scale up of algae biofuels: challenges and opportunities

Scale up of Algae Biofuels: Challenges and Opportunities

Christopher HartoArgonne 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

Environmental Science Division, IPEC 17th International Petroleum & Biofuels Environmental Conference

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(DOE)(DOE)

Outline

Economic Input-Output LCA Nutrient mass balance (C, N, P) Challenges and future research areas


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Algae Growth Requirements

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


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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

Results


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GWP g CO2e/gal Energy MJ/gal

Capital Impacts 149 1.7

Operating Impacts 3389 34.2

Total Impacts 3539 35.9

Diesel Fuel 10100 146

Output/Input 0.35 4.1

Results Breakdown


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Global Warming Potential

4%

53%20%

5%

1%

4%

13%

Capital powernutrientsmaintainancelaborflocculantwaste disposal

Energy Consumption

5%

61%

18%

6%

1%5%

4%

Capital powernutrientsmaintainancelaborflocculantwaste disposal

Sensitivity Studies


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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

Sensitivity Studies


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Sensitivity Studies


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Nutrient Mass Balances

Look at impact of scale up on flows and availability of C, N and P Use simple mass balance approach Assumptions:

– 100% utilization efficiency


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Source C% N% P%

shastri 2005 (Synechocystis) 51 11.3

Grobbelaar 2004 (microalgae) 51 6.6 1.3

Powell 2008 (Scenedesmus spp.) 0.4 to 3.2

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


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Algae Lipid Concentration Volume of Air at STP Required to Supply Carbon to Produce One Gallon of Fuel (m3)

15% 52,00030% 26,00050% 16,00070% 11,000

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!

scale up of algae biofuels: challenges and opportunities

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