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 CO 2 from fossil fuels. Outcomes include rising oceans, lowered inland waters, melting glaciers, more extreme weather events,
Trends in Atmospheric CO 2 1000-1800 -- ~ 280 ppmv (pre-industrial) 1870 -- ~ 300 ppmv (industrial revolution) 1950 -- ~ 305 ppmv (post WWII) 1970 -- ~ 325 ppmv 1988 -- ~ 350 ppmv 2000 -- ~ 360 ppmv 2006 -- ~ 375 ppmv 2010 -- ~ 390 ppmv 2050 -- est. from 450 to 550 ppmv 2100 -- est. from 490 to 1000 ppmv Emissions target to hold at today s CO 2 level About 1/3 rd of today s use rate IPCC hoped for stabilization level
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, CH 4, H 2, hydrocarbon fuels
Combining Principles 1 and 2 H 2 O CO 2 The C-neutral loop Hydrogen, methane, hydrocarbon fuels 1. Solar energy is captured by photosynthesis into biomass and takes up CO 2. The electrons come from H 2 O. 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 CO 2 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 2/3 rd 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 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 Plants or Microbes? 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 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 Plants or Microbes? 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 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 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 Plants or Microbes? 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 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 CH 4, electricity, or H 2.
An integrated, water- and microbe-based photobioenergy system will look like this Inputs are sunlight and CO 2, the true resources. The left side could be, instead of an MFC for electricity, an MEC for H 2, anaerobic digestion for CH 4, 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, CO 2 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.
6 5 4 3 2 1 0 Product Excretion Strategy standard 199.171 269.250 laurate 180 200 220 240 260 280 4 255.230 3 palmitate 2 1 0 180 200 220 240 260 280 m/z Dial in desired product with specific thioesterase New CO 2 fixation Phosphoglycerate Addition of thioesterase Acetyl CoA Free fatty acid Excrete from cell Fatty acyl ACP 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, CO 2 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.
Water As Part of the Solution to Using Photosynthetic Microorganisms to Generate Renewable Energy Feedstock 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
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