Generating Enough Renewable Energy

Bruce E. Rittmann

Director, Center for Environmental BiotechnologyBiodesign Institute at Arizona State University

Regents’ Professor, School of Sustainable Engineering and the Built Environment

Ira A. Fulton School of Engineering

Trends in Atmospheric CO2• 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 CO2 level

IPCC hoped for stabilization level

Scale! Scale! Scale! Scale!

• Human activities now use about 13-14 TerraWatts (TW = a trillion watts = 10-billion 100-watt light bulbs) of energy.– ~ 84% is from fossil fuels (~ 11 TW): 34%

oil, 32% coal, 14% natural gas• We need to replace about 7 TW with renewable

energy. This means doable at a large scale.• To get the most high value services of fossil

fuels, we need to produce a lot more biomass in an environmentally acceptable manner.

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

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

Example: The areal production of biomass and its energy content is roughly 100 times greater with photosynthetic microorganisms. This puts the output into the TW range.

Photobioreactors for Microbial Phototrophs

The lipids go to “biopetrol,” and the non-lipid biomass can be converted to CH4, electricity, or H2.

17-L bench-top PBR (left)

2100-L rooftop PBR (right)

Synechocystis PCC6803

Generating Enough Renewable Energy

Bruce E. Rittmann

Director, Center for Environmental BiotechnologyBiodesign Institute at Arizona State University

Regents’ Professor, School of Sustainable Engineering and the Built Environment

Ira A. Fulton School of Engineering