GCE P E nergy Workshop GCE P E nergy Workshop April 27, 2004, Alumni Center, Stanford University April 27, 2004, Alumni Center, Stanford University Biomass E nergy Biomass E nergy 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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200,000 ton Anaerobic Bioreactor Landfill 200,000 ton Anaerobic Bioreactor Landfill Davis, N. California (IE M, Inc. and Yolo County, 2004) Davis, N. California (IE M, Inc. and Yolo County, 2004) 3
Photosynthesis, Microalgae and H 2 Production 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
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Light-induced electron-transfer steps in PS II Light-induced electron-transfer steps in PS II ( Red arrows: when the central pigments are excited by ( Red arrows: when the central pigments are excited by light they share the excitation (Science, March 04) light they share the excitation (Science, March 04) Water Splitting and O2 producing Mn Center 6
7 Bessel Kok, 1973 Bessel Kok, 1973
E ffect of high E ffect of high light intensity light intensity on pigment on pigment Content Content Dunaliella salina High Light on left (yellow) Low Light on right 8 (green)
f f . 9 From Neidhardt, Benemann and Melis, 1998
Light-saturation Curves of Photosynthesis Light-saturation Curves of Photosynthesis Chlamydomonas reinhardtii Mutants, Dr. J. Polle, Brooklyn College 100 Chl b -less -1 S -1 80 Oxygen evolution Chl def. 2 (mol Chl) 60 WT 40 mmol O 20 0 -20 0 400 800 1200 1600 2000 2400 2800 3200 10 Light Intensity, µ E m-2 s-1
Next Step: Outdoor Testing Next Step: Outdoor Testing Dr. J. C. Weisaman, SeaAg, Inc. Vero Beach, FL 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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MICROALGAE R&D PONDS IN ROSSWE L, NE W ME XICO MICROALGAE R&D PONDS IN ROSSWE L, NE W ME XICO 13
14 Typical High Rate Pond Design Typical High Rate Pond Design
Microalgae Production Plant Microalgae Production Plant in Hawaii (Cyanotech Corp). in Hawaii (Cyanotech Corp). Red ponds for Haematococcus Red ponds for Haematococcus production, others cultivate the production, others cultivate the cyanobacterium Spirulina (known cyanobacterium Spirulina (known to produce H2 and candidate for to produce H2 and candidate for 15 indirect biophotolysis process) indirect biophotolysis process)
International Network on Biofixation of CO2 and Greenhouse Gas abatement with Microalgae EPRI EPRI Rio Tinto Rio Tinto Arizona Public Services Arizona Public Services TERI (India) TERI (India) PNNL PNNL Gas Technology Institute Gas Technology Institute 16 ENEL Produzione Ricerca ENEL Produzione Ricerca
St. Helena, CA Wastewater Treatment Ponds St. Helena, CA Wastewater Treatment Ponds 17
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Antenna Size and Photosynthetic Efficiency . 200 Chl 20 20 20 20 20 20 20 20 20 20 Photosynthetic Electron-Transport Chain Photosynthetic Electron-Transport Chains 20
SOLAR E FFICIE NCY TRAIN FOR PHOTOSYNTHE SIS SOLAR E FFICIE NCY TRAIN FOR PHOTOSYNTHE SIS Standard / Optimistic assumptions re. losses in photosynthesis Incident Solar Radiation Percent Percent Lost R emaining Factors Limiting Photosynthesis . Restricted to Visible Radiation 55 45 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
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
INTRODUCTION TO PHOTOBIOLOGICAL H 2 PRODUCTION 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 CO 2 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
March 2004, National Academy Sciences: “The Hydrogen March 2004, National Academy Sciences: “The Hydrogen E conomy: Opportunities, Costs Barriers and R&D Needs” E conomy: Opportunities, Costs Barriers and R&D Needs” Advanced Direct Photobiological H2 Production 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 several- fold... into the range of 20 -30 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 CT BIOPHOTOLYSIS MATIC OF DIRE SCHE
FROM Benemann et al (1973): H2 E VOLUTION BY A FROM Benemann et al (1973): H2 E VOLUTION BY A CHLOROPLAST-FE RRE DOXIN-HYDROGE NASE RE ACTION CHLOROPLAST-FE RRE DOXIN-HYDROGE NASE RE ACTION ( IN VITRO DIRE CT BIOPHOTOLYSIS RE ACTION] ( IN VITRO DIRE CT BIOPHOTOLYSIS RE ACTION] _____________________________________________________________________________ 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 produced in the process (with O2 absorber reaction runs >hours) 26
PROBLEM #1 OF DIRECT BIOPHOTOLYSIS: PROBLEM #1 OF DIRECT BIOPHOTOLYSIS: O 2 produced by PS inhibits H 2 production 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.
DIRE CT BIOPHOTOLYSIS: ME CHANISM AND ISSUE S DIRE CT BIOPHOTOLYSIS: ME CHANISM AND ISSUE S Simultaneous, single-cell, single stage, H 2 and O 2 Production 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 O 2 (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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