UUttaahh SSttaattee UUnniivveerrssiittyy DDiiggiittaallCCoommmmoonnss@@UUSSUU All Graduate Theses and Dissertations Graduate Studies 12-2011 RRoottaattiinngg AAllggaall BBiioofifillmm RReeaaccttoorrss:: MMaatthheemmaattiiccaall MMooddeelliinngg aanndd LLiippiidd PPrroodduuccttiioonn Paul A. Woolsey Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Cell and Developmental Biology Commons RReeccoommmmeennddeedd CCiittaattiioonn Woolsey, Paul A., "Rotating Algal Biofilm Reactors: Mathematical Modeling and Lipid Production" (2011). All Graduate Theses and Dissertations. 1107. https://digitalcommons.usu.edu/etd/1107 This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. ROTATING ALGAL BIOFILM REACTORS: MATHEMATICAL MODELING AND LIPID PRODUCTION By Paul A. Woolsey A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Biological Engineering Approved: ________________________________ ________________________________ Dr. Ronald C. Sims Dr. Byard Wood Committee Chairman Committee Member ________________________________ ________________________________ Mr. Issa Hamud Dr. Mark R. McLellan Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2011 ii Copyright © Paul Woolsey 2011 All rights Reserved iii ABSTRACT Rotating Algal Biofilm Reactors: Mathematical Modeling and Lipid Production by Paul A. Woolsey, Master of Science Utah State University, 2011 Major Professor: Dr. Ronald C. Sims Department: Biological Engineering Harvesting of algal biomass presents a large barrier to the success of biofuels made from algae feedstock. Small cell sizes coupled with dilute concentrations of biomass in lagoon systems make separation an expensive and energy intense-process. The rotating algal biofilm reactor (RABR) has been developed at USU to provide a sustainable technology solution to this issue. Algae cells grown as a biofilm are concentrated in one location for ease of harvesting of high density biomass. A mathematical model of this biofilm system was developed based on data generated from three pilot scale reactors at the City of Logan, Utah wastewater reclamation plant. The data were fit using nonlinear regression to a modified logistic growth equation. The logistic growth equation was used to estimate nitrogen and phosphorus removal from the system, and to find the best harvesting time for the reactors. These values were extrapolated to determine yields of methane and biodiesel from algae biomass that could be used to provide energy to the City of Logan if these reactors were implemented at full scale. For transesterification into biodiesel, algae need to have high lipid content. Algae iv biofilms have been relatively unexplored in terms of cell lipid composition accumulation and changes with regard to environmental stressors. Results indicated that biofilm biomass was largely unaffected by nutrient stresses. Neither nitrogen limitation nor excess inorganic carbon triggered a significant change in lipid content. Biofilm algae grown with indoor lighting produced an average of 4.2% lipid content by dry weight. Biofilm algae gown outdoors yielded an average of 6.2% lipid content by dry weight. (108 pages) v PUBLIC ABSTRACT Creating renewable biofuels from algal biomass has the potential both to replace fossil fuels as an energy source and remediate environmental issues. Harvesting this biomass for use as biofuel feedstock presents a large barrier to large scale implementation of this solution. Growing the biomass in the form of a film attached to a surface could solve this harvesting issue. This work seeks to better understand both the biomass production and environmental remediation of a novel biofilm cultivation system through mathematical modeling. Mathematical models will help predict how much biomass can be grown, how much nutrients can be removed, and potential inhibitors to system performance. In addition this work also explores ways to increase the biofuel potential of this system by manipulating nutrient concentrations in order to obtain a more desirable feedstock. Through better understanding of biofilm systems in addition to developing ways to produce a better feedstock these systems can be better implemented for both purposes. vi ACKNOWLEDGMENTS I would like to acknowledge the support provided by several organizations, including the United States Department of Energy, the Utah State University Biological Engineering Department, the Sustainable Waste-to-Bioproducts Engineering Center, the Utah Water Research Laboratory, the BioEnergy Center, and the Logan City Environmental Department. Thanks also to my committee members, Dr. Ronald Sims, Dr. Byard, and Mr. Issa Hamud, for their input and support. Special thanks go to my colleagues Dr. Daniel Dye, Logan Christenson, Ashton Young, Terrence Smith, and Ashik Sathish for their assistance throughout this research. I would also like to thank Dr. Powell, Department of Mathematics and Statistics, for his help with the modeling effort. Paul Woolsey vii CONTENTS ABSTRACT ....................................................................................................................... iii PUBLIC ABSTRACT ........................................................................................................ v ACKNOWLEDGMENTS ................................................................................................. vi LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ............................................................................................................ x LIST OF EQUATIONS ..................................................................................................... xi INTRODUCTION AND NEED FOR STUDY .................................................................. 1 Need for Renewable Energy ........................................................................................... 1 Benefits of Algae ............................................................................................................ 1 Benefits of Biofilms ........................................................................................................ 3 The Rotating Algal Biofilm Reactor ............................................................................... 4 Modeling of Biofilms ...................................................................................................... 6 Biofilms as a Source of Fatty Acid Methyl Esters .......................................................... 7 LITERATURE REVIEW ................................................................................................... 9 Biofilm Modeling............................................................................................................ 9 Wastewater Treatment and Biofilms ............................................................................ 11 Lipid Production in Algae ............................................................................................. 14 Biofilm and Suspended Algal Growth and Lipid Production Rates ............................. 17 Potential Benefits of Biofilm Cultivation ..................................................................... 20 MODEL CONSTRUCTION, ASSUMPTIONS, AND CONSTRAINTS ....................... 24 Initial Aquasim Modeling ............................................................................................. 24 Matlab Model ................................................................................................................ 25 Approach and Equations........................................................................................... 25 Assumptions .............................................................................................................. 30 Construction .............................................................................................................. 32 Model Constraints ..................................................................................................... 36 Model Applications ................................................................................................... 37 MODELING OF BIOMASS PRODUCTION.................................................................. 39 Model of Biomass Production ...................................................................................... 39 Ideal Harvesting Time and Biomass Production for a Full Scale RABR ..................... 42 viii MODELING OF NUTRIENT REMEDIATION ............................................................. 44 Phosphorus Uptake ....................................................................................................... 44 Discussion ..................................................................................................................... 45 DISCUSSION AND INSIGHTS FROM SYSTEM MODELING ................................... 47 FAME PRODUCTION OF ALGAL BIOFILM REACTORS ......................................... 50 Experimental Design ..................................................................................................... 50 Selection of Variables ............................................................................................... 50 Culture and Medium ................................................................................................. 52 Physical Setup ........................................................................................................... 53 Data Collection and Methods ................................................................................... 54 Effect of Nitrogen and Carbon on Fatty Acid Methyl Ester Yield ............................... 56 Biomass Yields ............................................................................................................. 58 Comparison to Other Studies ........................................................................................ 60 Potential Reasons for Static Fame Yield ...................................................................... 61 FAME YIELDS OF PILOT SCALE RABRS .................................................................. 64 RABR PRODUCT RECOVERY ..................................................................................... 67 COMPARISON TO PREVIOUS STUDY ....................................................................... 70 Study Operation Differences......................................................................................... 70 Biomass Yield ............................................................................................................... 72 FAME Yield.................................................................................................................. 74 FUTURE WORK .............................................................................................................. 76 Biofilm Fundamentals ................................................................................................... 76 Improving Existing Model ............................................................................................ 79 Additional Modeling Considerations ............................................................................ 80 REFERENCES ................................................................................................................. 83 Appendix A: MATLAB Code .................................................................................... 92 Appendix B: Calculations ........................................................................................... 97 ix LIST OF TABLES Table Page 1 Effect of Various Factors on Biomass Growth and Lipid Content in Microalgae...... 15 2 Lipid Productivity under Different Growth Conditions.............................................. 16 3 Growth and Lipid Yields of Chlorella under Varying Cultivation Modes ................. 19 4 Comparison of Biofilms as a Harvesting and Dewatering Method to Other Processes ......................................................................................... 22 5 Modeling Variables ..................................................................................................... 30 6 Pilot Scale RABR Operational Parameters ................................................................. 32 7 Constants used in Biomass Model .............................................................................. 39 8 Comparison of July and November Model Constants ................................................ 42 9 Experiment Scenarios ................................................................................................. 50 10 Synthetic Media Composition for Phototrophic Biofilm Growth............................... 52 11 Biomass Collection Setup ........................................................................................... 55 12 Comparison of Biomass and FAME Yields to Other Studies..................................... 60 13 Biodiesel Produced from RABR Implementation Scenarios ...................................... 67 14 Energy and Cost Recovery Via Anaerobic Digestion ................................................. 68