EFFECTS OF DIFFERENT AERATION CONDITIONS ON ISOCHRYSIS GALBANA (T-ISO) CCMP 1324 IN A BENCH-SCALE PHOTOBIOREACTOR A Thesis Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Master of Science By Kim Anne Falinski May 2009 ©2009 Kim Anne Falinski ABSTRACT The effects of superficial gas velocity (U ), gas entrance velocity (ν), and bubble size gr on the growth of Isochrysis galbana (T-ISO) was investigated in 0.6 L photobioreactors operated with airlift pumps. Superficial gas velocities ranging from 7 to 93 mm s-1 were created using a 1.6 mm diameter syringe. Four sparger diameters were used to test the effects of sparger velocities that ranged from 2.48 to 73.4 m s-1. The effect of bubble size was evaluated by using two styles of air stones and an open glass pipet, which created a bubble size range of 0.5 to 5 mm. The k a values for all L experimental conditions were obtained. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicate that smaller bubble size leads to some initial cell damage, but after time the increased gas transfer produces higher growth than larger bubbles. Two mechanisms were found to cause cell damage in I. galbana: increasing velocity at the sparger tip and reduced bubble size. The results show that airlift systems should be designed to mitigate hydrodynamic stress due to aeration. The implications for large-scale growth of microalgae in airlift-driven tubular reactors are discussed. BIOGRAPHICAL SKETCH Kim Falinski completed her B.S. in Electrical Science and Engineering at Massachusetts Institute of Technology in 2002. Prior to enrolling at Cornell University, she worked as an engineer in the semiconductor manufacturing industry, spent time as a community organizer in a small village in Nepal, and taught applied math at a boarding school in The Bahamas. Her experiences abroad motivated a degree that would address agriculture problems in the developing world. iii DEDICATION For my beekeeping friend. iv ACKNOWLEDGEMENTS I would like to thank all those who helped me complete this work at Oceanic Institute in Waimānalo, Hawaii. Foremost is Dr. Charles Laidley, whose time, input and resources have made this project possible. Thank you for accepting me into your lab, coming from 5,000 miles away, for hands-on training in algal culture. I especially appreciate your time in helping me to understand the world of science. For Eric Martinson, who not only helped me with the details of prepping the experiments, but was also a major sounding board for all steps of the process. Thank you for letting me carry buckets when I just needed to let my head think, and for taking me in without question when I flew onto the island with no where to stay. For members of the Finfish Department: Iokepa Aipa, Chad Callan, Melissa Carr, Dean Kline, Ken Liu, Don de la Pena, and Kim Pinkerton – thank you for the encouragement, holiday dinners, and general cheerleading towards graduation. And thank you so much for letting me learn about how to raise fish in the process- it will be put to good use. Thanks to Lytha Conquest, Dr. Carrie Holl and Dr. Z.Y. Ju for their assistance with lab techniques and equipment. And to Tom Ogawa, thank you much for all that coffee. For Willow Hetrick – whose apartment has been my grad school away from home. You are inspiring in your perseverance and I hope to be half as effective as you someday in getting things done. For my best friend Howard McGinnis. Thank you so much for everything. As for the other side of the world, here are my East Coast thanks: For my parents – thank you for the solid base I am now standing on. You never really complained when I decided to go into a very different field halfway around the world. For Dr. Neema Kudva. Your seminar class in 2006 was why I decided to stay in the colds of Ithaca, in an engineering degree, and have helped me to interpret the v always complex web of relationships between non-profit organizations and government. For Dr. Len Lion – chemistry has been the base of what I have done and I thank you for your diligence in teaching me the carbonate system. You were one of the first to have faith in me in this field. And, lastly, for my advisor Dr. Michael Timmons, who has guided me through this degree with patience. I truly appreciate you letting me figure out things the long way, and for getting me to a place where I could really learn. vi TABLE OF CONTENTS BIOGRAPHICAL SKETCH ..................................................................................... iii DEDICATION .............................................................................................................iv ACKNOWLEDGEMENTS ......................................................................................... v LIST OF FIGURES .................................................................................................. viii LIST OF TABLES .......................................................................................................ix LIST OF SYMBOLS .................................................................................................... x 1. Introduction ........................................................................................................... 1 1.1. Isochrysis galbana (T-ISO) ........................................................................... 1 1.2. Large-scale photobioreactor systems ............................................................ 2 1.3. Airlift systems ................................................................................................. 3 1.4. Turbulence as the key issue in photobioreactor systems .............................. 4 1.5. Methodologies for determining shear stress in bioreactors ......................... 8 1.6. Objective ....................................................................................................... 10 2. Materials and Methods ........................................................................................... 11 2.1 Theory and analysis ..................................................................................... 11 2.1.1. Statistical analyses ................................................................................ 11 2.1.2. Superficial gas velocity ......................................................................... 11 2.1.3. Sparger velocity .................................................................................... 12 2.1.4. Growth kinetics ..................................................................................... 12 2.1.5. Determining the k a .............................................................................. 13 L 2.1.6. Design of the model airlift system ......................................................... 14 2.2. Microalgae and culture media ..................................................................... 14 2.3. Cultivation system: experimental mini-airlift ............................................. 15 2.4. Analytical methods ....................................................................................... 18 2.4.1. Cell density and viability ...................................................................... 18 2.4.2. Measurements ....................................................................................... 19 2.5. Experiments .................................................................................................. 19 3. Results and Discussion........................................................................................ 21 3.1. Effects of superficial gas velocity ................................................................ 21 3.2. Effects of sparger velocity ............................................................................ 26 3.3. Effect of gas diffusers .................................................................................. 31 3.4. Implications for airlift-driven tubular photobioreactors ............................ 39 3.5. Design Example ........................................................................................... 42 4. Conclusion ........................................................................................................... 45 APPENDIX A .............................................................................................................. 46 APPENDIX B .............................................................................................................. 47 APPENDIX C .............................................................................................................. 48 REFERENCES ............................................................................................................ 49 vii LIST OF FIGURES Figure 1.1: Five different types of air-driven reactors .................................................. 4 Figure 2.1: Schematic drawing of the airlift bench-scale photobioreactor ................. 16 Figure 2.2: Photograph of the experimental setup of bench-scale internal airlift bioreactors .................................................................................................................... 18 Figure 3.1: Effect of superficial gas velocity in the riser, U on the cell density gr, of I. galbana at 120 hours. ........................................................................................... 22 Figure 3.2: Growth curve of I. galbana grown in batch culture at different superficial gas velocities. ............................................................................................. 22 Figure 3.3: Growth rates of I. galbana cultured at different superficial gas velocities. ..................................................................................................................... 23 Figure 3.4: Mass transfer coefficient, k a, as a function of superficial gas L velocity in the riser, U .. ............................................................................................. 24 gr Figure 3.5: Effects of increased sparger velocity on the cell density of I. galbana at 120 hours. ................................................................................................... 27 Figure 3.6: Growth rates of I. galbana cultivated at different sparger velocities ....... 27 Figure 3.7: Mass transfer coefficient, k a, for spargers (n=1) as a function of L sparger velocity ............................................................................................................ 29 Figure 3.8: Effects of three different sizes of bubbles on I. galbana over the first 24-hour period in a bench-scale split-cell photobioreactor .................................. 32 Figure 3.9: Growth rates of I. galbana cultured with different diffuser types ........... 34 Figure 3.10: Final cell densities and pH for each of the diffuser configurations. ...... 35 Figure 3.11: Mass transfer coefficients, k a, measured for different types of L diffusers. ...................................................................................................................... 36 viii LIST OF TABLES Table 3.1: Maximum specific net growth rate as affected by air flow and gas velocity. ........................................................................................................................ 21 Table 3.2: Experimental conditions for sparger velocity experiments. ...................... 26 Table 3.3: Results of an LSD post-hoc test on sparger velocity data. ........................ 28 Table 3.4 Typical values needed for 35 m s-1 liquid velocity in airlift-driven tubular photobioreactors.. ............................................................................................ 42 ix