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HYSYDAYS Turin8th October 2009
PARAMETERS AFFECTING THE GROWTH AND HYDROGEN PRODUCTION OF THE GREEN ALGA
CHLAMYDOMONAS REINHARDTII
Bojan Tamburic
Dr Fessehaye W. ZemichaelProf Geoffrey C. Maitland
Dr Klaus Hellgardt
CONTENT
• Solar Hydrogen Project
• Biophotolytic H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
CONTENT
• Solar Hydrogen Project
• Biophotolytic H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
SOLAR HYDROGEN PROJECT
Light Heat Wind Hydro Biomass Fossil
Solar energy conversion efficiency
Technological development
Sunlight Water Hydrogen
• Direct routes to solar H2 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 H2 supply:
SOLAR HYDROGEN PROJECT
Solar Hydrogen Project - direct routes to H2 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 H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
BIOPHOTOLYTIC H2 PRODUCTION - SCIENCE
Photosystem II protein complex splits water into oxygen, protons and electrons
Hydrogenase enzyme facilitates proton and electron recombination to produce H2 – but it is inactivated in the presence of O2
Unicellular green alga C.reinhardtii produces H2 under anaerobic conditions
Merchant et al., 2007
Anaerobic conditions imposed by sulphur deprivation
Melis, 2002
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
CONTENT
• Solar Hydrogen Project
• Biophotolytic H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
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
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 H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
C.REINHARDTII H2 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 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
C.REINHARDTII H2 PRODUCTION KINETICS
Stirred-tank batch reactor (centrifugation)
• 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
Tubular flow reactor (dilution)
• 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
CONTENT
• Solar Hydrogen Project
• Biophotolytic H2 Production
• C.reinhardtii Growth Kinetics
• C.reinhardtii H2 Production Kinetics
• Photobioreactor Design
PHOTOBIOREACTOR DESIGN
Flat plate reactor:• 1 litre system• Specifically constructed for H2
production• H2 detection by MIMS• Strong scale-up opportunity
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
