溶解固体的湿氧化外，有机化合物在高温高压水环境中的氧化几乎没有研究。如果成功，这项研究将有助于修复美国每年产生的大约565太克湿废物。此外，在本工作中实施的科学和工程原理将作为对一系列湿废物（包括农业残渣、食物垃圾、城市固体废物、污水污泥和动物粪便）进行HTL过程强化所需的基础研究。一个正式的博士后研究人员和研究生指导结构，结合从幼儿园到十二年级学生的有效外展，将有助于在这些工程实践中激励和培养新的研究人员。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。

This project explores new ways to address the growing problem of wet wastes ranging from animal manure produced on farms, to wastewater from processing fruits and vegetables in the food industry. Wet wastes usually contain more water than solid material wastes, preventing the normal transport and storage at landfills or treatment by burning. Instead, biological processes are often employed to treat wet wastes, but these processes are slow and often leave a significant solid residue requiring special disposal. This project explores the hydrothermal liquefaction (HTL) process, a high-temperate, high-pressure process that dissolves oxygen into the wet wastes, to convert this waste into liquid fuel without requiring external energy sources to drive the process. By turning waste into liquid fuel, the process both eliminates the waste and generates a valuable product. If successful, this project will provide new ways to scale up HTL processes to make them available for more common use, thereby strengthening the Nation’s energy security while reducing the amount of waste from agriculture and other food industries. This project will also train postdoctoral researchers graduate students to effectively mentor their own students in future engineering efforts through the use of a tiered mentoring approach guided by the lead investigator.This goal of this project is to intensify hydrothermal liquefaction (HTL) through directly coupled autothermal operation. This operation will overcome the heat transfer bottleneck of providing energy to the process and allow for scale-up to commercial use. Previous research at Iowa State University demonstrated autothermal operation of a fast pyrolyzer by admitting a small amount of air to the reactor. This increase in oxygen achieved a three-fold increase in throughput compared to conventional (non-oxidative) pyrolysis with minimal loss in bio-oil production. This study proposes a similar autothermal operation of an HTL reactor, providing the enthalpy for the process through partial oxidation of some of the low value aqueous phase products of liquefaction. It is hypothesized that oxygen will preferentially dissolve in the aqueous fraction of HTL products where it will readily react with dissolved organics. In contrast, the more valuable biocrude, an emulsion suspended in the aqueous fraction with far less exposure to the dissolved oxygen, will not substantially oxidize. The approach to this project is to develop a calorimetric HTL reactor that will allow energy flows as well as product composition to be determined during HTL of solid digestate from anaerobic digestion of animal manure. Experiments under both inert and oxidative environments will determine the extent that the enthalpy for liquefaction can be provided by partial oxidation of the less valuable products of liquefaction. The oxidation of organic compounds in high temperature, high pressure aqueous environments has been little studied outside wet oxidation of dissolved solids at atmospheric conditions. If successful, this research will help remediate the approximately 565 teragrams of wet waste generated annually in the United States. Additionally, the scientific and engineering principles implemented in this work will serve as foundational research required for the process intensification of HTL for a range of wet wastes including agricultural residue, food wastes, municipality solid wastes, sewage sludge, and animal manure. A formal postdoctoral researcher and graduate student mentoring structure, combined with effective outreach to kindergarten through twelfth grade students, will help inspire new and train future researchers in these engineering practices.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.