Bojan Tamburic Dr Fessehaye W. Zemichael Prof Geoffrey C. Maitland Dr Klaus Hellgardt

1. HYSYDAYS Turin8th October 2009Parameters Affecting the Growth and Hydrogen Production of the Green Alga Chlamydomonas Reinhardtii Bojan Tamburic Dr Fessehaye W. Zemichael Prof Geoffrey C. Maitland Dr Klaus Hellgardt

2. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

3. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

4. Solar Hydrogen Project • Direct routes to solar H2 from water • Funded by EPSRC • Run by the Energy Futures Lab at Imperial College London Sunlight Water Hydrogen Solar energy conversion efficiency Light Heat Wind Hydro Biomass Fossil Technological development • Steam methane reforming • Coal/biomass gasification • Electrolytic/photolytic processes • Thermal/thermochemical processes Diversity of H2 supply:

5. Solar Hydrogen Project • Cleanest: • Must consider entire life cycle – including production • Requires a carbon-neutral, sustainable process (e.g. use sunlight) • Most available: • Hydrogen found in hydrocarbons, carbohydrates and water • Water is the most plentiful and widespread resource • Hydrogen as a fuel: • Lightest (storage) • Most efficient (fuel cells) • Cleanest • Most available • ... maybe • Solar Hydrogen Project - direct routes to H2 from sunlight and water: • Photoelectrochemical • Biophotolytic

6. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

7. Biophotolytic H2 production - science Unicellular green alga C.reinhardtii produces H2 under anaerobic conditions Photosystem II protein complex splits water into oxygen, protons and electrons Merchant et al., 2007 Hydrogenase enzyme facilitates proton and electron recombination to produce H2– but it is inactivated in the presence of O2 Anaerobic conditions imposed by sulphur deprivation Melis, 2002

8. Biophotolytic H2 production - method • Algal growth • Tris-acetate phosphate (TAP) growth medium • Source of N, C, P, S and trace elements • Measured by: • Chlorophyll content • Optical density (OD) • Influenced by: • Light intensity and wavelength • Agitation and pH • Sulphur deprivation • Causes metabolic changes in algae that induce anaerobic H2 production • TAP medium replaced by sulphur-deplete TAP-S medium by: • Centrifugation • Dilution • Ultra-filtration • Sulphur re-insertion required to prolong algal lifetime • H2 measurement • Techniques: • Water displacement • Injection mass spectrometry • Reversed Clark electrode • Membrane inlet mass spectrometry (MIMS) • H2 production quantified in terms of: • Productivity • Yield • Photochemical efficiency (13% theoretical maximum, 2% attained) • Photobioreactors • Types: • Vertical column reactor • Stirred-tank batch reactor • Tubular flow reactor • Flat plate reactor

9. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

10. C.reinhardtii growth kinetics • C.reinhardtii grown in Aqua Medic® vertical column reactors • Agitation provided by bubbled air (or CO2) gas-lift system • 170 μEm-2s-1 PAR (18 Wm-2) of cool white light incident on culture • Room temperature • Absorption spectrum: • Pigments extracted by acetone or methanol • Absorption maxima in the purple and red regions of visible spectrum • Carotenoids absorb in 400-500 nm range • Photosystem II absorption peak at 663 nm

11. C.reinhardtii growth kinetics • C.reinhardtii reproduce by meiosis (cell splitting) • Initial exponential growth • Cell density limited by light penetration through culture causing saturation • Logistic (sigmoid) growth kinetics • Increase light intensity: • Increase growth rate and maximum attainable OD • What is the limit? • Increase agitation rate: • Decrease growth rate • Increase maximum attainable OD

12. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

13. C.reinhardtii H2 production kinetics • C.reinhardtii produce H2 under anaerobic conditions • Anaerobic conditions imposed by sulphur deprivation • Sulphur deprivation induced by centrifugation or dilution • H2 yield measured by water displacement • H2 identified by injection mass spectrometry • Sartorius® tubular flow reactor: • Peristaltic pump • Helix geometry illumination • Dilution • Stirred-tank batch reactor: • Mechanical agitation • Cool white light side-illumination • Centrifugation

14. C.reinhardtii H2 production kinetics Stirred-tank batch reactor (centrifugation) Tubular flow reactor (dilution) • 3 distinct phases: • Oxygen consumption • Hydrogen production • Cell death • H2 yield of 5.2±0.3 ml/l • Higher initial cell density • Brief start-up time • Continuous measurement of pO2, pH and OD • H2 yield of 3.1±0.3 ml/l • Photochemical efficiency of approximately 0.1% • Process easier to implement and scale up

15. Content • Solar Hydrogen Project • Biophotolytic H2 Production • C.reinhardtii Growth Kinetics • C.reinhardtii H2 Production Kinetics • Photobioreactor Design

16. Photobioreactor Design • Flat plate reactor: • 1 litre system • Specifically constructed for H2 production • H2 detection by MIMS • Strong scale-up opportunity

17. Conclusion • Solar Hydrogen Project • Clean and renewable H2 production • Integrated, cross-disciplinary approach to link green algal H2 production with engineering methods • Results • C.reinhardtii absorption peak at 663nm • Agitation rate and light intensity have significant effect on C.reinhardtii growth • H2 production by C.reinhardtii: • 5.2±0.3 ml/l in stirred-tank batch reactor following centrifugation • 3.1±0.3 ml/l in tubular flow reactor following dilution • Outlook • Improve H2 production efficiency • Advance photobioreactor design • H2 will become the sustainable fuel of the future

18. Thank you for listening! Any questions? bojan.tamburic@imperial.ac.uk