Scale up of Algae Biofuels:
Challenges and Opportunities
Christopher Harto
Argonne National Laboratory
Purpose
 Take a very wide perspective look at algae biofuel systems
 Identify major challenges to scale up
 propose potential pathways for overcoming them
(DOE)
(DOE)
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Outline
 Economic Input-Output LCA
 Nutrient mass balance (C, N, P)
 Challenges and future research areas
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Algae Growth Requirements
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
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Land/solar energy
Water
Energy
Carbon
Nitrogen
Phosphorus
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Economic Input-Output LCA
 Analysis based upon 1996 technoeconomic analysis by NREL
at the conclusion of aquatic species program (Benemann and
Oswalt 1996)
 Uses 1997 US model in EIOLCA.net
 Co-Products allocated based on energy content
 Impacts Considered
– CO2
– Energy
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System Specifications
 400 ha, unlined, open pond
 Paddle wheel mixing
 Harvest through flocculation and settling along with
3 phase centrifuge
 Extraction through hot oil emulsion in centrifugation
step
 Non-lipid biomass converted to methane through
anaerobic digestion
 Energy output 25% methane, 75% lipids
 N recycle 50%, P recycle 75%
 Productivity 30 g/m2/day and 50% lipids content
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Results
GWP g CO2e/gal
Capital Impacts
Energy MJ/gal
149
1.7
Operating Impacts
3389
34.2
Total Impacts
3539
35.9
10100
146
0.35
4.1
Diesel Fuel
Output/Input
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Results Breakdown
Global Warming Potential
13%
Energy Consumption
4%
1%
4%
4%
5%
6%
1%
5%
Capital
Capital
power
power
nutrients
nutrients
maintainance
20%
5%
53%
maintainance
18%
labor
labor
flocculant
flocculant
waste disposal
61%
waste disposal
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Sensitivity Studies
Scenario Name
Productivity
Lipid %
Allocation Method
N Recycle %
P Recycle %
Baseline
30
50 Energy (methane)
50
75
No Recycle
30
50 Energy (methane)
0
0
Displacement
30
50 Displacement (electricity)
50
50
Electricity Co-Product
30
50 Energy (electricity)
50
50
Double Productivity
60
50 Energy (methane)
50
75
Half Productivity
15
50 Energy (methane)
50
75
Half Lipids
30
25 Energy (methane)
50
75
Achievable EA
15
25 Energy (methane)
50
75
Achievable DA
15
25 Displacement (electricity)
50
75
Achievable NR
15
25 Energy (methane)
0
0
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Sensitivity Studies
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Sensitivity Studies
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Nutrient Mass Balances
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
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Look at impact of scale up on flows and availability of C, N and P
Use simple mass balance approach
Assumptions:
– 100% utilization efficiency
Source
C%
N%
P%
shastri 2005 (Synechocystis)
51
11.3
Grobbelaar 2004 (microalgae)
51
6.6
Powell 2008 (Scenedesmus spp.)
1.3
0.4 to 3.2
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Carbon
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Carbon Analysis
 Due to day/night cycle and fraction point sources likely only
20-30% of total emissions viable for feedstock
 Global carbon agreements may reduce total by as much as
80% of current flows
 Only 4-6% of current carbon emissions likely available for long
run algae fuels production
 Realistic long term US algae fuel production ~ 1,000,000
barrels per day (5% of current liquid fuels consumption)
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Carbon Mass Transfer
 In absence of point sources, growth likely to be mass transfer
limited
 At current atmospheric CO2 concentration and 30% lipids
content, CO2 from 1,100,000 m3 of air must be extracted to
produce 1 barrel of algae oil
Algae Lipid Concentration
Volume of Air at STP Required to Supply Carbon to
Produce One Gallon of Fuel (m3)
15%
52,000
30%
26,000
50%
16,000
70%
11,000
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Nitrogen
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Nitrogen Analysis
 Nitrogen probably a soft limit as fertilizer production can be
scaled up reasonably easily using Haber-Bosch process
– H2 for process from methane produced by biomass or solar
electrolysis
 Alternative N sources from NOx in flue gas, wastewater or
nitrogen fixing organisms
 Increasing demand will probably spill over and affect
agricultural markets through fertilizer price increases
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Phosphorus
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Phosphorus Analysis
 P uptake can vary by order of magnitude depending on
conditions
 Typically must be supplied in excess due to tendency to
complex with metal ions and become unavailable to
organisms
 P is mined with limited supplies in very few places – 50%
global reserves in Morocco
 Total P reserves maybe 50-100 years
 Like N, competes with agriculture for nutrient supply
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Key Research Areas
 Nutrient utilization efficiency and recycling processes
– Use of organisms that excrete product
– Organisms with low N and P demands
 Better understand potential for atmospheric carbon mass
transfer
 Improve understanding and management of global P cycle
 Seek synergies and ways to close loops, use waste streams as
nutrient sources
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Agricultural Run Off and Ocean Dead Zones?
 Opportunities?
 Rivers concentrate agricultural runoff w/ high N and P
concentration
– Can they act as a water AND nutrient source?
 Massive Algal blooms occur which subsequently die
– Can they be harvested?
 Dead organisms sink to bottom and decompose using up O2
supply creating anoxic conditions
– If nutrients or organisms removed before death, is there still harm to
the ecosystem?
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Thank You!
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