SIMULATION OF FLOW, MASS TRANSFER AND BIO-CHEMICAL REACTIONS IN ANAEROBIC DIGESTION By LIANG YU A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Biological Systems Engineering DECEMBER 2012 To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of LIANG YU find it satisfactory and recommend that it be accepted. _ JJJJjkkkk Shulin Chen, Ph.D., Chair _ JJJJj Robt Dillon Manuel Garcia-Perez, Ph.D. _ JJJJj Robt Dillon Dillon Robert, Ph.D. _ JJJJjkkkk Konstantin Matveev, Ph.D. D ii ACKNOWLEDGEMENTS I would like to expess my sincere thanks to my advisor, Dr. Shulin Chen, for allowing me to pursue this study at the Bioprocessing & Bioproducts Enigeering Laboratory (BBEL). I am extremely thankful for his personal guidance, assistance and supervision over the course of this study. My commetee members: Dr. Manuel Garcia-Perez, Dr. Dillon Robert and Dr. Konstantin Matveev are also gratefully acknowledged for their valuable comments and suggestions during the dissertation process. I warmly thank Dr. Craig Frear for his valuable advice and friendly help on my dissertation work. My warm thanks are also due to Jonathan Lomber, Cynthia Alwine for their kind help in lab data analysis. I appreciate AD group members: Jingwei Ma, Quanbao Zhao, Baisuo Zhao, and Nicholas Paul Kennedy, the former members and all BBEL members for their help and cooperation. Thanks go to John Anderson, Patricia Huggins, Pat King, and Joan Hagedorn for their administrative support. I extend my thanks to all those who have helped me with my work in the Department of Biological Systems Engineering at Washington State University. I also want to dedicate this dissertation to my parents, although they can not see it anymore. Finally, I thank my wife Dongming Zhao for giving up her claim on my time for these past four years. My gratitude also goes to my brother Jiang Yu for his support on my Professional Engineer (PE) Exam. iii SIMULATION OF FLOW, MASS TRANSFER AND BIO-CHEMICAL REACTIONS IN ANAEROBIC DIGESTION ABSTRACT By LIANG YU, Ph.D. Washington State University DECEMBER 2012 Chair: Dr. Shulin Chen The aims of the dissertation were to understand and simulate flow, mass transfer and bio-chemical reactions in anaerobic digesters. Computational fluid dynamics (CFD) and anaerobic digestion model No. 1 (ADM1) were used to assist the development of a new high solid anaerobic digestion system. The kinetic theory of granular flow (KTGF) was introduced and a multi-fluid model was developed to describe the phenomena of settling and suspension in the anaerobic digestor which is critical to increase biomass retention and improve digestion performance. To assess flow fields in a HSAD, a mechanical mixing model was constructed to predict flow characteristics. The model results show impeller A-310 was not suitable for agitating a high solid digester due to its impaired mixing performance and large shear rate. The helical ribbon had a better potential to be more suitable for the mixing of high solids digesters than the Impeller A-30. Its low shear environment is suitable for microbial flocs in anaerobic digestion. Through iv optimization, the power of the helical ribbon used in high solids digesters can be reduced significantly. A comprehensive model based on ADM1 was developed to describe a new two-stage HSAD system. The predictions indicate that a high rate HSAD system could be achieved by adjusting major parameters such as pH, recycled methanogenic bacteria, and UASB section area. Recycled methanogenic bacteria increased methane concentration and decreased hydrogen concentrations in the HSAD reactor, while pH increased in the batch mode, but decreased in the continuous mode with an increase of recycling rate. The UASB height had little impact on the acetic acid concentration and methane production. The mechnisim of a high rate digestor was explored by a multi-fluid model with KTGF. The simulation results suggest that the dairy manure particles tend to have soft and deformable fluid properties due to the lower contribution of collisional and kinetic components. The evaluation for biomass retention allowed the determination of the optimum SRT in anaerobic digestion. Aided with CFD simulation, the scale-up effect of the hydrodynamic nature from the bottle reactor to the column reactor was reduced. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................................... iii LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES ........................................................................................................................ x Chapter 1 : Introduction .................................................................................................................. 1 1.1. Introduction .......................................................................................................................... 1 1.2. Anaerobic Digestion Pathways and Reactions ..................................................................... 3 1.3. Bio-chemical kinetics models ............................................................................................ 17 1.4. Anaerobic Digestion Reactors ............................................................................................ 28 1.5. Black Box Models to Simulate Anaerobic Digestors......................................................... 37 1.6. Phenomenological Models for Simulating Anaerobic Digesters ....................................... 42 1.7. Conclusions ........................................................................................................................ 53 1.8. References .......................................................................................................................... 56 Chapter 2 : Numerical Simulation of Mechanical Mixing in High Solid Anaerobic Digester ....... 1 2.1. Abstract .............................................................................................................................. 74 2.2. Introduction ........................................................................................................................ 75 2.3. Methods .............................................................................................................................. 78 2.4. Results and discussion ........................................................................................................ 84 2.5. Conclusions ........................................................................................................................ 95 2.6. References .......................................................................................................................... 96 vi Chapter 3 : Experimental and Modeling Study of a Two-Stage Pilot Scale High Solid Anaerobic Digester System .......................................................................................................................... 100 3.1. Abstract ............................................................................................................................ 100 3.2. Introduction ...................................................................................................................... 101 3.3. Methods ............................................................................................................................ 104 3.4. Results and discussion ...................................................................................................... 113 3.5. Conclusions ...................................................................................................................... 132 3.6. References ........................................................................................................................ 134 Chapter 4 : Multiphase Modeling of Settling and Suspension in Anaerobic Digester ............... 139 4.1. Abstract ............................................................................................................................ 139 4.2. Introduction ...................................................................................................................... 140 4.3. Materials and methods ..................................................................................................... 143 4.4. Results and discussion ...................................................................................................... 152 4.5. Conclusions ...................................................................................................................... 171 4.6. References ........................................................................................................................ 173 Chapter 5 : General Conclusions ................................................................................................ 178 vii LIST OF TABLES Table 1.1. Typical composition for the common substrates used in anaerobic digestion ............... 2 Table 1.2. Biochemical rate coefficients (v ) and kinetic rate equations (ρ) for soluble i,j j components (i=1-12; j=1-19) ........................................................................................................ 15 Table 1.3. Biochemical rate coefficients (v ) and kinetic rate equations (ρ) for particulate i,j j components (i=1-12; j=1-19) ........................................................................................................ 16 Table 1.4. Kinetic coefficients of the first order rate of hydrolysis .............................................. 23 Table 2.1. Geometrical details for digesters with impeller A-310 and helical ribbon (Hoffmann et al., 2008; Karim et al., 2005) ........................................................................................................ 78 Table 2.2. Parameters of the power-law model for shear stress with temperature (T), flow behavior index n and consistency coefficient K (El-Mashad et al., 2005) ................................... 85 Table 2.3. Rheological properties and densities of liquid manure for T = 35 °C (Achkari-Begdouri and Goodrich, 1992; Landry et al., 2004; Wu and Chen, 2008) .................... 90 Table 2.4. Specifications and calculated results of ribbon mixers made in Aaron Process Equipment ..................................................................................................................................... 93 Table 3.1. Conditions for the mathematic model for the high solids anaerobic digester system 106 Table 3.2. Model parameters in the HSAD system (Batstone et al., 2002; Gali et al., 2009; Rosen and Jeppsson, 2006) .....................................................................................................................112 Table 3.3. Ranking of roots of mean squared sensitivities ......................................................... 121 Table 4.1. Particle size distribution in the bottle reactor ............................................................. 144 viii Table 4.2. Model parameters in the ADM1 model ...................................................................... 150 Table 4.3. Dairy manure initial concentration ............................................................................ 168 Table 4.4. Operational conditions and experimental results ....................................................... 168 ix LIST OF FIGURES Figure 1.1 Main pathways for anaerobic degradation of organic matter used in the model ........... 7 Figure 1.2. Main pathways for ADM1 model ............................................................................... 12 Figure 1.3. Plot shows the fit of the derived model to the experimental data points and the 95% confidence interval (Karim et al., 2007) ....................................................................................... 19 Figure 1.4. Dependence of the solids removal reciprocal rate upon solids concentration according to the firstorder (a) and Contois models with actual (b) and optimal design (c) Model parameters: first-order (k =0.047 day-1, k =0.45 day-1); Contois (X =0.005 g l-1, Y=0.13g g-1, µ =4 day-1; 1 2 0 m K* =10g g-1) (Vavilin et al., 2001) ................................................................................................ 26 S Figure 1.5. Batch reactor (Chynoweth and Isaacson, 1987) ......................................................... 30 Figure 1.6. Continuously stirred tank reactor (Chynoweth and Isaacson, 1987) .......................... 32 Figure 1.7. Plug flow reactor (Chynoweth and Isaacson, 1987) ................................................... 33 Figure 1.8. Up-flow anaerobic sludge blanket reactor (Chynoweth and Isaacson, 1987) ............ 35 Figure 1.9. Two-phase digesters (Chynoweth and Isaacson, 1987) .............................................. 37 Figure 1.10. Schematic diagram of (a) adaptive network-based fuzzy inference system (ANFIS) models with all input variables and (b) input–output mapping structure of ANFIS model with only on-line input variables (Pai et al., 2009) ............................................................................... 40 Figure 1.11. Prediction results of COD . (a) ANFIS2-1 and (b) ANN2-1 (Pai et al., 2009) ....... 41 eff Figure 1.12. Block diagram of Bolle et al.’s (A) (Bolle et al., 1986) and Wu and Hicky’s (B) (Wu and Hickey, 1997) ......................................................................................................................... 45 x