Carbon Dioxide Capture with Algae

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					            Carbon Dioxide Capture
                  with Algae
              Mark Rasmussen Ph.D.




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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”
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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




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            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 plate
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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/CO2
               System
Open pond system         Closed photobioreactor
• Larger area            • More controlled biology,
  requirements             select species
• Native midwest algae   • Greater productivity
• Midwestern winters     • Greater facility
• Less expensive           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 effects
  A metabolic burden and slower growth

• Subdued light: pigment preservation
  A 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 sunlight
                                             Light Effects on Growth Rate

                            4

                           3.5
  Doubling times per day




                            3

                           2.5
                                                                                         Scenedesmus
                            2
                                                                                         Chlamydomonas
                           1.5

                            1

                           0.5

                            0
                                 200   400   600     800      1000   2000   3000
                                                   Light FC                     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




                      Scenedesmus opoliensis

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