Aug 20, 2008 - 22. Research Areas: Algae. Production. ⢠Biomass productivity. ⢠Lipid accumulation. ⢠Cell harvest
Carbon Dioxide Capture with Algae Mark Rasmussen Ph.D.
8/20/2008
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Global Carbon Cycle Respiration + Combustion + Decay (releases CO2) Versus Photosynthesis (captures CO2)
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Global Carbon Cycle
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Algae: Basis of Food Chain
Algae bloom off of Newfoundland, NASA “Visible Earth” 8/20/2008
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Algae Blooms
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Algae: Nature’s CO2 Scrubber • Earth’s photosynthetic capacity is large. • It is estimated that algae fix >65 Gt of carbon per year. • Algae in nature fix carbon equal to the output of about 65,000, 500-MW generating plants
8/20/2008
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The Potential of Algae Cultivation:Wastes to Resources • Waste heat • Waste carbon dioxide • Plus Water & Sunlight • • • •
Commercial Food Supplements • Algae: Dunaliella salina • Halophilic algae • 20 tons/acre • Nutra-Kol Pty Ltd Australia • High value beta carotene 8/20/2008
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Algae Cultivation Methods • Open Pond or Tank Methods • Closed Bioreactor Systems
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Open Culture Systems Open systems – Less expensive – Temperature fluctuation – Open to contamination – Excess evaporation – Types: open pond, center pivot, raceway 8/20/2008
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Closed Culture Systems Closed bioreactors – Controlled environment – Less evaporation – Capital costs – Light issues – Productivity – Types: air lift, tubular, flat plate 8/20/2008
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Coal Plant Study: A Summary • DOE study in 2002 • Calculations based upon a pond yield of 4g/l/day • Assumption of 25% CO2 capture from flue gas • 2136 t/d algae biomass @ 26% lipid content • Breakeven = $97/ton of algae produced • Or $0.18/lb algae oil • Current soybean oil prices >$0.70/lb 9Productive algae: a competitive feedstock 8/20/2008
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Criteria for a Midwest Algae/CO2 System Open pond system • Larger area requirements • Native midwest algae • Midwestern winters • Less expensive
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Closed photobioreactor • More controlled biology, select species • Greater productivity • Greater facility requirements and costs
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Algae Culture System Criteria • • • • •
Fresh water versus salt water Moderate versus high temperature Natural versus artificial light Open versus closed system Native species versus introduced species
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Carbon Dioxide Solubility • Increased solubility in fresh water • Increased solubility at lower water temperatures 9Moderate temperature, fresh water system to maximize CO2 solubility and exchange 8/20/2008
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Light Intensity and Algal Growth • Bright light: pigment degradation and heating effects A metabolic burden and slower growth • Subdued light: pigment preservation A metabolic benefit and faster growth 9Faster growth means greater CO2 fixation 8/20/2008
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Lighting Effects on Algae Culture
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Algae only need 5-20% full sunlight Light Effects on Growth Rate 4
Doubling times per day
3.5 3 2.5 Scenedesmus
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Chlamydomonas
1.5 1 0.5 0 200
400
600
800 Light FC
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1000
2000
3000 Full sun = 10,000 FC Sorokin and Krauss, 1958
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Selecting algae with rapid growth and CO2 fixation capacity
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Determining Appropriate Growth Conditions with Lab Scale Photobioreactors
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Photobioreactor
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Research Areas: Algae Production • • • • • •
Biomass productivity Lipid accumulation Cell harvest Cell disruption Conversion to biodiesel Scale up
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The Future: Carbon Management and Biofuels using Algae
