Bioenergy, Photosynthetic Capacity
and
Environmental Impact
D. E. Brune
Professor and Endowed Chair, Dept. of Agri & Biol Engr
Clemson University, Clemson, S.C. 29634
Facts & Figures: U.S. Energy Use
Renewables
6%
Nuclear
8%
Petroleum
39%
Commercial
17%
Natural Gas
24%
Industry 33%
Residential
21%
Coal
23%
Transportation
28%
U.S. Energy Use
100 Quads
Population ~300 million
333 million Btu/capita
Current US Petroleum Usage
billion gal/yr
gasoline
138
diesel
47
jet fuel
25
refining
products
oil
322
quads/yr
17.3
6.5
3.5
~5
~8
40
Bioenergy = Photosynthesis
 U.S.
Energy
 Solar Footprint
 Conventional Crops; Food Footprint
 Algal High Rate Photosynthesis
 Integrated Renewal Energy Mix
 Fossil Fuel Replacement Targets
Solar Energy Area Requirement
5 kwh/m2 - day =25 billion BTU/acre-yr
To supply 100 quad energy
 @ 100% efficiency = 4 million acres

6 x Rhode Islands (0.67 million acres)
 @ 10% efficiency

0.9 x Missouri (44 million acres)
 @ 3% efficiency

3 x Missouri
 @ 1% efficiency

9 x Missouri
US Land
 Active



farmland; 350 million acres
Corn = 93 million acres
Soy = 64 million acres
Wheat = 60 million acres
 Grass
= 587 million acres
 Forest = 650 million acres
 Urban = 60 million acres
 Total
US; 2,264 million acres
Solar Conversion;
Conventional crop food and energy

Solar input
•

Conversion of corn to human food
•
•
•

~5,000 watts/m2- day = 4300 kcal/m2-day = 25 billion BTU/acre-yr
120 million BTU/acre-season; grain and stover = 0.5% solar capture;
grain = 50% of energy content
60 million BTU/acre converts to 5.5 million BTU human food energy; 9
% efficient
Fossil energy used to grow and process human food = 700% of food
energy supplied
Conversion of corn to ETOH
•
•
•
60 million BTU/acre converts to 26 million BTU/acre ETOH
Net ETOH = 0 – 8 million BTU from grain
Net ETOH = ~60 million BTU from sugarcane (burning baggas)
US Food/Energy Footprint
 U.S. food
= Delivered energy requires 3.6 million
BTU/person-yr
 Converted to typical US diet = requires 40 million
BTU/person-yr
 US gross energy consumption = requires 333 million
BTU/person-yr
 Food area = 0.6 acres/person @60 million BTU/acre + 0.2
acres/person @100 million BTU/acre supplement
180-255 million acres; 50-70% of active cropland

Vegetarian = 40 million acres; primary + supplement
Woody biomass and grass potential

Current biomass;



USDA/DOE;



190 million tons/yr (75% forest, 25% cropland)
3 Quads or 50% of renewable
1.0-1.3 billion tons/yr supplying 12% of US
energy
30% forest and 70% cropland & pasture
1.0 billion tons biomass/yr;



8 tons/acre-yr = 125 million acres
100 million BTU/acre yr = 12.5% of US energy
10% of US forests + 10% of US grassland
Algal Productivity
Why Algal Culture
Good
 4-5 X productivity over conventional crops
 Growth in brackish and saline water
 Production on under-utilized lands
 Fluid transport and handling
 Production at low nutrient concentration
 Short algal cell generation time
Bad
 Difficult to harvest, concentrate and dry
 Requires intensive processing to be useful
 Culture system capital investment high
Algal Productivity
Sustainable in open ponds
• Annual average 20 gm vs/m2-d, @ 250 days
= 50 tons/ha-yr (44,500 lbs/acre-yr)
Algal composition
• 20% oil, 55% protein, 35% carbohydrate
• Algal Yields =400 million BTU/acre-season total,
• 1270 gal oil/acre,10 tons protein/acre, 100 million
BTU stationary energy
• 2.3% solar energy capture
Energy Yield Comparison
 Soy
biodiesel; 50 gallons/acre on 64 million
acres ~ 0.3% of US energy
 Algal biodiesel, 600 - 1200 gallons/acre, on 4.5
million acres ~ 0.5% of US energy using arid
land using saline water
Current Soybean
Production and Costs

Current Soybean
 64 million acres (21% cropland), 2600 lbs/yr
 Cost = $0.075 -0.15/lb (dry wt)
 Algae Replacement of Soy



48,000 lb/ac-yr algal biomass
4.5 million acres (7% of soy footprint)
Cost = $0.18/lb
Soybean comparison
U.S. soy land = 64 million acres @100%
Soy
Algae
gal oil
3.2 billion
9x
tons protein
0.76 million
32x
100% of soybeans = ~12% of jet fuel, 0.4
% of US energy
Algae ~ 10-20% of jet fuel or 4-8% of oil
based products
Extrapolated Algal Yields
Observed; 20 gm/m2-day for 250 days = 50 tons/hayr or 1300 gal oil/acre season @ 20% oil
Extrapolations;
Production
50 tons/acre
100 tons/acre
gal/acre-yr 365 days1
1,300
2,600
1,900
3,900
50% oil2
4,750
9,750
1) Tropical production?; balance of trade, close to CO2, waste nutrients, close to
distribution of products
2) Not field demonstrated
ALGAL HARVEST CHALLENGES
Flocculation or Centrifuge
 0.3 meter deep @ 20 gm/m2-day with 3 day cell
age = 200 mg/l standing crop
 Direct harvest 100 hp centrifuge, 160 gpm = 5.2
kcal input energy/kcal algal energy = 520 % energy
cost
 Algal sedimentation to 5% solids followed by
centrifugation = 2% of energy content
 Chemical costs = 10-30% of product value
 Algal conversion to brine shrimp @ 50% respiratory
costs, 7 ft pumping head yields 650 gallon/acre
cost = 1.8% of energy content
Costs of Production;
Current Industry
Earthrise Spirulina production costs ~ $10/kg dry wt
Harvesting/processing with screens, filter-presses,
spray-drying; Energy use ~ Energy content
Algal System
Costs vs. Production
Capital Cost
Velocity
Type* $/acre
fps
u 30–50K
0.1 - 0.3
l
80–100 K
0.8 -1.0
p 350-1,000K
varies
Productivity
gm VS / m2
14 - 18
20 - 25
25 – 40
*unlined, lined, closed photobioreactors
best case production increase = 2.9 X
best case cost increase = 7 X
Build on Field-Scale Success;
Cost Effective Algal Systems
2-Ac Freshwater System for Aquaculture @ Clemson
18,000 lb/acre fish production; with high-yield algae
Clemson PAS Fish Production
25000
Max Catfish Carrying Capacity
Catfish Net Production
KG/HA
20000
Tilapia Net Production
15000
10000
5000
0
1995
1996
1997
1998
Year
1999
2000
2001
Integrating Environmental Remediation
with By-Product Recovery
Clemson/Kent SeaTech
Salton Sea Restoration & Remediation
Large-Scale Microalgae Cultivation in Agricultural Wastewaters
for Biofixation of CO2 and Greenhouse Gas Abatement
State of California and U.S. Department of Energy Project
Principal Investigator: Michael J. Massingill, Vice President, Kent SeaTech
Cooperating Investigators: David E. Brune, Professor, Clemson University,
CEP Algal Sedimentation Belt at Kent SeaTech in
California
Polishing Chamber
Belts harvest 3 d/wk, 12-16%; Solar drying on 400 ft2/24 hr
(1.2% of culture area) 98% solids,@45% VS, yielding 95 lb
dry solids/acre-day
Harvest and conversion; 9% oil algal-biomass to
22% oil animal-biomass @ 50% efficiency
Gravity separation; oil, water and biomass fractions
R&D Recommendations





NEAR-TERM
Install/operate 2-acre pilot algal reactors; openpond, paddle-wheel mixed, target 50 tons/ha
production at $20-40,000/ha cash-flow (< $0.5/kg),
$100,000/ha capital costs
Integrated products; animal feed (protein), liquid
fuels (oils), stationary energy (methane)
Integrated objectives; GHG reduction, waste CO2,
nutrient recovery, environmental remediation,
wastewater treatment
Optimize algal harvest; biofiltration, bioflocculation
Downstream processing; develop & optimize algal
protein, oil extraction, concentration, purification
R&D Recommendations





Demonstrate photobioreactor nutraceuticals &
pharmaceutical production at >$10/kg ($500,000
/ha income), 0.5 to 1 million/ha capital costs
LONGER-TERM
GMO algae; improved algal productivity and
composition
GMO filter-feeders; alternative and/or enhanced
harvest techniques
Water management on large scale
Economic species control; continuous inoculation.
Target Development of
Integrated Biorefineries
Integrated Energy Technologies
Biomass with other Solar Technology
Role of Photosynthesis?
Use carbon based photosynthetic processes
to provide carbon compds.
Use higher efficiency, direct conversion of
solar energy for electrical demand, convert
liquid fuel requirement to electrons
ETOH Land Area Requirements
 Food
= 0.6-0.8 acres/person
 ETOH at +30% = 36 acres/person
 ETOH at +80% = 13 acres/person (3,900
million acres)
 10 billion gallons ETOH supplies 0.2-0.6%
net U.S. energy
 100% of U.S. soy = 5% of diesel (+90%)
 100% of U.S. corn = 5% of gasoline (+30%)
 Food-cropland ETOH; transitional fuel only
Integrated Renewable Energy Mixture*
Energy
Resource
Petroleum
Natural gas
Coal
Nuclear
Quads Area;
2000 106 acres
37.7
22.1
21.7
7.7
Quads
2050
Area; 2050
106 acres
Expansion
Factor
-2.2
2.6
0.15
Biomass
Hydroelectric
Geothermal
Biogas
Wind
Solar thermal
Photovoltaics
Passive solar
3.6
3.9
0.3
0.001
0.04
0.04
0.04
0.30
185
64
1
-1
----
5.0
5.0
1.2
0.5
7.0
10.0
11.0
6.0
252
82
2.5
0.02
19.7
27.2
7.4
2.5
1.4
1.3
4.0
20
175
250
275
20
RENEWABLE
TOTAL
8.2
97
250
46
393
+5.6
*Pimentel, D., Renewable Energy; Current and Potential Issues, 2000
Infrastructure and Water and
Environmental Issues
Water Requirements
Algae on 4.5 million acres using saline
groundwater or seawater
Evaporative replacement = 23,000 MGD
Western US water withdrawal of 68,000
MGD
5% of Mississippi river flow
Infrastructure requirements
 Cellulosic
energy density = 6.7-10% of oil
volume
 Replacing 12% of US 100 quads
 30% of US oil energy
 Woody biomass/grass volume 3-5x over
30% of oil processing volume
Courtesy of US NREL
Courtesy of US NREL
Intensity of US Energy Footprint
From; Smil, V., “Energy in Nature and Society,”
MIT Press, 2008
Gross Energy Targets
106 BTU/acre
 Algal 460
 Soy
20
 Corn
60
 Wood 100
 Grass 100
acres
4.5
64
93
60
60
quads
2.0
1.3
5.5
6.0
6.0
limiting
water
food
food
biodiversity
biodiversity
Targets
 Distributed,
integrated, bioenergy and
renewable energy systems development
 Risk distribution; water system design and
usage, biodiversity protection
 Non-competitive with food production
 Future energy expansion; increasing
efficiency of energy and food footprint
 Infrastructure redesign/ development
 Social, political, economic, redesign,
adjustment
 The
advantage of renewable energy lies
NOT in the promise of cheap and
abundant energy supplies, but rather;
 “It
will be scarce and expensive …… we
will need to use it frugally … instead of
wasting it wantonly as we do with fossil
fuels.”*
* J.R. Benemann, Algal Biomass Summit, Seattle WA, 2008.