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Carbon Dioxide Capturewith Algae

Mark Rasmussen Ph.D.

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Global Carbon Cycle

Respiration + Combustion + Decay (releases CO2)

VersusPhotosynthesis (captures CO2)

Global Carbon Cycle

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Algae: Basis of Food Chain

Algae bloom off of Newfoundland, NASA “Visible Earth”

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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

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The Potential of Algae Cultivation:Wastes to Resources

• Waste heat• Waste carbon dioxide• Plus Water & Sunlight

• Watershed nutrients• Animal waste• Sewage waste• Marginal lands

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Commercial Food Supplements

• Algae: Dunaliella salina

• Halophilic algae• 20 tons/acre• Nutra-Kol Pty Ltd

Australia• High value beta

carotene

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Algae Cultivation Methods

• Open Pond or Tank Methods

• Closed Bioreactor Systems

Open Culture Systems

Open systems– Less expensive– Temperature

fluctuation– Open to

contamination– Excess evaporation– Types: open pond,

center pivot, raceway

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Closed Culture Systems

Closed bioreactors– Controlled

environment– Less evaporation – Capital costs– Light issues– Productivity– Types: air lift,

tubular, flat plate8/20/2008 11

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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

Productive algae: a competitive feedstock

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Criteria for a Midwest Algae/CO2System

Open pond system• Larger area

requirements • Native midwest algae• Midwestern winters • Less expensive

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

Moderate temperature, fresh water system to maximize CO2 solubility and exchange

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Light Intensity and Algal Growth

• Bright light: pigment degradation and heating effectsA metabolic burden and slower growth

• Subdued light: pigment preservationA metabolic benefit and faster growth

Faster growth means greater CO2 fixation

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Lighting Effects on Algae Culture

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Algae only need 5-20% full sunlightLight Effects on Growth Rate

0

0.5

1

1.5

2

2.5

3

3.5

4

200 400 600 800 1000 2000 3000

Light FC

Doub

ling

times

per

day

ScenedesmusChlamydomonas

Full sun = 10,000 FCSorokin 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

Scenedesmus opoliensis