Using Photosynthetic Microorganisms to
Generate Renewable Energy Feedstock
Bruce E. Rittmann
Director, Swette Center for Environmental Biotechnology
Biodesign Institute at Arizona State University
Regents’ Professor, School of Sustainable Engineering and the
Built Environment
Ira A. Fulton School of Engineering
Water As Part of the Solution to
Renewable Biofuel, Not a Roadblock
Bruce E. Rittmann
Director, Swette Center for Environmental Biotechnology
Biodesign Institute at Arizona State University
Regents’ Professor, School of Sustainable Engineering and the
Built Environment
Ira A. Fulton School of Engineering
What is our most fundamental
sustainability challenge?
Unsustainable use of fossil fuels
• Depletion of petroleum reserves
• Geopolitical and economic instabilities
• Global climate change
– Simply put, the Earth takes in more energy from the Sun
than it transmits away due to the build-up of energyabsorbing gases in the atmosphere.
– The primary greenhouse gas is CO2 from fossil fuels.
– Outcomes include rising oceans, lowered inland waters,
melting glaciers, more extreme weather events,…………
Trends in Atmospheric CO2
•
•
•
•
•
•
•
•
•
•
1000
1870
1950
1970
1988
2000
2006
2010
2050
2100
- 1800 -- ~ 280 ppmv (pre-industrial)
-- ~ 300 ppmv (industrial revolution)
-- ~ 305 ppmv (post WWII)
-- ~ 325 ppmv
-- ~ 350 ppmv
• Emissions target to hold at today’s CO2 level
-- ~ 360 ppmv
• About 1/3rd of today’s use rate
-- ~ 375 ppmv
-- ~ 390 ppmv
• IPCC hoped for
-- est. from 450 to 550 ppmv
stabilization level
-- est. from 490 to 1000 ppmv
Scale!
Scale!
Scale! Scale!
• Human activities now use about 16 TerraWatts (TW
= a trillion watts = 10-billion 100-watt light bulbs) of
energy.
– ~ 84% is from fossil fuels (~ 13 TW): 34% oil,
32% coal, 14% natural gas
• Current rates of energy use project a 60% increase
by 2030.
• Thus, bioenergy sources must work on a very large
scale to be of significant value towards the goal of
replacing fossil fuels.
Scale!
Scale!
Scale! Scale!
• Human Fossil-Energy Use Rate: ~ 13 TW
• Sunlight hitting the Earth’s surface: 173,000 TW
– More than 16,000 times what we use in fossil fuel now
– Here is the upside potential
• Sunlight energy captured as all biomass: ~140 TW
– Only ~10 times more than we use for all human energy use!
– Here lies the heart of the scale problem today: Human
society demands more energy than is routinely and safely
provided by natural and agricultural photosynthesis.
Bioenergy can play a big role in
large-scale renewable energy
IF
We let water work for us,
not against us
Crop-based biofuels have gained
a “bad rep,” in large part due to
water problems
• Insufficient supply, particularly when
irrigation is needed
• Severe nutrient pollution, leading to
eutrophication and hypoxia
• Other pollution problems
How can we make water work
for us, not against is in
bioenergy?
Bioenergy Principle 1
• Ultimately, the sun is the only large renewable source of energy.
• We have a lot, but it is diffuse and not in a form we can use of most things for which we need energy.
Bioenergy Principle 2
• Useful energy is in electrons!
• So, the goal is get the electrons
from renewable, but diffuse
sources into energy forms easily
used by society: e.g., electricity,
CH4, H2, hydrocarbon fuels
Combining Principles 1 and 2
1.
H2O
The C-neutral “loop”
CO2
Hydrogen, methane,
hydrocarbon fuels
Solar energy is captured by
photosynthesis into biomass
and takes up CO2. The
electrons come from H2O.
2. Some biomass can be used
directly as a bio-fuel, such as
wood. Most biomass is
converted into other useful
forms that are……
3. Converted to useful energy for
electricity, heating.
The generation steps return CO2 to
the biosphere – C-neutral loop.
Comparison to Fossil Fuels
• It is the same principle for fossil fuels: photosynthesis to yield biomass.
• The difference is that the fossil fuels were produced and accumulated over 100s of millions of years, while
• Humans are combusting the accumulation in just a few 100 years!
Residual Biomass
• If all residual biomass from agriculture and
human activities could be collected and
converted into useful energy, it would meet ~
25% of the worldwide energy demand.
• Although residual biomass could “make a real
dent” in meeting energy demand, we cannot
collect and covert nearly all of it.
• Thus, it is not nearly enough to displace
about 2/3rd of fossil-fuel at today’s use rate.
Yes, residual biomass is not enough!
We need to produce a lot more biomass
to make up the difference!
We need a lot more photosynthesis
carried out in an environmentally
acceptable manner!!
Plants or Microbes?
Traditional Biomass/Biofuel
Production Focus: Plants
Microorganisms:
photosynthetic algae and
bacteria
Plants or Microbes?
Plants
• Slow growing - usually only one
crop a year
• Require arable land
• Growth seasonal
• Low areal production
• Heterogeneous (leaves, seeds,
stems, etc.)
• Require water and fertilizer;
pollutes water
• Largely lignocellulosic
Photosynthetic Microorganisms
• Fast growing - doubling time 0.5-1
day
• Do not require arable land
• Growth year-round
• High areal production
• Homogeneous (all cells are the
same)
• Water-efficient; can recycle
minerals
• Not lignocellulosic
While plants must grow in arable soil, photosynthetic
microorganisms grow in a water slurry. We have control
of the water this way – like in wastewater treatment.
Plants or Microbes?
Plants
• Slow growing - usually only one
crop a year
• Require arable land
• Growth seasonal
Photosynthetic Microorganisms
• Fast growing - doubling time 0.5-1
day
• Do not require arable land
• Growth year-round
• Heterogeneous (leaves, seeds,
stems, etc.)
• Require water and fertilizer;
pollutes water
• Largely lignocellulosic
• Homogeneous (all cells are the
same)
• Water-efficient; can recycle
minerals
• Not lignocellulosic
• Low areal production
• High areal production
The areal production of biomass and its energy content is 10
to 100 times greater with photosynthetic microorganisms.
This puts the feasible output into the TW range.
Plants or Microbes?
Plants
• Slow growing - usually only one
crop a year
• Require arable land
• Growth seasonal
• Low areal production
• Heterogeneous (leaves, seeds,
stems, etc.)
Photosynthetic Microorganisms
• Fast growing - doubling time 0.5-1
day
• Do not require arable land
• Growth year-round
• High areal production
• Homogeneous (all cells are the
same)
• Largely lignocellulosic
• Not lignocellulosic
• Require water and
fertilizer; pollutes water
• Water-efficient; can
recycle minerals
A well-design photobioreactor system can be nearly “closed
loop” for water and nutrients, and any water that is discharged
can be treated to avoid pollution.
“New biomass” and “biopetrol” from
photosynthetic bacteria -- our ASU approach
•
•
Converting solar energy to lots
of high-energy biomass using the
cyanobacterium Synechocystis
– Areal yield is high enough to
replace all of the world’s
fossil fuel in the area of
Texas
– High lipid content to make
biopetrol, the highest-value
form
Leveraging
o Genetically tractable
microorganisms
o Modern engineering system
Benchtop and Rooftop Photobioreactors
16-L bench-top
PBR (left)
2100-L rooftop
PBR (right)
The Value Proposition
• We are able to create a large amount of “new biomass” to supplement the normal capture of biomass into plants and microorganisms.
• Thus, it is a solar‐powered factory for renewable energy forms at the scale needed to substitute fossil fuels in a major way!
• The lipids go to “biopetrol,” and the non‐lipid biomass can be converted to CH4, electricity, or
H2 .
An integrated, water- and microbe-based
photobioenergy system will look like this
Inputs are sunlight and CO2, the true resources.
The left side could
be, instead of an
MFC for electricity,
an MEC for H2,
anaerobic digestion
for CH4, or some
combination
A loop for
water and
nutrients
A Second Strategy
• Have the photosynthetic bacteria “pump out” the
feedstock, such as fatty acids as the precursor to lipids.
• This is the topic of our current ARPA-E project.
• Still, CO2 and sunlight are the prime resources, but we
do not need to hassle with harvesting the biomass and
recovering the different resources.
cyanobacteria as a “factory”
Biomass generation is not needed and even not desired.
Long‐chain fatty acids are immediate feedstock for jet fuel.
We can produce a range of renewable products from our factory. CO2 fixation
Product‐Excretion Strategy
6
5
4
3
2
1
0
180
4
3
2
1
0
180
199.171
laurate
standard
Phosphoglycerate
269.250
Acetyl‐CoA
New
200
220
240
260
Fatty acyl‐ACP
280
255.230
palmitate
200
220
“Dial in” desired product with specific thioesterase
240
Addition of thioesterase
260
280
m/z
Free fatty acid
Excrete from cell
Lipid
A Second Strategy
• Have the photosynthetic bacteria “pump out” the
feedstock, such as fatty acids as the precursor to lipids.
• This is the topic of our current ARPA-E project.
• Still, CO2 and sunlight are the prime resources, but we
do not need to hassle with harvesting the biomass and
recovering the different resources.
• All of it is in water and with almost no need to import
nutrients or harvest and convert biomass.
• It is a true photosynthetic factory!
Take Home Lessons
• Society must have renewable, C-neutral
alternatives on a very large scale – TWs!
• Photosynthetic microorganisms can produce
high-energy biomass and have the potential
to meet the TW-scale test.
• They do this in a water slurry that is largely a
closed loop for water and nutrients.
Thus, we let water work for us -- not against us
-- for generating enough renewable energy.
Using
Photosynthetic
Microorganisms
Water
As Part of the
Solution to to
Generate Renewable
Feedstock
Renewable
Biofuel, Energy
Not a Roadblock
Bruce E. Rittmann
Director, Swette Center for Environmental Biotechnology
Biodesign Institute at Arizona State University
Regents’ Professor, School of Sustainable Engineering and
the Built Environment
Ira A. Fulton School of Engineering
Water As Part of the Solution to
Renewable Biofuel, Not a Roadblock
Bruce E. Rittmann
Director, Swette Center for Environmental Biotechnology
Biodesign Institute at Arizona State University
Regents’ Professor, School of Sustainable Engineering and
the Built Environment
Ira A. Fulton School of Engineering