HYSYDAYS Turin 8 th October 2009 PARAMETERS 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

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

SOLAR HYDROGEN PROJECT LightHeatWindHydroBiomassFossil Solar energy conversion efficiency Technological development SunlightWaterHydrogen Direct routes to solar H 2 from water Funded by EPSRC Run by the Energy Futures Lab at Imperial College London Steam methane reforming Coal/biomass gasification Electrolytic/photolytic processes Thermal/thermochemical processes Diversity of H 2 supply:

SOLAR HYDROGEN PROJECT Solar Hydrogen Project - direct routes to H 2 from sunlight and water: Photoelectrochemical Biophotolytic Hydrogen as a fuel: Lightest (storage) Most efficient (fuel cells) Cleanest Most available... maybe 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

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

BIOPHOTOLYTIC H 2 PRODUCTION - SCIENCE Photosystem II protein complex splits water into oxygen, protons and electrons Hydrogenase enzyme facilitates proton and electron recombination to produce H 2 – but it is inactivated in the presence of O 2 Unicellular green alga C.reinhardtii produces H 2 under anaerobic conditions Merchant et al., 2007 Anaerobic conditions imposed by sulphur deprivation Melis, 2002

BIOPHOTOLYTIC H 2 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 H 2 production TAP medium replaced by sulphur- deplete TAP-S medium by: –Centrifugation –Dilution –Ultra-filtration Sulphur re-insertion required to prolong algal lifetime H 2 measurement Techniques: –Water displacement –Injection mass spectrometry –Reversed Clark electrode –Membrane inlet mass spectrometry (MIMS) H 2 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

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

C.REINHARDTII GROWTH KINETICS C.reinhardtii grown in Aqua Medic® vertical column reactors Agitation provided by bubbled air (or CO 2 ) gas-lift system 170 μEm -2 s -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 nm range –Photosystem II absorption peak at 663 nm

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 agitation rate: Decrease growth rate Increase maximum attainable OD Increase light intensity: Increase growth rate and maximum attainable OD What is the limit?

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

C.REINHARDTII H 2 PRODUCTION KINETICS Stirred-tank batch reactor: Mechanical agitation Cool white light side-illumination Centrifugation Sartorius® tubular flow reactor: Peristaltic pump Helix geometry illumination Dilution C.reinhardtii produce H 2 under anaerobic conditions Anaerobic conditions imposed by sulphur deprivation Sulphur deprivation induced by centrifugation or dilution H 2 yield measured by water displacement H 2 identified by injection mass spectrometry

C.REINHARDTII H 2 PRODUCTION KINETICS Stirred-tank batch reactor (centrifugation) 3 distinct phases: –Oxygen consumption –Hydrogen production –Cell death H 2 yield of 5.2±0.3 ml/l Higher initial cell density Brief start-up time Tubular flow reactor (dilution) Continuous measurement of pO2, pH and OD H 2 yield of 3.1±0.3 ml/l Photochemical efficiency of approximately 0.1% Process easier to implement and scale up

CONTENT Solar Hydrogen Project Biophotolytic H 2 Production C.reinhardtii Growth Kinetics C.reinhardtii H 2 Production Kinetics Photobioreactor Design

PHOTOBIOREACTOR DESIGN Flat plate reactor: 1 litre system Specifically constructed for H 2 production H 2 detection by MIMS Strong scale-up opportunity

CONCLUSION Solar Hydrogen Project – Clean and renewable H 2 production – Integrated, cross-disciplinary approach to link green algal H 2 production with engineering methods Results – C.reinhardtii absorption peak at 663nm – Agitation rate and light intensity have significant effect on C.reinhardtii growth – H 2 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 H 2 production efficiency – Advance photobioreactor design – H 2 will become the sustainable fuel of the future

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