Technical, economic, and carbon dioxide emission analyses of managing anaerobically digested sewage sludge through hydrothermal carbonization DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Luis Armando Huezo Sanchez Graduate Program in Food, Agricultural & Biological Engineering The Ohio State University 2020 Dissertation Committee: Dr. Ajay Shah Dr. Katrina Cornish Dr. Steve Culman Dr. Jay Martin Copyrighted by Luis Armando Huezo Sanchez 2020 Abstract Sewage sludge is the solid byproduct from wastewater treatment plants, and some of it is treated by anaerobic digestion (AD), which is a biological method that produces biogas and an AD effluent (ADE). Biogas is typically used for energy and heat. Anaerobic digestion effluent has a high concentration of microbes, nutrients, carbon, and water. It is typically dewatered, and its fates include incineration, landfilling, composting, or application to agricultural fields; in all these options, ADE needs to be transported. The storage and transportation of ADE have environmental impacts on water, soil, and air. Dewatering ADE is energy and cost intensive. A viable alternative to process ADE could be thermochemical methods, such as hydrothermal carbonization (HTC), that can treat ADE at high temperatures and pressures without the need to remove the water. HTC produces a carbonized char-like material called hydrochar with potential uses as solid fuel and soil amendment. Hydrochar as soil amendment has the potential to improve the properties of the soil and crop yield. Therefore, the objective of this study was to assess the technical, economic, and environmental feasibility of producing hydrochar through HTC of ADE from sewage sludge and analyze its use as soil amendment. Hydrothermal carbonization of ADE from sewage sludge was conducted between 180 and 260°C for a residence time between 30 and 70 minutes following a central composite design. The process parameters evaluated were temperature, time, and feedstock ii pH; the response variables included hydrochar and liquor yields and properties. The produced hydrochar was used as soil amendment at 1, 3, 5, 10, and 15 g per kg of soil. Seedling flats were filled with the char-soil mixtures, and lettuce seeds were planted and placed in a greenhouse. Soil properties and plant responses, such as nutrient retention, seed germination, and biomass production were analyzed based on char sources and rates. To scale-up the combined AD-HTC system to a sewage input flow of 15 ton hr-1, the process was modeled and a techno-economic analysis was performed with data from wastewater treatment plants, equipment and process conditions; properties of feedstock, intermediates, and final products; and cost of feedstock, materials, equipment, and utilities. The direct carbon dioxide emissions of the combined AD-HTC system were estimated. Temperature was the most influential parameter in producing hydrochar. Higher temperatures resulted in lower hydrochar yields, higher ash contents, and a more carbonized material. Soil amended with hydrochar had higher pH, phosphorus content, and cation exchange capacity compared to soil with no amendment. Lettuce emergence rates in soils amended with hydrochar were similar and higher compared to pyrochar and no- char. All dry weights from roots, leaves, and whole plants for amended soils were greater than those for no-char. When the combined AD-HTC system was scaled-up, the capital investment was calculated to be ~US$36 million, with a payback time of less than six years, internal rate of return of ~12%, and an operating cost of ~US$1,300 ton-1 of hydrochar. The direct carbon dioxide emissions of the combined AD-HTC system decreased compared to scenarios without AD or HTC to manage sewage sludge. In conclusion, the production of hydrochar from sewage sludge through a combined AD-HTC system has the potential iii to be technically, economically, and environmentally feasible and to be implemented in the current wastewater treatment plants. iv Dedicated to my sister, parents, and grandparents. v Acknowledgments I thank my advisor Dr. Ajay Shah for his guidance, support, dedication, and trust during my doctoral studies. I also thank Dr. Katrina Cornish, Dr. Steve Culman, and Dr. Jay Martin for serving on my committee and for their support and encouragement during the process. Thanks to Dr. Juliana Vasco-Correa for her technical support and coaching during my studies, experiments, and writing. Thanks to Dr. Ashish Manandhar, Asmita Khanal, Seyed Mousavi, Junqi Wang, Yangyang Li, and Zhifang Cui from the Biosystems Analysis Laboratory for working alongside and their assistance during this journey. I thank Quasar Energy Group members Josh Andre and Xumeng Ge for their help while running the experiments. Special thanks to Peggy Christman, Mary Wicks, Scott Wolfe, Mike Klingman, and Candy McBride, for their invaluable constant help and patience. I thank Dr. Luis Cañas, the Zamorano community, and Jhony Mera for opening the door to this opportunity. I thank my friends Uchit Nair, Aditya Raj, Dr. Ramon Salcedo, Andrea Landaverde, Dr. Anirudh Akula, Shyam Sivaprasad, Parisa Nazemi, Asmita Khanal, Champ Zhang, Dr. David Ramirez, Hugo Pantigoso, Juan Quijia, Andres Sanabria, and Julio Ramirez for their friendship and encouragement. Finally, I thank Kaylee South for her unconditional love and support in all aspects of my professional and personal life. vi Vita December 2011 ..............................................B.Sc. Environmental Science and Socioeconomic Development, Zamorano University May 2017 .......................................................M.Sc. Food, Agricultural, and Biological Engineering, The Ohio State University May 2015 to present ......................................Graduate Research Associate, Department of Food, Agricultural, and Biological Engineering, The Ohio State University Fields of Study Major Field: Food, Agricultural & Biological Engineering vii Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii Table of Contents ............................................................................................................. viii List of Tables ................................................................................................................... xiii List of Figures ................................................................................................................... xv Chapter 1: Introduction ....................................................................................................... 1 1.1. Background .............................................................................................................. 1 1.2. Problem statement .................................................................................................... 2 1.3. Dissertation objectives ............................................................................................. 4 1.4. Dissertation organization .......................................................................................... 5 Chapter 2. Literature Review .............................................................................................. 7 2.1. Introduction .............................................................................................................. 7 2.2. Types of organic waste ............................................................................................. 8 2.2.1. Manure ............................................................................................................... 9 2.2.2. Sewage sludge ................................................................................................... 9 viii 2.3. Waste biomass conversion methods and bioproducts ............................................ 10 2.3.1. Biochemical conversion methods .................................................................... 11 2.3.2. Thermochemical conversion methods ............................................................. 12 2.4. Hydrothermal carbonization of biomass ................................................................ 15 2.5. Biochar, pyrochar, and hydrochar .......................................................................... 18 2.6. Soil properties ........................................................................................................ 20 2.6.1. Soil pH ............................................................................................................. 20 2.6.2. Cation exchange capacity ................................................................................ 21 2.7. Techno-economic and life cycle analyses of anaerobic digestion and hydrothermal carbonization systems ................................................................................................... 22 2.7.1. Techno-economic analysis of anaerobic digestion and hydrothermal carbonization systems ................................................................................................ 24 2.7.2. Life-cycle assessment of anaerobic digestion and hydrothermal carbonization