GCEP Energy Workshop

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1 GCEP Energy Workshop April 27, 2004, Alumni Center, Stanford University Biomass Energy Photosynthesis, Algae, CO 2 and Bio-Hydrogen John R. Benemann Institute for Environmental Management, Inc. (Not for profit) Palo Alto and Walnut Creek, California jbenemann@aol.com 1

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3 200,000 ton Anaerobic Bioreactor Landfill Davis, N. California (IEM, Inc. and Yolo County, 2004) 3

4 Photosynthesis, Microalgae and H 2 Production Photosynthesis drives a carbon cycle that is 1 to 2 orders of magnitude greater than the fossil C cycle. Microalgae have been studied for over 50 years as potential sources of foods, feeds, fertilizers and fuels, based in large part on their reputed ability to efficiently convert solar energy into chemical energy, either CO2 into biomass or even directly into hydrogen. THIS TALK ADDRESSES THE HOPE AND THE HYPE. 4

Microalgae have been studied for over 50 years as potential sources of foods, feeds, fertilizers and fuels, based

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6 Light-induced electron-transfer steps in PS II (Red arrows: when the central pigments are excited by light they share the excitation (Science, March 04) Water Splitting and O2 producing Mn Center 6

7 Bessel Bessel Kok, Kok,

8 Effect of high light intensity on pigment Content Dunaliella salina High Light on left (yellow) Low Light on right (green) 8

9 f. From Neidhardt, Benemann and Melis,

10 Light-saturation Curves of Photosynthesis Chlamydomonas reinhardtii Mutants, Dr. J. Polle, Brooklyn College Oxygen evolution mmol O 2 (mol Chl) -1 S Chl b-less Chl def. WT Light Intensity, µe m-2 s-1 10

Polle, Brooklyn College Oxygen evolution mmol O 2 (mol Chl) -1 S

11 Next Step: Outdoor Testing Dr. J. C. Weisaman, SeaAg, Inc. Vero Beach, FL Generation mutants of strains that can grow outdoors (Prof. Polle) Diatom Cyclotella WT Mutant CM2 11

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13 MICROALGAE R&D PONDS IN ROSSWEL, NEW MEXICO 13

14 Typical High Rate Pond Design 14

15 Microalgae Production Plant in in Hawaii (Cyanotech Corp). Red ponds for Haematococcus production, others cultivate the cyanobacterium Spirulina (known to to produce H2 and candidate for indirect biophotolysis process) 15

16 International Network on Biofixation of CO2 and Greenhouse Gas abatement with Microalgae Rio Tinto EPRI TERI (India) Arizona Public Services PNNL Gas Technology Institute ENEL Produzione 16 Ricerca

Tinto EPRI TERI (India) Arizona Public Services

17 St. Helena, CA Wastewater Treatment Ponds 17

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20 Antenna Size and Photosynthetic Efficiency. 200 Chl Photosynthetic Electron-Transport Chain Photosynthetic Electron-Transport Chains 20

21 SOLAR EFFICIENCY TRAIN FOR PHOTOSYNTHESIS Standard / Optimistic assumptions re. losses in photosynthesis Factors Limiting Photosynthesis Incident Solar Radiation Percent Percent Lost Remaining. Restricted to Visible Radiation Losses to reflection, inactive absorption 20 / 10 36/40 Efficiency of primary reactions of PS 75 / 70 9 / 12 Respiration and dark metabolism 33 / 15 6 / 10 Light saturation and photoinhibition 50 / 10* 3 / 9 * 10% Loss assumes overcoming these limitations (see next slides) 1% Efficiency is about 33 t/ha/yr dry weight biomass production. Maximum is about 100 (higher plants) to 300 (microalgae?) t/ha-yr 21

22 Solar energy is diffuse, its energy content is low!! At a very favorable location: 5 kwh/m 2 /day = 6.6 GJ/year Under optimistic assumptions: 10% conversion efficiency $15 per GJ --> $10 H 2 /m 2 /year A AA more realistic assumptions: 3 % conversion efficiency $5 per GJ (based on current $30/barrel crude oil) $1 H 2 /m 2 /year 22

23 INTRODUCTION TO PHOTOBIOLOGICAL H 2 PRODUCTION Many different photobiological H 2 production processes both direct and indirect, single and two stage, microalgae or photosynthetic bacteria, have been studied for 30+ years. No practical applications have resulted. Some processes even lack a laboratory demonstration of the proposed reaction. For one example: direct biophotolysis, which produces H 2 directly from H 2 O without intermediate CO2 fixation. Direct biophotolysis is the Holy Grail of H 2 production, due to its perceived high efficiencies. Major projects ongoing at several National Labs, GCEP /Stanford U., UC Berkeley, TCAG/IBEA, others in U.S. and abroad. 23

24 March 2004, National Academy Sciences: The Hydrogen Economy: Opportunities, Costs Barriers and R&D Needs Advanced Direct Photobiological H2 Production H 2 production by direct cleavage of H 2 O mediated by photosynthetic microorganisms, without intermediate biomass formation, [direct biophotolysis] is an emerging technology at the early exploratory stage theoretically more efficient than biomass gasification by 1 or 2 orders of magnitude. bioengineering efforts on the light harvesting complex and reaction center chemistry could improve efficiency severalfold... into the range of percent (solar to hydrogen)... substantial fundamental research needs to be undertaken This presentation addresses the realism of these projections which are typical of claims and publicity for such processes. 24

25 SCHEMATIC OF DIRECT BIOPHOTOLYSIS 25

26 FROM Benemann et al (1973): H2 EVOLUTION BY A CHLOROPLAST-FERREDOXIN-HYDROGENASE REACTION (IN VITRO DIRECT BIOPHOTOLYSIS REACTION] Assay Contents umoles H2/15 min Basic System (spinach chloroplasts, ferredoxin, Hase) 0.25 " " + DCMU (inhibitor of O2 evolution) 0.00 " " - Light (dark) 0.00 " " + glucose + glucose Oxidase (O2 absorber) 1.21 " " + glucose + glucose oxidase + DCMU 0.00 Heated Chloroplasts 0.01 CONCLUSIONS: Reaction is very short lived (<20 min) and VERY sensitive to even the small amounts of O2 26 produced in the process (with O2 absorber reaction runs >hours)

27 PROBLEM #1 OF DIRECT BIOPHOTOLYSIS: O 2 produced by PS inhibits H 2 production The data from Benemann et al., 1973, shows that the O 2 produced by photosynthesis strongly inhibits H 2 production, at well below 0.1% O 2 (< 30 ppb O 2 ) This is at least 1,000-fold below what is required! Inhibition is not due to O 2 inactivation of hydrogenase (Hase). Inhibition is due to the reaction of O 2 with the electron transfer system (e.g. ferredoxin or in Hase). Development by biotechnology of an O 2 stable Hase reaction is NOT plausible (on thermodynamic and other grounds). O 2 absorbers (e.g. glucose-glucose oxidase) not practical 27 photosynthesis needed to produce the O 2 absorbers.

28 DIRECT BIOPHOTOLYSIS: MECHANISM AND ISSUES Simultaneous, single-cell, single stage, H 2 and O 2 Production O 2 H 2 O PSII PSI Ferredoxin Hydrogenase H 2 The fundamental problems of direct biophotolysis are: 1. The strong inhibition by O2 (from water) of H 2 evolution. 2. The high cost of photobioreactors (to capture light and H 2 ). 3. The production of highly explosive H 2 :O 2 mixtures. 4. The low practical efficiency of all photosynthetic processes. There are no plausible solutions to problems 1 to 3 (discussed next, Problem 4 was discussed above) 28

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30 PROBLEM #2 OF DIRECT BIOPHOTOLYSIS: High Cost of Photobioreactors. Any process that uses light for H 2 production must be contained inside a transparent photobioreactors For direct biophotolysis the photobioreactor must cover the entire area of the process. Photobioreactors are inherently expensive, due to major limitations in scale-up and unit sizes (< 100 m2). Photobioreactor costs will be well above $100/ m2 (even without cost of the tubes or other glazing materials). Photobioreactors are unaffordable even at the highest 30 possible solar conversion efficiencies (10% solar to H 2 ).

31 EARLY EXAMPLE OF PHOTOBIOREACTOR FOR H 2 PRODUCTION BY MICROALGAE (U.S., 1978) 31

32 Tubular Photobioreactors in Hawaii designed for H2 Production (20 m long tube manifold, inclined at 5%) 32

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34 ALTERNATIVE PHOTOBIOLOGICAL H2 PRODUCTION PROCESSES: INDIRECT BIOPHOTOLYSIS The limitations of direct biophotolysis for H2 production led to proposals for indirect biophotolysis in which: 1. CO2 is first fixed into storage carbohydrates by microalgae (e.g. starch in green algae, glycogen in cyanobacteria) growing in low-cost open ponds. 2. The accumulated polyglucose (starch, glycogen) is then converted to H2 in a second anaerobic stage in the light in photobioreactors or in the dark in fermentation tanks. Separating the O2 and H2 producing reactions avoids O2 inhibition, greatly reduces the size of the photobioreactors (if any) and avoids production of explosive O2-H2 mixtures. 34

35 First Indirect Biophotolysis Process used N2-FIXING CYANOBACTERIUM (NOSTOC)

36 Proposed Indirect Biophotolysis Process: Could use Spirulina, a mass cultured microalga 36

37 Proposed Indirect Biophotolysis Process (2 nd Stage shown as a dark fermentation) 37

38 Indirect Biophotolysis with Dark Fermentation as 2 nd Stage with high H 2 yield - Schematic C 6 H 12 O H 2 O 10 NADH + 2 FADH CO 2 hν Photosynthesis (10% Solar Efficiency) 10 H 2 Dark Fermentation (80-85% yield from Glu) H 2 O + CO 2 For high yields will need genetically engineered algal cell with high photosynthetic efficiency in producing carbohydrates and also high yields of H 2 production in the dark by fermentations. THESE ARE THE R&D CHALLENGES OF PHOTOBIOH38 2

Photosynthetic Efficiency and Biomass Productivity of Microalgae Mass Cultures

ALGAE BIOMASS SUMMIT San Diego, CA, 29 Sept. 2 Oct Photosynthetic Efficiency and Biomass Productivity of Microalgae Mass Cultures John Benemann MicroBio Engineering, Inc. (MBE) San Luis Obispo, California,